Store-operated Ca2+ Entry Inhibitors Research Articles

Abnormal Regulation of Intracellular Calcium in Human Megakaryocytes Contributes to the Pathophysiology of Calr-Mutant Myeloproliferative Neoplasms

The BCR-ABL-negative Myeloproliferative Neoplasms (MPNs), are a group of clonal hematopoietic malignancies, that consist of three disorders: Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF). Approximately one quarter of patients with ET or PMF carry a somatic mutation of CALR, the gene encoding for the endoplasmic reticulum (ER) chaperone calreticulin. A 52-bp deletion (Type I) and a 5-bp insertion (Type II mutation) are the most frequent lesions. Both generate a new carboxy-terminus of the mutant proteins, in which the ER retention signal KDEL is lost, causing abnormal interaction of the mutants with the thrombopoietin (TPO) receptor (MPL), thus constitutively activating its downstream signaling in megakaryocytes. CALR Type I mutation causes important changes in the charge of the carboxyl-terminal tail, which is responsible for calcium (Ca2+) binding activity. As a consequence, megakaryocytes from CALR Type I patients present enhanced activation of Store-Operated Ca2+ Entry (SOCE), the mechanisms that trigger extracellular Ca2+ inflow upon agonist-induced intracellular Ca2+ mobilization from the ER. A fine control of SOCE and overall Ca2+ homeostasis is fundamental to ensure proper megakaryocyte function. Despite this knowledge, the role of a crosstalk among MPL, CALR and SOCE in regulating megakaryopoiesis has never been hypothesised.Our research analysed the activation of MPL downstream pathways and Ca2+ signalling in human cord blood and peripheral blood-cultured megakaryocytes, upon stimulation with recombinant human TPO (rhTPO). Additionally, we cultured megakaryocytes from the peripheral blood of patients carrying the CALR Type I mutation to investigate whether CALR and SOCE alterations determine abnormal activation of the MPL downstream pathway in MPNs.We demonstrated that binding of rhTPO to MPL induces a series of downstream signaling events that lead to the activation of STAT5, AKT and ERK1/2 in human megakaryocytes. This activation relies on significant accumulation of inositol triphosphate (IP3), and consequent intracellular Ca2+ release from the ER followed by extracellular Ca2+ entry, indicative of activated SOCE. Pharmacologic inhibition of the IP3 receptor or SOCE, with 2-APB or BTP-2 respectively, resulted in the complete absence of rhTPO-induced MPL signaling activation. SOCE activation is thus dependent on the dissociation of CALR and STIM1, a protein of the SOCE machinery, which normally forms a complex in un-stimulated megakaryocytes. Importantly, we verified that in human megakaryocytes in rhTPO-starved conditions, CALR forms a molecular complex with its co-chaperone, ERp57, and STIM1, while they dissociate upon rhTPO stimulation. Conversely, we observed that CALR, ERp57 and STIM1 are constitutively dissociated in megakaryocytes from CALR Type I patients, even in complete absence of rhTPO. This dissociation resulted in markedly increased TPO-induced cytosolic Ca2+ flows with a consequent abnormal megakaryocyte proliferation that could be counteracted by pharmacological inhibition of SOCE with BTP-2.Our findings provide the first evidence that CARL Type I, in addition to MPL activation, concurs to the alteration of SOCE, which sustains the phosphorylation of STAT5, AKT and ERK1/2, and induces megakaryocyte proliferation. Further investigation is needed to understand whether this altered megakaryocyte function is determined by the decrease in CALR levels or by the presence of CALR mutants in the ER. Nevertheless, the abnormal regulation of Ca2+ flows may represent a potentially actionable target. DisclosuresNo relevant conflicts of interest to declare.

Autonomous Ca2+ Oscillations Reflect Oncogenic BCR-Signaling in Multiple B-Cell Malignancies and Are Essential for Survival and Proliferation

