title: Factor VIII alters tubular organization and functional properties of von Willebrand factor stored in Weibel-Palade bodies.
abstract: In endothelial cells, von Willebrand factor (VWF) multimers are packaged into tubules that direct biogenesis of elongated Weibel-Palade bodies (WPBs). WPB release results in unfurling of VWF tubules and assembly into strings that serve to recruit platelets. By confocal microscopy, we have previously observed a rounded morphology of WPBs in blood outgrowth endothelial cells transduced to express factor VIII (FVIII). Using correlative light-electron microscopy and tomography, we now demonstrate that FVIII-containing WPBs have disorganized, short VWF tubules. Whereas normal FVIII and FVIII Y1680F interfered with formation of ultra-large VWF multimers, release of the WPBs resulted in VWF strings of equal length as those from nontransduced blood outgrowth endothelial cells. After release, both WPB-derived FVIII and FVIII Y1680F remained bound to VWF strings, which however had largely lost their ability to recruit platelets. Strings from nontransduced cells, however, were capable of simultaneously recruiting exogenous FVIII and platelets. These findings suggest that the interaction of FVIII with VWF during WPB formation is independent of Y1680, is maintained after WPB release in FVIII-covered VWF strings, and impairs recruitment of platelets. Apparently, intra-cellular and extracellular assembly of FVIII-VWF complex involves distinct mechanisms, which differ with regard to their implications for platelet binding to released VWF strings.
authors.affiliation: Department of Plasma Proteins, Sanquin Research, Amsterdam, The Netherlands.
authors.forename: Eveline A M
authors.initials: EA
authors.lastname: Bouwens
authors.forename: Marjon J
authors.initials: MJ
authors.lastname: Mourik
authors.forename: Maartje
authors.initials: M
authors.lastname: van den Biggelaar
authors.forename: Jeroen C J
authors.initials: JC
authors.lastname: Eikenboom
authors.forename: Jan
authors.initials: J
authors.lastname: Voorberg
authors.forename: Karine M
authors.initials: KM
authors.lastname: Valentijn
authors.forename: Koen
authors.initials: K
authors.lastname: Mertens
mesh_terms: D019943:Amino Acid Substitution; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D005169:Factor VIII / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D010649:Phenylalanine / Q000235:genetics; D055503:Protein Multimerization / Q000187:drug effects* / Q000235:genetics; D014162:Transfection; D014443:Tyrosine / Q000235:genetics; D020302:Weibel-Palade Bodies / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D014841:von Willebrand Factor / Q000378:metabolism* / Q000502:physiology*
chemical_list: D014841:von Willebrand Factor; D014443:Tyrosine; D010649:Phenylalanine; D005169:Factor VIII