1. APOPTOSIS Chapter 18 Lecture 23 BMB 252H Lecture by Garam Han
Ph.D. Candidate at Penn State University
IBIOS, Bioinformatics and Genomics Option

2. Outline Programmed cell death: What & Why? Markers of Apoptosis
Apoptosis & its regulation
Caspase Cascade
2 Pathways: Extrinsic & Intrinsic Pathway
4) How excessive or insufficient apoptosis can contribute to human disease

3. Programmed Cell Death eliminates unwanted cells
Apoptosis
Necrosis
Accidental cell death
Figure Molecular Biology of the Cell (© Garland Science 2008)

4. Metamorphosis (Tadpole to frog)
Apoptosis. Why??
1) During animal development (morphological change)
Development of digits in mouse paw
Metamorphosis (Tadpole to frog)
2) Quality control during development
3) When excessive DNA damage
Figure 18-2 & 3 Molecular Biology of the Cell (© Garland Science 2008)

5. Size of organism (from the previous lecture…)
= Total number of cells + size of cells
Determined by:
Cell growth
Cell Division
Cell death
=> Balance between Cell Division & Cell Death (Examples)

6. Biochemical markers of apoptosis
1) Chromosomal DNA cleaved into fragments
Gel electrophoresis
2) Phospholipid: phosphatidylserine flips to outlet leaflet of lipid bilayer of plasma membrane (Fig 10-3, Fig 10-16)
Marker for apoptosis
Signal to neighboring cells, macrophages (“Eat me” signal)
TUNEL
3) Release of cytochrome c from mitochondria during apoptosis

7. Caspase Cascade (Key mechanism for Apoptosis)
Intracellular Proteolytic Cascade mediated by
Caspase
(Cystein ASPartic acid)
Procaspase: Inactive precursor synthesized in cell
Activation by proteolytic cleavage
Activate Caspase

8. Caspase Cascade => Apoptosis
1) Procaspase activation by cleavage
2) Caspase cascade
Fragmented chromosomal DNA
Initiator procaspase
Executioner procaspase
2 signaling pathways => activate Caspase Cascade => Apoptosis

9. ANTI Pro-apoptotic vs. Anti-apoptotic
Apoptosis: A Balance Game between
Pro-apoptotic vs. Anti-apoptotic
ANTI
Which team is the molecule part of?
Who is Winning?

10. Extrinsic pathway of Apoptosis
Death-Inducing Signaling complex
Activated through Fas death receptor
Initiator procaspase
Activation complex: DISC
Figure Molecular Biology of the Cell (© Garland Science 2008)

11. Intrinsic pathway - Players: Bcl2 proteins
ANTI
Figure Molecular Biology of the Cell (© Garland Science 2008)

12. Cytochrome c release from Mitochondria => Apoptosis
Intrinsic Pathway:
Cytochrome c release from Mitochondria => Apoptosis
(Inactive Pro = Anti)
(Pro)
Cytochrome c: Component of mitochondrial electron-transport chain
Release of cytochrome c from mitochondrial intermembrane space into cytosol initiates apoptosis

13. Intrinsic pathway of apoptosis - depends on Mitochondria
Bcl2 protein
By injury or stress (Bax, Bak => Mitochondria => cytochrome c)
Apaf1: procaspase-activation adaptor protein
Activator: Apoptosome

14. Intrinsic pathway - Players: Bcl2 proteins
ANTI
Figure Molecular Biology of the Cell (© Garland Science 2008) 14

15. How Pro-apoptotic & Anti-apoptotic work in Intrinsic pathway of apoptosis

16. IAP (Inhibitors of Apoptosis) proteins => Anti
IAP (Anti): soak up caspase
Anti-IAP = Pro
Pro

17. Extracellular Survival Factors inhibit Apoptosis in various ways
Figure Molecular Biology of the Cell (© Garland Science 2008)

18. 3 ways Survival Factors inhibit Apoptosis
Anti
Anti
Increase level of Bcl2 (Anti-apoptotic)

19. 3 ways Survival Factors inhibit Apoptosis
Anti
Anti
Pro
Activate Bcl2 (Anti-apoptotic) by blocking the inhibitor 19

20. 3 ways Survival Factors inhibit Apoptosis
Anti
Anti
Pro
IAP (Anti): soak up caspase
Hid (Anti-IAP = Pro)
Inactive Hid: soak caspase (Anti) 20

21. ANTI Pro-apoptotic vs. Anti-apoptotic
Apoptosis: A Balance Game between
Pro-apoptotic vs. Anti-apoptotic
ANTI
Which team is the molecule part of?
Who is Winning?