Background: Nuclear factor of activated T cells (NFAT) factors regulate activation and Ca2+ signaling in B-cells. Store-operated Ca2+ entry (SOCE) is regulated by Orai1 and Stim1 and upstream of NFAT. We previously reported on the observation of autonomous oscillatory Ca2+ signal activity in BCR-ABL1-driven B-ALL. Autonomous Ca2+ oscillations may provide oncogenic survival signals to B-ALL cells, however their significance and mechanism remained unclear.Results: Here we found that autonomous Ca2+ oscillations are common across multiple subtypes of B-cell lineage ALL and mature B-cell lymphoma and reflect downstream survival and proliferation signals from oncogenic BCR-signaling or oncogenes that mimic active BCR-signaling (e.g. ABL1-kinase fusions, CD79B mutation, EBV-encoded oncoprotein LMP2A, RAS-pathway lesions). By contrast, multiple myeloma and Hodgkin's lymphoma that lack BCR-expression and function also lack Ca2+ oscillations (Figure, top panel). As Orai1 and Stim1/2 are essential SOCE-effector genes, we performed genetic experiments to test the impact of Cre-mediated deletion of Orai1 and Stim1/2 in BCR-ABL1 and NRASG12D-dependent models of B-ALL. Inducible deletion of Orai1 or Stim1/2 not only abrogated SOCE but also autonomous Ca2+ oscillations. Signal amplitudes of residual autonomous Ca2+ oscillations were significantly reduced (P < 0.0001; Figure, bottom panel). Further, deletion of either Orai1 or Stim1/2 induced cell death and abrogated colony-forming capacity in both models of B-ALL. In agreement with these findings, NFATc1 no longer translocated to the nucleus upon Cre-mediated ablation of Orai1 or Stim1/2 induced, which reflected functional inactivation of NFATc1. These results demonstrated that Orai1- and Stim1/2-mediated SOCE signaling and autonomous Ca2+ oscillations are critical in BCR-ABL1 and NRASG12D-dependent B-ALL. A NFAT-calcineurin association inhibitor, INCA-6, was tested for its ability to suppress NFATc1 and autonomous Ca2+ signaling in patient-derived xenograft (PDX) models of B-ALL, mantle cell lymphoma and DLBCL. Treatment with INCA-6 suppressed survival and proliferation signals in all six PDX of B-ALL, mantle cell lymphoma and DLBCL but not multiple myeloma cells. Unlike myeloma cells, B-ALL, mantle cell and DLBCL cells expressed a functional (pre-)BCR. These findings suggest that the SOCE-NFAT pathway is linked to Ca2+ signaling downstream of a functional BCR- or oncogenic BCR-mimics. Furthermore, to determine whether high expression levels of ORAI1, STIM1, STIM2 and NFATC1 represents a biomarker of clinical outcome for patients with B-ALL, we segregated patients from two clinical trials (Children's Oncology Group P9906 (n=207) and Eastern Cooperative Oncology Group (E2993; n=215)) into two groups on the basis of higher or lower than median expression levels of ORAI1, STIM1, STIM2 and NFATC1 at the time of diagnosis. Higher than median expression levels of each of these four genes at the time of diagnosis predicted shorter overall and relapse-free survival (P < 0.02 or lower for each of these genes). These findings identify SOCE-NFAT signal as a novel biomarker with potential use in risk stratification of children and adults with B-ALL.Conclusions: We identified Orai1 and Stim1 as central mediators of SOCE. Most BCR-dependent B-cell malignancies are driven by oncogenic BCR-signals, which result in autonomous Ca2+ oscillations. While the significance of autonomous Ca2+-oscillations remains unclear, deletion of Orai1 and Stim1/2 resulted in a complete loss of Ca2+ oscillations, loss of NFATc1-activation and cell death. We conclude that previously unrecognized Ca2+-oscillations downstream of oncogenic BCR-signaling are required for survival and proliferation of B-ALL and B-cell lymphoma cells. Pharmacological inhibition of SOCE (Orai1 and Stim1/2) or NFATC1 (e.g. INCA-6) represents a selective strategy to disrupt autonomous Ca2+ oscillations and oncogenic BCR-signaling in a broad range of B-cell malignancies. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Addendum: Exercise-dependent formation of new junctions that promote STIM1-Orai1 assembly in skeletal muscle

Store-operated Ca2+ entry (SOCE), a ubiquitous mechanism that allows recovery of Ca2+ ions from the extracellular space, has been proposed to limit fatigue during repetitive skeletal muscle activity. However, the subcellular location for SOCE in muscle fibers has not been unequivocally identified. Here we show that exercise drives a significant remodeling of the sarcotubular system to form previously unidentified junctions between the sarcoplasmic reticulum (SR) and transverse-tubules (TTs). We also demonstrate that these new SR-TT junctions contain the molecular machinery that mediate SOCE: stromal interaction molecule-1 (STIM1), which functions as the SR Ca2+ sensor, and Orai1, the Ca2+-permeable channel in the TT. In addition, EDL muscles isolated from exercised mice exhibit an increased capability of maintaining contractile force during repetitive stimulation in the presence of 2.5 mM extracellular Ca2+, compared to muscles from control mice. This functional difference is significantly reduced by either replacement of extracellular Ca2+ with Mg2+ or the addition of SOCE inhibitors (BTP-2 and 2-APB). We propose that the new SR-TT junctions formed during exercise, and that contain STIM1 and Orai1, function as Ca2+ Entry Units (CEUs), structures that provide a pathway to rapidly recover Ca2+ ions from the extracellular space during repetitive muscle activity.

