TMEM16A inhibitors reveal TMEM16A as a minor component of calcium-activated chloride channel conductance in airway and intestinal epithelial cells

The effects of Cl- channel inhibitors and pyrethroid insecticides on calcium-activated chloride channels in neurons of Helicoverpa armigera

TMEM16A, a member of the Transmembrane protein 16 family, serves as the molecular basis for calcium activated chloride channels (CaCCs). We use RT-PCR to demonstrate the expression of TMEM16A in the neurons of Helicoverpa armigera, and record the CaCCs current of acute isolated neurons of H. armigera for the first time using patch clamp technology. In order to screen effective inhibitors of calcium-activated chloride channels, the inhibitory effects of four chloride channel inhibitors, CaCCinh-A01, NPPB, DIDS, and SITS, on CaCCs were compared. The inhibitory effects of the four inhibitors on the outward current of CaCCs were CaCCinh-A01 (10 μM, 56.31 %), NPPB (200 μM, 43.69 %), SITS (1 mM, 12.41 %) and DIDS (1 mM, 13.29 %). Among these inhibitors, CaCCinh-A01 demonstrated the highest efficacy as a blocker. To further explore whether calcium channel proteins can serve as potential targets of pyrethroids, we compared the effects of (type I) tefluthrin and (type II) deltamethrin on CaCCs. 10 μM and 100 μM tefluthrin can stimulate a large tail current in CaCCs, prolonging their deactivation time by 10.44 ms and 31.49 ms, and the V0.5 shifted in the hyperpolarization by 2-8 mV. Then, deltamethrin had no obvious effect on the deactivation and activation of CaCCs. Therefore, CaCCs of H. armigera can be used as a potential target of pyrethroids, but type I and type II pyrethroids have different effects on CaCCs.

Anoctamin 1, a multi-modal player in pain and itch

Anoctamin 1 (ANO1/TMEM16A) encodes a Ca2+-activated Cl- channel. Among ANO1's many physiological functions, it plays a significant role in mediating nociception and itch. ANO1 is activated by intracellular Ca2+ and depolarization. Additionally, ANO1 is activated by heat above 44 °C, suggesting heat as another activation stimulus. ANO1 is highly expressed in nociceptors, indicating a role in nociception. Conditional Ano1 ablation in dorsal root ganglion (DRG) neurons results in a reduction in acute thermal pain, as well as thermal and mechanical allodynia or hyperalgesia evoked by inflammation or nerve injury. Pharmacological interventions also lead to a reduction in nocifensive behaviors. ANO1 is functionally linked to the bradykinin receptor and TRPV1. Bradykinin stimulates ANO1 via IP3-mediated Ca2+ release from intracellular stores, whereas TRPV1 stimulates ANO1 via a combination of Ca2+ influx and release. Nerve injury causes upregulation of ANO1 expression in DRG neurons, which is blocked by ANO1 antagonists. Due to its role in nociception, strong and specific ANO1 antagonists have been developed. ANO1 is also expressed in pruritoceptors, mediating Mas-related G protein-coupled receptors (Mrgprs)-dependent itch. The activation of ANO1 leads to chloride efflux and depolarization due to high intracellular chloride concentrations, causing pain and itch. Thus, ANO1 could be a potential target for the development of new drugs treating pain and itch.

Structural and theoretical basis for drug development targeting TMEM16A: Inhibition mechanism of tracheloside analogs

Ion channels play a crucial role in the electrophysiological activities of organisms. The calcium-activated chloride channel TMEM16A is involved in various physiological processes. Therefore, inhibitors of TMEM16A are used to treat diseases caused by TMEM16A dysfunction. However, the unclear inhibition mechanism hinders the progress of drug development. Based on our previous study, we found that the molecular structures of TMEM16A inhibitors tracheloside, matairesinoside and arctigenin are similar. In this study, we conducted a structure-based virtual screening of tracheloside analogs from the PubChem database. The six tracheloside analogs with the highest affinity to TMEM16A were selected, and their inhibitory effects were detected by fluorescence and electrophysiological experiments. Subsequently, the interaction between the tracheloside analogs and TMEM16A was investigated through molecular docking and site-directed mutagenesis. Based on the above results, the mechanism of inhibition of TMEM16A gated conformation by tracheloside analogs was proposed. These findings provide a structural and theoretical basis for drug development targeting TMEM16A.

The anion exchanger slc26a3 regulates colonic mucus expansion during steady state and in response to prostaglandin E2, while Cftr regulates de novo mucus release in response to carbamylcholine

The intestinal epithelium is covered by mucus that protects the tissue from the luminal content. Studies have shown that anion secretion via the cystic fibrosis conductance regulator (Cftr) regulates mucus formation in the small intestine. However, mechanisms regulating mucus formation in the colon are less understood. The aim of this study was to explore the role of anion transport in the regulation of mucus formation during steady state and in response to carbamylcholine (CCh) and prostaglandin E2 (PGE2). The broad-spectrum anion transport inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS), CftrdF508 (CF) mice, and the slc26a3 inhibitor SLC26A3-IN-2 were used to inhibit anion transport. In the distal colon, steady-state mucus expansion was reduced by SLC26A3-IN-2 and normal in CF mice. PGE2 stimulated mucus expansion without de novo mucus release in wild type (WT) and CF colon via slc26a3 sensitive mechanisms, while CCh induced de novo mucus secretion in WT but not in CF colon. However, when added simultaneously, CCh and PGE2 stimulated de novo mucus secretion in the CF colon via DIDS-sensitive pathways. A similar response was observed in CF ileum that responded to CCh and PGE2 with DIDS-sensitive de novo mucus secretion. In conclusion, this study suggests that slc26a3 regulates colonic mucus expansion, while Cftr regulates CCh-induced de novo mucus secretion from ileal and distal colon crypts. Furthermore, these findings demonstrate that in the absence of a functional Cftr channel, parallel stimulation with CCh and PGE2 activates additional anion transport processes that help release mucus from intestinal goblet cells.

