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STIM is a Ca2+ sensor essential for Ca2+-store-depletion-triggered Ca2+ influx.

Current Biology

metabolism, Calcium, Calcium Channels, Cell Adhesion Molecules, Endoplasmic Reticulum, Fluorescence, HeLa Cells, Humans, Intracellular Signaling Peptides and Proteins, genetics, Jurkat Cells, Membrane Proteins, Mutation, Neoplasm Proteins, RNA, Small Interfering, Signal Transduction, physiology

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      Abstract

      Ca(2+) signaling in nonexcitable cells is typically initiated by receptor-triggered production of inositol-1,4,5-trisphosphate and the release of Ca(2+) from intracellular stores. An elusive signaling process senses the Ca(2+) store depletion and triggers the opening of plasma membrane Ca(2+) channels. The resulting sustained Ca(2+) signals are required for many physiological responses, such as T cell activation and differentiation. Here, we monitored receptor-triggered Ca(2+) signals in cells transfected with siRNAs against 2,304 human signaling proteins, and we identified two proteins required for Ca(2+)-store-depletion-mediated Ca(2+) influx, STIM1 and STIM2. These proteins have a single transmembrane region with a putative Ca(2+) binding domain in the lumen of the endoplasmic reticulum. Ca(2+) store depletion led to a rapid translocation of STIM1 into puncta that accumulated near the plasma membrane. Introducing a point mutation in the STIM1 Ca(2+) binding domain resulted in prelocalization of the protein in puncta, and this mutant failed to respond to store depletion. Our study suggests that STIM proteins function as Ca(2+) store sensors in the signaling pathway connecting Ca(2+) store depletion to Ca(2+) influx.

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      Journal
      16005298
      3186072
      10.1016/j.cub.2005.05.055

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