Term
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Definition
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•Intrinsic pathway triggered by toxicological damage or loss of growth factors
•Extrinsic pathway triggered by cell surface receptors - ‘death receptors’. Receptor-ligand interactions leads to binding of adaptor protein FADD, which provides for an assembly platform that activates procaspase 8.
–Fas/Cd95 - FasL/Cd95L ligand
–Tumor necrosis factor-a receptor 1 - TNF ligand
– Receptors DR4 and DR5 - TRAIL ligand
•Third pathway specific to CTL and NK cells
–apoptosis induced by granzyme activation of target caspase.
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Term
Two examples of the extrinsic pathway
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Definition
1)Fas/FasL (CD95/CD95L) (activated T cells)
2)TNF1 receptor/TNFa (tumor necrosis factor)
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Term
TNFR1/TNFa can lead to apoptosis or cell survival |
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Definition
•Binding of TNFa to TNFR1 results in receptor trimerisation and clustering of intracellular death domains. This allows binding of an intracellular adapter molecule called TRADD (TNFR-adapter protein with a death domain) via interactions between death domains.
•TRADD has the ability to recruit a number of different proteins to the activated receptor with two outcomes.
–Cell Death/Apoptosis. Recruitment of FADD by TRADD leads to the induction of apoptosis via the cleavage of pro-caspase 8
–Cell survival. Recruitment of TRAF2 (TNFR-associated factor 2) leads to activation of the NF-kB.
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Term
apoptotic inhibitors in the extrinsic pathway |
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Definition
•decoy receptors- have ligand binding domain but no death domain
•intracellular blocking proteins. FLIP
– structurally related to procaspase 8 but inactive
– competes with procaspase 8 for binding to FADD.
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Term
Sometimes the extrinsic pathway is not enough..... |
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Definition
•In some cells, DR-initiated signaling leads to full activation of caspase 8 and then caspase 3.
–Typified by lymphoid cells.
•In other cells, caspase 8 activation is not enough to activate caspase 3 directly, rather, caspase 8 activates the mitochondrial pathway by cleaving Bid (BH3-only protein)
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Term
An Additional Pathway for CTL to Kill Altered Cells
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Definition
-The cytotoxic T lymphocyte binds to target cells.
-CTL contains perforin and granzymes in stored granules .
-After contacting target cell membrane and a conformational change, the monomer perforin polymerizes to form cylindrical
pores and inserts into target cell membrane.
-Through these pores, granzymes
enter target cells, activate caspase cascades and finally lead to apoptosis.
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Term
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Definition
•Targets of caspases are limited:
–Disassembly of the nucleus (CAD nuclease)
•DFF45/ICAD--DFF40/CAD heterodimer.
•ICAD is cleaved by caspase to release active CAD
–Cytoskeletal components: actin, pacilllin, cyto-keratin, FAK, Akt
–Other protein kinases: MEKK, Pak2, Mst1 PKC
–Checkpoints and DNA repair
–Redistribution of membrane lipids (creation of ‘eat me’ signals)
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Term
How do you assay apoptosis? |
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Definition
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•activity of activated caspases
(M30 CytoDEATH Antibody that recognizes caspase-cleaved keratin 18)
•products of caspases
•cleaved nuclear DNA
(nuclei in apoptotic cells of developing limb bud through TUNEL assay)
•change in phospholipid distribution
-(Phosphatidylserine is on cytosolic side of membrane in normal cells, but “flips” to outer membrane in apoptosis)
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Term
Corpse removal is vital part of the apoptosis process in vivo because...... |
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Definition
1) Prevents inflammatory response.
2) Clears tissue.
3) Defects in corpse removal associated with atherosclerosis and autoimmune disease.
•Corpse removal is an active process.
–In some cases apoptotic cells are actively ejected from tissue.
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Term
Mechanism of corpse removal |
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Definition
•Expression of cell-surface signal in apoptotic cell
–Phosphatidylserine
•Detection of cell surface signal on neighboring phagocytic cell
•Mobilization and reorganization of the actin cytoskeleton to engulf apoptotic fragments.
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Term
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Definition
•Ischemia in brain and heart.
–Apotosis of ischemic cells after heart attack or stroke is the main cause of tissue death.
•Neurodegenerative Diseases.
–Respiratory defects in mitochondria can lead to premature death of neurons.
•Cancer.
–Loss of apoptosis accompanies many cancers.
•Liver disease
–Toxins, including ethanol, induce mitochondrial disfunction leading to apoptosis.
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Term
Cancer therapy an apoptosis |
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Definition
•most cancer therapies directly or indirection target apoptosis
•Some direct targets:
–Bcl-2 antagonists
•Bcl2 antisense Phase II and III trials
•Bcl2 small molecule antagonists Preclinical
•Bax adenovirus Phase I trials
•BH3 mimetics preclinical
–TRAIL-R agonists Phase I trial
–IAP-antagonists Preclinical
–Caspase 3 activator Preclinical
–XIAP antagonists
–cFLIP antagonists
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Term
Apoptosis - self killing
vs
Autophagy - self eating |
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Definition
•Specialized form of lysosomal transport -cytoplasm to vacuole targeting (Cvt)
•Selective lysosomal digestion of cytoplasm and organelles
•Biochemical pathway is evolutionarily conserved from yeast to humans
–Complex- at least 17 proteins in six functional complexs
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Term
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Definition
•Autophagy is usually induced by nutritional stress
–Can also be induced by some drugs
•Tissue/organs can be protected from nutrient starvation by lysosomal digestion of cytoplasm and organelles. This provides building blocks for macromolecular synthesis.
–yeast with autophagy (ATG) mutants cannot survive nitrogen starvation.
–Mice lacking ATG5 cannot survive the early postnatal/neonatal period.
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Term
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Definition
•i - sensation of starvation signal
•ii - transmission of signal to generate PAS (pre-autophagosomal structure)
–TOR kinase pathway inhibits autophagy
•iii - generation of isolation membrane or phagophore (IM)
•iv - expansion of IM
•v - fusion of leading edges of IM to generate autophagosome
•vi - fusion of outer autophagosome membrane with vacuole/lysosome membrane
•vii - hydrolysis of inner autophagosome membrane and contents
•viii - transport of resulting amino acids and lipids to the cytoplasm for recycling
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Term
Biological functions of autophagy |
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Definition
•cell survival during nutritional stress
•pathogen clearance
•antigen presentation
•activation of innate immunity
•cellular housekeeping
–removal of worn-out organelles- oxidized mitochondria (mitophagy), peroxisomes
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