Presence of a pre-apoptotic complex of pro-caspase-3, Hsp60 and Hsp10 in the mitochondrial fraction of Jurkat cells

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Abstract
Activation of pro‐caspase‐3 is a central event in the execution phase of apoptosis and appears to serve as the convergence point of different apoptotic signaling pathways. Recently, mitochondria were found to play a central role in apoptosis through release of cytochrome c and activation of caspases. Moreover, a sub‐population of pro‐caspase‐3 has been found to be localized to this organelle. In the present study, we demonstrate that pro‐caspase‐3 is present in the mitochondrial fraction of Jurkat T cells in a complex with the chaperone proteins Hsp60 and Hsp10. Induction of apoptosis with staurosporine led to the activation of mitochondrial pro‐caspase‐3 and its dissociation from the Hsps which were released from mitochondria. The release of Hsps occurred simultaneously with the release of other mitochondrial intermembrane space proteins including cytochrome c and adenylate kinase, prior to a loss of mitochondrial transmembrane potential. In in vitro systems, recombinant Hsp60 and Hsp10 accelerated the activation of pro‐caspase‐3 by cytochrome c and dATP in an ATP‐dependent manner, consistent with their function as chaperones. This finding suggests that the release of mitochondrial Hsps may also accelerate caspase activation in the cytoplasm of intact cells.