Apoptosis in cerebellar granule neurones: involvement of interleukin-1 beta converting enzyme-like proteases

Proteases of the interleukin-1 beta converting enzyme (ICE) family have been implicated as mediators of apoptosis in several cell types. Here we report the ability of peptide inhibitors of ICE-like proteases to inhibit apoptosis of cultured cerebellar granule neurones caused by reduction of extracellular K+ levels and by the broad-spectrum protein kinase inhibitor staurosporine. Unlike apoptosis induced by K+ deprivation, staurosporine-induced neuronal death does not require new protein synthesis. The ICE-like protease inhibitor benzyloxycarbonyl-Val-Ala-Asp (O-methyl)fluoromethyl ketone (zVAD-fmk) was found to be extremely effective at preventing staurosporine-induced death of cerebellar granule neurones and yet was completely ineffective in preventing K+ deprivation-induced death. Staurosporine induced cleavage of the 116-kDa poly (ADP-ribose) polymerase enzyme, a substrate of ICE-like proteases, to the 85-kDa product, and this cleavage was also blocked by zVAD. By comparison, K+ deprivation led to the disappearance of the 116-kDa protein, with no detectable increase in level of the 85-kDa cleavage product. Taken together, these results imply the existence of divergent ICE-like protease pathways in a CNS model of neuronal apoptosis.