Extracellular and ER-stored Ca2+ contribute to BIRD-2-induced cell death in diffuse large B-cell lymphoma\xa0cells

The anti-apoptotic protein Bcl-2 is upregulated in several cancers, including diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL). In a subset of these cancer cells, Bcl-2 blocks Ca2+-mediated apoptosis by suppressing the function of inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) located at the endoplasmic reticulum (ER). A peptide tool, called Bcl-2/IP3 receptor disruptor-2 (BIRD-2), was developed to disrupt Bcl-2/IP3R complexes, triggering pro-apoptotic Ca2+ signals and killing Bcl-2-dependent cancer cells. In DLBCL cells, BIRD-2 sensitivity depended on the expression level of IP3R2 channels and constitutive IP3 signaling downstream of the B-cell receptor. However, other cellular pathways probably also contribute to BIRD-2-provoked cell death. Here, we examined whether BIRD-2-induced apoptosis depended on extracellular Ca2+ and more particularly on store-operated Ca2+ entry (SOCE), a Ca2+-influx pathway activated upon ER-store depletion. Excitingly, DPB162-AE, a SOCE inhibitor, suppressed BIRD-2-induced cell death in DLBCL cells. However, DPB162-AE not only inhibits SOCE but also depletes the ER Ca2+ store. Treatment of the cells with YM-58483 and GSK-7975A, two selective SOCE inhibitors, did not protect against BIRD-2-induced apoptosis. Similar data were obtained by knocking down STIM1 using small interfering RNA. Yet, extracellular Ca2+ contributed to BIRD-2 sensitivity in DLBCL, since the extracellular Ca2+ buffer ethylene glycol tetraacetic acid (EGTA) blunted BIRD-2-triggered apoptosis. The protective effects observed with DPB162-AE are likely due to ER Ca2+-store depletion, since a similar protective effect could be obtained using the sarco/endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin. Thus, both the ER Ca2+-store content and extracellular Ca2+, but not SOCE, are critical factors underlying BIRD-2-provoked cell death.

Impaired Store-Operated Calcium Entry and STIM1 Loss Lead to Reduced Insulin Secretion and Increased Endoplasmic Reticulum Stress in the Diabetic β-Cell.

Store-operated Ca2+ entry (SOCE) is a dynamic process that leads to refilling of endoplasmic reticulum (ER) Ca2+ stores through reversible gating of plasma membrane Ca2+ channels by the ER Ca2+ sensor Stromal Interaction Molecule 1 (STIM1). Pathogenic reductions in β-cell ER Ca2+ have been observed in diabetes. However, a role for impaired SOCE in this phenotype has not been tested. We measured the expression of SOCE molecular components in human and rodent models of diabetes and found a specific reduction in STIM1 mRNA and protein levels in human islets from donors with type 2 diabetes (T2D), islets from hyperglycemic streptozotocin-treated mice, and INS-1 cells (rat insulinoma cells) treated with proinflammatory cytokines and palmitate. Pharmacologic SOCE inhibitors led to impaired islet Ca2+ oscillations and insulin secretion, and these effects were phenocopied by β-cell STIM1 deletion. STIM1 deletion also led to reduced ER Ca2+ storage and increased ER stress, whereas STIM1 gain of function rescued β-cell survival under proinflammatory conditions and improved insulin secretion in human islets from donors with T2D. Taken together, these data suggest that the loss of STIM1 and impaired SOCE contribute to ER Ca2+ dyshomeostasis under diabetic conditions, whereas efforts to restore SOCE-mediated Ca2+ transients may have the potential to improve β-cell health and function.

STIM1/Orai1 Inhibition Reduces Store-Operated Ca2+ Entry and Modulates a-Cell Glucagon Secretion

In type 2 diabetic patients glucagon secretion becomes dysregulated under elevated glucose conditions worsening hyperglycemia. However, the mechanisms of glucose inhibition of glucagon secretion remain incompletely understood. Therefore, we sought to uncover the glucose dependent mechanisms that modulate pancreatic α-cell glucagon secretion. One mechanism that regulates α-cell Ca2+ influx in a glucose dependent manner is store-operated Ca2+ entry (SOCE). Therefore, in our studies we used a small molecule (AnCoA4) that inhibits the STIM1/Orai1 protein interaction and prevents store-operated Ca2+ channel activation. In whole mouse islet α-cells inhibition of SOCE with AnCoA4 reduced Ca2+ influx in 1 mM glucose (8.4% ± 1.1%). We went on to test the influence of SOCE on glucose modulation of glucagon secretion, in 1 mM glucose AnCoA4 reduced glucagon secretion in mouse pancreatic islets (53.5% ± 11%). However, there was no significant change in glucose inhibition of glucagon secretion by inhibition of SOCE at 11 mM glucose. To follow-up on this, we used transgenic mice without STIM1 in α-cells and showed that AnCoA4 does not influence Ca2+ fluctuations in knockout islet α-cells. This proves in our hands that AnCoA4 works selectively. Additionally, we used transgenic GCAMP3 mice without STIM1 in α-cells for whole islet confocal studies to measure SOCE in 1 mM and 11 mM glucose conditions. We found that in whole islet α-cells without functional STIM1, Ca2+ influx due to SOCE was reduced in 1 mM glucose. Next, we wanted to test this molecule in human islet calcium homeostasis studies. Human dispersed α-cells show inhibition of SOCE with AnCoA4 treatment in 1 mM glucose conditions. Thus, our findings identify that inhibition of STIM1/Orai1 reduces SOCE in low glucose conditions leading to decreased α-cell glucagon secretion. Disclosure M.K. Altman: None. P. Dadi: None. D. Jacobson: None.

