The endogenous p20 protein generated during Fas-mediated apoptosis was associated with microsomes and remained resistant to alkali extraction (pH 11

The endogenous p20 protein generated during Fas-mediated apoptosis was associated with microsomes and remained resistant to alkali extraction (pH 11.5), indicative of a membrane-integrated protein (unpublished data). release, whereas prolonged expression of c-JUN peptide p20 on its own ultimately induced caspase activation and apoptosis through the mitochondrial apoptosome stress pathway. Therefore, caspase-8 cleavage of BAP31 at the ER stimulates Ca2+-dependent mitochondrial fission, enhancing the release of cyt.c in response to this initiator caspase. (cyt.c; Korsmeyer et al., 2000). Once in the cytosol, cyt.c complexes with Apaf-1 and procaspase-9 forming the apoptosome, a direct activator of downstream effector caspases 3 and 7 (Budihardjo et al., 1999). Activation of the TNF family of cell surface death receptors is usually coupled to the mitochondrial phase of apoptosis by the BH3-only protein BID. Binding of Fas to its ligand or agonistic antibody induces the recruitment and autoactivation of initiator procaspase-8 (Krammer, 2000). In turn, caspase-8 cleaves BID, generating tBID, which translocates from your cytosol to mitochondria and induces organelle dysfunction and cyt.c release (Li et al., 1998; Luo et al., 1998). BID plays an obligate role in transducing signals from death receptors to mitochondria in at least some cell types because hepatocytes from BID?/? mice do not release cyt.c in response to Fas, despite normal activation of caspase-8 (Yin et al., 1999). In some contexts, caspase-8 can bypass mitochondria and directly cleave downstream caspases. However, in many cell types, the BID-dependent mitochondrial loop is required c-JUN peptide to amplify weak death receptor signals and relieve the inhibitory effect of IAP proteins on caspase activity (Scaffidi et al., 1998; Yin et al., c-JUN peptide 1999; Deng et al., 2002; Fulda et al., 2002). Although it is usually obvious that BCL-2 family members govern mitochondrial dysfunction, it remains unclear at what point the functions of these proteins intercede with gross alterations in mitochondrial morphology that occur during apoptosis. Normal mitochondrial morphology can vary dramatically between cell types, but in most cases mitochondria form long wormlike tubules that may (Rizzuto et al., 1998) or may not (Collins et al., 2002) make up interconnected networks. The distribution of mitochondria depends on interactions with microtubules whereas mitochondrial size and shape is the result of constant fusion and fission processes (Bereiter-Hahn and Voth, 1994). Little is c-JUN peptide known about the mechanism of mitochondrial fission and fusion except that it is c-JUN peptide regulated by a group of evolutionary conserved GTPases; fusion is dependent on Fzo/Mfn, whereas fission relies on a dynamin related protein, Drp1 (Osteryoung, 2001; Shaw and Nunnari, 2002). During apoptosis mitochondria remodel inner membrane cristae (Scorrano et al., 2002), fragment into small punctiform organelles that sometimes cluster in the perinuclear region (Desagher and Martinou, 2000; Frank et al., 2001; Pinton et al., 2001), and eventually undergo matrix swelling leading to OMM rupture (Petit et al., 1998; Mootha et al., 2001). Recently, Frank et al. (2001) exhibited that fragmentation of the mitochondrial network during apoptosis is usually caused by large-scale activation of Drp1-dependent mitochondrial fission, and that this event is usually requisite for the mitochondrial phase of apoptosis. How apoptotic signals converge around the fission machinery, however, is usually unclear. In the current paper, we present evidence ACH that caspase cleavage of BAP31 at the ER can trigger the onset of mitochondrial fission. BAP31 is usually a polytopic integral protein of the ER membrane that forms a large hetero-oligomeric complex with the related BAP29 protein and components of the actomyosin network (Adachi et al., 1996; Ng et al., 1997; Nguyen et al., 2000). After activation of cell surface death receptors, human BAP31 is usually cleaved at two identical caspase acknowledgement sites in its cytosolic tail, generating a membrane-embedded fragment, called p20, which induces apoptosis when expressed ectopically (Ng et al., 1997; Nguyen et al., 2000). Cleavage of BAP31 seems to be an important event in the Fas pathway because cells expressing a caspase-resistant BAP31 (crBAP31) mutant retain a near normal morphology after activation.