Downregulation of Ca2+-activated Cl- channel TMEM16A by the inhibition of histone deacetylase in TMEM16A-expressing cancer cells

Function and Regulation of the Calcium-Activated Chloride Channel Anoctamin 1 (TMEM16A)

Various human tissues express the calcium-activated chloride channel Anoctamin 1 (ANO1), also known as TMEM16A. ANO1 allows the passive chloride flux that controls different physiological functions ranging from muscle contraction, fluid and hormone secretion, gastrointestinal motility, and electrical excitability. Overexpression of ANO1 is associated with pathological conditions such as hypertension and cancer. The molecular cloning of ANO1 has led to a surge in structural, functional, and physiological studies of the channel in several tissues. ANO1 is a homodimer channel harboring two pores - one in each monomer - that work independently. Each pore is activated by voltage-dependent binding of two intracellular calcium ions to a high-affinity-binding site. In addition, the binding of phosphatidylinositol 4,5-bisphosphate to sites scattered throughout the cytosolic side of the protein aids the calcium activation process. Furthermore, many pharmacological studies have established ANO1 as a target of promising compounds that could treat several illnesses. This chapter describes our current understanding of the physiological roles of ANO1 and its regulation under physiological conditions as well as new pharmacological compounds with potential therapeutic applications.

TMEM16A ion channel: A novel target for cancer treatment

Cancer draws attention owing to the high morbidity and mortality. It is urgent to develop safe and effective cancer therapeutics. The calcium-activated chloride channel TMEM16A is widely distributed in various tissues and regulates physiological functions. TMEM16A is abnormally expressed in several cancers and associate with tumorigenesis, metastasis, and prognosis. Knockdown or inhibition of TMEM16A in cancer cells significantly inhibits cancer development. Therefore, TMEM16A is considered as a biomarker and therapeutic target for some cancers. This work reviews the cancers associated with TMEM16A. Then, the molecular mechanism of TMEM16A overexpression in cancer was analyzed, and the possible signal transduction mechanism of TMEM16A regulating cancer development was summarized. Finally, TMEM16A inhibitors with anticancer effect and their anticancer mechanism were concluded. We hope to provide new ideas for pharmacological studies on TMEM16A in cancer.

Recent advancement of HDAC inhibitors against breast cancer

Recent studies highlight the great potential impact of HDAC inhibitors (HDACis) in suppressing TNBC, even though clinical trials including a single HDACis demonstrated unsatisfactory outcomes against TNBC. New compounds created to achieve isoform selectivity and/or a polypharmacological HDAC strategy have also produced interesting results. The current study discusses the HDACis pharmacophoric models and the structural alterations that produced drugs with strong inhibitory effects on TNBC progression. With more than 2 million new cases reported in 2018, breast cancer-the most common cancer among women worldwide-poses a significant financial burden on an already deteriorating public health system. Due to a lack of therapies being developed for triple-negative breast cancers and the development of resistance to the current treatment options, it is imperative to plan novel therapeutics in order to bring new medications to the pipeline. Additionally, HDACs deacetylate a large number of nonhistone cellular substrates that control a variety of biological processes, such as the beginning and development of cancer. The significance of HDACs in cancer and the therapeutic potential of HDAC inhibitor. Furthermore, we also reported molecular docking study with four HDAC inhibitors and performed molecular dynamic stimulation of the best dock score compound. Among the four ligands belinostat compound showed best binding affinity with histone deacetylase protein which was -8.7 kJ/mol. It also formed five conventional hydrogen bond with Gly 841, His 669, His 670, pro 809, and His 709 amino acid residues.

Role of ANO1 in tumors and tumor immunity

Dysregulation of gene amplification, cell-signaling-pathway transduction, epigenetic and transcriptional regulation, and protein interactions drives tumor-cell proliferation and invasion, while ion channels also play an important role in the generation and development of tumor cells. Overexpression of Ca²⁺-activated Cl- channel anoctamin 1 (ANO1) is shown in numerous cancer types and correlates with poor prognosis. However, the mechanisms involved in ANO1-mediated malignant cellular transformation and the role of ANO1 in tumor immunity remain unknown. In this review, we discuss recent studies to determine the role of ANO1 in tumorigenesis and provide novel insights into the role of ANO1 in the context of tumor immunity. Furthermore, we analyze the roles and potential mechanisms of ANO1 in different types of cancers, and provide novel notions for the role of ANO1 in the tumor microenvironment and for potential use of ANO1 in clinical applications. Our review shows that ANO1 is involved in tumor immunity and microenvironment, and may, therefore, be an effective biomarker and therapeutic drug target.

Pathophysiological role of ion channels and transporters in HER2-positive breast cancer

The incidence of breast cancer (BC) has been increasing each year, and BC is now the most common malignant tumor in women. Among the numerous BC subtypes, HER2-positive BC can be treated with a variety of strategies based on targeting HER2. Although there has been great progress in the treatment of HER2-positive BC, recurrence, metastasis and drug resistance remain considerable challenges. The dysfunction of ion channels and transporters can affect the development and progression of HER2-positive BC, so these entities are expected to be new therapeutic targets. This review summarizes various ion channels and transporters associated with HER2-positive BC and suggests potential targets for the development of new and effective therapies.

Activation of TMEM16A Ca2+-activated Cl- channels by ROCK1/moesin promotes breast cancer metastasis

Introduction

Transmembrane protein 16A (TMEM16A) is a Ca²⁺-activated chloride channel that plays a role in cancer cell proliferation, migration, invasion, and metastasis. However, whether TMEM16A contributes to breast cancer metastasis remains unknown.

Objective

In this study, we investigated whether TMEM16A channel activation by ROCK1/moesin promotes breast cancer metastasis.

