title: Local cytosolic Ca2+ elevations are required for stromal interaction molecule 1 (STIM1) de-oligomerization and termination of store-operated Ca2+ entry.
abstract: The Ca(2+) depletion of the endoplasmic reticulum (ER) activates the ubiquitous store-operated Ca(2+) entry (SOCE) pathway that sustains long-term Ca(2+) signals critical for cellular functions. ER Ca(2+) depletion initiates the oligomerization of stromal interaction molecules (STIM) that control SOCE activation, but whether ER Ca(2+) refilling controls STIM de-oligomerization and SOCE termination is not known. Here, we correlate the changes in free luminal ER Ca(2+) concentrations ([Ca(2+)](ER)) and in STIM1 oligomerization, using fluorescence resonance energy transfer (FRET) between CFP-STIM1 and YFP-STIM1. We observed that STIM1 de-oligomerized at much lower [Ca(2+)](ER) levels during store refilling than it oligomerized during store depletion. We then refilled ER stores without adding exogenous Ca(2+) using a membrane-permeable Ca(2+) chelator to provide a large reservoir of buffered Ca(2+). This procedure rapidly restored pre-stimulatory [Ca(2+)](ER) levels but did not trigger STIM1 de-oligomerization, the FRET signals remaining elevated as long as the external [Ca(2+)] remained low. STIM1 dissociation evoked by Ca(2+) readmission was prevented by SOC channel inhibition and was associated with cytosolic Ca(2+) elevations restricted to STIM1 puncta, indicating that Ca(2+) acts on a cytosolic target close to STIM1 clusters. These data indicate that the refilling of ER Ca(2+) stores is not sufficient to induce STIM1 de-oligomerization and that localized Ca(2+) elevations in the vicinity of assembled SOCE complexes are required for the termination of SOCE.
authors: Department of Cell Physiology and Metabolism, University of Geneva, rue Michel-Servet 1, CH-1211 Geneva 4, Switzerland.
authors: Wei-Wei
authors: WW
authors: Shen
authors: Maud
authors: M
authors: Frieden
authors: Nicolas
authors: N
authors: Demaurex
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization / Q000187:drug effects / Q000502:physiology*; D000071737:Stromal Interaction Molecule 1
chemical_list: D002614:Chelating Agents; D008565:Membrane Proteins; D009363:Neoplasm Proteins; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D002118:Calcium