The Experts below are selected from a list of 2040 Experts worldwide ranked by ideXlab platform
Indu S Ambudkar - One of the best experts on this subject based on the ideXlab platform.
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functional requirement for orai1 in store operated trpc1 stim1 channels
Journal of Biological Chemistry, 2008Co-Authors: Kwong Tai Cheng, Xibao Liu, Hwei Ling Ong, Indu S AmbudkarAbstract:Orai1 and TRPC1 have been proposed as core components of store-operated calcium release-activated calcium (CRAC) and store-operated calcium (SOC) channels, respectively. STIM1, a Ca2+ sensor protein in the endoplasmic reticulum, interacts with and mediates store-dependent regulation of both channels. We have previously reported that dynamic association of Orai1, TRPC1, and STIM1 is involved in activation of store-operated Ca2+ entry (SOCE) in salivary gland cells. In this study, we have assessed the molecular basis of TRPC1-SOC channels in HEK293 cells. We report that TRPC1+STIM1-dependent SOCE requires functional Orai1. Thapsigargin stimulation of cells expressing Orai1+STIM1 increased Ca2+ entry and activated typical ICRAC current. STIM1 alone did not affect SOCE, whereas expression of Orai1 induced a decrease. Expression of TRPC1 induced a small increase in SOCE, which was greatly enhanced by co-expression of STIM1. Thapsigargin stimulation of cells expressing TRPC1+STIM1 activated a non-selective cation current, ISOC, that was blocked by 1 μm Gd3+ and 2-APB. Knockdown of Orai1 decreased endogenous SOCE as well as SOCE with TRPC1 alone. siOrai1 also significantly reduced SOCE and ISOC in cells expressing TRPC1+STIM1. Expression of R91WOrai1 or E106QOrai1 induced similar attenuation of TRPC1+STIM1-dependent SOCE and ISOC, whereas expression of Orai1 with TRPC1+STIM1 resulted in SOCE that was larger than that with Orai1+STIM1 or TRPC1+STIM1 but not additive. Additionally, Orai1, E106QOrai1, and R91WOrai1 co-immunoprecipitated with similar levels of TRPC1 and STIM1 from HEK293 cells, and endogenous TRPC1, STIM1, and Orai1 were co-immunoprecipitated from salivary glands. Together, these data demonstrate a functional requirement for Orai1 in TRPC1+STIM1-dependent SOCE.
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Intracellular Ca^2+ release via the ER translocon activates store-operated calcium entry
Pflügers Archiv - European Journal of Physiology, 2007Co-Authors: Hwei L. Ong, Xibao Liu, Ajay Sharma, Ramanujan S. Hegde, Indu S AmbudkarAbstract:Store-operated Ca^2+ entry (SOCE) is activated in response to depletion of intracellular Ca^2+ from the endoplasmic reticulum (ER). A variety of agonists stimulate SOCE via IP_3-dependent Ca^2+ depletion. SOCE is also activated by thapsigargin, an inhibitor of Ca^2+ reuptake into the ER that induces a net Ca^2+ loss from the ER by unmasking a Ca^2+ “leak” pathway. The molecular identity of this Ca^2+ leak channel and the physiological conditions under which such agonist-independent Ca^2+ depletion might occur remain poorly characterized. In this study, we report that inhibition of the initiation step of protein synthesis (with pactamycin) resulted in detectable Ca^2+ depletion in ER and activation of SOCE. This was completely prevented if the ribosome–nascent chain complexes were first stabilized with an irreversible inhibitor of translational elongation (emetine), suggesting that ER Ca^2+ depletion had occurred through open translocons at the ER. Notably, emetine pretreatment also attenuated thapsigargin-mediated Ca^2+ release and SOCE. Furthermore, both pactamycin and thapsigargin stimulated translocation of STIM1, a protein required for activation of SOCE, to the subplasma membrane region and activated the SOCE-associated current, I _SOC. In aggregate, these data reveal an agonist-independent mechanism for internal Ca^2+ store depletion and activation of SOCE. We suggest that the functional coupling between SOCE and protein synthesis is likely to be critical for maintaining [Ca^2+]_ER within a range that is required to prevent ER stress during changes in cellular translational activity.
