Store-independent activation of Orai1 by SPCA2 in mammary tumors

Orai1 controls C5a-induced neutrophil recruitment in inflammation

Stromal interaction molecule 1 (STIM1)-dependent store operated calcium-entry (SOCE) through Orai1-mediated calcium (Ca(2+) ) influx is considered a major pathway of Ca(2+) signaling, serving T-cell, mast cell, and platelet responses. Here, we show that Orai1 is critical for neutrophil function. Orai1-deficient neutrophils present defects in fMLP and complement C5a-induced Ca(2+) influx and migration, although they respond normally to another chemoattractant, CXCL2. Up until now, no specific contribution of Orai1 independent from STIM1 or SOCE has been recognized in immune cells. Here, we observe that Orai1-deficient neutrophils exhibit normal STIM1-dependent SOCE and STIM1-deficient neutrophils respond to fMLP and C5a efficiently. Despite substantial cytokine production, Orai1(-/-) chimeric mice show impaired neutrophil recruitment in LPS-induced peritonitis. Moreover, Orai1 deficiency results in profoundly defective C5a-triggered neutrophil lung recruitment in hypersensitivity pneumonitis. Comparative evaluation of inflammation in Stim1(-/-) chimeras reveals a distinct pathogenic contribution of STIM1, including its involvement in IgG-induced C5a production. Our data establish Orai1 as key signal mediator of C5aR activation, contributing to inflammation by a STIM1-independent pathway of Ca(2+) -influx in neutrophils.

Regulation and roles of Ca2+ stores in human sperm

[Ca(2)(+)]i signalling is a key regulatory mechanism in sperm function. In mammalian sperm the Ca(2)(+)-permeable plasma membrane ion channel CatSper is central to [Ca(2)(+)]i signalling, but there is good evidence that Ca(2)(+) stored in intracellular organelles is also functionally important. Here we briefly review the current understanding of the diversity of Ca(2)(+) stores and the mechanisms for the regulation of their activity. We then consider the evidence for the involvement of these stores in [Ca(2)(+)]i signalling in mammalian (primarily human) sperm, the agonists that may activate these stores and their role in control of sperm function. Finally we consider the evidence that membrane Ca(2)(+) channels and stored Ca(2)(+) may play discrete roles in the regulation of sperm activities and propose a mechanism by which these different components of the sperm Ca(2)(+)-signalling apparatus may interact to generate complex and spatially diverse [Ca(2)(+)]i signals.

Elevated Orai1 expression mediates tumor-promoting intracellular Ca2+ oscillations in human esophageal squamous cell carcinoma

Effective treatment as well as prognostic biomarker for malignant esophageal squamous cell carcinoma (ESCC) is urgently needed. The present study was aimed at identifying oncogenic genes involving dysregulated intracellular Ca²⁺ signaling, which is known to function importantly in cellular proliferation and migration. Tumors from patients with ESCC were found to display elevated expression of Orai1, a store-operated Ca²⁺ entry (SOCE) channel, and the high expression of Orai1 was associated with poor overall and recurrence-free survival. In contrast to the quiescent nature of non-tumorigenic epithelial cells, human ESCC cells exhibited strikingly hyperactive in intracellular Ca²⁺ oscillations, which were sensitive to treatments with Orai1 channel blockers and to orai1 silencing. Moreover, pharmacologic inhibition of Orai1 activity or reduction of Orai1 expression suppressed proliferation and migration of ESCC in vitro and slowed tumor formation and growth in in vivo xenografted mice. Combined, these findings provide the first evidence to imply Orai1 as a novel biomarker for ESCC prognostic stratification and also highlight Orai1-mediated Ca²⁺ signaling pathway as a potential target for treatment of this deadly disease.

Disrupting the dynamic equilibrium of ORAI channels determines the phenotype of malignant cells

We recently unraveled a finely tuned oncogenic mechanism in which genetic and tumor microenvironment alterations act together on a crucial calcium signaling pathway. This pathway involves an interconnected equilibrium of calcium channels functioning like a binary star system in which ORAI1 homomers and ORAI1/3 heteromers are two companion stars under the influence of each other that orbit around the cancer hallmarks of apoptosis resistance and enhanced proliferation.

Cab45S promotes cell proliferation through SERCA2b inhibition and Ca2+ signaling

Cytosolic Ca(2+), closely related to endoplasmic reticulum (ER) Ca(2+), plays a critical role in regulating cell proliferation and tumorigenesis. However, the role of ER lumen proteins in regulating cytosolic Ca(2+) level remains poorly understood. Here, we find that the Cab45S, localizes in the ER lumen, inhibits sarco/ER Ca(2+)-ATPase 2b (SERCA2b) activity through its first EF-hand domain directly binding to the intra-lumenal loop 4 of SERCA2b, and reduces ER Ca(2+). STIM1 activation, induced by the Cab45S-dependent drop in ER Ca(2+), together with the upregulation of the plasma membrane Ca(2+) channel TRPC1 ultimately increases extracellular Ca(2+) influx. Furthermore, increased cytosolic Ca(2+) level elicits Ca(2+)-NFAT signaling and promotes cell proliferation. Consistently, in cervical carcinoma patients, Cab45S is upregulated. Thus, our data reveal that the ability of Cab45S to inhibit SERCA2b activity is crucial for its role as a modulator of cell proliferation and tumor growth.

Open Sesame: treasure in store-operated calcium entry pathway for cancer therapy

Store-operated Ca²⁺ entry (SOCE) controls intracellular Ca²⁺ homeostasis and regulates a wide range of cellular events including proliferation, migration and invasion. The discovery of STIM proteins as Ca²⁺ sensors and Orai proteins as Ca²⁺ channel pore forming units provided molecular tools to understand the physiological function of SOCE. Many studies have revealed the pathophysiological roles of Orai and STIM in tumor cells. This review focuses on recent advances in SOCE and its contribution to tumorigenesis. Altered Orai and/or STIM functions may serve as biomarkers for cancer prognosis, and targeting the SOCE pathway may provide a novel means for cancer treatment.

A protease-independent function for SPPL3 in NFAT activation

The signal peptide peptidase (SPP)-related intramembrane aspartyl proteases are a homologous group of polytopic membrane proteins, some of which function in innate or adaptive immunity by cleaving proteins involved in antigen presentation or intracellular signaling. Signal peptide peptidase-like 3 (SPPL3) is a poorly characterized endoplasmic reticulum (ER)-localized member of this family, with no validated cellular substrates. We report here the isolation of SPPL3 in a screen for activators of NFAT, a transcription factor that controls lymphocyte development and function. We find that SPPL3 is required downstream of T cell receptor engagement for maximal Ca(2+) influx and NFAT activation. Surprisingly, the proteolytic activity of SPPL3 is not required for its role in this pathway. SPPL3 enhances the signal-induced association of stromal interaction molecule 1 (STIM1) and Orai1 and is even required for the full activity of constitutively active STIM1 variants that bind Orai1 independently of ER Ca(2+) release. SPPL3 associates with STIM1 through at least two independent domains, the transmembrane region and the CRAC activation domain (CAD), and can promote the association of the STIM1 CAD with Orai1. Our results assign a function in lymphocyte signaling to SPPL3 and highlight the emerging importance of nonproteolytic functions for members of the intramembrane aspartyl protease family.

