Chapter 16Chapter 16

Cellular signal transductionCellular signal transduction

A general introductionA general introduction

Unicellular organism —— Directly responds to extraneous signals.

Multicellular ——

transmits the information by the intercellular complicated signal transduction system, and regulates the activity of body.

When outer environment changes ：

chemical substances which regulate the life activity of cells ——signaling substance

Intercellular signal transduction can be transduced by ：

* directly contact between adjacent cells.

* Regulation of metabolism and function of itself and other cells by means of secreting chemical substances by cells.

General manner of intercellular signal transduction :

target cell

stimulation

target cell

secretive cell

receptor second messengers

effector protein

effector protein

signal substance (first messenger)

signaling substances

section 1

Ⅰ 、 Intercellular signaling substance

* Chemical character protein, peptide, amino acid derivatives, s

teroid hormone, fatty acid derivatives, NO and so on

* Definition A general designation of chemical substances which are secreted by the cells in order to regulate the life activity of the target cells.

* Classification

1 、 Local chemical medium

Paracrine signal

characteristics ：

The effective time is usually short.

For instance:growth factor, NO, prostaglandins and so on.

Paracrine signal molecules are secreted by common cells in vivo ； Paracrine signal molecule do not enter blood circulation, but arrive nearby target cells by diffusion.

2 、 Hormones

Endocrine signal

Characteristics ：

effective time of most of them is longer.

For instance:Insulin, thyroxine, adrenalin and so on.

endocrine signal molecule are secreted by endocrine cells which are specially differentiated;

arrive the target cells through the blood circulation;

3. Neural transmitter

synapse-secreted signal;

Characteristic ：

effective time is short.

e.g.acetylcholine 、 noradrenaline and so on

.

secreted by nerve cell; arrive to the target cell through the synaptic cleft ；

Others ： Some intercellular signaling substances can act on the same cell or on the secreting cells themselves. They are called autocrine signal.

Some intercellular signaling substances can transmit information in different bodies, e.g. Insect sex hormone.

the pathways of intercellular signaling substances affect the cellular functions

Type Signal substance Receptor Changes in the cellsNeural

transmitter acetylcholine 、 glutamic acid 、 Υ–amido-butyric acid.

membrane receptor

Effect on the on-off of ion channel

Growth factor

insulin-linked growth factor-1 、 epidermal growth factor 、 platelet-derived growth factor.

membrane receptor

resulting in phosphorylation and dephosphorylation of enzyme protein and function protein, change the metabolism of cell and gene expression.

Hormone protein 、 polypeptide and amino acid ramification and so on hormone 、 steroid hormone 、thyroxine.

Membrane receptor

intracellular receptor

Ditto.

Effect the transcription of genes.

Ⅱ 、 Intracellular signaling substance

Inorganic ions ： Ca2+

Derivative of lipid ： DAG 、 CerDerivative of saccharide: IP3

nucleotide ： cAMP 、 cGMPsignal protein molecule

* Chemical property:

* Definition Chemical substance which is transmiting cell regulation signals within the cells .

Small molecules which are used to tr

ansduce information within the cells.

For instances ：

Ca2+ 、 DAG 、 IP3 、 Cer 、 cAMP 、

cGMP and so on .

※ Secondary messenger

Section 2

receptor

Receptors are proteins, anchored in cell membrane or in the cells, which can recognize and bind with specific biological active molecules, and result in biological effect.

biological active molecules which can bin

d with receptor are named as ligand.

※ Receptor

※ Ligand

The receptors located in the cytosol an

d nucleus are all DNA binding proteins.

Membrane receptor

Intracellular receptor

Large number of the receptors located on the plasma membrane are enchasing glycoprotein 。

Ⅰ.Classification, structure and function of receptors

1. Membrane receptor A. circular receptor——the ion channel dependent on the ligand

Acetylcholine receptor

B. -helix receptor with seven transmembrane fragments

—serpentine receptor

G protein couple region

※ GTP/GDP binding protein

（ G protein ） G protein, which is combined with GTP or GDP, is a kind of peripheric protein which is located on the cytosolic face of the plasma membrane. It is composed of three subunits: 、、 .

