Early release and subsequent caspase-mediated degradation of cytochrome c in apoptotic cerebellar granule cells

Cytochrome c (cyt c) release was investigated in cerebellargranule cells us ed as an in vitro neuronal model of apoptosis. We have found that cyt c is released into the cytoplasm as an intact, functionally active protein, that this event occurs early, in the commitment phase of the apoptotic process, and that after accumulation, this protein is progressively degraded. Degra dation, but not release, is fully blocked by benzyloxycarbonyl-Val-Ala-Asp- fluoromethylchetone (z-VAD-fmk) On the basis of previous findings obtained in the same neuronal population undergoing excitotoxic death, it is hypothe sized that release of cyt c may be part of a cellular attempt to maintain p roduction of ATP via cytochrome oxidase, which is reduced by cytosolic NADH in a cytochrome b(5)-soluble cyt c-mediated fashion. (C) 1999 Federation o f European Biochemical Societies.