Identification of determinants of lipid and ion transport in TMEM16/anoctamin proteins through a Bayesian statistical analysis

The TMEM16/Anoctamin protein family (TMEM16x) is composed of members with different functions; some members form Ca2+-activated chloride channels, while others are lipid scramblases or combine the two functions. TMEM16x proteins are typically activated in response to agonist-induced rises of intracellular Ca2+; thus, they couple Ca2+-signalling with cell electrical activity or plasmalemmal lipid homeostasis. The structural domains underlying these functions are not fully defined. We used a Naïve Bayes classifier to gain insights into these domains. The method enabled identification of regions involved in either ion or lipid transport, and suggested domains for possible pharmacological exploitation. The method allowed the prediction of the transport property of any given TMEM16x. We envisage this strategy could be exploited to illuminate the structure-function relationship of any protein family composed of members playing different molecular roles.

Extracellular glucose and dysfunctional insulin receptor signaling independently upregulate arterial smooth muscle TMEM16A expression

Diabetes alters the function of ion channels responsible for regulating arterial smooth muscle membrane potential, resulting in vasoconstriction. Our prior research demonstrated an elevation of TMEM16A in diabetic arteries. Here, we explored the mechanisms involved in Transmembrane protein 16A (TMEM16A) gene expression. Our data indicate that a Snail-mediated repressor complex regulates arterial TMEM16A gene transcription. Snail expression was reduced in diabetic arteries while TMEM16A expression was upregulated. The TMEM16A promoter contained three canonical E-box sites. Electrophoretic mobility and super shift assays revealed that the -154 nt E-box was the binding site of the Snail repressor complex and binding of the repressor complex decreased in diabetic arteries. High glucose induced a biphasic contractile response in pressurized nondiabetic mouse hindlimb arteries incubated ex vivo. Hindlimb arteries incubated in high glucose also showed decreased phospho-protein kinase D1 and TMEM16A expression. In hindlimb arteries from nondiabetic mice, administration of a bolus dose of glucose activated protein kinase D1 signaling to induce Snail degradation. In both in vivo and ex vivo conditions, Snail expression exhibited an inverse relationship with the expression of protein kinase D1 and TMEM16A. In diabetic mouse arteries, phospho-protein kinase D1 increased while Akt2 and pGSK3β levels declined. These results indicate that in nondiabetic mice, high glucose triggers a transient deactivation of the Snail repressor complex to increase arterial TMEM16A expression independently of insulin signaling. Conversely, insulin resistance activates GSK3β signaling and enhances arterial TMEM16A channel expression. These data have uncovered the Snail-mediated regulation of arterial TMEM16A expression and its dysfunction during diabetes.NEW & NOTEWORTHY The calcium-activated chloride channel, TMEM16A, is upregulated in the diabetic vasculature to cause increased vasoconstriction. In this paper, we have uncovered that the TMEM16A gene expression is controlled by a Snail-mediated repressor complex that uncouples with both insulin-dependent and -independent pathways to allow for upregulated arterial protein expression thereby causing vasoconstriction. The paper highlights the effect of short- and long-term glucose-induced dysfunction of an ion channel expression as a causative factor in diabetic vascular disease.

Predicting Mutational Effects on Ca2+-Activated Chloride Conduction of TMEM16A Based on a Simulation Study

The dysfunction and defects of ion channels are associated with many human diseases, especially for loss-of-function mutations in ion channels such as cystic fibrosis transmembrane conductance regulator mutations in cystic fibrosis. Understanding ion channels is of great current importance for both medical and fundamental purposes. Such an understanding should include the ability to predict mutational effects and describe functional and mechanistic effects. In this work, we introduce an approach to predict mutational effects based on kinetic information (including reaction barriers and transition state locations) obtained by studying the working mechanism of target proteins. Specifically, we take the Ca2+-activated chloride channel TMEM16A as an example and utilize the computational biology model to predict the mutational effects of key residues. Encouragingly, we verified our predictions through electrophysiological experiments, demonstrating a 94% prediction accuracy regarding mutational directions. The mutational strength assessed by Pearson's correlation coefficient is -0.80 between our calculations and the experimental results. These findings suggest that the proposed methodology is reliable and can provide valuable guidance for revealing functional mechanisms and identifying key residues of the TMEM16A channel. The proposed approach can be extended to a broad scope of biophysical systems.

p90RSK pathway inhibition synergizes with cisplatin in TMEM16A overexpressing head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) constitutes one of the most common types of human cancers and often metastasizes to lymph nodes. Platinum-based chemotherapeutic drugs are commonly used for treatment of a wide range of cancers, including HNSCC. Its mode of action relies on its ability to impede DNA repair mechanisms, inducing apoptosis in cancer cells. However, due to acquired resistance and toxic side-effects, researchers have been focusing on developing novel combinational therapeutic strategies to overcome cisplatin resistance. In the current study, we identified p90RSK, an ERK1/2 downstream target, as a key mediator and a targetable signaling node against cisplatin resistance. Our results strongly support the role of p90RSK in cisplatin resistance and identify the combination of p90RSK inhibitor, BI-D1870, with cisplatin as a novel therapeutic strategy to overcome cisplatin resistance. In addition, we have identified TMEM16A expression as a potential upstream regulator of p90RSK through the ERK pathway and a biomarker of response to p90RSK targeted therapy in the context of cisplatin resistance.

A Pharmacological Investigation of the TMEM16A Currents in Murine Skeletal Myogenic Precursor Cells

TMEM16A is a Ca2+-activated Cl- channel expressed in various species and tissues. In mammalian skeletal muscle precursors, the activity of these channels is still poorly investigated. Here, we characterized TMEM16A channels and investigated if the pharmacological activation of Piezo1 channels could modulate the TMEM16A currents in mouse myogenic precursors. Whole-cell patch-clamp recordings combined with the pharmacological agents Ani9, T16inh-A01 and Yoda1 were used to characterize TMEM16A-mediated currents and the possible modulatory effect of Piezo1 activity on TMEM16A channels. Western blot analysis was also carried out to confirm the expression of TMEM16A and Piezo1 channel proteins. We found that TMEM16A channels were functionally expressed in fusion-competent mouse myogenic precursors. The pharmacological blockage of TMEM16A inhibited myocyte fusion into myotubes. Moreover, the specific Piezo1 agonist Yoda1 positively regulated TMEM16A currents. The findings demonstrate, for the first time, a sarcolemmal TMEM16A channel activity and its involvement at the early stage of mammalian skeletal muscle differentiation. In addition, the results suggest a possible role of mechanosensitive Piezo1 channels in the modulation of TMEM16A currents.

Niclosamide, but not ivermectin, inhibits anoctamin 1 and 6 and attenuates inflammation of the respiratory tract

Inflammatory airway diseases like cystic fibrosis, asthma and COVID-19 are characterized by high levels of pulmonary cytokines. Two well-established antiparasitic drugs, niclosamide and ivermectin, are intensively discussed for the treatment of viral inflammatory airway infections. Here, we examined these repurposed drugs with respect to their anti-inflammatory effects in airways in vivo and in vitro. Niclosamide reduced mucus content, eosinophilic infiltration and cell death in asthmatic mouse lungs in vivo and inhibited release of interleukins in the two differentiated airway epithelial cell lines CFBE and BCi-NS1.1 in vitro. Cytokine release was also inhibited by the knockdown of the Ca2+-activated Cl- channel anoctamin 1 (ANO1, TMEM16A) and the phospholipid scramblase anoctamin 6 (ANO6, TMEM16F), which have previously been shown to affect intracellular Ca2+ levels near the plasma membrane and to facilitate exocytosis. At concentrations around 200 nM, niclosamide inhibited inflammation, lowered intracellular Ca2+, acidified cytosolic pH and blocked activation of ANO1 and ANO6. It is suggested that niclosamide brings about its anti-inflammatory effects at least in part by inhibiting ANO1 and ANO6, and by lowering intracellular Ca2+ levels. In contrast to niclosamide, 1 µM ivermectin did not exert any of the effects described for niclosamide. The present data suggest niclosamide as an effective anti-inflammatory treatment in CF, asthma, and COVID-19, in addition to its previously reported antiviral effects. It has an advantageous concentration-response relationship and is known to be well tolerated.

High ANO1 expression is a prognostic factor and correlated with an immunosuppressive tumor microenvironment in pancreatic cancer

Background

Aminooctylamine (ANO1) plays an oncogenic role in various cancers. However. its role in pancreatic cancer (PC) has rarely been studied. This study investigated the prognostic value of ANO1 and its correlation with the tumor microenvironment (TME) in PC.

Methods

Consecutive patients with PC (n = 119) were enrolled. The expression of ANO1 in cancer cells, the expression of fibroblast activation protein (FAP) and alpha smooth muscle actin in cancer-associated fibroblasts (CAFs), and the numbers of CD8- and FOXP3-positive tumor-infiltrating lymphocytes (TILs) were evaluated using immunohistochemistry. The prognostic value of ANO1 and its correlation with CAF subgroups and TILs were analyzed. The possible mechanism of ANO1 in the TME of PC was predicted using the the Cancer Genome Atlas (TCGA) dataset.

