Apoptosis regulation by BCL-2

Apoptosis and its classification

1. APOPTOSIS –REGULATION BY BCL –2 Presented by: Manju Jakhar Rollno.20PPC008 M.Pharm (Pharmacology) 1st Semester

2. content Apoptosis introduction Events of apoptosis Proteins participate in apoptosis Caspases Central regulation in Apoptosis Regulatory interactions between Bcl – 2 family members Role of mitochondrion in regulation of apoptosis

3. APOPTOSIS

4. Events of apoptosis:- During apoptosis chromosomal DNA is usually fragmented as a result of cleavage b/w nucleosomes chromatin condenses & nucleus breaks in to small pieces Finally the cell it self shrinks & Breaks up in to membrane enclosed fragments called apoptotic bodies. Apoptotic cells are usually recognized by both macrophages & neighboring cells so they removed from tissue.

5. The removal of apoptosis cell is mediated by signals induce phosphatidyl serine which is restricted to inner plasma membrane. During apoptosis phosphatidyl serine expressed on cell surface where it is recog . by receptor expressed on phagocytic cells.

6. Proteins participate in apoptosis :- 2 genes ced3 & ced4 were required for apoptosis. If either ced3 or was inactive by mutations. The normal programmed cell death did not take place. Ced9 functioned as – ve regulator of apoptosis if ced9 was inactived by mutation the cells cannot survive. If ced9 was expressed by higher levels apoptosis can not occur.

7. Caspases ( Executioners Of Pcd / Apoptosis) C ysteine Dependent Asp artate -directed Prote ase Caspases amplify the initial apoptotic signals :- Initiator caspases – cas 9 Effector caspases – cas 3 and cas 7 The caspases are named because they contain cysteine residue in the catalytic site & cleaves proteins at C terminal to aspartic residues. Caspases are the utimate effectors of the apoptosis cleaving nearly 100 cell target proteins. Key targets of caspases include:- Fragments of nuclear DNA Cleavage of nuclear lamins Cytoskletal proteins Ced 3 is only caspases in c. Elegans .

8. Caspases 9 activated as complex with apaf-1 & cytochrome c in the apoptosome . Caspases -9 that cleaves & activates effector caspases , such as caspases 3 & 7. The effector caspases clave variety of cell, cell protein, including nuclear lamins , cytoskeletal proteins & an inhibitor of DNAse , leading to cell death.

9. Central regulation in apoptosis :- Ced 9 gene in c. elegans was closely related to a mammalian gene Bcl-2. Bcl – 2 was found to inhibit apoptosis. Bcl – 2 & ced 9 was thus similar in function. In addition both Bcl – 2 & Ced 9 contain a single trans membrane domain in the outer mitochondrial membrane. Mammals encode approximately 20 related apoptotic proteins which were divided into 3 functional group.

10. Antiapoptotic family :- Function as an inhibit of apoptosis. Eg :- Bcl - 2 , Bcl XL. This family contains 4 bcl - 2 homology domains 2. Pro apoptotic multi domain :- Induce apoptosis. Eg :- BAX, BAK Contains 3 homologous domains. 3. Pro apoptotic BH- 3 only :- Induce apoptosis. Eg :- Bid, Bad, Noxa , PUMA, Bin. contains only one bcl -3 homology domain.

11. Classification of Bcl-2 family of proteins in respect to their subcellular localizations. Bcl-2 family members were classified based on their implication in the MOMP. The presence of conserved Bcl-2 homology (BH) and transmembrane (TM) domains were indicated with color dots. The main subcellular localizations were presented in the table on the right. Black dots indicate the presence of the protein to the corresponding subcellular localization. Classification of Bcl-2 family of proteins in respect to their subcellular localizations.

12. Regulatory interactions between Bcl – 2 family members Regulation interactions between Bcl – 2 family members in normal cells, the BH3- only pro apoptotic proteins are inactive, and the multidomain pro apoptotic proteins are inhibited by interaction with antiapoptotic proteins. Cell death signals activate the BH3 – only proteins, which then interact with the antiapoptotic proteins, leading to activation of the multidomain proapoptotic proteins and cell death.

13. Role of mitochondrion in regulation of apoptosis BAX and BAK is required for the induction of apoptosis. These residues in the outer mitochondrial membrane normally tightly bound to Bcl – 2 . When released from Bcl – 2 these residues form oligomers that generate pores in the outer mitochondrial membrane. These generates the release of mitochondrial protein cyt c.

14. Cyt – c bound to apaf – 1 forming a complex called apoptosomes . Apoptosomes results in the activation of caspases 9. Caspases are also regulated by a family of proteins called IAP ( inhibitor of apoptosis proteins). IAP has zinc binding domain that directly binds to caspases inhibit the protease activity. SMAC/ diablo & omi / htr 2 released by mitochondria which inhibits IAPs. Assembly of BAX/ BAK channels leads to release of these SMAC / diablo from mitochondria. These binds to IAPs in cytosol their by blocking the IAPs from binding to caspases .