title: The Epac-Rap1 signaling pathway controls cAMP-mediated exocytosis of Weibel-Palade bodies in endothelial cells.
abstract: Endothelial cells contain specialized storage organelles called Weibel-Palade bodies (WPBs) that release their content into the vascular lumen in response to specific agonists that raise intracellular Ca(2+) or cAMP. We have previously shown that cAMP-mediated WPB release is dependent on protein kinase A (PKA) and involves activation of the small GTPase RalA. Here, we have investigated a possible role for another PKA-independent cAMP-mediated signaling pathway in the regulation of WPB exocytosis, namely the guanine nucleotide exchange factor Epac1 and its substrate, the small GTPase Rap1. Epinephrine stimulation of endothelial cells leads to Rap1 activation in a PKA-independent fashion. siRNA-mediated knockdown of Epac1 abolished epinephrine-induced activation of Rap1 and resulted in decreased epinephrine-induced WPB exocytosis. Down-regulation of Rap1 expression and prevention of Rap1 activation through overexpression of Rap1GAP effectively reduced epinephrine- but not thrombin-induced WPB exocytosis. Taken together, these data uncover a new Epac-Rap1-dependent pathway by which endothelial cells can regulate WPB exocytosis in response to agonists that signal through cAMP.
authors.affiliation: Department of Plasma Proteins, Sanquin Research and Landsteiner Laboratory Amsterdam Medical Center, 1066 CX Amsterdam, The Netherlands.
authors.forename: Kathinka W E M
authors.initials: KW
authors.lastname: van Hooren
authors.forename: Ellen L
authors.initials: EL
authors.lastname: van Agtmaal
authors.forename: Mar
authors.initials: M
authors.lastname: Fernandez-Borja
authors.forename: Jan A
authors.initials: JA
authors.lastname: van Mourik
authors.forename: Jan
authors.initials: J
authors.lastname: Voorberg
authors.forename: Ruben
authors.initials: R
authors.lastname: Bierings
mesh_terms: D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D042783:Endothelial Cells / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D014471:Umbilical Veins / Q000166:cytology*; D020302:Weibel-Palade Bodies / Q000378:metabolism*; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C116122:RAPGEF3 protein, human; D034741:RNA, Small Interfering; D000242:Cyclic AMP; D020827:rap1 GTP-Binding Proteins