Methods

Wound healing assays and transwell migration and invasion assays were performed to study the migration and invasion of MCF-7 and T47D breast cancer cells. Western blotting was performed to evaluate the protein expression, and whole-cell patch clamp recordings were used to record TMEM16A Cl⁻ currents. A mouse model of breast cancer lung metastasis was generated by injecting MCF-7 cells via the tail vein. Metastatic nodules in the lung were assessed by hematoxylin and eosin staining. Lymph node metastasis, overall survival, and metastasis-free survival of breast cancer patients were assessed using immunohistochemistry and The Cancer Genome Atlas dataset.

Results

TMEM16A activation promoted breast cancer cell migration and invasion in vitro as well as breast cancer metastasis in mice. Patients with breast cancer who had higher TMEM16A levels showed greater lymph node metastasis and shorter survival. Mechanistically, TMEM16A promoted migration and invasion by activating EGFR/STAT3/ROCK1 signaling, and the role of the TMEM16A channel activity was important in this respect. ROCK1 activation by RhoA enhanced the TMEM16A channel activity via the phosphorylation of moesin at T558. The cooperative action of TMEM16A and ROCK1 was supported through clinical findings indicating that breast cancer patients with high levels of TMEM16A/ROCK1 expression showed greater lymph node metastasis and poor survival.

Conclusion

Our findings revealed a novel mechanism underlying TMEM16A-mediated breast cancer metastasis, in which ROCK1 increased TMEM16A channel activity via moesin phosphorylation and the increase in TMEM16A channel activities promoted cell migration and invasion. TMEM16A inhibition may be a novel strategy for treating breast cancer metastasis.

The Ca2+-activated chloride channel ANO1/TMEM16A: An emerging therapeutic target for epithelium-originated diseases?

Anoctamin 1 (ANO1) or TMEM16A gene encodes a member of Ca²⁺ activated Cl^– channels (CaCCs) that are critical for physiological functions, such as epithelial secretion, smooth muscle contraction and sensory signal transduction. The attraction and interest in ANO1/TMEM16A arise from a decade long investigations that abnormal expression or dysfunction of ANO1 is involved in many pathological phenotypes and diseases, including asthma, neuropathic pain, hypertension and cancer. However, the lack of specific modulators of ANO1 has impeded the efforts to validate ANO1 as a therapeutic target. This review focuses on the recent progress made in understanding of the pathophysiological functions of CaCC ANO1 and the current modulators used as pharmacological tools, hopefully illustrating a broad spectrum of ANO1 channelopathy and a path forward for this target validation.

Simvastatin inhibits oral squamous cell carcinoma by targeting TMEM16A Ca2+-activated chloride channel

PURPOSE

Ca²⁺-activated chloride channel TMEM16A has been found to be overexpressed in many cancers including head and neck squamous cell carcinoma (HNSCC). Nevertheless, the role of TMEM16A in oral squamous cell carcinoma (OSCC) remains unclear. Although simvastatin is known to produce anti-tumor effect, the mechanisms by which simvastatin inhibits cancer remain unclear.

METHODS

In this study, we explored the role of TMEM16A expression in human OSCC tissues using both TCGA dataset and immunohistochemistry. CCK-8 assay was applied to evaluate cell proliferation. Patch clamp technique was applied to record TMEM16A Cl^- currents.

RESULTS

We found that high TMEM16A expression is related with large tumor size, lymph node metastasis, and poor clinical outcome in patients with OSCC. In addition, TMEM16A overexpression could promote cell proliferation, and inhibition of TMEM16A channel activities could suppress cell proliferation in OSCC cells. Furthermore, simvastatin could suppress TMEM16A channel activities, and inhibited cell proliferation in OSCC cells via TMEM16A.

CONCLUSION

Our findings identify a novel anti-tumor mechanism of simvastatin by targeting TMEM16A. Simvastatin may represent an innovative strategy for treating OSCC with high TMEM16A expression.

Downregulation of the Ca2+-activated K+ channel KCa3.1 in mouse preosteoblast cells treated with vitamin D receptor agonist

The maturity of osteoblasts by proliferation and differentiation in preosteoblasts is essential for maintaining bone homeostasis. The beneficial effects of vitamin D on bone homeostasis in mammals have been demonstrated experimentally and clinically. However, the direct actions of vitamin D on preosteoblasts remain to be fully elucidated. In this study, we found that the functional activity of intermediate-conductance Ca²⁺-activated K⁺ channels (K_Ca3.1) positively regulated cell proliferation in MC3T3-E1 cells derived from mouse preosteoblasts by enhancing intracellular Ca²⁺ signaling. We examined the effects of treatment with vitamin D receptor (VDR) agonist on the expression and activity of K_Ca3.1 by real-time PCR examination, Western blotting, Ca²⁺ imaging, and patch clamp analyses in mouse MC3T3-E1 cells. Following the downregulation of K_Ca3.1 transcriptional modulators such as Fra-1 and HDAC2, K_Ca3.1 activity was suppressed in MC3T3-E1 cells treated with VDR agonists. Furthermore, application of the K_Ca3.1 activator DCEBIO attenuated the VDR agonist-evoked suppression of cell proliferation rate. These findings suggest that a decrease in K_Ca3.1 activity is involved in the suppression of cell proliferation rate in VDR agonist-treated preosteoblasts. Therefore, K_Ca3.1 plays an important role in bone formation by promoting osteoblastic proliferation under physiological conditions.

The multifaceted role of TMEM16A in cancer

The calcium-activated chloride channel TMEM16A is intimately linked to cancers. Over decades, TMEM16A over-expression and contribution to prognosis have been widely studied for multiple cancers strengthening the idea that TMEM16A could be a valuable biomarker and a promising therapeutic target. Surprisingly, from the survey of the literature, it appears that TMEM16A has been involved in multiple cancer-related functions and a large number of molecular targets of TMEM16A have been proposed. Thus, TMEM16A appears to be an ion channel with a multifaceted role in cancers. In this review, we summarize the latest development regarding TMEM16A contribution to cancers. We will survey TMEM16A contribution in cancer prognosis, the origins of its over-expression in cancer cells, the multiple biological functions and molecular pathways regulated by TMEM16A. Then, we will consider the question regarding the molecular mechanism of TMEM16A in cancers and the possible basis for the multifaceted role of TMEM16A in cancers.