Peripheral serotonin regulates maternal calcium trafficking in mammary epithelial cells during lactation in mice

Lactation is characterized by massive transcellular flux of calcium, from the basolateral side of the mammary alveolar epithelium (blood) into the ductal lumen (milk). Regulation of calcium transport during lactation is critical for maternal and neonatal health. The monoamine serotonin (5-HT) is synthesized by the mammary gland and functions as a homeostatic regulation of lactation. Genetic ablation of tryptophan hydroxylase 1 (Tph1), which encodes the rate-limiting enzyme in non-neuronal serotonin synthesis, causes a deficiency in circulating serotonin. As a consequence maternal calcium concentrations decrease, mammary epithelial cell morphology is altered, and cell proliferation is decreased during lactation. Here we demonstrate that serotonin deficiency decreases the expression and disrupts the normal localization of calcium transporters located in the apical (PMCA2) and basolateral (CaSR, ORAI-1) membranes of the lactating mammary gland. In addition, serotonin deficiency decreases the mRNA expression of calcium transporters located in intracellular compartments (SERCA2, SPCA1 and 2). Mammary expression of serotonin receptor isoform 2b and its downstream pathways (PLCβ3, PKC and MAP-ERK_1/2) are also decreased by serotonin deficiency, which might explain the numerous phenotypic alterations described above. In most cases, addition of exogenous 5-hydroxy-L-tryptophan to the Tph1 deficient mice rescued the phenotype. Our data supports the hypothesis that serotonin is necessary for proper mammary gland structure and function, to regulate blood and mammary epithelial cell transport of calcium during lactation. These findings can be applicable to the treatment of lactation-induced hypocalcemia in dairy cows and can have profound implications in humans, given the wide-spread use of selective serotonin reuptake inhibitors as antidepressants during pregnancy and lactation.

Calcium-dependent FAK/CREB/TNNC1 signalling mediates the effect of stromal MFAP5 on ovarian cancer metastatic potential

Ovarian cancer is the most lethal gynaecologic malignancy in the United States, and advanced serous ovarian adenocarcinoma is responsible for most ovarian cancer deaths. However, the stroma-derived molecular determinants that modulate patient survival are yet to be characterized. Here we identify a stromal gene signature for advanced high-grade serous ovarian cancer using microdissected stromal ovarian tumour samples and find that stromal microfibrillar-associated protein 5 (MFAP5) is a prognostic marker for poor survival. Further functional studies reveal that FAK/CREB/TNNC1 signalling pathways mediate the effect of MFAP5 on ovarian cancer cell motility and invasion potential. Targeting stromal MFAP5 using MFAP5-specific siRNA encapsulated in chitosan nanoparticles significantly decreases ovarian tumour growth and metastasis in vivo, suggesting that it may be a new modality of ovarian cancer treatment.

Remodeling of channel-forming ORAI proteins determines an oncogenic switch in prostate cancer

ORAI family channels have emerged as important players in malignant transformation, yet the way in which they reprogram cancer cells remains elusive. Here we show that the relative expression levels of ORAI proteins in prostate cancer are different from that in noncancerous tissue. By mimicking ORAI protein remodeling observed in primary tumors, we demonstrate in in vitro models that enhanced ORAI3 expression favors heteromerization with ORAI1 to form a novel channel. These channels support store-independent Ca(2+) entry, thereby promoting cell proliferation and a smaller number of functional homomeric ORAI1-based store-operated channels, which are important in supporting susceptibility to apoptosis. Thus, our findings highlight disrupted dynamic equilibrium of channel-forming proteins as an oncogenic mechanism.

Gene expression correlations in human cancer cell lines define molecular interaction networks for epithelial phenotype

Using gene expression data to enhance our knowledge of control networks relevant to cancer biology and therapy is a challenging but urgent task. Based on the premise that genes that are expressed together in a variety of cell types are likely to functions together, we derived mutually correlated genes that function together in various processes in epithelial-like tumor cells. Expression-correlated genes were derived from data for the NCI-60 human tumor cell lines, as well as data from the Broad Institute's CCLE cell lines. NCI-60 cell lines that selectively expressed a mutually correlated subset of tight junction genes served as a signature for epithelial-like cancer cells. Those signature cell lines served as a seed to derive other correlated genes, many of which had various other epithelial-related functions. Literature survey yielded molecular interaction and function information about those genes, from which molecular interaction maps were assembled. Many of the genes had epithelial functions unrelated to tight junctions, demonstrating that new function categories were elicited. The most highly correlated genes were implicated in the following epithelial functions: interactions at tight junctions (CLDN7, CLDN4, CLDN3, MARVELD3, MARVELD2, TJP3, CGN, CRB3, LLGL2, EPCAM, LNX1); interactions at adherens junctions (CDH1, ADAP1, CAMSAP3); interactions at desmosomes (PPL, PKP3, JUP); transcription regulation of cell-cell junction complexes (GRHL1 and 2); epithelial RNA splicing regulators (ESRP1 and 2); epithelial vesicle traffic (RAB25, EPN3, GRHL2, EHF, ADAP1, MYO5B); epithelial Ca(+2) signaling (ATP2C2, S100A14, BSPRY); terminal differentiation of epithelial cells (OVOL1 and 2, ST14, PRSS8, SPINT1 and 2); maintenance of apico-basal polarity (RAB25, LLGL2, EPN3). The findings provide a foundation for future studies to elucidate the functions of regulatory networks specific to epithelial-like cancer cells and to probe for anti-cancer drug targets.

Orai1 and STIM1 are critical for cell migration and proliferation of clear cell renal cell carcinoma

The intracellular Ca(2+) regulation has been implicated in tumorigenesis and tumor progression. Notably, store-operated Ca(2+) entry (SOCE) is a major Ca(2+) entry mechanism in non-excitable cells, being involved in cell proliferation and migration in several types of cancer. However, the expression and biological role of SOCE have not been investigated in clear cell renal cell carcinoma (ccRCC). Here, we demonstrate that Orai1 and STIM1, not Orai3, are crucial components of SOCE in the progression of ccRCC. The expression levels of Orai1 in tumor tissues were significantly higher than those in the adjacent normal parenchymal tissues. In addition, native SOCE was blunted by inhibiting SOCE or by silencing Orai1 and STIM1. Pharmacological blockade or knockdown of Orai1 or STIM1 also significantly inhibited RCC cell migration and proliferative capability. Taken together, Orai1 is highly expressed in ccRCC tissues illuminating that Orai1-mediated SOCE may play an important role in ccRCC development. Indeed, Orai1 and STIM1 constitute a native SOCE pathway in ccRCC by promoting cell proliferation and migration.

