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Mitochondrial desensitization to the second of two stimuli is partly lost if PKCß is inhibited (bottom).

Calcium signals destined for mitochondria are first screened by protein kinase C (PKC) isoforms, according to Pinton et al., on page 223. Different PKCs then adjust the organelles' responses to their liking.

PKC is a Ca²⁺-activated kinase that comes in many flavors. Pinton et al. analyzed the contribution of several of these flavors to Ca²⁺ signaling by overexpressing or inhibiting individual isoforms in cells. Their effects were assessed by stimulating cells with an extracellular agonist to elicit Ca²⁺ stores from the ER into the cytoplasm.

One flavor, PKC, limited all Ca²⁺ signaling by dampening this ER release. Others, however, worked specifically at the mitochondria. PKC increased mitochondrial Ca²⁺ uptake, whereas PKCß and reduced it. Thus, activation of PKC upon initial stimulation may alter the effect of subsequent Ca²⁺ spikes. Mitochondria are known to respond less to the second of two consecutive stimuli. The authors now show that PKCß is needed for this dampening. This function might make cells less sensitive to apoptotic signals, for example, which induce mitochondrial Ca²⁺ influx.

The PKC isoforms that decrease Ca²⁺ uptake also decrease mitochondrial membrane potential. There may be a causal link, but mitochondrial Ca²⁺ transporters have not been cloned, so identifying the relevant PKC substrates will require the purification of mitochondrial proteins that are phosphorylated in response to Ca²⁺.

Nicole LeBrasseur

lebrasn{at}rockefeller.edu

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Long-term modulation of mitochondrial Ca²⁺ signals by protein kinase C isozymes

Paolo Pinton, Sara Leo, Mariusz R. Wieckowski, Giulietta Di Benedetto, and Rosario Rizzuto
J. Cell Biol. 2004 165: 223-232. [Abstract] [Full Text] [PDF]

This Article PDF (Full Text) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by LeBrasseur, N. Search for Related Content PubMed Articles by LeBrasseur, N. Related Collections Related Article Social Bookmarking                      What's this?