Critical independent regions in the VWF propeptide and mature VWF that enable normal VWF storage

Von Willebrand factor (VWF) is synthesized in endothelial cells, where it is stored in Weibel-Palade bodies. Administration of 1-desamino-8-D-arginine-vasopressin (DDAVP) to patients with type 1 von Willebrand disease and to healthy individuals causes a rapid increase in plasma VWF levels. This increase is the result of stimulated release of VWF from Weibel-Palade bodies in certain beds of endothelial cells. The VWF propeptide (VWFpp) targets VWF to storage granules through a noncovalent association. The nature of the VWFpp/VWF interaction was investigated by using cross-species differences in VWF storage. While canine VWFpp traffics to storage granules and facilitates the multimerization of human VWF, it does not direct human VWF to storage granules. Since storage takes place after furin cleavage, this defect appears to be due to the defective interaction of canine VWFpp and human VWF. To determine the regions within VWFpp and VWF important for this VWFpp/VWF association and costorage, a series of human-canine chimeric VWFpp and propeptide-deleted VWF (Δpro) constructs were produced and expressed in AtT-20 cells. The intracellular localization of coexpressed proteins was examined by confocal microscopy. Two amino acids, 416 in VWFpp and 869 in the mature VWF molecule, were identified as being critical for the association and granular storage of VWF.