Inhibition of altered Orai1 channels in Müller cells protects photoreceptors in retinal degeneration.

The expressions of ion channels by Müller glial cells (MGCs) may change in response to various retinal pathophysiological conditions. There remains a gap in our understanding of MGCs' responses to photoreceptor degeneration towards finding therapies. The study explores how an inhibition of store-operated Ca2+ entry (SOCE) and its major component, Orai1 channel, in MGCs protects photoreceptors from degeneration. The study revealed increased Orai1 expression in the MGCs of retinal degeneration 10 (rd10) mice. Enhanced expression of oxidative stress markers was confirmed as a crucial pathological mechanism in rd10 retina. Inducing oxidative stress in rat MGCs resulted in increasing SOCE and Ca2+ release-activated Ca2+ (CRAC) currents. SOCE inhibition by 2-Aminoethoxydiphenyl borate (2-APB) protected photoreceptors in degenerated retinas. Finally, molecular simulations proved the structural and dynamical features of 2-APB to the target structure Orai1. Our results provide new insights into the physiology of MGCs regarding retinal degeneration and shed a light on SOCE and Orai1 as new therapeutic targets.

Beta-Glycerophosphate-Induced ORAI1 Expression and Store Operated Ca2+ Entry in Megakaryocytes.

Impairment of renal phosphate elimination in chronic kidney disease (CKD) leads to enhanced plasma and tissue phosphate concentration, which in turn up-regulates transcription factor NFAT5 and serum & glucocorticoid-inducible kinase SGK1. The kinase upregulates ORAI1, a Ca2+-channel accomplishing store-operated Ca2+-entry (SOCE). ORAI1 is stimulated following intracellular store depletion by Ca2+-sensors STIM1 and/or STIM2. In megakaryocytes and blood platelets SOCE and thus ORAI1 are powerful regulators of activity. The present study explored whether the phosphate-donor ß-glycerophosphate augments NFAT5, ORAI1,2,3 and/or STIM1,2 expressions and thus SOCE in megakaryocytes. Human megakaryocytic Meg01cells were exposed to 2 mM of phosphate-donor ß-glycerophosphate for 24 hours. Platelets were isolated from blood samples of patients with impaired kidney function or control volunteers. Transcript levels were estimated utilizing q-RT-PCR, cytosolic Ca2+-concentration ([Ca2+]i) by Fura-2-fluorescence, and SOCE from increase of [Ca2+]i following re-addition of extracellular Ca2+ after store depletion with thapsigargin (1 µM). NFAT5 and ORAI1 protein abundance was estimated with Western blots. As a result, ß-glycerophosphate increased NFAT5, ORAI1/2/3, STIM1/2 transcript levels, as well as SOCE. Transcript levels of NFAT5, SGK1, ORAI1/2/3, and STIM1/2 as well as NFAT5 and ORAI1 protein abundance were significantly higher in platelets isolated from patients with impaired kidney function than in platelets from control volunteers. In conclusion, phosphate-donor ß-glycerophosphate triggers a signaling cascade of NFAT5/SGK1/ORAI/STIM, thus up-regulating store-operated Ca2+-entry.

Phosphate-induced ORAI1 expression and store-operated Ca2+ entry in aortic smooth muscle cells.