Not expecting the unexpected: diacylglycerol kinase alpha as a cancer target

In this issue of Cancer Discovery, Dominguez and colleagues identify diacylglycerol kinase alpha (DGKα), an enzyme that converts the membrane lipid diacylglycerol to phosphatidic acid, as a central node upstream of mTOR and other oncogenic pathways. Importantly, targeting DGKα causes apoptosis in cancer cells and tumor growth inhibition in mice with no overt toxicity, implicating DGKα as a novel cancer-specific target.

KCa and Ca(2+) channels: the complex thought

Potassium channels belong to the largest and the most diverse super-families of ion channels. Among them, Ca(2+)-activated K(+) channels (KCa) comprise many members. Based on their single channel conductance they are divided into three subfamilies: big conductance (BKCa), intermediate conductance (IKCa) and small conductance (SKCa; SK1, SK2 and SK3). Ca(2+) channels are divided into two main families, voltage gated/voltage dependent Ca(2+) channels and non-voltage gated/voltage independent Ca(2+) channels. Based on their electrophysiological and pharmacological properties and on the tissue where there are expressed, voltage gated Ca(2+) channels (Cav) are divided into 5 families: T-type, L-type, N-type, P/Q-type and R-type Ca(2+). Non-voltage gated Ca(2+) channels comprise the TRP (TRPC, TRPV, TRPM, TRPA, TRPP, TRPML and TRPN) and Orai (Orai1 to Orai3) families and their partners STIM (STIM1 to STIM2). A depolarization is needed to activate voltage-gated Ca(2+) channels while non-voltage gated Ca(2+) channels are activated by Ca(2+) depletion of the endoplasmic reticulum stores (SOCs) or by receptors (ROCs). These two Ca(2+) channel families also control constitutive Ca(2+) entries. For reducing the energy consumption and for the fine regulation of Ca(2+), KCa and Ca(2+) channels appear associated as complexes in excitable and non-excitable cells. Interestingly, there is now evidence that KCa-Ca(2+) channel complexes are also found in cancer cells and contribute to cancer-associated functions such as cell proliferation, cell migration and the capacity to develop metastases. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

Orai1 and STIM1 mediate SOCE and contribute to apoptotic resistance of pancreatic adenocarcinoma

The store-operated calcium channels (SOCs) represent one of the major calcium-entry pathways in non-excitable cells. SOCs and in particular their major components ORAI1 and STIM1 have been shown to be implicated in a number of physiological and pathological processes such as apoptosis, proliferation and invasion. Here we demonstrate that ORAI1 and STIM1 mediate store-operated calcium entry (SOCE) in pancreatic adenocarcinoma cell lines. We show that both ORAI1 and STIM1 play pro-survival anti-apoptotic role in pancreatic adenocarcinoma cell lines, as siRNA-mediated knockdown of ORAI1 and/or STIM1 increases apoptosis induced by chemotherapy drugs 5-fluorouracil (5-FU) or gemcitabine. We also demonstrate that both 5-FU and gemcitabine treatments increase SOCE in Panc1 pancreatic adenocarcinoma cell line via upregulation of ORAI1 and STIM1. Altogether our results reveal the novel calcium-dependent mechanism of action of the chemotherapy drugs 5-FU and gemcitabine and emphasize the anti-apoptotic role of ORAI1 and STIM1 in pancreatic adenocarcinoma cells. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

The Ca(2+)/H(+) antiporter TMEM165 expression, localization in the developing, lactating and involuting mammary gland parallels the secretory pathway Ca(2+) ATPase (SPCA1)

Plasma membrane Ca(2+)-ATPase 2 (PMCA2) knockout mice showed that ~60% of calcium in milk is transported across the mammary cells apical membrane by PMCA2. The remaining milk calcium is thought to arrive via the secretory pathway through the actions of secretory pathway Ca(2+)-ATPase's 1 and/or 2 (SPCA1 and 2). However, another secretory pathway calcium transporter was recently described. The question becomes whether this Golgi Ca(2+)/H(+) antiporter (TMEM165) is expressed sufficiently in the Golgi of lactating mammary tissue to be a relevant contributor to secretory pathway mammary calcium transport. TMEM165 shows marked expression on day one of lactation when compared to timepoints prepartum. At peak lactation TMEM165 expression was 25 times greater than that of early pregnancy. Forced cessation of lactation resulted in a rapid ~50% decline in TMEM165 expression at 24h of involution and TMEM165 expression declined 95% at 96 h involution. It is clear that the timing, magnitude of TMEM165 expression and its Golgi location supports a role for this Golgi Ca2(+)/H(+) antiporter as a contributor to mammary Golgi calcium transport needs, in addition to the better-characterized roles of SPCA1&2.

Molecular regulation of the pore component of CRAC channels, Orai1

Store-operated Ca(2+) entry (SOCE) is a fundamental mechanism ubiquitously employed by cells to elevate intracellular Ca(2+) concentrations ([Ca(2+)]i). Increased intracellular Ca(2+) ions act as a second messenger that can stimulate a variety of downstream signaling pathways affecting proliferation, secretion, differentiation, and death of cells. In immune cells, immune receptor stimulation induces endoplasmic reticulum Ca(2+) store depletion that subsequently activates Ca(2+)-release-activated-Ca(2+) (CRAC) channels, a prototype of store-operated Ca(2+) (SOC) channels. Identification of Orai1 as the pore subunit of CRAC channels has provided the much-needed molecular tool to dissect the mechanism of activation and regulation of these channels. In this review, we discuss the recent advances in understanding the regulatory mechanisms and posttranslational modifications that regulate diverse aspects of CRAC channel function.

The neglected CRAC proteins: Orai2, Orai3, and STIM2

Plasma-membrane-localized Orai1 ion channel subunits interacting with ER-localized STIM1 molecules comprise the major subunit composition responsible for calcium release-activated calcium channels. STIM1 "translates" the Ca(2+) store content into Orai1 activity, making it a store-operated channel. Surprisingly, in addition to being the physical activator, STIM1 also modulates Orai1 properties, including its inactivation and permeation (see Chapter 1). STIM1 is thus more than a pure Orai1 activator. Within the past 7 years following the discovery of STIM and Orai proteins, the molecular mechanisms of STIM1/Orai1 activity and their functional importance have been studied in great detail. Much less is currently known about the other isoforms STIM2, Orai2, and Orai3. In this chapter, we summarize the current knowledge about STIM2, Orai2, and Orai3 properties and function. Are these homologues mainly modulators of predominantly STIM1/Orai1-mediated complexes or do store-dependent or -independent functions such as regulation of basal Ca(2+) concentration and activation of Orai3-containing complexes by arachidonic acid or by estrogen receptors point toward their "true" physiological function? Is Orai2 the Orai1 of neurons? A major focus of the review is on the functional relevance of STIM2, Orai2, and Orai3, some of which still remains speculative.

