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Stromal Interaction Molecule1 (STIM1) is an endoplasmic reticulum membrane-localized calcium (Ca 2+ ) sensor that plays a critical role in the store-operated Ca 2+ entry (SOCE) pathway. STIM1 regulates a variety of physiological processes and contributes to a plethora of pathophysiological conditions. Several disease states and enhanced biological phenomena are associated with increased STIM1 levels and activity. However, molecular mechanisms driving STIM1 expression remain largely unappreciated. We recently reported that STIM1 expression augments during pigmentation. Nonetheless, the molecular choreography regulating STIM1 expression in melanocytes is completely unexplored. Here, we characterized the molecular events that regulate STIM1 expression during pigmentation. We demonstrate that physiological melanogenic stimuli α-melanocyte stimulating hormone (αMSH) increases STIM1 mRNA and protein levels. Further, αMSH stimulates STIM1 promoter-driven luciferase activity, thereby suggesting transcriptional upregulation of STIM1. We show that downstream of αMSH, microphthalmia-associated transcription factor (MITF) drives STIM1 expression. By performing knockdown and overexpression studies, we corroborated that MITF regulates STIM1 expression and SOCE. Next, we conducted extensive bioinformatics analysis and identified MITF-binding sites on the STIM1 promoter. We validated significance of the MITF-binding sites in controlling STIM1 expression by performing ChIP and luciferase assays with truncated STIM1 promoters. Moreover, we confirmed MITF's role in regulating STIM1 expression and SOCE in primary human melanocytes. Importantly, analysis of publicly available datasets substantiates a positive correlation between STIM1 and MITF expression in sun-exposed tanned human skin, thereby highlighting physiological relevance of this regulation. Taken together, we have identified a novel physiologically relevant molecular pathway that transcriptionally enhances STIM1 expression., Competing Interests: Conflict of interest The authors declare that they do not have any conflict of interest with the content of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Acinar cell exocytosis requires spatiotemporal Ca 2+ signals regulated through endoplasmic reticulum (ER) stores, Ca 2+ ATPases, and store-operated Ca 2+ entry (SOCE). The secretory pathway Ca 2+ ATPase 2 (SPCA2) interacts with Orai1, which is involved in SOCE and store independent Ca 2+ entry (SICE). However, in the pancreas, only a C-terminally truncated form of SPCA2 (termed SPAC2C) exists. The goal of this study was to determine if SPCA2C effects Ca 2+ homeostasis in a similar fashion to the full-length SPCA2. Using epitope-tagged SPCA2C (SPCA2C FLAG ) expressed in HEK293A cells and Fura2 imaging, cytosolic [Ca 2+ ] was examined during SICE, SOCE and secretagogue-stimulated signaling. Exogenous SPCA2C expression increased resting cytosolic [Ca 2+ ], Ca 2+ release in response to carbachol, ER Ca 2+ stores, and store-mediated and independent Ca 2+ influx. Co-IP detected Orai1-SPCA2C interaction, which was altered by co-expression of STIM1. Importantly, SPCA2C's effects on store-mediated Ca 2+ entry were independent of Orai1. These findings indicate SPCA2C influences Ca 2+ homeostasis through multiple mechanisms, some of which are independent of Orai1, suggesting novel and possibly cell-specific Ca 2+ regulation., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Live yeast cell derivative (LYCD) is a medicinal yeast extract that has been used in the treatment of burns, wounds and hemorrhoids for over 70 years. It has been shown to enhance the closure of skin wounds in diabetic mice by increasing inflammation, angiogenesis, formation of granulation tissue and epithelial migration. An active fraction of LYCD has been identified as a mixture of peptides ranging in size from 5 kDA to 17 kDA. Despite its widespread use over many years, understanding of the mechanism by which LYCD acts to effect tissue repair responses is very limited. In this study, we have used a human monocyte-derived cell line, THP-1, as a representative of the inflammatory component of the wound healing process. We have identified two of the earliest responses to LYCD as an increase in cytoplasmic free calcium ([Ca2+]i) and the transcripts for c-fos. We have found that the increase in [Ca2+]i is both necessary and sufficient to account for the LYCD-induced elevation of c-fos. Furthermore, we have shown that the signaling pathway by which LYCD elevates [Ca2+]i involves both mobilization of Ca2+ from intracellular stores and influx of Ca2+ from the extracellular medium. Mobilization of store Ca2+ occurs first via activation of phospholipase C and this is followed by influx through activation of store operated calcium channels. These results constitute the first delineation of the early steps of the LYCD signaling pathway., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