Compromised renal phosphate elimination in chronic kidney disease (CKD) leads to hyperphosphatemia, which in turn triggers osteo-/chondrogenic signaling in vascular smooth muscle cells (VSMCs) and vascular calcification. Osteo-/chondrogenic transdifferentiation of VSMCs leads to upregulation of the transcription factors MSX2, CBFA1, and SOX9 as well as tissue-nonspecific alkaline phosphatase (ALPL) which fosters calcification by degrading the calcification inhibitor pyrophosphate. Osteo-/chondrogenic signaling in VSMCs involves the serum- and glucocorticoid-inducible kinase SGK1. As shown in other cell types, SGK1 is a powerful stimulator of ORAI1, a Ca2+-channel accomplishing store-operated Ca2+-entry (SOCE). ORAI1 is stimulated following intracellular store depletion by the Ca2+ sensor STIM1. The present study explored whether phosphate regulates ORAI1 and/or STIM1 expression and, thus, SOCE in VSMCs. To this end, primary human aortic smooth muscle cells (HAoSMCs) were exposed to the phosphate donor ß-glycerophosphate. Transcript levels were estimated by qRT-PCR, protein abundance by western blotting, ALPL activity by colorimetry, calcification by alizarin red S staining, cytosolic Ca2+-concentration ([Ca2+]i) by Fura-2-fluorescence, and SOCE from increase of [Ca2+]i following re-addition of extracellular Ca2+ after store depletion with thapsigargin. As a result, ß-glycerophosphate treatment increased ORAI1 and STIM1 transcript levels and protein abundance as well as SOCE in HAoSMCs. Additional treatment with ORAI1 inhibitor MRS1845 or SGK1 inhibitor GSK650394 virtually disrupted the effects of ß-glycerophosphate on SOCE. Moreover, the ß-glycerophosphate-induced MSX2, CBFA1, SOX9, and ALPL mRNA expression and activity in HAoSMCs were suppressed in the presence of the ORAI1 inhibitor and upon ORAI1 silencing. In conclusion, enhanced phosphate upregulates ORAI1 and STIM1 expression and store-operated Ca2+-entry, which participate in the orchestration of osteo-/chondrogenic signaling of VSMCs. KEY MESSAGES: • In aortic SMC, phosphate donor ß-glycerophosphate upregulates Ca2+ channel ORAI1. • In aortic SMC, ß-glycerophosphate upregulates ORAI1-activator STIM1. • In aortic SMC, ß-glycerophosphate upregulates store-operated Ca2+-entry (SOCE). • The effect of ß-glycerophosphate on SOCE is disrupted by ORAI1 inhibitor MRS1845. • Stimulation of osteogenic signaling is disrupted by MRS1845 and ORAI1 silencing.

Gut Bacterial Metabolite Urolithin A (UA) Mitigates Ca2+ Entry in T Cells by Regulating miR-10a-5p.

The gut microbiota influences several biological functions including immune responses. Inflammatory bowel disease is favorably influenced by consumption of several dietary natural plant products such as pomegranate, walnuts, and berries containing polyphenolic compounds such as ellagitannins and ellagic acid. The gut microbiota metabolizes ellagic acid resulting in the formation of bioactive urolithins A, B, C, and D. Urolithin A (UA) is the most active and effective gut metabolite and acts as a potent anti-inflammatory and anti-oxidant agent. However, whether gut metabolite UA affects the function of immune cells remains incompletely understood. T cell proliferation is stimulated by store operated Ca2+ entry (SOCE) resulting from stimulation of Orai1 by STIM1/STIM2. We show here that treatment of murine CD4+ T cells with UA (10 µM, 3 days) significantly blunted SOCE in CD4+ T cells, an effect paralleled by significant downregulation of Orai1 and STIM1/2 transcript levels and protein abundance. UA treatment further increased miR-10a-5p abundance in CD4+ T cells in a dose dependent fashion. Overexpression of miR-10a-5p significantly decreased STIM1/2 and Orai1 mRNA and protein levels as well as SOCE in CD4+ T cells. UA further decreased CD4+ T cell proliferation. Thus, the gut bacterial metabolite UA increases miR-10a-5p levels thereby downregulating Orai1/STIM1/STIM2 expression, store operated Ca2+ entry, and proliferation of murine CD4+ T cells.

Upregulation of Orai1 and STIM1 expression as well as store-operated Ca2+ entry in ovary carcinoma cells by placental growth factor.

Placental growth factor (PlGF) is produced by tumor cells and stimulates tumor growth and metastasis in part by upregulation of hypoxia inducible factor HIF1α. Orchestration of tumor cell proliferation and migration involves oscillations of cytosolic Ca2+ activity ([Ca2+]i). The [Ca2+]i oscillations could be accomplished by triggering of intracellular Ca2+ release followed by store-operated Ca2+-entry (SOCE). Mechanisms accomplishing SOCE include the pore-forming ion channel unit Orai1 and its regulator STIM1. The present study explored whether PlGF influences the expression of Orai1 and STIM1, as well as SOCE and whether this effect impacts on HIF1α expression. To this end, ovary carcinoma cells were cultured for 24 h without and with PlGF (10 ng/ml). Orai1, STIM1 and HIF1α transcript levels were quantified utilizing RT-PCR and Orai1, STIM1 and HIF1α protein levels by Western blotting. [Ca2+]i was estimated from Fura-2-fluorescence and SOCE from increase of [Ca2+]i following Ca2+ re-addition after Ca2+-store depletion with extracellular Ca2+ removal and sarcoendoplasmatic Ca2+-ATPase (SERCA) inhibitor thapsigargin (1 µM). As a result, exposure of ovary carcinoma cells to PlGF was followed by a significant increase of Orai1 as well as STIM1 transcript and protein levels. PlGF significantly increased store-operated Ca2+-entry following re-addition of extracellular Ca2+, an effect virtually abrogated by Orai1 inhibitor MRS1845 (10 µM). PlGF further increased HIF1α transcript and protein levels, an effect again significantly blunted by MRS1845 (10 µM). In conclusion, PlGF upregulates expression of both, Orai1 and STIM1 thus enhancing store-operated Ca2+-entry with subsequent upregulation of HIF1α.