TNF-α-induced miR-450a mediates TMEM182 expression to promote oral squamous cell carcinoma motility

Distant metastasis leads oral cancer patients into a poor survival rate and a high recurrence stage. During tumor progression, dysregulated microRNAs (miRNAs) have been reported to involve tumor initiation and modulate oral cancer malignancy. MiR-450a was significantly upregulated in oral squamous cell carcinoma (OSCC) patients without functional reports. This study was attempted to uncover the molecular mechanism of novel miR-450a in OSCC. Mir-450a expression was examined by quantitative RT-PCR, both in OSCC cell lines and patients. Specific target of miR-450a was determined by software prediction, luciferase reporter assay, and correlation with target protein expression. The functions of miR-450a and TMEM182 were accessed by adhesion and transwell invasion analyses. Determination of the expression and cellular localization of TMEM182 was examined by RT-PCR and by immunofluorescence staining. The signaling pathways involved in regulation of miR-450a were investigated using the kinase inhibitors. Overexpression of miR-450a in OSCC cells impaired cell adhesion ability and induced invasiveness, which demonstrated the functional role of miR-450a as an onco-miRNA. Interestingly, tumor necrosis factor alpha (TNF-α)-mediated expression of TMEM182 was regulated by miR-450a induction. MiR-450a-reduced cellular adhesion was abolished by TMEM182 restoration. Furthermore, the oncogenic activity of TNF-α/miR-450a/TMEM182 axis was primarily through activating extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. ERK1/2 inhibitor prevented the TNF-α-induced miR-450a expression and enhanced adhesion ability. Our data suggested that TNF-α-induced ERK1/2-dependent miR-450a against TMEM182 expression exerted a great influence on increasing OSCC motility. Overall, our results provide novel molecular insights into how TNF-α contributes to oral carcinogenesis through miR-450a that targets TMEM182.

Lipid Peroxidation Drives Renal Cyst Growth In Vitro through Activation of TMEM16A

BACKGROUND

Transepithelial chloride^- secretion, through the chloride channels cystic fibrosis transmembrane conductance regulator (CFTR) and TMEM16A (anoctamin 1), drives cyst enlargement in polycystic kidney disease (PKD). Polycystic kidneys are hypoxic, and oxidative stress activates TMEM16A. However, mechanisms for channel activation in PKD remain obscure.

METHODS

Using tissue samples from patients with autosomal dominant PKD, embryonic kidney cultures, and an MDCK in vitro cyst model, we assessed peroxidation of plasma membrane phospholipids in human and mouse polycystic kidneys. We also used electrophysiologic Ussing chamber and patch clamp experiments to analyze activation of TMEM16A and growth of renal cysts.

RESULTS

Peroxidation of phospholipids in human and mouse kidneys as well as MDCK cysts in vitro is probably due to enhanced levels of reactive oxygen species. Lipid peroxidation correlated with increased cyst volume as shown in renal cultures and MDCK cysts in three-dimensional cultures. Reactive oxygen species and lipid peroxidation strongly activated TMEM16A, leading to depletion of calcium ion stores and store-operated calcium influx. Activation of TMEM16A- and CFTR-dependent chloride secretion strongly augmented cyst growth. Exposure to scavengers of reactive oxygen species, such as glutathione, coenzyme Q10, or idebenone (a synthetic coenzyme Q10 homolog), as well as inhibition of oxidative lipid damage by ferrostatin-1 largely reduced activation of TMEM16A. Inhibition of TMEM16A reduced proliferation and fluid secretion in vitro.

CONCLUSIONS

These findings indicate that activation of TMEM16A by lipid peroxidation drives growth of renal cysts. We propose direct inhibition of TMEM16A or inhibition of lipid peroxidation as potentially powerful therapeutic approaches to delay cyst development in PKD.

TMEM Proteins in Cancer: A Review

A transmembrane protein (TMEM) is a type of protein that spans biological membranes. Many of them extend through the lipid bilayer of the plasma membrane but others are located to the membrane of organelles. The TMEM family gathers proteins of mostly unknown functions. Many studies showed that TMEM expression can be down- or up-regulated in tumor tissues compared to adjacent healthy tissues. Indeed, some TMEMs such as TMEM48 or TMEM97 are defined as potential prognostic biomarkers for lung cancer. Furthermore, experimental evidence suggests that TMEM proteins can be described as tumor suppressors or oncogenes. TMEMs, such as TMEM45A and TMEM205, have also been implicated in tumor progression and invasion but also in chemoresistance. Thus, a better characterization of these proteins could help to better understand their implication in cancer and to allow the development of improved therapy strategies in the future. This review gives an overview of the implication of TMEM proteins in cancer.

