S. Kagaya et al., A FUNCTIONAL-ROLE FOR DEATH PROTEASES IN S-MYC-MEDIATED AND C-MYC-MEDIATED APOPTOSIS, Molecular and cellular biology, 17(11), 1997, pp. 6736-6745
Upon activation, cell surface death receptors, Fas/APO-1/CD95 and tumo
r necrosis factor receptor-1 (TNFR-1), are attached to cytosolic adapt
or proteins, which in turn recruit caspase-8 (MACH/FLICE/Mch5) to acti
vate the interleukin-1 beta-converting enzyme (ICE)/CED-3 family prote
ase (caspase) cascade. However, it remains unknown whether these apopt
otic proteases are generally involved in apoptosis triggered by other
stimuli such as Myc and p53. In this study, we provide lines of eviden
ce that a death protease cascade consisting of caspases and serine pro
teases plays an essential role in Myc-mediated apoptosis. When Rat-1 f
ibroblasts stably expressing either s-Myc or c-Myc were induced to und
ergo apoptosis by serum deprivation, a caspase-3 (CPP32)-like protease
activity that cleaves a specific peptide substrate, Ac-DEVD-MCA, appe
ared in the cell lysates. Induction of s-Myc- and c-Myc-mediated apopt
otic cell death was effectively prevented by caspase inhibitors such a
s Z-Asp-CH2-DCB and Ac-DEVD-CHO. Furthermore, exposing the cells to a
serine protease inhibitor, 4-(2-aminoethyl)benzenesulfonyl fluoride (A
EBSF), also significantly inhibited s-Myc- and c-Myc-mediated apoptosi
s and the appearance of the caspase-3-like protease activity in vivo,
However, AEBSF did not directly inhibit caspase-3-like protease activi
ty in the apoptotic cell lysates in vitro. Together, these results ind
icate that caspase-3-like proteases play a critical role in both s-Myc
- and c-Myc-mediated apoptosis and that caspase-3-like proteases funct
ion downstream of the AEBSF-sensitive step in the signaling pathway of
Myc-mediated apoptosis.