Niclosamide potentiates TMEM16A and induces vasoconstriction

The TMEM16A calcium-activated chloride channel is a promising therapeutic target for various diseases. Niclosamide, an anthelmintic medication, has been considered a TMEM16A inhibitor for treating asthma and chronic obstructive pulmonary disease (COPD) but was recently found to possess broad-spectrum off-target effects. Here, we show that, under physiological Ca2+ (200-500 nM) and voltages, niclosamide acutely potentiates TMEM16A. Our computational and functional characterizations pinpoint a putative niclosamide binding site on the extracellular side of TMEM16A. Mutations in this site attenuate the potentiation. Moreover, niclosamide potentiates endogenous TMEM16A in vascular smooth muscle cells, triggers intracellular calcium increase, and constricts the murine mesenteric artery. Our findings advise caution when considering clinical applications of niclosamide as a TMEM16A inhibitor. The identification of the putative niclosamide binding site provides insights into the mechanism of TMEM16A pharmacological modulation and provides insights into developing specific TMEM16A modulators to treat human diseases.

Anoctamin pharmacology

TMEM16 proteins, also known as anoctamins, are a family of ten membrane proteins with various tissue expression and subcellular localization. TMEM16A (anoctamin 1) is a plasma membrane protein that acts as a calcium-activated chloride channel. It is expressed in many types of epithelial cells, smooth muscle cells and some neurons. In airway epithelial cells, TMEM16A expression is particularly enhanced by inflammatory stimuli that also promote goblet cell metaplasia and mucus hypersecretion. Therefore, pharmacological modulation of TMEM16A could be beneficial to improve mucociliary clearance in chronic obstructive respiratory diseases. However, the correct approach to modulate TMEM16A activity (activation or inhibition) is still debated. Pharmacological inhibitors of TMEM16A could also be useful as anti-hypertensive agents given the TMEM16A role in smooth muscle contraction. In contrast to TMEM16A, TMEM16F (anoctamin 6) behaves as a calcium-activated phospholipid scramblase, responsible for the externalization of phosphatidylserine on cell surface. Inhibitors of TMEM16F could be useful as anti-coagulants and anti-viral agents. The role of other anoctamins as therapeutic targets is still unclear since their physiological role is still to be defined.

The anoctamins: Structure and function

When activated by increase in intracellular Ca2+, anoctamins (TMEM16 proteins) operate as phospholipid scramblases and as ion channels. Anoctamin 1 (ANO1) is the Ca2+-activated epithelial anion-selective channel that is coexpressed together with the abundant scramblase ANO6 and additional intracellular anoctamins. In salivary and pancreatic glands, ANO1 is tightly packed in the apical membrane and secretes Cl-. Epithelia of airways and gut use cystic fibrosis transmembrane conductance regulator (CFTR) as an apical Cl- exit pathway while ANO1 supports Cl- secretion mainly by facilitating activation of luminal CFTR and basolateral K+ channels. Under healthy conditions ANO1 modulates intracellular Ca2+ signals by tethering the endoplasmic reticulum, and except of glands its direct secretory contribution as Cl- channel might be small, compared to CFTR. In the kidneys ANO1 supports proximal tubular acid secretion and protein reabsorption and probably helps to excrete HCO3-in the collecting duct epithelium. However, under pathological conditions as in polycystic kidney disease, ANO1 is strongly upregulated and may cause enhanced proliferation and cyst growth. Under pathological condition, ANO1 and ANO6 are upregulated and operate as secretory channel/phospholipid scramblases, partly by supporting Ca2+-dependent processes. Much less is known about the role of other epithelial anoctamins whose potential functions are discussed in this review.

The physiological roles of anoctamin2/TMEM16B and anoctamin1/TMEM16A in chemical senses

Chemical senses allow animals to detect and discriminate a vast array of molecules. The olfactory system is responsible of the detection of small volatile molecules, while water dissolved molecules are detected by taste buds in the oral cavity. Moreover, many animals respond to signaling molecules such as pheromones and other semiochemicals through the vomeronasal organ. The peripheral organs dedicated to chemical detection convert chemical signals into perceivable information through the employment of diverse receptor types and the activation of multiple ion channels. Two ion channels, TMEM16B, also known as anoctamin2 (ANO2) and TMEM16A, or anoctamin1 (ANO1), encoding for Ca2+-activated Cl¯ channels, have been recently described playing critical roles in various cell types. This review aims to discuss the main properties of TMEM16A and TMEM16B-mediated currents and their physiological roles in chemical senses. In olfactory sensory neurons, TMEM16B contributes to amplify the odorant response, to modulate firing, response kinetics and adaptation. TMEM16A and TMEM16B shape the pattern of action potentials in vomeronasal sensory neurons increasing the interspike interval. In type I taste bud cells, TMEM16A is activated during paracrine signaling mediated by ATP. This review aims to shed light on the regulation of diverse signaling mechanisms and neuronal excitability mediated by Ca-activated Cl¯ channels, hinting at potential new roles for TMEM16A and TMEM16B in the chemical senses.

