THE CONTRASTING ROLES OF ICE FAMILY PROTEASES AND INTERLEUKIN-1-BETA IN APOPTOSIS INDUCED BY TROPHIC FACTOR WITHDRAWAL AND BY COPPER ZINC SUPEROXIDE-DISMUTASE DOWN-REGULATION/

We compare here the mechanisms of apoptotic death of PC12 cells induce d by down-regulation of Cu2+,Zn2+ superoxide dismutase (SOD1) and with drawal of trophic support (serum/nerve growth factor). Our previous re sults indicated that the initiating causes of death are different in e ach paradigm. However, bcl-2 rescues cells in either paradigm, suggest ing common downstream elements to the cell death pathway. To determine whether the ICE [interleukin 1 beta converting enzyme] family of prot eases, which is required for apoptosis on trophic factor withdrawal, i s also required for apoptosis induced by oxidative stress, we have dev eloped a novel peptide inhibitor that mimics the common catalytic site of these enzymes and thereby blocks their access to substrates. This differs from the more usual pseudosubstrate approach to enzyme inhibit ion. Blockade of ICE family proteases by either this inhibitor or by a permeant competitive ICE family antagonist rescues PC12 cells from ap optotic death following apoptosis induced by down-regulation of SOD1, as well as from trophic factor/nerve growth factor deprivation. SOD1 d own-regulation results in an increase in interleukin 1 beta (IL-1 beta ) production by the cells, and cell death under these conditions can b e prevented by either blocking antibodies against IL-1 beta or the IL- 1 receptor antagonist (IL-1R alpha). In contrast, trophic factor withd rawal does not increase IL-1 beta secretion, and the blocking antibody failed to protect PC12 cells from trophic factor withdrawal, whereas the receptor antagonist was only partially protective at very high con centrations. There were substantial differences in the concentrations of pseudosubstrate inhibitors which rescued cells from SOD1 down-regul ation and trophic factor deprivation. These results suggest the involv ement of different members of the ICE family, different substrates, or both in the two different initiating causes of cell death.