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Ferrata Storti Foundation
Haematologica 2021 Volume 106(4):1138-1147
Hemostasis
Sec22b determines Weibel-Palade body length by controlling anterograde endoplasmic reticulum-Golgi transport
Ellie Karampini,1 Petra E. Bürgisser,2 Jenny Olins,1 Aat A. Mulder,3 Carolina R. Jost,3 Dirk Geerts,4 Jan Voorberg1,5 and Ruben Bierings1,2
1Molecular and Cellular Hemostasis, Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center, University of Amsterdam, Amsterdam; 2Hematology, Erasmus MC, University Medical Center Rotterdam, Rotterdam; 3Molecular Cell Biology, Leiden University Medical Center, Leiden and 4Medical Biology Amsterdam University, Medical Center, University of Amsterdam, Amsterdam and 5Experimental Vascular Medicine, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, the Netherlands
ABSTRACT
Von Willebrand factor (VWF) is a multimeric hemostatic protein that is synthesized in endothelial cells, where it is stored for secretion in elongated secretory organelles called Weibel-Palade bodies (WPB). The hemostatic activity of VWF is strongly related to the length of these bodies, but how endothelial cells control the dimensions of their WPB is unclear. In this study, using a targeted short hairpin RNA screen, we identified longin-SNARE Sec22b as a novel determinant of WPB size and VWF trafficking. We found that Sec22b depletion resulted in loss of the typically elongated WPB morphology together with disin- tegration of the Golgi and dilation of rough endoplasmic reticulum cis- ternae. This was accompanied by reduced proteolytic processing of VWF, accumulation of VWF in the dilated rough endoplasmic reticulum and reduced basal and stimulated VWF secretion. Our data demonstrate that the elongation of WPB, and thus adhesive activity of their cargo VWF, is determined by the rate of anterograde transport between endo- plasmic reticulum and Golgi, which depends on Sec22b-containing SNARE complexes.
Introduction
Endoplasmic reticulum (ER)-to-Golgi transport is the first step in the secretory pathway.1 As eukaryotic cells are extremely compartmentalized, ER is the first stop in protein production as well as the initial quality check point of whether proteins are correctly folded.2 Correctly folded proteins are then trafficked to the Golgi where they are additionally modified before being directed to their appro- priate destination: endo/lysosome, plasma membrane or secretion.3 At the trans- Golgi network (TGN), proteins will either enter the “constant” constitutive path- way for unimpeded release, or will be temporarily stored in secretory vesicles, often of the family of lysosome-related organelles, for regulated secretion. Storage and regulated secretion allow the immediate discharge of larger quanti- ties of protein in a correct physiological setting.4
The biogenesis of lysosome-related organelles is crucial for the proper function of a wide variety of cells, their importance being well-highlighted by the fact that defec- tive formation of these organelles results in the manifestation of a large number of clinical abnormalities including bleeding, immunodeficiency, hypopigmentation and neurological defects.5 Within the family of lysosome-related organelles, Weibel- Palade bodies (WPB) are the storage organelles of endothelial cells.6,7 WPB primarily contain von Willebrand factor (VWF), a large multimeric hemostatic protein that serves a critical role in platelet adhesion and as a chaperone for coagulation factor VIII.8 The biogenesis of WPB is directly dependent on the synthesis and correct post- translational processing of VWF.9-12 WPB have a distinct, elongated morphology that is intrinsically linked to the inherent ability of VWF multimers to self-organize in
Correspondence:
RUBEN BIERINGS
r.bierings@erasmusmc.nl
Received: November 11, 2019. Accepted: March 24, 2020. Pre-published: March 26, 2020.
https://doi.org/10.3324/haematol.2019.242727
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