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Cancer and the Cell Cycle : An overview Ken Wu. Disclaimer This tutorial is a simple and conceptual guide to the cancer module and the cell cycle If there.

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Presentation on theme: "Cancer and the Cell Cycle : An overview Ken Wu. Disclaimer This tutorial is a simple and conceptual guide to the cancer module and the cell cycle If there."— Presentation transcript:

1 Cancer and the Cell Cycle : An overview Ken Wu

2 Disclaimer This tutorial is a simple and conceptual guide to the cancer module and the cell cycle If there are any conflicts between my slides and the lecturers, THE LECTURER IS ALWAYS RIGHT… …maybe not always but they set your exams so if in doubt, refer back to their teaching

3 The Cell Cycle Most adult cells, without growth stimulus, will go into the G 0 phase of the cell cycle However, when a growth factor binds to its receptor on the cell membrane, a cascade starts and the cell prepares to enter G 1

4 Growth stimulus Growth factors – Epidermal Growth Factor (EGF) – Platelet-Derived Growth Factor (PDGF) Binds to Receptors Protein Tyrosine Kinase (RPTK)

5 Preparing the cascade Grb2 (adaptor protein) binds to phosphorylated tyrosine – Recruits SoS (Ras activating protein) SoS exchanges GDP for GTP – Activates Ras Ras must be membrane bound to be active

6 The ERK Cascade RAS – Raf MEK – ERK Causes gene expression changes via proteins such as c-Myc

7 Cyclin dependent kinases (Cdk) Cyclically activated protein kinases Activation depends on – Cyclin – Cdk interaction – Phosphorylation Cyclins – Expressed at different points in cell cycle – Transiently expressed and degraded

8 Cyclin – Cdk interation Cdk 4,6 + cyclin D (up regulated by c-Myc) – G 0 – G 1 – Also stimulates cyclin E synthesis Cdk 2 + cyclin E – S phase entry Cdk 2 + cyclin A – Metaphase of mitosis entry Cdk 1 + mitotic cyclin (cyclin B) – Promotes mitosis

9 Cell cycle timing and direction Due to sequentially active Cdk, and synthesis of Cdk for the next phase of cell cycle

10 Cyclin – Cdk function Phosphorylate pRb protein Phosphorylated pRb ‘releases’ E2F transcription factor E2F is now free to facilitate gene transcription pRb Cdk4/6 pRb P P P Cdk2 E2F D EA P P Cdk1TF B Mitosis pRb

11 Cdk inhibition INK4 family – Inhibit Cdk 4,6 – G1 phase inhibitors CIP/KIP family – Inhibit all Cdks – S phase inhibitors Degradation allows cell cycle progression

12 The Big Picture G 0 + EGF – RAS, Raf, MEK, ERK, c-Myc Cyclin – Cdk – D + 4,6 (G 0 – G 1 ) – E + 2 (G 1 – S) – A + 2 (Metaphase) – B + 1 (Anaphase)

13 Cancer – when it goes wrong Overexpressed EGFR Mutant RAS – Does not dephosphorylate GTP – Constantly bound to GTP thus constantly active Overexpressed c-Myc, cyclin D Inactive pRB

14 Apoptosis vs Necrosis - basics Necrosis – Unregulated – Trauma, cellular disruption – Inflammatory response Apoptosis – Regulated – Controlled disassembly – No inflammatory response

15 Apoptosis vs necrosis - process Necrosis – Plasma membrane becomes permeable – Cell swelling – Membrane rupture – Protease autodigestion – Localised inflammation Apoptosis – Activate death pathway – Cell shrinkage – Nuclear condensation – DNA fragmentation – Apoptotic bodies – Macrophages

16 Caspases Activation – Proteolysis – Cascade Initiator caspases – CARD or DED domain Effector caspases

17 Caspase function Initiator caspase – Activation via proteolytic cleavage – Caspase cascade Effector caspase – Cleave and inactive proteins – Activate enzymes in apoptosis

18 Receptor mediated caspase activation (extrinsic pathway) Fas receptor – Fas – Fas ligand interation – Has DD intracellular domain Recruits FADD – DD of FADD attaches to DD of Fas DED domain of FADD interacts with DED domain of caspase Recruits caspase 8 – Caspase cascade – Cleaves Bid – mitochondrial pathway Process inhibited by FLIP DEDDD FADD DED FLIP

19 Mitochondrial death pathway (intrinsic pathway) Loss of mitochondrial membrane potential – Releases cytochrome c + other factors Forms apoptosome complex – Apaf 1 Binds to cytochrome c CARD domain binds to CARD of caspase 9 – Caspase cascade Needs ATP – Therefore energy levels decide apoptosis vs necrosis

20 Apoptosis modulators Bcl – 2 family – Anti – apoptotic Bcl – 2 Bcl –xL – Pro – apoptotic Bid Bad Bax

21 Mechanism of apoptosis modulation Growth factor presence – PI3 – K pathway PKB/Akt production – Inactivates Bad, caspase 9 Inhibited by PTEN Bax – Forms pore on mitochondrial matrix

22 Cancer – when it goes wrong Overexpressed Bcl – 2 Overexpressed PKB/Akt Inactive PTEN

23 Any questions? me at Visit the ICSM Year 1+2 past paper bank Facebook group/the note bank on the ICSMSU website Good luck with exams next term!


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