Von Willebrand factor propeptide missense mutations affect anterograde
transport to Golgi resulting in ER accumulation
Abstract
Von Willebrand disease (VWD), the most prevalent congenital bleeding
disorder, arises from a deficiency in von Willebrand factor (VWF), which
has crucial roles in hemostasis. The present study investigated
functional consequences and underlying pathomolecular mechanisms of
several VWF propeptide (VWFpp) variants detected in our cohort of VWD
patients for the first time. Transient expression experiments in HEK293T
cells demonstrated that four out of the six investigated variants
(p.Gly55Glu, p.Val86Glu, p.Trp191Arg, and p.Cys608Trp) severely impaired
secretion. Their co-transfections with the wt partly corrected VWF
secretion, displaying loss of large/intermediate multimers.
Immunostaining of the transfected HEK293 cells illustrated the retention
of the VWF variants in the endoplasmic reticulum (ER). Docking of the
COP I and COP II cargo recruitment proteins, ADP-ribosylation factor 1
and Sec24, onto the N-terminal VWF model (D1D2D´D3) revealed that these
variants occur at VWFpp putative interfaces, which can hinder VWF
loading at the ER exit quality control. Furthermore, quantitative and
automated morphometric exploration of the 3-dimensional
immunofluorescence images showed changes in the number/size of the VWF
storage organelles, Weibel-Palade body (WPB)-like vesicles. The result
of this study highlighted the significance of the VWFpp variants on
anterograde ER-Golgi trafficking of VWF as well as the biogenesis of
WPB-like vesicles.