Retinoids, Thymosins, Actin and Apoptosis

Interleukin-le converting enzyme (ICE)-like proteases, which are synthesised as inactive precursors, play a key role in the induction of apoptosis. A number of ICE homologues have now been identified including CPP32, Ich-1, MchZ and Mch3. We now show that in both human monocytic tumor THP.1 cells, exposed to apoptotic stimuli and Jurkat T cells exposed to anti-Fas, cleavage of the 32-kd precursor of CPP32 and the 48-kd precursor of ICH-I was concommitant with the induction of apoptosis in both cell lines. Further examination of a pure population of apoptotic THP.1 cells obtained by Fluorescence Activated Cell Sorting revealed that the putative protein substrates of ICE-like proteases, poly(ADP-ribose) polymerase (PARP), U1-70K and Lamin B2 were extensively cleaved. In lysates from cells treated with the apoptotic stimuli an ICE-like protease activity was detected by a continuous fluoromemc assay using the -tide substrate ZDEVD.AFC. Funhermore, preincubation of either THP.1 or Jurkat cells with the tri-peptide ICE-like protease inhibitor ZVAD.FMK, prior to the induction of apoptosis, resulted in inhibition of both apoptosis and the cleavage of CPP32 and Ich-I. These data support the hypothesis that processing of more than one ICE-homologue is required for the execution of apoptosis.