Purinergic Signaling Drives Multiple Aspects of Rotavirus Pathophysiology

Rotavirus causes life-threatening diarrhea in children, resulting in ∼200,000 deaths/year. The current treatment during infection is Oral Rehydration Solution which successfully replenishes fluids but does not alleviate diarrhea volume or severity. As a result, there is an urgent need to better understand rotavirus pathophysiology and develop more effective pediatric therapeutics. Rotavirus primarily infects the tips of small intestinal villi, yet has far-reaching effects on cell types distant from infected cells. We recently identified that rotavirus infected cells release the purinergic signaling molecule ADP, which activates P2Y1 receptors on nearby uninfected cells in vitro . To elucidate the role of purinergic signaling via P2Y1 receptors during rotavirus infection in vivo , we used the mouse-like rotavirus strain D6/2 which generates a severe infection in mice. C57BL/6J mouse pups were given an oral gavage of D6/2 rotavirus and assessed over the course of 5-7 days. Beginning at day 1 post infection, infected pups were treated daily by oral gavage with saline or 4 mg/kg MRS2500, a selective P2Y1 antagonist. Mice were monitored for diarrhea severity, diarrhea incidence, and viral shedding. Neonatal mice were euthanized at days 3 and 5 post-infection and small intestine was collected to observe infection. MRS2500 treatment decreased the severity, prevalence, and incidence of rotavirus diarrhea. Viral stool shedding, assessed by qPCR for rotavirus gene levels, revealed that MRS2500 treated pups had significantly lower viral shedding starting at day 4 post infection compared to saline treated pups, which suggests P2Y1 signaling may enhance rotavirus replication. Finally, we found that inhibition of P2Y1 with MRS2500 limited transmitted rotavirus diarrhea to uninfected pups within a litter. Together, these results suggest that P2Y1 signaling is involved in the pathogenesis of a homologous murine rotavirus strain, making P2Y1 receptors a promising anti-diarrheal, anti-viral therapeutic target to reduce rotavirus disease burden.

Stress stimulation promotes the injury repair process of airway epithelial cells through the [Cl-]i-FAK signaling axis

The airway epithelium serves as a critical interface with the external environment, making it vulnerable to various external stimuli. Airway epithelial stress acts as a catalyst for the onset of numerous pulmonary and systemic diseases. Our previous studies have highlighted the impact of acute stress stimuli, especially bacterial lipopolysaccharide (LPS) and hydrogen peroxide (H2O2), on the continuous elevation of intracellular chloride concentration ([Cl-]i). However, the precise mechanism behind this [Cl-]i elevation and the consequential effects of such stress on the injury repair function of airway epithelial cells remain unclear. Our findings indicate that H2O2 induces an elevation in [Cl-]i by modulating the expression of CF transmembrane conductance regulator (CFTR) and Ca-activated transmembrane protein 16 A (TMEM16A) in airway epithelial cells (BEAS-2B), whereas LPS achieves this solely through CFTR. Subsequently, the elevated [Cl-]i level facilitated the injury repair process of airway epithelial cells by activating focal adhesion kinase (FAK). In summary, the [Cl-]i-FAK axis appears to play a promoting effect on the injury repair process triggered by stress stimulation. Furthermore, our findings suggest that abnormalities in the [Cl-]i-FAK signaling axis may play a crucial role in the pathogenesis of chronic airway diseases. Therefore, controlling the structure and function of airway epithelial barriers through the modulation of [Cl-]i holds promising prospects for future applications in managing and treating such conditions.

Loureirin C extracted from Dracaena cochinchinensis S.C. Chen prevents rotaviral diarrhea in mice by inhibiting the intestinal Ca2+-activated Cl- channels

ETHNOPHARMACOLOGICAL RELEVANCE

Resina Draconis (RD) is the red resin of Dracaena cochinchinensis (Lour.) S.C. Chen and most used as a hemostatic drug in traditional Chinese medicine. Recent studies have reported that RD has a therapeutic effect on gastrointestinal diseases. Loureirin A, B, and C (LA, LB, and LC) are dihydrochalcone compounds isolated from RD.

AIM OF THE STUDY

Dehydration is the primary cause of death in rotaviral diarrhea. Inhibition of Ca2+-activated Cl- channels (CaCCs)-mediated Cl- secretion significantly reduced fluid secretion in rotaviral diarrhea. RD was used to treat digestive diseases such as diarrhea and abdominal pain; however, the pharmacological mechanism remains unclear. This study investigated the effects of RD and loureirin on intestinal Cl- channels and their therapeutic effects on rotavirus-induced diarrhea, aiming to reveal RD's molecular basis, targets, and mechanisms for treating rotaviral diarrhea.

MATERIALS AND METHODS

Cell-based fluorescence quenching assays were used to examine the effect of RD and loureirin on Cl- channels activity. Electrophysiological properties were tested using short-circuit current experiments in epithelial cells or freshly isolated mouse intestinal tissue. Fecal water content, intestinal peristalsis rate, and smooth muscle contraction were measured in neonatal mice infected with SA-11 rotavirus before and after LC treatment or adult mice.

RESULTS

RD, LA, LB, and LC inhibited CaCCs-mediated Cl- current in HT-29 cells and colonic epithelium. The inhibitory effect of LC on CaCCs was primarily on the apical side in epithelial cells, which may be partially produced by affecting cytoplasmic Ca2+ levels. LC significantly inhibited TMEM16A-mediated Cl- current. Characterization studies revealed that LC inhibited basolateral K+ channel activity without affecting Na+/K+-ATPase activity in the colonic epithelium. Although LC activated the cystic fibrosis transmembrane regulator in epithelial cells, its effect was not apparent in colonic epithelium. In vivo, LC significantly reduced the fecal water content, intestinal peristalsis rate, and smooth muscle contraction of mice infected with rotavirus.

CONCLUSION

RD and its active compound LC inhibit intestinal CaCCs activity, which might mediate the anti-rotaviral diarrheal effect of RD.

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.