Histone Deacetylases Enhance Ca2+-Activated K⁺ Channel KCa3.1 Expression in Murine Inflammatory CD4⁺ T Cells

The up-regulated expression of the Ca²⁺-activated K⁺ channel K_Ca3.1 in inflammatory CD4⁺ T cells has been implicated in the pathogenesis of inflammatory bowel disease (IBD) through the enhanced production of inflammatory cytokines, such as interferon-γ (IFN-γ). However, the underlying mechanisms have not yet been elucidated. The objective of the present study is to clarify the involvement of histone deacetylases (HDACs) in the up-regulation of K_Ca3.1 in the CD4⁺ T cells of IBD model mice. The expression levels of K_Ca3.1 and its regulators, such as function-modifying molecules and transcription factors, were quantitated using a real-time polymerase chain reaction (PCR) assay, Western blotting, and depolarization responses, which were induced by the selective K_Ca3.1 blocker TRAM-34 (1 μM) and were measured using a voltage-sensitive fluorescent dye imaging system. The treatment with 1 μM vorinostat, a pan-HDAC inhibitor, for 24 h repressed the transcriptional expression of K_Ca3.1 in the splenic CD4⁺ T cells of IBD model mice. Accordingly, TRAM-34-induced depolarization responses were significantly reduced. HDAC2 and HDAC3 were significantly up-regulated in the CD4⁺ T cells of IBD model mice. The down-regulated expression of K_Ca3.1 was observed following treatments with the selective inhibitors of HDAC2 and HDAC3. The K_Ca3.1 K⁺ channel regulates inflammatory cytokine production in CD4⁺ T cells, mediating epigenetic modifications by HDAC2 and HDAC3.

MicroRNAs in cancer drug resistance: Basic evidence and clinical applications

Development of drug resistance has considerably limited the efficacy of cancer treatments, including chemotherapy and targeted therapies. Hence, understanding the molecular mechanisms underpinning the innate or the acquired resistance to these therapies is critical to improve drug efficiency and clinical outcomes. Several studies have implicated microRNAs (miRNA) in this process. MiRNAs repress gene expression by specific binding to complementary sequences in the 3' region of target messenger RNAs (mRNAs), followed by target mRNA degradation or blocked translation. By targeting molecules specific to a particular pathway within tumor cells, the new generation of cancer treatment strategies has shown significant advantages over conventional chemotherapy. However, the long-term efficacy of targeted therapies often remains poor, because tumor cells develop resistance to such therapeutics. Targeted therapies often involve monoclonal antibodies (mAbs), such as those blocking the ErB/HER tyrosine kinases, epidermal growth factor receptor (cetuximab) and HER2 (trastuzumab), and those inhibiting vascular endothelial growth factor receptor signaling (e.g., bevacizumab). Even though these are among the most used agents in tumor medicine, clinical response to these drugs is reduced due to the emergence of drug resistance as a result of toxic effects in the tumor microenvironment. Research on different types of human cancers has revealed that aberrant expression of miRNAs promotes resistance to the aforementioned drugs. In this study, we review the mechanisms of tumor cell resistance to mAb therapies and the role of miRNAs therein. Emerging treatment strategies combine therapies using innovative miRNA mimics or antagonizers with conventional approaches to maximize outcomes of patients with cancer.

Transcriptional repression of human epidermal growth factor receptor 2 by ClC-3 Cl- /H+ transporter inhibition in human breast cancer cells

Recent studies have indicated that the intracellular concentration of chloride ions (Cl⁻) regulates gene expression in several types of cells and that Cl⁻ modulators positively or negatively regulate the PI3K/AKT/mammalian target of rapamycin (mTOR) and signal transducer and activator of transcription (STAT)3 signaling pathways. We previously reported that the Ca²⁺‐activated Cl⁻ channel anoctamine (ANO)1 regulated human epidermal growth factor receptor 2 (HER2) transcription in breast cancer YMB‐1 cells. However, the mechanisms underlying ANO1‐regulated HER2 gene expression have not yet been elucidated. In the present study, we showed the involvement of intracellular organelle ClC‐3 Cl⁻/H⁺ transporter in HER2 transcription in breast cancer MDA‐MB‐453 cells. The siRNA‐mediated inhibition of ClC‐3, but not ANO1, markedly repressed HER2 transcription in MDA‐MB‐453 cells. Subsequently, treatments with the AKT inhibitor AZD 5363 and mTOR inhibitor everolimus significantly enhanced HER2 transcription in MDA‐MB‐453 cells, whereas that with the STAT3 inhibitor 5,15‐diphenylporphyrin (5,15‐DPP) inhibited it. AKT and mTOR inhibitors also significantly enhanced HER2 transcription in YMB‐1 cells. The siRNA‐mediated inhibition of ClC‐3 and ANO1 resulted in increased AKT phosphorylation and decreased STAT3 phosphorylation in MDA‐MB‐453 and YMB‐1 cells, respectively. The intracellular Cl⁻ channel protein CLIC1 was expressed in both cells; however, its siRNA‐mediated inhibition did not elicit the transcriptional repression of HER2. Collectively, our results demonstrate that intracellular Cl⁻ regulation by ANO1/ClC‐3 participates in HER2 transcription, mediating the PI3K/AKT/mTOR and/or STAT3 signaling pathway(s) in HER2‐positive breast cancer cells, and support the potential of ANO1/ClC‐3 blockers as therapeutic options for patients with resistance to anti‐HER2 therapies.

The association between the expression of PAR2 and TMEM16A and neuropathic pain

Chronic constriction injury (CCI) of the sciatic nerve may induce dorsal root ganglion (DRG) neuronal hyperexcitability and behaviorally expressed hyperalgesia. CCI is a model of neuropathic pain. To investigate the association between the expression of protease activated receptor 2 (PAR2), TMEM16A and neuropathic pain, the expression of PAR2 and TMEM16A proteins in the DRG neurons of rats following CCI of the sciatic nerve was investigated. Following the creation of the CCI model, the thermal withdrawal latency (TWL) was examined by a hot plate test. An immunofluorescence assay and western blot assay were performed to determine the expression of PAR2 and TMEM16A proteins in the ipsilateral L_4–6 DRG neurons. The concentration of inositol 1,4,5-triphosphate (IP₃) in the L_4–6 DRG was determined by ELISA. In the CCI-D7 (7 days after CCI) and CCI-D14 (14 days after CCI) treatment groups, the TWL of rats was significantly shorter than that in the sham operated group (P<0.01; n=12). The expression of PAR2 and TMEM16A proteins in the CCI-D7 and CCI-D14 groups were significantly upregulated compared with the sham operated group (P<0.05; n=12). Additionally, it was revealed that PAR2 and TMEM16A were co-expressed in DRG neurons. It was also observed that IP₃ significantly increased in the CCI-D7 and CCI-D14 groups compared with the sham operation group (P<0.05; n=6) as PAR2 and TMEM16A also increased. These findings suggest that the upregulation of PAR2 and TMEM16A in DRG neurons, the co-expression of the two proteins and increasing IP₃ are critical to the development of neuropathic pain.

