Prof. R. V. Skibbens. Cell Cycle, Cell Division and Cancer (Part 2)

Transcription

1 Prof. R. V. Skibbens November 22, 2010 BIOS 10: BioScience in the 21 st Century Cell Cycle, Cell Division and Cancer (Part 2)

2 Directionality - clocks go in only one direction G1 doesn t have replication-inducing activity S but not G2 can not induce G1 cell to replicate DNA S cells has feedback controls that ensure replication completion Molecular mechanism For gaining i and then losing an Activity...

3 Master Regulator of the Cell Cycle: Cyclin-dependent Kinase (CDK) Cell cycle progression requires CDK activity Controls timing of divison sequence of division Respond to cues Partners in crime: Cyclin binds/activates kinase subunit

4 Cyclin-CDK complexes: budding Different catalytic CDK kinase proteins vertebrate G1 Cdc28 CDK4, CDK6 CLN3 Cyclin D1-3 G1/S Cdc28 CDK2 CLN1,2 S Cdc28 CDK2 Cyclin E CLB5,6 Cyclin A M Cdc28 CDK1 CLB1-4 Cyclin B... And Different cyclins

5 Cyclin-dependent Kinase (CDK) Nuclear envelope breakdown Condense chromosomes (Lamins) (Histone 1) Microtubule re-organization (MAPs) Cell cycle progression requires CDK activity Different cyclins - different substrates Unidirectionality - cyclin expression and Transcription of DNA replication factors (Polymerase, RFCs) Initiate DNA replication (ORC)

6 CDK regulation Cyclin degradation d Mitotic cyclin degradation = Anaphase Promoting Complex or APC G1 and S-phase cyclin degradation SCF (Skp1-Cullin-F box complex)

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8 Low CDK G1 cells can enter Quiescence (G 0 0) G 0 Differentiated cells or Cells that control the clock via external cues Understanding cancer often involves understanding how cells Reenter the cell cycle in the absence of cues!

9 G1 (and S) cyclin-cdk typically activated by external cues : Mitogens!! Releasing the brakes that keep cells in G1 MITOGENS PDGF Platelet-derived growth factor EGF epidermal growth factor TGF- Transforming growth factor

10 G1 cyclin-cdk activated by external cues: Mitogens!! Releasing the brakes that keep cells in G1 PDGF EGF Mitogen receptor activates small GTPase -> Ras pathway MAP kinase activates TFs TGF-

11 G1 cyclin-cdk activated by external cues: Mitogens!! Releasing the brakes that keep cells in G1 PDGF EGF TGF- Mitogen receptor activates small GTPase -> Ras pathway MAP kinase activates TFs TFs induce MYC expression Td!!Th Tada!! The target tof Mitogen activation...

12 Actions of MYC: 1. Express G1 cyclins G 0

13 Actions of MYC (plus Max binding partner): 1. Express G1 cyclins - G1-CDK will phosph p Rb Mitogen-induced?

14 E2F transcription factor

15 E2F - transcription factor... Rb (retinoblastoma protein) binds E2F > E2F OFF (inhibits cell cycle progression until external signal)

16 E2F - regulating a S-phase transcription factor... Rb (retinoblastoma protein) binds E2F > E2F OFF (inhibits cell cycle progression until external signal) G1-CDK phosphorylates Rb turn inhibitor off -> E2F ON

17 Actions of MYC (Mitogen induced!): 1. Express G1 cyclins - G1-CDK will phosph p Rb

18 Cancer pathways: Oncogene a stuck accelerator in a Driver s Ed Car... (2 of everything) Causes: mutation that falsely signals mitogen dosage too much

19 Overactive Accelerators - dosage effects General mechanisms of gene expansion

20 General mechanisms of gene expansion

21 Expansion of genes that regulate cell cycle progression: Myc proto-oncogene amplification homogenously staining regions (HSR)

22 Expansion of genes that regulate cell cycle progression: Examples of Myc proto-oncogene amplification homogenously staining regions (HSR) Double minute chromosomes

23 Myc expansion is downstream of mitogen... what htabout mitogenic i signal mis-regulation lti Unregulated ltdentry into it S

24 Overactive Accelerators loss of control receptor active without mitogen PDGF receptor No longer needs PDGF for Activation

25 Overactive Accelerators loss of control receptor active without mitogen - Dosage HER2 receptor - transmembrane tyrosine kinase (EGFR-like ) at high levels no longer Needs ligand for activation Her-2 OE accounts EGF-like 20-30% of all Her2 breast cancers dimerization Names change Herceptin: Ab that blocks Her2 dimerization i Tamoxifen small molecule l tyrosine kinase inhibitors -> gefitinib Estrogen HER2 E-receptor ERE

26 Cancer pathways: Oncogene a stuck accelerator Causes: mutation that falsely mimics mitogen dosage too much no longer dependent on mitogen

27 Cancer pathways: Rb, p53, viruses and BRCA1 Tumor Suppressors Brakes needed to slow car down! Driver ED car!!!!!!!!

28 Loss of heterozygosity (LOH) mutation need not be the same!!

29 Without Rb, E2F free to promote S-phase Bypasses G1-CDK activation via Mitogens X

30 p53 - gatekeeper of the cell p53 mutated ttdin ~1/2 of all cancers.. p53 highly hl unstable Associates with Mdm2 Ub-ligase co-factor X Made for destruction

31 p53 - gatekeeper of the cell DNA damage-induced id d p53 phosphorylation ATM/ATR CHK1 p53 - Mdm2 release -> stabilization by p53 kinase ATM = ataxia telangiectasia mutated ATR = ATM related i i h di i i patients with predisposition to cancer and extremely UV sensitive

32 p53 - gatekeeper of the cell Cells replication Damaged DNA p53 is transcription factor induces p21 expression X p21 IS a CKI!! CDK-Inhibitor BRAKES!!! cell locked in G1

33 Viral mechanisms of cancer progression papilloma virus genome stably maintained in epithelial cells

34 Viral mechanisms of cancer progression papilloma virus genome stably maintained in epithelial cells Viral E7 upregulated - binds and inactivates Rb Viral E6 upregulated - drives p53 proteoloysis

35 1 Breast Cancer Gene 1 - BRCA1 (tumor suppressor cell cycle brakes) Ring finger BRCT BARD1 MRN p300 CPB Mre11,Rad50,Nbs1 p53 prb BRCC complex = BACH1/FANCJ BRCA1/2, BARD1 CtIP Rad51, etc... H2AX E3 Ub-ligase Chromatin remodeling DNA damage signal Co-activator Modified from Boulton 2007

36 BRCA1 slows growth BRCA1 (Wt) Vector G1788V* *G1788V present in human brca1 patients K1601E Humphrey et al., 1997; Coyne et al., 2004

37 Chromosome segregation DNA replication

38 1. Cancer cells typically aneuploid inappropriate chromosome number chromosome segregation - microtubules 2. Cancer unregulated cell growth Tumor Suppressor Genes Oncogenes 3. Cancer cells often exhibit heightened migration Cell motility - actin

39 Metastasis cell migration and ignoring cues leaving home without a forwarding address

40 Wildtype cells Tumor cells Scratch test Time Tumor cells Show Increased mobility Zhu et al 2004

41 Cell motility how do cells move and where?

42 Limiting cell movement Reducing chromosome segregation g Infidelity Adhering to cell cycle cues: accelerators and brakes