Remodelling of Ca2+ transport in cancer: how it contributes to cancer hallmarks?

Cancer involves defects in the mechanisms underlying cell proliferation, death and migration. Calcium ions are central to these phenomena, serving as major signalling agents with spatial localization, magnitude and temporal characteristics of calcium signals ultimately determining cell's fate. Cellular Ca(2+) signalling is determined by the concerted action of a molecular Ca(2+)-handling toolkit which includes: active energy-dependent Ca(2+) transporters, Ca(2+)-permeable ion channels, Ca(2+)-binding and storage proteins, Ca(2+)-dependent effectors. In cancer, because of mutations, aberrant expression, regulation and/or subcellular targeting of Ca(2+)-handling/transport protein(s) normal relationships among extracellular, cytosolic, endoplasmic reticulum and mitochondrial Ca(2+) concentrations or spatio-temporal patterns of Ca(2+) signalling become distorted. This causes deregulation of Ca(2+)-dependent effectors that control signalling pathways determining cell's behaviour in a way to promote pathophysiological cancer hallmarks such as enhanced proliferation, survival and invasion. Despite the progress in our understanding of Ca(2+) homeostasis remodelling in cancer cells as well as in identification of the key Ca(2+)-transport molecules promoting certain malignant phenotypes, there is still a lot of work to be done to transform fundamental findings and concepts into new Ca(2+) transport-targeting tools for cancer diagnosis and treatment.

Calcium influx pathways in breast cancer: opportunities for pharmacological intervention

Ca(2+) influx through Ca(2+) permeable ion channels is a key trigger and regulator of a diverse set of cellular events, such as neurotransmitter release and muscle contraction. Ca(2+) influx is also a regulator of processes relevant to cancer, including cellular proliferation and migration. This review focuses on calcium influx in breast cancer cells as well as the potential for pharmacological modulators of specific Ca(2+) influx channels to represent future agents for breast cancer therapy. Altered expression of specific calcium permeable ion channels is present in some breast cancers. In some cases, such changes can be related to breast cancer subtype and even prognosis. In vitro and in vivo models have now helped identify specific Ca(2+) channels that play important roles in the proliferation and invasiveness of breast cancer cells. However, some aspects of our understanding of Ca(2+) influx in breast cancer still require further study. These include identifying the mechanisms responsible for altered expression and the most effective therapeutic strategy to target breast cancer cells through specific Ca(2+) channels. The role of Ca(2+) influx in processes beyond breast cancer cell proliferation and migration should become the focus of studies in the next decade.

Methods to measure cytoplasmic and mitochondrial Ca(2+) concentration using Ca(2+)-sensitive dyes

Ca(2+) is a ubiquitous second messenger that is involved in regulation of various signaling pathways. Cytoplasmic Ca(2+) is maintained at low concentrations (~100 nM) by many active mechanisms. Increases in intracellular Ca(2+) concentration ([Ca(2+)]i) indeed can initiate multiple signaling pathways, depending both on their pattern and subcellular localization. In T cells, the stimulation of T-cell receptor leads to an increase in [Ca(2+)]i upon the opening of Ca(2+) release-activated calcium (CRAC) channels. T cells can actually sustain high [Ca(2+)]i for several hours, resulting in the activation of transcriptional programs orchestrated by members of the nuclear factor of activated T-cell (NFAT) protein family. Here, we describe an imaging method widely employed to measure cytoplasmic [Ca(2+)] in naïve and effector T cells based on the ratiometric dye Fura-2. Furthermore, we discuss a pharmacological method relying on an inhibitor of CRAC channels, 2-aminoethyldiphenyl borate, to validate the role of CRAC channels in cytoplasmic Ca(2+) elevation. Finally, we describe an approach to measure mitochondrial [Ca(2+)] based on another fluorescent dye, Rhod-2. With appropriate variations, our methodological approach can be employed to assess the effect and regulation of cytosolic and mitochondrial Ca(2+) waves in multiple experimental settings, including cultured cancer cells.

Assessment of ORAI1-mediated basal calcium influx in mammary epithelial cells

BACKGROUND

The entry of calcium ions into mammary gland epithelial cells is one of the least well-understood processes in the transport of calcium into milk during lactation. The store-operated calcium entry channel ORAI1, has been suggested as a potential mechanism for the entry of Ca(2+) into mammary gland epithelial cells from the maternal blood supply during lactation. The down regulation of the canonical ORAI1 activator STIM1 during lactation suggests that other known ORAI activators such as STIM2 and SPCA2 may be important during lactation.

RESULTS

Differentiation of HC11 mammary gland epithelial cells was associated with enhanced basal Ca(2+) influx. Silencing of Orai1 abolished this enhancement of Ca(2+) influx. Stim2 had a modest effect on Ca(2+) influx in this in vitro model of lactation, whereas Stim1 and Spca2 silencing had no effect. Despite pronounced increases in Spca2 mRNA during lactation there was no change in the generation of the alternative splice product generated by Mist1, which increases during lactation.

CONCLUSIONS

These studies support the hypothesis that lactation is associated with a remodelling of Ca(2+) influx and this is associated with enhancement of basal Ca(2+) influx. This enhanced Ca(2+) influx appears to occur through the calcium channel Orai1.

Cellular calcium dynamics in lactation and breast cancer: from physiology to pathology

Breast cancer is the second leading cause of cancer mortality in women, estimated at nearly 40,000 deaths and more than 230,000 new cases diagnosed in the U.S. this year alone. One of the defining characteristics of breast cancer is the radiographic presence of microcalcifications. These palpable mineral precipitates are commonly found in the breast after formation of a tumor. Since free Ca(2+) plays a crucial role as a second messenger inside cells, we hypothesize that these chelated precipitates may be a result of dysregulated Ca(2+) secretion associated with tumorigenesis. Transient and sustained elevations of intracellular Ca(2+) regulate cell proliferation, apoptosis and cell migration, and offer numerous therapeutic possibilities in controlling tumor growth and metastasis. During lactation, a developmentally determined program of gene expression controls the massive transcellular mobilization of Ca(2+) from the blood into milk by the coordinated action of calcium transporters, including pumps, channels, sensors and buffers, in a functional module that we term CALTRANS. Here we assess the evidence implicating genes that regulate free and buffered Ca(2+) in normal breast epithelium and cancer cells and discuss mechanisms that are likely to contribute to the pathological characteristics of breast cancer.

hGAAP promotes cell adhesion and migration via the stimulation of store-operated Ca2+ entry and calpain 2

Golgi antiapoptotic proteins (GAAPs) are highly conserved Golgi membrane proteins that inhibit apoptosis and promote Ca(2+) release from intracellular stores. Given the role of Ca(2+) in controlling cell adhesion and motility, we hypothesized that human GAAP (hGAAP) might influence these events. In this paper, we present evidence that hGAAP increased cell adhesion, spreading, and migration in a manner that depended on the C-terminal domain of hGAAP. We show that hGAAP increased store-operated Ca(2+) entry and thereby the activity of calpain at newly forming protrusions. These hGAAP-dependent effects regulated focal adhesion dynamics and cell migration. Indeed, inhibition or knockdown of calpain 2 abrogated the effects of hGAAP on cell spreading and migration. Our data reveal that hGAAP is a novel regulator of focal adhesion dynamics, cell adhesion, and migration by controlling localized Ca(2+)-dependent activation of calpain.

