Desmin interacts with STIM1 and coordinates Ca2+ signaling in skeletal muscle.

Stromal interaction molecule 1 (STIM1), the sarcoplasmic reticulum (SR) transmembrane protein, activates store-operated Ca2+ entry (SOCE) in skeletal muscle and, thereby, coordinates Ca2+ homeostasis, Ca2+-dependent gene expression, and contractility. STIM1 occupies space in the junctional SR membrane of the triads and the longitudinal SR at the Z-line. How STIM1 is organized and is retained in these specific subdomains of the SR is unclear. Here, we identified desmin, the major type III intermediate filament protein in muscle, as a binding partner for STIM1 based on a yeast 2-hybrid screen. Validation of the desmin-STIM1 interaction by immunoprecipitation and immunolocalization confirmed that the CC1-SOAR domains of STIM1 interact with desmin to enhance STIM1 oligomerization yet limit SOCE. Based on our studies of desmin-KO mice, we developed a model wherein desmin connected STIM1 at the Z-line in order to regulate the efficiency of Ca2+ refilling of the SR. Taken together, these studies showed that desmin-STIM1 assembles a cytoskeletal-SR connection that is important for Ca2+ signaling in skeletal muscle.

Vasopressin-stimulated ORAI1 expression and store-operated Ca2+ entry in aortic smooth muscle cells.

Vascular calcification may result from stimulation of osteogenic signalling with upregulation of the transcription factors CBFA1, MSX2 and SOX9, as well as alkaline phosphatase (ALPL), which degrades and thus inactivates the calcification inhibitor pyrophosphate. Osteogenic signalling further involves upregulation of the Ca2+-channel ORAI1. The channel is activated by STIM1 and then accomplishes store-operated Ca2+ entry. ORAI1 and STIM1 are upregulated by the serum & glucocorticoid inducible kinase 1 (SGK1) which is critically important for osteogenic signalling. Stimulators of vascular calcification include vasopressin. The present study explored whether exposure of human aortic smooth muscle cells (HAoSMCs) to vasopressin upregulates ORAI1 and/or STIM1 expression, store-operated Ca2+ entry and osteogenic signalling. To this end, HAoSMCs were exposed to vasopressin (100 nM, 24 h) without or with additional exposure to ORAI1 blocker MRS1845 (10 µM) or SGK1 inhibitor GSK-650394 (1 µM). Transcript levels were measured using q-RT-PCR, cytosolic Ca2+-concentration ([Ca2+]i) by Fura-2-fluorescence, and store-operated Ca2+ entry from increase of [Ca2+]i following re-addition of extracellular Ca2+ after store depletion with thapsigargin (1 µM). As a result, vasopressin enhanced the transcript levels of ORAI1 and STIM1, store-operated Ca2+ entry, as well as the transcript levels of CBFA1, MSX2, SOX9 and ALPL. The effect of vasopressin on store-operated Ca2+ entry as well as on transcript levels of CBFA1, MSX2, SOX9 and ALPL was virtually abrogated by MRS1845 and GSK-650394. In conclusion, vasopressin stimulates expression of ORAI1/STIM1, thus augmenting store-operated Ca2+ entry and osteogenic signalling. In HAoSMCs, vasopressin (VP) upregulates Ca2+ channel ORAI1 and its activator STIM1. VP upregulates store-operated Ca2+ entry (SOCE) and osteogenic signalling (OS). VP-induced SOCE, OS and Ca2+-deposition are disrupted by ORAI1 inhibitor MRS1845. VP-induced SOCE, OS and Ca2+-deposition are disrupted by SGK1 blocker GSK-650394. KEY MESSAGES: • In HAoSMCs, vasopressin (VP) upregulates Ca2+ channel ORAI1 and its activator STIM1. • VP upregulates store-operated Ca2+ entry (SOCE) and osteogenic signalling (OS). • VP-induced SOCE, OS and Ca2+-deposition are disrupted by ORAI1 inhibitor MRS1845. • VP-induced SOCE, OS and Ca2+-deposition are disrupted by SGK1 blocker GSK-650394.

