1

Umeå University Medical Dissertations

New Series nr. 1235 ISSN: 0346-6612 ISBN: 978-91-7264-708-4

Investigating the function of

Anaplastic Lymphoma Kinase

Emma Vernersson Lindahl

Department of Medical Bioscience, Pathology

Umeå University, Sweden

Umeå 2008

2

Umeå University Medical Dissertations

New Series nr. 1235 ISSN: 0346-6612 ISBN: 978-91-7264-708-4

Cover: wild type mouse embryo, developmental day 13.5. ALK is visualized (red) in part of

the diencephalon. Immunohistochemistry conducted 041215, picture acquired 041216

by Emma Vernersson Lindahl

Copyright© 2008 Emma Vernersson Lindahl

Printed by Arkitektkopia, Umeå, Sweden

Umeå 2008

3

Abstract

naplastic Lymphoma Kinase (ALK) was discovered in 1994, as a chromosomal

translocation, t(2;5)(p23;q35), often seen in Anaplastic Large Cell Lymphomas (ALCL).

Since then ALK has been extensively studied in this disease as well as in different model

organisms. Due to its expression pattern within the central and peripheral nervous system

ALK has been implicated in neuronal development. This hypothesis has been further

strengthened by studies from Drosophila which have shown ALK to have an important role in

optic lobe development. A recently described ALK mouse knockout model do not indicate an

essential role for ALK in development, although a potential role within the central nervous

system was strengthened. This since ALK-/-

animals has an increased number of progenitor

cells in the hippocampus and display altered behavior.

The overall aim of the studies included in this thesis was to elucidate the function of ALK in

the mouse. As a first step toward this goal we conducted an analysis of ALK mRNA and

protein expression patterns during development. The strong expression of ALK in neuronal

structures supports a role for ALK in neuronal development during embryogenesis.

To further investigate the function of ALK in a physiological context we have developed two

different ALK knockout strains, the ALK Kinase knockout (KO) and the ALK exon1 KO. The

only visible phenotype in these strains is a reduction of total body weight which is apparent in

the ALK-/-

population when compared to wild type littermates. This size difference seems to

take place after birth and is not due to an alteration in food consumption. We have also

extensively studied the ALK Kinase KO with respect to gross development, the

gastrointestinal canal and the olfactory system. ALK displays a very distinct expression

pattern within the gastrointestinal canal being confined to enteric neuron precursors during

embryogenesis and enteric nerves in the adult tissue. From these studies we conclude that

ALK is not needed for development and viability in mice although it does play a role in

regulation of body weight via a presently unknown mechanism.

In addition, we have investigated the relationship between the Drosophila and mouse ALK

receptor by examining the ability of the Drosophila Alk ligand Jelly-Belly, Jeb, to activate

mouse ALK. Using different in vivo and in vitro techniques, we have shown that activation of

mouse ALK cannot be accomplished by Drosophila Jeb. From this study we draw the

conclusion that during development ligands for the Drosophila and mouse ALK has diverged

to a level at which they can no longer substitute for each other.

Keywords: ALK, nervous system, knockout, development, Jelly-Belly

Author: Emma Vernersson, Department of Medical Bioscience, Pathology, Building 6M, 2nd

floor, Umeå University, S-901 85 UMEÅ, Sweden. E-mail:

emma.vernersson@medbio.umu.se; phone: +46 (0)90 785 12 96

A

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Table of Content

Papers Included in this Thesis 6 1. Published Articles 6

2. Manuscripts 6

Abbreviations 7

Introduction 10 1. Receptor Tyrosine Kinases 10

2. Receptor Tyrosine Kinases in Cancer 10 3. Discovery of the RTK Anaplastic Lymphoma Kinase 11

4. Structural Features of Anaplastic Lymphoma Kinase 11

5. Function of Anaplastic Lymphoma Kinase 13 5.1 Drosophila Anaplastic lymphoma kinase 13

5.2 C. elegans Anaplastic Lymphoma Kinase 14

5.3 Mammalian Anaplastic Lymphoma Kinase 14

6. Anaplastic Lymphoma Kinase in Disease 19

6.1 Anaplastic Lymphoma Kinase Fusion Proteins in Cancer 19

6.1.1 Anaplastic Large Cell Lymphoma 19

6.1.2 Mouse Models for ALK Driven ALCL 20

6.1.3 ALK Fusion Proteins in ALCL 21

6.1.4 Oncogenic Signaling via ALK Fusion Proteins 22

6.1.5 Inflammatory Myofibroblastic Tumour 27

6.1.6 Non-Small Cell Lung Cancer 27

6.1.7 ALK Positive Diffuse B-cell lymphoma 28 6.2 Anaplastic Lymphoma Kinase Overexpression in Cancer 28

6.3 Anaplastic Lymphoma Kinase Gain-of-Function in Cancer 29

6.3.1 Neuroblastoma 29 7. Potential Treatments Strategies for ALK Positive Cancers 31

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Aim 33 1. Overall Aim 33

1.1 Specific Aim: Article I 33

1.2 Specific Aim: Article II 33 1.3 Specific Aim: Manuscript I 33

1.4 Specific Aim: Manuscript II 33

Results and Discussion 34

1. Article I: ALK Expression during Development 34

2. Article II: Can Drosophila Jeb activate mouse ALK? 35

2.1 Why is Drosophila Jeb unable to activate mouse ALK? 36

2.2 What about the LDLa domain? 36

3. Manuscript I and II: What is the physiological

consequence of loss of ALK function? 37 3.1 The ALK Kinase KO and the ALK exon1 KO 37

3.2 What function might ALK have during mouse 37

embryogenesis?

3.3 Is there a role for ALK in the adult olfactory bulb? 38

3.4 The ALK Kinase KO and the ALK exon1 KO are small…

…but why? 39

3.5 Why are animals smaller? Lessons from the literature. 40

3.6 Why is ALK not vital for life in the mouse? 40

Conclusions 42 1. Article I 42

2. Article II 42 3. Manuscript I and II 42

Acknowledgement 43

References 45

Original Papers and Manuscripts 60

6

Papers Included in this Thesis

1. Published Articles

I. Vernersson E, Khoo NK, Henriksson ML, Roos G, Palmer RH, Hallberg B. (2006)

Characterization of the expression of the ALK receptor tyrosine kinase in mice.

Gene Expr. Patterns, 6(5):448-61*

II. Yang HL, Eriksson T, Vernersson E, Vigny M, Hallberg B, Palmer RH. (2007)

The ligand Jelly Belly (Jeb) activates the Drosophila Alk RTK to drive PC12 cell

differentiation, but is unable to activate the mouse ALK RTK. J. Exp. Zoolog. B

Mol. Dev. Evol, 308(3):269-82**

2. Manuscripts

I. Vernersson E, Khoo NK, Roos G, Palmer RH, Hallberg B. (2008) The ALK KO

display an idiopathic reduction of total body weight. Manuscript

II. Vernersson E, Berghard A, Bohm S, Roos G, Palmer RH, Hallberg B. (2008) ALK

expression within the olfactory bulb. Manuscript

*Reprinted from Gene Expression Patterns, 6(5), Vernersson E, Khoo NK, Henriksson ML, Roos G, Palmer RH, Hallberg B, Characterization of the expression of the ALK receptor tyrosine kinase in mice, page 448-461,

copyright (2006), with permission from Elsevier

**Reprinted from Journal of experimental zoology. part B, molecular and developmental evolution, 308(3), Yang

HL, Eriksson T, Vernersson E, Vigny M, Hallberg B, Palmer RH, The ligand Jelly Belly (Jeb) activates the Drosophila Alk RTK to drive PC12 cell differentiation, but is unable to activate the mouse ALK RTK, page 269-

282, copyright (2007), with permission of Wiley-Liss, Inc. a subsidiary of John Wiley & Sons, Inc.

7

Abbreviations

AKT AKR Thymoma

ALCL Anaplastic Large Cell Lymphoma

ALK Anaplastic Lymphoma Kinase

ALO17 ALK lymphoma oligomerization partner on chromosome 17

ATIC 5-aminoimidazole-4-carboxamide ribonucleotide

formyltransferase/IMP cyclohydrolase

ATP Adenosinetriphosphate

Bin Biniou

BMP4 Bone Morphogenetic Protein 4

CARS Cysteinyl-tRNA synthetase

CD4 Cluster of Differentiation 4

CD30 Cluster of Differentiation 30

CDC42 Cell Division Cycle 42

CLTC1 Clathrin heavy chain-like 1

CML Chronic Myeloid Leukemia

c-Myc cellular-myelocytomatosis viral oncogene

CSN Central nervous system

dALK Drosophila Anaplastic Lymphoma kinase

daf3 and 5 abnormal dauer formation 3 and 5

DBA Dolichos biflorus agglutinin

DDR1 Discoidin Domain Receptor 1

DIG Digoxigenin

Dpp Decapentaplegic

duf Dumbfounded

EGF-like Epidermal Growth Factor-like

EML4 Echinoderm microtubule-associated protein like 4

ERK Extracellular signal Regulated Kinase

FGFR1-4 Fibroblast Growth Factor Receptor 1-4

FoxF1 Forkhead box F1

FOXO3a Forkhead box O3A

fsn-1 F-box protein at the synapse

GIST Gastrointestinal Stromal Tumour

Grb2 Growth Factor Receptor-Bound protein 2

HARP Heparin Affin Regulatory Peptide

Hen-1 Hesitation-1

HB-GAM Heparin Binding Growth-Associated Molecule

HBNF Heparin-binding Neurotrophic Factor

IgG Immunoglobulin G

IL-1ra InterLeukin 1 Receptor Antagonist

IMT Inflammatory Myofibroblastic Tumor

IR insulin receptor

IRS-1 Insulin receptor substrate 1

JAK3 Janus Kinase-3

Jeb Jelly-Belly

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kirrel1 and 2 Kin of IRREgular chiasm-Like 1 and 2

LDL Low-Density Lipoprotein

LDLa Low-Density Lipoprotein receptor class A,

LDLR Low-Density Lipoprotein Receptor

LTK Leukocyte Tyrosine Kinase

LRP low-density Lipoprotein Related protein

MAM Meprin A-5 protein and receptor protein tyrosine phosphatase Mu

MAPK Mitogen-Activated Protein Kinase

MEK MAPK/ERK Kinase

mig-13 MIGration

Miple 1 and 2 MIdkine and PLEiotrophin

MK Midkine

mKirre3 mammalian Kin of IRREgular chiasm-Like 3

MSN Moesin

mTOR mammalian Target Of Rapamycin

MYH9 Non muscle myosin heavy chain

NEPH1 Nephrosis 1 homolog

NFκB Nuclear Factor Kappa B

NPM Nucleophosmin

OB Olfactory Bulb

OSF-1 Osteoblast-Specific Factor-1

OSN Olfactory sensory Neurons

p130Cas p130 Crk-associated substrate

PC12 Pheocytochroma cells 12

p.c. post coitum

PDGFR Platelet-Derived Growth Factor Receptor

PI3K Phosphoinositide-3 Kinase

PKB Protein Kinase B

PLCγ Phospholipase C γ

PP2 Protein Phosphatase 2

PTK Protein Tyrosine Kinase

PTN Pleiotrophin

RANBP2 Ran-binding protein 2

RAS rat sarcoma

RET Rearranged during Transfection

RIHB Retinoic Acid-inducible Heparin Binding protein

RPTPβ/δ Receptor Protein Tyrosine Phosphatase β/δ

RTK Receptor Tyrosine Kinase

SCD-2 Suppressor of Constitutive Dauer 2

SH2 domain Src homology 2 domain

Shc Src homology 2 containing

SDS-PAGE Sodium Dodecyl Sulfate PolyAcrylamide Gel Electrophoresis

SEC31L1 SEC31 homologue A

SF steel factor

Shp-1 and 2 SH2 domain-containing phosphatase 1 and 2

SMαA Smooth Muscle alpha Actin

9

sma-5 small body size

soc-1 Suppressor Of Clr

Sox8 SRY-box containing gene 8

STAT3 and 5 Signal Transducer and Activator of Transcription 3 and 5

TACE TNFα Converting Enzyme

TBX1/2/3/10 T BoX family 1/2/3/10

TFG TRK-fused gene

TGFβ Transforming Growth Factor-beta

TMP3 and 4 Tropomyosin 3 and 4

vSrc viral Sarcoma

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Introduction

1. Receptor Tyrosine Kinases

he enzymatic phosphorylation reaction was first described in 1954 by Burnett and

Kennedy with their discovery that a protein present in rat liver mitochondria could

catalyze the transfer of a phosphate group from ATP to serine hydroxyl groups of the protein

Casein [1]. However the phenomenon of phosphate in protein was demonstrated already in

1906, almost 50 years earlier, so the concept was not entirely new [2]. From the discovery of

Burnett and Kennedy it took almost 25 years before modification of tyrosine via phosphate

would be identified [3], and in 1980 Hunter and Sefton demonstrated the first protein with

tyrosine phosphorylation activity, vSrc [4].

