NFAT5-sensitive Orai1 expression and store-operated Ca2+ entry in megakaryocytes

The transcription factor nuclear factor of activated T cells 5 ( NFAT5) is up-regulated in several clinical disorders, including dehydration. NFAT5-sensitive genes include serum and glucocorticoid-inducible kinase 1 ( SGK1). The kinase is a powerful regulator of Orai1, a Ca2+ channel accomplishing store-operated Ca2+ entry (SOCE). Orai1is stimulated after intracellular store depletion by the Ca2+ sensors stromal interaction molecule 1 ( STIM1), or STIM2, or both. In the present study, we explored whether nuclear factor of activated T cell ( NFAT)-5 influences Ca2+ signaling in megakaryocytes. To this end, human megakaryocytic(MEG-01) cells were transfected with NFAT5or with siNFAT5. Platelets and megakaryocyteswere isolated from wild-type mice with either access to water ad libitum or dehydration by 36 h of water deprivation. Transcript levels were determined with quantitative RT-PCR and protein abundance by Western blot analysisand flowcytometry, cytosolic (intracellular) Ca2+ concentration ([Ca2+]i) b...