title: 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 NFκB-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.
authors.affiliation: Secretory Physiology Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Hwei Ling
authors.initials: HL
authors.lastname: Ong
authors.forename: Shyh-Ing
authors.initials: SI
authors.lastname: Jang
authors.forename: Indu Suresh
authors.initials: IS
authors.lastname: Ambudkar
mesh_terms: D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D020013:Calcium Signaling; D002478:Cells, Cultured; D015870:Gene Expression; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D000071740:ORAI1 Protein; D050052:TRPC Cation Channels / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D016328:NF-kappa B; D050778:NFATC Transcription Factors; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D050052:TRPC Cation Channels; C096351:transient receptor potential cation channel, subfamily C, member 1; D002118:Calcium