Structure and Function of Calcium-Activated Chloride Channels and Phospholipid Scramblases in the TMEM16 Family

The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated chloride channels and phospholipid scramblases. Ten mammalian TMEM16 proteins, TMEM16A-K (with no TMEM16I), and several non-mammalian TMEM16 proteins, such as afTMEM16 and nhTMEM16, have been discovered. All known TMEM16 proteins are homodimeric proteins containing two subunits. Each subunit consists of ten transmembrane helices with Ca2+-binding sites and a single ion-permeation/phospholipid transport pathway. The ion-permeation pathway and the phospholipid transport pathway of TMEM16 proteins have a wide intracellular vestibule, a narrow neck, and a smaller extracellular vestibule. Interestingly, the lining wall of the ion-permeation/phospholipid transport pathway may be formed, at least partially, by membrane phospholipids, though the degree of pore-wall forming by phospholipids likely varies among TMEM16 proteins. Thus, the biophysical properties and activation mechanisms of TMEM16 proteins could differ from each other accordingly. Here we review the current understanding of the structure and function of TMEM16 molecules.

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.

Inhibitory effect of daidzein on the calcium-activated chloride channel TMEM16A and its anti-lung adenocarcinoma activity

TMEM16A is highly expressed in a variety of tumor cells and is involved in the growth and metastasis of malignancies. It has been established that down-regulation of TMEM16A expression or functional activity can inhibit tumor cells growth. However, there is a lack of targeted inhibitors with high efficiency and low toxicity. Here, we identified a novel inhibitor daidzein from dozens of natural product molecules. Whole-cell patch clamp data indicated that daidzein inhibits TMEM16A channel in a dose-dependent manner, with IC50 of 1.39 ± 0.59 μM. Western blot result showed that daidzein can also reduce the expression of TMEM16A protein in LA795 cells. These results indicated that the inhibitory effects of daidzein exert on TMEM16A in two ways, both inhibiting TMEM16A current and decreasing its protein expression. In addition, the putative binding sites of daidzein on TMEM16A are G608, G628, and K839 through molecular docking. Moreover, daidzein concentration-dependently reduced cell viability and cell migration, causing G1/S cell cycle arrest in vitro. It was also confirmed that daidzein can effectively inhibit the growth of LA795 lung adenocarcinoma cells implanted nude mice in vivo. In conclusion, daidzein can be used as a lead compound for the development of therapeutic drugs for lung adenocarcinoma.

Anion efflux mediates transduction in the hair cells of the zebrafish lateral line

Hair cells are the principal sensory receptors of the vertebrate auditory system, where they transduce sounds through mechanically gated ion channels that permit cations to flow from the surrounding endolymph into the cells. The lateral line of zebrafish has served as a key model system for understanding hair cell physiology and development, often with the belief that these hair cells employ a similar transduction mechanism. In this study, we demonstrate that these hair cells are exposed to an unregulated external environment with cation concentrations that are too low to support transduction. Our results indicate that hair cell excitation is instead mediated by a substantially different mechanism involving the outward flow of anions. Further investigation of hair cell transduction in a diversity of sensory systems and species will likely yield deep insights into the physiology of these unique cells.

Discovery of Fungus-Derived Nornidulin as a Novel TMEM16A Inhibitor: A Potential Therapy to Inhibit Mucus Secretion in Asthma

Introduction

Inhibition of Ca2+-activated transmembrane protein 16A (TMEM16A) Cl- channels has been proposed to alleviate mucus secretion in asthma. In this study, we identified a novel class of TMEM16A inhibitors from natural sources in airway epithelial Calu-3 cells and determine anti-asthmatic efficacy of the most potent candidate in a mouse model of asthma.

Methods

For electrophysiological analyses, IL-4-primed Calu-3 cell monolayers were mounted in Ussing chamber and treated with various fungus-derived depsidones prior to the addition of UTP, ionomycin, thapsigargin, or Eact to stimulate TMEM16A Cl- current. Ca2+-induced mucus secretion in Calu-3 cell monolayers was assessed by determining MUC5AC protein remaining in the cells using immunofluorescence staining. OVA-induced female BALB/c mice was used as an animal model of asthma. After the course of induction, cellular and mucus components in bronchoalveolar lavage were analyzed. Lungs were fixed and undergone with H&E and PAS staining for the evaluation of airway inflammation and mucus production, respectively.

Results

The screening of fungus-derived depsidones revealed that nornidulin completely abolished the UTP-activated TMEM16A current in Calu-3 cell monolayers with the IC50 and a maximal effect being at ~0.8 µM and 10 µM, respectively. Neither cell viability nor barrier function was affected by nornidulin. Mechanistically, nornidulin (10 µM) suppressed Cl- currents induced by ionomycin (a Ca2+-specific ionophore), thapsigargin (an inhibitor of the endoplasmic reticulum Ca2+ ATPase), and Eact (a putative TMEM16A activator) without interfering with intracellular Ca2+ ([Ca2+]i) levels. These results suggest that nornidulin exerts its effect without changing [Ca2+]i, possibly through direct effect on TMEM16A. Interestingly, nornidulin (at 10 µM) reduced Ca2+-dependent mucus release in the Calu-3 cell monolayers. In addition, nornidulin (20 mg/kg) inhibited bronchoalveolar mucus secretion without impeding airway inflammation in ovalbumin-induced asthmatic mice.

Discussion and Conclusion

Our study revealed that nornidulin is a novel TMEM16A inhibitor that suppresses mucus secretion without compromising immunologic activity. Further development of nornidulin may provide a new remedy for asthma or other diseases associated with allergic mucus hypersecretion without causing opportunistic infections.

