Differential functional role of Orai1 variants in constitutive Ca entry and calcification in luminal breast cancer cells.

Resting cytosolic Ca concentration is tightly regulated to fine-tune Ca-dependent cellular functions. Luminal breast cancer cells exhibit constitutive Ca entry mediated by Orai1 and the secretory pathway Ca-ATPase, SPCA2, which result in mammary microcalcifications that constitute a prognostic marker of mammary lesions. Two Orai1 isoforms have been identified, the full-length Orai1α, consisting of 301 amino acids, and the short variant, Orai1β, lacking the 63 or 70 N-terminal amino acids comprising residues involved in channel inactivation and binding sites with Orai1 partners.

The Ca Sensor STIM in Human Diseases.

The STIM family of proteins plays a crucial role in a plethora of cellular functions through the regulation of store-operated Ca entry (SOCE) and, thus, intracellular calcium homeostasis. The two members of the mammalian STIM family, STIM1 and STIM2, are transmembrane proteins that act as Ca sensors in the endoplasmic reticulum (ER) and, upon Ca store discharge, interact with and activate the Orai/CRACs in the plasma membrane. Dysregulation of Ca signaling leads to the pathogenesis of a variety of human diseases, including neurodegenerative disorders, cardiovascular diseases, cancer, and immune disorders.

Functional differences in agonist-induced plasma membrane expression of Orai1α and Orai1β.

Orai1 is the pore-forming subunit of the store-operated Ca release-activated Ca (CRAC) channels involved in a variety of cellular functions. Two Orai1 variants have been identified, the long form, Orai1α, containing 301 amino acids, and the short form, Orai1β, which arises from alternative translation initiation from methionines 64 or 71, in Orai1α. Orai1 is mostly expressed in the plasma membrane, but a subset of Orai1 is located in intracellular compartments.

Role of Orai-family channels in the activation and regulation of transcriptional activity.

Store operated Ca entry (SOCE) is a cornerstone for the maintenance of intracellular Ca homeostasis and the regulation of a variety of cellular functions. SOCE is mediated by STIM and Orai proteins following the activation of inositol 1,4,5-trisphosphate receptors. Then, a reduction of the endoplasmic reticulum intraluminal Ca concentration is sensed by STIM proteins, which undergo a conformational change and activate plasma membrane Ca channels comprised by Orai proteins.

Correction: Sanchez-Collado et al. Orai2 Modulates Store-Operated Ca Entry and Cell Cycle Progression in Breast Cancer Cells. 2021, , 114.

In the original publication [...

The store-operated Ca channel Orai1α is required for agonist-evoked NF-κB activation by a mechanism dependent on PKCβ2.

Store-operated Ca entry is a ubiquitous mechanism for Ca influx in mammalian cells that regulates a variety of physiological processes. The identification of two forms of Orai1, the predominant store-operated channel, Orai1α and Orai1β, raises the question whether they differentially regulate cell function. Orai1α is the full-length Orai1, containing 301 amino acids, whereas Orai1β lacks the N-terminal 63 amino acids.

Store-Operated Calcium Entry in Breast Cancer Cells Is Insensitive to Orai1 and STIM1 N-Linked Glycosylation.

N-linked glycosylation is a post-translational modification that affects protein function, structure, and interaction with other proteins. The store-operated Ca entry (SOCE) core proteins, Orai1 and STIM1, exhibit N-glycosylation consensus motifs. Abnormal SOCE has been associated to a number of disorders, including cancer, and alterations in Orai1 glycosylation have been related to cancer invasiveness and metastasis.

Similarities and Differences between the Orai1 Variants: Orai1α and Orai1β.

Orai1, the first identified member of the Orai protein family, is ubiquitously expressed in the animal kingdom. Orai1 was initially characterized as the channel responsible for the store-operated calcium entry (SOCE), a major mechanism that allows cytosolic calcium concentration increments upon receptor-mediated IP generation, which results in intracellular Ca store depletion. Furthermore, current evidence supports that abnormal Orai1 expression or function underlies several disorders.

Store-Operated Calcium Entry and Its Implications in Cancer Stem Cells.

Tumors are composed by a heterogeneous population of cells. Among them, a sub-population of cells, termed cancer stem cells, exhibit stemness features, such as self-renewal capabilities, disposition to differentiate to a more proliferative state, and chemotherapy resistance, processes that are all mediated by Ca. Ca homeostasis is vital for several physiological processes, and alterations in the patterns of expressions of the proteins and molecules that modulate it have recently become a cancer hallmark.