Inhibition of Lithium Sensitive Orai1/ STIM1 Expression and Store Operated Ca2+ Entry in Chorea-Acanthocytosis Neurons by NF-κB Inhibitor Wogonin.

BACKGROUND/AIMS: The neurodegenerative disease Chorea-Acanthocytosis (ChAc) is caused by loss-of-function-mutations of the chorein-encoding gene VPS13A. In ChAc neurons transcript levels and protein abundance of Ca2+ release activated channel moiety (CRAC) Orai1 as well as its regulator STIM1/2 are decreased, resulting in blunted store operated Ca2+-entry (SOCE) and enhanced suicidal cell death. SOCE is up-regulated and cell death decreased by lithium. The effects of lithium are paralleled by upregulation of serum & glucocorticoid inducible kinase SGK1 and abrogated by pharmacological SGK1 inhibition. In other cell types SGK1 has been shown to be partially effective by upregulation of NFκB, a transcription factor stimulating the expression of Orai1 and STIM. The present study explored whether pharmacological inhibition of NFκB interferes with Orai1/STIM1/2 expression and SOCE and their upregulation by lithium in ChAc neurons. METHODS: Cortical neurons were differentiated from induced pluripotent stem cells generated from fibroblasts of ChAc patients and healthy volunteers. Orai1 and STIM1 transcript levels and protein abundance were estimated from qRT-PCR and Western blotting, respectively, cytosolic Ca2+-activity ([Ca2+]i) from Fura-2-fluorescence, SOCE from increase of [Ca2+]i following Ca2+ re-addition after Ca2+-store depletion with sarco-endoplasmatic Ca2+-ATPase inhibitor thapsigargin (1µM), as well as CRAC current utilizing whole cell patch clamp recording. RESULTS: Orai1 and STIM1 transcript levels and protein abundance as well as SOCE and CRAC current were significantly enhanced by lithium treatment (2 mM, 24 hours). These effects were reversed by NFκB inhibitor wogonin (50 µM). CONCLUSION: The stimulation of expression and function of Orai1/STIM1/2 by lithium in ChAc neurons are disrupted by pharmacological NFκB inhibition.

Epigallocatechin-3-gallate (EGCG) up-regulates miR-15b expression thus attenuating store operated calcium entry (SOCE) into murine CD4+ T cells and human leukaemic T cell lymphoblasts.

CD4+ T cells are key elements in immune responses and inflammation. Activation of T cell receptors in CD4+ T cells triggers cytosolic Ca2+ release with subsequent store operated Ca2+ entry (SOCE), which is accomplished by the pore forming Ca2+ release activated Ca2+ (CRAC) channel Orai1 and its regulator stromal cell-interaction molecule 2 (STIM2). Green tea polyphenol epigallocatechin-3-gallate (EGCG) acts as a potent anti-inflammatory and anti-oxidant agent for various types of cells including immune cells. However, how post-transcriptional gene regulators such as miRNAs are involved in the regulation of Ca2+ influx into murine CD4+ T cells and human Jurkat T cells through EGCG is not defined. EGCG treatment of murine CD4+ T cells significantly down-regulated the expression of STIM2 and Orai1 both at mRNA and protein levels. Furthermore, EGCG significantly decreased SOCE in both murine and human T cells. EGCG treatment increased miRNA-15b (miR-15b) abundance in both murine and human T cells. Bioinformatics analysis reveals that miR-15b, which has a STIM2 binding site, is involved in the down-regulation of SOCE. Overexpression of miR-15b significantly decreased the mRNA and protein expression of STIM2 and Orai1 in murine T cells. Treatment of Jurkat T cells with 10 µM EGCG further decreased mTOR and PTEN protein levels. EGCG decreased mitochondrial membrane potential (MMP) in both human and murine T cells. In conclusion, the observations suggest that EGCG inhibits the Ca2+ entry into murine and human T cells, an effect accomplished at least in part by up-regulation of miR-15b.

