Dataset Information

STIM2 is a feedback regulator that stabilizes basal cytosolic and endoplasmic reticulum Ca2+ levels.

ABSTRACT: Deviations in basal Ca2+ levels interfere with receptor-mediated Ca2+ signaling as well as endoplasmic reticulum (ER) and mitochondrial function. While defective basal Ca2+ regulation has been linked to various diseases, the regulatory mechanism that controls basal Ca2+ is poorly understood. Here we performed an siRNA screen of the human signaling proteome to identify regulators of basal Ca2+ concentration and found STIM2 as the strongest positive regulator. In contrast to STIM1, a recently discovered signal transducer that triggers Ca2+ influx in response to receptor-mediated depletion of ER Ca2+ stores, STIM2 activated Ca2+ influx upon smaller decreases in ER Ca2+. STIM2, like STIM1, caused Ca2+ influx via activation of the plasma membrane Ca2+ channel Orai1. Our study places STIM2 at the center of a feedback module that keeps basal cytosolic and ER Ca2+ concentrations within tight limits.

SUBMITTER: Brandman O

PROVIDER: S-EPMC2680164 | biostudies-literature | 2007 Dec

REPOSITORIES: biostudies-literature

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STIM2 is a feedback regulator that stabilizes basal cytosolic and endoplasmic reticulum Ca2+ levels.

Brandman Onn O Liou Jen J Park Wei Sun WS Meyer Tobias T

Cell 20071201 7

Deviations in basal Ca2+ levels interfere with receptor-mediated Ca2+ signaling as well as endoplasmic reticulum (ER) and mitochondrial function. While defective basal Ca2+ regulation has been linked to various diseases, the regulatory mechanism that controls basal Ca2+ is poorly understood. Here we performed an siRNA screen of the human signaling proteome to identify regulators of basal Ca2+ concentration and found STIM2 as the strongest positive regulator. In contrast to STIM1, a recently disc ...[more]

PMID: 18160041

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Project description:Phototransduction in Drosophila is mediated by phospholipase C (PLC) and Ca2+-permeable TRP channels, but the function of endoplasmic reticulum (ER) Ca2+ stores in this important model for Ca2+ signaling remains obscure. We therefore expressed a low affinity Ca2+ indicator (ER-GCaMP6-150) in the ER, and measured its fluorescence both in dissociated ommatidia and in vivo from intact flies of both sexes. Blue excitation light induced a rapid (tau ∼0.8 s), PLC-dependent decrease in fluorescence, representing depletion of ER Ca2+ stores, followed by a slower decay, typically reaching ∼50% of initial dark-adapted levels, with significant depletion occurring under natural levels of illumination. The ER stores refilled in the dark within 100-200 s. Both rapid and slow store depletion were largely unaffected in InsP3 receptor mutants, but were much reduced in trp mutants. Strikingly, rapid (but not slow) depletion of ER stores was blocked by removing external Na+ and in mutants of the Na+/Ca2+ exchanger, CalX, which we immuno-localized to ER membranes in addition to its established localization in the plasma membrane. Conversely, overexpression of calx greatly enhanced rapid depletion. These results indicate that rapid store depletion is mediated by Na+/Ca2+ exchange across the ER membrane induced by Na+ influx via the light-sensitive channels. Although too slow to be involved in channel activation, this Na+/Ca2+ exchange-dependent release explains the decades-old observation of a light-induced rise in cytosolic Ca2+ in photoreceptors exposed to Ca2+-free solutions.SIGNIFICANCE STATEMENT Phototransduction in Drosophila is mediated by phospholipase C, which activates TRP cation channels by an unknown mechanism. Despite much speculation, it is unknown whether endoplasmic reticulum (ER) Ca2+ stores play any role. We therefore engineered flies expressing a genetically encoded Ca2+ indicator in the photoreceptor ER. Although NCX Na+/Ca2+ exchangers are classically believed to operate only at the plasma membrane, we demonstrate a rapid light-induced depletion of ER Ca2+ stores mediated by Na+/Ca2+ exchange across the ER membrane. This NCX-dependent release was too slow to be involved in channel activation, but explains the decades-old observation of a light-induced rise in cytosolic Ca2+ in photoreceptors bathed in Ca2+-free solutions.

Dataset Information

STIM2 is a feedback regulator that stabilizes basal cytosolic and endoplasmic reticulum Ca2+ levels.

Publications

STIM2 is a feedback regulator that stabilizes basal cytosolic and endoplasmic reticulum Ca2+ levels.

Similar Datasets

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