FAS ACTIVATION OF THE P38 MITOGEN-ACTIVATED PROTEIN-KINASE SIGNALING PATHWAY REQUIRES ICE CED-3 FAMILY PROTEASES/

The Fas receptor mediates a signalling cascade resulting in programmed cell death (apoptosis) within hours of receptor cross-linking. In thi s study Fas activated the stress-responsive mitogen activated protein kinases, p38 and JNK within 2 h in Jurkat T lymphocytes but not the mi togen-responsive kinase ERK1 or pp70(S6k). Fas activation of p38 corre lated temporally with the onset of apoptosis, and transfection of cons titutively active MKK3(glu), an upstream regulator of p38. potentiated Fas-induced cell death, suggesting a potential involvement of the MKK 3/p38 activation pathway in Fas-mediated apoptosis. Fas has been shown to require ICE (interleukin-1 beta-converting enzyme) family protease s to induce apoptosis from studies utilizing the cowpox ICE inhibitor protein CrmA, the synthetic tetrapeptide ICE inhibitor YVAD-CMK and th e tripeptide yen-ICE inhibitor Z-VAD-FMK. In this study, crmA antagoni zed, and YVAD-CMK and Z-VAD-FMK completely inhibited, Fas activation o f p38 kinase activity, demonstrating that Fas-dependent activation of p38 requires ICE/CED-3 family members and conversely that the MKK3/p38 activation cascade represents a downstream target for the ICE/CED-3 f amily proteases. Intriguingly, p38 activation hv sorbitol and etoposid e was resistant to YVAD-CMK and Z-VAD-FMK suggesting the existence of an additional mechanism(s) of p38 regulation. The ICE/CED-3 family-p38 regulatory relationship described in the current work indicates that in addition to the previously described destructive cleavage of substr ates such as poly(ADP ribose) polymerase, lamins, and topoisomerase, t he apoptotic cysteine proteases also function to regulate stress kinas e signalling cascades.