Targeting Orai1-mediated store-operated calcium entry by RP4010 for anti-tumor activity in esophagus squamous cell carcinoma

Esophageal cancer (EC) is the 6th leading cause of cancer mortality worldwide with poor prognosis, hence more effective chemotherapeutic drugs for this deadly disease are urgently needed. We previously reported that high expression of Orai1, a store-operated Ca2+entry (SOCE) channel, was associated with poor survival rate in EC patients and Orai1-mediated intracellular Ca2+ oscillations regulated cancer cell proliferation. Previous studies suggested that Orai1-mediated SOCE is a promising target for EC chemotherapy. Here, we evaluated the anti-cancer effect of a novel SOCE inhibitor, RP4010, in cultured EC cells and xenograft models. Compared to other previously reported SOCE channel inhibitors, RP4010 is more potent in blocking SOCE and inhibiting cell proliferation in EC and other cancer cells. Treatment with RP4010 resulted in reduction of intracellular Ca2+ oscillations, caused cell cycle arrest at G0/G1 phase in vitro, decreased nuclear translocation of nuclear factor kappa B (NF-κB) in vivo and in vitro, and inhibited tumor growth in vivo. Taken together, data demonstrated the therapeutic potential of RP4010 in EC patients via inhibition of SOCE-mediated intracellular Ca2+ signaling.

A charge-sensing region in the stromal interaction molecule 1 luminal domain confers stabilization-mediated inhibition of SOCE in response to S-nitrosylation

Store-operated Ca2+ entry (SOCE) is a major Ca2+ signaling pathway facilitating extracellular Ca2+ influx in response to the initial release of intracellular endo/sarcoplasmic reticulum (ER/SR) Ca2+ stores. Stromal interaction molecule 1 (STIM1) is the Ca2+ sensor that activates SOCE following ER/SR Ca2+ depletion. The EF-hand and the adjacent sterile α-motif (EFSAM) domains of STIM1 are essential for detecting changes in luminal Ca2+ concentrations. Low ER Ca2+ levels trigger STIM1 destabilization and oligomerization, culminating in the opening of Orai1-composed Ca2+ channels on the plasma membrane. NO-mediated S-nitrosylation of cysteine thiols regulates myriad protein functions, but its effects on the structural mechanisms that regulate SOCE are unclear. Here, we demonstrate that S-nitrosylation of Cys49 and Cys56 in STIM1 enhances the thermodynamic stability of its luminal domain, resulting in suppressed hydrophobic exposure and diminished Ca2+ depletion-dependent oligomerization. Using solution NMR spectroscopy, we pinpointed a structural mechanism for STIM1 stabilization driven by complementary charge interactions between an electropositive patch on the core EFSAM domain and the S-nitrosylated nonconserved region of STIM1. Finally, using live cells, we found that the enhanced luminal domain stability conferred by either Cys49 and Cys56S-nitrosylation or incorporation of negatively charged residues into the EFSAM electropositive patch in the full-length STIM1 context significantly suppresses SOCE. Collectively, our results suggest that S-nitrosylation of STIM1 inhibits SOCE by interacting with an electropositive patch on the EFSAM core, which modulates the thermodynamic stability of the STIM1 luminal domain.

An SAR study of hydroxy-trifluoromethylpyrazolines as inhibitors of Orai1-mediated store operated Ca2+ entry in MDA-MB-231 breast cancer cells using a convenient Fluorescence Imaging Plate Reader assay

The proteins Orai1 and STIM1 control store-operated Ca2+ entry (SOCE) into cells. SOCE is important for migration, invasion and metastasis of MDA-MB-231 human triple negative breast cancer (TNBC) cells and has been proposed as a target for cancer drug discovery. Two hit compounds from a medium throughput screen, displayed encouraging inhibition of SOCE in MDA-MB-231 cells, as measured by a Fluorescence Imaging Plate Reader (FLIPR) Ca2+ assay. Following NMR spectroscopic analysis of these hits and reassignment of their structures as 5-hydroxy-5-trifluoromethylpyrazolines, a series of analogues was prepared via thermal condensation reactions between substituted acylhydrazones and trifluoromethyl 1,3-dicarbonyl arenes. Structure-activity relationship (SAR) studies showed that small lipophilic substituents at the 2- and 3-positions of the RHS and 2-, 3- and 4-postions of the LHS terminal benzene rings improved activity, resulting in a novel class of potent and selective inhibitors of SOCE.

Blockage of store-operated Ca2+ entry antagonizes Epstein-Barr virus-promoted angiogenesis by inhibiting Ca2+ signaling-regulated VEGF production in nasopharyngeal carcinoma.

