Local Ca2+ Entry Via Orai1 Regulates Plasma Membrane Recruitment of TRPC1 and Controls Cytosolic Ca2+ Signals Required for Specific Cell Functions

Abstract

Store-operated Ca2+ entry (SOCE) has been associated with two types of channels: CRAC channels that require Orai1 and STIM1 and SOC channels that involve TRPC1, Orai1, and STIM1. While TRPC1 significantly contributes to SOCE and SOC channel activity, abrogation of Orai1 function eliminates SOCE and activation of TRPC1. The critical role of Orai1 in activation of TRPC1-SOC channels following Ca2+ store depletion has not yet been established. Herein we report that TRPC1 and Orai1 are components of distinct channels. We show that TRPC1/Orai1/STIM1-dependent ISOC, activated in response to Ca2+ store depletion, is composed of TRPC1/STIM1-mediated non-selective cation current and Orai1/STIM1-mediated ICRAC; the latter is detected when TRPC1 function is suppressed by expression of shTRPC1 or a STIM1 mutant that lacks TRPC1 gating, STIM1(684EE685). In addition to gating TRPC1 and Orai1, STIM1 mediates the recruitment and association of the channels within ER/PM junctional domains, a critical step in TRPC1 activation. Importantly, we show that Ca2+ entry via Orai1 triggers plasma membrane insertion of TRPC1, which is prevented by blocking SOCE with 1 µM Gd3+, removal of extracellular Ca2+, knockdown of Orai1, or expression of dominant negative mutant Orai1 lacking a functional pore, Orai1-E106Q. In cells expressing another pore mutant of Orai1, Orai1-E106D, TRPC1 trafficking is supported in Ca2+-containing, but not Ca2+-free, medium. Consistent with this, ICRAC is activated in cells pretreated with thapsigargin in Ca2+-free medium while ISOC is activated in cells pretreated in Ca2+-containing medium. Significantly, TRPC1 function is required for sustained KCa activity and contributes to NFκB activation while Orai1 is sufficient for NFAT activation. Together, these findings reveal an as-yet unidentified function for Orai1 that explains the critical requirement of the channel in the activation of TRPC1 following Ca2+ store depletion. We suggest that coordinated regulation of the surface expression of TRPC1 by Orai1 and gating by STIM1 provides a mechanism for rapidly modulating and maintaining SOCE-generated Ca2+ signals. By recruiting ion channels and other signaling pathways, Orai1 and STIM1 concertedly impact a variety of critical cell functions that are initiated by SOCE.

A Reciprocal Shift in Transient Receptor Potential Channel 1 (TRPC1) and Stromal Interaction Molecule 2 (STIM2) Contributes to Ca2+ Remodeling and Cancer Hallmarks in Colorectal Carcinoma Cells

“…Conversely, TRPC1 silencing nearly abolishes outward I SOC , but it also reduces significantly the extent of the inward component. Consistently, it has been shown that STIM1 may drive interactions between ORAI1 and TRPC1 (39,50).…”

Calcium signaling in axon guidance

“…A complex pathway which interprets these intracellular Review Trends in Neurosciences August 2014, Vol. 37,No. 8 Ca 2+ signals to determine attraction or repulsion has been described [45,47], together with a recent model which represents this pathway mathematically [42].…”

“…When ER stores are depleted, the ER-resident stromal interaction molecule 1 (STIM1) localizes to the ER and plasma membrane junctions [31][32][33]. From here, STIM1 facilitates SOCE [34] through store-operated calcium (SOC) channels which utilize transient receptor potential cation (TRPC) channels and ORAI1, and calcium release-activated calcium (CRAC) channels which depend primarily on ORAI1 [33,[35][36][37]. Importantly, STIM1 localization in response to gradients of guidance cues is biased towards the up-gradient side of the growth cone, facilitating propagation of asymmetric Ca 2+ elevations [33].…”

Blockade of NOX2 and STIM1 signaling limits lipopolysaccharide-induced vascular inflammation

“…In addition to InsP 3 R subtype specificity, maintenance of Ca 2+ oscillations is shown to require SOCe (25,32). SOCe requires STIM1, the ER luminal Ca 2+ sensor, which, upon Ca 2+ store depletion, translocates into ER/plasma membrane junctions and couples to activate Orai1 (50) and possibly transient receptor potential channels (TRPCs) (51,52). However, we recently revealed that STIM1 can act independently of ER Ca 2+ as a ROS sensor to induce Ca 2+ entry (14).…”