There are approximately 520 different protein kinases in the human genome that can be

subdivided into 9 different groups (not including the atypical protein kinases) [5]. One of these

is the tyrosine kinase group containing 90 different members further subdivided into two

major classes, the receptor tyrosine kinases (RTK) and the non-receptor tyrosine kinases [5,

6].

All RTKs share a common domain structure with 1) an extracellular ligand binding domain

that is usually glycosylated; 2) a transmembrane domain and; 3) a cytoplasmic domain

containing a highly conserved kinase domain with the catalytic function of the protein [7].

The general activation of an RTK is envisioned to occur via ligand mediated receptor

dimerisation leading to autophosphorylation of specific tyrosine‟s in the intracellular region

followed by conformational changes of the kinase domain allowing ATP and substrate to bind

and transmit downstream signals [7]. There are different variations of this scenario depending

on which ligand/receptor pair is being considered. For example all known RTKs are

monomers in the absence of ligand, except the insulin receptor (IR) family of RTKs with the

IR being a disulfide linked dimer of two polypeptide chains forming a heterodimer in the cell

membrane [8]. The ligand for the IR - insulin - functions as a monomer in activating the

receptor [9]. Conversely, other ligands, such as Steel factor (SF), need to be present as dimers

to activate their target receptor [10].

2. Receptor Tyrosine Kinases in Disease

n their article from 1979, where Eckhart, Hutchinson and Hunter establish tyrosine

phosphorylation as an event occurring within mammalian cells they stated in their

discussion that “The phosphorylation of tyrosine is intriguing…and suggests that purification

of the activity would be worthwhile” [3]. Almost 30 years later tyrosine phosphorylation is

acknowledged as a key event regulating diverse cellular functions such as differentiation,

proliferation, migration and metabolism. Furthermore since the discovery of the first tyrosine

kinase [4], they have notoriously been found deregulated in numerous oncogenic malignancies

[11, 12].

T

I

11

More than half of the known RTKs have been implicated in mediating cellular transformation

via either of three main principles firstly) RTK overexpression; secondly) gain of function

mutations or; thirdly) genomic re-arrangement [11].

The Fibroblast Growth Factor Receptor (FGFR) family contains 4 members, FGFR1, FGFR2,

FGFR3 and FGFR4, which are all being implicated in different oncogenic processes via either

of the above principles [13]. Stem-cell myeloproliferative disorder is caused via genomic re-

arrangements resulting in fusion of the FGFR1 kinase domain to various partner protein

creating constitutively kinase active chimeric proteins with oncogenic potential, such as

CEP110-FGFR1 [14] and FIM-FGFR1 [15]. Over expression of FGFR1 and FGFR3 have

been implicated in breast cancer [16] and thyroid carcinoma [17] respectively while activating

point mutations in FGFR3 have been indicated in bladder carcinoma development [18]. These

activating mutations for FGFR3 occur either in the kinase domain, promoting a more open

(active) conformation, or in the extracellular domain leading to ligand-independent receptor

dimerisation [19, 20]. Regardless of alteration the outcome is the same with unregulated

downstream signaling via the receptor.

As well as being implicated in oncogenic development, deregulated RTKs can also be found

in developmental syndromes. Indeed, we can continue to utilize the FGFR family to exemplify

this. Mutations within the extracellular domain of FGFR3, conferring ligand independent

activation [21], are causative for one form of dwarfism [22]. Other mutations generate active

versions of FGFR1 and FGFR2 which cause Pfeiffer syndrome [23-25]. Pfeiffer syndrome is a

genetic disorder characterized by premature fusion of certain skull bones and depending on

type (I, II or III) the affected individual present with more or less severe symptoms [23].

3. Discovery of the RTK Anaplastic Lymphoma Kinase

naplastic Lymphoma Kinase (ALK) was discovered by two groups in 1994 [26, 27].

Shiota et. al. characterized a previously unknown tyrosine kinase protein from an

Anaplastic Large Cell Lymphoma (ALCL) cell line, terming it p80 due to its molecular size of

80 kDa. They speculated that this protein could be a chimeric protein created via a fusion

event [26]. This would indeed be verified later the same year when Morris and colleagues

demonstrated that the translocation, t(2;5)(p23:q35), often seen in ALCL, created a fusion

protein (NPM-ALK), of approximately 80 kDa, containing the amino-terminal portion of the

nucleophosmin (NPM) protein and the kinase domain of a tyrosine kinase protein that they

termed ALK after the disease [27].

4. Structural Features of Anaplastic Lymphoma Kinase

eing an RTK, ALK display the classical structural features of ligand binding extracellular

domain, a transmembrane spanning region and an intracellular tyrosine kinase domain.

Based on homology ALK is grouped with Leukocyte Tyrosine Kinase (LTK) and together

they form their own subgroup within the IR super family [28, 29].

The human ALK gene encodes a protein of 1620 amino acids giving rise to a protein of

approximately 180 kDa. However, as a result of posttranslational modifications (N-linked

A

B

12

glycosylations) ALK migrates at approximately 220 kDa in a conventional SDS-PAGE [28,

29]. Mouse ALK consists of 1621 amino acids [28, 29], and human ALK of 1620, while

Drosophila Alk [30] and C.elegans ALK [31, 32] are 1701 and 1421 amino acids in length

respectively.

Characterizing both mouse and human ALK, both Morris and Iwahara defined a signal peptide

in the amino-terminus of ALK, thought to be important for localization of the protein to the

cell membrane, one EGF-like cysteine rich motif, one large glycine rich domain in the

extracellular region and the kinase domain within the C-terminal region [28, 29] (figure 1).

The EGF-like structure, also noted in LTK [33], plays a role in ligand binding [34], although,

so far, no such function have been reported for this motif in ALK. Beside the EGF-like

domain Morris and colleagues also identified a second cysteine rich motif [28] that would be

further characterized in Drosophila Alk (dAlk) by Loren et. al. in 2001 and identified as an

LDLa domain [30]. Within ALK the LDLa (Low-density lipoprotein receptor class A) domain

has an unknown function. However this module mediates the binding between the LDL-

receptor and LDL [35, 36] implying a role for this domain of ALK in ligand binding.

In the work by Loren and colleagues they also identified one MAM (Meprin A-5 protein and

receptor protein tyrosine phosphatase Mu) domain within the amino-terminal region of dALK

[30]. Further work lead to the identification of a second MAM domain in the extracellular

region of dALK [37]. Using Pfam [38] or SMART [39], one MAM domain is denoted in

human ALK localized at amino acid 480-636. Using PROSIT [40] a second MAM domain is

localized ranging from amino acid 264-427 within the extracellular region in human, however

it displays weaker homology with the core MAM domain relative to the one denoted at

position 480-636. In mouse, both MAM domains, localized at amino acid position 270-428

and 484-635, are readily displayed using either of the above domain prediction programs.

MAM domains are thought to participate in cell/cell interactions [41] but their significance for

ALK is not determined. The importance of the MAM domain is nevertheless emphasized via

work from Drosophila which show that a point mutation at amino acid 681 (in Alk2) altering a

highly conserved aspartic acid in the MAM domain to arginine renders dAlk inactive [37].

During this study they also demonstrated the functional significance of the glycine rich

domain since in four independent dAlk mutants (Alk4, Alk

5, Alk

6 and Alk

7) a single glycine

within the glycine rich domain was found to be mutated to an acidic amino acid rendering

dALK inactive [37].

The ALK receptor is structurally highly conserved throughout evolution with the overall

protein homology between dAlk and mouse ALK being approximately 30%. However

conserved domains exhibit a higher degree of similarity e.g. the kinase domains showing 58%

similarity. This can be compared with the mouse and human ALK, which show 87% overall

homology on protein level and within the kinase domains differs in only 4 amino acids. It

should be emphasized that mouse and human ALK are highly similar; however, human ALK

contains one extra tyrosine, Y1604. Site-directed mutagenesis of this tyrosine residue in NPM-

ALK, a fusion protein of NPM and ALK found in the disease ALCL (discussed in more

details in coming sections), results in loss of oncogenic potential [42].

13

5. Function of Anaplastic Lymphoma Kinase

5.1 Drosophila Anaplastic lymphoma kinase

he in vivo function of Alk has been most thoroughly studied in Drosophila melanogaster

were Alk was first characterized in 2001 and shown to drive ERK activation in vivo [30].

Additional studies would illustrate a vital role for dAlk in formation of the visceral

musculature of the gut [37]. This phenotype would later be attributed to a lack of founder cells

in Drosophila embryos deficient in dAlk signaling [43, 44]. In a wild type context founder

cells are specified in the visceral mesoderm, thereafter fusing with fusion competent cells to

give rise to the multinucleated visceral musculature of the gut [45, 46]. Since dAlk signaling

specifies the founder cells, it follows that in the absence of founder cell no fusion event occurs

and as a consequence no assembly of a functional gut musculature occurs in dALK mutant

flies.

The Jelly-belly (Jeb) protein has been reported as the activating ligand for dAlk, and as such is

also required for founder cell specification [43, 44]. Jeb is a secreted protein of approximately

61 kDa containing a secretory signal and an LDLa domain [47]. The interaction of Jeb and

dAlk appears to be mediated via the LDLa domain in Jeb, since Jeb mutant protein lacking the

Figure 1: Mouse and human ALK display

87% overall homology on protein level

with identical domain layout. The amino

acid (a.a) position for human ALK is

entered below. The positioning of mouse

ALK domains is nearly identical. Human

ALK include a signal peptide (s.s) at a.a 1-

26, two Meprin A-5 protein and receptor

protein tyrosine phosphatase Mu (MAM)

domains at a.a 264-427 and 480-626, one

Low-density lipoprotein receptor class A

(LDLa) domain at a.a 453-471, one

Glycine rich (G-rich) domain at aa 816-940

and one epidermal growth factor (EGF) -

like domain at a.a 994-1021. A

transmembrane spanning segment (TM)

connects the extracellular region with the

protein tyrosine kinase (PTK) domain at

a.a 1116-1383. The closest family member,

LTK, is depictured with the coresponding

regions denoted. The s.s at a.a 1-16, G-

rich domain at a.a 63-334, the EGF-like

domain at a.a 400-428 and the kinase

domain at a.a 510-777.

extr

acel

lula

rS.S

MAM

MAM

LDLa

G-rich

TM

PTK

intr

acel

lula

r

hALK hLTK

EGF-like

PTK

G-rich

S.S

EGF-like

T

14

LDLa domain is unable to bind dAlk [44]. Activation of the Jeb-Alk signaling pathway leads

to ERK activation and further downstream transcription of target molecules such as, Duf/Kirre

[43, 44], Org [44] and Hand [48] (figure 2).

Recent data have implicated dAlk in two additional events. First Shirinian et. al. established

the importance of dAlk in development of the endoderm, showing that dAlk activity in the

visceral mesoderm is a requirement for TGFβ signaling in the adjacent endoderm [49].

Secondly Bazigou and colleagues demonstrated a role for the Jeb-Alk signaling pathway

during optic lobe development, where lack of either protein leads to miss targeting of the R-8

axons during later maturation of the optic lobe neuropil [50].

5.2 C. elegans Anaplastic Lymphoma Kinase

n C. elegans ALK has been implicated in neuronal control of entry of dauer and synapse

stabilization [31, 32]. In 2004 Liao et. al. characterized the C. elegans protein Fsn-1 as

being part of a ubiquitin ligase complex stabilizing synapse formation in GABAergic

neuromuscular junctions. This function was partly mediated via down regulation of T10H9.2

the C. elegans homologue of mammalian ALK [31]. More recently mutants of T10H9.2, or

SCD-2 as it´s now formally known were characterized. These mutants display a temperature

sensitive adaptation for entry of dauer stage. Epistasis analysis places SCD-2 in the TGFβ

pathway upstream of Daf3/Daf5. Furthermore, Hen-1 was identified as the SCD-2 ligand [32].

Hen-1 is the homologue of the Drosophila ALK ligand Jeb, and is also a secreted ligand

containing an LDLa domain [51].