EGR-mediated control of STIM expression and function.

Ca2+ is a ubiquitous, dynamic and pluripotent second messenger with highly context-dependent roles in complex cellular processes such as differentiation, proliferation, and cell death. These Ca2+ signals are generated by Ca2+-permeable channels located on the plasma membrane (PM) and endoplasmic reticulum (ER) and shaped by PM- and ER-localized pumps and transporters. Differences in the expression of these Ca2+ homeostasis proteins contribute to cell and context-dependent differences in the spatiotemporal organization of Ca2+ signals and, ultimately, cell fate. This review focuses on the Early Growth Response (EGR) family of zinc finger transcription factors and their role in the transcriptional regulation of Stromal Interaction Molecule (STIM1), a critical regulator of Ca2+ entry in both excitable and non-excitable cells.

Expression of STIM1 is associated with tumor aggressiveness and poor prognosis in breast cancer.

STIM1 has been confirmed a key role involving in breast cancer proliferation and metastasis in vitro studies and its value in breast cancer patients is still to be defined. In this study, we investigate the correlation between STIM1 expressions with clinicopathologic features and prognosis quantified by disease-free survival (DFS) and overall survival (OS). To assess STIM1 expression, we conducted immunohistochemistry assays using breast cancer tissues encompassing a total of 165 breast cancer cases with detailed follow-up data and 40 cases of matched samples including cancer and adjacent normal tissues. STIM1 expression was present in 66.1% (109/165) of breast cancer cases which was significantly higher than adjacent non-tumor tissues. Larger tumors, lymphnode metastasis and negative estrogen receptor were positively associated with STIM1 overexpression. Furthermore, STIM1 expression was significantly associated with worse DFS (P=0.03) rather than OS in breast cancer patients.

Role of STIM1 (Stromal Interaction Molecule 1) in Hypertrophy-Related Contractile Dysfunction.

RATIONALE: Pathological increases in cardiac afterload result in myocyte hypertrophy with changes in myocyte electrical and mechanical phenotype. Remodeling of contractile and signaling Ca2+ occurs in pathological hypertrophy and is central to myocyte remodeling. STIM1 (stromal interaction molecule 1) regulates Ca2+ signaling in many cell types by sensing low endoplasmic reticular Ca2+ levels and then coupling to plasma membrane Orai channels to induce a Ca2+ influx pathway. Previous reports suggest that STIM1 may play a role in cardiac hypertrophy, but its role in electrical and mechanical phenotypic alterations is not well understood. OBJECTIVE: To define the contributions of STIM1-mediated Ca2+ influx on electrical and mechanical properties of normal and diseased myocytes, and to determine whether Orai channels are obligatory partners for STIM1 in these processes using a clinically relevant large animal model of hypertrophy. METHODS AND RESULTS: Cardiac hypertrophy was induced by slow progressive pressure overload in adult cats. Hypertrophied myocytes had increased STIM1 expression and activity, which correlated with altered Ca2+-handling and action potential (AP) prolongation. Exposure of hypertrophied myocytes to the Orai channel blocker BTP2 caused a reduction of AP duration and reduced diastolic Ca2+ spark rate. BTP2 had no effect on normal myocytes. Forced expression of STIM1 in cultured adult feline ventricular myocytes increased diastolic spark rate and prolonged AP duration. STIM1 expression produced an increase in the amount of Ca2+ stored within the sarcoplasmic reticulum and activated Ca2+/calmodulin-dependent protein kinase II. STIM1 expression also increased spark rates and induced spontaneous APs. STIM1 effects were eliminated by either BTP2 or by coexpression of a dominant negative Orai construct. CONCLUSIONS: STIM1 can associate with Orai in cardiac myocytes to produce a Ca2+ influx pathway that can prolong the AP duration and load the sarcoplasmic reticulum and likely contributes to the altered electromechanical properties of the hypertrophied heart.

STIM1 Ca2+ Sensor Control of L-type Ca2+-Channel-Dependent Dendritic Spine Structural Plasticity and Nuclear Signaling.