Cell-specific mechanisms of TMEM16A Ca2+-activated chloride channel in cancer

TMEM16A (known as anoctamin 1) Ca2+-activated chloride channel is overexpressed in many tumors. TMEM16A overexpression can be caused by gene amplification in many tumors harboring 11q13 amplification. TMEM16A expression is also controlled in many cancer cells via transcriptional regulation, epigenetic regulation and microRNAs. In addition, TMEM16A activates different signaling pathways in different cancers, e.g. the EGFR and CAMKII signaling in breast cancer, the p38 and ERK1/2 signaling in hepatoma, the Ras-Raf-MEK-ERK1/2 signaling in head and neck squamous cell carcinoma and bladder cancer, and the NFκB signaling in glioma. Furthermore, TMEM16A overexpression has been reported to promote, inhibit, or produce no effects on cell proliferation and migration in different cancer cells. Since TMEM16A exerts different roles in different cancer cells via activation of distinct signaling pathways, we try to develop the idea that TMEM16A regulates cancer cell proliferation and migration in a cell-dependent mechanism. The cell-specific role of TMEM16A may depend on the cellular environment that is predetermined by TMEM16A overexpression mechanisms specific for a particular cancer type. TMEM16A may exert its cell-specific role via its associated protein networks, phosphorylation by different kinases, and involvement of different signaling pathways. In addition, we discuss the role of TMEM16A channel activity in cancer, and its clinical use as a prognostic and predictive marker in different cancers. This review highlights the cell-type specific mechanisms of TMEM16A in cancer, and envisions the promising use of TMEM16A inhibitors as a potential treatment for TMEM16A-overexpressing cancers.

Cell-specific regulation of proliferation by Ano1/TMEM16A in breast cancer with different ER, PR, and HER2 status

The calcium-activated chloride channel Ano1 (TMEM16A) is overexpressed in many tumors. However, conflicting data exist regarding the role of Ano1 in cell proliferation. Here, we performed immunohistochemistry to investigate the expression of Ano1 and Ki67 in 403 patients with breast cancer, and analyzed the association between the expression of Ano1 and Ki67 in breast cancer subtypes categorized according to estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Ano1 expression was negatively correlated with Ki67 expression. Ano1 overexpression more frequently occurred in ER-positive or HER2-negative patients with the low expression of Ki67. Ano1 overexpression was associated with longer overall survival (OS) in breast cancer with the low expression of Ki67, especially in ER-positive, PR-positive, and HER2-negative breast cancer. Multivariate Cox regression analysis showed that Ano1 overexpression was a prognostic factor for longer overall survival in ER-positive, PR-positive, or HER2-negative patients with the low expression of Ki67. Furthermore, Ano1 promoted cell proliferation in ER-positive, PR-positive, and HER2-negative MCF7 cells, but inhibited cell proliferation in ER-negative, PR-negative, and HER2-negative MDA-MB-435S cells. Our findings suggest that Ano1 may differentially regulate cell proliferation in a subtype of breast cancer defined by ER, PR, and HER2. Combined expression of Ano1 and Ki67 may be used for predicting clinical outcomes of breast cancer patients with different subtypes of ER, PR, and HER2.

MicroRNA-381 inhibits the metastasis of gastric cancer by targeting TMEM16A expression

Background

MicroRNA-381 (miR-381) has been reported to play suppressive or promoting roles in different malignancies. However, the expression level, biological function, and underlying mechanisms of miR-381 in gastric cancer remain poorly understood. Our previous study indicated that transmembrane protein 16A (TMEM16A) contributed to migration and invasion of gastric cancer and predicted poor prognosis. In this study, we found that miR-381 inhibited the metastasis of gastric cancer through targeting TMEM16A expression.

Methods

MiR-381 expression was analyzed using bioinformatic software on open microarray datasets from the Gene Expression Omnibus (GEO) and confirmed by quantitative RT-PCR (qRT-PCR) in human gastric cancer tissues and cell lines. Cell proliferation was investigated using MTT and cell count assays, and cell migration and invasion abilities were evaluated by transwell assay. Xenograft nude mouse models were used to observe tumor growth and pulmonary metastasis. Luciferase reporter assay, western blot, enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry were employed to explore the mechanisms of the effect of miR-381 on gastric cancer cells.

Results

MiR-381 was significantly down-regulated in gastric cancer tissues and cell lines. Low expression of miR-381 was negatively related to lymph node metastasis, advanced tumor stage and poor prognosis. MiR-381 decreased gastric cancer cell proliferation, migration and invasion in vitro and in vivo. TMEM16A was identified as a direct target of miR-381 and the expression of miR-381 was inversely correlated with TMEM16A expression in gastric cancer tissues. Combination analysis of miR-381 and TMEM16A revealed the improved prognostic accuracy for gastric cancer patients. Moreover, miR-381 inhibited TGF-β signaling pathway and down-regulated epithelial–mesenchymal transition (EMT) phenotype partially by mediating TMEM16A.

Conclusions

MiR-381 may function as a tumor suppressor by directly targeting TMEM16A and regulating TGF-β pathway and EMT process in the development of progression of gastric cancer. MiR-381/TMEM16A may be a novel therapeutic candidate target in gastric cancer treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0499-z) contains supplementary material, which is available to authorized users.