G protein has two conformations ： inactive state; active state.

Inactive

Active

G protein cycleG protein cycle

Signal transduction mediated by this receptor can be reduced to ：

hormone receptor

G protein enzyme second messenger

Protein kinase

Enzyme or other functional protein

biological effect

G proteins in the process of the signal transduction

Type of G protein -subunit Function

Gs s S timulating AC

Ｇ i ｉ Inhibiting AC

Ｇ q q PLC stimulating specifically phosphoinositol

Ｇ o* o In brain the main G protein

which can regulate the ion channel

Transportor Ｔ a Stimulating visionAC: adenylate cyclase

PLC: phospholipase C

TPK

EGF-R

C ． -helix receptor with single transmembrane fragment ：

membrane

IgG: immunoglobulins

IgG-linked sequence

Receptor has the activity of tyrosine protein kinase after binding with ligand. For instance: insulin receptor IGF-R epithelium growth factor EGF-R ）

Receptor is linked with tyrosine protein kinase after binding with ligand so to produce the activity of TPK. For instance: growth hormone receptor, interferon receptor.

Receptor not linked with tyrosine protein kinase ：

Tyrosine protein kinase-linked receptor：

Some receptors with a single transmembrane

fragment have the activity of catalysis. When

they bind with ligand, they will form a recept

or-dimer. The TPK in each monomer will be

activated, and phosphorylate their counterpa

rt in dimer. This process is known as autoph

osphorylatoin.

Autophosphorylation ：

Acting mechanism of EGF:

2. Intracellular receptor

A ． Structure of receptor

COOH

DNA binding domain

hormone binding site

ＮＨ 2

Highly variable domain

B. Correlated ligand ——

Steroid hormone, thyroxine and retinoic acid and so on

C. Function ——

Most of intracellular receptors are trans-acting factors. After binding to the corresponding ligands, they can bind with DNA cis-acting elements to regulate gene transcription.

Ⅱ 、 acting characteristic of receptor

• High specificity

• High affinity

• Saturability • Reversibility • Specifically acting mode

Ⅲ 、 Regulation of the activity of receptor

•Influence of phosphorylation and dephosphorylation

•Influence of metabolism of membrane lipid

• enzymatic hydrolysis

•Regulation of Ｇ protein

section 3The pathway of signal

transduction

Sign

al transd

uction

med

iaed in

tracellular recep

tor：

Sign

al transd

uction

med

iaed m

emb

rane recep

tor：

1. Signal transduction mediated by membrane receptor ：

– The pathway of cAMP-protein kinase

– The pathway of Ca2+-dependent protein kinase

– The pathway of cGMP-protein kinase

– the pathway of tyrosine protein kinase

– the pathway of nuclear factor

A. The pathway of signal transduction mediated by cAMP-protein kinase A

a 、 constituents ： Extracellular signaling molecules（ mainly are glucagon 、 adrenalin and adrenotrophin ） .

Receptor ， G protein ， AC ， cAMP , PKA

b ． Synthesis and degradation of cAMP ：

PPi

ATPＡＣ

Mg2+

cAMP 5`-AMPphosphodiesterase

H2OMg2+

NO

CH2O

OHO

N

NN

NH2

PO

OH

cAMP

NO

CH2O

OHOH

N

NN

NH2

P

O

OH

OP

O

OH

OP

O

OH

OH

ATP

AC

PPi

NO

CH2O

OHOH

N

NN

NH2

P

O

OH

OH

AMP

PDE

H2O

(Phosphodiesterase, PDE)

(Adenylate cyclase, AC)

C ． Acting mechanism of cAMP ：

＋ 4cAMP

＋

•Activates of cAMP protein kinase Ｃ： catalytic subunit Ｒ： regulation subunit

C

C

R

R C

C

cAMP

R

R

cAMP

cAMPcAMP

（ cAMP-dependent protein kinase ， PKA ）

R ： regulation subunit

C ： catalytic subunit

Serine/threonine protein kinases familySerine/threonine protein kinases family

D ． Effect of PKA ：

（ a ） regulation on metabolism

realize the regulation by phosphorylati

ng the effector proteins.