Potentiation of synaptic strength relies on postsynaptic Ca2+ signals, modification of dendritic spine structure, and changes in gene expression. One Ca2+ signaling pathway supporting these processes routes through L-type Ca2+ channels (LTCC), whose activity is subject to tuning by multiple mechanisms. Here, we show in hippocampal neurons that LTCC inhibition by the endoplasmic reticulum (ER) Ca2+ sensor, stromal interaction molecule 1 (STIM1), is engaged by the neurotransmitter glutamate, resulting in regulation of spine ER structure and nuclear signaling by the NFATc3 transcription factor. In this mechanism, depolarization by glutamate activates LTCC Ca2+ influx, releases Ca2+ from the ER, and consequently drives STIM1 aggregation and an inhibitory interaction with LTCCs that increases spine ER content but decreases NFATc3 nuclear translocation. These findings of negative feedback control of LTCC signaling by STIM1 reveal interplay between Ca2+ influx and release from stores that controls both postsynaptic structural plasticity and downstream nuclear signaling.

Store-Operated Ca2+ Entry (SOCE) contributes to angiotensin II-induced cardiac fibrosis in cardiac fibroblasts.

Store-operated Ca2+ entry (SOCE) is an important mechanism of extracellular Ca2+ entry into cells. It has been proved that SOCE is involved in many pathologic and physiological processes. Two key participants of SOCE, stromal interaction molecule1 (STIM1) and Orai1, have been identified. But their function in cardiac fibroblasts remains elusive. In present study, our findings suggested the expression of STIM1 and Orai1 were increased followed by angiotensin II (Ang II) stimulation in vivo and in vitro. In cultured adult rat cardiac fibroblasts, Ang II led to STIM1 interact with Orai1 and Ca2+ release from intracellular calcium store. In addition, the upregulation of fibronectin (FN), connective tissue growth factor (CTGF) and smooth muscle α-actin (α-SMA) induced by Ang II were attenuated by SOCE inhibitor SKF-96365, similar results were observed by knocking down STIM1 and Orai1. Furthermore, we found that silencing Orai1 by RNA interference also suppressed the translocation of Nuclear Factor of Activated T-cells (NFAT) Isoforms NFATc4 and decreased the phosphorylation of Smad2 and Smad3 induced by Ang II. These results unraveled a novel role of SOCE as a key modulator in the Ang II-induced cardiac fibrosis by mediating Ca2+ influx.

Stromal Interaction Molecule 1 rescues store-operated calcium entry and protects NG115-401L cells against cell death induced by endoplasmic reticulum and mitochondrial oxidative stress.

In this study we sought to investigate the hypothesis that expression of the Stromal Interaction Molecule 1 (STIM1) could provide protection against cell death induced by ER and oxidative stress. STIM1 performs an essential role in regulating store operated calcium entry (SOCE) and thereby provides an important route for replenishment of endoplasmic reticulum (ER) Ca(2+) stores. We used NG115-401L as a model neuronal cell phenotype with a predicted high susceptibility to ER stress due to SOCE deficiency and the absence of STIM1 expression. We show that STIM1 rescue vigorously re-establishes SOCE responses inducible by sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) blockers and Ca(2+)- linked receptors, producing a useful cell line with a simple STIM1/SOCE on/off switch. Surprisingly, we find that expressing STIM1 in NG115-401L cells appears to not have a significant impact on stored ER Ca(2+) levels. Yet, even though we find no evidence for an influence on ER Ca(2+) levels, we observed that provision of STIM1 function and rescue of SOCE activity produced a neuronal phenotype with significantly greater resistance to ER stress induced by SERCA blockade. Moreover, we also report that STIM1 expression, despite elevating mitochondrial reactive oxygen species, endows the NG115-401L neuronal cells with significant resistance to agents that mediate glutathione depletion and subsequent oxidative stress induced apoptosis. Our findings thus suggest that STIM1 warrants further investigation as a potential mediator of neuroprotective pathways against ER and oxidative stress.