P38 Kinase, SGK1 and NF-κB Dependent Up-Regulation of Na+/Ca2+ Exchanger Expression and Activity Following TGFß1 Treatment of Megakaryocytes.

BACKGROUND: TGFß1, a decisive regulator of megakaryocyte maturation and platelet formation, has previously been shown to up-regulate both, store operated Ca2+ entry (SOCE) and Ca2+ extrusion by Na+/Ca2+ exchange. The growth factor thus augments the increase of cytosolic Ca2+ activity ([Ca2+]i) following release of Ca2+ from intracellular stores and accelerates the subsequent decline of [Ca2+]i. The effect on SOCE is dependent on a signaling cascade including p38 kinase, serum & glucocorticoid inducible kinase SGK1, and nuclear factor NFκB. The specific Na+/Ca2+ exchanger isoforms involved and the signalling regulating the Na+/Ca2+ exchangers remained, however elusive. The present study explored, whether TGFß1 influences the expression and function of K+ insensitive (NCX) and K+ sensitive (NCKX) Na+/Ca2+ exchangers, and aimed to shed light on the signalling involved. METHODS: In human megakaryocytic cells (MEG01) RT-PCR was performed to quantify NCX/NCKX isoform transcript levels, [Ca2+]i was determined by Fura-2 fluorescence, and Na+/Ca2+ exchanger activity was estimated from the increase of [Ca2+]i following switch from an extracellular solution with 130 or 90 mM Na+ and 0 mM Ca2+ to an extracellular solution with 0 Na+ and 2 mM Ca2+. K+ concentration was 0 mM for analysis of NCX and 40 mM for analysis of NCKX. RESULTS: TGFß1 (60 ng/ml, 24 h) significantly increased the transcript levels of NCX1, NCKX1, NCKX2 and NCKX5. Moreover, TGFß1 (60 ng/ml, 24 h) significantly increased the activity of both, NCX and NCKX. The effect of TGFß1 on NCX and NCKX transcript levels and activity was significantly blunted by p38 kinase inhibitor Skepinone-L (1 µM), the effect on NCX and NCKX activity further by SGK1 inhibitor GSK-650394 (10 µM) and NFκB inhibitor Wogonin (100 µM). CONCLUSIONS: TGFß1 markedly up-regulates transcription of NCX1, NCKX1, NCKX2, and NCKX5 and thus Na+/Ca2+ exchanger activity, an effect requiring p38 kinase, SGK1 and NFκB.

Istaroxime Inhibits Motility and Down-Regulates Orai1 Expression, SOCE and FAK Phosphorylation in Prostate Cancer Cells.

BACKGROUND/AIMS: Istaroxime is a validated inotropic Na+/K+ ATPase inhibitor currently in development for the treatment of various cardiac conditions. Recent findings established that this steroidal drug exhibits potent apoptotic responses in prostate tumors in vitro and in vivo, by affecting key signaling orchestrating proliferation and apoptosis, such as c-Myc and caspase 3, Rho GTPases and actin cytoskeleton dynamics. In the present study we examined whether istaroxime is affecting cell motility and analyzed the underlying mechanism in prostate tumor cells. METHODS: Migration was assessed by transwell and wound healing assays, Orai1 and Stim1 abundance by RT-PCR and confocal immunofluorescence microscopy, Fura-2 fluorescence was utilized to determine intracellular Ca2+ and Western blotting for FAK/pFAK measurements. RESULTS: We observed strong inhibition of cell migration in istaroxime treated DU-145 prostate cancer cells. Istaroxime further decreased Orai1 and Stim1 transcript levels and downregulated Orai1 protein expression. Moreover, SOCE was significantly decreased upon istaroxime treatment. Furthermore, istaroxime strikingly diminished phosphorylated FAK levels. Interestingly, the efficacy of istaroxime on the inhibition of DU-145 cell migration was further enhanced by blocking Orai1 with 2-APB and FAK with the specific inhibitor PF-00562271. These results provide strong evidence that istaroxime prevents cell migration and motility of DU-145 prostate tumor cells, an effect at least partially attributed to Orai1 downregulation and FAK de-activation. CONCLUSION: Collectively our results indicate that this enzyme inhibitor, besides its pro-apoptotic action, affects motility of cancer cells, supporting its potential role as a strong candidate for further clinical cancer drug development.