Results

The expression of AN01 was correlated with overall survival (OS) and disease-free survival. Multi-factor analysis showed that high ANO1 expression was an independent adverse prognostic factor for OS (hazard ratio, 4.137; P = 0.001). ANO1 expression was positively correlated with the expression of FAP in CAFs (P < 0.001) and negatively correlated with the number of CD8-positive TILs (P = 0.005), which was also validated by bioinformatics analysis in the TCGA dataset. Moreover, bioinformatic analysis of the TCGA dataset revealed that ANO1 may induce an immunosuppressive tumor microenvironment in pancreatic cancer in a paracrine manner.

Conclusion

ANO1 is a prognostic factor in patients with PC after radical resection. ANO1 may induce an immunosuppressive tumor microenvironment in PC in a paracrine manner, suggesting that ANO1 may be a novel therapeutic target.

Low dose cadmium exposure regulates miR-381-ANO1 interaction in airway epithelial cells

Chronic obstructive pulmonary disease (COPD) is the 3rd leading cause of death worldwide. Cigarette smoke which has approximately 2-3 µg of Cadmium (Cd) per cigarette contributes to the environmental exposure and development and severity of COPD. With the lack of a cadmium elimination mechanism in humans, the contribution of cadmium induced stress to lung epithelial cells remains unclear. Studies on cadmium responsive miRNAs suggest regulation of target genes with an emphasis on the critical role of miRNA-mRNA interaction for cellular homeostasis. Mir-381, the target miRNA in this study is negatively regulated by cadmium in airway epithelial cells. miR-381 is reported to also regulate ANO1 (Anoctamin 1) expression negatively and in this study low dose cadmium exposure to airway epithelial cells was observed to upregulate ANO1 mRNA expression via mir-381 inhibition. ANO1 which is a Ca2+-activated chloride channel has multiple effects on cellular functions such as proliferation, mucus hypersecretion and fibroblast differentiation in inflamed airways in chronic respiratory diseases. In vitro studies with cadmium at a high concentration range of 100-500 µM is reported to activate chloride channel, ANO1. The secretory epithelial cells are regulated by chloride channels like CFTR, ANO1 and SLC26A9. We examined "ever" smokers with COPD (n = 13) lung tissue sections compared to "never" smoker without COPD (n = 9). We found that "ever" smokers with COPD had higher ANO1 expression. Using mir-381 mimic to inhibit ANO1, we demonstrate here that ANO1 expression is significantly (p < 0.001) downregulated in COPD derived airway epithelial cells exposed to cadmium. Exposure to environmental cadmium contributes significantly to ANO1 expression.

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.

Anoctamin-1 is induced by TGF-β and contributes to lung myofibroblast differentiation

Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by progressive scarring of the lungs and resulting in deterioration in lung function. Transforming growth factor-β (TGF-β) is one of the most established drivers of fibrotic processes. TGF-β promotes the transformation of tissue fibroblasts to myofibroblasts, a key finding in the pathogenesis of pulmonary fibrosis. We report here that TGF-β robustly upregulates the expression of the calcium-activated chloride channel anoctamin-1 (ANO1) in human lung fibroblasts (HLFs) at mRNA and protein levels. ANO1 is readily detected in fibrotic areas of IPF lungs in the same area with smooth muscle α-actin (SMA)-positive myofibroblasts. TGF-β-induced myofibroblast differentiation (determined by the expression of SMA, collagen-1, and fibronectin) is significantly inhibited by a specific ANO1 inhibitor, T16Ainh-A01, or by siRNA-mediated ANO1 knockdown. T16Ainh-A01 and ANO1 siRNA attenuate profibrotic TGF-β signaling, including activation of RhoA pathway and AKT, without affecting initial Smad2 phosphorylation. Mechanistically, TGF-β treatment of HLFs results in a significant increase in intracellular chloride levels, which is prevented by T16Ainh-A01 or by ANO1 knockdown. The downstream mechanism involves the chloride-sensing "with-no-lysine (K)" kinase (WNK1). WNK1 siRNA significantly attenuates TGF-β-induced myofibroblast differentiation and signaling (RhoA pathway and AKT), whereas the WNK1 kinase inhibitor WNK463 is largely ineffective. Together, these data demonstrate that 1) ANO1 is a TGF-β-inducible chloride channel that contributes to increased intracellular chloride concentration in response to TGF-β; and 2) ANO1 mediates TGF-β-induced myofibroblast differentiation and fibrotic signaling in a manner dependent on WNK1 protein but independent of WNK1 kinase activity.NEW & NOTEWORTHY This study describes a novel mechanism of differentiation of human lung fibroblasts (HLFs) to myofibroblasts: the key process in the pathogenesis of pulmonary fibrosis. Transforming growth factor-β (TGF-β) drives the expression of calcium-activated chloride channel anoctmin-1 (ANO1) leading to an increase in intracellular levels of chloride. The latter recruits chloride-sensitive with-no-lysine (K) kinase (WNK1) to activate profibrotic RhoA and AKT signaling pathways, possibly through activation of mammalian target of rapamycin complex-2 (mTORC2), altogether promoting myofibroblast differentiation.

Mechanistic basis of ligand efficacy in the calcium-activated chloride channel TMEM16A

Agonist binding in ligand-gated ion channels is coupled to structural rearrangements around the binding site, followed by the opening of the channel pore. In this process, agonist efficacy describes the equilibrium between open and closed conformations in a fully ligand-bound state. Calcium-activated chloride channels in the TMEM16 family are important sensors of intracellular calcium signals and are targets for pharmacological modulators, yet a mechanistic understanding of agonist efficacy has remained elusive. Using a combination of cryo-electron microscopy, electrophysiology, and autocorrelation analysis, we now show that agonist efficacy in the ligand-gated channel TMEM16A is dictated by the conformation of the pore-lining helix α6 around the Ca2+ -binding site. The closure of the binding site, which involves the formation of a π-helix below a hinge region in α6, appears to be coupled to the opening of the inner pore gate, thereby governing the channel's open probability and conductance. Our results provide a mechanism for agonist binding and efficacy and a structural basis for the design of potentiators and partial agonists in the TMEM16 family.

ANO1-Mediated Inhibition of Cancer Ferroptosis Confers Immunotherapeutic Resistance through Recruiting Cancer-Associated Fibroblasts

The application of immunotherapy in gastrointestinal (GI) cancers remains challenging because of the limited response rate and emerging therapeutic resistance. Combining clinical cohorts, multi-omics study, and functional/molecular experiments, it is found that ANO1 amplification or high-expression predicts poor outcomes and resistance to immunotherapy for GI cancer patients. Knocking-down or inhibiting ANO1 suppresses the growth/metastasis/invasion of multiple GI cancer cell lines, cell-derived xenograft, and patient-derived xenograft models. ANO1 contributes to an immune-suppressive tumor microenvironment and induces acquired resistance to anti-PD-1 immunotherapy, while ANO1 knockdown or inhibition enhances immunotherapeutic effectiveness and overcomes resistance to immunotherapy. Mechanistically, through inhibiting cancer ferroptosis in a PI3K-Akt signaling-dependent manner, ANO1 enhances tumor progression and facilitates cancer-associated fibroblast recruitment by promoting TGF-β release, thus crippling CD8+ T cell-mediated anti-tumor immunity and generating resistance to immunotherapy. This work highlights ANO1's role in mediating tumor immune microenvironment remodeling and immunotherapeutic resistance, and introduces ANO1 as a promising target for GI cancers' precision treatment.

LXR Signaling-Mediated Cholesterol Metabolism Reprogramming Regulates Cancer Cell Metastasis

Metastasis is a key contributor to mortality in patients with cancer. While many regulators of metastasis have been identified, critical targets to prevent and inhibit metastatic tumor growth remain elusive. A recent study in this issue of Cancer Research by Deng and colleagues compared gene expression signatures between primary esophageal squamous cell carcinoma tumors and metastatic tumors and combined the analysis with genes induced in metastatic cancer cell lines, which identified anoctamin 1 (ANO1) as a key driver of metastasis. ANO1 caused cholesterol accumulation by inhibiting LXR signaling and decreased cholesterol hydroxylation by downregulating the expression of cholesterol hydroxylase CYP27A1. ANO1 also regulated tumor cell-fibroblast cross-talk that contributed to inflammatory cytokine signaling (IL1β) and metastasis. Through in silico analysis, the study identified a novel small-molecule inhibitor of ANO1 that decreased tumor burden at a metastatic site. These studies provide novel insights into the role of ANO1 in cellular cholesterol metabolism and associated signaling in mediating metastasis. See related article by Deng et al., p. 1851.

