INVOLVEMENT OF CPP32 CASPASE-3 IN C-MYC-INDUCED APOPTOSIS/

c-Myc is a transcriptional activator implicated in the control of cell proliferation, differentiation and transformation, but is also involv ed in the regulation of programmed cell death, apoptosis. Despite inte nsive research, the molecular mechanisms by which c-Myc triggers and e xecutes cell death remain still elusive. Here, we made use of Rat 1A M ycER cells expressing a conditionally active c-Myc protein and tested first the hypothesis that ornithine decarboxylase (ODC), which is a tr anscriptional target of c-Myc, were a mediator of c-Myc-induced apopto sis. However, our results show that the activity of ODC is not require d for the c-Myc-mediated apoptosis to occur in these cells. We also fo und that the expression of p53, p21(waf1/cip1), Bcl-2, Bax, Bcl-x(L), Bad and cyclins D1, E, A and B did not show any significant changes fo llowing c-Myc induction. But, our studies revealed that the c-Myc indu ced apoptosis is associated with a specific cleavage of poly(ADPribose ) polymerase (PARP), suggesting that a cysteine protease of the ICE/CE D-3 family is involved. Moreover, we found that the cysteine protease CPP32/Caspase-3, which is known to cleave PARR, is processed from its inactive form to an active protease composed of 17 and 12 kDa subunits ; whilst Ich-1/Caspase-2 belonging to another subset of this protease family was not processed/activated following c-Myc activation. The act ivation of CPP32 and apoptotic cell death were inhibited by addition o f Z-VAD-fmk, a universal inhibitor of ICE-like proteases. Further, a s elective inhibitor of CPP32-like proteases (Z-DEVD-fmk) partly inhibit ed apoptosis. These results provide evidence that the ICE/CED3-family proteases, CPP32 and likely others, play a critical role in the execut ion of a nuclear proto-oncogene, c-Myc-induced apoptosis.