Apoptosis : caspases, extrinsic and intrinsic pathways.
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
1st MSc Botany
St Teresa’s college,
Ernakulam
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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
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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.
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8. • Help to maintain the homeostasis.
• Maintain the proper body size.
• Maintains 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.
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9. Outline of Apoptosis
• Cell shrinkage
• Nuclear fragmentation
• Chromatin condensation
• Chromosomal DNA fragmentation
• Formation of cytoplasmic blebs and
apoptotic bodies
• Phagocytosis
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10. CASPASES
• Caspases – Cysteine aspartic proteases 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.
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11. • Initiator caspases initiate the apoptosis
• Executioner carry out the mass proteolysis that leads to apoptosis
• Inflammatory involved in inflammatory cytokine signaling
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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
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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.
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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.
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17. INTRINSIC PATHWAY
• Non-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:
1) Proapoptotic members – BAX, BAK(contain several BH domains – promote apoptosis)
2) Antiapoptotic – Bclx,Bclw,Bcl2 (prevent cell from apoptosis)
3) BH3 only proteins– BID , Puma BIM (only one BH domain promote apoptosis by indirect
mechanism)
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18. • BH3-only proteins can be pro-apoptotic and they can promote apoptosis in two
different ways
By inhibiting the anti-apoptotic Bcl-2 members
Activating pro-apoptotic Bcl-2 members
• When stimulus evoked,BH3 only protein level increases and imbalance in pro and
anti apoptotic factors
• Pro-apoptotic factor called BAX is translocated from the cytosol to the outer
mitochondrial membrane.
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19. • BAX protein undergoes a conformational change and gets inserted into the outer
mitochondrial membrane.
• Creates protein-lined channels or pores on the outer membrane.
• The 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
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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
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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 Apoptosis cytology
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