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calmodulin regulates ca2 dependent feedback inhibition of store operated ca2 influx by interaction with a site in the c terminus of trpc1
Molecular Cell, 2002Co-Authors: Brij B Singh, Xibao Liu, Michael X Zhu, Jisen Tang, Indu S AmbudkarAbstract:Abstract The mechanism involved in [Ca 2+ ] i -dependent feedback inhibition of store-operated Ca 2+ entry (SOCE) is not yet known. Expression of Ca 2+ -insensitive calmodulin (Mut-CaM) but not wild-type CaM increased SOCE and decreased its Ca 2+ -dependent inactivation. Expression of TrpC1 lacking C terminus aa 664–793 (TrpC1ΔC) also attenuated Ca 2+ -dependent inactivation of SOCE. CaM interacted with endogenous and expressed TrpC1 and with GST-TrpC1 C terminus but not with TrpC1ΔC. Two CaM binding domains, aa 715–749 and aa 758–793, were identified. Expression of TrpC1Δ758–793 but not TrpC1Δ715–749 mimicked the effects of TrpC1ΔC and Mut-CaM on SOCE. These data demonstrate that CaM mediates Ca 2+ -dependent feedback inhibition of SOCE via binding to a domain in the C terminus of TrpC1. These findings reveal an integral role for TrpC1 in the regulation of SOCE.
Robert T Dirksen - One of the best experts on this subject based on the ideXlab platform.
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role of stim1 orai1 mediated store operated ca2 entry in skeletal muscle physiology and disease
Cell Calcium, 2018Co-Authors: Antonio Michelucci, Maricela Garciacastaneda, Simona Boncompagni, Robert T DirksenAbstract:Abstract Store-operated Ca2+ entry (SOCE) is a Ca2+ entry mechanism activated by depletion of intracellular Ca2+ stores. In skeletal muscle, SOCE is mediated by an interaction between stromal-interacting molecule-1 (STIM1), the Ca2+ sensor of the sarcoplasmic reticulum, and ORAI1, the Ca2+-release-activated-Ca2+ (CRAC) channel located in the transverse tubule membrane. This review focuses on the molecular mechanisms and physiological role of SOCE in skeletal muscle, as well as how alterations in STIM1/ORAI1-mediated SOCE contribute to muscle disease. Recent evidence indicates that SOCE plays an important role in both muscle development/growth and fatigue. The importance of SOCE in muscle is further underscored by the discovery that loss- and gain-of-function mutations in STIM1 and ORAI1 result in an eclectic array of disorders with clinical myopathy as central defining component. Despite differences in clinical phenotype, all STIM1/ORAI1 gain-of-function mutations-linked myopathies are characterized by the abnormal accumulation of intracellular membranes, known as tubular aggregates. Finally, dysfunctional STIM1/ORAI1-mediated SOCE also contributes to the pathogenesis of muscular dystrophy, malignant hyperthermia, and sarcopenia. The picture to emerge is that tight regulation of STIM1/ORAI1-dependent Ca2+ signaling is critical for optimal skeletal muscle development/function such that either aberrant increases or decreases in SOCE activity result in muscle dysfunction.