Orai2 Modulates Store-Operated Ca Entry and Cell Cycle Progression in Breast Cancer Cells.

Breast cancer is a heterogeneous disease from the histological and molecular expression point of view, and this heterogeneity determines cancer aggressiveness. Store-operated Ca entry (SOCE), a major mechanism for Ca entry in non-excitable cells, is significantly remodeled in cancer cells and plays an important role in the development and support of different cancer hallmarks. The store-operated CRAC (Ca release-activated Ca) channels are predominantly comprised of Orai1 but the participation of Orai2 and Orai3 subunits has been reported to modulate the magnitude of Ca responses.

Orai1α, but not Orai1β, co-localizes with TRPC1 and is required for its plasma membrane location and activation in HeLa cells.

The identification of two variants of the canonical pore-forming subunit of the Ca release-activated Ca (CRAC) channel Orai1, Orai1α and Orai1β, in mammalian cells arises the question whether they exhibit different functional characteristics. Orai1α and Orai1β differ in the N-terminal 63 amino acids, exclusive of Orai1α, and show different sensitivities to Ca-dependent inactivation, as well as distinct ability to form arachidonate-regulated channels. We have evaluated the role of both Orai1 variants in the activation of TRPC1 in HeLa cells.

Role of Orai3 in the Pathophysiology of Cancer.

The mammalian exclusive Orai3 channel participates in the generation and/or modulation of two independent Ca currents, the store-operated current, I, involving functional interactions between the stromal interaction molecules (STIM), STIM1/STIM2, and Orai1/Orai2/Orai3, as well as the store-independent arachidonic acid (AA) (or leukotriene C4)-regulated current I, which involves Orai1, Orai3 and STIM1. Overexpression of functional Orai3 has been described in different neoplastic cells and cancer tissue samples as compared to non-tumor cells or normal adjacent tissue. In these cells, Orai3 exhibits a cell-specific relevance in Ca influx.

The Orai1-AC8 Interplay: How Breast Cancer Cells Escape from Orai1 Channel Inactivation.

The interplay between the Ca-sensitive adenylyl cyclase 8 (AC8) and Orai1 channels plays an important role both in the activation of the cAMP/PKA signaling and the modulation of Orai1-dependent Ca signals. AC8 interacts with a N-terminal region that is exclusive to the Orai1 long variant, Orai1α. The interaction between both proteins allows the Ca that enters the cell through Orai1α to activate the generation of cAMP by AC8.

Cross-Talk Between the Adenylyl Cyclase/cAMP Pathway and Ca Homeostasis.

Cyclic AMP and Ca are the first second or intracellular messengers identified, unveiling the cellular mechanisms activated by a plethora of extracellular signals, including hormones. Cyclic AMP generation is catalyzed by adenylyl cyclases (ACs), which convert ATP into cAMP and pyrophosphate. By the way, Ca, as energy, can neither be created nor be destroyed; Ca can only be transported, from one compartment to another, or chelated by a variety of Ca-binding molecules.

Functional role of TRPC6 and STIM2 in cytosolic and endoplasmic reticulum Ca2+ content in resting estrogen receptor-positive breast cancer cells.

TRPC6 forms non-selective cation channels activated by a variety of stimuli that are involved in a wide number of cellular functions. In estrogen receptor-positive (ER+) breast cancer cells, the store-operated Ca2+ entry has been reported to be dependent on STIM1, STIM2 and Orai3, with TRPC6 playing a key role in the activation of store-operated Ca2+ entry as well as in proliferation, migration and viability of breast cancer cells. We have used a combination of biotinylation, Ca2+ imaging as well as protein knockdown and overexpression of a dominant-negative TRPC6 mutant (TRPC6dn) to show that TRPC6 and STIM2 are required for the maintenance of cytosolic and endoplasmic reticulum Ca2+ content under resting conditions in ER+ breast cancer MCF7 cells.

Arachidonic Acid Attenuates Cell Proliferation, Migration and Viability by a Mechanism Independent on Calcium Entry.

