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

J Biol Chem. 2001 Apr 20;276(16):12813-21. doi: 10.1074/jbc.M008482200. Epub 2001 Jan 24.

Abstract

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 / cytology
  • Animals
  • Annexin A7 / metabolism*
  • Calcium / metabolism
  • Cattle
  • Cells, Cultured
  • Chromaffin Cells / cytology
  • Chromaffin Cells / metabolism*
  • Chromaffin Cells / physiology
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Cyclic GMP-Dependent Protein Kinases / metabolism
  • Exocytosis
  • Kinetics
  • Liposomes
  • Membrane Fusion
  • Phosphates / metabolism
  • Phosphorylation
  • Protein Kinase C / metabolism*
  • Proto-Oncogene Proteins pp60(c-src) / metabolism

Substances

  • Annexin A7
  • Liposomes
  • Phosphates
  • Proto-Oncogene Proteins pp60(c-src)
  • Cyclic AMP-Dependent Protein Kinases
  • Cyclic GMP-Dependent Protein Kinases
  • Protein Kinase C
  • Calcium