Down-Regulation of Ca2+-Activated K⁺ Channel KCa1.1 in Human Breast Cancer MDA-MB-453 Cells Treated with Vitamin D Receptor Agonists

Vitamin D (VD) reduces the risk of breast cancer and improves disease prognoses. Potential VD analogs are being developed as therapeutic agents for breast cancer treatments. The large-conductance Ca²⁺-activated K⁺ channel K_Ca1.1 regulates intracellular Ca²⁺ signaling pathways and is associated with high grade tumors and poor prognoses. In the present study, we examined the effects of treatments with VD receptor (VDR) agonists on the expression and activity of K_Ca1.1 in human breast cancer MDA-MB-453 cells using real-time PCR, Western blotting, flow cytometry, and voltage-sensitive dye imaging. Treatments with VDR agonists for 72 h markedly decreased the expression levels of K_Ca1.1 transcripts and proteins in MDA-MB-453 cells, resulting in the significant inhibition of depolarization responses induced by paxilline, a specific K_Ca1.1 blocker. The specific proteasome inhibitor MG132 suppressed VDR agonist-induced decreases in K_Ca1.1 protein expression. These results suggest that K_Ca1.1 is a new downstream target of VDR signaling and the down-regulation of K_Ca1.1 through the transcriptional repression of K_Ca1.1 and enhancement of K_Ca1.1 protein degradation contribute, at least partly, to the antiproliferative effects of VDR agonists in breast cancer cells.

Transcriptional repression of HER2 by ANO1 Cl- channel inhibition in human breast cancer cells with resistance to trastuzumab

The Ca²⁺-activated Cl^- channel ANO1 contributes to tumorigenesis and metastasis in several carcinomas including breast cancer (BCA). Cl^- channels have recently been attracting attention as 'transcriptional modulators'. Human epidermal growth factor receptor 2 (HER2) is overexpressed in approximately 30% of patients with BCA, and anti-HER2 monoclonal antibodies such as trastuzumab have emerged as a treatment for metastatic BCA. Among the seven human BCA cell lines examined in the present study, MDA-MB-453 and YMB-1 cells were HER2-positive; however, YMB-1 cell viability showed resistance to trastuzumab. Whole-cell patch-clamp configurations indicated that ANO1 was the main Cl^- conductance in YMB-1 cells, and the pharmacological and siRNA-mediated inhibition of ANO1 significantly prevented HER2 transcription in YMB-1 cells. The expression levels of insulin-like growth factor-binding protein 5 (IGFBP5), which is a risk factor for BCA recurrence and metastasis, was not affected by the inhibition of ANO1 in YMB-1 cells. These results suggest that ANO1 Cl^- channels may function as a transcriptional regulator of HER2, and ANO1 inhibitors have potential in the treatment of BCA patients with resistance to HER2-targeted therapy.

HDACs and HDAC Inhibitors in Cancer Development and Therapy

Over the last several decades, it has become clear that epigenetic abnormalities may be one of the hallmarks of cancer. Posttranslational modifications of histones, for example, may play a crucial role in cancer development and progression by modulating gene transcription, chromatin remodeling, and nuclear architecture. Histone acetylation, a well-studied posttranslational histone modification, is controlled by the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). By removing acetyl groups, HDACs reverse chromatin acetylation and alter transcription of oncogenes and tumor suppressor genes. In addition, HDACs deacetylate numerous nonhistone cellular substrates that govern a wide array of biological processes including cancer initiation and progression. This review will discuss the role of HDACs in cancer and the therapeutic potential of HDAC inhibitors (HDACi) as emerging drugs in cancer treatment.

Ion channels in regulated cell death

Activation of ion channels and pores are essential steps during regulated cell death. Channels and pores participate in execution of apoptosis, necroptosis and other forms of caspase-independent cell death. Within the program of regulated cell death, these channels are strategically located. Ion channels can shrink cells and drive them towards apoptosis, resulting in silent, i.e. immunologically unrecognized cell death. Alternatively, activation of channels can induce cell swelling, disintegration of the cell membrane, and highly immunogenic necrotic cell death. The underlying cell death pathways are not strictly separated as identical stimuli may induce cell shrinkage and apoptosis when applied at low strength, but may also cause cell swelling at pronounced stimulation, resulting in regulated necrosis. Nevertheless, the precise role of ion channels during regulated cell death is far from being understood, as identical channels may support regulated death in some cell types, but may cause cell proliferation, cancer development, and metastasis in others. Along this line, the phospholipid scramblase and Cl(-)/nonselective channel anoctamin 6 (ANO6) shows interesting features, as it participates in apoptotic cell death during lower levels of activation, thereby inducing cell shrinkage. At strong activation, e.g. by stimulation of purinergic P2Y7 receptors, it participates in pore formation, causes massive membrane blebbing, cell swelling, and membrane disintegration. The LRRC8 proteins deserve much attention as they were found to have a major role in volume regulation, apoptotic cell shrinkage and resistance towards anticancer drugs.

Ani9, A Novel Potent Small-Molecule ANO1 Inhibitor with Negligible Effect on ANO2

Anoctamin1 (ANO1)/transmembrane protein 16A (TMEM16A), a calcium-activated chloride channel (CaCC), is involved in many physiological functions such as fluid secretion, smooth muscle contraction, nociception and cancer progression. To date, only a few ANO1 inhibitors have been described, and these have low potency and selectivity for ANO1. Here, we performed a high-throughput screening to identify highly potent and selective small molecule inhibitors of ANO1. Three novel ANO1 inhibitors were discovered from screening of 54,400 synthetic small molecules, and they were found to fully block ANO1 channel activity with an IC₅₀ < 3 μM. Electrophysiological analysis revealed that the most potent inhibitor, 2-(4-chloro-2-methylphenoxy)-N-[(2-methoxyphenyl)methylideneamino]-acetamide (Ani9), completely inhibited ANO1 chloride current with submicromolar potency. Notably, unlike previous small-molecule ANO1 inhibitors identified to date, Ani9 displayed high selectivity for ANO1 as compared to ANO2, which shares a high amino acid homology to ANO1. In addition, Ani9 did not affect the intracellular calcium signaling and CFTR chloride channel activity. Our results suggest that Ani9 may be a useful pharmacological tool for studying ANO1 and a potential development candidate for drug therapy of cancer, hypertension, pain, diarrhea and asthma.

