CRAC channel activity in C. elegans is mediated by Orai1 and STIM1 homologues and is essential for ovulation and fertility.
The Ca(2+) release-activated Ca(2+) (CRAC) channel is a plasma membrane Ca(2+) entry pathway activated by endoplasmic reticulum (ER) Ca(2+) store depletion. STIM1 proteins function as ER Ca(2+) sensors and regulate CRAC channel activation. Recent studies have demonstrated that CRAC channels are encoded by the human Orai1 gene and a homologous Drosophila gene. C. elegans intestinal cells express a store-operated Ca(2+) channel (SOCC) regulated by STIM-1. We cloned a full-length C. elegans cDNA that encodes a 293 amino acid protein, ORAI-1, homologous to human and Drosophila Orai1 proteins. ORAI-1 GFP reporters are co-expressed with STIM-1 in the gonad and intestine. Inositol 1,4,5-trisphosphate (IP(3))-dependent Ca(2+) signalling regulates C. elegans gonad function, fertility and rhythmic posterior body wall muscle contraction (pBoc) required for defecation. RNA interference (RNAi) silencing of orai-1 expression phenocopies stim-1 knockdown and causes sterility and prevents intestinal cell SOCC activation, but has no effect on pBoc or intestinal Ca(2+) signalling. Orai-1 RNAi suppresses pBoc defects induced by intestinal expression of a STIM-1 Ca(2+)-binding mutant, indicating that the proteins function in a common pathway. Co-expression of stim-1 and orai-1 cDNAs in HEK293 cells induces large inwardly rectifying cation currents activated by ER Ca(2+) depletion. The properties of this current recapitulate those of the native SOCC current. We conclude that C. elegans expresses bona fide CRAC channels that require the function of Orai1- and STIM1-related proteins. CRAC channels thus arose very early in animal evolution. In C. elegans, CRAC channels do not play obligate roles in all IP(3)-dependent signalling processes and ER Ca(2+) homeostasis. Instead, we suggest that CRAC channels carry out highly specialized and cell-specific signalling roles and that they may function as a failsafe mechanism to prevent Ca(2+) store depletion under pathophysiological and stress conditions.
Lorin-Nebel
Catherine
C
Vanderbilt University Medical Center, T-4208 Medical Center North, Nashville, TN 37232-2520, USA.
Xing
Juan
J
Yan
Xiaohui
X
Strange
Kevin
K
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000378:metabolism / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000096:biosynthesis / Q000502:physiology*; D015220:Calcium Channels / Q000096:biosynthesis / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D004594:Electrophysiology; D004625:Embryo, Nonmammalian / Q000166:cytology; D005260:Female; D005298:Fertility / Q000502:physiology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology; D007422:Intestines / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000502:physiology*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000502:physiology; D000071740:ORAI1 Protein; D010060:Ovulation / Q000502:physiology; D018408:Patch-Clamp Techniques; D034622:RNA Interference; D000071737:Stromal Interaction Molecule 1; D019076:Transgenes / Q000235:genetics
D029742:Caenorhabditis elegans Proteins; D015220:Calcium Channels; D008565:Membrane Proteins; C519796:ORAI-1 protein, C elegans; D000071740:ORAI1 Protein; D000071737:Stromal Interaction Molecule 1; C516629:stim-1 protein, C elegans; D015544:Inositol 1,4,5-Trisphosphate