Assessment of gene expression of intracellular calcium channels, pumps and exchangers with epidermal growth factor-induced epithelial-mesenchymal transition in a breast cancer cell line

Background

Epithelial-mesenchymal transition (EMT) is a process implicated in cancer metastasis that involves the conversion of epithelial cells to a more mesenchymal and invasive cell phenotype. In breast cancer cells EMT is associated with altered store-operated calcium influx and changes in calcium signalling mediated by activation of cell surface purinergic receptors. In this study, we investigated whether MDA-MB-468 breast cancer cells induced to undergo EMT exhibit changes in mRNA levels of calcium channels, pumps and exchangers located on intracellular calcium storing organelles, including the Golgi, mitochondria and endoplasmic reticulum (ER).

Methods

Epidermal growth factor (EGF) was used to induce EMT in MDA-MB-468 breast cancer cells. Serum-deprived cells were treated with EGF (50 ng/mL) for 12 h and gene expression was assessed using quantitative RT-PCR.

Results and conclusions

These data reveal no significant alterations in mRNA levels of the Golgi calcium pump secretory pathway calcium ATPases (SPCA1 and SPCA2), or the mitochondrial calcium uniporter (MCU) or Na⁺/Ca²⁺ exchanger (NCLX). However, EGF-induced EMT was associated with significant alterations in mRNA levels of specific ER calcium channels and pumps, including (sarco)-endoplasmic reticulum calcium ATPases (SERCAs), and inositol 1,4,5-trisphosphate receptor (IP₃R) and ryanodine receptor (RYR) calcium channel isoforms. The most prominent change in gene expression between the epithelial and mesenchymal-like states was RYR2, which was enriched 45-fold in EGF-treated MDA-MB-468 cells. These findings indicate that EGF-induced EMT in breast cancer cells may be associated with major alterations in ER calcium homeostasis.

SPCA2 regulates Orai1 trafficking and store independent Ca2+ entry in a model of lactation

An unconventional interaction between SPCA2, an isoform of the Golgi secretory pathway Ca(2+)-ATPase, and the Ca(2+) influx channel Orai1, has previously been shown to contribute to elevated Ca(2+) influx in breast cancer derived cells. In order to investigate the physiological role of this interaction, we examined expression and localization of SPCA2 and Orai1 in mouse lactating mammary glands. We observed co-induction and co-immunoprecipitation of both proteins, and isoform-specific differences in the localization of SPCA1 and SPCA2. Three-dimensional cultures of normal mouse mammary epithelial cells were established using lactogenic hormones and basement membrane. The mammospheres displayed elevated Ca(2+) influx by store independent mechanisms, consistent with upregulation of both SPCA2 and Orai1. Knockdown of either SPCA2 or Orai1 severely depleted Ca(2+) influx and interfered with mammosphere differentiation. We show that SPCA2 is required for plasma membrane trafficking of Orai1 in mouse mammary epithelial cells and that this function can be replaced, at least in part, by a membrane-anchored C-terminal domain of SPCA2. These findings clearly show that SPCA2 and Orai1 function together to regulate Store-independent Ca(2+) entry (SICE), which mediates the massive basolateral Ca(2+) influx into mammary epithelia to support the large calcium transport requirements for milk secretion.

Emerging roles of Orai3 in pathophysiology

Calcium (Ca(2+)) is a ubiquitous second messenger that regulates a plethora of physiological functions. Deregulation of calcium homeostasis has been reported in a wide variety of pathological conditions including cardiovascular disorders, cancer and neurodegenerative diseases. One of the most ubiquitous pathways involved in regulated Ca(2+) influx into cells is the store-operated Ca(2+) entry (SOCE) pathway. In 2006, Orai1 was identified as the channel protein that mediates SOCE in immune cells. Orai1 has two mammalian homologs, Orai2 and Orai3. Although Orai1 has been the most widely studied Orai isoform, Orai3 has recently received significant attention. Under native conditions, Orai3 was demonstrated to be an important component of store-independent arachidonate-regulated Ca(2+) (ARC) entry in HEK293 cells, and more recently of a store-independent leukotrieneC4-regulated Ca(2+) (LRC) entry pathway in vascular smooth muscle cells. Recent studies have shown upregulation of Orai3 in estrogen receptor-expressing breast cancers and a critical role for Orai3 in breast cancer development in immune-compromised mice. Orai3 upregulation was also shown to contribute to vascular smooth muscle remodeling and neointimal hyperplasia caused by vascular injury. Furthermore, Orai3 has been shown to contribute to proliferation of effector T-lymphocytes under oxidative stress. In this review, we will discuss the role of Orai3 in reported pathophysiological conditions and will contribute ideas on the potential role of Orai3 in native Ca(2+) signaling pathways and human disease.

New insights into store-independent Ca(2+) entry: secretory pathway calcium ATPase 2 in normal physiology and cancer

Recent studies in secretory pathway calcium ATPases (SPCA) revealed novel functions of SPCA2 in interacting with store-operated Ca(2+) channel Orai1 and inducing Ca(2+) influx at the cell surface. Importantly, SPCA2-mediated Ca(2+) signaling is uncoupled from its conventional role of Ca(2+)-ATPase and independent of store-operated Ca(2+) signaling pathway. SPCA2-induced store-independent Ca(2+) entry (SICE) plays essential roles in many important physiological processes, while unbalanced SICE leads to enhanced cell proliferation and tumorigenesis. Finally, we have summarized the clinical implication of SICE in oral cancer prognosis and treatment. Inhibition of SICE may be a new target for the development of cancer therapeutics.

Remodeling of calcium signaling in tumor progression

Intracellular Ca²⁺ is one of the crucial signalings that modulate various cellular functions. The dysregulation of Ca²⁺ homeostasis has been suggested as an important event in driving the expression of the malignant phenotypes, such as proliferation, migration, invasion, and metastasis. Cell migration is an early prerequisite for tumor metastasis that has a significant impact on patient prognosis. During cell migration, the exquisite spatial and temporal organization of intracellular Ca²⁺ provides a rapid and robust way for the selective activation of signaling components that play a central role in cytoskeletal reorganization, traction force generation, and focal adhesion dynamics. A number of known molecular components involved in Ca²⁺ influx pathways, including stromal interaction molecule (STIM)/Orai-mediated store-operated Ca²⁺ entry (SOCE) and the Ca²⁺-permeable transient receptor potential (TRP) channels, have been implicated in cancer cell migration and tumor metastasis. The clinical significance of these molecules, such as STIM proteins and the TRPM7 channel, in tumor progression and their diagnostic and prognostic potentials have also been demonstrated in specific cancer types. In this review, we summarize the recent advances in understanding the important roles and regulatory mechanisms of these Ca²⁺ influx pathways on malignant behaviors of tumor cells. The clinical implications in facilitating current diagnostic and therapeutic procedures are also discussed.

