PARTICIPATION OF CED-3 ICE AND YAMA PROTEINASES IN THE EXECUTION OF APOPTOSIS IN AK-5 TUMOR-CELLS LEADING TO SPONTANEOUS TUMOR-REGRESSION/

AK-5, which is a spontaneously regressing rat histiocytoma, is killed by necrosis (perforin mediated) and apoptosis. We have studied the ind uction of apoptosis in AK-5 tumor cells by each of the following: a fa ctor from anti-AK-5 antiserum, dexamethasone, and natural killer cells . Partial inhibition in apoptosis was observed when AK-5 cells were tr ansfected with Crm A gene, a specific inhibitor of ICE protease. Simil arly peptide inhibitors Ac-YVAD-cmk and Ac-DEVD-CHO inhibited partiall y the formation of nuclear bodies and DNA fragmentation induced by eac h of the above-mentioned apoptotic inducers. Although NR cells were ab le to kill Crm A and bcl-2 transfected clones by cytotoxic action, the y failed to induce DNA fragmentation in these clones, suggesting a dua l mode of action by NK cells in the induction of target cell death. We were unable to detect ICE and YAMA/CPP32 transcripts in control AK-5 cells, but upon induction of the apoptotic process, there was signific ant expression of these transcripts in AK-5 cells. When bcl-2 gene was introduced into AK-5 cells there was complete inhibition of apoptosis , suggesting its affect to be upstream of ICE and YAMA proteases. Thes e results suggest an important role for cysteine proteases in the exec ution of apoptosis, leading to tumor cell death and the regression of AK-5 tumor in syngeneic hosts. (C) 1997 Academic Press.