BackgroundEpstein–Barr virus (EBV) actively contributes to the pathological process of nasopharyngeal carcinoma (NPC) by enabling NPC cells to acquire various capacities required for their malignant biological actions. Our earlier works demonstrated that EBV-encoded latent membrane protein 1 (LMP1) enhanced vascular endothelial growth factor (VEGF)-mediated angiogenesis by boosting store-operated Ca2+ entry (SOCE) upon extracellular epidermal growth factor (EGF) stimulation. However, the antagonistic effects of SOCE blockage on EBV-promoted angiogenesis must be appropriately evaluated in vivo, and the global effect of EBV infection on the EGF-elicited cytosolic Ca2+ signaling, which regulates VEGF-mediated angiogenesis remains to be further clarified.Materials and methodsTwo EBV-infected NPC cell lines, CNE2-EBV and HK1-EBV, along with their parental cell lines were employed in the present study. Dynamic cytosolic Ca2+ changes were measured in individual fluorescent Ca2+ indicator-loaded cells. Amounts of VEGF production were determined by enzyme-linked immunosorbent assay (ELISA). Human umbilical vein endothelial cells (HUVECs)-formed tube networks were quantitatively evaluated as an in vitro angiogenesis assay. A mouse model concurrently bearing EBV-positive/negative xenografts was utilized to evaluate the tumor growth and angiogenesis in vivo.ResultsEBV infection reliably promoted transplanted tumor growth while enhancing angiogenesis. Introduction of EBV into EBV-negative NPC cells increased the EGF-stimulated VEGF production while amplifying the EGF-evoked Ca2+ responses. Inhibition of the EBV-boosted Ca2+ signaling using 2-aminoethyl diphenylborinate (2-APB), a specific SOCE inhibitor, effectively antagonized the EBV-promoted VEGF production and endothelial tube formation in vitro. Pharmacological blockage of SOCE exhibited anti-angiogenic effect in the EBV-positive xenografts.ConclusionSOCE can serve as a candidate pharmacological target for treating NPC, as blockage of the Ca2+ signaling via SOCE is a feasible strategy to suppress the EBV-driven malignant profiles in NPC cells.

Transient Receptor Potential Melastatin-8 Activation Induces Relaxation of Pulmonary Artery by Inhibition of Store-Operated Calcium Entry in Normoxic and Chronic Hypoxic Pulmonary Hypertensive Rats.

Pulmonary hypertension (PH) is characterized by enhanced vasoconstriction and vascular remodeling, which are attributable to the alteration of Ca2+ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). It is well established that store-operated Ca2+ entry (SOCE) is augmented in PASMCs during PH and that it plays a crucial role in PH development. Our previous studies showed that the melastatin-related transient receptor potential 8 (TRPM8) is down-regulated in PASMCs of PH animal models, and activation of TRPM8 causes relaxation of pulmonary arteries (PAs). However, the mechanism of TRPM8-induced PA relaxation is unclear. Here we examined the interaction of TRPM8 and SOCE in PAs and PASMCs of normoxic and chronic hypoxic pulmonary hypertensive (CHPH) rats, a model of human group 3 PH. We found that TRPM8 was down-regulated and TRPM8-mediated cation entry was reduced in CHPH-PASMCs. Activation of TRPM8 with icilin caused concentration-dependent relaxation of cyclopiazonic acid (CPA) and endothelin-1 contracted endothelium-denuded PAs, and the effect was abolished by the SOCE antagonist Gd3+ Application of icilin to PASMCs suppressed CPA-induced Mn2+ quenching and Ca2+ entry, which was reversed by the TRPM8 antagonist N-(3-aminopropyl)-2-([(3-methylphenyl)methyl])-oxy-N-(2-thienylmethyl)benzamide hydrochloride salt (AMTB). Moreover, the inhibitory effects of icilin on SOCE in PA and PASMCs of CHPH rats were significantly augmented due to enhanced SOCE activity in PH. Our results, therefore, demonstrated a novel mechanism of TRPM8-mediated inhibition of SOCE in pulmonary vasculature. Because SOCE is important for vascular remodeling and enhanced vasoconstriction, down-regulation of TRPM8 in PASMCs of CHPH rats may minimize its inhibitory influence to allow unimpeded SOCE activity for PH development.

Transient Receptor Potential Melastatin 8 (TRPM8) Induced Relaxation of Pulmonary Artery is Mediated Through Inhibition of Store‐Operated Ca2+ Entry in Normoxic and Chronic Hypoxic Rats