STIM1 and Orai1 mediate CRAC channel activity and are essential for human glioblastoma invasion

The Ca(2+) sensor stromal interacting molecule 1 (STIM1) and the Ca(2+) channel Orai1 mediate the ubiquitous store-operated Ca(2+) entry (SOCE) pathway activated by depletion of internal Ca(2+) stores and mediated through the highly Ca(2+)-selective, Ca(2+) release-activated Ca(2+) (CRAC) current. Furthermore, STIM1 and Orai1, along with Orai3, encode store-independent Ca(2+) currents regulated by either arachidonate or its metabolite, leukotriene C4. 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(2+) 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.

Emerging roles of store-operated Ca²⁺ entry through STIM and ORAI proteins in immunity, hemostasis and cancer

Store-operated Ca(2+) entry (SOCE) is an important Ca(2+) influx pathway, which is defined by the fact that depletion of intracellular Ca(2+) stores, mainly the endoplasmic reticulum (ER), triggers the opening of Ca(2+) channels in the plasma membrane. The best characterized SOC channel is the Ca(2+) release-activated Ca(2+) (CRAC) channel, which was first described in cells of the immune system but has since been reported in many different cell types. CRAC channels are multimers of ORAI family proteins, of which ORAI1 is the best characterized. They are activated by stromal interaction molecules (STIM) 1 and 2, which respond to the depletion of intracellular Ca(2+) stores with oligomerization and binding to ORAI proteins. The resulting SOCE is critical for the physiological function of many cell types including immune cells and platelets. Recent studies using cell lines, animal models and primary cells from human patients with defects in SOCE have highlighted the importance of this Ca(2+) entry mechanism in a variety of pathophysiological processes. This review focuses on the role of SOCE in immunity to infection, allergy, hemostasis and cancer.

Regulation of CRAC channels by protein interactions and post-translational modification

Store-operated Ca(2+) entry (SOCE) is a widespread mechanism to elevate the intracellular Ca(2+) concentrations and stimulate downstream signaling pathways affecting proliferation, secretion, differentiation and death in different cell types. In immune cells, immune receptor stimulation induces intracellular Ca(2+) store depletion that subsequently activates Ca(2+)-release-activated-Ca(2+) (CRAC) channels, a prototype of store-operated Ca(2+) (SOC) channels. CRAC channel opening leads to activation of diverse downstream signaling pathways affecting proliferation, differentiation, cytokine production and cell death. Recent identification of STIM1 as the endoplasmic reticulum Ca(2+) sensor and Orai1 as the pore subunit of CRAC channels has provided the much-needed molecular tools to dissect the mechanism of activation and regulation of CRAC channels. In this review, we discuss the recent advances in understanding the associating partners and posttranslational modifications of Orai1 and STIM1 proteins that regulate diverse aspects of CRAC channel function.

Orai1-NFAT signalling pathway triggered by T cell receptor stimulation

T cell receptor (TCR) stimulation plays a crucial role in development, homeostasis, proliferation, cell death, cytokine production, and differentiation of T cells. Thus, in depth understanding of TCR signalling is crucial for development of therapy targeting inflammatory diseases, improvement of vaccination efficiency, and cancer therapy utilizing T cell-based strategies. TCR activation turns on various signalling pathways, one of the important one being the Ca(2+)-calcineurin-nuclear factor of activated T cells (NFAT) signalling pathway. Stimulation of TCRs triggers depletion of intracellular Ca(2+) store and in turn, initiates store-operated Ca(2+) entry (SOCE), one of the major mechanisms to raise the intracellular Ca(2+) concentrations in T cells. Ca(2+)-release-activated-Ca(2+) (CRAC) channels are a prototype of store-operated Ca(2+) (SOC) channels in immune cells that are very well characterized. Recent identification of STIM1 as the endoplasmic reticulum (ER) Ca(2+) sensor and Orai1 as the pore subunit has dramatically advanced the understanding of CRAC channels and provides a molecular tool to investigate the physiological outcomes of Ca(2+) signalling during immune responses. In this review, we focus on our current understanding of CRAC channel activation, regulation, and downstream calcineurin-NFAT signaling pathway.

Cab45 is required for Ca(2+)-dependent secretory cargo sorting at the trans-Golgi network

The Golgi resident protein Cab45 is required for trans-Golgi network Ca²⁺ homeostasis and sorting of cargos that are destined for secretion.

Ca²⁺ import into the lumen of the trans-Golgi network (TGN) by the secretory pathway calcium ATPase1 (SPCA1) is required for the sorting of secretory cargo. How is Ca²⁺ retained in the lumen of the Golgi, and what is its role in cargo sorting? We show here that a soluble, lumenal Golgi resident protein, Cab45, is required for SPCA1-dependent Ca²⁺ import into the TGN; it binds secretory cargo in a Ca²⁺-dependent reaction and is required for its sorting at the TGN.

Overlapping ATP2C1 and ASTE1 genes in human genome: implications for SPCA1 expression?

The ATP2C1 gene encodes for the secretory pathway calcium (Ca²⁺)-ATPase pump (SPCA1), which localizes along the secretory pathway, mainly in the trans-Golgi. The loss of one ATP2C1 allele causes Hailey-Hailey disease in humans but not mice. Examining differences in genomic organization between mouse and human we speculate that the overlap between ATP2C1 and ASTE1 genes only in humans could explain this different response to ATP2C1 dysregulation. We propose that ASTE1, overlapping with ATP2C1 in humans, affects alternative splicing, and potentially protein expression of the latter. If dysregulated, the composition of the SPCA1 isoform pool could diverge from the physiological status, affecting cytosolic Ca²⁺-signaling, and in turn perturbing cell division, leading to cell death or to neoplastic transformation.

Store-operated Orai channels: structure and function

In many animal cells, store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels function as an essential route for Ca(2+) entry. CRAC channels control many fundamental cellular functions including gene expression, motility, and cell proliferation, are involved in the etiology of several disease processes including a severe combined immunodeficiency syndrome, and have emerged as major targets for drug development. Although little was known of the molecular mechanisms of CRAC channel operation for several decades, the discovery of Orai1 as a prototypic CRAC channel protein and STIM1 as the endoplasmic reticulum (ER) Ca(2+) sensor has led to rapid progress in our understanding of the mechanisms and functions of CRAC channels. It is now known that activation of CRAC channels following ER Ca(2+) store depletion is governed by several events, which include the redistributions and accumulations of STIM1 and Orai1 into overlapping puncta at peripheral cellular sites, resulting in direct protein-protein interactions between the two proteins. In this chapter, I review the molecular features of the STIM and Orai proteins that regulate the gating and ion conduction mechanisms of CRAC channels.

