archipelago/hcdc 4 and endometrial cancer
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Archipelago/hCDC 4 and Endometrial Cancer
Keji Baruwa
March 20, 2003
SCF Ubiquitin Ligase Complex (Budding yeast) Triggers DNA replication by catalyzing ubiquitination
of SIC13 components: ySKP1, CDC53 (cullin), & F-box protein
CDC4
Lyapina et. al
Proteolytic Degradation
Proteins are marked for proteolytic degradation by attachment of multiubiqutin chains
Activated by E1 Ubiquitin then transferred to E2 (ubiquitin
conjugating enzyme) E3 Once substrate is multiubiquitinated, it is then
recognized and degraded by 26S proteasome
Lyapina et al.
Ubiquitination Pathway Discovered in Budding Yeast Components of this pathway: CDC53,
CDC4, & ySKP1-assemble into ubiquitin ligase complex, SCFCDC4
SCFCDC4, collaborates with yCDC34 to catalyze ubiquitination of SIC1
Lyapina et al.
Multiple SCF Complexes in Yeast Analysis has revealed that SIC1 proteolysis
requires CDC4 G1 cyclin proteolysis depends on GRR1
(distinct F-box containing protein) SCF complexes assembled with GRR1
instead of CDC4 bind G1 cyclins but not
SIC15
Lyapina et al.
Components of SCF Ubiquitination Highly Conserved During Evolution Human homologs of yCDC34 and ySKP1 have
been identified F-box containing proteins like CDC4 (WD 40
repeats) and GRR1 have been reported in many eukaryotes
Potential human counterpart of GRR1 & SKP2 identified with hSKP1 as a cyclin A/CDK2-associated protein needed for S phase progression
Lyapina et al.
Phosphorylation of SCF
SCF substrates in budding yeast must be phosphorylated before ubiquitination
Many human cell cycle regulators are targeted for ubiquitination after CDK phosphorylation. (example p27)
Cyclins E and D1 are degraded by ubiquitin-dependent pathway after phosphorylation at a specific site
Lyapina et al.
Phosphorylation, Cont’d
SCF-bound Cyclin A/CDK2 may phosphorylate SCF subunits or potential substrates like E2F-1/DP-1, which will activate SCF-dependent ubiquitination
Lyapina et al.
Does SCF Activity Really Exist in Animal Cells S. cerevisiae cdc53ts mutants arrest at G1/S
transition; C. elegans cul-1mutants fail to exit cycle
Ubiquitin-like proteins that are conjugated to proteins that involve E1 and E2 homologs
Human Cullin, Cul 2 assembles with von Hippel-Lindau tumor suppressor protein ElonginB/Elongin C complex
Lyapina et al.
hCUL1 and hSKP1 interact in vivo
Lyapina et al.
Human Cul1, hSKP1, & SKP2
Human Cul1 can interact with human SKP1, SKP2, and Cyclin A/CDK2
Association mediated by SKP2
Lyapina et al.
Human Cul1 directly interacts with hSKP1 and SKP2
hCul1, hSKP1, and SKP2 can assemble into an SCF-like particle when co expressed in insect cells
Lyapina et al.
Functions of Homologues of SCF Complex Kinectochore function S-phase progression Exit from the cell cycle Transcript elongation Regulation of Hypoxia-inducible genes Suppression of tumor genesis
Lyapina et al.
hCUL1 Assembles to SCF-like complexes in human cells Associates with hSKP1 in transfected HeLa S3
cells Assembles into complexes with both hSKP1 and
F-box protein SKP2 in vitro Complements the growth of cdc53ts mutant Associates with ubiquitination-promoting activity
in HeLa S3 cell lysate SUBUNIT OF AN SCF-LIKE E3 COMPLEX IN
HUMAN CELLSLyapina et al.
Archipelago
Contains 7 WD 40 Repeats and F-box Binds Cyclin E Down regulates cyclin in vivo (SCF complex might be involved in
turnover of cyclin E)
Mitchell
Fbw7
Over expression decreases levels of cyclin E hCDC4 and Fbw7 interact with cyclin e
– This interaction depends upon cyclin e being phosphorylated at the threonine position
– Mutation in cdc4 cyclin e stabiliz ed
Mutations in WD 40 domain of hCDC4/Fbw7 stop phosphorylation of cyclin e
Mitchell
hCDC4/Fbw7/Ago
Tumor suppressor Negative regulator of cell proliferation that
normally prevents cancer progression Disruption may deregulate cell division at
more than one level
Schwab & Tyers
Cell Cycle Balancing Acts(Schwab and Tyers)
hCDC4
Targets cyclin E to SCF Mutated in at least 16% of endometrial tumors Mutations are found either in the substrate binding
domain of protein or at the amino terminus If mutated-loss of heterozygosity Localized to chromosome 4q32- (deleted in 30%
of human tumors)
Schwab & Tyers
hCDC4 Cont’d
Mutated in primary human tumors May function as a tumor suppressor Accumulation of Cyclin E may depend on
ability of hCDC4 to bind substrate 2 hit hypothesis
Schwab and Tyers
Endometrial Cancer Originates in the endometrial lining of the uterus Most common gynecologic malignancy Normally occurs in postmenopausal women Estrogen dependent disease Chronic exposure to estrogen without normal
balance of progesterone is believed to be major risk of this cancer
http://www.oncologychannel.com/endometrialcancer/
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