5.3 Mammalian Anaplastic Lymphoma Kinase

ammalian ALK has been postulated to play a role in the normal development and

function of the nervous system. This dogma within the field had its birth in the

extensive expression of ALK mRNA throughout the nervous system during mouse

embryogenesis [28, 29]. Further, this pattern of ALK mRNA expression is recapitulated in the

developing central nervous system of the chicken were ALK localizes to a subset of spinal

motor neurons, the sympathetic ganglia and dorsal root ganglia [52]. In mice the intensity of

the ALK transcript diminishes after birth, reaching minimum levels at 3 weeks of age, and is

thereafter maintained at low levels in the adult animal [29]. Immunohistochemical studies of

adult human tissue by Pulford et. al. have shown a pattern consistent with that earlier reported

for mouse ALK with a week ALK signal observed in scattered neuronal cells of the

hypothalamus, basal ganglia and thalamic nuclei [53]. While Pulford and colleagues did not

detect ALK protein in any other tissue studied, including the testis and duodenum [53], Morris

et. al observed ALK mRNA transcripts of different sizes in testis, small intestine and brain of

adult human material [27]. This suggesting, that differential splicing of ALK occurs.

Interestingly, the most extensive ALK expression was noted in the testis and small intestine

[27] implicating a function for ALK in these structures.

In vitro studies have also suggested a role for ALK in neuronal development. Souttou et. al. in

2001, substituted the extracellular region of ALK with the mouse IgG 2b Fc domain, resulting

in the creation of a constitutively active membrane bound ALK:IgG 2b Fc hybrid protein,

I

M

15

Figure 2: Signaling via Drosophila Alk occurs via binding of the ligand Jeb, downstream

activation of ERK and transcription of downstream target genes. Signaling via mammalian

ALK is thought to occur via ligand mediated dimerisation, the potential ligands being MK and

PTN. ALK mediate signaling via the JAK/STAT, RAS/MAPK, PI3K and PLCγ pathways.

Activation of ALK via PTN, independent of direct ALK/ligand interactions has been

proposed. Last, ALK is suggested to function as a dependency receptor that in the absence of

ligand is cleaved via Caspase 3 thereby promoting apoptosis.

__________________________________________________________________________

which induced neuronal differentiation of PC12 cells. Further, they showed that this activity,

generated via the ALK:IgG 2b Fc hybrid protein, was mediated via the MAPK-pathway since

inhibition of MEK abolished PC12 cell neurite outgrowth [54]. This study has been further

validated by other groups reporting a role for ALK in neuronal differentiation [55, 56].

Moreover activating full-length ALK via an activating antibody, Degoutin et. al. demonstrated

Shc association with ALK and consequent phosphorylation as a requirement for downstream

ERK1/2 activation and neurite extension [57] further strengthening the notion that neuronal

differentiation via ALK is mediated via the MAPK-pathway.

Signaling via Drosophila Alk

Jeb

Jeb

JebJeb

ERK

dpp, duf, org, hand,flamingo

Signaling via human/mouse ALK

PTN

RPTPβ/ζ

RPTPβ/ζ

RAS/MAPK

pathway

Proliferation

Differentiation

Anti-Apoptosis

PLCγ

pathway

PI3KAKT

pathwayJAK/STAT3

pathway

Casp.3

Apoptosis

PTN

MK ?

?

Intr

acel

lula

rE

xtr

acel

lula

rN

ucl

eus

Intr

acel

lula

rE

xtr

acel

lula

r

ALK

ALK

P P

ALK

ALK

ALK

P P

16

Using a similar approach, replacing the extracellular domain of ALK with the epidermal

growth factor receptor extracellular region, Piccinini and coworkers demonstrated that ALK

had the capacity to phosphorylated and activate PLCγ and PI3K. Activation of the chimeric

EGFR/ALK protein effectively transformed NIH3T3 cells [58] illustrating the potential

oncogenic properties of ALK when deregulated.

In mammals Pleiotrophin (PTN) also known as heparin binding growth-associated molecule

(HB-GAM) [59], osteoblast-specific factor-1 (OSF-1) [60], heparin affin regulatory peptide

(HARP) [61] and heparin-binding neurotrophic factor (HBNF) [62] and Midkine (MK) also

known as retinoic acid-inducible heparin binding protein (RIHB) [63], have been postulated

to be the activating ligands for ALK [64, 65]. In 2001, using PTN as bait to screen a phage

display cDNA library prepared from human foetal brain, the Wellstein group would identify a

putative PTN binding sequence that they matched to the extracellular region of ALK [64].

Subsequently they reported the identification of a second ligand, the PTN related protein MK.

Using cross-competing assays they showed that MK and PTN competed for the binding to

ALK. In addition, using antibodies directed toward the extracellular region of ALK they were

able to block the in vitro ligand/receptor interaction [65] suggesting a role of MK and PTN in

binding ALK. MK and PTN are small, heparin binding, growth factors implicated in diverse

processes such as neural development, cell migration and angiogenesis [66, 67]. They are

conserved throughout evolution and are found in species ranging from Drosophila to man

[67]. In addition to ALK there are a number of other proposed receptors for MK and PTN. To

date, MK and PTN have been shown to bind and signal via the RPTPβ/δ [68, 69] and N-

syndecan [70, 71] while MK can also bind LRP [72] as well as the α4β1- and α6β1-integrins

[73].

Enhanced proliferation is a commonly observed phenomenon when investigating ALK

activation via PTN [64, 74, 75]. This function seems to be dependent on protein kinase B

(PKB)/AKT activation implicating the PI3K pathway as a target of ALK mediated signaling

[74, 75]. Indeed, Bowden et. al. demonstrated a role for ALK, after PTN activation, as an anti-

apoptotic agent functioning via the MAPK-pathway in NIH3T3 cells [74]. This role has been

further emphasized by studies utilizing glioblastoma cell lines expressing full length ALK

were ribozyme mediated reduction of ALK lead to increased apoptosis [75].

The MK/ALK signaling pathway has been reported, as with PTN/ALK, to be important for

proliferation [65, 76]. Kuo et. al. demonstrated that ALK after activation with MK, interacts

with IRS-1 leading to further downstream signaling and ultimately activation of NF-κB

thereby inducing cell growth. On knockdown of the p65 subunit of NF-κB the proliferation

noted after ALK activation via MK was abolished [76].

Even though several groups have shown that PTN and MK are able to activate ALK [64, 65,

74-77] there are several reports of the opposite [55, 56, 78-80] leading to a degree of

controversy in the field. Moog-Lutz et. al. have clearly shown that agonist monoclonal

antibodies directed toward ALK mediate efficient ERK1/2 phosphorylation and differentiation

of PC12 cells. However, this effect could not be reproduced with PTN which failed to induce

phosphorylation of ALK [56]. The group of Tadashi Yamamoto also showed a dependence on

ALK signaling for neuronal differentiation of SK-H-SH cells using activating antibodies

17

toward ALK. The neuritogenic signal could be blocked with the MEK inhibitor PD98059, thus

implicating the MAPK pathway. Using MK and PTN there were unable to reproduce the

activation of ALK [55].

In 2005 Lu and colleagues demonstrated the presence of two different species of PTN, PTN15

and PTN18. Upon stimulation with PTN15 ALK promoted glioblastoma growth. Conversely

PTN18 promoted glioblastoma migration in an RPTPβ/δ dependent manner [77]. As

mentioned above, RPTPβ/δ has also been suggested as a receptor for PTN [68]. The existence

of two different PTN isoforms was hypothesized to explain the discrepancy in result presented

previously concerning the ability of PTN to activate ALK. However, Mathivet et. al. was

unable to reproduce the effects of either PTN15 or PTN18 on ALK, although they did agree

with Lu et. al. that PTN18 indeed promoted migration of glioblastoma cells via the RPTPβ/δ

receptor [78]. Thus the physiological significance of ALK activation via PTN and MK is still

a matter of debate and investigation within the field

One new theory concerning ALK activation via PTN has arisen recently from the finding of

Perez-Pinera et. al. They showed that PTN indirectly lead to phosphorylation of ALK via

binding to and inactivation of the phosphatase RPTPβ/δ [81]. This phosphorylation of ALK

was not dependent on the ALK extracellular region since a membrane bound construct

containing the ALK intracellular region was phosphorylated equally as well as the full length

ALK receptor [81].

It is important to note when discussing MK and PTN as ligands for ALK that they show no

homology toward the Drosophila Alk ligand Jeb. Jeb harbors a signal peptide and an LDLa

domain [47], while MK and PTN are composed of two domains, one N-terminal N-domain

and one C-terminal C-domain [82, 83], which contain heparin binding modules important for

their activity [82, 84]. In Drosophila the homologues for MK and PTN are the orphan ligands

Miple1 and Miple2 (Miple for Midkine and Pleiotrophin) [85]. The combined expression

pattern of Miple1 and Miple2 complement the expression pattern of dAlk indicating that a

role as activating ligands for dAlk is possible [85]. However, this has so far not been formally

tested at the genetic level and remains a hypothesis.

The group of Allouche recently suggested that ALK might have a function independent of

activation, being a dependency receptor. They showed that ALK was cleaved, via caspase 3

activity, thereby exposing a proapoptotic domain, within the intracellular region, leading to

enhanced apoptosis in cells of lymphoid (Jurkat) or neuronal (13.S.1.24) origin exposed to

apoptosis inducing agents. This proapoptotic function was counteracted via activation of the

ALK receptor using activating antibodies [79] (figure 2).

Throughout the ALK literature a number of comments within different reports can be found

regarding an investigation of a mouse ALK knockout (KO) strain generated by the Morris

group, stating that it is viable without any gross alterations [86-90]. A recent publication has

described an independently generated mouse ALK KO [91]. This strain lack the

transmembrane and intracellular region of ALK, and display increased hippocampal

progenitor proliferation, increased performance in hippocampal associated tasks and an

increased level of dopamine within the basal cortex [91]. Further, the authors also high-lighted

18

an increase in the number of calretinin positive cells within hippocampus [91], a phenotype

also noted in the MK knockout. In this report, Nakamura et. al. characterize the MK KO and

describes a delay in hippocampus development illustrated by the increased/prolonged stain

with calretinin [92]. Within the hippocampus PTN has been shown to act as a regulator of long

term potential in a PTN KO mouse model [93, 94]. While not conclusive, the results of both

the receptor ALK and the putative ligands MK and PTN in the context of hippocampal

development and function suggest a possible link between ALK and PTN/MK.

MK and PTN have similar expression patterns in the mouse [95-98] and studies of MK-/-

embryos, which display a strong up regulation of PTN expression during development,

suggest that PTN and MK are functionally redundant [99]. Indeed, the MK/PTN double KO

shows a more severe phenotype then either of the single KOs. These phenotypes include

female infertility [100] and hearing impairments [101]. If MK and PTN are true ligands for

ALK there is a strong probability they could counteract the loss of ALK via signaling through

any of the other known MK/PTN receptors. The only known ALK family member, LTK, is

expressed in pre-B-cells and adult neurons of hippocampus and cerebral cortex [33]. Since the

ALK KO phenotype is related to hippocampus [91], the idea that LTK might compensate for

ALK loss is intriguing and relevant. Furthermore Yamada and coworkers have demonstrated a

role for LTK in promoting neuronal differentiation of PC12 cells [102], underscoring the fact

that ALK and LTK may potentially compensate for each other. A role for LTK during

development was recently demonstrated by Lopes and coworkers. They could show that

during zebrafich embryogenesis LTK specifies iridophores, from the neural crest linage,

needed for correct pigmentation patterns [103]. Thus far, however mouse LTK appears to only

be expressed in the adult and not during development [33], suggesting a clear distinction from

the ALK receptor, which is extensively expressed during embryogenesis [28, 29]. In addition,

even though LTK and ALK share a highly similar intracellular tyrosine kinase domain there

are notable differences in the extracellular region. LTK lacks several domains found in ALK,

such as the MAM and LDLa domains (figure 1). There is no published LTK knockout (in

higher mammals) to date that might give clues to its role in an in vivo context and the question

regarding whether or not LTK might substitute for loss of ALK will have to await future

scientific investigations.

Upon investigation of the human ALK protein product several groups have reported the

presence of a 140 kDa protein in addition to the 220 kDa full-length ALK species [29, 55-57,

78]. The 140 kDa species is thought to be the result of a cleavage within the extracellular

region of full-length ALK generating an 80 kDa form present in culture medium [56].

Moreover the 140 kDa ALK protein is phosphorylated in response to activation of ALK [55,

57, 78]. The presence of an 85 kDa ALK protein in NIH3T3 cells expressing full-length ALK

was reported by Motegi and coworkers. This protein was phosphorylated in response to

activating antibodies directed toward the extracellular region of ALK [55]. However, to date

no one has been able to show any physiological function for these shorter ALK variants. It is

possible that the shorter forms of ALK are generated after activation of the receptor as part of

the downregulation/degradation processes within the cell. It would be interesting to investigate

whether the shorter variants of ALK show signs of increased ubiquination pattern or

increased/decreased signaling properties compared with the full length ALK receptor. Future

19

work should lead to the definition of the cleavage sites, and the functional relevance of these

forms of ALK in vivo.