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differential dependence of store operated and excitation coupled ca2 entry in skeletal muscle on stim1 and orai1
The Journal of Physiology, 2008Co-Authors: Alla D Lyfenko, Robert T DirksenAbstract:In non-excitable cells, agonist-induced depletion of intracellular Ca2+ stores triggers Ca2+ influx via a process termed store-operated Ca2+ entry (SOCE). In T-lymphocytes, stromal interaction molecule 1 (STIM1) acts as the intra-store Ca2+ sensor and Orai1 functions as the Ca2+-permeable SOCE channel activated by STIM1 following store depletion. Two functionally distinct Ca2+ entry pathways exist in skeletal muscle; one activated by store depletion (SOCE) and a second by sustained/repetitive depolarization that does not require store depletion (excitation-coupled Ca2+ entry, ECCE). However, the role of STIM1 and Orai1 in coordinating SOCE and ECCE activity in skeletal muscle and whether these two Ca2+ entry pathways represent distinct molecular entities or two different activation mechanisms of the same channel complex is unknown. Here we address these issues using siRNA-mediated STIM1 knockdown, dominant-negative Orai1, and permeation-defective Orai1 to determine the role of STIM1 and Orai1 in store-operated and excitation-coupled Ca2+ entry in skeletal myotubes. SOCE and ECCE activity were quantified from both intracellular Ca2+ measurements and Mn2+ quench assays. We found that STIM1 siRNA reduced STIM1 protein by more than 90% and abolished SOCE activity, while expression of siRNA-resistant hSTIM1 fully restored SOCE. SOCE was also abolished by dominant-negative Orai1 (E106Q) and markedly reduced by expression of a permeation-defective Orai1 (E190Q). In contrast, ECCE was unaffected by STIM1 knockdown, E106Q expression or E190Q expression. These results are the first to demonstrate that SOCE in skeletal muscle requires both STIM1 and Orai1 and that SOCE and ECCE represent two distinct molecular entities.
Luc Wasungu - One of the best experts on this subject based on the ideXlab platform.
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randomised comparison of a bioresorbable everolimus eluting scaffold with a metallic everolimus eluting stent for ischaemic heart disease caused by de novo native coronary artery lesions the 2 year clinical outcomes of the absorb ii trial
Eurointervention, 2016Co-Authors: Bernard Chevalier, Pieter C Smits, Jan J Piek, Manel Sabate, Ad J Van Boven, Steffen Helqvist, Andreas Baumbach, Ravindra Kumar, Luc WasunguAbstract:AIMS The one-year randomised data of the ABSORB II trial showed that the everolimus-eluting bioresorbable scaffold and the everolimus-eluting metallic stent were comparable for the composite secondary clinical outcomes of patient-oriented composite endpoint (PoCE) and device-oriented composite endpoint (DoCE)/target lesion failure (TLF), MACE and TVF. This report describes the two-year clinical outcomes of the ABSORB II trial. METHODS AND RESULTS Patients were randomly assigned in a 2:1 ratio to receive treatment with an everolimus-eluting bioresorbable scaffold (Absorb; Abbott Vascular, Santa Clara, CA, USA) or treatment with an everolimus-eluting metallic stent (XIENCE; Abbott Vascular). The trial enrolled 501 patients. Clinical follow-up at two years was available in 320 patients in the Absorb BVS arm and 160 patients in the XIENCE arm. At two years, the PoCE for the Absorb and XIENCE arms was 11.6% and 12.8% (p=0.70) and the DoCE/TLF was 7.0% and 3.0% (p=0.07), respectively. The hierarchical ID-MACE rate was 7.6% vs. 4.3% (p=0.16) and the rate of TVF was 8.5% vs. 6.7% (p=0.48). The definite/probable thrombosis rate was 1.5% in the Absorb arm vs. 0% in the XIENCE arm (p=0.17). Thirty-six percent and 34% of patients remained on DAPT at two years, respectively. Ninety-two percent of patients in both arms remained on aspirin. CONCLUSIONS Two-year clinical results demonstrate sustained low rates of PoCE, MACE, DoCE and TVF with the Absorb BVS as compared to the XIENCE stent.
Alexei Verkhratsky - One of the best experts on this subject based on the ideXlab platform.