TRPV3-ANO1 interaction positively regulates wound healing in keratinocytes

Transient receptor potential vanilloid 3 (TRPV3) belongs to the TRP ion channel super family and functions as a nonselective cation channel that is highly permeable to calcium. This channel is strongly expressed in skin keratinocytes and is involved in warmth sensation, itch, wound healing and secretion of several cytokines. Previous studies showed that anoctamin1 (ANO1), a calcium-activated chloride channel, was activated by calcium influx through TRPV1, TRPV4 or TRPA1 and that these channel interactions were important for TRP channel-mediated physiological functions. We found that ANO1 was expressed by normal human epidermal keratinocytes (NHEKs). We observed that ANO1 mediated currents upon TRPV3 activation of NHEKs and mouse skin keratinocytes. Using an in vitro wound-healing assay, we observed that either a TRPV3 blocker, an ANO1 blocker or low chloride medium inhibited cell migration and proliferation through p38 phosphorylation, leading to cell cycle arrest. These results indicated that chloride influx through ANO1 activity enhanced wound healing by keratinocytes.

Inhibition of ANO1 by Cis- and Trans-Resveratrol and Their Anticancer Activity in Human Prostate Cancer PC-3 Cells

Anoctamin1 (ANO1), a calcium-activated chloride channel, is involved in the proliferation, migration, and invasion of various cancer cells including head and neck squamous cell carcinoma, lung cancer, and prostate cancer. Inhibition of ANO1 activity or downregulation of ANO1 expression in these cancer cells is known to exhibit anticancer effects. Resveratrol, a natural polyphenol abundant in wines, grapes, berries, soybeans, and peanuts, shows a wide variety of biological effects including anti-inflammatory, antioxidant, and anticancer activities. In this study, we investigated the effects of two stereoisomers of resveratrol on ANO1 activity and found that cis- and trans-resveratrol inhibited ANO1 activity with different potencies. Cis- and trans-resveratrol inhibited ANO1 channel activity with IC₅₀ values of 10.6 and 102 μM, respectively, and had no significant effect on intracellular calcium signaling at 10 and 100 μM, respectively. In addition, cis-resveratrol downregulated mRNA and protein expression levels of ANO1 more potently than trans-resveratrol in PC-3 prostate cancer cells. Cis- and trans-resveratrol significantly reduced cell proliferation and cell migration in an ANO1-dependent manner, and both resveratrol isomers strongly increased caspase-3 activity, PARP cleavage, and apoptotic sub-G1 phase ratio in PC-3 cells. These results revealed that cis-resveratrol is a potent inhibitor of ANO1 and exhibits ANO1-dependent anticancer activity against human metastatic prostate cancer PC-3 cells.

Generation of two TMEM16A knockout iPSC clones each from a healthy human iPSC line, from a Cystic Fibrosis patient specific line with p.Phe508del mutation and from the gene corrected iPSC line

The Transmembrane member 16A (TMEM16A), also known as anoctamin-1 (ANO1), is a calcium-activated chloride channel present in the airway epithelium. It is known to be involved in the apical chloride secretion indicating that TMEM16A could be addressed for the treatment of chloride secretion defects like in Cystic- Fibrosis (CF). In this paper we generated knockout cell lines using CRISPR/Cas9-mediated ablation in a healthy human iPSC line (MHHi001-A), in a CF patient iPSC line (MHHi002-A) and in its corrected counterpart (MHHi002-A-1). These lines can be used for gaining information about the role of TMEM16A for mucus secretion and/or production and evaluating its therapeutic potential.

Near-Infrared Light-Responsive Nanoinhibitors for Tumor Suppression through Targeting and Regulating Anion Channels

The gated state of anion channels is involved in the regulation of proliferation and migration of tumors. Specific regulators are urgently needed for efficacious cancer ablation. For this purpose, it is essential to understand the molecular mechanisms of interaction between the regulators and anion channels and apply this knowledge to regulate anion channels. Transmembrane 16A (TMEM16A) is the molecular basis of the calcium-activated chloride channels. It is an anion channel activated by Ca²⁺, and the inhibition of TMEM16A is associated with a decrease in tumorigenesis. Herein, we characterized a natural compound procyanidin (PC) as an efficacious and selective inhibitor of TMEM16A with an IC₅₀ of 10.6 ± 0.6 μM. Our research revealed the precise sites (D383, R535, and E624) of electrostatic interactions between PC and TMEM16A. Near-infrared (NIR)-light-responsive photothermal conjugated polymer nanoparticles encapsulating PC (CPNs-PC) were established to remotely target and regulate the TMEM16A anion channel. Upon NIR irradiation, CPNs-PC downregulated the signaling pathway downstream of TMEM16A and arrested the cell cycle progression of cancer cells and improved the bioavailability of PC. The tumor inhibition ratio of CPNs-PC was superior to PC by 13.4%. Our findings enabled the development of a strategy to accurately and remotely regulate anion channels to promote tumor regression using NIR-light-responsive conjugated polymer nanoparticles containing specific inhibitors of TMEM16A.

Anticancer effect of verteporfin on non-small cell lung cancer via downregulation of ANO1

Anoctamin 1 (ANO1) is a calcium-activated chloride channel found in various cell types and is overexpressed in non-small cell lung cancer (NSCLC), a major cause of cancer-related mortality. With the rising interest in development of druggable compounds for NSCLC, there has been a corresponding rise in interest in ANO1, a novel drug target for NSCLC. However, as ANO1 inhibitors that have been discovered simultaneously exhibit both the functions of an inhibition of ANO1 channel as well as a reduction of ANO1 protein levels, it is unclear which of the two functions directly causes the anticancer effect. In this study, verteporfin, a chemical compound that reduces ANO1 protein levels was identified through high-throughput screening. Verteporfin did not inhibit ANO1-induced chloride secretion but reduced ANO1 protein levels in a dose-dependent manner with an IC₅₀ value of ~300 nM. Moreover, verteporfin inhibited neither P2Y receptor-induced intracellular Ca²⁺ mobilization nor cystic fibrosis transmembrane conductance regulator (CFTR) channel activity, and molecular docking studies revealed that verteporfin bound to specific sites of ANO1 protein. Confirming that verteporfin reduces ANO1 protein levels, we then investigated the molecular mechanisms involved in its effect on NSCLC cells. Interestingly, verteporfin decreased ANO1 protein levels, the EGFR-STAT3 pathway as well as ANO1 mRNA expression. Verteporfin reduced the viability of ANO1-expressing cells (PC9, and gefitinib-resistant PC9) and induced apoptosis by increasing caspase-3 activity and PARP-1 cleavage. However, it did not affect hERG channel activity. These results show that the anticancer mechanism of verteporfin is caused via the down-regulation of ANO1.

VI-116, A Novel Potent Inhibitor of VRAC with Minimal Effect on ANO1

Volume-regulated anion channel (VRAC) is ubiquitously expressed and plays a pivotal role in vertebrate cell volume regulation. A heterologous complex of leucine-rich repeat containing 8A (LRRC8A) and LRRC8B-E constitutes the VRAC, which is involved in various processes such as cell proliferation, migration, differentiation, intercellular communication, and apoptosis. However, the lack of a potent and selective inhibitor of VRAC limits VRAC-related physiological and pathophysiological studies, and most previous VRAC inhibitors strongly blocked the calcium-activated chloride channel, anoctamin 1 (ANO1). In the present study, we performed a cell-based screening for the identification of potent and selective VRAC inhibitors. Screening of 55,000 drug-like small-molecules and subsequent chemical modification revealed 3,3′-((2-hydroxy-3-methoxyphenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (VI-116), a novel potent inhibitor of VRAC. VI-116 fully inhibited VRAC-mediated I⁻ quenching with an IC₅₀ of 1.27 ± 0.18 μM in LN215 cells and potently blocked endogenous VRAC activity in PC3, HT29 and HeLa cells in a dose-dependent manner. Notably, VI-116 had no effect on intracellular calcium signaling up to 10 μM, which completely inhibited VRAC, and showed high selectivity for VRAC compared to ANO1 and ANO2. However, DCPIB, a VRAC inhibitor, significantly affected ATP-induced increases in intracellular calcium levels and Eact-induced ANO1 activation. In addition, VI-116 showed minimal effect on hERG K⁺ channel activity up to 10 μM. These results indicate that VI-116 is a potent and selective VRAC inhibitor and a useful research tool for pharmacological dissection of VRAC.