6. Anaplastic Lymphoma Kinase in Disease

LK was first discovered as a fusion protein, NPM-ALK, in patients suffering from the

disease ALCL [27]. ALK fusion proteins have also been denoted in inflammatory

myofibroblastic tumour [104], non-small cell lung cancer [105] and diffuse B-cell lymphoma

[106]. In comparison with other tyrosine kinases ALK has also been implicated in oncogenic

processes via overexpression [107] and gain-of function mutations [108-112].

As well as being described as an oncogene, ALK has also been implicated in one case of

disease, schizophrenia [113]. Here Kunugi et. al. reported that a polymorphism at

Glu1529Asp present within the intracellular region of ALK was positively correlated with

susceptibility towards schizophrenia. However they were unable to rule out the possibility that

other polymorphisms, in linkage disequilibrium with the ALK polymorphism, were

responsible for the susceptibility noted in the patient population [113]. One additional study

correlates ALK to schizophrenia, the ALK KO mouse described by Bilsland and colleagues

display an increased level of the dopamine metabolite HVA, together with specific behavioral

changes. In fact, similar phenomenon are observed in schizophrenia patients receiving

antipsychotic treatment, which may suggest a potential involvement of ALK in modulating

schizophrenia [91]. However this is far from being understood at the molecular level.

MK has also been implicated in schizophrenia. Shimizu et. al. detected both increased and

decreased levels of MK in blood serum of schizophrenia patients and suggested that there are

two different entities of MK alterations within schizophrenia [114].

6.1 Anaplastic Lymphoma Kinase Fusion Proteins in Cancer

6.1.1 Anaplastic Large Cell Lymphoma

LK has mostly been studied in the context of ALCL. This disease was denoted already in

1985 [115] and with today‟s nomenclature for lymphomas it can be subdivided into three

different subtypes based on morphology. ALCL is a Non-Hodgkin‟s lymphoma arising from

T-cells characterized by the expression of CD30. ALK positive ALCL is most common in

young adults and children and account for 3% of total Non-Hodgkin‟s lymphoma and 10-30%

of all Non-Hodgkin‟s lymphoma in children [116]. A combinatorial chemotherapy treatment,

CHOP (Cyclophosphamide, Hydroxydaunorubicin (Doxorubicin), Oncovin (Vincristine) and

Prednisone) is applied in Sweden for treatment of ALCL patients [117]. Cyclophosphamide is

an alkylating agent [118] while Doxorubicin intercalates DNA thereby inhibiting cell growth

[119]. Oncovin is a mitotic inhibitor that mediates arrest of mitosis in the metaphase [120]

while Prednisone is a synthetic corticosteroid drug [121]. There is no treatment for ALK

positive ALCL aimed at directly targeting ALK.

ALK expression in ALCL is a prognostic factor used to predict clinical outcome for patients

presenting with ALCL. These patients have a higher 5-year survival rate as compared to ALK

A

A

20

negative cases [122, 123]. Within the ALK positive cohort levels of NPM-ALK transcripts can

also predict outcome of disease with a more unfavorable outcome being apparent in the cohort

having high expression of NPM-ALK [124]. ALK positive ALCL occurs to a higher extent in

children and young adults [122, 123]. However, ALK expression in ALCL is a positive

prognostic factor independent of patient age [125].

Currently there is insufficient information to explain the discrepancy observed between ALK

positive and ALK negative ALCL. However, a few plausible explanations have been

proposed. ten Berge et. al. demonstrated that active caspase 3 expression in ALCL was a

strong prognostic indicator for favorable outcome. The activity of caspase 3 was strongly

correlated with expression of ALK [126]. Since caspase 3 is a key-player in executing

apoptosis the authors suggested that this might partially explain the more favorable outcome

of ALK positive ALCL in correlation to ALK negative ALCL [126]. Khoury and coworkers

detected STAT3 in both ALK positive and ALK negative ALCL cases, leading them to

suggest activated STAT3 as a negative prognostic factor independent of ALK expression in

ALCL [127]. Survivin [128] and MUC-1 [129] are two other marker that indicate a poorer

outcome in ALCL regardless of ALK status. However within the ALK positive cohort of

ALCL MUC-1 expression is indicative of a poorer prognosis with a decrease in overall

survival [129]. The exact action of MUC-1 in modulating ALK positive ALCL is not

determined. However, MUC-1 is commonly over-expressed in oncogenic processes and via its

adhesive properties thought to modulate both metastatic capacity and provide hindrance for

immune cells trying to access the tumour cells [130].

There have been a number of reports regarding expression of ALK fusion protein in healthy

individuals. Trumper et. al. detected minor amounts of NPM-ALK transcript in blood from

healthy donors [131] while Maes and colleagues detected NPM-ALK fusion transcripts in

healthy lymphoid tissue via RT-PCR [132]. Both groups raised the question of whether the

fusion transcript on its own is enough for inducing oncogenic transformation or if secondary

events are needed.

6.1.2 Mouse Models for ALK Driven ALCL

PM-ALK has been established as the causative protein in ALCL by a number of groups

both in vitro and in vivo. For example, Kuefer et. al. in 1997, could induce lymphoid

malignancies in lethally irradiated mice receiving bone marrow expressing human NPM-ALK

[133]. Thereby, lending in vivo support for NPM-ALK as an oncogenic protein as suggested

by in vitro experiments [134, 135]. Further, Chiarle et. al. created transgenic animals

expressing NPM-ALK under the control of the CD4 promoter. This strain developed CD30

positive NPM-ALK T-cell lymphomas as well as plasma cell tumors [136]. Other strategies of

investigating NPM-ALK within the development of ALCL using animal models have been

reviewed recently by Turner et. al. [137].

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21

6.1.3 ALK Fusion Proteins in ALCL

ue to a translocation event, already established during the late 80th [138-140], the kinase

domain of ALK is fused to the 5´end of NPM creating the constitutively expressed fusion

protein NPM-ALK [27] within the disease ALCL. NPM is a multifunctional protein, which

serves as a molecular chaperone involved in ribosome biogenesis with shuttling of pre-

ribosome subunits from the nucleus to the cytoplasm, in addition to playing a role in DNA

repair, transcription and genomic stability [141]. NPM-ALK is constitutively phosphorylated

as a result of the oligomerization domain within NPM bringing two ALK tyrosine kinase

domains together thereby stimulating autophosphorylation and activation [134]. Bischof and

coworkers further explored this dependency upon NPM for oncogenic potential via NPM-

ALK. By using different deletion mutants of NPM-ALK they demonstrated that the complete

NPM portion was required for dimerisation and phosphorylation of the fusion protein and

subsequent transformation of NPM-ALK transfected Fr3T3 cells [142]. NPM-ALK appears to

be present in both the cytoplasm and in the nucleus. However, the nuclear localization seems

to be of no importance for transformation via NPM-ALK. Instead the nuclear localization is a

consequence of the internal properties of NPM as demonstrated by Bischof et. al. [142] and

Mason et. al. [143] and it is the presence of NPM-ALK in the cytoplasm that induces

malignant transformation.

Beside the NPM-portion the ALK kinase domain of NPM-ALK is an absolute requirement for

transforming activity. This is illustrated via a mutation in the ATP binding region of the ALK

catalytic domain, K210R, which renders NPM-ALK kinase dead and eliminate the malignant

phenotype of this protein [142].

In addition to NPM, numerous other fusion partners exist for ALK in ALCL namely; ALO17

(ALK lymphoma oligomerization partner on chromosome 17) [144], TFG (TRK-fused gene)

[145, 146], MSN (moesin) [147], TPM3 and 4 (Tropomyosin 3 and 4) [148-150], ATIC (5-

aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase) [151,

152], MYH9 (Non-muscle myosin heavy chain) [153] and CLTC1 (Clathrin heavy chain-like

1) [154](table 1). Furthermore, all partner proteins of ALK share common characteristics.

Firstly) the transcription of the fusion protein is driven via the promoter of the ALK partner

protein; secondly) the localization of the fusion protein is determined via the ALK partner

protein and; finally) the ALK partner protein has some mode of oligomerization thereby

inducing phosphorylation and activation of the ALK kinase domain [88].

As mentioned above, NPM is responsible for the dimerisation essential for

autophosphorylation of and downstream signaling via the NPM-ALK tyrosine kinase domain

[134, 142]. The TRP3 and TFG fusion partners contain dimeric α-coiled-coil structures that

are hypothesized to be responsible for the dimerisation of TPM3-ALK [148] and TFG-ALK

[145] respectively. Since ATIC exists as a homodimer [155] this property is assumed to be

responsible for the activation of ATIC-ALK [151]. For Moesin, MYH9 and CLTC the reason

behind dimerisation is slightly more complex. CLTC is a component of Clathrin coated

vesicles [156] and Touriol et. al. proposed that clathrin coat formation activate the kinase

domain of ALK via close proximity of the CLTC-ALK fusion proteins. This hypothesis is

supported by data concerning the localization of CLTC-ALK showing a punctuated pattern,

D

22

within the cell, consistent with clathrin coated vesicles [154]. The theory of “close proximity”

as a mean of activating a tyrosine kinase domain is also implemented by Tort and coworkers

[147]. They speculate that MSN-ALK is activated via the ability of moesin to crosslink the

plasma membrane with the actin cytoskeleton [147]. Myosin heavy chain forms as a dimer

however the MYH9 sequence that is fused to ALK is missing the dimerisation domain of the

full-length protein. Still the MYH9-ALK fusion protein is phosphorylated in vivo, which

indicates either an uncharacterized dimerisation domain or, as suggested by the authors, that

MYH9 potentially interacts with other proteins leading to multimerization and consequent

activation of ALK [153].

6.1.4 Oncogenic Signaling via ALK Fusion Proteins

PM-ALK signals via the PLCγ, the PI3K , the RAS/MAPK and the JAK/STAT pathways

[157] as described below in more detail.

PLCγ catalyses the generation of diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP3)

from phosphatidylinositol-4,5-biphosphate (PIP2). DAG and IP3 activate protein kinase C and

trigger the release of Ca2+

[158], respectively. Via its SH2 domain PLCγ has been shown to

directly interact with NPM-ALK. This interaction is of importance for the transforming

potential of NPM-ALK since mutated NPM-ALK which lacks the NPM-ALK/PLCγ

interaction site fails to induce transformation in transfected cell culture systems [42].

Generating NPM-ALK constructs with tyrosine to phenylalanine mutants of all possible

autophosphorylation sites (figure 3), Y664 (corresponding to Y1604 in human full-length

ALK) was noted as responsible for the PLCγ interaction. Of note is that all other mutants

(except the kinase dead Y338, Y342 and Y343 mutants) retained their ability to confer IL3

independent growth of Ba/F3 cells [42] indicating a key role for the PLCγ pathway in ALK

dependent transformation.

PI3K consists of two different subunits, the p110 catalytic subunit and the p85 regulatory

subunit [159]. NPM-ALK interacts with the PI3K p85 subunit [160, 161] thereby activating

the catalytic subunit of PI3K [160, 161]. Inactivation of the PI3K pathway induces apoptosis

in NPM-ALK positive cells [160, 162], indicating a role for the PI3K/AKT pathway in anti-

apoptotic signaling. Further, PKB/AKT activation appears to be a critical step for the

malignant transformation potential by NPM-ALK. This is supported by the work of Slupianek

et. al. who inoculated mice with NPM-ALK positive cells expressing dominant negative

PKB/AKT, leading to a strong impairment of tumour growth, and a delay in tumour formation

as compared to control animals [162].

FOXO3a is a transcription factor which regulates a number of genes involved in cell cycle

progression, promoting cell-cycle arrest when active [163]. NPM-ALK can, via the

PI3K/PKB/AKT pathway, deregulate FOXO3a. Active PKB/AKT phosphorylates FOXO3a,

leading to retention of FOXO3a in the cytoplasm. This results in alteration in the level of

transcription of several FOXO3a target genes in NPM-ALK expressing lymphoma [164], such

as cyclin D2, Bin-1 and p27kip1

, which thereby promote cell survival and cell cycle

progression.

