Transient receptor potential channel C3 contributes to the progression of human ovarian cancer

Transient receptor potential cation 3 channel regulates melanoma proliferation and migration

Melanoma has an extremely poor prognosis due to its rapidly progressive and highly metastatic nature. Several therapeutic drugs have recently become available, but are effective only against melanoma with specific BRAF gene mutation. Thus, there is a need to identify other target molecules. We show here that Transient receptor potential, canonical 3 (TRPC3) is widely expressed in human melanoma. We found that pharmacological inhibition of TRPC3 with a pyrazole compound, Pyr3, decreased melanoma cell proliferation and migration. Similar inhibition was observed when the TRPC3 gene was silenced with short-hairpin RNA (shRNA). Pyr3 induced dephosphorylation of signal transducer and activator of transcription (STAT) 5 and Akt. Administration of Pyr3 (0.05 mg/kg) to mice implanted with human melanoma cells (C8161) significantly inhibited tumor growth. Our findings indicate that TRPC3 plays an important role in melanoma growth, and may be a novel target for treating melanoma in patients.

Protein Lipidation As a Regulator of Apoptotic Calcium Release: Relevance to Cancer

Calcium is a critical regulator of cell death pathways. One of the most proximal events leading to cell death is activation of plasma membrane and endoplasmic reticulum-resident calcium channels. A large body of evidence indicates that defects in this pathway contribute to cancer development. Although we have a thorough understanding of how downstream elevations in cytosolic and mitochondrial calcium contribute to cell death, it is much less clear how calcium channels are activated upstream of the apoptotic stimulus. Recently, it has been shown that protein lipidation is a potent regulator of apoptotic signaling. Although classically thought of as a static modification, rapid and reversible protein acylation has emerged as a new signaling paradigm relevant to many pathways, including calcium release and cell death. In this review, we will discuss the role of protein lipidation in regulating apoptotic calcium signaling with direct therapeutic relevance to cancer.

Current and upcoming mitochondrial targets for cancer therapy

Mitochondria are essential intracellular organelles that regulate energy metabolism, cell death, and signaling pathways that are important for cell proliferation and differentiation. Therefore, mitochondria are fundamentally implicated in cancer biology, including initiation, growth, metastasis, relapse, and acquired drug resistance. Based on these implications, mitochondria have been proposed as a major therapeutic target for cancer treatment. In addition to classical view of mitochondria in cancer biology, recent studies found novel pathophysiological roles of mitochondria in cancer. In this review, we introduce recent concepts of mitochondrial roles in cancer biology including mitochondrial DNA mutation and epigenetic modulation, energy metabolism reprogramming, mitochondrial channels, involvement in metastasis and drug resistance, and cancer stem cells. We also discuss the role of mitochondria in emerging cancer therapeutic strategies, especially cancer immunotherapy and CRISPR-Cas9 system gene therapy.

Pyrazolopyrimidines as Potent Stimulators for Transient Receptor Potential Canonical 3/6/7 Channels

Transient receptor potential canonical 3/6/7 (TRPC3/6/7) are highly homologous receptor-operated nonselective cation channels. Despite their physiological significance, very few selective and potent agonists are available for functional examination of these channels. Using a cell-based high throughput screening approach, a lead compound with the pyrazolopyrimidine skeleton was identified as a TRPC6 agonist. Synthetic schemes for the lead and its analogues were established, and structural-activity relationship studies were carried out. A series of potent and direct agonists of TRPC3/6/7 channels were identified, and among them, 4m-4p have a potency order of TRPC3 > C7 > C6, with 4n being the most potent with an EC50 of <20 nM on TRPC3. Importantly, these compounds exhibited no stimulatory activity on related TRP channels. The potent and selective compounds described here should be suitable for evaluation of the roles of TRPC channels in the physiology and pathogenesis of diseases, including glomerulosclerosis and cancer.

Knockdown of sodium-calcium exchanger 1 induces epithelial-to-mesenchymal transition in kidney epithelial cells

Mesenchymal-to-epithelial transition (MET) and epithelial-to-mesenchymal transition (EMT) are important processes in kidney development. Failure to undergo MET during development leads to the initiation of Wilms tumor, whereas EMT contributes to the development of renal cell carcinomas (RCC). The role of calcium regulators in governing these processes is becoming evident. We demonstrated earlier that Na⁺/Ca²⁺ exchanger 1 (NCX1), a major calcium exporter in renal epithelial cells, regulates epithelial cell motility. Here, we show for the first time that NCX1 mRNA and protein expression was down-regulated in Wilms tumor and RCC. Knockdown of NCX1 in Madin-Darby canine kidney cells induced fibroblastic morphology, increased intercellular junctional distance, and induced paracellular permeability, loss of apico-basal polarity in 3D cultures, and anchorage-independent growth, accompanied by expression of mesenchymal markers. We also provide evidence that NCX1 interacts with and anchors E-cadherin to the cell surface independent of NCX1 ion transport activity. Consistent with destabilization of E-cadherin, NCX1 knockdown cells showed an increase in β-catenin nuclear localization, enhanced transcriptional activity, and up-regulation of downstream targets of the β-catenin signaling pathway. Taken together, knockdown of NCX1 in Madin-Darby canine kidney cells alters epithelial morphology and characteristics by destabilization of E-cadherin and induction of β-catenin signaling.

TRPC Channels and Cell Proliferation

TRPCs have been demonstrated to be widely expressed in different cancers. In recent years, a number of studies closely investigated the roles of TRPCs in cancer cells. Most of the results show that both mRNA and protein levels of TRPCs significantly increase in cancer tissues compared with healthy controls. TRPCs regulate Ca²⁺ homeostasis, contribute to cell cycle regulation and the expression/activation of Ca²⁺-related factors, and thus play critical roles in the proliferation of cancer cells. Therefore, TRPCs could act as potential drug targets for cancer diagnosis and therapy.