SMYD3 regulates the abnormal proliferation of non-small-cell lung cancer cells via the H3K4me3/ANO1 axis

Non-small-cell lung cancer (NSCLC) is the most prevalent type of lung cancer. This study evaluated the mechanism of histone methyltransferase SET and MYND domain-containing 3 (SMYD3) in the abnormal proliferation of NSCLC cells. The human bronchial epithelial cell (HBEC) line (16HBE) and NSCLC cell lines (H1299, A549, H460, and H1650) were collected. A549 and H1650 cells were transfected with si-SMYD3 and Anoctamin-1 (ANO1) and their negative controls or treated with BCI-121, or A549 cells were treated with CPI-455. SMYD3, H3 lysine 4 tri-methylation (H3K4me3), and ANO1 levels in the cells were detected. The proliferation ability of A549 and H1650 cells were examined. We found that SMYD3, H3K4me3, and ANO1 were highly expressed in NSCLC cell lines. Silencing SMYD3 or SMYD3 activity in A549 and H1650 cells inhibited the cell proliferation ability and decreased H3K4me3 level and ANO1 mRNA level in the cells. H3K4me3 upregulation orANO1 overexpression reversed the inhibitory effects of silencing SMYD3 on the abnormal proliferation of NSCLC cells. Chromatin-Immunoprecipitation (Ch-IP) assay detected that SMYD3 bound to and enriched in the ANO1 promoter region, and the ANO1 promoter region was enriched with H3K4me3. Collectively, SMYD3 promoted ANO1 transcription by upregulating H3K4me3 in the ANO1 promoter region, thus facilitating the abnormal proliferation of NSCLC cells.

Cucumis sativus extract elicits chloride secretion by stimulation of the intestinal TMEM16A ion channel

CONTEXT

Cucumber (Cucumis sativus Linn. [Cucurbitaceae]) is widely known for its purgative, antidiabetic, antioxidant, and anticancer therapeutic potential. However, its effect on gastrointestinal (GI) disease is unrecognised.

OBJECTIVE

This study investigated the effect of C. sativus fruit extract (CCE) on intestinal chloride secretion, motility, and motor function, and the role of TMEM16A chloride channels.

MATERIALS AND METHODS

CCE extracts were obtained from commercially available cucumber. Active fractions were then purified by HPLC and analysed by high resolution mass spectrometry. The effect of CCE on intestinal chloride secretion was investigated in human colonic T84 cells, ex vivo mouse intestinal tissue using an Ussing chamber, and the two-electrode voltage-clamp technique to record calcium sensitive TMEM16A chloride currents in Xenopus laevis oocytes. In vivo, intestinal motility was investigated using the loperamide-induced C57BL/6 constipation mouse model. Ex vivo contractility of mouse colonic smooth muscles was assessed by isometric force measurements.

RESULTS

CCE increased the short-circuit current (ΔIsc 34.47 ± µA/cm²) and apical membrane chloride conductance (ΔI_Cl 95 ± 8.1 µA/cm²) in intestinal epithelial cells. The effect was dose-dependent, with an EC₅₀ value of 0.06 µg/mL. CCE stimulated the endogenous TMEM16A-induced Cl^- current in Xenopus laevis oocytes. Moreover, CCE increased the contractility of smooth muscle in mouse colonic tissue and enhanced small bowel transit in CCE treated mice compared to loperamide controls. Mass spectrometry suggested a cucurbitacin-like analogue with a mass of 512.07 g/mol underlying the bioactivity of CCE.

CONCLUSION

A cucurbitacin-like analog present in CCE activates TMEM16A channels, which may have therapeutic potential in cystic fibrosis and intestinal hypodynamic disorders.

Mouse organoid culture is a suitable model to study esophageal ion transport mechanisms

Altered esophageal ion transport mechanisms play a key role in inflammatory and cancerous diseases of the esophagus, but epithelial ion processes have been less studied in the esophagus because of the lack of a suitable experimental model. In this study, we generated three-dimensional (3D) esophageal organoids (EOs) from two different mouse strains and characterized the ion transport processes of the EOs. EOs form a cell-filled structure with a diameter of 250-300 µm and were generated from epithelial stem cells as shown by FACS analysis. Using conventional PCR and immunostaining, the presence of Slc26a6 Cl-/HCO3- anion exchanger (AE), Na+/H+ exchanger (NHE), Na+/HCO3- cotransporter (NBC), cystic fibrosis transmembrane conductance regulator (CFTR), and anoctamin 1 Cl- channels was detected in EOs. Microfluorimetric techniques revealed high NHE, AE, and NBC activities, whereas that of CFTR was relatively low. In addition, inhibition of CFTR led to functional interactions between the major acid-base transporters and CFTR. We conclude that EOs provide a relevant and suitable model system for studying the ion transport mechanisms of esophageal epithelial cells, and they can be also used as preclinical tools to assess the effectiveness of novel therapeutic compounds in esophageal diseases associated with altered ion transport processes.

A fungus-derived purpactin A as an inhibitor of TMEM16A chloride channels and mucin secretion in airway epithelial cells

TMEM16A is a Ca2+-activated Cl- channel involved in mucus secretion in inflamed airways and proposed as a drug target for diseases associated with mucus hypersecretion including asthma. This study aimed to identify novel inhibitors of TMEM16A-mediated Cl- secretion in airway epithelial cells from a collection of compounds isolated from fungi indigenous in Thailand and examine its potential utility in mitigating airway mucus secretion using Calu-3 cells as a study model. Screening of > 400 fungal metabolites revealed purpactin A isolated from a soil-derived fungus Penicillium aculeatum PSU-RSPG105 as an inhibitor of TMEM16A-mediated Cl- transport with an IC50 value of ~2 µM. A consistent inhibitory effect of purpactin A on TMEM16A were observed regardless of TMEM16A activators or in the presence of an inhibitor of Ca2+/calmodulin-dependent protein kinase II (CaMKII), a negative regulator of TMEM16A. In addition, purpactin A did not affect cell viability, epithelial barrier integrity and activities of membrane transport proteins essential for maintaining airway hydration including CFTR Cl- channels and apical BK K+ channels. Intriguingly, purpactin A prevented a Ca2+-induced mucin release in cytokine-treated airway cells. Taken together, purpactin A represents the first class of TMEM16A inhibitor derived from fungus, which may be beneficial for the treatment of diseases associated with mucus hypersecretion.

Nimodipine inhibits intestinal and aortic smooth muscle contraction by regulating Ca2+-activated Cl- channels

Nimodipine is a clinically used dihydropyridine L-type calcium channel antagonist that effectively inhibits transmembrane Ca2+ influx following the depolarization of smooth muscle cells, but the detailed effect on smooth muscle contraction is not fully understood. Ca2+-activated Cl- channels (CaCCs) in vascular smooth muscle cells (VSMCs) may regulate vascular contractility. We found that nimodipine can inhibit transmembrane protein 16A (TMEM16A) activity in a concentration-dependent manner by cell-based fluorescence-quenching assay and short-circuit current analysis, with an IC50 value of ~5 μM. Short-circuit current analysis also showed that nimodipine prevented Ca2+-activated Cl- current in both HT-29 cells and mouse colonic epithelia accompanied by significantly decreased cytoplasmic Ca2+ concentrations. In the absence of extracellular Ca2+, nimodipine still exhibited an inhibitory effect on TMEM16A/CaCCs. Additionally, the application of nimodipine to CFTR-expressing FRT cells and mouse colonic mucosa resulted in mild activation of CFTR-mediated Cl- currents. Nimodipine inhibited basolateral CCh-activated K+ channel activity with no effect on Na+/K+-ATPase activity. Evaluation of intestinal smooth muscle contraction showed that nimodipine inhibits intestinal smooth muscle contractility and frequency, with an activity pattern that was similar to that of non-specific inhibitors of CaCCs. In aortic smooth muscle, the expression of TMEM16A in thoracic aorta is higher than that in abdominal aorta, corresponding to stronger maximum contractility in thoracic aorta smooth muscle stimulated by phenylephrine (PE) and Eact. Nimodipine completely inhibited the contraction of aortic smooth muscle stimulated by Eact, and partially inhibited the contraction stimulated by PE. In summary, the results indicate that nimodipine effectively inhibits TMEM16A/CaCCs by reduction transmembrane Ca2+ influx and directly interacting with TMEM16A, explaining the mechanisms of nimodipine relaxation of intestinal and aortic smooth muscle contraction and providing new targets for pharmacological applications.

Opposing roles of E3 ligases TRIM23 and TRIM21 in regulation of ion channel ANO1 protein levels

Anoctamin-1 (ANO1) (TMEM16A) is a calcium-activated chloride channel that plays critical roles in diverse physiological processes, such as sensory transduction and epithelial secretion. ANO1 levels have been shown to be altered under physiological and pathological conditions, although the molecular mechanisms that control ANO1 protein levels remain unclear. The ubiquitin–proteasome system is known to regulate the levels of numerous ion channels, but little information is available regarding whether and how ubiquitination regulates levels of ANO1. Here, we showed that two E3 ligases, TRIM23 and TRIM21, physically interact with the C terminus of ANO1. In vitro and in vivo assays demonstrated that whereas TRIM23 ubiquitinated ANO1 leading to its stabilization, TRIM21 ubiquitinated ANO1 and induced its degradation. Notably, ANO1 regulation by TRIM23 and TRIM21 is involved in chemical-induced pain sensation, salivary secretion, and heart-rate control in mice, and TRIM23 also mediates ANO1 upregulation induced by epidermal growth factor treatment. Our results suggest that these two antagonistic E3 ligases act together to control ANO1 expression and function. Our findings reveal a previously unrecognized mechanism for regulating ANO1 protein levels and identify a potential molecular link between ANO1 regulation, epidermal growth factor, and other signaling pathways.

