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Haematologica. 2019 Sep;104(9):1892-1905. doi: 10.3324/haematol.2018.194241. Epub 2018 Dec 20.

Tspan18 is a novel regulator of the Ca2+ channel Orai1 and von Willebrand factor release in endothelial cells.

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School of Biosciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
University Hospital Würzburg and Rudolf Virchow Center for Experimental Biomedicine, Würzburg, Germany.
Department of Haematology, University College London, London, UK.
Institute of Immunology and Immunotherapy, Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK.
Scar Free Foundation for Burns Research, Queen Elizabeth Hospital Birmingham, University Hospitals Birmingham National Health Service (NHS) Foundation Trust, Birmingham, UK.
Institute of Inflammation and Ageing, University of Birmingham, Birmingham, UK.
Department of Biological Sciences, University of Chester, Chester, UK.
Centre of Membrane Proteins and Receptors (COMPARE), Universities of Birmingham and Nottingham, Birmingham-Nottingham, UK.
Department of Pathophysiology, Sechenov First Moscow State Medical University, Moscow, Russia.
School of Biosciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK


Ca2+ entry via Orai1 store-operated Ca2+ channels in the plasma membrane is critical to cell function, and Orai1 loss causes severe immunodeficiency and developmental defects. The tetraspanins are a superfamily of transmembrane proteins that interact with specific 'partner proteins' and regulate their trafficking and clustering. The aim of this study was to functionally characterize tetraspanin Tspan18. We show that Tspan18 is expressed by endothelial cells at several-fold higher levels than most other cell types analyzed. Tspan18-knockdown primary human umbilical vein endothelial cells have 55-70% decreased Ca2+ mobilization upon stimulation with the inflammatory mediators thrombin or histamine, similar to Orai1-knockdown. Tspan18 interacts with Orai1, and Orai1 cell surface localization is reduced by 70% in Tspan18-knockdown endothelial cells. Tspan18 overexpression in lymphocyte model cell lines induces 20-fold activation of Ca2+ -responsive nuclear factor of activated T cell (NFAT) signaling, in an Orai1-dependent manner. Tspan18-knockout mice are viable. They lose on average 6-fold more blood in a tail-bleed assay. This is due to Tspan18 deficiency in non-hematopoietic cells, as assessed using chimeric mice. Tspan18-knockout mice have 60% reduced thrombus size in a deep vein thrombosis model, and 50% reduced platelet deposition in the microcirculation following myocardial ischemia-reperfusion injury. Histamine- or thrombin-induced von Willebrand factor release from endothelial cells is reduced by 90% following Tspan18-knockdown, and histamine-induced increase of plasma von Willebrand factor is reduced by 45% in Tspan18-knockout mice. These findings identify Tspan18 as a novel regulator of endothelial cell Orai1/Ca2+ signaling and von Willebrand factor release in response to inflammatory stimuli.

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