Targeting calcium signaling in cancer therapy

The intracellular calcium ions (Ca2+) act as second messenger to regulate gene transcription, cell proliferation, migration and death. Accumulating evidences have demonstrated that intracellular Ca2+ homeostasis is altered in cancer cells and the alteration is involved in tumor initiation, angiogenesis, progression and metastasis. Targeting derailed Ca2+ signaling for cancer therapy has become an emerging research area. This review summarizes some important Ca2+ channels, transporters and Ca2+-ATPases, which have been reported to be altered in human cancer patients. It discusses the current research effort toward evaluation of the blockers, inhibitors or regulators for Ca2+ channels/transporters or Ca2+-ATPase pumps as anti-cancer drugs. This review is also aimed to stimulate interest in, and support for research into the understanding of cellular mechanisms underlying the regulation of Ca2+ signaling in different cancer cells, and to search for novel therapies to cure these malignancies by targeting Ca2+ channels or transporters.

The calcium pump plasma membrane Ca(2+)-ATPase 2 (PMCA2) regulates breast cancer cell proliferation and sensitivity to doxorubicin

Regulation of Ca(2+) transport is vital in physiological processes, including lactation, proliferation and apoptosis. The plasmalemmal Ca(2+) pump isoform 2 (PMCA2) a calcium ion efflux pump, was the first protein identified to be crucial in the transport of Ca(2+) ions into milk during lactation in mice. In these studies we show that PMCA2 is also expressed in human epithelia undergoing lactational remodeling and also report strong PMCA2 staining on apical membranes of luminal epithelia in approximately 9% of human breast cancers we assessed. Membrane protein expression was not significantly associated with grade or hormone receptor status. However, PMCA2 mRNA levels were enriched in Basal breast cancers where it was positively correlated with survival. Silencing of PMCA2 reduced MDA-MB-231 breast cancer cell proliferation, whereas silencing of the related isoforms PMCA1 and PMCA4 had no effect. PMCA2 silencing also sensitized MDA-MB-231 cells to the cytotoxic agent doxorubicin. Targeting PMCA2 alone or in combination with cytotoxic therapy may be worthy of investigation as a therapeutic strategy in breast cancer. PMCA2 mRNA levels are also a potential tool in identifying poor responders to therapy in women with Basal breast cancer.

Calcium sensing receptor suppresses human pancreatic tumorigenesis through a novel NCX1/Ca(2+)/β-catenin signaling pathway

The calcium sensing receptor (CaSR) is functionally expressed in normal human pancreases, but its pathological role in pancreatic tumorigenesis is currently unknown. We sought to investigate the role of CaSR in pancreatic cancer (PC) and the underlying molecular mechanisms. We revealed that the expression of CaSR was consistently downregulated in the primary cancer tissues from PC patients, which was correlated with tumor size, differentiation and poor survival of the patients. CaSR activation markedly suppressed pancreatic tumorigenesis in vitro and in vivo likely through the Ca(2+) entry mode of Na(+)/Ca(2+) exchanger 1 (NCX1) to induce Ca(2+) entry into PC cells. Moreover, NCX1-mediated Ca(2+) entry resulted in Ca(2+)-dependent inhibition of β-catenin signaling in PC cells, eventually leading to the inhibition of pancreatic tumorigenesis. Collectively, we demonstrate for the first time that CaSR exerts a suppressive function in pancreatic tumorigenesis through a novel NCX1/Ca(2+)/β-catenin signaling pathway. Targeting this specific signaling pathway could be a potential therapeutic strategy for PC.

Synthesis of radioiodinated probes to evaluate the biodistribution of a potent TRPC3 inhibitor

The transient receptor potential canonical 3 (TRPC3) channel is a member of the TRPC family that contributes to the entry of Ca²⁺through the plasma membrane or modulates the driving force for Ca²⁺entry channels.

SOCE and cancer: Recent progress and new perspectives

Ca²⁺ acts as a universal and versatile second messenger in the regulation of a myriad of biological processes, including cell proliferation, differentiation, migration and apoptosis. Store‐operated Ca²⁺ entry (SOCE) mediated by ORAI and the stromal interaction molecule (STIM) constitutes one of the major routes of calcium entry in nonexcitable cells, in which the depletion of intracellular Ca²⁺ stores triggers activation of the endoplasmic reticulum (ER)‐resident Ca²⁺ sensor protein STIM to gate and open the ORAI Ca²⁺ channels in the plasma membrane (PM). Accumulating evidence indicates that SOCE plays critical roles in cancer cell proliferation, metastasis and tumor neovascularization, as well as in antitumor immunity. We summarize herein the recent advances in our understanding of the function of SOCE in various types of tumor cells, vascular endothelial cells and cells of the immune system. Finally, the therapeutic potential of SOCE inhibitors in the treatment of cancer is also discussed.