Calcium, cancer and killing: the role of calcium in killing cancer cells by cytotoxic T lymphocytes and natural killer cells

Killing cancer cells by cytotoxic T lymphocytes (CTL) and by natural killer (NK) cells is of vital importance. Cancer cell proliferation and apoptosis depend on the intracellular Ca(2+) concentration, and the expression of numerous ion channels with the ability to control intracellular Ca(2+) concentrations has been correlated with cancer. A rise of intracellular Ca(2+) concentrations is also required for efficient CTL and NK cell function and thus for killing their targets, in this case cancer cells. Here, we review the data on Ca(2+)-dependent killing of cancer cells by CTL and NK cells. In addition, we discuss emerging ideas and present a model how Ca(2+) may be used by CTL and NK cells to optimize their cancer cell killing efficiency. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

STIM proteins: dynamic calcium signal transducers

Stromal interaction molecule (STIM) proteins function in cells as dynamic coordinators of cellular calcium (Ca(2+)) signals. Spanning the endoplasmic reticulum (ER) membrane, they sense tiny changes in the levels of Ca(2+) stored within the ER lumen. As ER Ca(2+) is released to generate primary Ca(2+) signals, STIM proteins undergo an intricate activation reaction and rapidly translocate into junctions formed between the ER and the plasma membrane. There, STIM proteins tether and activate the highly Ca(2+)-selective Orai channels to mediate finely controlled Ca(2+) signals and to homeostatically balance cellular Ca(2+). Details are emerging on the remarkable organization within these STIM-induced junctional microdomains and the identification of new regulators and alternative target proteins for STIM.

mTORC1 enhancement of STIM1-mediated store-operated Ca2+ entry constrains tuberous sclerosis complex-related tumor development

The protein complex of tuberous sclerosis complex (TSC)1 and TSC2 tumor suppressors is a key negative regulator of mammalian target of rapamycin (mTOR). Hyperactive mTOR signaling due to the loss-of-function of mutations in either TSC1 or TSC2 gene causes TSC, an autosomal dominant disorder featured with benign tumors in multiple organs. As the ubiquitous second messenger calcium (Ca(2+)) regulates various cellular processes involved in tumorigenesis, we explored the potential role of mTOR in modulation of cellular Ca(2+) homeostasis, and in turn the effect of Ca(2+) signaling in TSC-related tumor development. We found that loss of Tsc2 potentiated store-operated Ca(2+) entry (SOCE) in an mTOR complex 1 (mTORC1)-dependent way. The endoplasmic reticulum Ca(2+) sensor, stromal interaction molecule 1 (STIM1), was upregulated in Tsc2-deficient cells, and was suppressed by mTORC1 inhibitor rapamycin. In addition, SOCE repressed AKT1 phosphorylation. Blocking SOCE either by depleting STIM1 or ectopically expressing dominant-negative Orai1 accelerated TSC-related tumor development, likely because of restored AKT1 activity and enhanced tumor angiogenesis. Our data, therefore, suggest that mTORC1 enhancement of store-operated Ca(2+) signaling hinders TSC-related tumor growth through suppression of AKT1 signaling. The augmented SOCE by hyperactive mTORC1-STIM1 cascade may contribute to the benign nature of TSC-related tumors. Application of SOCE agonists could thus be a contraindication for TSC patients. In contrast, SOCE agonists should attenuate mTOR inhibitors-mediated AKT reactivation and consequently potentiate their efficacy in the treatment of the patients with TSC.

Molecular regulation of CRAC channels and their role in lymphocyte function

Calcium (Ca(2+)) influx is required for the activation and function of all cells in the immune system. It is mediated mainly by store-operated Ca(2+) entry (SOCE) through Ca(2+) release-activated Ca(2+) (CRAC) channels located in the plasma membrane. CRAC channels are composed of ORAI proteins that form the channel pore and are activated by stromal interaction molecules (STIM) 1 and 2. Located in the membrane of the endoplasmic reticulum, STIM1 and STIM2 have the dual function of sensing the intraluminal Ca(2+) concentration in the ER and to activate CRAC channels. A decrease in the ER's Ca(2+) concentration induces STIM multimerization and translocation into puncta close to the plasma membrane where they bind to and activate ORAI channels. Since the identification of ORAI and STIM genes as the principal mediators of CRAC channel function, substantial advances have been achieved in understanding the molecular regulation and physiological role of CRAC channels in cells of the immune system and other organs. In this review, we discuss the mechanisms that regulate CRAC channel function and SOCE, the role of recently identified proteins and mechanisms that modulate the activation of ORAI/STIM proteins and the consequences of CRAC channel dysregulation for lymphocyte function and immunity.

Modification of STIM1 by O-linked N-acetylglucosamine (O-GlcNAc) attenuates store-operated calcium entry in neonatal cardiomyocytes

Store-operated calcium entry (SOCE) is a major Ca(2+) signaling pathway responsible for regulating numerous transcriptional events. In cardiomyocytes SOCE has been shown to play an important role in regulating hypertrophic signaling pathways, including nuclear translocation of NFAT. Acute activation of pathways leading to O-GlcNAc synthesis have been shown to impair SOCE-mediated transcription and in diabetes, where O-GlcNAc levels are chronically elevated, cardiac hypertrophic signaling is also impaired. Therefore the goal of this study was to determine whether changes in cardiomyocyte O-GlcNAc levels impaired the function of STIM1, a widely recognized mediator of SOCE. We demonstrated that acute activation of SOCE in neonatal cardiomyocytes resulted in STIM1 puncta formation, which was inhibited in a dose-dependent manner by increasing O-GlcNAc synthesis with glucosamine or inhibiting O-GlcNAcase with thiamet-G. Glucosamine and thiamet-G also inhibited SOCE and were associated with increased O-GlcNAc modification of STIM1. These results suggest that activation of cardiomyocyte O-GlcNAcylation attenuates SOCE via STIM1 O-GlcNAcylation and that this may represent a new mechanism by which increased O-GlcNAc levels regulate Ca(2+)-mediated events in cardiomyocytes. Further, since SOCE is a fundamental mechanism underlying Ca(2+) signaling in most cells and tissues, it is possible that STIM1 represents a nexus linking protein O-GlcNAcylation with Ca(2+)-mediated transcription.