Role of Na+/Ca2+ Exchangers in Therapy Resistance of Medulloblastoma Cells.

BACKGROUND/AIMS: Alterations of cytosolic Ca2+-activity ([Ca2+]i) are decisive in the regulation of tumor cell proliferation, migration and survival. Transport processes participating in the regulation of [Ca2+]i include Ca2+ extrusion through K+-independent (NCX) and/or K+-dependent (NCKX) Na+/Ca2+-exchangers. The present study thus explored whether medulloblastoma cells express Na+/Ca2+-exchangers, whether expression differs between therapy sensitive D283 and therapy resistant UW228-3 medulloblastoma cells, and whether Na+/Ca2+-exchangers participate in the regulation of cell survival. METHODS: In therapy sensitive D283 and therapy resistant UW228-3 medulloblastoma cells transcript levels were estimated by RT-PCR, protein abundance by Western blotting, cytosolic Ca2+-activity ([Ca2+]i) from Fura-2-fluorescence, Na+/ Ca2+-exchanger activity from the increase of [Ca2+]i (Δ[Ca2+]i) and from whole cell current (Ica) following abrupt replacement of Na+ containing (130 mM) and Ca2+ free by Na+ free and Ca2+ containing (2 mM) extracellular perfusate as well as cell death from PI -staining and annexin-V binding in flow cytometry. RESULTS: The transcript levels of NCX3, NCKX2, and NCKX5, protein abundance of NCX3, slope and peak of Δ[Ca2+]i as well as Ica were significantly lower in therapy sensitive D283 than in therapy resistant UW228-3 medulloblastoma cells. The Na+/Ca2+-exchanger inhibitor KB-R7943 (10 µM) significantly blunted Δ[Ca2+]i, and augmented the ionizing radiation-induced apoptosis but did not significantly modify clonogenicity of medulloblastoma cells. Apoptosis was further enhanced by NCX3 silencing. CONCLUSIONS: Na+/Ca2+-exchanger activity significantly counteracts apoptosis but does not significantly affect clonogenicity after radiation of medulloblastoma cells.

NFAT5-sensitive Orai1 expression and store-operated Ca2+ entry in megakaryocytes.

The transcription factor nuclear factor of activated T cells 5 (NFAT5) is up-regulated in several clinical disorders, including dehydration. NFAT5-sensitive genes include serum and glucocorticoid-inducible kinase 1 (SGK1). The kinase is a powerful regulator of Orai1, a Ca2+ channel accomplishing store-operated Ca2+ entry (SOCE). Orai1 is stimulated after intracellular store depletion by the Ca2+ sensors stromal interaction molecule 1 (STIM1), or STIM2, or both. In the present study, we explored whether nuclear factor of activated T cell (NFAT)-5 influences Ca2+ signaling in megakaryocytes. To this end, human megakaryocytic (MEG-01) cells were transfected with NFAT5 or with siNFAT5. Platelets and megakaryocytes were isolated from wild-type mice with either access to water ad libitum or dehydration by 36 h of water deprivation. Transcript levels were determined with quantitative RT-PCR and protein abundance by Western blot analysis and flow cytometry, cytosolic (intracellular) Ca2+ concentration ([Ca2+]i) by fura-2-fluorescence. SOCE was estimated from the increase of [Ca2+]i following readdition of extracellular Ca2+ after store depletion with thapsigargin (1 µM). Platelet degranulation was estimated from P-selectin abundance and integrin activation from αIIbß3 integrin abundance determined by flow cytometry. As a result, NFAT5 transfection or exposure to hypertonicity (+40 mM NaCl) of MEG-01 cells increased Orai1, Orai2, STIM1, and STIM2 transcript levels. Orai1 transcript levels were decreased by NFAT5 silencing. NFAT5 transfection and IκB inhibitor BMS 345541 (5 µM) increased SOCE, whereas NFAT5 silencing and SGK1 inhibitor GSK650394 (10 µM) decreased SOCE. In the mice, dehydration increased NFAT5 and Orai1 protein abundance in megakaryocytes and NFAT5, Orai1, and Orai2 abundance in platelets. Dehydration further augmented the degranulation and integrin activation by thrombin and collagen-related peptide. In summary, NFAT5 is a powerful regulator of Orai1-expression and SOCE in megakaryocytes.-Sahu, I., Pelzl, L., Sukkar, B., Fakhri, H., al-Maghout, T., Cao, H., Hauser, S., Gutti, R., Gawaz, M., Lang, F. NFAT5-sensitive Orai1 expression and store-operated Ca2+ entry in megakaryocytes.

