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

Abstract

Receptor-evoked Ca2+ signalling involves Ca2+ release from the endoplasmic reticulum, followed by Ca2+ influx across the plasma membrane. 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. Although the molecular identity and regulation of I(crac) and SOC channels have not been precisely determined, 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, 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(crac) and TRPC channel activation by STIM1.

Thapsigargin activates Ca2+ entry both by store-dependent, STIM1/Orai1-mediated, and store-independent, TRPC3/PLC/PKC-mediated pathways in human endothelial cells

“…Moreover, recent papers showed that STIM1 directly or indirectly binds to all TRPC (except TRPC7) and activated them [28,29]. Orai1 was also shown to be associated with the complex formed by STIM1 and TRPC.…”

“…The interaction between STIM1 and Orai1 leads to channel opening and Ca 2+ entry [23,25,27]. An additional level of complexity emerged as several recent reports showed that STIM1 binds to TRPC1, TRPC4 and TRPC5 [28] and indirectly regulates TRPC3 and TRPC6 [29]. Furthermore, it was Table 1 Sequences of siRNA and primers used for the real time RT-PCR (all sequences are oriented 5 -3 ).…”

Calcium signaling in lymphocytes

“…The propensity of STIM1 to aggregate when its EF-hands are not bound by Ca 2+ can be demonstrated using just a short recombinant N-terminal fragment of STIM1, containing only the EF-hands and the adjacent SAM (sterile α-motif) domain [56,57]. Once formed, the STIM1 clusters preferentially localize to sites of ER-plasma membrane apposition and colocalize partially with clusters of ORAI1 [55,58, [61,62]. A coiled-coil domain in the cytoplasmic region of STIM1 is crucial for puncta formation and store-operated Ca 2+ entry [63,64], and this region has been suggested to interact directly with a coiled-coil domain at the C-terminus of ORAI1, both in cell-free systems and by FRET after store depletion in cells [62].…”

Homer proteins in Ca2+ signaling by excitable and non-excitable cells

“…Similarly, store-depletion is required for coalescence of stromal interacting molecule 1 (STIM1) to plasma membrane punctae and activation of TRPC channels by STIM1 [54]. It will be of interest to determine how the two TRPC channels regulatory mechanisms are related to each other and are integrated to regulate TRPC channels activity.…”