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23

Table 1: Fusion Partners of Anaplastic Lymphoma Kinase in Disease

Disease Fusion Protein Chromosomal Abnormality References

ALCL NPM-ALK t(2;5)(p23;q35) [27]

ALCL ALO17-ALK t(2;17)(p23;q25) [144]

ALCL TFG-ALK t(2;3)(p23;q21) [145, 146]

ALCL MSN-ALK t(2;X)(p23;q11-12) [147]

ALCL TMP3-ALK t(1;2)(q25;p23) [148, 149]

ALCL TMP4-ALK t(2;19)(p23;p13) [150]

ALCL ATIC-ALK inv(2)(p23;q35) [151, 152]

ALCL MYH9-ALK t(2;22)(p23;q11.2) [153]

ALCL CLTC1-ALK t(2;17)(p23;q23) [154]

IMT TMP4-ALK t(2;19)(p23;p13) [165]

IMT TMP3-ALK t(1;2)(q25;p23) [165]

IMT CLTC1-ALK t(2;17)(p23;q23) [166, 167]

IMT SEC31L1-ALK t(2;4)(p23;q21) [168]

IMT RANBP2-ALK t(2;2)(p23;q13)

inv(2)(p23;q11-13)

[169]

IMT CARS-ALK t(2;11;2)(p23;p15;q31) [144, 170]

NSCLC EML4-ALK inv(2)(p21;p23) [105]

DLBCL NPM-ALK t(2;5)(p23;q35) [171]

DLBCL CLTC-ALK t(2;17)(p23;q23) [172]

Table 1; Fusion Partners of Anaplastic Lymphoma Kinase in Disease; NPM; nucleophosmin,

ALO17; ALK lymphoma oligomerization partner on chromosome 17, TFG; TRK-fused gene,

MSN; moesin, TPM3 and 4; Tropomyosin 3 and 4, ATIC; 5-aminoimidazole-4-carboxamide

ribonucleotide formyltransferase/IMP cyclohydrolase, MYH9; Non-muscle myosin heavy

chain, CLTC1; Clathrin heavy chain-like 1, SEC31L1; SEC31 homologue A, RANBP2; Ran-

binding protein 2, CARS; Cysteinyl-tRNA synthetase, EML4; Echinoderm microtubule--

associated protein like 4.

________________________________________________________________________

24

Exclusion of FOXO3a from the nucleus due to phosphorylation via PKB/AKT leads to the

repression of p27kip1

[164], a negative regulator of cell cycle progression [173]. Rassidakis et.

al. would further demonstrate that up-regulating p27kip1

via inactivation of PKB/AKT induces

cell-cycle arrest in NPM-ALK positive cells [174].

A second target for PI3K/PKB/AKT signaling in ALK positive ALCL is mTOR. Vega et. al.,

presented data showing that direct inhibition of PKB/AKT mediates a reduced

phosphorylation of mTOR. However, phosphorylation of mTOR was not completely

abrogated and the authors concluded that additional pathways must function in regulating

mTOR [175]. Marzec et. al. validated the results implicating the PI3K/PKB/AKT pathway in

regulating mTOR. They also showed a stronger dependency on the RAS/MAPK pathway as

an upstream regulator of mTOR in NPM-ALK expressing cells [176].

The RAS/MAPK pathway as a downstream target of NPM-ALK was first reported by the

Yamamoto group. They demonstrated an interaction between NPM-ALK and three different

adaptor proteins IRS-1, Shc and Grb2 [134]. Since Shc and Grb2 are required for recruiting

RAS to the plasma membrane [177], this implicated the RAS/MAPK pathway as a

downstream target of NPM-ALK activity. Interactions with IRS-1 and Shc were however not

essential for transformation since NPM-ALK mutants unable to interact with Shc and IRS-1

still had the ability to transform NIH3T3 cells [134]. A more recent study has shown that

NPM-ALK seems to activate MEK directly. Further, depletion of ERK1 and ERK2, which are

downstream targets of MEK, simultaneously impaired cell proliferation while ERK1

depletion alone induced apoptosis in an ALCL derived ALK positive cell line [178],

indicating that ERK1/2 are involved in survival and proapoptotic functions.

The last major pathway, which is engaged in survival mechanisms of NPM-ALK expressing

ALCL is the JAK/STAT pathway. Several reports have demonstrated a direct interaction

between NPM-ALK and the phosphorylation status of STAT3 and consequent increased

activation of STAT3 [179-181]. The fusion protein NPM-ALK also interacts with and

activates JAK3 [179, 182], the receptor associated tyrosine kinase responsible for STAT3

activation [183]. However whether JAK3 is necessary for the activation of STAT3 in ALCL is

unclear. Zamo et. al., reported strong phosphorylation of STAT3, using truncated NPM-ALK,

which lacks the interaction site for JAK3. This indicates that the JAK3 interaction with NPM-

ALK is not required for STAT3 phosphorylation [179]. Conversely Amin et. al. obtained a

direct interaction between NPM-ALK and JAK3 and through inhibition of JAK3 they

demonstrated a clear reduction in STAT3 activation [182]. This dependency of STAT3

activation by JAK3 phosphorylation in ALK positive ALCL was further supported by Qiu and

coworkers [184], who observed similar results. In a recent study Marc et. al. showed that

depleting JAK3, using inhibitors and RNA knockdown techniques, had no effect on STAT3

phosphorylation in cells expressing NPM-ALK [185]. These data then arguing against the data

presented by Amin [182] and Qiu [184]. Further, the methods used and conclusions drawn by

Marc and colleagues [185] was strongly questioned by Amin and coworkers in editorial

correspondence [186]. However, JAK3 activity is strongly associated with ALK expression

and STAT3 phosphorylation in vivo [187] arguing for a role of JAK3 in ALK positive ALCL

pathogenesis. Disregarding the conflicting data concerning STAT3 phosphorylation it is clear

25

__________________________________________________________________________

that down-regulation of active STAT3 is incompatible with a transforming phenotype in ALK

positive ALCL with cells displaying increased apoptosis and cell-cycle arrest [182, 184, 185,

188].

Several groups have reported additional information of the importance of the JAK/STAT

pathway in ALCL [180, 188]. One finding is the loss of Shp1 in ALK positive ALCL due to

DNA methylation [189]. Shp1 is a negative regulator for the JAK/STAT pathway [183] and

by restoring Shp1 levels in NPM-ALK expressing cells the pathway is inactivated and cell-

cycle progression halted [188]. In addition, PP2, a protein interacting with STAT3 and

necessary for sustained phosphorylation, was found to be over-expressed in ALK positive

ALCL by Zhang et. al. Inhibition of PP2 lead to the abrogation of STAT3 phosphorylation

independently of NPM-ALK activity [180].

Figure 3: The intracellular region of

human and mouse ALK contains the

protein tyrosine kinase (PTK) domain

and span amino acid (aa) 1058-1620 and

1062-1621 respectively. Herein all

potential autophosphorylation sites

within human and mouse ALK are

depictured. Note that there is no

equivalent tyrosine in mouse ALK for

human ALK Y1604. Tyrosines within the

activation loop are depictured in bold

(ref). Localization of tyrosines within the

intracellular region is not depictured at

accurate scale. TM, transmembrane

domain.

hALK mALK

Hum

an A

LK

PT

K d

om

ain

aa 1

116-1

38

3

Mo

use

AL

K P

TK

do

mai

n a

a 11

20

-13

87

TM

Y1139

Y1278

Y1282

Y1283

Y1359

Y1385

Y1135

Y1282

Y1286

Y1287

Y1363

Y1389

Y1063

Y1082

Y1096

Y1059

Y1078

Y1092

Y1405

Y1590

Y1592

Y1401

Y1584

Y1586

Y1604

26

STAT3 has been shown to play a role in NPM-ALK mediated proliferation and anti-apoptotic

actions. However another member of the STAT family, STAT5, displays a more unclear role

in the pathogenesis of ALK positive ALCL. Several reports indicate that STAT5 is

undetectable in ALCL using both in vitro cell culture and in vivo patient samples [179, 180].

However Nieborowska-Skorska et. al. demonstrate an interaction between STAT5 and NPM-

ALK. Further, expressing a dominant negative STAT5B construct they report induction of

apoptosis and cell-cycle arrest in ALCL derived cell lines expressing NPM-ALK [190]. A

more intriguing result was observed after the initial down-regulation of STAT5B, and the

concomitant apoptosis and cell-cycle arrest. Here, a small population of cells regained their

ability to proliferate and induce tumour formation although with a slower growth rate

compared to the parental cell line [190]. This implicates STAT5B as a target for NPM-ALK

mediated proliferation, although perhaps not as an obligatory player. The phosphorylation of

STAT5B in ALCL has also been demonstrated by Zhang and coworkers [191]. In their study

they demonstrated a tumour suppressor function for STAT5A in ALK positive ALCL derived

cell lines. In these cells STAT5A was silenced via methylations in a STAT3 dependent

manner and up-regulation of STAT5A, mediated by inhibition of methylation, resulted in

decreased transcription of NPM-ALK due to the ability of STAT5A to interact with the NPM-

ALK promoter region [191].

Beside the above mentioned players there a number of other novel proteins implicated in

NPM-ALK mediated malignancy. Cdc42, a protein clearly established in regulating cell shape

and migration [192], is regulated via NPM-ALK in ALCL. Upon depleted of Cdc42 cell cycle

arrest and apoptosis are induced [193]. Another protein, which has been implicated is

p130Cas; NPM-ALK can no longer cause transformation on depletion of p130Cas protein.

This dependency on p130Cas has been suggested to be modulated via Grab2 in NPM-ALK

positive ALCL cells [194]. Further, knockdown of Shp2 reduces the migratory capacity of

cells expressing NPM-ALK [195] and Src kinases, especially pp60Src, have been suggested to

be important for the proliferative ability of NPM-ALK positive ALCL cells [196].

Few of the other known ALK fusion proteins have been studied as extensively as NPM-ALK

with respect to downstream signaling mediated by the ALK fusion protein. Nevertheless they

are assumed to function in similar manners as the NPM-ALK fusion protein. This assumption

is supported by studies executed by Hernández et. al. [146] and Trinei et. al. [152]. Trinei et.

al. show an association between ATIC-ALK and Grb2 and Shc [152]. Similar observations

were demonstrated by Hernández et. al. for the TFG-ALK fusion protein. Moreover, in this

study they also demonstrated an association between TFG-ALK and PLCγ [146].

Armstrong and colleagues made an extensive study were they evaluated NPM-ALK, TPM3-

ALK, TFG-ALK, CLTC-ALK and ATIC-ALK with respect to their oncogenic potential both

in vivo and in vitro. They demonstrated, in an in vitro assay, that TPM3-ALK displayed higher

migratory and invasive capacity when compared with the four other ALK fusion proteins

examined. Conversely, when grafting transfected cells subcutaneously in nude mice, NPM-

ALK and TFG-ALK mediated tumours were readily detected 6 days after inoculation, while

TPM3-ALK mediated tumours were detected a few days later [197]. The invasive properties

of the ALK fusion proteins were further evaluated, by an in vivo lung metastasis assay. Here

the TPM3-ALK fusion product shows an increased capacity to form metastases in comparison

27

to the other ALK fusion proteins [198]. Whether or not this increased ability for TPM-ALK

transfected cells to induce metastases will have any clinical relevance is currently unclear.

Employing patient samples, Khoury and coworkers, observed that activated STAT3 was only

expressed in approximately 85% of the ALK positive ALCL cases. The authors speculate that

this could be due to differences in signaling via the different ALK fusion proteins [127]. This

theory is supported by Armstrong et. al. who demonstrated effective phosphorylation of

STAT3 via NPM-ALK, TPM3-ALK, TFG-ALK and ATIC-ALK while showing that CLTC-

ALK was incapable of phosphorylating STAT3 [197].

6.1.5 Inflammatory Myofibroblastic Tumour

nflammatory Myofibroblastic Tumour (IMT) is a benign malignancy of mesenchymal

origin with a prominent inflammatory component consisting of plasma cells and

lymphocytes [199]. First described in the lung these “inflammatory pseudotumours” was

considered a post inflammatory condition rather than a malignant process [200]. They can

manifest in almost any anatomical site [199] although the most common places are the lung,

abdomen and retroperitoneum [201]. In 1999, the 2p23 chromosomal rearrangement and

expression of ALK was reported by Griffin et. al. as a sign that IMTs, or a subpopulation of

IMTs, were neoplastic in origin rather than reactive [104]. Further studies have confirmed the

presence of several different ALK fusion proteins containing the kinase domain of ALK and

partner proteins responsible for dimerisation (table 1).

35-60% of all IMTs appear to exhibit ALK rearrangements [202, 203] with ALK positive

IMTs preferentially affecting young individuals [165, 202, 203]. This pattern of occurrence is

similar to that noted for ALK positive ALCL. Moreover the prognosis appears to be better for

ALK positive IMTs [204] as with ALK positive ALCL.