Role of Dicer Enzyme in the Regulation of Store Operated Calcium Entry (SOCE) in CD4+ T Cells.

BACKGROUND/AIMS: Activation of T cell receptors (TCRs) in CD4+ T cells leads to a cascade of signalling reactions including increase of intracellular calcium (Ca2+) levels with subsequent Ca2+ dependent stimulation of gene expression, proliferation, cell motility and cytokine release. The increase of cytosolic Ca2+ results from intracellular Ca2+ release with subsequent activation of store-operated Ca2+ entry (SOCE). Previous studies suggested miRNAs are required for the development and functions of CD4+ T cells. An enzyme called Dicer is required during the process of manufacturing mature miRNAs from the precursor miRNAs. In this study, we explored whether loss of Dicer in CD4+ T cells affects SOCE and thus Ca2+ dependent regulation of cellular functions. METHODS: We tested the expression of Orai1 by q-RT-PCR and flow cytometry. Further, we measured SOCE by an inverted phase-contrast microscope with the Incident-light fluorescence illumination system using Fura-2. Intracellular Ca2+ was also measured by flow cytometry using Ca2+ sensitive dye Fluo-4. RESULTS: We found that in Dicer deficient (DicerΔ/Δ) mice Orai1 was downregulated at mRNA and protein level in CD4+ T cells. Further, SOCE was significantly smaller in DicerΔ/Δ CD4+ T cells than in CD4+ T cells isolated from wild-type (Dicerfl/fl) mice. CONCLUSION: Our data suggest that miRNAs are required for adequate Ca2+ entry into CD4+ T cells and thus triggering of Ca2+ sensitive immune functions.

Impact of Na+/Ca2+ Exchangers on Therapy Resistance of Ovary Carcinoma Cells.

BACKGROUND/AIMS: According to previous observations, enhanced store-operated Ca2+-entry (SOCE) accomplished by the pore forming ion channel unit Orai1 and its regulator STIM1 contribute to therapy resistance of ovary carcinoma cells. Ca2+ signaling is further shaped by Ca2+ extrusion through K+-independent (NCX) and/or K+-dependent (NCKX) Na+/Ca2+-exchangers. The present study thus explored whether therapy resistance is further paralleled by altered expression and/or function of Na+/Ca2+-exchangers. METHODS: In therapy resistant (A2780cis) and therapy sensitive (A2780sens) ovary carcinoma cells transcript levels were estimated from RT-PCR, cytosolic Ca2+-activity ([Ca2+]i) from Fura-2-fluorescence, Na+/Ca2+-exchanger activity from the increase of [Ca2+]i (x0394;[Ca2+]i) and from whole cell current (Ica) following abrupt replacement of Na+ containing (130 mM) and Ca2+ free extracellular perfusate by Na+ free and Ca2+ containing (2 mM) extracellular perfusate, as well as cell death from PI -staining in flow cytometry. RESULTS: The transcript levels of NCX3, NCKX4, NCKX5, and NCKX6, slope and peak of x0394;[Ca2+]i as well as Ica were significantly higher in therapy resistant than in therapy sensitive ovary carcinoma cells. The Na+/Ca2+-exchanger inhibitor KB-R7943 (10 µM) significantly blunted x0394;[Ca2+]i and significantly augmented the cisplatin-induced cell death of therapy resistant ovary carcinoma cells without significantly modifying cisplatin-induced cell death of therapy sensitive ovary carcinoma cells. CONCLUSION: Enhanced Na+/Ca2+-exchanger activity may contribute to the therapy sensitivity of ovary carcinoma cells.