Downregulation of the Ca(2+)-activated K(+) channel KC a3.1 by histone deacetylase inhibition in human breast cancer cells

The intermediate‐conductance Ca²⁺‐activated K⁺ channel K_Ca3.1 is involved in the promotion of tumor growth and metastasis, and is a potential therapeutic target and biomarker for cancer. Histone deacetylase inhibitors (HDACis) have considerable potential for cancer therapy, however, the effects of HDACis on ion channel expression have not yet been investigated in detail. The results of this study showed a significant decrease in K_Ca3.1 transcription by HDAC inhibition in the human breast cancer cell line YMB‐1, which functionally expresses K_Ca3.1. A treatment with the clinically available, class I, II, and IV HDAC inhibitor, vorinostat significantly downregulated K_Ca3.1 transcription in a concentration‐dependent manner, and the plasmalemmal expression of the K_Ca3.1 protein and its functional activity were correspondingly decreased. Pharmacological and siRNA‐based HDAC inhibition both revealed the involvement of HDAC2 and HDAC3 in K_Ca3.1 transcription through the same mechanism. The downregulation of K_Ca3.1 in YMB‐1 was not due to the upregulation of the repressor element‐1 silencing transcription factor, REST and the insulin‐like growth factor‐binding protein 5, IGFBP5. The significant decrease in K_Ca3.1 transcription by HDAC inhibition was also observed in the K_Ca3.1‐expressing human prostate cancer cell line, PC‐3. These results suggest that vorinostat and the selective HDACis for HDAC2 and/or HDAC3 are effective drug candidates for K_Ca3.1‐overexpressing cancers.

TMEM16A overexpression contributes to tumor invasion and poor prognosis of human gastric cancer through TGF-β signaling

TMEM16A is a newly identified calcium activated chloride channel, and has been reported to be overexpressed by various solid malignant cancers to promote proliferation and invasion, yet little is known about its role in gastric cancer(GC). Therefore, we investigated the role of TMEM16A in GC and its clinical significance by a retrospective analysis of 367 GC patients, and in vitro study was performed for validation and underlying molecular mechanism.

TMEM16A was significantly upregulated and amplified in GC tissues, and its overexpression was positively correlated with disease stage, negatively with patient survival and identified as an independent prognostic factor for patient outcome. A negative correlation between TMEM16A and E-cadherin was found in 367 GC specimens. TMEM16A silencing significantly decreased calcium activated chloride currents, impaired TGF-β secretion, reduced E-cadherin expression, and inhibited the migration and invasion without affecting proliferation of GC cells (AGS and BGC-823). Supplement of TGF-β reverted the effects of TMEM16A silencing on E-cadherin expression, cell migration and invasion.

In conclusion, TMEM16A promotes invasion and metastasis in GC, and might be a novel prognostic biomarker and potential therapeutic target in the treatment of GC.

Recent advances in therapeutic strategies that focus on the regulation of ion channel expression

A number of different ion channel types are involved in cell signaling networks, and homeostatic regulatory mechanisms contribute to the control of ion channel expression. Profiling of global gene expression using microarray technology has recently provided novel insights into the molecular mechanisms underlying the homeostatic and pathological control of ion channel expression. It has demonstrated that the dysregulation of ion channel expression is associated with the pathogenesis of neural, cardiovascular, and immune diseases as well as cancers. In addition to the transcriptional, translational, and post-translational regulation of ion channels, potentially important evidence on the mechanisms controlling ion channel expression has recently been accumulated. The regulation of alternative pre-mRNA splicing is therefore a novel therapeutic strategy for the treatment of dominant-negative splicing disorders. Epigenetic modification plays a key role in various pathological conditions through the regulation of pluripotency genes. Inhibitors of pre-mRNA splicing and histone deacetyalase/methyltransferase have potential as potent therapeutic drugs for cancers and autoimmune and inflammatory diseases. Moreover, membrane-anchoring proteins, lysosomal and proteasomal degradation-related molecules, auxiliary subunits, and pharmacological agents alter the protein folding, membrane trafficking, and post-translational modifications of ion channels, and are linked to expression-defect channelopathies. In this review, we focused on recent insights into the transcriptional, spliceosomal, epigenetic, and proteasomal regulation of ion channel expression: Ca(2+) channels (TRPC/TRPV/TRPM/TRPA/Orai), K(+) channels (voltage-gated, KV/Ca(2+)-activated, KCa/two-pore domain, K2P/inward-rectifier, Kir), and Ca(2+)-activated Cl(-) channels (TMEM16A/TMEM16B). Furthermore, this review highlights expression of these ion channels in expression-defect channelopathies.

Cellular functions of TMEM16/anoctamin

Ca²⁺-activated Cl⁻ channels (CaCCs) are a class of Cl⁻ channels activated by intracellular Ca²⁺ that are known to mediate numerous physiological functions. In 2008, the molecular identity of CaCCs was found to be anoctamin 1 (ANO1/TMEM16A). Its roles have been studied in electrophysiological, histological, and genetic aspects. ANO1 is known to mediate Cl⁻ secretion in secretory epithelia such as airways, salivary glands, intestines, renal tubules, and sweat glands. ANO1 is a heat sensor activated by noxious heat in somatosensory neurons and mediates acute pain sensation as well as chronic pain. ANO1 is also observed in vascular as well as airway smooth muscles, controlling vascular tone as well as airway hypersensitivity. ANO1 is upregulated in numerous types of cancers and thus thought to be involved in tumorigenesis. ANO1 is also found in proliferating cells. In addition to ANO1, involvement of its paralogs in pathophysiological conditions was also reported. ANO2 is involved in olfaction, whereas ANO6 works as a scramblase whose mutation causes a rare bleeding disorder, the Scott syndrome. ANO5 is associated with muscle and bone diseases. Recently, an X-ray crystal structure of a fungal TMEM16 was reported, which explains a precise molecular gating mechanism as well as ion conduction or phospholipid transport across the plasma membrane.