Anoctamin-1 is induced by TGF-beta 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-beta (TGF-β) is one of the most established drivers of fibrotic processes. TGF-β promotes 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 (HLF) at mRNA and protein levels. ANO1 is readily detected in fibrotic areas of IPF lungs in the same area with smooth muscle alpha-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 pro-fibrotic TGF-β signaling, including activation of RhoA pathway and AKT, without affecting initial Smad2 phosphorylation. Mechanistically, TGF-β treatment of HLF 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 (i) ANO1 is a TGF-β-inducible chloride channel that contributes to increased intracellular chloride concentration in response to TGF-β; and (ii) ANO1 mediates TGF-β-induced myofibroblast differentiation and fibrotic signaling in a manner dependent on WNK1 protein, but independent of WNK1 kinase activity.

ANO1, CaV1.2, and IP3R form a localized unit of EC-coupling in mouse pulmonary arterial smooth muscle

Pulmonary arterial (PA) smooth muscle cells (PASMC) generate vascular tone in response to agonists coupled to Gq-protein receptor signaling. Such agonists stimulate oscillating calcium waves, the frequency of which drives the strength of contraction. These Ca2+ events are modulated by a variety of ion channels including voltage-gated calcium channels (CaV1.2), the Tmem16a or Anoctamin-1 (ANO1)-encoded calcium-activated chloride (CaCC) channel, and Ca2+ release from the sarcoplasmic reticulum through inositol-trisphosphate receptors (IP3R). Although these calcium events have been characterized, it is unclear how these calcium oscillations underly a sustained contraction in these muscle cells. We used smooth muscle-specific ablation of ANO1 and pharmacological tools to establish the role of ANO1, CaV1.2, and IP3R in the contractile and intracellular Ca2+ signaling properties of mouse PA smooth muscle expressing the Ca2+ biosensor GCaMP3 or GCaMP6. Pharmacological block or genetic ablation of ANO1 or inhibition of CaV1.2 or IP3R, or Ca2+ store depletion equally inhibited 5-HT-induced tone and intracellular Ca2+ waves. Coimmunoprecipitation experiments showed that an anti-ANO1 antibody was able to pull down both CaV1.2 and IP3R. Confocal and superresolution nanomicroscopy showed that ANO1 coassembles with both CaV1.2 and IP3R at or near the plasma membrane of PASMC from wild-type mice. We conclude that the stable 5-HT-induced PA contraction results from the integration of stochastic and localized Ca2+ events supported by a microenvironment comprising ANO1, CaV1.2, and IP3R. In this model, ANO1 and CaV1.2 would indirectly support cyclical Ca2+ release events from IP3R and propagation of intracellular Ca2+ waves.

Zinc pyrithione induces endothelium-dependent hyperpolarization-mediated mesenteric vasorelaxation in healthy and colitic mice

BACKGROUND

Although Zinc pyrithione (ZPT) could lower blood pressure by inducing vasorelaxation, it is unclear if it is able to induce vasorelaxation of mesenteric arterioles in health and ulcerative colitis (UC) to exert anti-colitic action.

METHODS

The vasorelaxation of the second-order branch of the mesenteric artery from wide type (WT) mice, TRPV1-/-(KO) mice, and TRPV4-/-(KO) mice was determined using a Mulvany-style wire myograph. Calcium imaging and patch clamp were applied to analyze the actions of ZPT in human vascular endothelial cells. Mouse model of UC was used to evaluate the anti-colitic action of ZPT.

RESULTS

ZPT dose-dependently induced mesenteric vasorelaxation predominately through endothelium-dependent hyperpolarization (EDH), which could be attenuated by intracellular Zn2+ and Ca2+ chelators TPEN and BAPTA-AM. The ZPT/EDH-mediated vasorelaxation via TRPV1, TRPV4 and TRPA1 channels was verified by a combination of selective pharmacological inhibitors and TRPV1-KO and TRPV4-KO mice. Moreover. ZPT induced Ca2+ entry via vascular endothelial TRPV1/4 and TRPA1 channels and enhanced membrane non-selective currents through these channels. Notably, ZPT exerted anti-colitic effects by rescuing the impaired acetylcholine (ACh)-induced mesenteric vasorelaxation in colitic mice.

CONCLUSIONS

ZPT/Zn2+ induces EDH-mediated mesenteric vasorelaxation through activating endothelial multiple TRPV1/4 and TPPA1 channels in health, and rescues the impaired ACh-induced vasorelaxation to exert anti-colitic action. Our study may open a new avenue of potential vessel-specific targeted therapy for UC.

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.

Sesquiterpene lactones improve secretory diarrhea symptoms by inhibiting intestinal Ca2+-activated Cl- channel activities directly and indirectly

Secretory diarrhea caused by bacteria and viruses is usually accompanied by activation of the cystic fibrosis transmembrane conductance regulator (CFTR) and calcium-activated Cl- channels (CaCCs) in the intestinal epithelium. Inhibition of CFTR and CaCCs activities significantly reduces fluid losses and intestinal motility in diarrheal diseases. For this reason, CFTR and CaCCs are potential targets of therapeutic drug screening. Here, we reported that the sesquiterpene lactones, alantolactone (AL) and isoalantolactone (iAL), significantly inhibited ATP and Eact-induced short-circuit currents in T84, HT-29 and Fischer rat thyroid (FRT) cells expressing transmembrane protein 16A (TMEM16A) in a concentration-dependent manner. AL and iAL also inhibited the CaCC-mediated short-circuit currents induced by carbachol in the mouse colons. Both compounds inhibited forskolin-induced currents in T84 cells but did not significantly affect mouse colons. In vivo studies indicated that AL and iAL attenuated gastrointestinal motility and decreased watery diarrhea in rotavirus-infected neonatal mice. Preliminary mechanism studies showed that AL and iAL inhibited CaCCs at least partially by inhibiting Ca2+ release and basolateral membrane K+ channels activity. These findings suggest a new pharmacological activity of sesquiterpene lactone compounds that might lead to the development of treatments for rotaviral secretory diarrhea.

