title: cAMP-induced secretion of endothelial von Willebrand factor is regulated by a phosphorylation/dephosphorylation switch in annexin A2.
abstract: The large multimeric glyocoprotein von Willebrand factor (VWF) is a crucial component of both primary and secondary hemostasis. It is stored in secretory granules of vascular endothelial cells, the Weibel-Palade bodies (WPBs), and is released following stimulation by agonists that raise intracellular Ca(2+) or cyclic adenosine monophosphate (cAMP) levels. cAMP-induced exocytosis of WPBs requires protein kinase A activity, but downstream factors that are regulated by phosphorylation/dephosphorylation are not known. Here we identify the complex consisting of the lipid-binding protein annexin A2 (AnxA2) and S100A10 as such a factor. Knockdown and specific rescue approaches reveal that a functional AnxA2-S100A10 complex is required for the forskolin-induced, cAMP-dependent release of VWF. Forskolin triggers dephosphorylation of AnxA2 that is mediated by a calcineurin-like phosphatase and stabilizes the AnxA2-S100A10 complex, thereby promoting VWF release. Serine 11 of AnxA2 was identified as the target residue of this phosphorylation switch because a phosphomimicking mutation at this site prevents complex formation with S100A10 and, in contrast to wild-type or S11A-AnxA2, is unable to restore cAMP-dependent VWF secretion in AnxA2-depleted cells. Thus, complex formation of AnxA2 with S100A10 is a central regulatory mechanism in the acute release of VWF in response to cAMP-elevating agonists.
authors.affiliation: Institute of Medical Biochemistry, Centre for Molecular Biology of Inflammation, University of Muenster, Von-Esmarch-Strasse 56, Muenster, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Brandherm
authors.forename: Jennifer
authors.initials: J
authors.lastname: Disse
authors.forename: Dagmar
authors.initials: D
authors.lastname: Zeuschner
authors.forename: Volker
authors.initials: V
authors.lastname: Gerke
mesh_terms: D017306:Annexin A2 / Q000378:metabolism*; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004727:Endothelium / Q000378:metabolism*; D005089:Exocytosis; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport; D009418:S100 Proteins / Q000378:metabolism; D020302:Weibel-Palade Bodies / Q000378:metabolism / Q000473:pathology; D014841:von Willebrand Factor / Q000378:metabolism*; D000099248:S100 Calcium Binding Protein A10
chemical_list: D017306:Annexin A2; D019703:Calcineurin; D002118:Calcium; D005576:Colforsin; D000242:Cyclic AMP; D009418:S100 Proteins; D014841:von Willebrand Factor; D000099248:S100 Calcium Binding Protein A10