TMEM16A channel upregulation in arterial smooth muscle cells produces vasoconstriction during diabetes

The pathological involvement of anion channels in vascular dysfunction that occurs during type 2 diabetes (T2D) is unclear. Here, we tested the hypothesis that TMEM16A, a calcium-activated chloride (Cl-) channel, contributes to modifications in arterial contractility during T2D. Our data indicate that T2D increased TMEM16A mRNA in arterial smooth muscle cells and total and surface TMEM16A protein in resistance-size cerebral and hindlimb arteries of mice. To examine vascular cell types in which TMEM16A protein increased and the functional consequences of TMEM16A upregulation during T2D, we generated tamoxifen-inducible, smooth muscle cell-specific TMEM16A knockout (TMEM16A smKO) mice. T2D increased both TMEM16A protein and Cl- current density in arterial smooth muscle cells of control (TMEM16Afl/fl) mice. In contrast, T2D did not alter arterial TMEM16A protein or Cl- current density in smooth muscle cells of TMEM16A smKO mice. Intravascular pressure stimulated greater vasoconstriction (myogenic tone) in the arteries of T2D TMEM16Afl/fl mice than in the arteries of nondiabetic TMEM16Afl/fl mice. This elevation in myogenic tone in response to T2D was abolished in the arteries of T2D TMEM16A smKO mice. T2D also reduced Akt2 protein and activity in the arteries of T2D mice. siRNA-mediated knockdown of Akt2, but not Akt1, increased arterial TMEM16A protein in nondiabetic mice. In summary, data indicate that T2D is associated with an increase in TMEM16A expression and currents in arterial smooth muscle cells that produces vasoconstriction. Data also suggest that a reduction in Akt2 function drives these pathological alterations during T2D.NEW & NOTEWORTHY We investigated the involvement of TMEM16A channels in vascular dysfunction during type 2 diabetes (T2D). TMEM16A message, protein, and currents were higher in smooth muscle cells of resistance-size arteries during T2D. Pressure stimulated greater vasoconstriction in the arteries of T2D mice that was abolished in the arteries of TMEM16A smKO mice. Akt2 protein and activity were both lower in T2D arteries, and Akt2 knockdown elevated TMEM16A protein. We propose that a decrease in Akt2 function stimulates TMEM16A expression in arterial smooth muscle cells, leading to vasoconstriction during T2D.

Mechanism of pore opening in the calcium-activated chloride channel TMEM16A

The anion channel TMEM16A is activated by intracellular Ca2+ in a highly cooperative process. By combining electrophysiology and autocorrelation analysis, we investigated the mechanism of channel activation and the concurrent rearrangement of the gate in the narrow part of the pore. Features in the fluctuation characteristics of steady-state current indicate the sampling of intermediate conformations that are successively occupied during gating. The initial step is related to conformational changes induced by Ca2+ binding, which is ensued by rearrangements that open the pore. Mutations in the gate shift the equilibrium of transitions in a manner consistent with a progressive destabilization of this region during pore opening. We come up with a mechanism of channel activation where the binding of Ca2+ induces conformational changes in the protein that, in a sequential manner, propagate from the binding site and couple to the gate in the narrow pore to allow ion permeation.

Gating the pore of the calcium-activated chloride channel TMEM16A

The binding of cytoplasmic Ca2+ to the anion-selective channel TMEM16A triggers a conformational change around its binding site that is coupled to the release of a gate at the constricted neck of an hourglass-shaped pore. By combining mutagenesis, electrophysiology, and cryo-electron microscopy, we identified three hydrophobic residues at the intracellular entrance of the neck as constituents of this gate. Mutation of each of these residues increases the potency of Ca2+ and results in pronounced basal activity. The structure of an activating mutant shows a conformational change of an α-helix that contributes to Ca2+ binding as a likely cause for the basal activity. Although not in physical contact, the three residues are functionally coupled to collectively contribute to the stabilization of the gate in the closed conformation of the pore, thus explaining the low open probability of the channel in the absence of Ca2+.

Prognostic significance of ANO1 expression in cancers

BACKGROUND

Anoctamin-1 (ANO1) plays a pivotal role in cancer progression. A meta-analysis was conducted to assess the potential prognostic role of ANO1 in cancers.

METHODS

A total of 1760 patients from 7 eligible studies were included into the analysis. Pooled hazard ratios or odds ratios were extracted and calculated with a random-effects model, and analyses of heterogeneity bias were conducted.

RESULTS

Our results showed that over expression of ANO1 was significantly correlated with poor overall survival in all cancers (HR = 1.52; 95% CI: 1.19-1.92; P = .0006). Subgroup analysis indicated that there was a significant association between over expression of ANO1 and poor prognosis breast cancer (HR = 3.24; 95% CI: 1.74-6.04), head and neck squamous cell carcinoma (HR = 1.14; 95% CI: 1.00-1.30), esophageal squamous cell carcinoma (HR = 1.93; 95% CI: 1.07-3.50), gastric cancer (HR = 1.62; 95% CI: 1.12-2.34) and colorectal cancer (HR = 1.38; 95% CI: 1.03-1.85). In addition, over expression of ANO1 was not associated with TNM stage, histological grade, lymph node metastasis, tumor size, age and gender. However, ANO1 was significantly associated with human epidermal growth factor receptor 2, but not associated with progesterone receptor or estrogen receptor in breast cancer.

CONCLUSIONS

Our results indicate that ANO1 can be a predictive factor for prognosis of cancer.

Oncogene mutational analysis in imatinib naive population of gastrointestinal stromal tumor patients

There are very scanty reports on gastro-intestinal stromal tumors (GISTs), a very common tumor of mesenchymal cells in GIT track primary resistance to imatinib. This comprehensive study identifies the prevalence, clinical presentation and GIST genotype association in the imatinib naïve population. Prospectively a record of anthropometric, baseline demographic data and clinical details for the patients diagnosed with GIST were scrutinized. Pathological information included the presence or absence of necrosis, tumor size, mitotic counts, immune-histochemical staining for CD 34, CD 117 and DOG1 was performed using biopsy sample. Selected exon genes of KIT, PDGFRA and BRAF were amplified and subjected to mutation analysis by direct sequencing. Appropriate statistical analyses were performed. The male/female ratio was 1.8:1 among 54 patients with GIST. The mean GIST size was comparatively bigger in females (2.49±0.855) than males (2.26±1.13). The stomach was the most common site for GIST followed by the Small bowel and rectum. The majority of the tumours were spindle cell. This study reports 12 different types of mutation among 39 KIT, 8 PDGFRA and 7 BRAF mutations. In KIT, the most prevalent was exon 11 mutation with the KITdelinc557/558 (14/30) being the major exon 11 type mutation. In PDGRFA, five exons 18 with p.D842V substitution and three exons 12 deletion mutation was reported. Seven patients had strong or diffuse BRAF staining having V600E type mutation as major BRAF type mutation. Drug-resistant GIST due to acquired mutations remains a serious issue, therefore genetic information of such mutational related to drug-resistant may provide the imperative clue for diagnosis and clinical treatment. These mutations are pivotal for prognosis and associated with imatinib as not all of them but only a few are reported resistant to the imatinib.

Cell Sheets Restore Secretory Function in Wounded Mouse Submandibular Glands

Thermoresponsive cell culture plates release cells as confluent living sheets in response to small changes in temperature, with recovered cell sheets retaining functional extracellular matrix proteins and tight junctions, both of which indicate formation of intact and functional tissue. Our recent studies demonstrated that cell sheets are highly effective in promoting mouse submandibular gland (SMG) cell differentiation and recovering tissue integrity. However, these studies were performed only at early time points and extension of the observation period is needed to investigate duration of the cell sheets. Thus, the goal of this study was to demonstrate that treatment of wounded mouse SMG with cell sheets is capable of increasing salivary epithelial integrity over extended time periods. The results indicate that cell sheets promote tissue organization as early as eight days after transplantation and that these effects endure through Day 20. Furthermore, cell sheet transplantation in wounded SMG induces a significant time-dependent enhancement of cell polarization, differentiation and ion transporter expression. Finally, this treatment restored saliva quantity to pre-wounding levels at both eight and twenty days post-surgery and significantly improved saliva quality at twenty days post-surgery. These data indicate that cell sheets engineered with thermoresponsive cell culture plates are useful for salivary gland regeneration and provide evidence for the long-term stability of cell sheets, thereby offering a potential new therapeutic strategy for treating hyposalivation.

