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Distinct contributions of Orai1 and TRPC1 to agonist-induced [Ca(2+)](i) signals determine specificity of Ca(2+)-dependent gene expression.

ABSTRACT: Regulation of critical cellular functions, including Ca(2+)-dependent gene expression, is determined by the temporal and spatial aspects of agonist-induced Ca(2+) signals. Stimulation of cells with physiological concentrations of agonists trigger increases [Ca(2+)](i) due to intracellular Ca(2+) release and Ca(2+) influx. While Orai1-STIM1 channels account for agonist-stimulated [Ca(2+)](i) increase as well as activation of NFAT in cells such as lymphocytes, RBL and mast cells, both Orai1-STIM1 and TRPC1-STIM1 channels contribute to [Ca(2+)](i) increases in human submandibular gland (HSG) cells. However, only Orai1-mediated Ca(2+) entry regulates the activation of NFAT in HSG cells. Since both TRPC1 and Orai1 are activated following internal Ca(2+) store depletion in these cells, it is not clear how the cells decode individual Ca(2+) signals generated by the two channels for the regulation of specific cellular functions. Here we have examined the contributions of Orai1 and TRPC1 to carbachol (CCh)-induced [Ca(2+)](i) signals and activation of NFAT in single cells. We report that Orai1-mediated Ca(2+) entry generates [Ca(2+)](i) oscillations at different [CCh], ranging from very low to high. In contrast, TRPC1-mediated Ca(2+) entry generates sustained [Ca(2+)](i) elevation at high [CCh] and contributes to frequency of [Ca(2+)](i) oscillations at lower [agonist]. More importantly, the two channels are coupled to activation of distinct Ca(2+) dependent gene expression pathways, consistent with the different patterns of [Ca(2+)](i) signals mediated by them. Nuclear translocation of NFAT and NFAT-dependent gene expression display "all-or-none" activation that is exclusively driven by local [Ca(2+)](i) generated by Orai1, independent of global [Ca(2+)](i) changes or TRPC1-mediated Ca(2+) entry. In contrast, Ca(2+) entry via TRPC1 primarily regulates NF?B-mediated gene expression. Together, these findings reveal that Orai1 and TRPC1 mediate distinct local and global Ca(2+) signals following agonist stimulation of cells, which determine the functional specificity of the channels in activating different Ca(2+)-dependent gene expression pathways.

SUBMITTER: Ong HL

PROVIDER: S-EPMC3480383 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Distinct contributions of Orai1 and TRPC1 to agonist-induced [Ca(2+)](i) signals determine specificity of Ca(2+)-dependent gene expression.

Ong Hwei Ling HL Jang Shyh-Ing SI Ambudkar Indu Suresh IS

PloS one 20121024 10

Regulation of critical cellular functions, including Ca(2+)-dependent gene expression, is determined by the temporal and spatial aspects of agonist-induced Ca(2+) signals. Stimulation of cells with physiological concentrations of agonists trigger increases [Ca(2+)](i) due to intracellular Ca(2+) release and Ca(2+) influx. While Orai1-STIM1 channels account for agonist-stimulated [Ca(2+)](i) increase as well as activation of NFAT in cells such as lymphocytes, RBL and mast cells, both Orai1-STIM1 ...[more]

PMID: 23115638

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Project description: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 I(SOC), activated in response to Ca²+ store depletion, is composed of TRPC1/STIM1-mediated non-selective cation current and Orai1/STIM1-mediated I(CRAC); the latter is detected when TRPC1 function is suppressed by expression of shTRPC1 or a STIM1 mutant that lacks TRPC1 gating, STIM1(???EE???). 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, I(CRAC) is activated in cells pretreated with thapsigargin in Ca²+-free medium while I(SOC) is activated in cells pretreated in Ca²+-containing medium. Significantly, TRPC1 function is required for sustained K(Ca) activity and contributes to NF?B 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.

Dataset Information

Distinct contributions of Orai1 and TRPC1 to agonist-induced [Ca(2+)](i) signals determine specificity of Ca(2+)-dependent gene expression.

Publications

Distinct contributions of Orai1 and TRPC1 to agonist-induced [Ca(2+)](i) signals determine specificity of Ca(2+)-dependent gene expression.

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