Lecture 23: Apoptosis Flashcards
What are the two forms of cell death
- Necrosis: dirty way
- Apoptosis: programmed cell death (clean way)
Phenotype of Apoptosis
- Overall shrinkage in volume of cell and its nucleus
- Loss of adhesion to neighboring cells
- Formation of blebs on surface
- DNA fragmentation
- Cytoskeleton collapses
- Nuclear envelope disassemebles
- Rapid engulfment of dying cell by phagocytosis (macrophages)
What is the marker for apoptosis
Cytochrome C released from mitochondria
Apoptosis is an intracellular proteolytic cascade mediated by proteases called
Caspases
What is the active site for Caspases
Cysteine (Caspase= cysteine aspartyl specific protease)
Procaspases are celaved at specific sites to form large and small subunit which form a
heterodimer
What are the iniator caspases
- initiates apoptosis
- (includes caspase-8 and caspase-9)
What is the executioner caspase
- destroys actual targes, executes apoptosis
- Ex. Caspase-3
- cleaves downstream proteins
- cleaves inactive endonuclease
- Targets cytoskeleton
- attacks cell adhesion proteins- cells roll up in ball
What are the two pathways for apoptosis
- internal pathway
- e.g. abnormalities in DNA
- intrinsic pathway is mitochondrial dependent
- External pathway
- e.g. removal of survival factors and proteins of tumor necrosis factor family
- extrinsic pathway is mitochondrial independent
Extrinsic pathway
- Extracellular signals bind to cell surface death receptors and trigger extrinsic pathway
- ex. Fas binds to Fas Death receptor- ligand forms homotrimer and adpator protein, FADD adaptor (Fas associated death domain) and procaspase-8 with death effector domain are recruited
- forms trimers- bring death domains together (forms DISC: Death inducing Signal Complex)
- activates caspase-8 or -10
- activates downstream executioner caspases- caspase-3
What are the 3 domains of the transmembrane death receptors
- Extracellular binding domain
- Single transmembrane domain
- Intracellular death domain
Death receptors are homotrimers: three proteins of same type (members of the ____ family of proteins
TNF family of proteins
What are some inhinitors of the extrinsic pathway
- Decoy receptors
- have ligand bidning domain but no death domain
- thus can bind death ligand but does not activate apoptosis
- FLIP
- is a protein resembling initiator procaspase with no proteolytic domain
- is a competitve inhibitor against procaspase-8 and procaspase-10: prevening apoptosis
In the intrinsic pathway- the translocation of ____ from the intermediate space of mitochondria is key event
Cytochrome C (when in cytosol binds to adaptor protein to activate procaspases , Apaf1)
When cytochrom c is released form mitochondria, it binds to _____ called ____ which forms the apoptosome, which activates caspase-9
- Procaspase-activating adaptor protein called Apaf1 (apoptotic protease activating factor-1)
Intrinsic pathway
what are the two types of Bcl2 proteins
- Pro-apoptotic
- promotes release of cytochrome C
- Bcl2: Anti-Apoptotic (pro-survival)
- blocks release of cytochrome c
Anti-apoptotic protein Bcl has ___ distinctive domains
- 4
- called Bcl homology domains or BH domains
Pro-apoptotic proteins include
BH123 protein and BH-3 only protein
_____ proteins become activated, form aggregation in mitochondrial outer membrane and induce release of cytochrome C- then apoptosome formed by bidning to Apaf1
BH 123
How do Anti-apoptotic Bcl proteins work
prevent apoptosis by bindng to pro-apototic proteins (BH 123) and prevent aggregation into active form
How does BH3-only protein work
inhibits anti-apoptotic Bcl2 protein from inhibiting aggregation to release cytochrome c
IAPs inhibit caspases (anti-apoptotic)
- IAPs: Inhibitors of Apoptosis
- Bind and inhibit caspases
- thus blocking apoptosis
- some add ubiquitin to caspases to mark them for destruction by proteasome
Functions of Anti-IAPs
block activity fo IAPs and thus are pro-apoptotic
