Changes in cytoplasmic Ca2+ levels regulate a variety of fundamental cellular functions in virtually all cells. In nonexcitable cells, a major pathway of Ca2+ entry involves receptor-mediated depletion of intracellular Ca2+ stores followed by the activation of store-operated calcium channels in the plasma membrane. We have established a mouse line expressing an activating EF hand motif mutant of stromal interaction molecule 1 (Stim1), an ER receptor recently identified as the Ca2+ sensor responsible for activation of Ca2+ release–activated (CRAC) channels in T cells, whose function in mammalian physiology is not well understood. Mice expressing mutant Stim1 had macrothrombocytopenia and an associated bleeding disorder. Basal intracellular Ca2+ levels were increased in platelets, which resulted in a preactivation state, a selective unresponsiveness to immunoreceptor tyrosine activation motif–coupled agonists, and increased platelet consumption. In contrast, basal Ca2+ levels, but not receptor-mediated responses, were affected in mutant T cells. These findings identify Stim1 as a central regulator of platelet function and suggest a cell type–specific activation or composition of the CRAC complex.
Johannes Grosse, Attila Braun, David Varga-Szabo, Niklas Beyersdorf, Boris Schneider, Lutz Zeitlmann, Petra Hanke, Patricia Schropp, Silke Mühlstedt, Carolin Zorn, Michael Huber, Carolin Schmittwolf, Wolfgang Jagla, Philipp Yu, Thomas Kerkau, Harald Schulze, Michael Nehls, Bernhard Nieswandt
Isolated thrombocytopenia in