6.1.6 Non-Small Cell Lung Cancer

ung cancer is the most common cancer in the world and the leading cause of cancer

deaths [205]. Lung carcinoma can be subdivided into two major groups, small-cell lung

carcinoma and non-small cell lung carcinoma (NSCLC) with NSCLC constituting the larger

proportion of cases. As a result of a transformation screen Soda et. al. identified the ALK

fusion protein EML4-ALK in NSCLC [105]. In further investigations employing ALK

inhibitors, they observed a reduction of cell growth in BA/F3 cells expressing EML4-ALK,

supporting an oncogenic role for the fusion protein [105]. Other fusion partners of ALK have

so far not been reported for NSCLC [206] and the EML4-ALK event seem to be a rare

occurrence present in only 3% of all NSCLC cases [207]. However, activating EGFR

mutations have also been found in a small proportion of NSCLC responsive to treatment with

gefitinib (Iressa) [208, 209], an EGFR kinase inhibitor [210, 211]. ALK, being an

uncontrolled activated tyrosine kinase in NSCLC just like EGFR, may prove to be an effective

target in the treatment of NSCLC cases presenting with EML4-ALK. In fact a recent study has

demonstrated an effect of the ALK inhibitor TAE684 in EML4-ALK NSCLC cell lines [212].

However this effect was only seen in one out of three tested cell lines demonstrating a need to

further characterize the EML4-ALK subpopulation of NSCLC.

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6.1.7 ALK Positive Diffuse B-cell lymphoma

iffuse large B-cell lymphoma (DLBCL) is of interest from the perspective that there

seem to be an ALK positive subpopulation expressing either full-length ALK [213] or

ALK fusion protein, NPM-ALK [106, 171] or CLTC-ALK [172] respectively. Arber et. al. in

1996 reported the occurrence of NPM-ALK transcript in large cell lymphomas of B-cell origin

[106] which was subsequently verified by Adam et. al. [171]. CLTC-ALK was reported by

several groups as a rare finding in DLBCL [172, 214, 215] and full-length ALK protein have

so far only been detected in 7 cases of DLBCL [213].

Expression of ALK, either as full-length or as a fusion protein, in DLBCL appears to be a rare

event with only 33 reported cases to date. However, when summarized they seem to occur

preferentially in males spanning all age groups and be correlated with a more aggressive

clinical outcome and a poor response to chemotherapy [216].

6.2 Anaplastic Lymphoma Kinase Overexpression in Cancer

verexpression of ALK in different tumour materials has been evaluated by several

groups. Dirks et. al., evaluated ALK expression in a large panel of human tumour cell

lines and reported expression of the ALK kinase domain in thyroid carcinoma, NSCLC, breast

cancer, melanoma, neuroblastoma, glioblastoma, astrocytoma, retinoblastoma, ewing sarcoma

and rhabdomyosarcoma [80]. Besides these tumour types, ALK expression has also been

noted in leiomyosarcoma, malignant peripheral nerve sheath tumours and malignant fibrous

histocytoma [107]. Some of these - NSCLC, glioblastoma and neuroblastoma - have been

evaluated with respect to ALK activation. However, several of these cancer types are

uncharacterized at the molecular level.

In the case of rhabdomyosarcoma, leiomyosarcoma and malignant fibrous histocytomas an

increased copy number of the chromosomal region 2p23 might explain the overexpression of

ALK [107]. Furthermore, in rhabdomyosarcoma ALK expression appears to be preferentially

found in the alveolar subtype [107, 217].

In glioblastoma ALK phosphorylation and subsequent downstream PKB/AKT activation

appears to occur via PTN. Moreover, in vitro experiments demonstrate a dose dependent role

for ALK with glioblastoma cell lines depleted of ALK growing at a reduced rate compared to

the parental cell line [75].

In breast cancer, a clear role for ALK has not been firmly established, however several line of

evidence point toward a role for ALK in this disease. Firstly; ALK is strongly expressed in

several different subtypes of human breast cancers in a pattern not consistent with wt tissue

[218]. Secondly; PTN, the proposed mammalian ALK ligand, is extensively expressed in

breast cancer [219, 220] and expression of truncated PTN in a human breast cancer cell line

abrogated tumours formation in nude mice, implicating PTN as a player in the malignant

phenotype of breast cancer [221]. Thirdly; the PTN receptor RPTPβ/δ is strongly expressed in

different subtypes of human breast cancer [218]. These three observations together with the

data from Perez-Pinera et. al. which suggest that ALK is indirectly activated via

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PTN/RPTPβ/δ signaling [81] have lead to the proposal that ALK may be activated via the

PTN/RPTPβ/δ pathway and potentially harbor an oncogenic potential in breast cancer

development.

6.3 Anaplastic Lymphoma Kinase Gain-of-Function in Cancer

6.3.1 Neuroblastoma

euroblastoma is derived from neural crest cells of the sympaticoadrenal lineage and can

therefore arise throughout the sympathetic nervous system. It is the most common solid

tumour in childhood and accounts for 15% of all pediatric oncology deaths [222].

Expression of full-length ALK in neuroblastoma was first demonstrated by Lamant and

coworkers in 2000 [223]. Further studies from the group of Sakai show that the ALK locus is

amplified in neuroblastoma cell lines and also in primary patient samples [224, 225].

Furthermore, they found a physical association between ALK and ShcC [224]. Through

disruption of ALK expression in the neuroblastoma cell lines, NB-39-nu and Nagai,

employing siRNA, ShcC phosphorylation (as well as PKB/AKT activation) was down

regulated with concomitant apoptosis of the disrupted cells [225].

During the present year (2008) 5 groundbreaking studies have been published regarding the

presence of activating ALK mutations in both familiar and sporadic cases of neuroblastoma

[108-112]. All mutations (except one) are localized within the kinase domain of ALK and are

assumed to be activating in nature (table 2). Further, neuroblastoma patients who are positive

for ALK mutations appear to have a worse prognosis [108-112].

The initial report by Mossé et. al. [108] resulted from the investigation of familiar cases of

neuroblastoma. A number of different mutations in the ALK protein kinase domain were

described (table 2). In addition, several neuroblastoma cell lines were shown to contain

activating ALK mutations. Knockdown of ALK in these cell lines resulted in an inhibition of

proliferation [108]. The data of Chen et. al. verified the oncogenic potential of the activating

ALK mutants, F1174L and K1062M. They further expressed these mutants in NIH3T3 cells

and employing grafts of ALK mutant expressing cells onto nude mice observed rapid

formation of subcutaneous tumours [111].

Different mutants of ALK found in neuroblastoma patients seem to respond differently to

inhibition of ALK via the chemical inhibitor, TAE684. Using this ALK inhibitor, George et.

al. observed a reduction of cell proliferation and increased apoptosis in a neuroblastoma line

harboring the ALK F1174L mutation, while a neuroblastoma cell line containing the ALK

R1274Q mutant did not respond. Nevertheless when expressed in NIH3T3 cells, both the ALK

R1274Q and the ALKF1174 mutants induced a transformed phenotype and apoptosis was

initiated when cells were exposed to TAE684. Moreover the ALK T1151M mutant protein

was not phosphorylated when expressed in NIH3T3 cell and neither did the cells survive when

grown in IL3 depleted medium. The authors concluded that potential ALK inhibitors should

be investigated with regard to the complete panel of ALK mutants as well as the cellular

milieu in vivo [109].

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Table 2: Activating Mutations of Human Anaplastic Lymphoma Kinase in Neuroblastoma

Nucleotide Changes aa Mutation Targeted Region References

3260 C T T1087I Juxtamembrane domain [111]

3271 G A D1091N Juxtamembrane domain [108]

3383 G C G1128A P loop [108]

3452 C T T1151M Kinase domain [109]

3497 T G M1166R C helix [108]

3512 T A I1171N C helix [108]

3520 T A F1174I End of C helix [108, 109, 111,

112]

3521 T G F1174C End of C helix [110, 111]

3520 T G F1174V End of C helix [111]

3522 C A F1174L End of C helix [108, 111, 112]

3575 G C R1192P β4 strand [108]

3700 G A A1234T Catalytic loop? [109]

3733 T G F1245V Catalytic loop [108]

3733 T A F1245I Catalytic loop [112]

3735 C A F1245L Catalytic loop [111, 112]

3734 T G F1245C Catalytic loop [108, 109]

3749 T C I1250T Catalytic loop [108]

3824 G T R1275L Activation loop [110]

3824 G A R1275Q Activation loop [108-112]

3833 A C Y1278S Activation loop? [110] Table 2; Activating mutations within the ALK kinase domain in neuroblastoma patients

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7. Potential Treatments Strategies for Anaplastic Lymphoma Kinase

Positive Cancers

he development of tyrosine kinase inhibitors for use in cancer therapy have proven

effective in several cases. Most well-known is Gleevec which target the ABL PTK in

chronic myeloid leukemia (CML) [226]. In CML, ABL is present as a fusion protein (BCR-

ABL) due to a translocation event t(9;22) [227]. In addition to inactivating ABL Gleevec also

targets the c-Kit RTK and PDGFR [228, 229]. c-Kit is highly expressed in gastrointestinal

stromal tumours (GIST) [230] and clinical trials in 2001 and 2002 established that Gleevec

could be used in treatment of the malignancy [231, 232]. Other examples of RTK inhibitors

are Gefitinib and Erlotinib, which are selective inhibitors for EGFR (ErbB1) and used in

treatment of NSCLC [233].

The Settleman group is one of many that have investigated the potential clinical application

for ALK inhibitors in ALK positive malignancies. Using the ALK inhibitor TAE684 in more

the 600 different cell lines derived from human cancers they show inhibition of proliferation

in ALK positive ALCL, neuroblastoma and NSCLC cell lines [234]. TAE684 is a 5-chloro-

2,4-diaminophenylpyrimidine which most likely targets the ALK ATP binding pocket thereby

blocking ATP binding [235]. Subsequent administration of TAE684 after injections of NPM-

ALK positive ALCL cells (Karpas 299) in mice prevented development of disease as well as

regression of preinduced ALCL [235]. PF-2341066, an ATP competitive compound, targeting

c-MET and ALK [236] has also been shown to reduce ALK positive ALCL development in an

animal model [237].

UNC-01, a staurosporine derivative, inhibiting PKC [238] and chk1 [239] has been reported to

cause disease regression in one patient with ALK positive ALCL however the effect on ALK

was never validated [240]. Further, Gunby and colleagues when investigating potential

inhibitor of ALK kinase activity, could not confirm a direct relationship between UNC-01 and

ALK [241]. Currently there is a phase 1 clinical trial using UNC-1 in patients with relapsed or

refractory systemic ALCL or mature T-cell lymphoma with the secondary intent to investigate

its effect in ALK positive ALCL (www.ClinicalTrial.gov).

Besides using inhibitors, ALK has also been the target of strategies aimed at reducing the

mRNA thereby depleting the protein. Employing RNA interference to silence ALK Piva et. al.

could induce cell death in ALK positive ALCL cell lines. More importantly in an in vivo

animal model ALCL tumour growth was severely impaired by injection of adenovirus

expressing shRNA targeting ALK [242].

Direct targeting of ALK may be the preferential way to influence ALK positive malignancies

since downstream signaling might be redundant. Yet, by targeting different ALK related

proteins several authors have demonstrated reduced viability and tumour forming capacity of

NPM-ALK positive cell lines. Bonvini et. al. showed an interaction between the chaperone

Hsp90 and NPM-ALK. Using 17-allyl-amino-demethoxygeldanamycin (17-AAG), a

compound specifically inactivating Hsp90 they induced degradation of NPM-ALK and

subsequent apoptosis in ALCL cell lines [243]. Another example of possible downstream

targets in ALK positive ALCL is PKB/AKT. Injecting mice with cells expressing NPM-ALK

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and a dominant negative PKB/AKT construct, Slupianek et. al. demonstrated a severely

impaired tumour forming capacity as compared to animals receiving NPM-ALK expressing

cells with an active PKB/AKT pathway [162].

ALK therapy in the form of vaccination has been brought forward as a possible treatment

since a few reports indicate immunological responses towards ALK in patients [244, 245].

Indeed, Chiarle et. al. tested this hypothesis, vaccinating animals toward human ALK prior to

challenge them with ALK expressing lymphoma cells. They observed protection against

disease in vaccinated animals and in already diseased animals the vaccination in combination

with standard treatment increased the cure rate [246].

Currently, there are no approved treatments for oncogenic malignancies caused via aberrant

ALK activation that directly targets ALK or the downstream ALK activated signaling

pathways. However ALK directed treatments would most likely benefit a number of different

cancer patient populations and is an area of intense research.

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Aim

1. Overall Aim

he overall aim of this thesis has been to evaluate the function of the Receptor Tyrosine

Kinase Anaplastic Lymphoma Kinase. This is however a rather large area to cover and

there are several different directions available for a PhD student to enter, so for each project a

specific aim have been employed.

