Protein kinase C and guanosine triphosphate combine to potentiate calcium-dependent membrane fusion driven by annexin 7.
Exocytotic secretion is promoted by the concerted action of calcium, guanine nucleotide, and protein kinase C. We now show that the calcium-dependent membrane fusion activity of annexin 7 in vitro is further potentiated by the combined addition of guanine nucleotide and protein kinase C. The observed increment involves the simultaneous activation of annexin 7 by these two effectors. Guanosine triphosphate (GTP) and its non-hydrolyzable analogues optimally enhance the phosphorylation of annexin 7 by protein kinase C in vitro. Reciprocally, phosphorylation by protein kinase C significantly potentiates the binding and hydrolysis of GTP by annexin 7. Only protein kinase C-dependent phosphorylation has a significant positive effect on annexin 7 GTPase, although other protein kinases, including cAMP-dependent protein kinase, cGMP-dependent protein kinase, and pp60(c-)(src), have been shown to label the protein with high efficiency. In vivo, the ratio of bound GDP/GTP and phosphorylation of annexin 7 change in direct proportion to the extent of catecholamine release from chromaffin cells in response to stimulation by carbachol, or to inhibition by various protein kinase C inhibitors. These results thus lead us to hypothesize that annexin 7 may serve as a common site of action for calcium, guanine nucleotide, and protein kinase C in the exocytotic membrane fusion process in chromaffin cells.
Caohuy
Hung
H
Department of Anatomy, Physiology, and Genetics, Uniformed Services University School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA.
Pollard
Harvey B
HB
D017310:Annexin A7 / Q000502:physiology*; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D005089:Exocytosis; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D008561:Membrane Fusion / Q000502:physiology*; D010766:Phosphorylation; D019920:Photoaffinity Labels; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*
D017310:Annexin A7; D019920:Photoaffinity Labels; D006160:Guanosine Triphosphate; D011493:Protein Kinase C; D020558:GTP Phosphohydrolases; D002118:Calcium