Transcription Factor NF-κB Regulates Expression of Pore-forming Ca2+ Channel Unit, Orai1, and Its Activator, STIM1, to Control Ca2+ Entry and Affect Cellular Functions

The serum and glucocorticoid-inducible kinase SGK1 increases the activity of Orai1, the pore forming unit of store-operated Ca2+ entry, and thus influences Ca2+-dependent cellular functions such as migration. SGK1 further regulates transcription factor nuclear factor κB (NF-κB). This study explored whether SGK1 influences transcription of Orai1 and/or STIM1, the Orai1-activating Ca2+ sensor. Orai1 and STIM1 transcript levels were decreased in mast cells from SGK1 knock-out mice and increased in HEK293 cells transfected with active S422DSGK1 but not with inactive K127NSGK1 or in S422DSGK1-transfected cells treated with the NF-κB inhibitor Wogonin (100 μm). Treatment with the stem cell factor enhanced transcript levels of STIM1 and Orai1 in sgk1+/+ but not in sgk1−/− mast cells and not in sgk1+/+ cells treated with Wogonin. Orai1 and STIM1 transcript levels were further increased in sgk1+/+ and sgk1−/− mast cells by transfection with active NF-κB subunit p65 as well as in HEK293 cells by transfection with NF-κB subunits p65/p50 or p65/p52. They were decreased by silencing of NF-κB subunits p65, p50, or p52 or by NF-κB inhibitor Wogonin (100 μm). Luciferase assay and chromatin immunoprecipitation defined NF-κB-binding sites in promoter regions accounting for NF-κB sensitive genomic regulation of STIM1 and Orai1. Store-operated Ca2+ entry was similarly increased by overexpression of p65/p50 or p65/p52 and decreased by treatment with Wogonin. Transfection of HEK293 cells with p65/p50 or p65/p52 further augmented migration. The present observations reveal powerful genomic regulation of Orai1/STIM1 by SGK1-dependent NF-κB signaling.