1.1 Specific Aim: Article I

o evaluate the mRNA and protein expression pattern of ALK during mouse development

to gain new insight regarding possible structures dependent on ALK signaling

1.2 Specific Aim: Article II

o explore the potential conservation of the ALK signaling pathway by evaluating the

ability of Drosophila Jeb in activating mouse ALK.

1.3 Specific Aim: Manuscript I

o investigate the potential phenotype in two different mouse models lacking functional

Anaplastic Lymphoma Kinase thereby exploring the in vivo function of the receptor.

1.4 Specific Aim: Manuscript II

o elucidate the functional role of Anaplastic Lymphoma Kinase in the olfactory system of

the adult mice by clarifying the localization of Anaplastic Lymphoma Kinase mRNA and

protein.

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Results and Discussion

1. Article I: ALK Expression during Development

e have conducted an extensive investigation of ALK mRNA and protein expression

during mouse embryogenesis focusing on developmental days 10.5 to 16.5. Prior to this

study two other groups have independently described ALK expression at the mRNA level [28,

29] however ALK protein expression had not been reported before. Throughout the

investigated developmental stages ALK was strongly expressed, both at the mRNA and

protein level, in structures of the central nervous system (CNS) e.g. the diencephalon, medulla

oblongata, pons and spinal cord.

In the spinal cord ALK mRNA can be visualized from day 11.5 to 14.5 throughout the ventral

compartment. However, between days 12.5 to 14.5 ALK mRNA in the spinal cord displays a

peculiar pattern. In the most caudal part of the spinal cord there is a shift in expression from

the ventral to the dorsal side. This shift in expression is also observed during developmental

day 13.5 in rat for PTN [96], a potential ALK ligand [64]. Within the spinal cord a

subpopulation of the ALK positive cells most likely represents the future motor neurons as

depicted using the markers Isl1 and nkx6.2 [247]. Hurley et. al., investigating ALK expression

during chicken development, also noted ALK expression in the Isl1 positive subpopulation of

spinal motor neurons [52].

In the gastrointestinal canal we detected ALK mRNA and protein in the anterior part of the

structure and with increasing developmental stages the expression progressed posterior.

However ALK was never observed in the hindgut, regardless of the stage investigated. This

may be due to regional differences in the structures examined, and there is also the possibility

that ALK might be expressed in the hindgut during later developmental stages. In addition,

ALK appears to be expressed in a layer just proximal to the musculature presumably

representing the developing enteric neurons.

Beside the above mentioned structures we could also detect ALK in a number of different

ganglions as well as in potentially non neuronal areas including the testis and ovary.

The ALK mRNA and protein expression patterns are in general overall agreement. However,

in some structures such as the diencephalon and spinal cord ALK mRNA and protein, even

though localized within the same structure, do not overlap. We assume this is due to the

subcellular localization of ALK in developing nerve cells with mRNA and protein being

localized in different compartments of the nerve (e.g. cell body and axon).

In conclusion we detect ALK mRNA in numerous neuronal compartments verifying and

extending the result presented in 1997 by Morris et. al. and Iwahara et. al. [28, 29]. Further we

present comprehensive novel data addressing the localization of ALK protein during mouse

development.

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2. Article II: Can Drosophila Jeb activate mouse ALK?

hen discussing ALK function one important and somewhat controversial question is;

how is mammalian ALK activated? Being an RTK the presumed first step toward

activation of ALK would be postulated to occur via ligand binding to the extracellular region

[7]. For dALK this is indeed the case, with the secreted protein Jeb being an established

activating ligand [43, 44]. For mammalian ALK the picture is more complex. Thus far two

different ligands have been proposed for mammalian ALK, MK and PTN [64, 65], however

their assumed role as ligands for ALK are strongly debated (discussed in detail in section 5.3).

Whether or not there is a vertebrate “Jeb-like” ligand capable of activating ALK is a question

of great interest in the light of establishing the in vivo function of ALK as well as clarifying

the signaling pathways driven by ALK. Thus far no “Jeb-like” molecule has been described in

vertebrates that might function as an ALK ligand. To circumvent the issue of not finding

suitable Jeb candidates in vertebrates we reasoned that if there is a Jeb-like molecule in

vertebrates serving the same function as Jeb in Drosophila then in theory Jeb should be able to

activate mouse ALK (if the Jeb/dALK interaction is conserved throughout evolution). To

investigate this theory we employed several different strategies as discussed below.

In Drosophila lack of functional Alk is lethal [43, 44]. This phenotype can be rescued via

expression of the full length dAlk. However expression of full-length mouse ALK fails to

rescue the dAlk mutant phenotype indicating that mouse ALK is unable in substituting for loss

of dAlk. This further suggests that Jeb, even if it associates with mouse ALK, is ineffective in

inducing the appropriate signals needed to rescue the dAlk mutant. Expression of a dominant

negative dAlk protein in a wild type Drosophila background phenocopies the dAlk mutant

phenotype. Conversely, expression of the dominant negative mouse ALK construct does not

interfere with normal gut formation confirming that Jeb lacks the ability to activate mouse

ALK in an in vivo Drosophila context.

To further investigate the potential Jeb/mouse ALK relationship we used a cell based system

were we are able to induce either dAlk or mouse ALK using tetracycline. Stimulating mouse

ALK using an activating antibody directed toward mammalian ALK we could demonstrate

ALK phosphorylation, however dAlk was not phosphorylated. Moreover using recombinant

purified Jeb we could strongly stimulate tyrosine phosphorylation of dAlk, yet no effect on

mouse ALK was apparent. Thus, this further supports our conclusion that Jeb is not able to

activate mouse ALK. Further, in PC12 cells recombinant Jeb could initiate differentiation of

dAlk expressing, but not, mouse ALK expressing cells. This is in perfect agreement with the

above results and we conclude that Drosophila Jeb protein is incapable at inducing signaling

via the mouse ALK RTK. Furthermore, we were able to show that Jeb/dALK signaling could

efficiently induce neurite outgrowth in PC12 cells. This suggest a certain degree of

conservation at the level of functional readout between the two receptors.

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2.1 Why is Drosophila Jeb unable to activate mouse ALK?

iven that Drosophila Jeb is unable to activate mouse ALK, we naturally raised the

question of why? What evolutionary processes have rendered mouse ALK insensitive to

Drosophila Jeb given the conservation of the RTK domain structure? It is theoretically

possible that during evolution either mouse ALK on its own or the vertebrate “Jeb”/ALK pair

have evolved to such an extent that substituting either with the Drosophila counterpart is no

longer feasible. A similar situation has been reported for the RTK RET where the mammalian

ligand is unable in activating the Drosophila Ret receptor although both human and

Drosophila Ret can induce PC12 cell differentiation [248].

The overall amino acid identity between Drosophila and mouse ALK is approximately 30%.

So the idea of mouse ALK evolving to the extent of no longer recognizing the Drosophila Jeb

ligand is not without context. However this raises another interesting topic, is the function

described for Drosophila Alk conserved for mouse ALK? Within Drosophila, Alk has an

essential role in visceral muscle development [43, 44] and lacking Alk signaling is not

compatible with life. However the recently published mouse ALK knockout strain, and our

own ALK knockout mouse, is viable without any notable intestinal defects [91]. Yet the

distribution of ALK protein throughout the gastrointestinal tract during mouse embryogenesis

as illustrated by us [249] and others [28, 29] indicate ALK as a potential player during

developmental processes in the gastrointestinal tract. The idea of redundancy between ALK

and its family member LTK [28, 29] is an interesting question that might explain the non

lethal phenotype of the ALK-/-

mice.

Beside the critical requirement for dAlk function in muscle development it is also of

importance for correct targeting of axon originating in the adult Drosophila optic lobe [50].

The published mouse ALK knockout display an overproduction of neuronal progenitor cells

within the hippocampus [91] supporting a neuronal function for ALK. This study, by Bilsland

et. al., did not address the question of axonal targeting and to date there is no available

information regarding this area in mammalian systems. It would be intriguing to address this

topic in an ALK knockout mouse model especially as we have demonstrated previous that

ALK is heavily expressed in the optic nerve during embryogenesis [249].

2.2 What about the LDLa domain?

he Jeb LDLa domain is important for its interaction with dAlk [44]. This implies that

possible Jeb-like molecules in other organisms responsible for activating ALK

presumably contain the LDLa domain. We proposed that Hen-1 [51] and Mig-13 [250] from

C. elegans might be possible ligands for ALK on the basis of their LDLa domain. Indeed,

Hen-1 has recently been confirmed as an ALK (SCD-2) ligand experimentally by Reiner et.

al. [32] suggesting that the concept of the Jeb/ALK interaction is conserved, at least in lower

organisms.

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3. Manuscript I and II: What is the physiological consequence of loss

of ALK function?

3.1 The ALK Kinase KO and the ALK exon1 KO

hen the project described in the sections below was initiated there was no available

mouse models for investigating the in vivo function of ALK. During the course of this

project Bilsland et. al. published a study regarding a mouse ALK knockout strain [91]. This

strain will be discussed below were appropriate. In addition, over recent years the group of

Stephan Morris has mentioned, in the discussion of several articles, that a mouse ALK

knockout exhibit no apparent phenotypes [86-90].

We were primarily interested in exploring the physiological function of ALK in the context of

higher vertebrates. The mouse ALK gene consists of 29 transcribed exons, spanning 730 kbp

of genomic DNA. By adopting a strategy to delete exons 20 to 23, we created a mutant ALK

locus with a disrupted ATP binding site within the kinase domain [90]. ALK transcript and

protein can still be detected in this strain, however the mutant ALK protein expressed should

be kinase dead.

In the process of generating the ALK Kinase KO we discovered that a company (Lexicon

Pharmaceutical) had designed an ALK knockout lacking the first exon of ALK. This region

contains the starting ATG and the signal peptide and the hypothesis was that the ALK protein

should not be expressed in this mutant, or if expressed the mutant ALK protein should not

localize to the cell membrane. Examination of this ALK knockout strain (referred to as the

ALK exon1 KO) revealed expression of ALK protein. We have not addressed the issue of

whether or not the ALK protein produced localizes to the right compartment in this animal.

The ALK protein produced, although truncated, could possibly contain a functional tyrosine

kinase domain and technically be able to transmit signals downstream.

The ALK kinase KO and the ALK exon1 KO mice are viable. They can be kept as

homozygous stocks and display no gross morphological defects neither during development

nor as adult animals.

3.2 What function might ALK have during mouse embryogenesis?

o investigate the ALK homozygous population in greater detail we examined ALK

homozygous mouse embryos, comparing them to wild type littermates. In Drosophila

org-1 and duf/kirre are transcriptionally regulated via Alk signaling and in the absence of Alk

they are not expressed [43, 44]. The mammalian counterparts are TBX1 and mkirre3

respectively. mKirre3 is thought to participate in axonal pathfinding and synapse formation

during embryogenesis [251], moreover it is heavily expressed in structures that correlate with

ALK expression during development [251-253]. TBX1 is expressed during embryogenesis

[254] and is important for cardio and craniofacial development [255]. However, the ALK

Kinase KO homozygous embryos displayed no alterations in expression pattern for either

TBX1 or mkirre3.

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Kirrel1 (NEPH1) and Kirrel2 are closely related to mKirre3. Kirrel2 modulates neuronal

targeting within the olfactory bulb [256] while Kirrel1 has been implicated in synapse

formation during embryogenesis [257]. The possibility that either of these could be regulated

via ALK was investigated in ALK Kinase KO mice. As for mkirre3, both kirrel1 and kirrel2

exhibited wild type expression in ALK-/-

mice.

TBX1 belongs to a family of 16 different members in mammals [255]. TBX2 and TBX3 are

functionally important in heart, limb and mammary gland development [258, 259] and since

their expression patterns overlap with ALK during development [254] we employed them in

our development study. For both TBX2 and TBX3 we observed a strong overlap with ALK

during development. However, in the ALK Kinase KO homozygote embryos there were no

alterations in expression detected.

Beside the above discussed markers we also investigated the potential ALK ligands PTN and

MK [64, 65]. We could show a close relationship between PTN and ALK protein expression

in the developing central nervous system consistent with the hypothesis that PTN may be a

ligand for ALK. In contrast, MK was not expressed in any areas that could be correlated with

ALK either directly or by close proximity. Furthermore there were no alterations in PTN or

MK protein localization in ALK-/-

embryos. Finally, we examined three different markers,

pSMAD, SMαA and Sox8. Sox8 was used since the expression pattern of this protein is

similar to that of ALK [260]. SMαA was utilized to investigate the visceral musculature of the

gastrointestinal canal while pSMAD was employed due to its dependency on functional ALK

signaling in Drosophila [49]. In conclusion none of these three markers displayed any

irregular expression patterns when examined in ALK Kinase KO homozygous embryos.