Pi

phosphorylase

G-1-P

glycogen n+1

G-6-P Glu

glycogen synthase

UTP

UDPG

PPi

UDP

phosphorylase ｂ phosphorylase ａ

ATP

PPi

phosphoprotein phosphatase

phosphoprotein phosphatase

H2OPPi

⊕PKA

inhibitor Ｉ a

inhibitor Ｉb

ATP

phosphoprotein phosphatase

PPiEffection of Adrenalin on the metabolism of glycogen

adrenalin ＋ receptor

adrenalin · receptor complex

Activating Ｇ -protein

Activating AC

ATP cAMP

PKA

⊕

phosphorlatase kinase b

ATP

phosphorlatase kinase a

Phosphorylation of substrate protein by PKA

substrate results of physilologocal phosphorylation significance histone lose repression promote transcription on transcription and synthesis of protein

ribosome promote promote the synthesisProtein translation of protein

membrane change of conformation change of permeabilityprotein and function of membrane ion channel

tubulin change of conformation influence the secretion and function function of cells

myogen of eacy to bind with Ca2+ enhance the contractioncardiac muscle cardiac muscle

In transcription regulatory region of the genes regul

ated by cAMP, there is a consensus sequenc （ TG

ACGTCA ） which is known as cAMP response ele

ment (CRE).

cAMP response element binding protein (CREB) c

an interact with CRE to regulate the transcription o

f the gene.

（ b ） Regulation effect on gene expression

cell membrane

nucleus membrane

（二） the pathway of Ca2+-dependent protein kinase

1. The pathway of Ca2+ － phospholipid dependent protein kinase

(1) Second messenger ： DAG ， IP3

* The production of DAG ， IP3:

PIP2

PLCDAG + IP ３

lecithin

phosphatidic acid

phosphatidic acid hydrolase

Regulation of metabolism

Gene expression

Ca2+-DAG-PKC pathway

* Function of DAG ， IP3 ：

DAG ：

DAG, phosphatidylserine and Ca2+ cooperate to activate PKC by allosteric effect.

IP3 ：

bind to the receptor on endoplasmic reticulum so to promote the release of Ca2+.

(2) Structure and function of PKC

There are four conservative regions of amino acid sequence (C1, C2, C3, C4 ) and variable regions （Ｖ）， dividing into regulation region and catalytic region.

Structure and typing:

C1 ：

C2 ：

regulation region

C3 ：

C4 ：

catalytic region

Cys-richDAG binding site and TPA binding site

Ca2+ binding site

ATP binding site

substrate binding, site of transfer of phosphate group

classification

Ca2+-dependent type ：，，

Ca2+ non-dependent type ： 、、、、

regulatory region catalytic

region

C1 C2 C3 C4

，，

C1 C3 C4

、、、

C3 C4C1

* The function of physiology of PKC

The activated PKC cause a series of phosphorylation of Ser, Thr residues of target proteins.

Membrane receptors, Membrane proteins and various enzymes.

① Regulating metabolism

Target proteins include ：

② Regulation on gene expression ：

The activation of genes by PKC include early response and late response.

PKC c-fos

AP1 / c-jun

Pi

PiPi

PimRNAs

C-fos

AP1/C-jun

signal

Early activation and late activation of genes by PKC

Early activation

Late activation

Cell membrane

receptor

nucleus TRE

5’TGACTCA3’ DNA

2. The pathway of Ca2+-CaM-dependent protein kinase

(1) constituents ： receptor, G protein, PLC, IP3, Ca2+, calmodulin, CaM-kinase

(the pathway of Ca2+-CaM kinase )

calmodulin (CaM)

CaM has four Ca2+-binding sites. CaM and Ca2+ w

ork together to activate CaM-kinase, and phosph

orylate many proteins (Ser/Thr residues).

