Apoptosis : caspases, extrinsic and intrinsic pathways.

Apoptosis

1. APOPTOSIS PROGRAMMED CELL DEATH Submitted to, Dr . Arya P. Mohan Asst . Prof of Dept . Botany St Teresa’s college , Ernakulam Submitted by, Adhithya Madhavan 1 st MSc Botany St Teresa’s college, Ernakulam 1

2. CONTENTS INTRODUCTION HISTORY CELL DEATH OUTLINES OF APOPTOSIS CASPASES EXTRINSIC PATHWAY INTRINSIC PATHWAY REFERENCES 2

3. INTRODUCTION Apoptosis is process of programmed cell death. It is a highly regulated process that allows a cell to self degrade and there by eliminate unwanted or dysfunctional cells. Between 50 and 70 billion cells die each day due to apoptosis in average human adult and in children 20 to 30 billion cells dies a day . Apoptosis occurs normally during development and aging and as a homeostatic mechanism to maintain cell populations in tissues. It also occurs as a defense mechanism such as in immune reactions or when cells are damaged by disease or noxious agents. Plays a major roles in diseases like cancer,AIDS , Neurodegenerative disorders 3

4. HISTORY Carl Vogt John Kerr 4

5. Cell Death Cell death occurs by means of two ways, Necrosis – Cell death by injury Apoptosis – Death by suicide 5

6. 6 Cell contents ingested by macrophages Cell contents ingested by neighboring cells

7. WHY SHOULD A CELL COMMIT SUICIDE ? Apoptosis is essential for proper development of fingers and toes of the foetus , resorption of the tadpole tail , proper connection between neurons. It destroy the cells which is infected with viruses , or DNA damages ,cancer cells. 7

8. H elp to maintain the homeostasis. M aintain the proper body size. M aintains the constancy of cell number in an organ or organism. By the process of apoptosis, the body can eliminate unwanted cells, damaged cells ,   a pathogen (virus) infected cell. Apoptosis is involved in some neurodegenerative diseases such as Alzheimer’s, Parkinson’s disease, and Huntington’s disease by the elimination of essential neurons. 8

9. Outline of Apoptosis Cell shrinkage Nuclear fragmentation Chromatin condensation Chromosomal DNA fragmentation Formation of cytoplasmic blebs and apoptotic bodies Phagocytosis 9

10. CASPASES Caspases – C ysteine aspa rtic protea ses are a family of cysteine proteases. Major executioners of apoptosis. Synthesized as inactive pro-enzymes --- Pro caspases . Contain an NH2 terminal domain , a small sub unit, a large subunit . High specificity for substrates containing Asp and other Cys for peptide bond cleavage. Synthesized as inactive form and become active by proteolytic cleavage. 10

11. Initiator caspases initiate the apoptosis Executioner carry out the mass proteolysis that leads to apoptosis Inflammatory involved in inflammatory cytokine signaling 11

12. PATHWAYS OF APOPTOSIS INTRINSIC PATHWAY – MITOCHONDRIAL PATHWAY EXTRINSIC PATHWAY- THE DEATH RECEPTOR PATHWAY 12

13. EXTRINSIC PATHWAY OF APOPTOSIS The extrinsic pathway of apoptosis starts from external stimuli to the cell . It is triggered by proteins from the superfamily of Death receptors. Pathway is triggered when DR are activated by ligand binding. DR belong to the Tumor necrosis factor(TNF) receptor super family , it has a cysteine rich extracellular domains and cytoplasmic death domain. Fas , TNFR1, DR3, DR4, DR5, and DR6 are other members of this family 13

14. The stimulus for apoptosis is carried by an extra cellular messenger protein (TNF) They show responses to radiation , temperature, viral infections toxic chemical agents etc. Receptor is TNFR1 (Trimeric protein) – Death domain mediates protein-protein interaction. Binding of TNF causes a conformation changes in death domain of receptor and recruits adaptor proteins In this case TRADD is the adaptor protein which bind with death domain of receptor It also recruits FADD and RIP FADD and RIP then associates with procaspase-8 via dimerization of the death effector domain. 14

15. Formation of DISC complex and auto catalytic activation of procaspase-8. Activates caspase-8 which in turn activates executioner caspase -3. It activates endonuclease degradation of chromosomal DNA. Degradation of nuclear and cytoskeletal proteins by activation of protease. Cytomorphological changes and finally formation of apoptotic bodies. 15

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17. INTRINSIC PATHWAY N on-receptor-mediated stimuli that produce intracellular signals that act directly on target cell and are mitochondrial-initiated events. Stimuli can be genetic damage , lack of oxygen , viral infection , ER stress etc This pathway is regulated by members of Bcl-2 family proteins which have BH domains Bcl2 family has 3 groups : Proapoptotic members – BAX, BAK(contain several BH domains – promote apoptosis) Antiapoptotic – Bclx,Bclw,Bcl2 (prevent cell from apoptosis) BH3 only proteins– BID , Puma BIM (only one BH domain promote apoptosis by indirect mechanism) 17

18. BH3-only proteins can be pro-apoptotic and they can promote apoptosis in two different ways B y inhibiting the anti-apoptotic Bcl-2 members A ctivating pro-apoptotic Bcl-2 members When stimulus evoked,BH3 only protein level increases and imbalance in pro and anti apoptotic factors P ro-apoptotic factor called BAX is translocated from the cytosol to the outer mitochondrial membrane. 18

19. BAX protein undergoes a conformational change and gets inserted into the outer mitochondrial membrane. C reates protein-lined channels or pores on the outer membrane. T he permeability of the OMM dramatically increased. Through these pores, cytochrome C is released out of the mitochondria to the cytosol. In the cytoplasm, the cytochrome c molecules combine together with Apaf -1 ( apoptotic protease activating factor) and Pro-caspase-9 in an ATP-dependent manner to form a multi-subunit complex Apoptosome 19

20. The binding of Apaf-1 induce a conformational change in the pro-caspase-9 and it is activated to its fully proteolytic form (caspase-9). Caspase 9 activates the executioner caspases such as caspases -3 and Caspase-7. Activated caspase-3 and caspase-7 cleaves its target molecules in the cell and cell death occurs 20

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23. REFERENCES Karp.g .(2013).Cell biology.New Jersey:Wiley Lodish ,H.(2008).Molecular cell biology.Newyork:W.H.Freeman and company https://www.ncbi.nlm.nih.gov - Molecular Biology of the Cell. 4th edition. https://link.springer.com - Essentials of Apoptosis https://www.researchgate.net/publication/42768088_Essentials_of_apoptosis A guide for basic and clinical research https://www.britannica.com/science/apoptosis A poptosis cytology 23

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