Allosteric modulation of alternatively spliced Ca2+-activated Cl- channels TMEM16A by PI(4,5)P2 and CaMKII

Transmembrane 16A (TMEM16A, anoctamin1), 1 of 10 TMEM16 family proteins, is a Cl- channel activated by intracellular Ca2+ and membrane voltage. This channel is also regulated by the membrane phospholipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. We find that two splice variants of TMEM16A show different sensitivity to endogenous PI(4,5)P2 degradation, where TMEM16A(ac) displays higher channel activity and more current inhibition by PI(4,5)P2 depletion than TMEM16A(a). These two channel isoforms differ in the alternative splicing of the c-segment (exon 13). The current amplitude and PI(4,5)P2 sensitivity of both TMEM16A(ac) and (a) are significantly strengthened by decreased free cytosolic ATP and by conditions that decrease phosphorylation by Ca2+/calmodulin-dependent protein kinase II (CaMKII). Noise analysis suggests that the augmentation of currents is due to a rise of single-channel current (i), but not of channel number (N) or open probability (PO). Mutagenesis points to arginine 486 in the first intracellular loop as a putative binding site for PI(4,5)P2, and to serine 673 in the third intracellular loop as a site for regulatory channel phosphorylation that modulates the action of PI(4,5)P2 In silico simulation suggests how phosphorylation of S673 allosterically and differently changes the structure of the distant PI(4,5)P2-binding site between channel splice variants with and without the c-segment exon. In sum, our study reveals the following: differential regulation of alternatively spliced TMEM16A(ac) and (a) by plasma membrane PI(4,5)P2, modification of these effects by channel phosphorylation, identification of the molecular sites, and mechanistic explanation by in silico simulation.

Smooth muscle cell-specific TMEM16A deletion does not alter Ca2+ signaling, uterine contraction, gestation length, or litter size in mice†

Ion channels in myometrial cells play critical roles in spontaneous and agonist-induced uterine contraction during the menstrual cycle, pregnancy maintenance, and parturition; thus, identifying the genes of ion channels in these cells and determining their roles are essential to understanding the biology of reproduction. Previous studies with in vitro functional and pharmacological approaches have produced controversial results regarding the presence and role of TMEM16A Ca2+-activated Cl- channels in myometrial cells. To unambiguously determine the function of this channel in these cells, we employed a genetic approach by using smooth muscle cell-specific TMEM16A deletion (i.e. TMEM16ASMKO) mice. We found that myometrial cells from TMEM16ASMKO mice generated the same pattern and magnitude in Ca2+ signals upon stimulation with KCl, oxytocin, and PGF2α compared to the isogenic control myometrial cells. At the uterine tissue level, TMEM16A deletion also did not cause detectable changes in either spontaneous or agonist (i.e. KCl, oxytocin, and PGF2α)-induced contractions. Moreover, in vivo the TMEM16ASMKO mice gave birth at full term with the same litter size as genetically identical control mice. Finally, TMEM16A immunostaining in both control and TMEM16ASMKO mice revealed that this protein was highly expressed in the endometrial stroma, but did not co-localize with a smooth muscle specific marker MYH11. Collectively, these results unequivocally demonstrate that TMEM16A does not serve as a pacemaking channel for spontaneous uterine contraction, neither does it function as a depolarizing channel for agonist-evoked uterine contraction. Yet these two functions could underlie the normal gestation length and litter size in the TMEM16ASMKO mice.

TMEM16A-encoded anoctamin 1 inhibition contributes to chrysin-induced coronary relaxation

BACKGROUND

Chrysin, a natural flavonoid available in honey, propolis and medicinal plants, has been shown to be vasorelaxant in some vascular beds. Proper intake of an alimental vasodilator as a food additive may be a promising strategy for prevention and treatment of coronary spasmodic disorders.

PURPOSE

TMEM16A-encoded anoctamin 1 (ANO1), a Ca²⁺ activated Cl^- channel (CaCC), plays an important role in the modulation of vascular tone. We tested the possibility that inhibition of CaCCs contributes to chrysin-induced coronary arterial relaxation.

METHODS

The vascular tone of the rat coronary artery (RCA) was recorded with a wire myograph. CaCC currents were assessed using whole-cell patch clamp in arterial smooth muscle cell (ASMC) freshly isolated from RCAs. An inhibitor study was performed to explore the mechanisms underlying the vasomotor and electrophysiological effects of chrysin.

RESULTS

Pre-incubation with chrysin depressed the contractions elicited by thromboxane A2 analog U46619, vasopressin (VP), depolarization and extracellular Ca²⁺ elevation/depolarization without significant preference among these vasoconstrictors. Besides, chrysin inhibited both intracellular Ca²⁺ release-dependent and extracellular Ca²⁺ influx-dependent components of contractions induced by U46619 or VP. In RCAs pre-contracted with U46619, VP or KCl, chrysin elicited concentration-dependent relaxations, which were weakened by Cl^- -deprivation. The electrophysiological study showed that chrysin reduced ANO1-antibody-sensitive CaCC currents and depressed CaCC increments induced by U46619. Inhibitor study showed that both the vasorelaxation and the CaCC current reduction induced by chrysin were attenuated by blocking CaCCs and inhibiting cAMP/PKA and NO/PKG pathways.

CONCLUSION

The present findings indicate that inhibition of RCA ASMC CaCC currents, which may be consequential following intracellular Ca²⁺ availability reduction and activation of cAMP/PKA and NO/cGMP signaling pathways, contributes to chrysin-induced RCA relaxation.

Ca2+-activated Cl- channel TMEM16A inhibition by cholesterol promotes angiogenesis in endothelial cells

Introduction

Ca²⁺-activated Cl^- channel TMEM16A is expressed in endothelial cells, and contributes to many diseases such as hypertension, blood-brain barrier dysfunction, and pulmonary hypertension. It remains unclear whether TMEM16A regulates endothelial angiogenesis, which participates in many physiological and pathological processes. Cholesterol regulates many ion channels including TMEM16A, and high cholesterol levels contribute to endothelial dysfunction. It remains to be determined whether cholesterol regulates TMEM16A expression and function in endothelial cells.

Objective

This study aimed to investigate whether cholesterol regulated TMEM16A expression and function in endothelial angiogenesis.

Methods

Whole-cell patch clamp techniques were used to record Ca²⁺-activated Cl^- currents in human aortic endothelial cells (HAECs) and HEK293 cells transfected with TMEM16A-overexpressing plasmids. Western blot was used to examine the expression of TMEM16A and DNA methyltransferase 1 (DNMT1) in HAECs. CCK-8 assay, would healing assay, and tube formation assay were used to test endothelial cell proliferation, migration and angiogenesis, respectively.

Results

TMEM16A mediates the Ca²⁺-activated Cl^- channel in HAECs. Cholesterol treatment inhibited TMEM16A expression via upregulation of DNMT1 in HAECs, and the inhibitory effect of cholesterol on TMEM16A expression was blocked by 5-aza, the DNMT1 inhibitor. In addition, direct application of cholesterol inhibited TMEM16A currents in heterologous HEK293 cells with an IC₅₀ of 0.1209 μM. Similarly, cholesterol directly inhibited TMEM16A currents in HAECs. Furthermore, TMEM16A knockdown increased in vitro tube formation, cell migration and proliferation of HAECs, and TMEM16A overexpression produced the opposite effect.

Conclusion

This study reveals a novel mechanism of cholesterol-mediated TMEM16A inhibition, by which cholesterol reduces TMEM16A expression via DNMT1-mediated methylation and directly inhibits channel activities. TMEM16A channel inhibition promotes endothelial cell angiogenesis.

Novel ANO1 Inhibitor from Mallotus apelta Extract Exerts Anticancer Activity through Downregulation of ANO1

Anoctamin1 (ANO1), a calcium-activated chloride channel, is frequently overexpressed in several cancers, including human prostate cancer and oral squamous cell carcinomas. ANO1 plays a critical role in tumor growth and maintenance of these cancers. In this study, we have isolated two new compounds (1 and 2) and four known compounds (3-6) from Mallotus apelta. These compounds were evaluated for their inhibitory effects on ANO1 channel activity and their cytotoxic effects on PC-3 prostate cancer cells. Interestingly, compounds 1 and 2 significantly reduced both ANO1 channel activity and cell viability. Electrophysiological study revealed that compound 2 (Ani-D2) is a potent and selective ANO1 inhibitor, with an IC₅₀ value of 2.64 μM. Ani-D2 had minimal effect on cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel activity and intracellular calcium signaling. Notably, Ani-D2 significantly reduced ANO1 protein expression levels and cell viability in an ANO1-dependent manner in PC-3 and oral squamous cell carcinoma CAL-27 cells. In addition, Ani-D2 strongly reduced cell migration and induced activation of caspase-3 and cleavage of PARP in PC-3 and CAL-27 cells. This study revealed that a novel ANO1 inhibitor, Ani-D2, has therapeutic potential for the treatment of several cancers that overexpress ANO1, such as prostate cancer and oral squamous cell carcinoma.

