APOPTOSIS
Chapter 18
Lecture 23
BMB 252H
Lecture by Garam Han
Ph.D. Candidate at Penn State University
IBIOS, Bioinformatics and Genomics Option
Outline
1) Programmed cell death: What & Why?
2) Markers of Apoptosis
3) Apoptosis & its regulation
•
Caspase Cascade
•
2 Pathways: Extrinsic & Intrinsic Pathway
4) How excessive or insufficient apoptosis can
contribute to human disease
Programmed Cell Death eliminates unwanted cells
Apoptosis
Necrosis
Accidental cell death
Figure 18-1 Molecular Biology of the Cell (© Garland Science 2008)
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)
Size of organism (from the previous lecture…)
= Total number of cells + size of cells
Determined by:
1) Cell growth
1) Cell Division
1) Cell death
=> Balance between Cell Division & Cell Death (Examples)
Biochemical markers of apoptosis
1) Chromosomal DNA cleaved into fragments
 Gel electrophoresis
 TUNEL
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)
3) Release of cytochrome c from mitochondria during apoptosis
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
Caspase Cascade => Apoptosis
1) Procaspase activation by cleavage
2) Caspase cascade
• Initiator procaspase
• Executioner procaspase
• Fragmented chromosomal DNA
• 2 signaling pathways => activate Caspase Cascade => Apoptosis
Apoptosis: A Balance Game between
Pro-apoptotic vs. Anti-apoptotic
Which team is the molecule part of?
Who is Winning?
ANTI
Extrinsic pathway of Apoptosis
DeathInducing
Signaling
complex
• Activated through Fas death receptor
• Initiator procaspase
• Activation complex: DISC
Figure 18-6 Molecular Biology of the Cell (© Garland Science 2008)
Intrinsic pathway - Players: Bcl2 proteins
ANTI
Figure 18-9 Molecular Biology of the Cell (© Garland Science 2008)
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
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
Intrinsic pathway - Players: Bcl2 proteins
ANTI
Figure 18-9 Molecular Biology of the Cell (© Garland Science 2008)
Anti
Pro
How Pro-apoptotic & Anti-apoptotic
work in Intrinsic pathway of apoptosis
IAP (Inhibitors of
Apoptosis) proteins
=> Anti
(Anti)
• IAP (Anti): soak
up caspase
• Anti-IAP = Pro
Pro
Extracellular Survival Factors inhibit Apoptosis in various ways
Figure 18-13 Molecular Biology of the Cell (© Garland Science 2008)
3 ways Survival Factors inhibit Apoptosis
Anti
• Increase level of
Bcl2 (Anti-apoptotic)
Anti
3 ways Survival Factors inhibit Apoptosis
Anti
Pro
• Activate Bcl2 (Antiapoptotic) by blocking
the inhibitor
Anti
3 ways Survival Factors inhibit Apoptosis
Anti
Anti
Pro
• IAP (Anti): soak up caspase
• Hid (Anti-IAP = Pro)
• Inactive Hid: soak caspase (Anti)
Apoptosis: A Balance Game between
Pro-apoptotic vs. Anti-apoptotic
Which team is the molecule part of?
Who is Winning?
ANTI