Furthermore, results obtained with the ALK exon1 KO results were similar to those with the

ALK Kinase KO. Thus, we were unable to define any apparent defect during embryogenesis

indicating that ALK is not important for vital embryological developmental stages.

3.3 Is there a role for ALK in the adult olfactory bulb?

n the published ALK knockout mouse strain, β-Gal was inserted upon removal of part of the

ALK kinase domain, thereafter visualizing ALK positive cells via expression of β-gal.

Utilizing this approach the areas of strongest β-gal expression was within the olfactory bulb

(OB) [91]. This prompted us to investigate this structure more closely in our ALK Kinase KO

model. In adult animals we detected ALK mRNA within the mitral cell layer and in scattered

cells of the external plexiform layer, with very strong ALK expression throughout the

glomerular layer of the OB. The expression of ALK in the glomerular layer is indicative of the

ALK protein being present in axonal projections. ALK could also be detected both at the RNA

and protein level in the basal part of the nasal epithelium.

From the olfactory epithelium, olfactory sensory neurons (OSN) project to structures termed

glomeruli within the OB leading to establishment of the olfactory map [261]. In order to

investigate the role of ALK in setting up the olfactory map we utilized the markers Kirrel2 and

DBA. Kirrel2 was analyzed since it has been shown to be important for targeting of OSN to

glomeruli [256]. DBA was analyzed since it recognizes specific subpopulations of glomeruli

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[262]. However, within ALK Kinase KO homozygote animals these markers display wild type

expression patterns suggesting that ALK is not involved in establishing the olfactory map.

mKirre3 is expressed in the adult olfactory bulb [253]. This, together with the fact that

Drosophila ALK regulates transcription of duf/kirre (the mammalian counterpart being

mKirre3) [43, 44], encouraged us to investigated mKirre3 in an ALK-/-

context. However,

mKirre3 levels were unaltered between ALK+/+

and ALK-/-

animals.

Using tyrosine hydroxylase and cFos, two markers displaying increased intensity within the

OB when olfactory sensory neurons are activated, no alterations could be noted when

examining ALK kinase KO homozygous adult animals as compared with wild type controls.

This indicates that the olfactory neurons of the nasal epithelium can efficiently converge on

the olfactory bulb even in the absence of ALK activity.

In conclusion, we suggest that ALK does not play an essential role in establishing the

olfactory map or in converging odor information from the OSN to the OB. Nevertheless, the

apparent expression of ALK in areas of synaptic contact suggests that it may have a role in

neuronal transmission. Furthermore, ALK can be detected in the olfactory sensory area of the

nasal epithelium and since the MK/PTN double knockout presents down regulation of odor

receptors [101] it would be intriguing to investigate the possible relationship between ALK

and the odor receptors.

3.4 The ALK Kinase KO and the ALK exon1 KO are small…but why?

ne obvious phenotype is apparent in the ALK Kinase KO and the ALK exon1 KO

homozygous populations; they both exhibit a reduction of total body weight.

Comparing the two strains, ALK-/-

females seem to be affected to a higher extent than males.

Since disrupting ALK gives a more pronounced phenotype in the female population we

suggest that ALK is gender specific. A phenotype dependent on gender has been proposed for

the MK/PTN double knockout were MK-/-

PTN-/-

females are sterile while the corresponding

males can breed. Also there is a distortion in the gender ratio with fewer MK-/-

PTN-/-

females

being born compared to MK-/-

PTN-/-

males [100].

This decrease in total body weight is not apparent before birth and investigating nutritional

intake in the ALK kinase KO strain did not reveal any significant alterations between the

ALK-/-

and ALK+/+

animals indicating that the ALK-/-

reduced weight is not due to a lack of

food intake.

In mouse, ALK is expressed throughout the gastrointestinal canal during embryogenesis [28,

29, 249]. Furthermore Morris et. al. detected strong expression of ALK in the small intestine

of adult human tissue [27]. This motivated us to investigate the intestine in the ALK Kinase

KO strain comparing ALK-/-

and ALK+/+

littermates as alterations in this structure might

explain the reduction in weight noted for the ALK-/-

population. We could identify ALK

positive cells in the gastrointestinal canal of both developing embryos and adult animals, as

developing enteric neuron precursors and mature enteric neurons respectively. No obvious

O

40

morphological defects were detected in the ALK-/- population, and markers employed to

visualize specialized structures of the intestine displayed similar patterns in ALK-/-

and wild

type littermates. Even though we cannot detect any obvious alterations there might be subtle

defects present that might explain the reduced weight noted. In addition, we note that the

enteric nerve system is responsible for control and coordination of intestinal motility, secretion

and blood flow [263] needed for proper digestion. Thus, further analysis will be required to

shed light on the mechanism behind the reduced weigh observed in ALK-/- mutant mice. At

the present time, we state that the ALK knockout display an idiopathic reduction in weight.

3.5 Why are animals smaller? Lessons from the literature

hat are the reasons in the literature for genetically modified animals presenting a

smaller size then there wild type counterparts? Altering fat deposits and regulation of

fat cells is one way to affect body size. This is apparent in the Interleukin 1 receptor antagonist

(IL-1ra) knockout were defective regulation of adiposive tissue give a lean mice phenotype

[264]. Another example is the acetylating enzyme, spermidine/spermine N1-acetyltransferase,

that when overexpressed in mice results in a lean phenotype due to alterations of fat

homeostasis [265]. The skeleton is another area often targeted when size is disrupted as

apparent for both the transcription factor Sox8 and the RTK discoidin domain receptor 1

(DDR1). Loss of Sox8 is concurrent with a small body size due to premature osteoblast

differentiation and reduced bone mass [266] while mice deficient in DDR1 display dwarfism

due to reduced chondrocyte proliferation and bone growth [267]. Besides the above mentioned

examples several other mouse models displaying a small body size are found in the literature.

TNFα converting enzyme (TACE) is responsible for cleavage of the TNFα precursor to

generate the mature cytokine TNFα. Mice deficient in TACE fail in controlling energy

homeostasis since they cannot respond to energy depletion with the appropriate behavior (e.g.

increased food consumption and decrease of energy expenditure) [268]. c-Myc is embryonic

lethal when depleted. However in a c-Myc+/-

context animals are viable yet smaller when

compared to wild type littermates, this due to multiorgan hypoplasi due to decreased amount

of cells [269]. Last it is of interest that the MK/PTN double knockout has a reduced body

weight, although the molecular mechanisms behind this phenotype have not been established

[100]. Presently we can only speculate on the mechanism involved in ALK-/-

animals,

however, it is clear that ALK has an important role in the regulation of total body weight.

3.6 Why is ALK not vital for life in the mouse?

he ALK knockouts presented here and the one published by Bilsland et. al. [91] do not

display any severe phenotypes and can be maintained via homozygous breeding. Since

Drosophila mutants lacking functional ALK signaling have such an apparent and deleterious

phenotype [44] the question arise of why this not the case in mouse?

There are several different theories which may address the above question of which a few are

discussed below. Firstly, the ALK knockout strain established by Bilsland and coworkers, just

like our ALK Kinase KO strain, lacks the kinase domain and presents residual ALK mutant

transcript in the adult mouse brain [91]. Expression of the mutant ALK proteins can also be

detected in our ALK Kinase KO and ALK exon1 KO strains. This suggests that the function

W

T

41

of ALK may not be completely abrogated although the protein is altered. Furthermore, for the

ALK exon1 KO, it is possible that the mutant protein made contains a functional kinase

domain. This may explain the milder phenotype seen in the ALK exon1 KO-/-

populations

when compared with the ALK Kinase KO strain, indicating that it still retains some ALK

signaling properties. Thus, while impossible to address with the current mouse mutants, it

could be that complete deletion of the ALK locus – or at least complete abrogation of the

production of ALK protein - may result in a lethal phenotype. Secondly, ALK has one close

family member, LTK, and it is very possible that LTK function is able to rescues the loss of

ALK. While this is still an unaddressed question, it should be noted that ALK is highly

expressed during embryogenesis [28, 29, 249], while LTK is absent [33]. Conclusion of this

open question will require generation of an LTK knockout, together with a combined

LTK/ALK double knockout. Thirdly, if PTN and MK are the ligand for ALK as proposed by

Stoica et. al. [64, 65] it is possible that they could compensate for loss of ALK. Such a

scenario can be envisioned, since there are multiple receptors proposed for MK and PTN.

Fourthly, ALK may not be essential for life in mouse. However, even if ALK is not vital for

“staying alive” in a mouse context one must remember that laboratory animals are kept in a

safe and secluded environment. Maybe if subjected to the natural environment loss of ALK

will prove incompatible with life from the perspective of „survival of the fittest‟.

42

Conclusions

1. Article I

ALK mRNA and protein is strongly expressed during development mostly confined

to the CNS

2. Article II

Mouse ALK is unable to substitute for the loss of dALK in an in vivo Drosophila

assay

Drosophila Jeb cannot associate with and signal via mouse ALK neither in an in vivo

Drosophila context or in different in vitro cell based assays

Drosophila Alk, when activated via recombinant purified Jeb protein, induces neurite

outgrowth in PC12 cells.

3. Manuscript I and II

ALK-/-

animals are viable, fertile and can be maintained as a homozygous stock

ALK is not vital for developmental processes during embryogenesis

ALK is expressed within the adult olfactory bulb however it does not have an essential

role in establishing the odor map or converging odor information from the olfactory

sensory neurons to the olfactory bulb

ALK-/-

knockout animals display a reduction in total body weight that is not dependent

on food intake, organ weight or fat content

ALK is expressed in the enteric nerve system of the gastrointestinal canal in the adult

and developing gastrointestinal canal.

43

Acknowledgement

First and most importantly, my supervisor Bengt Hallberg. I´m grateful for the opportunity

you presented me with several years ago, to do my PhD in your lab. Over the years you have

been a guiding light pointing me in the right direction (never saying directly what my mistake

was – but rather making sure I know where to find the answer and have me report it back). I

can only say thank you, for all the knowledge and encouragement you have given me.

Secondly, my co-supervisor Ruth Palmer, your guidance and support in all issues has been

deeply appreciated and acknowledged. Thirdly , my second co-supervisor Göran Roos. We

may not have had such a close supervisor/student relationship but I have appreciated you input

in my work

To all people contributing to the results presented in this thesis (beside the once presented

above), Professor Marc Vigny, Dr. Maria Henriksson, Dr. Nelson Khoo, Dr. Hai-Ling

Yang, Therese Eriksson, Professor Anna Berghard and Professor Staffan Bohm.

Special thanks to Christina Schönherr for giving me her table with ALK point mutations to

use in my thesis

Special thanks to the staff in the animal house especially Ulla-Britt, Kerstin, Carola and Maria

for excellent caretaking of my animals and always helping out when needed. Without you life

in the animal house would not be fun.

To all members of the laboratory that have passed over the years. Maria, Anna, Charlotte

(without you me English have deteriorated to “Svengelska”), Lubna (I will not forget you in

USA), Hai-Ling (you are always present in my mind), Christina (my one and only labmate)

and all student non mentioned and none forgotten

Everyone in the laboratory of Ruth Palmer, walking over and having a chat/FIKA/gossip have

made the working day slightly more endurable (when my motivation have been low).

To Åsa, Terry and Karin for all help over the years with administrative issues as well as all

other questions I would not have known have to solve if not asking you

To everyone at the department of Medical Bioscience (floor 2 and 3). A workplace is nothing

without your workmates - You have all made the working day more than just work.

To my friends online and irl, Zarkan, Zarkana and Lich. I appreciate all moments spent with

you, both in front and away from the computer screen. Snittaren, lunch is an always

appreciated moment to gossip about work, family and foremost online playing . Maria and

Anne-May, I may be extremely bad at keeping contact but I have valued our lunch dates.

Till min familj. Mary (mamma) och Bert (pappa) utan erat stöd hade jag inte varit den jag är

idag. Ni är ovärdeligt, älskar er. Frida, Lisa och Kajsa, jag kunde inte ha fått bättre

småsystrar, älskar er

44

Johnny, tack för att du finns där, för inhandlad risen när blodsockernivån var låg, för att du

inte klagat när jag spenderat aldeles för många timmar på jobbet, och sköt all markservice

medans jag skrivit min avhandling, för att du finns där när jag behöver dig som mest och

accepterar mig för den jag är, älskar dig

And remember it can be hard to differentiate between people…

“Magicians and scientists are, on the face of it, poles apart. Certainly, a group of people who

often dress strangely, live in a world of their own, speak a specialized language and frequently

make statements that appear to be in flagrant breach of common sense have nothing in

common with a group of people who often dress strangely, speak a specialized language, live

in ... er ...”

Terry Pratchet, Ian Stewart and Jack Cohen

The science of Discworld

45

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