There is increasing evidence indicating that aquaporins (AQPs) exert an influence in cell signaling by the interplay with the TRPV4 Ca 2+ channel. Ca 2+ release from intracellular stores and plasma membrane hyperpolarization due to opening of Ca 2+ -activated potassium channels (KCa) are events that have been proposed to take place downstream of TRPV4 activation. A major mechanism for Ca 2+ entry, activated after depletion of intracellular Ca 2+ stores and driven by electrochemical forces, is the store-operated Ca 2+ entry (SOCE). The consequences of the interplay between TRPV4 and AQPs on SOCE have not been yet investigated. The aim of our study was to test the hypothesis that AQP2 can modulate SOCE by facilitating the interaction of TRPV4 with KCa channels in renal cells. Using fluorescent probe techniques, we studied intracellular Ca 2+ concentration and membrane potential in response to activation of TRPV4 in two rat cortical collecting duct cell lines (RCCD 1 ), one not expressing AQPs (WT-RCCD 1 ) and the other transfected with AQP2 (AQP2-RCCD 1 ). We found that AQP2 co-immunoprecipitates with TRPV4 and with the small-conductance potassium channel (SK3). We also showed that AQP2 is crucial for the activation of SK3 by TRPV4, leading to hyperpolarization of the plasma membrane. This seems to be relevant to modulate the magnitude of SOCE and is accompanied by TRPV4 translocation to the plasma membrane only in AQP2 expressing cells. These findings open the perspective to further investigate whether the interplay between different AQPs with TRPV4 and KCa channels can be an important mechanism to modulate SOCE with physiological relevance., (© 2017 Wiley Periodicals, Inc.)

In 1986, J.W. Putney presented a model for capacitative calcium (Ca 2+ ) entry conveying that depletion of endoplasmic reticulum stored Ca 2+ levels leads to activation of plasma membrane Ca 2+ channels which mediate influx of Ca 2+ from the extracellular space into cells. Presently, the biomolecules regulating this process, more widely known as store operated Ca 2+ entry (SOCE) which is vital to myriad signaling pathways in health and disease, are known and the focus of intense structural biology research aiming to illuminate the atomic mechanisms of function. This brief review highlights the known structures with respect to the mechanisms of SOCE regulation and possible future directions in this field developed out of Putney's conceptualization of this process., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Exercise promotes the formation of intracellular junctions in skeletal muscle between stacks of sarcoplasmic reticulum (SR) cisternae and extensions of transverse-tubules (TT) that increase co-localization of proteins required for store-operated Ca2+ entry (SOCE). Here, we report that SOCE, peak Ca2+ transient amplitude and muscle force production during repetitive stimulation are increased after exercise in parallel with the time course of TT association with SR-stacks. Unexpectedly, exercise also activated constitutive Ca2+ entry coincident with a modest decrease in total releasable Ca2+ store content. Importantly, this decrease in releasable Ca2+ store content observed after exercise was reversed by repetitive high-frequency stimulation, consistent with enhanced SOCE. The functional benefits of exercise on SOCE, constitutive Ca2+ entry and muscle force production were lost in mice with muscle-specific loss of Orai1 function. These results indicate that TT association with SR-stacks enhances Orai1-dependent SOCE to optimize Ca2+ dynamics and muscle contractile function during acute exercise.

The Ca sensor stromal interacting molecule 1 (STIM1) and the Ca channel Orai1 mediate the ubiquitous store-operated Ca entry (SOCE) pathway activated by depletion of internal Ca stores and mediated through the highly Ca-selective, Ca release-activated Ca (CRAC) current. Furthermore, STIM1 and Orai1, along with Orai3, encode store-independent Ca currents regulated by either arachidonate or its metabolite, leukotriene C. Orai channels are emerging as important contributors to numerous cell functions, including proliferation, migration, differentiation, and apoptosis. Recent studies suggest critical involvement of STIM/Orai proteins in controlling the development of several cancers, including malignancies of the breast, prostate, and cervix. Here, we quantitatively compared the magnitude of SOCE and the expression levels of STIM1 and Orai1 in non-malignant human primary astrocytes (HPA) and in primary human cell lines established from surgical samples of the brain tumor glioblastoma multiforme (GBM). Using Ca imaging, patch-clamp electrophysiology, pharmacological reagents, and gene silencing, we established that in GBM cells, SOCE and CRAC are mediated by STIM1 and Orai1. We further found that GBM cells show upregulation of SOCE and increased Orai1 levels compared to HPA. The functional significance of SOCE was evaluated by studying the effects of STIM1 and Orai1 knockdown on cell proliferation and invasion. Utilizing Matrigel assays, we demonstrated that in GBM, but not in HPA, downregulation of STIM1 and Orai1 caused a dramatic decrease in cell invasion. In contrast, the effects of STIM1 and Orai1 knockdown on GBM cell proliferation were marginal. Overall, these results demonstrate that STIM1 and Orai1 encode SOCE and CRAC currents and control invasion of GBM cells. Our work further supports the potential use of channels contributed by Orai isoforms as therapeutic targets in cancer. [ABSTRACT FROM AUTHOR]