Diversity-oriented generation and biological evaluation of new chemical scaffolds bearing a 2,2-dimethyl-2H-chromene unit: Discovery of novel potent ANO1 inhibitors

Chemical territory bearing a 2,2-dimethyl-2H-chromene motif was expanded by utilizing an o-hydroxy aldehyde group of 5-hydroxy-2,2-dimethyl-2H-chromene-6-carbaldehyde as a synthetic handle to install distinctive morphology and functionality of each scaffold. Cell based assays and in silico docking analysis led us to discover that these new compounds exhibit inhibitory effect on anoctamin1 (ANO1). ANO1 is amplified and highly expressed in various carcinomas including prostate cancer, esophageal cancer, breast cancer, and pancreatic cancer. Biological assays revealed that (E)-1-(7,7-dimethyl-7H-furo[2,3-f]chromen-2-yl)-3-(1H-pyrrol-2-yl)prop-2-en-1-one (3n, Ani-FCC) is a novel, potent and selective ANO1 inhibitor with an IC₅₀ value of 1.23 μM. 3n showed 144 times stronger activity on ANO1 inhibition than ANO2 inhibition and did not alter the chloride channel activity of CFTR and the intracellular calcium signaling. Notably, 3n strongly decreased cell viability of PC-3 and FaDu cells expressing high levels of ANO1 with a decrease in ANO1 protein levels. In addition, 3n significantly enhanced apoptosis via activation of caspase 3 and cleavage of PARP in PC-3 and FaDu cells. This study shows that a novel ANO1 inhibitor, 3n, can be a potential candidate for the treatment of cancers overexpressing ANO1, such as prostate cancer and esophageal cancer.

Regulation of TMEM16A by CK2 and Its Role in Cellular Proliferation

Casein kinase 2 (CK2) is a highly ubiquitous and conserved serine/threonine kinase that forms a tetramer consisting of a catalytic subunit (CK2α) and a regulatory subunit (CK2β). Despite being ubiquitous, CK2 is commonly found at higher expression levels in cancer cells, where it inhibits apoptosis, and supports cell migration and proliferation. The Ca²⁺-activated chloride channel TMEM16A shows similar effects in cancer cells: TMEM16A increases cell proliferation and migration and is highly expressed in squamous cell carcinoma of the head and neck (HNSCC) as well as other malignant tumors. A microscopy-based high-throughput screening was performed to identify proteins that regulate TMEM16A. Within this screen, CK2 was found to be required for proper membrane expression of TMEM16A. small interfering (si) RNA-knockdown of CK2 reduced plasma membrane expression of TMEM16A and inhibited TMEM16A whole cell currents in (cystic fibrosis bronchial epithelial) CFBE airway epithelial cells and in the head and neck cancer cell lines Cal33 and BHY. Inhibitors of CK2, such as TBB and the preclinical compound CX4549 (silmitasertib), also blocked membrane expression of TMEM16A and Ca²⁺-activated whole cell currents. siRNA-knockout of CK2 and its pharmacological inhibition, as well as knockdown or inhibition of TMEM16A by either niclosamide or Ani9, attenuated cell proliferation. Simultaneous inhibition of CK2 and TMEM16A strongly potentiated inhibition of cell proliferation. Although membrane expression of TMEM16A is reduced by inhibition of CK2, our data suggest that the antiproliferative effects by inhibition of CK2 are mostly independent of TMEM16A. Simultaneous inhibition of TMEM16A by niclosamide and inhibition of CK2 by silmitasertib was additive with respect to blocking cell proliferation, while cytotoxicity was reduced when compared to solely blockade of CK2. Therefore, parallel blockade TMEM16A by niclosamide may assist with anticancer therapy by silmitasertib.

Chloride channels regulate differentiation and barrier functions of the mammalian airway

The conducting airway forms a protective mucosal barrier and is the primary target of airway disorders. The molecular events required for the formation and function of the airway mucosal barrier, as well as the mechanisms by which barrier dysfunction leads to early onset airway diseases, remain unclear. In this study, we systematically characterized the developmental landscape of the mouse airway using single-cell RNA sequencing and identified remarkably conserved cellular programs operating during human fetal development. We demonstrated that in mouse, genetic inactivation of chloride channel Ano1/Tmem16a compromises airway barrier function, results in early signs of inflammation, and alters the airway cellular landscape by depleting epithelial progenitors. Mouse Ano1-/-mutants exhibited mucus obstruction and abnormal mucociliary clearance that resemble the airway defects associated with cystic fibrosis. The data reveal critical and non-redundant roles for Ano1 in organogenesis, and show that chloride channels are essential for mammalian airway formation and function.

Pharmacological Inhibition and Activation of the Ca2+ Activated Cl- Channel TMEM16A

TMEM16A is a Ca²⁺ activated Cl⁻ channel with important functions in airways, intestine, and other epithelial organs. Activation of TMEM16A is proposed as a therapy in cystic fibrosis (CF) to reinstall airway Cl⁻ secretion and to enhance airway surface liquid (ASL). This CFTR-agnostic approach is thought to improve mucociliary clearance and lung function in CF. This could indeed improve ASL, however, mucus release and airway contraction may also be induced by activators of TMEM16A, particularly in inflamed airways of patients with asthma, COPD, or CF. Currently, both activators and inhibitors of TMEM16A are developed and examined in different types of tissues. Here we compare activation and inhibition of endogenous and overexpressed TMEM16A and analyze potential off-target effects. The three well-known blockers benzbromarone, niclosamide, and Ani9 inhibited both TMEM16A and ATP-induced Ca²⁺ increase by variable degrees, depending on the cell type. Niclosamide, while blocking Ca²⁺ activated TMEM16A, also induced a subtle but significant Ca²⁺ store release and inhibited store-operated Ca²⁺ influx. Niclosamide, benzbromarone and Ani9 also affected TMEM16F whole cell currents, indicating limited specificity for these inhibitors. The compounds Eact, cinnamaldehyde, and melittin, as well as the phosphatidylinositol diC8-PIP₂ are the reported activators of TMEM16A. However, the compounds were unable to activate endogenous TMEM16A in HT₂₉ colonic epithelial cells. In contrast, TMEM16A overexpressed in HEK293 cells was potently stimulated by these activators. We speculate that overexpressed TMEM16A might have a better accessibility to intracellular Ca²⁺, which causes spontaneous activity even at basal intracellular Ca²⁺ concentrations. Small molecules may therefore potentiate pre-stimulated TMEM16A currents, but may otherwise fail to activate silent endogenous TMEM16A.

Calcium- and Voltage-Dependent Dual Gating ANO1 is an Intrinsic Determinant of Repolarization in Rod Bipolar Cells of the Mouse Retina

TMEM16A/anoctamin1 (ANO1), a calcium (Ca²⁺)-activated chloride (Cl^-) channel, has many functions in various excitable cells and modulates excitability in both Ca²⁺- and voltage-gating modes. However, its gating characteristics and role in primary neural cells remain unclear. Here, we characterized its Ca²⁺- and voltage-dependent components in rod bipolar cells using dissociated and slice preparations of the mouse retina. The I-V curves of Ca²⁺-dependent ANO1 tail current and voltage-gated Ca²⁺ channel (VGCC) are similar; as ANO1 is blocked by VGCC inhibitors, ANO1 may be gated by Ca²⁺ influx through VGCC. The voltage-dependent component of ANO1 has outward rectifying and sustained characteristics and is clearly isolated by the inhibitory effect of Cl^- reduction and T16Ainh-A01, a selective ANO1 inhibitor, in high EGTA, a Ca²⁺ chelator. The voltage-dependent component disappears due to VGCC inhibition, suggesting that Ca²⁺ is the essential trigger for ANO1. In perforated current-clamping method, the application of T16Ainh-A01 and reduction of Cl^- extended excitation periods in rod bipolar cells, revealing that ANO1 induces repolarization during excitation. Overall, ANO1 opens by VGCC activation during physiological excitation of the rod bipolar cell and has a voltage-dependent component. These two gating-modes concurrently provide the intrinsic characteristics of the membrane potential in rod bipolar cells.

Mammary analogue secretory carcinoma: A case report

BACKGROUND

Mammary analogue secretory carcinoma is a rare new entity of low-grade malignant tumor of salivary glands. It shared the same histologic features and the chromosomal translocation t(12;15)(p13;q25) as secretory carcinoma of the breast.

AIM

To highlight the diagnosis approaches and the attitude of management in a case of MASC which is the first case reported in Tunisia. Reported case: A case of MASC of the lower left jugal mucosa was reviewed for its microscopic and immunohistochemical features. Fluorescence in situ hybridization (FISH) for the ETV6-NTRK3 translocation was performed. Surgery was the only treatment required in this case. No signs of local or regional recurrence during the one-year follow-up were noticed.

COMMENTARIES

Secretory carcinoma was confused with other salivary gland tumors especially acinic cell carcinoma due to their morphological similarities, making diagnosis dilemma. Fluorescence in-situ hybridization (FISH) is the one definitive finding to confirm the diagnosis of MASC and to differentiate it from the other types of salivary gland tumor. At the present time, no specific therapy is available for patients with MASC.

