Apoptotic protease activating factor

It is now well estahlished that activation of the caspase cascade is an indispensable and sufficient process in the execution phase of apoptosis (Nunez et al, 1998). As for mitochondria-mediated apoptosis, cytochrome c released from the mitochondrial inner membrane is well known to play an important role in the activation of caspase 9, one of the upstream proteases in the cascade (Zou et al, 1997). For activation of caspase 9, cytochrome c or apoptotic protease activating factor 2 (Apaf 2) induces the formation of the complex between Apaf 1 and caspase 9. The resultant activated caspase 9 then activates caspase 3, which in turn leads to the genomic DNA fragmentation and apoptotic cell death. 

Fig. 1. Proposed mechanism of action of rituximab associated with the apoptosis pathway. Binding of rituximab with the CD20 antigen up-regulates the production of interleukin-10 (IL-10). The IL-10 autocrine loop down-regulates the expression of the bcl-2 protein, which inhibits the intrinsic pathway (or mitochondrial mediated pathway) of apoptosis. The mitochondrial pathway is induced by intracellular stress signals. The translocation of the bcl-2 protein into the mitochondria leads to the activation of caspase 9 via release of cytochrome c and apoptotic protease-activating factor 1. The other pathway, the extrinsic pathway (or death receptor mediated pathway) activates caspase 8. Subsequently, caspase 8 or 9 activates caspase 3, leading to programmed cell death (apoptosis).

Qin H, Srinivasula SM, Wu G, Fernandes-Alnemri T, Alnemri ES, Shi Y (1999), Structural basis of procaspase-9 recruitment by the apoptotic protease-activating factor 1, Nature 399 549-557. 

Apaf-1 Apoptotic protease-activating factor APAF1... 

Sustained elevations in intracellular Ca levels promote mitochondrial Ca uptake, which decreases the mitochondrial membrane potential and blocks the electron transport chain leading to ATP depletion. Large increases in mitochondrial Ca uptake also increase mitochondrial membrane permeability (Dubinsky and Levi, 1998) resulting in the release of proapoptotic factors such as cytochrome c and apoptosis inducing factor (AIL) (Luetjens et al, 2000). Cytochrome c binds to apoptotic protease-activation factor 1 (APAFl) and procaspase-9, forming a multiprotein complex known as the apoptosome that activates the caspase cascade. The apoptosome activates caspase-9, which in turn activates caspase-3. Caspase-3 activates caspase-activated DNase (CAD), resulting in DNA fragmentation, characteristic of apoptosis. 

Apoptotic protease activation factor-1, a cytosolic protein involved in cell death or apoptosis, interacts with cytochrome c to activate caspase 9... 

In cytosol, cytochrome c combines with very high affinity with a cytosolic protein called Apoptotic Protease-Activating Factor 1 (Apaf-1) and dATP. The complex, in turn, combines with an inactive protease precursor, procaspase 9, to form the apoptosome . As a result, several procaspase 9 molecules are placed near each other, and they cleave each other to form active caspases 9. When formed, caspase 9 attacks procaspase 3 and cleaves it to form active caspase 3, a protease that hydrolyses certain enzymes occupying key positions on the metabolic map. This causes cell death. 

Analyte A substance or chemical that is detected by an analytical procedure. Antigen A molecule that elicits an immune response (i.e., antibody production). Apaf-1 Apoptotic protease activating factor 1 a cytosolic protein that forms part... 

Novel pathways include apoptotic protease-activating factor-1 (APAF-1) with an N-terminal caspase recruitment domain (CARD) recruiting caspase-9, or the RIP-like kinase CARDIAK specifically interacting with the CARD of caspase-1 (Thome et al., 1998). The overall structure of the... 

Binds pro-apoptotic protease activating factor (Apaf-1)... 

In the cytosol, cytochrome c binds Apaf (pro-apoptotic protease activating factor). The Apaf/cytochrome c complex binds caspase 9, an initiator caspase, to form an active complex called the apoptosome. The apoptosome in turn activates execution caspases by zymogen cleavage. 

Fig. 1. Modulation of apoptosis by v-FLIP and v-Bcl-2. v-FLIPs specifically inhibit apoptosis mediated by death receptors. v-lCA specifically targets caspase-8 and inhibits its activation. v-Bcl-2 and vMIA inhibit those apoptotic pathways that are signaled through mitochondrial release of cytochrome c. FADD, Fas-associated death domain FLICE, FADD-like interleukin-converting enzyme CARD, cas-pase-recruiting domain PTPC. permeability transition pore complex FLIP, FLICE-inhibitory protein vie A, viral inhibitor of caspase 8-induced-apoptosis MIA. viral mitochondrial inhibitor of apoptosis Apcif-l, apoptotic protease-activating factor 1...

Interestingly, evidence has been obtained that Fas may induce apoptosis via different pathways that are used almost exclusively in different cells (Scaffidi et al. 1998). In some cells. Fas ligation induced a rapid and strong activation of caspase-8 and caspase-3 (see above and Fig. 1) and subsequent apoptosis was not blocked by Bcl-2. In other cells, Fas-ligation resulted in a considerably weaker activation of FLICE (caspase-8), which cleaves Bid, a proapoptotic member of the Bcl-2 family (Luo et al. 1998 Li et al. 1998). Cleaved Bid subsequently translocates to mitochondria, where it promotes, either alone or together with Bax, cytochrome c efflux (Eskes et al. 2000). Subsequently, cytochrome c can interact with the cytosolic apoptotic protease-activating factor 1 (Apaf-1), which in turn activates caspase 9... 

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