APOPTOSIS: Can the cell be Programmed to suicide ?: APOPTOSIS: Can the cell be Programmed to suicide ?


INTRODUCTION: INTRODUCTION Cell death by injury -Mechanical damage -Exposure to toxic chemicals Cell death by suicide -Internal signals -External signals


Why should a cell commit suicide?: Why should a cell commit suicide? Apoptosis is needed for proper development The resorption of the tadpole tail The formation of the fingers and toes of the fetus The sloughing off of the inner lining of the uterus The formation of the proper connections between neurons in the brain Apoptosis is needed to destroy cells Cells infected with viruses Cells of the immune system Cells with DNA damage Cancer cells


Slide4: Importance of Apoptosis Important in normal physiology / development Development: Immune systems maturation, Morphogenesis, Neural development Adult: Immune privilege, DNA Damage and wound repair. Excess apoptosis Neurodegenerative diseases Deficient apoptosis Cancer Autoimmunity


What makes a cell decide to commit suicide?: What makes a cell decide to commit suicide? Withdrawal of positive (Growth) signals growth factors for neurons Interleukin-2 (IL-2) Receipt of negative (Death) signals increased levels of oxidants within the cell damage to DNA by oxidants death activators : Tumor necrosis factor alpha (TNF-) Lymphotoxin (TNF-β) Fas ligand (FasL)


History of cell death / apoptosis research: History of cell death / apoptosis research 1800s Numerous observation of cell death 1908 Mechnikov wins Nobel prize (phagocytosis) 1930-40 Studies of metamorphosis 1948-49 Cell death in chick limb & exploration of NGF 1955 Beginning of studies of lysomes 1965 Necrosis & PCD described 1971 Term apoptosis coined 1977 Cell death genes in C. elegans 1980-82 DNA ladder observed & ced-3 identified 1990 Apoptosis genes identified, including bcl-2, fas/apo1 & p53, ced-3 sequenced (Richerd et.al., 2001)


Apoptosis vs. Necrosis: Apoptosis vs. Necrosis Cellular condensation Membranes remain intact Requires ATP Cell is phagocytosed, no tissue reaction Ladder-like DNA fragmentation In vivo, individual cells appear involved Cellular swelling Membranes are broken ATP is depleted Cell lyses, eliciting an inflammatory reaction DNA fragmentation is random, or smeared In vivo, whole areas of the tissue are affected Necrosis Apoptosis


Apoptosis: Pathways: Apoptosis: Pathways


Slide9: MAJOR PLAYERS IN APOPTOSIS Caspases Death signals e.g. TNF & TNFR p53 BAX Bcl-2 family


CONCLUSION: CONCLUSION an important process of cell death can be initiated extrinsically through death ligands (e.g. TRAIL, FasL) activating initiator caspase 8 through induced proximity. can be initiated intrinsically through DNA damage (via cytochrome c) activating initiator caspase 9 through oligomerization. Initiator caspases 8 and 9 cleave and activate effector caspase 3, which leads to cell death.


Slide12: The bcl-2 family Receptor domain phosphorylation Raf-1 calcineurin Pore formation Membrane anchor Ligand domain


Slide13: P53 & Apoptosis p53 is an unstable tumor suppressor protein. It is and acts via zinc finger DNA binding model. It arrests cell growth between G1  S, thus DNA repair can take place. p53  production of CIP(p21)  CDKs inhibition  Cell cycle stop.


Slide14: 3 mechanisms of caspase activation a. Proteolytic cleavage e.g. pro-caspase 3 b. Induced proximity, e.g. pro-caspase 8 c. Oligomerization, e.g. cyt c, Apaf-1 & caspase 9