Niclosamide potentiates TMEM16A and induces vasoconstriction

The TMEM16A calcium-activated chloride channel is a promising therapeutic target for various diseases. Niclosamide, an anthelmintic medication, has been considered as a TMEM16A inhibitor for treating asthma and chronic obstructive pulmonary disease, but was recently found to possess broad-spectrum off-target effects. Here we show that, under physiological conditions, niclosamide acutely potentiates TMEM16A without having any inhibitory effect. Our computational and functional characterizations pinpoint a putative niclosamide binding site on the extracellular side of TMEM16A. Mutations in this site attenuate the potentiation. Moreover, niclosamide potentiates endogenous TMEM16A in vascular smooth muscle cells, triggers intracellular calcium increase, and constricts the murine mesenteric artery. Our findings advise caution when considering niclosamide as a TMEM16A inhibitor to treat diseases such as asthma, COPD, and hypertension. The identification of the putative niclosamide binding site provides insights into the mechanism of TMEM16A pharmacological modulation, shining light on developing specific TMEM16A modulators to treat human diseases.

Discovery of ANO1 Inhibitors based on Machine learning and molecule docking simulation approaches

Calcium-activated chloride channels (CaCCs) are chloride channels that are regulated according to intracellular calcium ion concentrations. The channel protein ANO1 is widely present in cells and is involved in physiological activities including cellular secretion, signaling, cell proliferation and vasoconstriction and diastole. In this study, the ANO1 inhibitors were investigated with machine learning and molecular simulation. Two-dimensional structure-activity relationship (2D-SAR) and three-dimensional quantitative structure-activity relationship (3D-QSAR) models were developed for the qualitative and quantitative prediction of ANO1 inhibitors. The results showed that the prediction accuracies of the model were 85.9% and 87.8% for the training and test sets, respectively, and 85.9% and 87.8% for the rotating forest (RF) in the 2D-SAR model. The CoMFA and CoMSIA methods were then used for 3D QSAR modeling of ANO1 inhibitors, respectively. The q² coefficients for model cross-validation were all greater than 0.5, implying that we were able to obtain a stable model for drug activity prediction. Molecular docking was further used to simulate the interactions between the five most promising compounds predicted by the model and the ANO1 protein. The total score for the docking results between all five compounds and the target protein was greater than 6, indicating that they interacted strongly in the form of hydrogen bonds. Finally, simulations of amino acid mutations around the docking cavity of the target proteins showed that each molecule had two or more sites of reduced affinity following a single mutation, indicating outstanding specificity of the screened drug molecules and their protein ligands.

The TMEM16A blockers benzbromarone and MONNA cause intracellular Ca2+-release in mouse bronchial smooth muscle cells

We investigated effects of TMEM16A blockers benzbromarone, MONNA, CaCC_inhA01 and Ani9 on isometric contractions in mouse bronchial rings and on intracellular calcium in isolated bronchial myocytes. Separate concentrations of carbachol (0.1-10 μM) were applied for 10 min periods to bronchial rings, producing concentration-dependent contractions that were well maintained throughout each application period. Benzbromarone (1 μM) markedly reduced the contractions with a more pronounced effect on their sustained component (at 10 min) compared to their initial component (at 2 min). Iberiotoxin (0.3 μM) enhanced the contractions, but they were still blocked by benzbromarone. MONNA (3 μM) and CaCC_inhA01 (10 μM) had similar effects to benzbromarone, but were less potent. In contrast, Ani9 (10 μM) had no effect on carbachol-induced contractions. Confocal imaging revealed that benzbromarone (0.3 μM), MONNA (1 μM) and CaCC_inhA01 (10 μM) increased intracellular calcium in isolated myocytes loaded with Fluo-4AM. In contrast, Ani9 (10 μM) had no effect on intracellular calcium. Benzbromarone and MONNA also increased calcium in calcium-free extracellular solution, but failed to do so when intracellular stores were discharged with caffeine (10 mM). Caffeine was unable to cause further discharge of the store when applied in the presence of benzbromarone. Ryanodine (100 μM) blocked the ability of benzbromarone (0.3 μM) to increase calcium, while tetracaine (100 μM) reversibly reduced the rise in calcium induced by benzbromarone. We conclude that benzbromarone and MONNA caused intracellular calcium release, probably by opening ryanodine receptors. Their ability to block carbachol contractions was likely due to this off-target effect.

Drug repurposing and molecular mechanisms of the antihypertensive drug candesartan as a TMEM16A channel inhibitor

TMEM16A, a Ca²⁺-activated chloride channel (CaCC), and its pharmacological inhibitors can inhibit the growth of lung adenocarcinoma cells. However,the poor efficacy, safety, and stability of TMEM16A inhibitors limit the development of these agents. Therefore, finding new therapeutic directions from already marketed drugs is a feasible strategy to obtain safe and effective therapeutic drugs. Here, we screened a library contain more than 2400 FDA, EMA, and NMPA-approved drugs through virtual screening. We identified a drug candidate, candesartan (CDST), which showed strong inhibitory effect on the TMEM16A in a concentration-dependent manner with an IC₅₀ of 24.40 ± 3.21 μM. In addition, CDST inhibited proliferation, migration and induced apoptosis of LA795 cells targeting TMEM16A, and significantly inhibited lung adenocarcinoma tumor growth in vivo. The molecular mechanism of CDST inhibiting TMEM16A channel indicated it bound to R515/R535/E623/E624 in the drug pocket, thereby blocked the pore. In conclusion, we identified a novel TMEM16A channel inhibitor, CDST, which exhibited excellent inhibitory activity against lung adenocarcinoma. Considering that CDST has been used in clinical treatment of hypertension, it may play an important role in the combined treatment of hypertension and lung adenocarcinoma as a multi-target drug in the future.