Pulmonary hypertension (PH) is characterized by profound vascular remodeling and alterations in Ca2+ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Members of multiple transient receptor potential subfamilies (TRPC, TRPV, and TRPM) have been identified in pulmonary vascular tissue. Our previous studies showed that the expression and functions of the store‐operated TRPC1, receptor‐operated TRPC6, and the mechanosensitive TRPV4 channels are augmented in PASMCs during PH, and their upregulation contribute to PH development. In contrast, TRPM8 is down‐regulated in PASMCs of rats PH models, and activation of TRPM8 with agonists causes relaxation of pulmonary arteries (PAs)(Liu et al., Cell Physiol Biochem 2013, 31:892–904). However, the mechanism of TRPM8‐induced PA relaxation has not been determined. In this study, we examined the possible interactions of TRPM8 activation and store‐operated Ca2+ entry (SOCE) in PAs and PASMCs of normoxic and chronic hypoxic pulmonary hypertensive (CHPH) rats. We found that TRPM8 expression was down‐regulated in PAs and the TRPM8‐mediated cation entry was reduced significantly in the PASMCs of rats after 3 weeks of hypoxia (10% O2) exposure. Activation of TRPM8 with icilin (0.1–100 μM) caused concentration‐dependent relaxation of cyclopiazonic acid (CPA) and ET‐1 pre‐contracted endothelium‐denuded PAs in the presence of nifedipine. The vasorelaxant effect of icilin was abolished in the presence of the SOCE antagonist Gd3+ at submicromolar concentration. Icilin suppressed the CPA‐induced cation entry in PASMCs determined by the Mn2+ quenching technique and by Ca2+ transient measurement. The inhibitory effect of icilin on SOCE‐induced PA relaxation and Ca2+ entry were abolished by the TRPM8 antagonist AMTB, indicating that the effect was mediated specifically by TRPM8 channels. Moreover, TRPM8‐mediated inhibitory effects on CPA‐induced contraction in PAs and SOCE in PASMCs were significantly augmented in CHPH rats, probably related to the enhanced SOCE caused by PH. These results demonstrate for the first time that TRPM8 activation can cause relaxation of PA through inhibition of SOCE. Since SOCE plays many important roles in pulmonary vascular functions and is crucial for the vascular remodeling and the enhanced vasoconstriction in PH, the downregulation of TRPM8 expression and activity in PASMCs during PH may minimized the TRPM8‐dependent inhibition of SOCE, and allow unimpeded SOCE activity for PH development.Support or Funding InformationSupported by grants NSFC31571179, NSFC31371165, NSF of Fujian Province 2015J01313, and Fujian Province Hundred Experts Award.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hydrogen Sulfide inhibits store‐operated calcium influx by selectively targeting STIM1‐Orai3 interactions.

Hydrogen sulfide (H2S) is an endogenous signaling molecule that posttranslationally modifies cysteine residues on target proteins involved in regulating the physiology and pathophysiology of neurodegeneration, blood pressure, metabolism, and inflammation. We recently determined that H2S impinges on Ca2+ signaling‐regulated processes by inhibiting store operated Ca2+ entry (SOCE). The SOCE machinery consists of the plasma membrane‐localized Orai channels and ER‐localized STIM proteins. Interestingly, H2S inhibits SOCE mediated by STIM1‐Orai3 and not STIM1‐Orai1 or Orai2 interactions. The current study tested the hypothesis that H2S achieves selectively and disrupts STIM1‐Orai3 interactions by targeting cysteines unique to Orai3. The approach was to transiently transfect either CFP‐ or mCherry‐tagged Orai3 into HEK293 cells stably expressing STIM1‐YFP and measure SOCE by Ca2+ imaging. Two cysteines (C226 and C232) are present in Orai3 that are absent in the Orai1 and Orai2 sequences. Mutation of either of these cysteines to serine, alone or in combination, abolished SOCE inhibition by the H2S donor GYY4137. Residues C226 and C232 in Orai3 are predicted to form an extracellular intermolecular disulfide. To determine the requirement for disulfide formation, cells were pretreated with DTT. When performed prior to GYY4137 treatment, disulfide reduction also abolished inhibition of SOCE by GYY4137. SOCE is activated upon ER Ca2+ store depletion when STIM interacts with and gates open Orai channels. We postulated that H2S inhibited SOCE by inhibiting STIM1‐Orai3 interactions. To test this, cells were treated with GYY4137 both before and after store depletion. GYY4137 treatment decreased SOCE only when cells were pretreated with GYY4137. These data suggest that H2S modification of Orai3 inhibits the initiation of STIM1‐Orai3 interactions but cannot disrupt them once formed. We next visualized the interaction between STIM1‐YFP and Orai3‐mCherry using confocal microscopy and measured the rate of YFP‐mCherry puncta formation upon store depletion. Pre‐treatment with GYY4137 caused a decrease in puncta formation rate. Taken together, these data are consistent with a model in which H2S impairs SOCE by modifying a disulfide bridge on Orai3 resulting in decreased STIM1‐Orai3 interactions.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

On the Role of Store-Operated Calcium Entry in Acute and Chronic Neurodegenerative Diseases.

