Depletion of intracellular calcium (Ca 2؉ ) stores induces storeoperated Ca 2؉ (SOC) entry across the plasma membrane (PM). STIM1, a putative Ca 2؉ sensor in the endoplasmic reticulum (ER), has been recently shown to be necessary for SOC channel activation. Here we show that STIM1 dynamically moves in tubulovesicular shape on the ER and its subcompartment in resting living cells, whereas, upon Ca 2؉ store depletion, it is rapidly redistributed into discrete puncta that are located underneath, but not inserted into the PM. Normal constitutive movement of STIM1 is mediated through the coiled-coil and Ser͞Thr-rich C-terminal domains in the cytoplasmic region of STIM1, whereas subsequent inducible puncta formation further requires the sterile ␣ motif domain protruding into the ER lumen. Each of these three domains (coiled-coil, Ser͞Thr-rich, and sterile ␣ motif) was essential for activating SOC channels. Hence, our findings based on structure-function experiments suggest that constitutive dynamic movement of STIM1 in the ER and its subcompartment is obligatory for subsequent depletion-dependent redistribution of STIM1 into puncta underneath the PM and activation of SOC channels.B cell receptor ͉ calcium signaling ͉ DT40 ͉ store-operated calcium C ytosolic Ca 2ϩ signals are a key to the regulation of various physiological events (1, 2). Two stages of calcium mobilization have been distinguished in lymphocytes and other nonexcitable cells (3-5). The first stage involves activation of phospholipase C by trimeric G protein-or tyrosine kinase-coupled receptors. This enzyme hydrolyzes phosphatidylinositol bisphosphate to release the second messenger inositol-1,4,5-trisphosphate, which binds to its receptor in the endoplasmic reticulum (ER) membrane, thereby causing rapid but transient release of Ca 2ϩ from ER stores. The second stage involves a sustained influx of extracellular Ca 2ϩ across the plasma membrane (PM) in a process termed store-operated Ca 2ϩ (SOC) entry. In this process, depletion of Ca 2ϩ within the ER lumen serves as the primary trigger to open SOC channels residing in the PM.STIM1 has recently emerged to play a critical role in coupling the first and second stages of calcium mobilization (6, 7). The STIM1 protein is thought to function primarily as a sensor of Ca 2ϩ within the ER stores, because a single N-terminal EF-hand Ca 2ϩ binding motif is located within the ER lumen (7,8). The activation mechanism of STIM1, however, has remained elusive. For instance, Zhang and colleagues (9, 10) proposed that insertion of STIM1 from the ER to the PM, presumably through vesicular transport, would be a prerequisite for subsequent SOC channel activation. Furthermore, STIM1 in the PM has been reported to play a role for SOC activation (11). But others have shown that STIM1 redistributed into puncta near the PM without inserting into the PM and proposed that this aggregated STIM1 might activate SOC channels (7, 12).To elucidate the mechanisms by which STIM1 activates SOC channels, we have constructed STIM1 mutants and ...

Mast cells have key functions as effectors of immunoglobulin E-mediated allergic inflammatory diseases. Allergen stimulation induces Ca2+ influx and elicits the secretion of inflammatory mediators from mast cells. Here we show that the Ca2+-binding endoplasmic reticulum protein STIM1 is critical to mast cell function. STIM1-deficient fetal liver-derived mast cells had impaired Ca2+ influx mediated by the high-affinity immunoglobulin E receptor FcepsilonRI and activation of the transcription factors NF-kappaB and NFAT. Mast cells lacking STIM1 also had much less degranulation and cytokine production after FcepsilonRI stimulation. In addition, alterations in STIM1 expression affected the sensitivity of immunoglobulin E-mediated immediate-phase anaphylactic responses in vivo. Thus, STIM1 is key in promoting the Ca2+ influx that is essential for FcepsilonRI-mediated mast cell activation and anaphylaxis.

A chief Ca(2+) entry pathway in immune cells is store-operated Ca(2+) (SOC) influx, which is triggered by depletion of Ca(2+) from the endoplasmic reticulum (ER). However, its physiological role in B cells remains elusive. Here, we show that ER calcium sensors STIM1- and STIM2-induced SOC influx is critical for B cell regulatory function. B cell-specific deletion of STIM1 and STIM2 in mice caused a profound defect in B cell receptor (BCR)-induced SOC influx and proliferation. However, B cell development and antibody responses were unaffected. Remarkably, B cells lacking both STIM proteins failed to produce the anti-inflammatory cytokine IL-10 because of defective activation of nuclear factor of activated T cells (NFAT) after BCR stimulation. This resulted in exacerbation of experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis. Our data establish STIM-dependent SOC influx as a key signal for B cell regulatory function required to limit autoimmunity.

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One of the major neuropathological hallmarks of Alzheimer's disease (AD) is the deposition of amyloid β-protein (Aβ) in the brain. Aβ accumulation seems to arise from an imbalance between Aβ production and clearance. Neprilysin (NEP) and insulin-degrading enzyme (IDE) are the important Aβ-degrading enzymes in the brain, and deficits in their expression may promote Aβ deposition in patients with sporadic late-onset AD. Statins, which are used clinically for reducing cholesterol levels, can exert beneficial effects on AD. Therefore, we examined whether various statins are associated with Aβ degradation by inducing NEP and IDE expression, and then evaluating the relation between activation of intracellular signaling transduction, inhibition of cholesterol production, and morphological changes to astrocytes. Treating cultured rat astrocytes with simvastatin and atorvastatin significantly decreased the expression of NEP but not IDE in a concentration- and time-dependent manner. The decrease in NEP expression was a result of activation of extracellular signal-regulated kinase (ERK) but not the reduction of cholesterol synthesis pathway. This NEP reduction was achieved by the release to the extracellular space of cultured astrocytes. Furthermore, the cultured medium prepared from simvastatin- and atorvastatin-treated astrocytes significantly induced the degradation of exogenous Aβ. These results suggest that simvastatin and atorvastatin induce the increase of Aβ degradation of NEP on the extracellular of astrocytes by inducing ERK-mediated pathway activity and that these reagents regulate the differential mechanisms between the secretion of NEP, the induction of cholesterol reduction, and the morphological changes in the cultured astrocytes.