Orai3 is an estrogen receptor α-regulated Ca²⁺ channel that promotes tumorigenesis

Store-operated Ca(2+) entry (SOCE) encoded by Orai1 proteins is a ubiquitous Ca(2+)-selective conductance involved in cellular proliferation and migration. We recently described up-regulation of Orai3 channels that selectively mediate SOCE in estrogen receptor α-expressing (ERα(+)) breast cancer cells. However, the connection between ERα and Orai3 and the role of Orai3 in tumorigenesis remain unknown. Here, we show that ERα knockdown decreases Orai3 mRNA (by ∼63%) and protein (by ∼44%) with no effect on Orai1. ERα knockdown decreases Orai3-mediated SOCE (by ∼43%) and the corresponding Ca(2+) release-activated Ca(2+) (CRAC) current (by ∼42%) in ERα(+) MCF7 cells. The abrogation of SOCE in MCF7 cells on ERα knockdown can be rescued by ectopic expression of Orai3. ERα activation increased Orai3 expression and SOCE in MCF7 cells. Epidermal growth factor (EGF) and thrombin stimulate Ca(2+) influx into MCF7 cells through Orai3. Orai3 knockdown inhibited SOCE-dependent phosphorylation of extracellular signal-regulated kinase (ERK1/2; by ∼44%) and focal adhesion kinase (FAK; by ∼46%) as well as transcriptional activity of nuclear factor for activated T cells (NFAT; by ∼49%). Significantly, Orai3 knockdown selectively decreased anchorage-independent growth (by ∼58%) and Matrigel invasion (by ∼44%) of ERα(+) MCF7 cells with no effect on ERα(-) MDA-MB231 cells. Moreover, Orai3 knockdown inhibited ERα(+) cell tumorigenesis in immunodeficient mice (∼66% reduction in tumor volume). These data establish Orai3 as an ERα-regulated channel and a potential selective therapeutic target for ERα(+) breast cancers.

STIM1 regulates platelet-derived growth factor-induced migration and Ca2+ influx in human airway smooth muscle cells

It is suggested that migration of airway smooth muscle (ASM) cells plays an important role in the pathogenesis of airway remodeling in asthma. Increases in intracellular Ca(2+) concentrations ([Ca(2+)](i)) regulate most ASM cell functions related to asthma, such as contraction and proliferation. Recently, STIM1 was identified as a sarcoplasmic reticulum (SR) Ca(2+) sensor that activates Orai1, the Ca(2+) channel responsible for store-operated Ca(2+) entry (SOCE). We investigated the role of STIM1 in [Ca(2+)](i) and cell migration induced by platelet-derived growth factor (PDGF)-BB in human ASM cells. Cell migration was assessed by a chemotaxis chamber assay. Human ASM cells express STIM1, STIM2, and Orai1 mRNAs. SOCE activated by thapsigargin, an inhibitor of SR Ca(2+)-ATPase, was significantly blocked by STIM1 siRNA and Orai1 siRNA but not by STIM2 siRNA. PDGF-BB induced a transient increase in [Ca(2+)](i) followed by sustained [Ca(2+)](i) elevation. Sustained increases in [Ca(2+)](i) due to PDGF-BB were significantly inhibited by a Ca(2+) chelating agent EGTA or by siRNA for STIM1 or Orai1. The numbers of migrating cells were significantly increased by PDGF-BB treatment for 6 h. Knockdown of STIM1 and Orai1 by siRNA transfection inhibited PDGF-induced cell migration. Similarly, EGTA significantly inhibited PDGF-induced cell migration. In contrast, transfection with siRNA for STIM2 did not inhibit the sustained elevation of [Ca(2+)](i) or cell migration induced by PDGF-BB. These results demonstrate that STIM1 and Orai1 are essential for PDGF-induced cell migration and Ca(2+) influx in human ASM cells. STIM1 could be an important molecule responsible for airway remodeling.

Calcium channels and pumps in cancer: changes and consequences

Increases in intracellular free Ca(2+) play a major role in many cellular processes. The deregulation of Ca(2+) signaling is a feature of a variety of diseases, and modulators of Ca(2+) signaling are used to treat conditions as diverse as hypertension to pain. The Ca(2+) signal also plays a role in processes important in cancer, such as proliferation and migration. Many studies in cancer have identified alterations in the expression of proteins involved in the movement of Ca(2+) across the plasma membrane and subcellular organelles. In some cases, these Ca(2+) channels or pumps are potential therapeutic targets for specific cancer subtypes or correlate with prognosis.

The association between single-nucleotide polymorphisms of ORAI1 gene and breast cancer in a Taiwanese population

Background. Breast cancer is the most common malignancy in women. There is increasing evidence suggesting that ORAI1, components of store-operated calcium channel, play a pivotal role in breast cancer progression and metastasis. Methods. A total of 384 female patients with breast cancer were included in this study. We selected five representative tagging ORAI1 SNPs from HapMap database with minimum allele frequency (MAF) >10%. Genotyping was performed using TaqMan allelic discrimination assay. Chi-square (χ²) test was used to analyze statistical differences among control and patient groups in genotype and allelic frequencies. Results. Two of the ORAI1 SNPs (rs12320939 and rs12313273) were associated with estrogen receptors positive in breast cancer patients under the recessive model. When the Bonferroni correction was performed, the significance still existed. In addition, rs12320939 also associated with the lymph nodal involvement. Conclusion. We showed that genetic polymorphisms of ORAI1 associated strongly with lymph nodal involvement and estrogen receptors (ERs) positive breast cancer patients in a Taiwanese population.

Non-stimulated, agonist-stimulated and store-operated Ca2+ influx in MDA-MB-468 breast cancer cells and the effect of EGF-induced EMT on calcium entry

In addition to their well-defined roles in replenishing depleted endoplasmic reticulum (ER) Ca²⁺ reserves, molecular components of the store-operated Ca²⁺ entry pathway regulate breast cancer metastasis. A process implicated in cancer metastasis that describes the conversion to a more invasive phenotype is epithelial-mesenchymal transition (EMT). In this study we show that EGF-induced EMT in MDA-MB-468 breast cancer cells is associated with a reduction in agonist-stimulated and store-operated Ca²⁺ influx, and that MDA-MB-468 cells prior to EMT induction have a high level of non-stimulated Ca²⁺ influx. The potential roles for specific Ca²⁺ channels in these pathways were assessed by siRNA-mediated silencing of ORAI1 and transient receptor potential canonical type 1 (TRPC1) channels in MDA-MB-468 breast cancer cells. Non-stimulated, agonist-stimulated and store-operated Ca²⁺ influx were significantly inhibited with ORAI1 silencing. TRPC1 knockdown attenuated non-stimulated Ca²⁺ influx in a manner dependent on Ca²⁺ influx via ORAI1. TRPC1 silencing was also associated with reduced ERK1/2 phosphorylation and changes in the rate of Ca²⁺ release from the ER associated with the inhibition of the sarco/endoplasmic reticulum Ca²⁺-ATPase (time to peak [Ca²⁺]_CYT = 188.7±34.6 s (TRPC1 siRNA) versus 124.0±9.5 s (non-targeting siRNA); P<0.05). These studies indicate that EMT in MDA-MB-468 breast cancer cells is associated with a pronounced remodeling of Ca²⁺ influx, which may be due to altered ORAI1 and/or TRPC1 channel function. Our findings also suggest that TRPC1 channels in MDA-MB-468 cells contribute to ORAI1-mediated Ca²⁺ influx in non-stimulated cells.