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Cell Cycle. 2004 Mar;3(3):252-4. Epub 2004 Mar 1.

Apoptosis and calcium: new roles for cytochrome c and inositol 1,4,5-trisphosphate.

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Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.


Mounting evidence suggests that calcium released from internal stores plays a critical role in the progression of apoptosis. The primary calcium release channel on endoplasmic reticulum membranes is the inositol 1,4,5-trisphosphate receptor (IP3R). Deletion of the gene for IP3R results in defects in apoptosis in response to multiple stimuli. Conversely, augmented IP3R levels are associated with increased cell death. A mechanistic basis for altered IP3R function during apoptosis was revealed with the discovery that cytochrome c binds to IP3R early in apoptosis. This interaction blocks the calcium-dependent inhibition of IP3R function, resulting in increased calcium release from internal stores. The resultant cytoplasmic and mitochondrial calcium overload culminates in cell-wide cytochrome c release and maximal caspase activation. These findings highlight the importance of intracellular calcium stores in apoptosis, and the multi-functional role of cytochrome c released from mitochondria in cell death.

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