Calcium signals inhibition sensitizes ovarian carcinoma cells to anti-Bcl-xL strategies through Mcl-1 down-regulation

Ovarian carcinoma is the leading cause of death from gynecologic cancer in the developed world and is characterized by acquired chemoresistance leading to an overall 5-year survival rate of about 30 %. We previously showed that Bcl-xL and Mcl-1 cooperatively protect platinum-resistant ovarian cancer cells from apoptosis. Despite BH3-mimetics represent promising drugs to target Bcl-xL, anti-Mcl-1 strategies are still in pre-clinical studies and required new investigations. Calcium is a universal second messenger and dysregulation of calcium signal is often observed during carcinogenesis. As change in cytosolic free calcium concentration [Ca(2+)]i is known to control the fate of the cell by regulating Bcl-2 family members, we wonder if calcium signal could impact on Mcl-1 expression and if its pharmacological inhibition could be useful to sensitize ovarian carcinoma cells to anti-Bcl-xL strategies. We therefore studied the effect of different calcium signals inhibitors in ovarian carcinoma cell lines SKOV3 and IGROV1-R10 and analysed their effects on proliferation and Mcl-1 expression. We also exposed these cells to these inhibitors in combination with anti-Bcl-xL strategies (siRNA or BH3-mimetic: ABT-737). We found that calcium signaling regulates Mcl-1 through translational events and a calmodulin-mediated pathway. BAPTA-AM and calmodulin inhibitor combination with ABT-737 leads to apoptosis, a process that is reversed by Mcl-1 enforced expression. As Mcl-1 represents a crucial hurdle to the success of chemotherapy, these results could open to new area of investigation using calcium modulators to directly or indirectly target Mcl-1 and thus efficiently sensitize ovarian carcinoma cells to anti-Bcl-xL strategies.

Extending information retrieval methods to personalized genomic-based studies of disease

Genomic-based studies of disease now involve diverse types of data collected on large groups of patients. A major challenge facing statistical scientists is how best to combine the data, extract important features, and comprehensively characterize the ways in which they affect an individual’s disease course and likelihood of response to treatment. We have developed a survival-supervised latent Dirichlet allocation (survLDA) modeling framework to address these challenges. Latent Dirichlet allocation (LDA) models have proven extremely effective at identifying themes common across large collections of text, but applications to genomics have been limited. Our framework extends LDA to the genome by considering each patient as a “document” with “text” detailing his/her clinical events and genomic state. We then further extend the framework to allow for supervision by a time-to-event response. The model enables the efficient identification of collections of clinical and genomic features that co-occur within patient subgroups, and then characterizes each patient by those features. An application of survLDA to The Cancer Genome Atlas ovarian project identifies informative patient subgroups showing differential response to treatment, and validation in an independent cohort demonstrates the potential for patient-specific inference.

Inhibition of transient receptor potential channel 5 reverses 5-Fluorouracil resistance in human colorectal cancer cells

5-Fluorouracil (5-Fu) is commonly used in the chemotherapy of colorectal cancer (CRC), but resistance to 5-Fu occurs in most cases, allowing cancer progression. Suppressing ABCB1 (ATP-binding cassette, subfamily B, member 1), which is a pump overproduced in cancer cells to export cytotoxic drugs, is an attractive strategy to overcome drug resistance. In the present study, transient receptor potential channel TrpC5 was found to be overproduced at the mRNA and protein levels together with ABCB1 in 5-Fu-resistant human CRC HCT-8 (HCT-8/5-Fu) and LoVo (LoVo/5-Fu) cells. More nuclear-stabilized β-catenin accumulation was found in HCT-8/5-Fu and LoVo/5-Fu cells than in HCT-8 and LoVo cells. Suppressing TrpC5 expression with TrpC5-specific siRNA inhibited the canonical Wnt/β-catenin signal pathway, reduced the induction of ABCB1, weakened the ABCB1 efflux pump, and caused a remarkable reversal of 5-Fu resistance in HCT-8/5-Fu and LoVo/5-Fu cells. On the contrary, enforcing TrpC5 expression resulted in an activated Wnt/β-catenin signal pathway and up-regulation of ABCB1. Taken together, we demonstrated an essential role of TrpC5 in ABCB1 induction and drug resistance in human CRC cells via promoting nuclear β-catenin accumulation.

Transient receptor potential (TRP) channels, promising potential diagnostic and therapeutic tools for cancer

Despite the advances in detection of and therapies for various tumors, high rates of treatment failure and mortality still exist throughout the world. These high rates are mainly due to the powerful capability of tumor cells to proliferate and migrate. Recent studies regarding the transient receptor potential (TRP) have indicated that TRP channels are associated with tumors and that TRP channels might represent potential targets for cancer treatment. TRP channels are important calcium-selective ion channels in many different tissues and cell types in mammals and are crucial regulators of calcium and sodium. TRP were first discovered in the photoreceptors of Drosophila with gene defects or mutations. TRP channels can be divided into seven subfamilies: TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPML (mucolipin), TRPP (polycystin), TRPA (ankyrin transmembrane protein), and TRPN (NomPC-like). TRPC proteins are conserved across organisms since they are most homologous to Drosophila TRP. TRP superfamilies have been linked to many physiological and pathological functions, including cell differentiation, proliferation, apoptosis, and ion homeostasis. This review focuses on the properties of TRP in oncogenesis, cancer proliferation, and cell migration.

Altered calcium signaling in cancer cells

It is the nature of the calcium signal, as determined by the coordinated activity of a suite of calcium channels, pumps, exchangers and binding proteins that ultimately guides a cell's fate. Deregulation of the calcium signal is often deleterious and has been linked to each of the 'cancer hallmarks'. Despite this, we do not yet have a full understanding of the remodeling of the calcium signal associated with cancer. Such an understanding could aid in guiding the development of therapies specifically targeting altered calcium signaling in cancer cells during tumorigenic progression. Findings from some of the studies that have assessed the remodeling of the calcium signal associated with tumorigenesis and/or processes important in invasion and metastasis are presented in this review. The potential of new methodologies is also discussed. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Consequences of activating the calcium-permeable ion channel TRPV1 in breast cancer cells with regulated TRPV1 expression

Increased expression of specific calcium channels in some cancers and the role of calcium signaling in proliferation and invasion have led to studies assessing calcium channel inhibitors as potential therapies for some cancers. The use of channel activators to promote death of cancer cells has been suggested, but the risk of activators promoting cancer cell proliferation and the importance of the degree of channel over-expression is unclear. We developed an MCF-7 breast cancer cell line with inducible TRPV1 overexpression and assessed the role of TRPV1 levels on cell death mediated by the TRPV1 activator capsaicin and the potential for submaximal activation to promote proliferation. The TRPV1 level was a determinant of cell death induced by capsaicin. A concentration response curve with varying TRPV1 expression levels identified the minimum level of TRPV1 required for capsaicin induced cell death. At no level of TRPV1 over-expression or capsaicin concentration did TRPV1 activation enhance proliferation. Cell death induced by capsaicin was necrotic and associated with up-regulation of c-Fos and RIP3. These studies suggest that activators of specific calcium channels may be an effective way to induce necrosis and that this approach may not always be associated with enhancement of cancer cell proliferation.

Canonical transient receptor potential channel 2 (TRPC2): old name-new games. Importance in regulating of rat thyroid cell physiology

In addition to the TSH-cyclic AMP signalling pathway, calcium signalling is of crucial importance in thyroid cells. Although the importance of calcium signalling has been thoroughly investigated for several decades, the nature of the calcium channels involved in signalling is unknown. In a recent series of investigations using the well-studied rat thyroid FRTL-5 cell line, we showed that these cells exclusively express the transient receptor potential canonical 2 (TRPC2) channel. Our results suggested that the TRPC2 channel is of significant importance in regulating thyroid cell function. These investigations were the first to show that thyroid cells express a member of the TRPC family of ion channels. In this review, we will describe the importance of the TRPC2 channel in regulating TSH receptor expression, thyroglobulin maturation, intracellular calcium and iodide homeostasis and that the channel also regulates thyroid cell proliferation.

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.

Calcium channels, external calcium concentration and cell proliferation

Evidence for a role for calcium channel proteins in cell proliferation is numerous suggesting that calcium influx is essential in this physiological process. Several studies in the past thirty years have demonstrated that calcium channel expression levels are determinant in cell proliferation. Voltage-gated, store-operated, second messengers and receptor-operated calcium channels have been associated to cell proliferation. However, the relationship between calcium influx and cell proliferation can be uncoupled in transformed and cancer cells, resulting in an external calcium-independent proliferation. Thus, protein expression could be more important than channel function to trigger cell proliferation suggesting that additional channel functions may be responsible to reconcile calcium channel expression and cell proliferation. When needed, external calcium concentration is obviously important for calcium channel function but it also regulates calcium sensing receptor (CaSR) activity. CaSR can up- or down-regulate cell proliferation depending on physiological conditions. CaSR sensitivity to external calcium is within the 0.5 to 5 mM range and therefore, the role of these receptors in cell proliferation must be taken into account. We therefore suggest here that cell proliferation rates could depend on the relative balance between calcium influx and CaSR activation.

The histone variant MacroH2A regulates Ca(2+) influx through TRPC3 and TRPC6 channels

The histone variant macroH2A replaces canonical H2A in the designated region of chromatin where its incorporation has the potential to establish a functionally distinct chromatin domain. The transient receptor potential canonical (TRPC) channels are a family of Ca²⁺-permeable cationic channels controlling changes in the cytosolic Ca²⁺ concentration. The proper regulation of Trpc gene expression requires chromatin remodeling, but little is known about the nature of these regulatory processes. Here, we show that macroH2A1 represses two Trpc family genes, Trpc3 and Trpc6, and attenuates Ca²⁺-dependent proliferative responses in bladder cancer cells. MacroH2A1 recruits histone deacetylase 1 (HDAC1) and HDAC2 to facilitate its persistent action, resulting in a compromise of histone acetylation across the Trpc3 and Trpc6 loci. Further, macroH2A1 depletion augments histone acetylation and Ca²⁺ influx, leading to increased cell growth and invasion. Our data provide new insights into TRPC3/TRPC6-mediated Ca²⁺ signaling and indicate a central role for macroH2A1 in regulating transcriptional competence of Trpc3 and Trpc6 genes.

Involvement of TRPC channels in lung cancer cell differentiation and the correlation analysis in human non-small cell lung cancer

The canonical transient receptor potential (TRPC) channels are Ca(2+)-permeable cationic channels controlling the Ca(2+) influx evoked by G protein-coupled receptor activation and/or by Ca(2+) store depletion. Here we investigate the involvement of TRPCs in the cell differentiation of lung cancer. The expression of TRPCs and the correlation to cancer differentiation grade in non-small cell lung cancer (NSCLC) were analyzed by real-time PCR and immunostaining using tissue microarrays from 28 patient lung cancer samples. The association of TRPCs with cell differentiation was also investigated in the lung cancer cell line A549 by PCR and Western blotting. The channel activity was monitored by Ca(2+) imaging and patch recording after treatment with all-trans-retinoic acid (ATRA). The expression of TRPC1, 3, 4 and 6 was correlated to the differentiation grade of NSCLC in patients, but there was no correlation to age, sex, smoking history and lung cancer cell type. ATRA upregulated TRPC3, TRPC4 and TRPC6 expression and enhanced Ca(2+) influx in A549 cells, however, ATRA showed no direct effect on TRPC channels. Inhibition of TRPC channels by pore-blocking antibodies decreased the cell mitosis, which was counteracted by chronic treatment with ATRA. Blockade of TRPC channels inhibited A549 cell proliferation, while overexpression of TRPCs increased the proliferation. We conclude that TRPC expression correlates to lung cancer differentiation. TRPCs mediate the pharmacological effect of ATRA and play important roles in regulating lung cancer cell differentiation and proliferation, which gives a new understanding of lung cancer biology and potential anti-cancer therapy.

FSH enhances the proliferation of ovarian cancer cells by activating transient receptor potential channel C3

Recent studies have suggested that FSH plays an important role in ovarian epithelial carcinogenesis. We demonstrated that FSH stimulates the proliferation and invasion of ovarian cancer cells, inhibits apoptosis and facilitates neovascularisation. Our previous work has shown that transient receptor potential channel C3 (TRPC3) contributes to the progression of human ovarian cancer. In this study, we further investigated the interaction between FSH and TRPC3. We found that FSH stimulation enhanced the expression of TRPC3 at both the mRNA and protein levels. siRNA-mediated silencing of TRPC3 expression inhibited the ability of FSH to stimulate proliferation and blocked apoptosis in ovarian cancer cell lines. FSH stimulation was associated with the up-regulation of TRPC3, while also facilitating the influx of Ca(2)(+) after treatment with a TRPC-specific agonist. Knockdown of TRPC3 abrogated FSH-stimulated Akt/PKB phosphorylation, leading to decreased expression of downstream effectors including survivin, HIF1-α and VEGF. Ovarian cancer specimens were analysed for TRPC3 expression; higher TRPC3 expression levels correlated with early relapse and worse prognosis. Association with poor disease-free survival and overall survival remained after adjusting for clinical stage and grade. In conclusion, TRPC3 plays a significant role in the stimulating activity of FSH and could be a potential therapeutic target for the treatment of ovarian cancer, particularly in postmenopausal women with elevated FSH levels.

Induction of epithelial-mesenchymal transition (EMT) in breast cancer cells is calcium signal dependent

Signals from the tumor microenvironment trigger cancer cells to adopt an invasive phenotype through epithelial-mesenchymal transition (EMT). Relatively little is known regarding key signal transduction pathways that serve as cytosolic bridges between cell surface receptors and nuclear transcription factors to induce EMT. A better understanding of these early EMT events may identify potential targets for the control of metastasis. One rapid intracellular signaling pathway that has not yet been explored during EMT induction is calcium. Here we show that stimuli used to induce EMT produce a transient increase in cytosolic calcium levels in human breast cancer cells. Attenuation of the calcium signal by intracellular calcium chelation significantly reduced epidermal growth factor (EGF)- and hypoxia-induced EMT. Intracellular calcium chelation also inhibited EGF-induced activation of signal transducer and activator of transcription 3 (STAT3), while preserving other signal transduction pathways such as Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. To identify calcium-permeable channels that may regulate EMT induction in breast cancer cells, we performed a targeted siRNA-based screen. We found that transient receptor potential-melastatin-like 7 (TRPM7) channel expression regulated EGF-induced STAT3 phosphorylation and expression of the EMT marker vimentin. Although intracellular calcium chelation almost completely blocked the induction of many EMT markers, including vimentin, Twist and N-cadherin, the effect of TRPM7 silencing was specific for vimentin protein expression and STAT3 phosphorylation. These results indicate that TRPM7 is a partial regulator of EMT in breast cancer cells, and that other calcium-permeable ion channels are also involved in calcium-dependent EMT induction. In summary, this work establishes an important role for the intracellular calcium signal in the induction of EMT in human breast cancer cells. Manipulation of calcium-signaling pathways controlling EMT induction in cancer cells may therefore be an important therapeutic strategy for preventing metastases.

Calcium-dependent deceleration of the cell cycle in muscle cells by simulated microgravity

Of all our mechanosensitive tissues, skeletal muscle is the most developmentally responsive to physical activity. Conversely, restricted mobility due to injury or disease results in muscle atrophy. Gravitational force is another form of mechanical input with profound developmental consequences. The mechanical unloading resulting from the reduced gravitational force experienced during spaceflight results in oxidative muscle loss. We examined the early stages of myogenesis under conditions of simulated microgravity (SM). C2C12 mouse myoblasts in SM proliferated more slowly (2.23× less) as a result of their being retained longer within the G2/M phase of the cell cycle (2.10× more) relative to control myoblasts at terrestrial gravity. Blocking calcium entry via TRP channels with SKF-96365 (10-20 μM) accumulated myoblasts within the G2/M phase of the cell cycle and retarded their proliferation. On the genetic level, SM resulted in the reduced expression of TRPC1 and IGF-1 isoforms, transcriptional events regulated by calcium downstream of mechanical input. A decrease in TRPC1-mediated calcium entry thus appears to be a pivotal event in the muscle atrophy brought on by gravitational mechanical unloading. Hence, relieving the constant force of gravity on cells might prove one valid experimental approach to expose the underlying mechanisms modulating mechanically regulated developmental programs.

Expression of transient receptor potential channel 6 in cervical cancer

BACKGROUND

Recent studies have reported that aberrant expression of transient receptor potential channel C6 (TRPC6) in a variety of human cancers is associated with aggressive behavior. However, the functional significance of TRPC6 in human cervical cancer is not known. This study was planned to detect whether TRPC6 is expressed in cervical cancer tissue and to evaluate the association between TPRC6 expression and clinicopathologic features.

METHODS

Tissue samples were collected from the West China Second UNIV Hospital of Sichuan University. TRPC6 expression was detected by quantitative real-time reverse transcription polymerase chain reaction and Western blotting. TRPC6 expression was evaluated by immunohistochemistry analysis of 40 cervical cancer specimens, and correlations were sought between elevated expression of TRPC6 and clinicopathologic features.

RESULTS

Increased expression of TRPC6 was detected in 25 of the 40 cervical cancer samples. Positive cells found in cervical carcinomas were significantly increased in numbers compared with specimens without lymphovascular space invasion. Elevated expression of TRPC6 was neither related to International Federation of Gynecology and Obstetrics stage nor pelvic lymph metastases. Indeed, the clinicopathologic analysis indicated that overexpression of TRPC6 was significantly associated with lymphovascular space invasion.

CONCLUSION

These results indicate that elevated expression of TRPC6 might be associated with an aggressive cervical cancer phenotype.

[TRP calcium channel and breast cancer: expression, role and correlation with clinical parameters]

Breast cancer (BC) has the highest incidence rate in women in industrialized countries. Statistically, it is estimated that one out of 10 women will develop BC during her life. Evidence is accumulating for the role of ion channels in the development of cancer. Most studied ion channels in BC are K(+) channels, which are involved in cell proliferation, cell cycle progression and cell migration, and Na(+) channels, which correlate with invasiveness. Emerging studies demonstrated the role of Ca(2+) signaling in cancer cell proliferation, survival and migration. Recent findings demonstrated that the expression and/or activity of the transient receptor potential (TRP) channels are altered in several cancers. Among the TRP families, TRPC (canonical or classical), TRPM (melastatin) and TRPV (vanilloid) are related to malignant growth and cancer progression. Although these channels are frequently and abundantly expressed in many tumors, their specific expression, activity and roles in BC are still poorly understood. The expression of TRP channels has also been proposed as a tool for diagnosis, prognosis and/or therapeutic issues of several diseases. In cancer, TRPV6 and TRPM8 have been proposed as tumor progression markers of prostate cancer outcome and TRPC6 as a novel therapeutic target for esophageal carcinoma. Interestingly high levels of TRPC3 expression correlate with a favorable prognosis in patients with lung adenocarcinoma. Our team has recently reported the expression and role of TRPC1, TRPC6, TRPM7, TRPM8 and TRPV6 in BC cell lines and primary cultures. We have also investigated TRP expression and their clinical significance in human breast adenocarcinoma and we suggest that TRP channels are new potential BC markers. Indeed TRPC1 and TRPM8 may be considered as good prognosis markers of well-differentiated tumors, TRPM7 as a proliferative marker of poorly differentiated tumors and TRPV6 as a prognosis marker of aggressive cancers. In this review, we summarize the data reported to date regarding the changes in TRP expression associated with BC. We also discuss the importance of TRP channels in BC cells proliferation and migration and their interest as new BC markers.

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.

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.

High-dose siRNAs upregulate mouse Eri-1 at both transcription and posttranscription levels

The eri-1 gene encodes a 3′ exonuclease that can negatively regulate RNA interference via siRNase activity. High-dose siRNAs (hd-siRNAs) can enhance Eri-1 expression, which in return degrade siRNAs and greatly reduces RNAi efficiency. Here we report that hd-siRNAs induce mouse Eri-1 (meri-1) expression through the recruitment of Sp1, Ets-1, and STAT3 to the meri-1 promoter and the formation of an Sp1-Ets-1-STAT3 complex. In addition, hd-siRNAs also abolish the 3′ untranslated region (UTR) mediated posttranscriptional repression of meri-1. Our findings demonstrate the molecular mechanism underlying the upregulation of meri-1 by hd-siRNA.

The transient receptor potential (TRP) channel TRPC3 TRP domain and AMP-activated protein kinase binding site are required for TRPC3 activation by erythropoietin

Modulation of intracellular calcium ([Ca(2+)](i)) by erythropoietin (Epo) is an important signaling pathway controlling erythroid proliferation and differentiation. Transient receptor potential (TRP) channels TRPC3 and homologous TRPC6 are expressed on normal human erythroid precursors, but Epo stimulates an increase in [Ca(2+)](i) through TRPC3 but not TRPC6. Here, the role of specific domains in the different responsiveness of TRPC3 and TRPC6 to erythropoietin was explored. TRPC3 and TRPC6 TRP domains differ in seven amino acids. Substitution of five amino acids (DDKPS) in the TRPC3 TRP domain with those of TRPC6 (EERVN) abolished the Epo-stimulated increase in [Ca(2+)](i). Substitution of EERVN in TRPC6 TRP domain with DDKPS in TRPC3 did not confer Epo responsiveness. However, substitution of TRPC6 TRP with DDKPS from TRPC3 TRP, as well as swapping the TRPC6 distal C terminus (C2) with that of TRPC3, resulted in a chimeric TRPC6 channel with Epo responsiveness similar to TRPC3. Substitution of TRPC6 with TRPC3 TRP and the putative TRPC3 C-terminal AMP-activated protein kinase (AMPK) binding site straddling TRPC3 C1/C2 also resulted in TRPC6 activation. In contrast, substitution of the TRPC3 C-terminal leucine zipper motif or TRPC3 phosphorylation sites Ser-681, Ser-708, or Ser-764 with TRPC6 sequence did not affect TRPC3 Epo responsiveness. TRPC3, but not TRPC6, and TRPC6 chimeras expressing TRPC3 C2 showed significantly increased plasma membrane insertion following Epo stimulation and substantial cytoskeletal association. The TRPC3 TRP domain, distal C terminus (C2), and AMPK binding site are critical elements that confer Epo responsiveness. In particular, the TRPC3 C2 and AMPK site are essential for association of TRPC3 with the cytoskeleton and increased channel translocation to the cell surface in response to Epo stimulation.

Dendrotoxin-κ suppresses tumor growth induced by human lung adenocarcinoma A549 cells in nude mice

Voltage-gated K(+) (Kv) channels have been considered to be a regulator of membrane potential and neuronal excitability. Recently, accumulated evidence has indicated that several Kv channel subtypes contribute to the control of cell proliferation in various types of cells and are worth noting as potential emerging molecular targets of cancer therapy. In the present study, we investigated the effects of the Kv1.1-specific blocker, dendrotoxin-κ (DTX-κ, on tumor formation induced by the human lung adenocarcinoma cell line A549 in a xenograft model. Kv1.1 mRNA and protein was expressed in A549 cells and the blockade of Kv1.1 by DTX-κ, reduced tumor formation in nude mice. Furthermore, treatment with DTX-κ significantly increased protein expression of p21(Waf1/Cip1), p27(Kip1), and p15(INK4B) and significantly decreased protein expression of cyclin D3 in tumor tissues compared to the control. These results suggest that DTX-κ has anti-tumor effects in A549 cells through the pathway governing G1-S transition.

Ion channels and transporters in cancer. 4. Remodeling of Ca(2+) signaling in tumorigenesis: role of Ca(2+) transport

The Ca(2+) signal has major roles in cellular processes important in tumorigenesis, including migration, invasion, proliferation, and apoptotic sensitivity. New evidence has revealed that, aside from altered expression and effects on global cytosolic free Ca(2+) levels via direct transport of Ca(2+), some Ca(2+) pumps and channels are able to contribute to tumorigenesis via mechanisms that are independent of their ability to transport Ca(2+) or effect global Ca(2+) homeostasis in the cytoplasm. Here, we review some of the most recent studies that present evidence of altered Ca(2+) channel or pump expression in tumorigenesis and discuss the importance and complexity of localized Ca(2+) signaling in events critical for tumor formation.

Down-regulation of Orai3 arrests cell-cycle progression and induces apoptosis in breast cancer cells but not in normal breast epithelial cells

Breast cancer (BC) is the leading cancer in the world in terms of incidence and mortality in women. However, the mechanism by which BC develops remains largely unknown. The increase in cytosolic free Ca(2+) can result in different physiological changes including cell growth and death. Orai isoforms are highly Ca(2+) selective channels. In the present study, we analyzed Orai3 expression in normal and cancerous breast tissue samples, and its role in MCF-7 BC and normal MCF-10A mammary epithelial cell lines. We found that the expression of Orai3 mRNAs was higher in BC tissues and MCF-7 cells than in normal tissues and MCF-10A cells. Down-regulation of Orai3 by siRNA inhibited MCF-7 cell proliferation and arrested cell cycle at G1 phase. This phenomenon is associated with a reduction in CDKs 4/2 (cyclin-dependent kinases) and cyclins E and D1 expression and an accumulation of p21(Waf1/Cip1) (a cyclin-dependent kinase inhibitor) and p53 (a tumor-suppressing protein). Orai3 was also involved in MCF-7 cell survival. Furthermore, Orai3 mediated Ca(2+) entry and contributed to intracellular calcium concentration ([Ca(2+)](i)). In MCF-10A cells, silencing Orai3 failed to modify [Ca(2+)](i), cell proliferation, cell-cycle progression, cyclins (D1, E), CDKs (4, 2), and p21(Waf1/Cip1) expression. Our results provide strong evidence for a significant effect of Orai3 on BC cell growth in vitro and show that this effect is associated with the induction of cell cycle and apoptosis resistance. Our study highlights a possible role of Orai3 as therapeutic target in BC therapy.

Oncogenic TRP channels

Ion channels and notably TRP channels play a crucial role in a variety of physiological functions and in addition these channels have been also shown associated with several diseases including cancer. The process of cancer initiation and progression involves the altered expression of one or more of TRP proteins, depending on the nature of the cancer. The most clearly described role in pathogenesis has been evidenced for TRPM8, TRPV6 and TRPM1 channels. The increased expression of some other channels, such as TRPV1, TRPC1, TRPC6, TRPM4, and TRPM5 has also been demonstrated in some cancers. Further investigations are required to precise the role of TRP channels in cancer development and/or progression and to specifically develop further knowledge of TRP proteins as discriminative markers and prospective targets for pharmaceutical intervention in treating cancer.

Transient receptor potential canonical 3 (TRPC3) mediates thrombin-induced astrocyte activation and upregulates its own expression in cortical astrocytes

Reactive astrogliosis, defined by abnormal morphology and excessive cell proliferation, is a characteristic response of astrocytes to CNS injuries, including intracerebral hemorrhage. Thrombin, a major blood-derived serine protease, leaks into the brain parenchyma upon blood-brain barrier disruption and can induce brain injury and astrogliosis. Transient receptor potential canonical (TRPC) channels, Ca(2+)-permeable, nonselective cation channels, are expressed in astrocytes and involved in Ca(2+) influx after receptor stimulation; however, their pathophysiological functions in reactive astrocytes remain unknown. We investigated the pathophysiological roles of TRPC in thrombin-activated cortical astrocytes. Application of thrombin (1 U/ml, 20 h) upregulated TRPC3 protein, which was associated with increased Ca(2+) influx after thapsigargin treatment. Pharmacological manipulations revealed that the TRPC3 upregulation was mediated by protease-activated receptor 1 (PAR-1), extracellular signal-regulated protein kinase, c-Jun NH(2)-terminal kinase, and nuclear factor-κB signaling and required de novo protein synthesis. The Ca(2+) signaling blockers BAPTA-AM, cyclopiazonic acid, and 2-aminoethoxydiphenyl borate and a selective TRPC3 inhibitor, pyrazole-3, attenuated TRPC3 upregulation, suggesting that Ca(2+) signaling through TRPC3 contributes to its increased expression. Thrombin-induced morphological changes at 3 h upregulated S100B, a marker of reactive astrocytes, at 20 h and increased astrocytic proliferation by 72 h, all of which were inhibited by Ca(2+)-signaling blockers and specific knockdown of TRPC3 using small interfering RNA. Intracortical injection of SFLLR-NH(2), a PAR-1 agonist peptide, induced proliferation of astrocytes, most of which were TRPC3 immunopositive. These results suggest that thrombin dynamically upregulates TRPC3 and that TRPC3 contributes to the pathological activation of astrocytes in part through a feedforward upregulation of its own expression.

Disruption of transient receptor potential canonical channel 1 causes incomplete cytokinesis and slows the growth of human malignant gliomas

Despite decades of research, primary brain tumors, gliomas, lack effective treatment options and present a huge clinical challenge. Particularly, the most malignant subtype, Glioblastoma multiforme, proliferates extensively and cells often undergo incomplete cell divisions, resulting in multinucleated cells. We now present evidence that multinucleated glioma cells result from the functional loss of transient receptor potential canonical 1 (TRPC1) channels, plasma membrane proteins involved in agonist-induced calcium entry and reloading of intracellular Ca(2+) stores. Pharmacological inhibition or shRNA mediated suppression of TRPC1 causes loss of functional channels and store-operated calcium entry in D54MG glioma cells. This is associated with reduced cell proliferation and, frequently, with incomplete cell division. The resulting multinucleated cells are reminiscent of those found in patient biopsies. In a flank tumor model, tumor size was significantly decreased when TRPC1 expression was disrupted using a doxycycline inducible shRNA knockdown approach. These results suggest that TRPC1 channels play an important role in glioma cell division most likely by regulating calcium signaling during cytokinesis.

[Expression of transient receptor potential canonical channel proteins in human non-small cell lung cancer]

背景与目的

经典瞬时受体电位（transient receptor potential canonical, TRPC）通道蛋白是一种非选择性阳离子通道蛋白家族，主要位于细胞膜表面，对钙离子具有通透性。研究认为，TRPC可能构成钙池操纵性钙通道（store-operated calcium channels, SOCC）并介导钙池操纵性钙内流（store-operated calcium entry, SOCE），从而参与细胞的增殖、迁移、基因转录等生命活动。本研究检测非小细胞肺癌（non-small cell lung cancer, NSCLC）组织中TRPC mRNA及蛋白质的表达情况，初步探讨TRPC与NSCLC的可能关系。

方法

建立TRPC1-7等7个家族成员的荧光定量PCR检测方法，对24例NSCLC患者的肿瘤组织进行了TRPC mRNA的定量检测，并通过蛋白质免疫印迹法对TRPC在蛋白质水平的表达进行了验证。

结果

在NSCLC患者癌组织检测到TRPC1、TRPC3、TRPC4和TRPC6 mRNA的表达，未检测到TRPC2、TRPC5和TRPC7 mRNA的表达。肺癌组织中TRPC表达丰度为：TRPC1≈TRPC6>TRPC3>TRPC4。蛋白质免疫印迹证实了非小细胞肺癌组织中TRPC1、TRPC3、TRPC4和TRPC6在蛋白质水平的表达。

结论

非小细胞肺癌组织在mRNA和蛋白质水平均表达TRPC1、TRPC3、TRPC4和TRPC6，其中主要表达TRPC1和TRPC6，它们在构成肺癌细胞中SOCC、介导产生SOCE中的作用有待进一步研究。

Essential role of TRPC6 channels in G2/M phase transition and development of human glioma

BACKGROUND

Patients with glioblastoma multiforme, the most aggressive form of glioma, have a median survival of approximately 12 months. Calcium (Ca(2+)) signaling plays an important role in cell proliferation, and some members of the Ca(2+)-permeable transient receptor potential canonical (TRPC) family of channel proteins have demonstrated a role in the proliferation of many types of cancer cells. In this study, we investigated the role of TRPC6 in cell cycle progression and in the development of human glioma.

METHODS

TRPC6 protein and mRNA expression were assessed in glioma (n = 33) and normal (n = 17) brain tissues from patients and in human glioma cell lines U251, U87, and T98G. Activation of TRPC6 channels was tested by platelet-derived growth factor-induced Ca(2+) imaging. The effect of inhibiting TRPC6 activity or expression using the dominant-negative mutant TRPC6 (DNC6) or RNA interference, respectively, was tested on cell growth, cell cycle progression, radiosensitization of glioma cells, and development of xenografted human gliomas in a mouse model. The green fluorescent protein (GFP) and wild-type TRPC6 (WTC6) were used as controls. Survival of mice bearing xenografted tumors in the GFP, DNC6, and WTC6 groups (n = 13, 15, and 13, respectively) was compared using Kaplan-Meier analysis. All statistical tests were two-sided.

RESULTS

Functional TRPC6 was overexpressed in human glioma cells. Inhibition of TRPC6 activity or expression attenuated the increase in intracellular Ca(2+) by platelet-derived growth factor, suppressed cell growth and clonogenic ability, induced cell cycle arrest at the G2/M phase, and enhanced the antiproliferative effect of ionizing radiation. Cyclin-dependent kinase 1 activation and cell division cycle 25 homolog C expression regulated the cell cycle arrest. Inhibition of TRPC6 activity also reduced tumor volume in a subcutaneous mouse model of xenografted human tumors (P = .014 vs GFP; P < .001 vs WTC6) and increased mean survival in mice in an intracranial model (P < .001 vs GFP or WTC6).

CONCLUSIONS

In this preclinical model, TRPC6 channels were essential for glioma development via regulation of G2/M phase transition. This study suggests that TRPC6 might be a new target for therapeutic intervention of human glioma.