Arachidonic acid (AA) is a phospholipase A2 metabolite that has been reported to mediate a plethora of cellular mechanisms involved in healthy and pathological states such as platelet aggregation, lymphocyte activation, and tissue inflammation. AA has been described to activate Ca entry through the arachidonate-regulated Ca-selective channels (ARC channels). Here, the analysis of the changes in the intracellular Ca homeostasis revealed that, despite MDA-MB-231 cells expressing the ARC channel components Orai1, Orai3, and STIM1, AA does not evoke Ca entry in these cells.

TRPC Channels in the SOCE Scenario.

Transient receptor potential (TRP) proteins form non-selective Ca permeable channels that contribute to the modulation of a number of physiological functions in a variety of cell types. Since the identification of TRP proteins in , it is well known that these channels are activated by stimuli that induce PIP hydrolysis. The canonical TRP (TRPC) channels have long been suggested to be constituents of the store-operated Ca (SOC) channels; however, none of the TRPC channels generate Ca currents that resemble .

Adenylyl Cyclase Type 8 Overexpression Impairs Phosphorylation-Dependent Orai1 Inactivation and Promotes Migration in MDA-MB-231 Breast Cancer Cells.

Orai1 plays a major role in store-operated Ca entry (SOCE) in triple-negative breast cancer (TNBC) cells. This channel is inactivated via different mechanisms, including protein kinase C (PKC) and protein kinase A (PKA)-dependent phosphorylation at Ser-27 and Ser-30 or Ser-34, respectively, which shapes the Ca responses to agonists. The Ca calmodulin-activated adenylyl cyclase type 8 (AC8) was reported to interact directly with Orai1, thus mediating a dynamic interplay between the Ca- and cyclic adenosine monophosphate (cAMP)-dependent signaling pathways.

Molecular Basis and Regulation of Store-Operated Calcium Entry.

Store-operated Ca entry (SOCE) is a ubiquitous mechanism for Ca influx in mammalian cells with important physiological implications. Since the discovery of SOCE more than three decades ago, the mechanism that communicates the information about the amount of Ca accumulated in the intracellular Ca stores to the plasma membrane channels and the nature of these channels have been matters of intense investigation and debate. The stromal interaction molecule-1 (STIM1) has been identified as the Ca sensor of the intracellular Ca compartments that activates the store-operated channels.

EFHB is a Novel Cytosolic Ca2+ Sensor That Modulates STIM1-SARAF Interaction.

Background/aims: STIM1 and Orai1 are the key components of store-operated Ca2+ entry (SOCE). Among the proteins involved in the regulation of SOCE, SARAF prevents spontaneous activation of SOCE and modulates STIM1 function.

Methods: Cytosolic Ca2+ mobilization was estimated in fura-2-loaded cells using an epifluorescence inverted microscope.

Filamin A Modulates Store-Operated Ca Entry by Regulating STIM1 (Stromal Interaction Molecule 1)-Orai1 Association in Human Platelets.

Objective: Here, we provide evidence for the role of FLNA (filamin A) in the modulation of store-operated calcium entry (SOCE).

Approach And Results: SOCE is a major mechanism for calcium influx controlled by the intracellular Ca stores. On store depletion, the endoplasmic reticulum calcium sensor STIM1 (stromal interaction molecule 1) redistributes into puncta at endoplasmic reticulum/plasma membrane junctions, a process supported by the cytoskeleton, where it interacts with the calcium channels; however, the mechanism for fine-tuning SOCE is not completely understood.

New Insights into Adipokines as Potential Biomarkers for Type-2 Diabetes Mellitus.

A large number of studies have been focused on investigating serum biomarkers associated with risk or diagnosis of type-2 diabetes mellitus. In the last decade, promising studies have shown that circulating levels of adipokines could be used as a relevant biomarker for diabetes mellitus progression as well as therapeutic future targets. Here, we discuss the possible use of recently described adipokines, including apelin, omentin-1, resistin, FGF-21, neuregulin-4 and visfatin, as early biomarkers for diabetes.

TRPs in Pain Sensation.

According to the International Association for the Study of Pain (IASP) pain is characterized as an "unpleasant sensory and emotional experience associated with actual or potential tissue damage". The TRP super-family, compressing up to 28 isoforms in mammals, mediates a myriad of physiological and pathophysiological processes, pain among them. TRP channel might be constituted by similar or different TRP subunits, which will result in the formation of homomeric or heteromeric channels with distinct properties and functions.