title: Intracellular Ca(2+) release via the ER translocon activates store-operated calcium entry.
abstract: Store-operated Ca(2+) entry (SOCE) is activated in response to depletion of intracellular Ca(2+) from the endoplasmic reticulum (ER). A variety of agonists stimulate SOCE via IP(3)-dependent Ca(2+) depletion. SOCE is also activated by thapsigargin, an inhibitor of Ca(2+) reuptake into the ER that induces a net Ca(2+) loss from the ER by unmasking a Ca(2+) "leak" pathway. The molecular identity of this Ca(2+) leak channel and the physiological conditions under which such agonist-independent Ca(2+) depletion might occur remain poorly characterized. In this study, we report that inhibition of the initiation step of protein synthesis (with pactamycin) resulted in detectable Ca(2+) depletion in ER and activation of SOCE. This was completely prevented if the ribosome-nascent chain complexes were first stabilized with an irreversible inhibitor of translational elongation (emetine), suggesting that ER Ca(2+) depletion had occurred through open translocons at the ER. Notably, emetine pretreatment also attenuated thapsigargin-mediated Ca(2+) release and SOCE. Furthermore, both pactamycin and thapsigargin stimulated translocation of STIM1, a protein required for activation of SOCE, to the subplasma membrane region and activated the SOCE-associated current, I (SOC). In aggregate, these data reveal an agonist-independent mechanism for internal Ca(2+) store depletion and activation of SOCE. We suggest that the functional coupling between SOCE and protein synthesis is likely to be critical for maintaining [Ca(2+)](ER) within a range that is required to prevent ER stress during changes in cellular translational activity.
authors.affiliation: Secretory Physiology Section, Gene Therapy and Therapeutics Branch, National Institute of Dental and Craniofacial Research, Bethesda, MD 20892, USA.
authors.forename: Hwei L
authors.initials: HL
authors.lastname: Ong
authors.forename: Xibao
authors.initials: X
authors.lastname: Liu
authors.forename: Ajay
authors.initials: A
authors.lastname: Sharma
authors.forename: Ramanujan S
authors.initials: RS
authors.lastname: Hegde
authors.forename: Indu S
authors.initials: IS
authors.lastname: Ambudkar
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004640:Emetine / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D010142:Pactamycin / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012270:Ribosomes / Q000502:physiology; D012469:Salivary Glands / Q000166:cytology* / Q000502:physiology; D000071737:Stromal Interaction Molecule 1; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection
chemical_list: D001426:Bacterial Proteins; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D008164:Luminescent Proteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D011500:Protein Synthesis Inhibitors; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; C054562:yellow fluorescent protein, Bacteria; D010142:Pactamycin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium; D004640:Emetine