Submitted December 21, 2007
Accepted March 10, 2008
Basal secretion of von Willebrand factor from human endothelial cells
Jonathan P Giblin, Lindsay J Hewlett, and Matthew J Hannah*
Department of Molecular Neuroendocrinology, Medical Research Council National Institute for Medical Research, London, United Kingdom
* Corresponding author; email: mhannah{at}nimr.mrc.ac.uk.
Endothelial cells store the adhesive glycoprotein von Willebrand factor (VWF) in Weibel-Palade Bodies (WPBs), distinctively shaped regulated secretory organelles that undergo exocytosis in response to secretagogue. A significant proportion of newly synthesised VWF is also secreted spontaneously from non-stimulated cells, through what is thought to be the constitutive secretory pathway. To learn more about VWF trafficking we performed kinetic analyses of the storage and non-stimulated secretion of VWF in cultured human endothelial cells. We found that the majority of VWF was secreted through a route that was significantly delayed compared to constitutive secretion, although this pathway was responsible for secretion of a small amount of un-cleaved VWF precursor. Disruption of pH-dependent sorting processes with ammonium chloride converted the secretion kinetics of mature VWF to that of its precursor. Conversely, preventing constitutive secretion of nascent protein with brefeldin A had only a modest effect on the spontaneous release of VWF demonstrating that the majority of VWF secreted by non-stimulated cells was not constitutive secretion but basal release of a post-Golgi storage organelle, presumably the WPB. These data suggest that VWF is sorted to the regulated secretory pathway in endothelial cells much more efficiently than previously reported.
