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.
Caohuy
H
H
Department of Anatomy and Cell Biology, Uniformed Services University School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA.
Pollard
H B
HB
D000313:Adrenal Medulla / Q000166:cytology; D000818:Animals; D017310:Annexin A7 / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D005089:Exocytosis; D007700:Kinetics; D008081:Liposomes; D008561:Membrane Fusion; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism
D017310:Annexin A7; D008081:Liposomes; D010710:Phosphates; D016392:Proto-Oncogene Proteins pp60(c-src); D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium