Critical role of TRPC6 channels in G2 phase transition and the development of human oesophageal cancer

MARVELD1 inhibited cell proliferation and enhance chemosensitivity via increasing expression of p53 and p16 in hepatocellular carcinoma

We have previously found that expression of MARVELD1 was remarkably downregulated in multiple tumor tissues, but unclear in hepatocellular carcinoma (HCC) and its function has not been explored yet. In the present study, to uncover the underlying mechanism of MARVELD1 in the pathogenesis and development of HCC, we investigated the expression pattern of MARVELD1 and its effect on tumor proliferation in HCC. The results indicated the frequent downregulation of MARVELD1 in clinic samples and cell lines of HCC resulted from promoter methylation, as well as genetic deletion. Furthermore, treatment of MARVELD1 unexpressing Hep3B2.1-7 and PLC/PRF/5 cells with the demethylating agent 5-aza-2' deoxycytidine restored its expression. Overexpression of MARVELD1 suppressed the proliferation of HCC cells in vitro and in vivo, whereas downregulation of endogenous MARVELD1 by shRNAs significantly enhanced these characters. MARVELD1 overexpression could enhance chemosensitivity of HCC cells to epirubicin and 10-hydroxycamptothecin. Corresponding to these results, the expression of p-ERK1/2 and cyclin D1 were decreased, whereas p16 and p53 were increased in MARVELD1-transfected cells. We also demonstrated that knockdown of MARVELD1 resulted in upregulation of p-ERK1/2 and cyclin D1, and downregulation of p16 and p53. Moreover, the effect of the decreased cell growth rate was significantly reversed when MARVELD1-overexpressing cells were trasfected with p53 or p16 siRNA. Our findings suggest that MARVELD1 is a tumor suppressor by negatively regulating proliferation, tumor growth and chemosensitivity of HCC cells via increasing p53 and p16 in vitro and in vivo. MARVELD1 may be a potential target for HCC therapy.

Integration of transient receptor potential canonical channels with lipids

Transient receptor potential canonical (TRPC) channels are the canonical (C) subset of the TRP proteins, which are widely expressed in mammalian cells. They are thought to be primarily involved in determining calcium and sodium entry and have wide-ranging functions that include regulation of cell proliferation, motility and contraction. The channels are modulated by a multiplicity of factors, putatively existing as integrators in the plasma membrane. This review considers the sensitivities of TRPC channels to lipids that include diacylglycerols, phosphatidylinositol bisphosphate, lysophospholipids, oxidized phospholipids, arachidonic acid and its metabolites, sphingosine-1-phosphate, cholesterol and some steroidal derivatives and other lipid factors such as gangliosides. Promiscuous and selective lipid sensing have been detected. There appear to be close working relationships with lipids of the phospholipase C and A₂ enzyme systems, which may enable integration with receptor signalling and membrane stretch. There are differences in the properties of each TRPC channel that are further complicated by TRPC heteromultimerization. The lipids modulate activity of the channels or insertion in the plasma membrane. Lipid microenvironments and intermediate sensing proteins have been described that include caveolae, G protein signalling, SEC14-like and spectrin-type domains 1 (SESTD1) and podocin. The data suggest that lipid sensing is an important aspect of TRPC channel biology enabling integration with other signalling systems.

Protons and Ca2+: ionic allies in tumor progression?

Ion channels and G-protein-coupled receptors (GPCRs) play a fundamental role in cancer progression by influencing Ca(2+) influx and signaling pathways in transformed cells. Transformed cells thrive in a hostile environment that is characterized by extracellular acidosis that promotes the pathological phenotype. The pathway(s) by which extracellular protons achieve this remain unclear. Here, a role for proton-sensing ion channels and GPCRs as mediators of the effects of extracellular protons in cancer cells is discussed.

The critical role of CD133(+)CD44(+/high) tumor cells in hematogenous metastasis of liver cancers

Metastatic hepatocellular carcinoma (HCC) is one of the most lethal cancers worldwide. However, the cell population responsible for its metastasis remains largely unknown. Here, we reported that CD133(+)CD44(+/high) defined a subgroup of tumor cells that was responsible for hematogenous metastasis of liver cancers. Immunohistochemical investigation of human HCC specimens revealed that the number of CD133(+) and CD44(+) HCC cells was increased and was associated with portal vein invasion. Purified CD133(+) or CD44(high) HCC cells were superior in clonogenic growth and vascular invasion, respectively. Thus, the combination of CD133 and CD44 was used to define a novel HCC sub-population. CD133(+)CD44(high), but not CD133(+)CD44(low/-), CD133(-)CD44(high) or CD133(-)CD44(low/-) xenografts, produced intrahepatic or lung metastasis in nude mice. Further analysis of human HCC samples by flow cytometry showed that the number of CD133(+)CD44(+) tumor cells was associated with portal vein metastasis. The cDNA microarray analysis of CD133(+)CD44(+) and CD133(+)CD44(-) tumor cells isolated from metastatic HCC patients revealed that these cells comprised of two different populations possessing distinct gene expression profiles. Our results suggest that CD133(+)CD44(+) tumor cells are a particular population responsible for hematogenous metastasis in liver cancers and that these cells might be targets for treatment of HCC metastasis.

Ion channels and transporters in cancer. 1. Ion channels and cell proliferation in cancer

Progress through the cell mitotic cycle requires precise timing of the intrinsic molecular steps and tight coordination with the environmental signals that maintain a cell into the proper physiological context. Because of their great functional flexibility, ion channels coordinate the upstream and downstream signals that converge on the cell cycle machinery. Both voltage- and ligand-gated channels have been implicated in the control of different cell cycle checkpoints in normal as well as neoplastic cells. Ion channels mediate the calcium signals that punctuate the mitotic process, the cell volume oscillations typical of cycling cells, and the exocytosis of autocrine or angiogenetic factors. Other functions of ion channels in proliferation are still matter of debate. These may or may not depend on ion transport, as the channel proteins can form macromolecular complexes with growth factor and cell adhesion receptors. Direct conformational coupling with the cytoplasmic regulatory proteins is also possible. Derangement or relaxed control of the above processes can promote neoplasia. Specific types of ion channels have turned out to participate in the different stages of the tumor progression, in which cell heterogeneity is increased by the selection of malignant cell clones expressing the ion channel types that better support unrestrained growth. However, a comprehensive mechanistic picture of the functional relations between ion channels and cell proliferation is yet not available, partly because of the considerable experimental challenges offered by studying these processes in living mammalian cells. No doubt, such studies will constitute one of the most fruitful research fields for the next generation of cell physiologists.

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.

Transient receptor potential (TRP) channels as drug targets for diseases of the digestive system

Approximately 20 of the 30 mammalian transient receptor potential (TRP) channel subunits are expressed by specific neurons and cells within the alimentary canal. They subserve important roles in taste, chemesthesis, mechanosensation, pain and hyperalgesia and contribute to the regulation of gastrointestinal motility, absorptive and secretory processes, blood flow, and mucosal homeostasis. In a cellular perspective, TRP channels operate either as primary detectors of chemical and physical stimuli, as secondary transducers of ionotropic or metabotropic receptors, or as ion transport channels. The polymodal sensory function of TRPA1, TRPM5, TRPM8, TRPP2, TRPV1, TRPV3 and TRPV4 enables the digestive system to survey its physical and chemical environment, which is relevant to all processes of digestion. TRPV5 and TRPV6 as well as TRPM6 and TRPM7 contribute to the absorption of Ca²⁺ and Mg²⁺, respectively. TRPM7 participates in intestinal pacemaker activity, and TRPC4 transduces muscarinic acetylcholine receptor activation to smooth muscle contraction. Changes in TRP channel expression or function are associated with a variety of diseases/disorders of the digestive system, notably gastro-esophageal reflux disease, inflammatory bowel disease, pain and hyperalgesia in heartburn, functional dyspepsia and irritable bowel syndrome, cholera, hypomagnesemia with secondary hypocalcemia, infantile hypertrophic pyloric stenosis, esophageal, gastrointestinal and pancreatic cancer, and polycystic liver disease. These implications identify TRP channels as promising drug targets for the management of a number of gastrointestinal pathologies. As a result, major efforts are put into the development of selective TRP channel agonists and antagonists and the assessment of their therapeutic potential.

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.

Rb+ efflux assay for assessment of non-selective cation channel activities

ABSTRACT Transient receptor potential (TRP) channels have been found to play important roles in cellular physiology and hold promise as therapeutic targets. These channels activate in response to a variety of chemical or physical stimuli and conduct non-selective cation currents (NSCC). Due to their unique activation properties, application of automated electrophysiology to measure the channel activity has been difficult. Using HEK293 cells stably expressing human TRP channels, hTRPC6 and hTRPA1, we developed and validated a high-throughput Rb(+) efflux assay for NSCC channels. The assay was performed in cell-based 96-well format. A significant increase in Rb(+) efflux can be detected upon channel activation by specific agonists, confirming that both TRPC6 and TRPA1 channels are permeable to Rb(+) ions. The agonists induced Rb(+) efflux can be blocked by known channel blockers and selected compounds from our high-throughput screening (HTS) hits. The assay is suitable for HTS with Z' factors of 0.53 and above. We also tested the Ca(2+) effect on channel activities in this assay. Both TRPC6 and TRPA1 channels were found to be inhibited by increasing the concentration of Ca(2+) in the assay buffer. However, Ca(2+) significantly reduced the potency of allyl isothiocyanate (AITC) on TRPA1 but did not affect the potency of carbochol on TRPC6. Using this assay for secondary confirmation screen, we successfully identified and confirmed the positive hits as TRPC6 inhibitors.

The role of TRPC6 in HGF-induced cell proliferation of human prostate cancer DU145 and PC3 cells

Hepatocyte growth factor (HGF) is a glycoprotein that induces prostate cancer cell proliferation, migration and invasion. The activation of transient receptor potential canonical 6 (TRPC6) channels is considered important in promoting prostate cancer cell proliferation. In this study, we assessed the role of endogenous TRPC6 channels in the HGF-induced cell proliferation of prostate cancer. Reverse transcription-PCR and Western blotting were used to investigate TRPC6 expression. Electrophysiological techniques (whole-cell patch clamp configuration) and Ca(2+) imaging analysis were used to investigate the channel activity in cells. The effects of TRPC6 channels on cell cycle progression, cell apoptosis and cell growth were also examined. TRPC6 and c-MET were expressed in DU145 and PC3 cells. In addition, functional TRPC6 channels were present in DU145 and PC3 cells, and TRPC6 knockdown suppressed TRPC-like currents evoked by oleoyl-2-acetyl-sn-glycerol (OAG). Inhibition of TRPC6 channels in DU145 and PC3 cells abolished OAG- and HGF-induced Ca(2+) entry. Furthermore, inhibition of TRPC6 channels arrested DU145 and PC3 cells at the G(2)/M phase and suppressed HGF-induced cell proliferation. Collectively, our results indicate that TRPC6 has an important role in HGF-induced DU145 and PC3 cell proliferation.

[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.