Cell cycle

1. Cell cycle Unicellular Multicellular • Division through defined phases • Cell growth continuous • DNA synthesis is in only one phase • Cell growth and DNA synthesis highly co-ordinated and regulated • Cell cycle controlled by a series of protein kinases • Defects in cell cycle regulation-cancer Cell growth and DNA replication throughout cell cycle Cell division

3. cancer Infections fungal & viral Atheriosklerosis Restenosis Cell cycle Malaria Tissue engeneering Tissue repair & regeneration Yield Growth rate Why cell cycle? • Cell division is regulated by highly conserved networks • The comparative approach will illuminate the variation in the intrinsic stability of • cell cycle controls in the different species • Cell cycle progression regulating mechanisms in eukaryotes are largely conserved: • cells as different as yeast and mammalian cells use the same kind of regulatory molecules to trigger cell cycle progression • new insights in cell cycle regulation and the mechanisms that prevent uncontrolled proliferation of cells  way to novel anti-tumor drugs

4. INTERPHASE S (DNA synthesis) G1 Mitosis Cytokinesis G2 MITOTIC (M) PHASE

5. 0.5 µm Mitosis Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Separation of sister chromatids Centromeres Sister chromatids

6. http://www.biologymad.com/CellDivision/CellDi1.gif

7. 11 hrs 90 min. 8 hrs 1 hr 4hrs Human cells (24 hours) Yeast cells (90 minutes) Mitosis G0 Synthesis Embryo cells (less than 30 min.) Skin fibroblasts, liver cells

8. Cells at different stages of cell cycle can be distinguished by their DNA content

9. Nutrients Regulation of cell cycle Start Mating factors Cell size S. cerevisiae G0 Animal cells Restriction point Growth factors

10. Regulation of cell cycle

11. Daughter chromosomes not aligned properly Spindle checkpoint S -checkpoint DNA damage Cell cycle checkpoints? DNA repair

12. Summary • Cells divide by following carefully scripted program of molecular events collectively called the cell cycle. • The cell cycle is subdivided into five phases named G1, S, G2, M, and G0. Cells not actively dividing reside in G1 or G0 phase. • Several checkpoints define critical decision-making events in the cell cycle

13. Key molecule responsible for cell cycle regulation • Identification of MPF MPF: Maturation Promoting Factor

14. Yeast Is a Model System for Analyzing Cell Cycle S. pombelengthens and then divides with a septum, while S. cerevisiaebuds during a cycle in which G2 is absent and M occupies the greatest part.

15. Key molecule responsible for cell cycle Regulation • S. cereviceae • Temperature sensitive mutants (cell division cycle mutants) • Cell cycle arrested at START, (mutation in protein called Cdc2) • A similar protein identified in S. pombe • Protein Cdc2 controls both G1 and G2 checkpoints • Characterization- Cdc is a protein kinase START

16. Key molecule responsible for cell cycle Regulation • Accumulation and degradation of cyclins The cyclins were identified as proteins that accumulate throughout interphase and are rapidly degraded toward the end of mitosis.

17. Key molecule responsible for cell cycle Regulation MPF: M-phase Promoting Factor • MPF is composed of two key subunits: Cdc2 and Cyclin B. • Cdc2 is the protein that encoded by genes which are required for passage through START as well as for entry into mitosis. • Cyclin B is a regulatory subunit required for catalytic activity of the Cdc2 protein kinase. Cyclin dependant Kinases (Cdks)

18. Leland H. Hartwell checkpoints Tim Hunt Cdks Sir Paul Nurse cyclins 1970s-80s | 2001 Cyclins & Cdks • Interaction of Cdk’s & different cyclins triggers the stages of the cell cycle

19. Summary • Progression through the cell cycle is under the control of proteins that form checkpoints • These proteins are protein kinases • Protein kinases can function only with cyclins Cyclin Cyclin Kinase √ Kinase X

20. Four molecular mechanisms that regulate Activities of Cdk's • Mechanisms of Cdk regulation

21. Families of Cyclins and Cyclin-Dependent Kinases The cell cycles of higher eukaryotes is controlled by multiple cyclins and cdc2 Cyclins Labelled –alphabets Cyclin-B, cyclin-G, cyclin E Cdc2 Cyclin dependent kinases (cdks) Labelled numerically Cdc2- Cdk1 Cdk1-Cdk8

22. Control by cyclin/CDK complexes Distinct cyclin-cdk complexes control progression through cell cycle checkpoints.

23. Growth Factors and D-type Cyclins Growth factors D-type cyclin Restriction point

25. Control of the G1 checkpoint expression of most CDKs does not vary much throughout the cycle, but without their corresponding cyclins, they are not functional

26. RB = tumour suppressor

27. Control of the G1 checkpoint Cyclin A E2F turns on the expression of genes required for DNA synthesis

28. Regulation of Cell Cycle INK4 (RB) Cell 2004;116:221-34

29. Cyclin E Cyclin A Cyclin B Cyclin D G0 G1 S M G2 Cyclins • Cyclines and cyclin-dependent kinases (cdks) • The cyclines have oscillating levels during cell cycle • The cyclines are regulatory subunits of the CDK-kinases • cyclines+ cdk  cell cycle-dependent variations in the activity of the kinases determined by mitogenic growth factors

33. Control of the S checkpoint Assembly of the prereplication complex.

34. Control of the S checkpoint • 3 key steps Activation of the replication complex.

35. G2 check point- check for DNA damage Cyclin B synthesized Cyclin B accumulates

36. G2- check point Wee 1 protein kinase Inactive Cdc 25 ADP Inactive CDK1

37. Control of the G2 checkpoint ATP ATM/R P ADP

38. CDK inhibitors

39. CDKs are regulated by Cyclin Dependent Kinase Inhibitors (CKIs) active inactive CDK4/6 CDK4/6 INK4 INK4 + + p21 p21 Cyclin D Cyclin D CDK Cyclin CDK4 CDK4 Cyclin p16 p16 CDK Cyclin

40. DNA damage, other insults p53 p21 Growth Signal cyclin/ CDK G1 phase S phase

41. Inhibitor of Cell Cycle Progression Mdm2 Mdm2 Mdm2 stimulates degradation of p53. Cellular levels of p53 are low p53 p53 Normal Cells

42. P ATM/R p53 p53 X Mdm2

43. Inhibitor of Cell Cycle Progression p21 p21 CDK Cyclin • Induction of p21 by DNA damage P Conc. increase p53 CDK Cyclin

44. Overview of checkpoint controls in the cell cycle Lodish et al., 2004

46. Overview of checkpoint controls in the cell cycle Lodish et al., 2004