Endophilin A2 regulates calcium-activated chloride channel activity via selective autophagy-mediated TMEM16A degradation

TMEM16A Ca2+-activated chloride channel (CaCC) plays an essential role in vascular homeostasis. In this study we investigated the molecular mechanisms underlying downregulation of TMEM16A CaCC activity during hypertension. In cultured basilar artery smooth muscle cells (BASMCs) isolated from 2k2c renohypertesive rats, treatment with angiotensin II (0.125-1 μM) dose-dependently increased endophilin A2 levels and decreased TMEM16A expression. Similar phenomenon was observed in basilar artery isolated from 2k2c rats. We then used whole-cell recording to examine whether endophilin A2 could regulate TMEM16A CaCC activity in BASMCs and found that knockdown of endophilin A2 significantly enhanced CaCC activity, whereas overexpression of endophilin A2 produced the opposite effect. Overexpression of endophilin A2 did not affect the TMEM16A mRNA level, but markedly decreased TMEM16A protein level in BASMCs by inducing ubiquitination and autophagy of TMEM16A. Ubiquitin-binding receptor p62 (SQSTM1) could bind to ubiquitinated TMEM16A and resulted in a process of TMEM16A proteolysis in autophagosome/lysosome. These data provide new insights into the regulation of TMEM16A CaCC activity by endophilin A2 in BASMCs, which partly explains the mechanism of angiotensin-II-induced TMEM16A inhibition during hypertension-induced vascular remodeling.

Structural and Biophysical Analysis of the CLCA1 VWA Domain Suggests Mode of TMEM16A Engagement

The secreted protein calcium-activated chloride channel regulator 1 (CLCA1) utilizes a von Willebrand factor type A (VWA) domain to bind to and potentiate the calcium-activated chloride channel TMEM16A. To gain insight into this unique potentiation mechanism, we determined the 2.0-Å crystal structure of human CLCA1 VWA bound to Ca2+. The structure reveals the metal-ion-dependent adhesion site (MIDAS) in a high-affinity "open" conformation, engaging in crystal contacts that likely mimic how CLCA1 engages TMEM16A. The CLCA1 VWA contains a disulfide bond between α3 and α4 in close proximity to the MIDAS that is invariant in the CLCA family and unique in VWA structures. Further biophysical studies indicate that CLCA1 VWA is preferably stabilized by Mg2+ over Ca2+ and that α6 atypically extends from the VWA core. Finally, an analysis of TMEM16A structures suggests residues likely to mediate interaction with CLCA1 VWA.

Wasted TMEM16A channels are rescued by phosphatidylinositol 4,5-bisphosphate

Recently there has been a flurry of interest in the regulation of the homo-dimeric calcium-activated chloride channel ANO1 (also known as TMEM16A) by phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2). These recent studies show that upon Ca2+ binding, PI(4,5)P2 cooperates to maintain the conductive state of ANO1. PI(4,5)P2 does so by binding to sites or modules on the protein's cytosolic side. These findings add a new function to the PI(4,5)P2 repertoire and a new dimension to ANO1 gating.

Slc26a6 is an apical membrane anion exchanger that drives HCO3--dependent fluid secretion in murine pancreatic acinar cells

The nonselective anion exchanger Slc26a6, also known as putative anion transporter 1 and chloride/formate exchanger, is thought to play a major role in HCO 3 - transport in exocrine glands. In this study, Slc26a6 null mice were used to explore the function of Slc26a6 in the exocrine pancreas. Slc26a6 primarily localized to the apical membrane of pancreatic exocrine acinar cells. The volume of stimulated juice secretion by the ex vivo pancreas was significantly reduced ~35% in Slc26a6-/- mice, but no changes occurred in the gross structure or gland weights of Slc26a6 null mice. The secretion of pancreatic juice by Slc26a6+/+ mice was dependent on HCO 3 - while, in contrast, fluid secretion by Slc26a6-/- mice was independent of HCO 3 - , suggesting that Slc26a6 mediates the HCO 3 - -dependent component of fluid secretion. Consistent with these observations, disruption of Slc26a6 also significantly reduced HCO 3 - secretion by the pancreas ~35%. Taken together, these results demonstrate that the apical Slc26a6 anion exchanger in acinar cells is involved in HCO 3 - -dependent fluid secretion but that another major HCO 3 - -independent pathway is the primary driver of the fluid secretion process in the mouse pancreas.

Slowed gastric emptying and improved oral glucose tolerance produced by a nanomolar-potency inhibitor of calcium-activated chloride channel TMEM16A

Interstitial cells of Cajal, which express the calcium-activated chloride channel transmembrane member 16A (TMEM16A), are an important determinant of gastrointestinal (GI) motility. We previously identified the acylaminocycloalkylthiophene class of TMEM16A inhibitors, which, following medicinal chemistry, gave analog 2-bromodifluoroacetylamino-5,6,7,8-tetrahydro-4H-cyclohepta[b]thiophene-3-carboxylic acid o-tolylamide (TMinh-23) with 30 nM half-maximal inhibitory concentration. Here, we tested the efficacy of TMinh-23 for inhibition of GI motility in mice. In isolated murine gastric antrum, TMinh-23 strongly inhibited spontaneous and carbachol-stimulated rhythmic contractions. Pharmacokinetic analysis showed predicted therapeutic concentrations of TMinh-23 for at least 4 h following a single oral or intraperitoneal dose at 10 mg/kg. Gastric emptying, as assessed following an oral bolus of phenol red or independently by [99mTc]-diethylenetriamine pentaacetic acid scintigraphy, was reduced by TMinh-23 by ∼60% at 20 min. Interestingly, there was little effect of TMinh-23 on baseline whole-gut transit time or time to diarrhea induced by castor oil. Consequent to the delay in gastric emptying, TMinh-23 administration significantly reduced the elevation in blood sugar in mice following an oral but not intraperitoneal glucose load. These results provide pharmacological evidence for involvement of TMEM16A in gastric emptying and suggest the utility of TMEM16A inhibition in disorders of accelerated gastric emptying, such as dumping syndrome, and potentially for improving glucose tolerance in diabetes mellitus/metabolic syndrome and enhancing satiety in obesity.-Cil, O., Anderson, M. O., Yen, R., Kelleher, B., Huynh, T. L., Seo, Y., Nilsen, S. P., Turner, J. R., Verkman, A. S. Slowed gastric emptying and improved oral glucose tolerance produced by a nanomolar-potency inhibitor of calcium-activated chloride channel TMEM16A.

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.

Molecular basis of PIP2-dependent regulation of the Ca2+-activated chloride channel TMEM16A

The calcium-activated chloride channel (CaCC) TMEM16A plays crucial roles in regulating neuronal excitability, smooth muscle contraction, fluid secretion and gut motility. While opening of TMEM16A requires binding of intracellular Ca2+, prolonged Ca2+-dependent activation results in channel desensitization or rundown, the mechanism of which is unclear. Here we show that phosphatidylinositol (4,5)-bisphosphate (PIP2) regulates TMEM16A channel activation and desensitization via binding to a putative binding site at the cytosolic interface of transmembrane segments (TMs) 3-5. We further demonstrate that the ion-conducting pore of TMEM16A is constituted of two functionally distinct modules: a Ca2+-binding module formed by TMs 6-8 and a PIP2-binding regulatory module formed by TMs 3-5, which mediate channel activation and desensitization, respectively. PIP2 dissociation from the regulatory module results in ion-conducting pore collapse and subsequent channel desensitization. Our findings thus provide key insights into the mechanistic understanding of TMEM16 channel gating and lipid-dependent regulation.

Plasma membrane-localized TMEM16 proteins are indispensable for expression of CFTR

The cystic fibrosis transmembrane conductance regulator (CFTR) is the secretory chloride channel in epithelial tissues that has a central role in cystic fibrosis (CF) lung and gastrointestinal disease. A recent publication demonstrates a close association between CFTR and TMEM16A, the calcium-activated chloride channel. Thus, no CFTR chloride currents could be detected in airways and large intestine from mice lacking epithelial expression of TMEM16A. Here, we demonstrate that another plasma membrane-localized TMEM16 paralogue, TMEM16F, can compensate for the lack of TMEM16A. Using TMEM16 knockout mice, human lymphocytes, and a number of human cell lines with endogenous protein expression or heterologous expression, we demonstrate that CFTR can only function in the presence of either TMEM16A or TMEM16F. Double knockout of intestinal epithelial TMEM16A/F expression did not produce offsprings, suggesting a lethal phenotype in utero. Plasma membrane-localized TMEM16A or TMEM16F is required for exocytosis and expression of CFTR in the plasma membrane. TMEM16A/F proteins may therefore have an impact on disease severity in CF. KEY MESSAGES: • Cystic fibrosis is caused by the defective Cl- channel cystic fibrosis transmembrane conductance regulator (CFTR). • A close relationship exists between CFTR and the calcium-activated chloride channels TMEM16A/TMEM16F. • In conditional airway and intestinal knockout mice, lymphocytes from Scott disease patients and in overexpressing cells, CFTR is not functional in the absence of TMEM16A and TMEM16F. • TMEM16A and TMEM16F support membrane exocytosis and are essential for plasma membrane insertion of CFTR.