Identification of the Novel TMEM16A Inhibitor Dehydroandrographolide and Its Anticancer Activity on SW620 Cells

TMEM16A, a calcium-activated chloride channel (CaCC), is highly amplified and expressed in human cancers and is involved in the growth and metastasis of some malignancies. Inhibition of TMEM16A represents a novel pharmaceutical approach for the treatment of cancers and metastases. The purpose of this study is to identify a new TMEM16A inhibitor, investigate the effects of this inhibitor on the proliferation and metastasis of TMEM16A-amplified SW620 cells, and to elucidate the underlying molecular mechanism in vitro. We identified a novel small-molecule TMEM16A inhibitor dehydroandrographolide (DP). By using patch clamp electrophysiology, we showed that DP inhibited TMEM16A chloride currents in Fisher rat thyroid (FRT) cells that were transfected stably with human TMEM16A and in TMEM16A-overexpressed SW620 cells but did not alter cystic fibrosis transmembrane conductance regulator (CFTR) chloride currents. Further functional studies showed that DP suppressed the proliferation of SW620 cells in a dose- and time-dependent manner using MTT assays. Moreover, DP significantly inhibited migration and invasion of SW620 cells as detected by wound-healing and transwell assays. Further mechanistic study demonstrated that knockdown of human TMEM16A decreased the inhibitory effect of DP on the proliferation of SW620 cells and that TMEM16A-dependent cells (SW620 and HCT116) were more sensitive to DP than TMEM16A-independent cells (SW480 and HCT8). In addition, we found that treatment of SW620 cells with DP led to a decrease in TMEM16A protein levels but had no effect on TMEM16A mRNA levels. The current work reveals that DP, a novel TMEM16A inhibitor, exerts its anticancer activity on SW620 cells partly through a TMEM16A-dependent mechanism, which may introduce a new targeting approach for an antitumour therapy in TMEM16A-amplified cancers.

Molecular identification of the dominant-negative, splicing isoform of the two-pore domain K(+) channel K(2P)5.1 in lymphoid cells and enhancement of its expression by splicing inhibition

The two-pore domain background K(+) channel K2P5.1 is expected as a possible therapeutic target for autoimmune and inflammatory disorders and cancers because it plays an important role in maintaining the resting membrane potential and regulation of Ca(2+) signaling in T lymphocytes and cancer cells. However, the lack of selective K2P5.1 blockers has led to difficulties conducting experimental studies on this K(+) channel. We identified a novel splicing isoform of K2P5.1, K2P5.1B from the mammalian spleen, which lacked the N-terminus of full-length K2P5.1A. A co-immunoprecipitation assay using mice spleen lysates revealed an interaction between K2P5.1A and K2P5.1B in the cytoplasmic C-terminal domain. In a heterologous HEK293 expression system, K2P5.1B inhibited the trafficking of K2P5.1A to the plasma membrane. The alkaline pHe-induced hyperpolarizing response was significantly suppressed in K2P5.1B-transfected human leukemia K562 cells. Enhancement in cell proliferation by the overexpression of K2P5.1A in K562 was significantly prevented by the transfection of K2P5.1B. The spliceosome inhibitor pladienolide B significantly enhanced the relative expression of K2P5.1B in K562, resulting in decreases in the activity of K2P5.1A. K2P5.1B suppresses the function of the K2P5.1 K(+) channel in a dominant-negative manner, suggesting that the mRNA splicing mechanisms underlying the transcriptional regulation of K2P5.1B may be a new therapeutic strategy for autoimmune and inflammatory disorders and cancers.

Ano1/TMEM16A Overexpression Is Associated with Good Prognosis in PR-Positive or HER2-Negative Breast Cancer Patients following Tamoxifen Treatment

The calcium-activated chloride channel Ano1 (TMEM16A) is overexpressed in many tumors. Although Ano1 overexpression is found in breast cancer due to 11q13 amplification, it remains unclear whether signaling pathways are involved in Ano1 overexpression during breast cancer tumorigenesis in vivo. Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) have been known to contribute to breast cancer progression. It is unclear whether Ano1 is associated with clinical outcomes in breast cancer patients with different ER, PR and HER2 status. In the present study, we investigated the Ano1 expression in 431 patients with invasive ductal breast carcinoma and 46 patients with fibroadenoma, using immunohistochemistry, and analyzed the association between Ano1 expression and clinical characteristics and outcomes of breast cancer patients with different ER, PR, and HER2 status. Ano1 was overexpressed in breast cancer compared with fibroadenoma. Ano1 was significantly more associated with breast cancer with the lower clinical stage (stage I or II), or triple-negative status. Mostly importantly, Ano1 overexpression was associated with good prognosis in patients with the PR-positive or HER2-negative status, and in patients following tamoxifen treatment. Multivariate Cox regression analysis showed that Ano1 overexpression was a prognostic factor for longer overall survival in PR-positive or HER2-negative patients, and a predictive factor for longer overall survival in patients following tamoxifen treatment. Our findings suggest that Ano1 may be a potential marker for good prognosis in PR-positive or HER2-negative patients following tamoxifen treatment. The PR and HER2 status defines a subtype of breast cancer in which Ano1 overexpression is associated with good prognosis following tamoxifen treatment.