STIM1 carboxyl-terminus activates native SOC, Icrac and TRPC1 channels

Receptor- evoked Ca2+ signalling involves Ca2+ release from the endoplasmic reticulum, followed by Ca2+ influx across the plasma membrane(1). Ca2+ influx is essential for many cellular functions, from secretion to transcription, and is mediated by Ca2+- release activated Ca2+ (I-crac) channels and store- operated calcium entry ( SOC) channels(2). Although the molecular identity and regulation of I-crac and SOC channels have not been precisely determined(1), notable recent findings are the identification of STIM1, which has been indicated to regulate SOC and I-crac channels by functioning as an endoplasmic reticulum Ca2+ sensor(3-6), and ORAI1 ( ref. 7) or CRACM1 ( ref. 8) - both of which may function as I-crac channels or as an I-crac subunit. How STIM1 activates the Ca2+ influx channels and whether STIM1 contributes to the channel pore remains unknown. Here, we identify the structural features that are essential for STIM1- dependent activation of SOC and I-crac channels, and demonstrate that they are identical to those involved in the binding and activation of TRPC1. Notably, the cytosolic carboxyl terminus of STIM1 is sufficient to activate SOC, I-crac and TRPC1 channels even when native STIM1 is depleted by small interfering RNA. Activity of STIM1 requires an ERM domain, which mediates the selective binding of STIM1 to TRPC1, 2 and 4, but not to TRPC3, 6 or 7, and a cationic lysine- rich region, which is essential for gating of TRPC1. Deletion of either region in the constitutively active STIM1(D76A) yields dominant- negative mutants that block native SOC channels, expressed TRPC1 in HEK293 cells and I-crac in Jurkat cells. These observations implicate STIM1 as a key regulator of activity rather than a channel component, and reveal similar regulation of SOC, I(cra)c and TRPC channel activation by STIM1.