The role of Transmembrane Protein 16A (TMEM16A) in pulmonary hypertension

Transmembrane protein 16A (TMEM16A), a member of the TMEM16 family, is the molecular basis of Ca2+-activated chloride channels (CaCCs) and is involved in a variety of physiological and pathological processes. Previous studies have focused more on respiratory-related diseases and tumors. However, recent studies have identified an important role for TMEM16A in cardiovascular diseases, especially in pulmonary hypertension. TMEM16A is expressed in both pulmonary artery smooth muscle cells and pulmonary artery endothelial cells and is involved in the development of pulmonary hypertension. This paper presents the structure and function of TMEM16A, the pathogenesis of pulmonary hypertension, and highlights the role and mechanism of TMEM16A in pulmonary hypertension, summarizing the controversies in this field and taking into account hypertension and portal hypertension, which have similar pathogenesis. It is hoped that the unique role of TMEM16A in pulmonary hypertension will be illustrated and provide ideas for research in this area.

High level of ANO1 promotes pancreatic cancer growth in concert with oncogenic KRAS

BACKGROUND

Anoctamin-1 (ANO1) was identified as an unfavorable prognostic marker in pancreatic cancer. However, the exact implication of ANO1 in pancreatic cancer is still poorly understood. Here we investigated the effect of ANO1 in pancreatic cancer progression under the context of oncogenic KRAS, aiming at finding a new therapeutic target.

METHODS

Knockdown and overexpression of oncogenic KRAS as well as ANO1 in PDAC cell lines were performed by lentivirus infection. Cell proliferation and migration assay, RNA seq analysis were performed in PDAC cells bearing different status of ANO1 and KRAS. In vivo mice model was used to investigate the xenograft tumor growth with different status of KRAS and ANO1.

RESULTS

Our results showed that ANO1 expression level is elevated in poorly differentiated cancer cells. Overexpression of ANO1 in PDAC cancer cells was found to promote cancer cell proliferation in vitro and in vivo, which synergized with the introduction of oncogenic KRAS. Consistently, knockdown of ANO1 expression was found to suppress cancer growth in vitro and in vivo. RNA seq analysis revealed that the observed synergistic cancer-promoting effect from ANO1 and oncogenic KRAS is likely due to concurrent activating key genes involved in lipid metabolism including HMGCS1.

CONCLUSION

The outcome from our study suggests that ANO1 plays an important role in promoting pancreatic cancer development, especially at the presence of oncogenic KRAS. Considering the prevalence of KRAS mutation in pancreatic cancer patients, suppression ANO1 may represent a potential effective therapeutic measure in pancreatic cancer treatment.

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.

Niclosamide does not modulate airway epithelial function through blocking of the calcium activated chloride channel, TMEM16A

Niclosamide and benzbromarone have been described as inhibitors of the calcium activated chloride channel, TMEM16A, and on this basis have been considered and tested as clinical candidates for the treatment of airway diseases. However, both compounds have previously demonstrated activity on a range of additional biological targets and it is unclear from the literature to what extent any activity on TMEM16A may contribute to efficacy in these models of airway disease. The aim of the present study was therefore to examine the pharmacology and selectivity of these clinical candidates together with a structurally unrelated TMEM16A blocker, Ani9, in a range of functional assays to better appreciate the putative role of TMEM16A in the regulation of both epithelial ion transport and the development of an airway epithelial mucus secretory phenoptype. Benzbromarone and Ani9 both attenuated recombinant TMEM16A activity in patch clamp studies, whereas in contrast, niclosamide induced a paradoxical potentiation of the TMEM16A-mediated current. Niclosamide and benzbromarone were also demonstrated to attenuate receptor-dependent increases in intracellular Ca²⁺ levels ([Ca²⁺]_i) which likely contributed to their concomitant attenuation of the Ca²⁺-stimulated short-circuit current responses of FRT-TMEM16A and primary human bronchial epithelial (HBE) cells. In contrast, Ani9 attenuated the Ca²⁺-stimulated short-circuit current responses of both cell systems without influencing [Ca²⁺]_i which supports a true channel blocking mechanism for this compound. Additional studies using HBE cells revealed effects of both niclosamide and benzbromarone on global ion transport processes (absorptive and secretory) as well as signs of toxicity (elevated LDH levels, loss of transepithelial resistance) that were not shared by Ani9. Ani9 also failed to influence the IL-13 induced differentiation of HBE towards a goblet cell rich, mucus hypersecreting epithelium, whereas niclosamide and benzbromarone attenuated numbers of both goblet and multiciliated cells, that would be consistent with cellular toxicity. Together these data challenge the description of niclosamide as a TMEM16A blocker and illustrate a range of off-target effects of both niclosamide and benzbromarone which may contribute to the reported activity in models of airway function.

Molecular mechanism of ion channel protein TMEM16A regulated by natural product of narirutin for lung cancer adjuvant treatment

Cancer chemotherapy drugs are widely criticized for their serious side effects and low cure rate. Therefore, adjuvant therapy as a combination with chemotherapy administration is being accepted by many patients. However, unclear drug targets and mechanisms limit the application of adjuvant treatment. In this study, we confirmed TMEM16A is a key drug target for lung adenocarcinoma, and narirutin is an effective anti-lung adenocarcinoma natural product. Virtual screening and fluorescence experiments confirmed that narirutin inhibits the molecular target TMEM16A, which is specific high-expression in lung adenocarcinoma. Molecular dynamics simulations and electrophysiological experiments revealed the precise molecular mechanism of narirutin regulating TMEM16A. The anticancer effect of narirutin and its synergistic effect on cisplatin were explored by cell proliferation, migration, and apoptosis assays. The signaling pathways regulated by narirutin were analyzed by western blot. Tumor xenograft mice experiments demonstrated the synergistic anticancer effect of narirutin and cisplatin, and the side effects of high concentrations of cisplatin were almost eliminated. Pharmacokinetic experiments showed the biological safety of narirutin is satisfactory in vivo. Based on the significant anticancer effect and high biosafety, naringin has great potential as a functional food in the adjuvant treatment of lung cancer.