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store operated calcium entry in neuroglia
Neuroscience Bulletin, 2014Co-Authors: Alexei Verkhratsky, Vladimir ParpuraAbstract:Neuroglial cells are homeostatic neural cells. Generally, they are electrically non-excitable and their activation is associated with the generation of complex intracellular Ca(2+) signals that define the "Ca(2+) excitability" of glia. In mammalian glial cells the major source of Ca(2+) for this excitability is the lumen of the endoplasmic reticulum (ER), which is ultimately (re)filled from the extracellular space. This occurs via store-operated Ca(2+) entry (SOCE) which is supported by a specific signaling system connecting the ER with plasmalemmal Ca(2+) entry. Here, emptying of the ER Ca(2+) store is necessary and sufficient for the activation of SOCE, and without Ca(2+) influx via SOCE the ER store cannot be refilled. The molecular arrangements underlying SOCE are relatively complex and include plasmalemmal channels, ER Ca(2+) sensors, such as stromal interaction molecule, and possibly ER Ca(2+) pumps (of the SERCA type). There are at least two sets of plasmalemmal channels mediating SOCE, the Ca(2+)-release activated channels, Orai, and transient receptor potential (TRP) channels. The molecular identity of neuroglial SOCE has not been yet identified unequivocally. However, it seems that Orai is predominantly expressed in microglia, whereas astrocytes and oligodendrocytes rely more on TRP channels to produce SOCE. In physiological conditions the SOCE pathway is instrumental for the sustained phase of the Ca(2+) signal observed following stimulation of metabotropic receptors on glial cells.
Taufiq Rahman - One of the best experts on this subject based on the ideXlab platform.
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unveiling some fda approved drugs as inhibitors of the store operated ca 2 entry pathway
Scientific Reports, 2017Co-Authors: Saifur Rahman, Taufiq RahmanAbstract:The store-operated calcium entry (SOCE) pathway is an important route for generating cytosolic Ca2+ signals that regulate a diverse array of biological processes. Abnormal SOCE seem to underlie several diseases that notably include allergy, inflammation and cancer. Therefore, any modulator of this pathway is likely to have significant impact in cell biology under both normal and abnormal conditions. In this study, we screened the FDA-approved drug library for agents that share significant similarity in 3D shape and surface electrostatics with few, hitherto best known inhibitors of SOCE. This has led to the identification of five drugs that showed dose-dependent inhibition of SOCE in cell-based assay, probably through interacting with the Orai1 protein which effectively mediates SOCE. Of these drugs, leflunomide and teriflunomide could suppress SOCE significantly at clinically-relevant doses and this provides for an additional mechanism towards the therapeutic utility of these drugs as immunosuppressants. The other three drugs namely lansoprazole, tolvaptan and roflumilast, were less potent in suppressing SOCE but were more selective and thus they may serve as novel scaffolds for future development of new, more efficacious SOCE inhibitors.
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Unveiling some FDA-approved drugs as inhibitors of the store-operated Ca2+ entry pathway
Nature Publishing Group, 2017Co-Authors: Saifur Rahman, Taufiq RahmanAbstract:Abstract The store-operated calcium entry (SOCE) pathway is an important route for generating cytosolic Ca2+ signals that regulate a diverse array of biological processes. Abnormal SOCE seem to underlie several diseases that notably include allergy, inflammation and cancer. Therefore, any modulator of this pathway is likely to have significant impact in cell biology under both normal and abnormal conditions. In this study, we screened the FDA-approved drug library for agents that share significant similarity in 3D shape and surface electrostatics with few, hitherto best known inhibitors of SOCE. This has led to the identification of five drugs that showed dose-dependent inhibition of SOCE in cell-based assay, probably through interacting with the Orai1 protein which effectively mediates SOCE. Of these drugs, leflunomide and teriflunomide could suppress SOCE significantly at clinically-relevant doses and this provides for an additional mechanism towards the therapeutic utility of these drugs as immunosuppressants. The other three drugs namely lansoprazole, tolvaptan and roflumilast, were less potent in suppressing SOCE but were more selective and thus they may serve as novel scaffolds for future development of new, more efficacious SOCE inhibitors
