Cytochrome c: a crosslink between the mitochondria and the endoplasmic reticulum in calcium-dependent apoptosis.

Early and pivotal events in apoptosis are now known to occur in the mitochondria and the endoplasmic reticulum, and release of cytochrome c from the mitochondria and calcium from the endoplasmic recticulum into the cytosol are considered to be requisites for apoptosis in response to different stimuli. In the December 2003 issue of Nature Cell Biology, Boehning et al. report that early in apoptosis mitochondrial cyctochrome c translocates to the endoplasmic reticulum where it specifically binds inositol (1,4,5) triphosphate receptors, leading to sustained calcium release. The released calcium then triggers a mass exodus of cytochrome c from all mitochondria in the cells, thus amplifying the apoptotic signal.