Hsp60 accelerates the maturation of pro-caspase-3 by upstream activator proteases during apoptosis

The activation of caspases represents a critical step in the pathways leadi ng to the biochemical and morphological changes that underlie apoptosis. Mu ltiple pathways leading to caspase activation appear to exist and vary depe nding on the death-inducing stimulus. We demonstrate that the activation of caspase-3, in Jurkat cells stimulated to undergo apoptosis by a Fas-indepe ndent pathway, is catalyzed by caspase-6, Caspase-6 was found to co-purify with caspase-3 as part of a multiprotein activation complex from extracts o f camptothecin-treated Jurkat cells. A biochemical analysis of the protein constituents of the activation complex showed that Hsp60 was also present. Furthermore, an interaction between Hsp60 and caspase-3 could be demonstrat ed by co-immunoprecipitation experiments using HeLa as well as Jurkat cell extracts. Using a reconstituted in vitro system, Hsp60 was able to substant ially accelerate the maturation of procaspase-3 by different upstream activ ator caspases and this effect was dependent on ATP hydrolysis. We propose t hat the ATP-dependent 'foldase' activity of Hsp60 improves the vulnerabilit y of pro-caspase-3 to proteolytic maturation by upstream caspases and that this represents an important regulatory event in apoptotic cell death.