In both excitable and non-excitable cells, calcium (Ca2+) signals are maintained by a highly integrated process involving store-operated Ca2+ entry (SOCE), namely the opening of plasma membrane (PM) Ca2+ channels following the release of Ca2+ from intracellular stores. Upon depletion of Ca2+ store, the stromal interaction molecule (STIM) senses Ca2+ level reduction and migrates from endoplasmic reticulum (ER)-like sites to the PM where it activates the channel proteins Orai and/or the transient receptor potential channels (TRPC) prompting Ca2+ refilling. Accumulating evidence suggests that SOCE dysregulation may trigger perturbation of intracellular Ca2+ signaling in neurons, glia or hematopoietic cells, thus participating to the pathogenesis of diverse neurodegenerative diseases. Under acute conditions, such as ischemic stroke, neuronal SOCE can either re-establish Ca2+ homeostasis or mediate Ca2+ overload, thus providing a non-excitotoxic mechanism of ischemic neuronal death. The dualistic role of SOCE in brain ischemia is further underscored by the evidence that it also participates to endothelial restoration and to the stabilization of intravascular thrombi. In Parkinson’s disease (PD) models, loss of SOCE triggers ER stress and dysfunction/degeneration of dopaminergic neurons. Disruption of neuronal SOCE also underlies Alzheimer’s disease (AD) pathogenesis, since both in genetic mouse models and in human sporadic AD brain samples, reduced SOCE contributes to synaptic loss and cognitive decline. Unlike the AD setting, in the striatum from Huntington’s disease (HD) transgenic mice, an increased STIM2 expression causes elevated synaptic SOCE that was suggested to underlie synaptic loss in medium spiny neurons. Thus, pharmacological inhibition of SOCE is beneficial to synapse maintenance in HD models, whereas the same approach may be anticipated to be detrimental to cortical and hippocampal pyramidal neurons. On the other hand, up-regulation of SOCE may be beneficial during AD. These intriguing findings highlight the importance of further mechanistic studies to dissect the molecular pathways, and their corresponding targets, involved in synaptic dysfunction and neuronal loss during aging and neurodegenerative diseases.

Exercise-dependent formation of new junctions that promote STIM1-Orai1 assembly in skeletal muscle

Store-operated Ca2+ entry (SOCE), a ubiquitous mechanism that allows recovery of Ca2+ ions from the extracellular space, has been proposed to limit fatigue during repetitive skeletal muscle activity. However, the subcellular location for SOCE in muscle fibers has not been unequivocally identified. Here we show that exercise drives a significant remodeling of the sarcotubular system to form previously unidentified junctions between the sarcoplasmic reticulum (SR) and transverse-tubules (TTs). We also demonstrate that these new SR-TT junctions contain the molecular machinery that mediate SOCE: stromal interaction molecule-1 (STIM1), which functions as the SR Ca2+ sensor, and Orai1, the Ca2+-permeable channel in the TT. In addition, EDL muscles isolated from exercised mice exhibit an increased capability of maintaining contractile force during repetitive stimulation in the presence of 2.5 mM extracellular Ca2+, compared to muscles from control mice. This functional difference is significantly reduced by either replacement of extracellular Ca2+ with Mg2+ or the addition of SOCE inhibitors (BTP-2 and 2-APB). We propose that the new SR-TT junctions formed during exercise, and that contain STIM1 and Orai1, function as Ca2+Entry Units (CEUs), structures that provide a pathway to rapidly recover Ca2+ ions from the extracellular space during repetitive muscle activity.

Store-Operated Ca2+ Entry Controls Clonal Expansion of T Cells through Metabolic Reprogramming

Store-operated Ca2+ entry (SOCE) is the main Ca2+ influx pathway in lymphocytes and is essential for Tcell function and adaptive immunity. SOCE is mediated by Ca2+ release-activated Ca2+ (CRAC) channels that are activated by stromal interaction molecule (STIM) 1 and STIM2. SOCE regulates many Ca2+-dependent signaling molecules, including calcineurin, and inhibition of SOCE or calcineurin impairs antigen-dependent Tcell proliferation. We here report that SOCE and calcineurin regulate cell cycle entry of quiescent Tcells by controlling glycolysis and oxidative phosphorylation. SOCE directs the metabolic reprogramming of naive Tcells by regulating the expression of glucose transporters, glycolytic enzymes, and metabolic regulators through the activation of nuclear factor of activated Tcells (NFAT) and the PI3K-AKT kinase-mTOR nutrient-sensing pathway. We propose that SOCE controls a critical "metabolic checkpoint" at which Tcells assess adequate nutrient supply to support clonal expansion and adaptive immune responses.

STIM1-dependent Ca2+ signaling regulates podosome formation to facilitate cancer cell invasion

The clinical significance of STIM proteins and Orai Ca2+ channels in tumor progression has been demonstrated in different types of cancers. Podosomes are dynamic actin-rich cellular protrusions that facilitate cancer cell invasiveness by degrading extracellular matrix. Whether STIM1-dependent Ca2+ signaling facilitates cancer cell invasion through affecting podosome formation remains unclear. Here we show that the invasive fronts of cancer tissues overexpress STIM1, accompanied by active store-operated Ca2+ entry (SOCE). Interfering SOCE activity by SOCE inhibitors and STIM1 or Orai1 knockdown remarkably affects podosome rosettes formation. Mechanistically, STIM1-silencing significantly alters the podosome rosettes dynamics, shortens the maintenance phase of podosome rosettes and reduces cell invasiveness. The subsequently transient expression of STIM1 cDNA in STIM1-null (STIM1−/−) mouse embryo fibroblasts rescues the suppression of podosome formation, suggesting that STIM1-mediated SOCE activation directly regulates podosome formation. This study uncovers SOCE-mediated Ca2+ microdomain that is the molecular basis for Ca2+ sensitivity controlling podosome formation.

Polychlorinated biphenyl 19 blocks the most common form of store-operated Ca2+ entry through Orai.

