Activation of annexin 7 by protein kinase C in vitro and in vivo.

Annexin 7, a Ca(2+)/GTP-activated membrane fusion protein, is preferentially phosphorylated in intact chromaffin cells, and the levels of annexin 7 phosphorylation increase quantitatively in proportion to the extent of catecholamine secretion. Consistently, various protein kinase C inhibitors proportionately reduce both secretion and phosphorylation of annexin 7 in these cells. In ...
vitro, annexin 7 is quantitatively phosphorylated by protein kinase C to a mole ratio of 2.0, and phosphorylation is extraordinarily sensitive to variables such as pH, calcium, phospholipid, phorbol ester, and annexin 7 concentration. Phosphorylation of annexin 7 by protein kinase C significantly potentiates the ability of the protein to fuse phospholipid vesicles and lowers the half-maximal concentration of calcium needed for this fusion process. Furthermore, other protein kinases, including cAMP-dependent protein kinase, cGMP-dependent protein kinase, and protein-tyrosine kinase pp60(c-)(src), also label annexin 7 with high efficiency but do not have this effect on membrane fusion. In the case of pp60(c-)(src), we note that this kinase, if anything, modestly suppresses the membrane fusion activity of annexin 7. These results thus lead us to hypothesize that annexin 7 may be a positive mediator for protein kinase C action in the exocytotic membrane fusion reaction in chromaffin cells.
Mesh Terms:
Adrenal Medulla, Animals, Annexin A7, Calcium, Cattle, Cells, Cultured, Chromaffin Cells, Cyclic AMP-Dependent Protein Kinases, Cyclic GMP-Dependent Protein Kinases, Exocytosis, Kinetics, Liposomes, Membrane Fusion, Phosphates, Phosphorylation, Protein Kinase C, Proto-Oncogene Proteins pp60(c-src)
J. Biol. Chem.
Date: Apr. 20, 2001
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