三、 The pathway of cGMP-protein kinase

Receptor ， Guanylate cyclase (GC ) ，cGMP, PKG

1. constituents ：

2 、 Synthesis and degradation of cGMP

GTPG Ｃ

Mg2+

PPi

cGMPphosphodiesterase

H2OCa2+ or Mg2+

5′- GMP

Phosphorylate Ser/Thr residues of proteins or

enzymes

3 、 function of PKG

NOGC

PKG phosphorylation of proteins

GCG protein

GTP cGMP

hormone

R Cell membrane

四、 The pathway of tyrosine protein kinase

（ tyrosine – protein kinase , TPK ）

Classificatoin:Receptor-TPK （ on cell membrane ） for instance: insulin receptor, growth facter receptor, an

d receptors coded by proto-oncogenes (erb-B, kit, fins etc.)

Non-receptor-TPK （ in cytosol ） such as JAK and TPK coded by proto-oncogenes （ src, ye

s, bcr-abl ）

1. Receptor-TPK-ras-MAPK pathway

Grb2 (growth factor receptor bound protein 2)

SH2 domain ( src homology domain 2) ：

SH2 is the consensus amino acid sequence in some linking proteins in cells. SH2 domain is homologous to tyrosine-protein kinase region coded by proto-oncogene src. This region can recognize and bind the phosphorylated tyrosine residue.

catalytic receptor, Grb2, SOS , Ras protein, Raf protein, MAPK system

1 、 constituents:

SH2 SH3

SOS （ son of sevenless) ：Proline-rich ， can bind to SH3, and promote the conversion of GDP in Ras to GTP.

Ras ： product of proto-oncogene ， similar to G subunit of G protein

Raf protein ： has the activity of Ser/Thr protein kinase.

MAPK system （ mitogen-activated protein kinase) ：Include MAPK, MAPK kinase (MAPKK), MAPKK k

inase (MAPKKK) ， a group of proteins which are bot

h enzymes and substrates.

extracellular signalEGF 、 PDF and so on.

PTK-linked active receptor GRB2 SOS Ras-GTP

PRaf

Regulation of other proteins activated

MAPKK

MAPK P

P

Pnucleus trans-acting factor

Regulation of gene expression

dimer

Cell membrane

unactivated receptor

unactivated Ras

activation of receptor

activation of Ras

kinases systemOther enzyme effector

The activation of Ras protein and its action in signal transduction

outside of cell

inside of cell

dimerization

Cell membrane

cytosol

Activation of PDGF receptor and signal transduction

2. The pathway of JAKs-STAT

form ： noncatalytic receptor ； JAKs;

signal transducer and transcription

activator （ STAT ）

（ 五） The pathway of nuclear factor Ｂ

nuclear factor- B (NF- B) :

TNFCer etc. kinase system

Infection by virus, lipidsaccharide, active oxygen intermediates and so on

PKA 、 PKC etc.

Activation of NF- B

• Sketch map of activation pathway of NF- B

the pathway mainly involves the signal trans

duction in the process of body defence response,

tissue damage and stress, differentiation and apo

ptosis, and inhibitation on the growth of tumor.

Ⅱ 、 Signal transduction mediated by intracellular receptor

• Intracellular receptor ： nuclear receptor

cytosolic receptor

• ligand ： steroid hormone

thyroxine

section 4

crosstalking of signal transduction

• Member of one signal pathway can join to activate or inhibit another signal pathway.

• Two different signal pathway can together effect on same effectic proteins or same regulatory region of gene to bring into play effection.

• A kind of signal molecule can effect on several pathways of signal transduction.

section 5

signal transduction and disease

* Familial hypercholesterolemia ： deficiency of LDL receptor

* insulin-independent diabetes mellitus ：decrease of insulin receptor or deficiency of function

* others:For instance: cholera and pertussis are related to the abnormality of G protein.

summary

• Basic concepts

Signaling substances ： classification ， concep

t

receptor ： concept ， types ， characteristics of interaction with ligand

Second messengers

• Important signal transduction pathway