PCB19, a 2,2',6-trichlorinated biphenyl, is one of many non-dioxin-like polychlorinated biphenyls (NDL-PCBs), which are ubiquitous pollutants. NDL-PCBs affect cytosolic Ca2+ signaling by promoting Ca2+ release from ryanodine receptor-sensitive Ca2+ pools and inhibiting store-operated Ca2+ entry (SOCE) from the extracellular space. However, NDL-PCB-mediated SOCE inhibition has only been demonstrated in PC12 cells, in which SOCE is thought to be mainly mediated by TRPC family channels. Here, we investigated the effect of PCB19 on SOCE using human embryonic kidney 293 (HEK293) cells, human leukemia T cell line Jurkat-T cells and human promyelocytoma HL-60 cells which are the cell lines that are previously demonstrated to mediate the most common form of SOCE solely by the intrinsic Orai channels. PCB19 reduced thapsigargin-induced Ca2+ influx after Ca2+ pool depletion in HEK293 cells. SOCEs in HEK293, Jurkat T, HL-60 and PC12 cells showed distinct sensitivities to SOCE inhibitors such as Gd3+ and ML-9; however, PCB19 also showed a common effect of inhibiting SOCEs in all cell lines. PCB19-mediated SOCE inhibition was confirmed by demonstrating the ability of PCB19 to inhibit the SOCE current but not the TRPM7 current. These results imply that PCB19 inhibits not only TRPC-mediated SOCE as in PC12 cells but also Orai-mediated SOCE as in many other cells including HEK293, Jurkat T and HL-60 cells.

VEGF-induced intracellular Ca2+ oscillations are down-regulated and do not stimulate angiogenesis in breast cancer-derived endothelial colony forming cells.

Endothelial colony forming cells (ECFCs) represent a population of truly endothelial precursors that promote the angiogenic switch in solid tumors, such as breast cancer (BC). The intracellular Ca2+ toolkit, which drives the pro-angiogenic response to VEGF, is remodelled in tumor-associated ECFCs such that they are seemingly insensitive to this growth factor. This feature could underlie the relative failure of anti-VEGF therapies in cancer patients. Herein, we investigated whether and how VEGF uses Ca2+ signalling to control angiogenesis in BC-derived ECFCs (BC-ECFCs). Although VEGFR-2 was normally expressed, VEGF failed to induce proliferation and in vitro tubulogenesis in BC-ECFCs. Likewise, VEGF did not trigger robust Ca2+ oscillations in these cells. Similar to normal cells, VEGF-induced intracellular Ca2+ oscillations were triggered by inositol-1,4,5-trisphosphate-dependent Ca2+ release from the endoplasmic reticulum (ER) and maintained by store-operated Ca2+ entry (SOCE). However, InsP3-dependent Ca2+ release was significantly lower in BC-ECFCs due to the down-regulation of ER Ca2+ levels, while there was no remarkable difference in the amplitude, pharmacological profile and molecular composition of SOCE. Thus, the attenuation of the pro-angiogenic Ca2+ response to VEGF was seemingly due to the reduction in ER Ca2+ concentration, which prevents VEGF from triggering robust intracellular Ca2+ oscillations. However, the pharmacological inhibition of SOCE prevented BC-ECFC proliferation and in vitro tubulogenesis. These findings demonstrate for the first time that BC-ECFCs are insensitive to VEGF, which might explain at cellular and molecular levels the failure of anti-VEGF therapies in BC patients, and hint at SOCE as a novel molecular target for this disease.

Mitochondria sustain store-operated currents in colon cancer cells but not in normal colonic cells: reversal by non-steroidal anti-inflammatory drugs.

Tumor cells undergo a critical remodeling of intracellular Ca2+ homeostasis that contribute to important cancer hallmarks. Store-operated Ca2+ entry (SOCE), a Ca2+ entry pathway modulated by mitochondria, is dramatically enhanced in colon cancer cells. In addition, most cancer cells display the Warburg effect, a metabolic switch from mitochondrial metabolism to glycolysis that provides survival advantages. Accordingly, we investigated mitochondria control of store-operated currents (SOCs) in two cell lines previously selected for representing human normal colonic cells and colon cancer cells. We found that, in normal cells, mitochondria are important for SOCs activity but they are unable to prevent current inactivation. In contrast, in colon cancer cells, mitochondria are dispensable for SOCs activation but are able to prevent the slow, Ca2+-dependent inactivation of SOCs. This effect is associated to increased ability of tumor cell mitochondria to take up Ca2+ due to increased mitochondrial potential (ΔΨ) linked to the Warburg effect. Consistently with this view, selected non-steroidal anti-inflammatory drugs (NSAIDs) depolarize mitochondria, inhibit mitochondrial Ca2+ uptake and promote SOC inactivation, leading to inhibition of both SOCE and cancer cell proliferation. Thus, mitochondria sustain store-operated currents in colon cancer cells but not in normal colonic cells and this effect is counteracted by selected NSAIDs providing a mechanism for cancer chemoprevention.