Translational potential of targeting Anoctamin-1-Encoded Calcium-Activated chloride channels in hypertension

Calcium-activated chloride channels (CaCC) provide a depolarizing stimulus to a variety of tissues through chloride efflux in response to a rise in internal Ca²⁺ and voltage. One of these channels, Anoctamin-1 (ANO1 or TMEM16A) is now recognized to play a central role in promoting smooth muscle tone in various types of blood vessels. Its role in hypertension, and thus the therapeutic promise of targeting ANO1, is less straightforward. This review gives an overview of our current knowledge about the potential role ANO1 may play in hypertension within the systemic, portal, and pulmonary vascular systems and the importance of this information when pursuing potential treatment strategies. While the role of ANO1 is well-established in several forms of pulmonary hypertension, its contributions to both the generation of vascular tone and its role in hypertension within the systemic and portal systems are much less clear. This, combined with ANO1's various roles throughout a multitude of tissues throughout the body, command caution when targeting ANO1 as a therapeutic target and may require tissue-selective strategies.

Molecular logic of salt taste reception in special reference to transmembrane channel-like 4 (TMC4)

The taste is biologically of intrinsic importance. It almost momentarily perceives environmental stimuli for better survival. In the early 2000s, research into taste reception was greatly developed with discovery of the receptors. However, the mechanism of salt taste reception is not fully elucidated yet and many questions still remain. At present, next-generation sequencing and genome-editing technologies are available which would become pivotal tools to elucidate the remaining issues. Here we review current mechanisms of salt taste reception in particular and characterize the properties of transmembrane channel-like 4 as a novel salt taste-related molecule that we found using these sophisticated tools.

Arctigenin Attenuates Vascular Inflammation Induced by High Salt through TMEM16A/ESM1/VCAM-1 Pathway

Salt-sensitive hypertension is closely related to inflammation, but the mechanism is barely known. Transmembrane member 16A (TMEM16A) is the Ca2+-activated chloride channel in epithelial cells, smooth muscle cells, and sensory neurons. It can promote inflammatory responses by increasing proinflammatory cytokine release. Here, we identified a positive role of TMEM16A in vascular inflammation. The expression of TMEM16A was increased in high-salt-stimulated vascular smooth muscle cells (VSMCs), whereas inhibiting TMEM16A or silencing TMEM16A with small interfering RNA (siRNA) can abolish this effect in vitro or in vivo. Transcriptome analysis of VSMCs revealed some differential downstream genes of TMEM16A related to inflammation, such as endothelial cell-specific molecule 1 (ESM1) and CXC chemokine ligand 16 (CXCL16). Overexpression of TMEM16A in VSMCs was accompanied by high levels of ESM1, CXCL16, intercellular adhesion molecule-1 (ICAM-1), and vascular adhesion molecule-1 (VCAM-1). We treated VSMCs cultured with high salt and arctigenin (ARC), T16Ainh-A01 (T16), and TMEM16A siRNA (siTMEM16A), leading to greatly decreased ESM1, CXCL16, VCAM-1, and ICAM-1. Beyond that, silencing ESM1, the expression of VCAM-1 and ICAM-1, and CXCL16 was attenuated. In conclusion, our results outlined a signaling scheme that increased TMEM16 protein upregulated ESM1, which possibly activated the CXCL16 pathway and increased VCAM-1 and ICAM-1 expression, which drives VSMC inflammation. Beyond that, arctigenin, as a natural inhibitor of TMEM16A, can reduce the systolic blood pressure (SBP) of salt-sensitive hypertension mice and alleviate vascular inflammation.

Functional evaluation of the cystic fibrosis transmembrane conductance regulator in the endocervix†

The cystic fibrosis transmembrane conductance regulator (CFTR) is an apical membrane chloride/bicarbonate ion channel in epithelial cells. Mutations in CFTR cause cystic fibrosis, a disease characterized by thickened mucus secretions and is associated with subfertility and infertility. CFTR function has been well characterized in vitro and in vivo in airway and other epithelia studies. However, little is known about CFTR function in the cervix in health and its contribution to cyclic regulation of fertility from endocervical mucus changes. Contributing to this research gap is the lack of information on the effect of sex steroid hormones on CFTR expression in cervical epithelial cells across the menstrual cycle. Herein, we demonstrate the hormonal regulation of CFTR expression in endocervical cells both in vitro and in vivo, and that conditionally reprogrammed endocervical epithelial cells can be used to interrogate CFTR ion channel function. CFTR activity was demonstrated in vitro using electrophysiological methods and functionally inhibited by the CFTR-specific inhibitors inh-172 and GlyH-101. We also report that CFTR expression is increased by estradiol in the macaque cervix both in vitro and in vivo in Rhesus macaques treated with artificial menstrual cycles. Estrogen upregulation of CFTR is blocked in vivo by cotreatment with progesterone. Our findings provide the most comprehensive evidence to date that steroid hormones drive changes in CFTR expression. These data are integral to understanding the role of CFTR as a fertility regulator in the endocervix.

Multi-target tracheloside and doxorubicin combined treatment of lung adenocarcinoma

Chemotherapy is one of the main methods for malignant lung cancer treatment. However, the side effects of chemotherapy drugs are serious and it is prone to drug resistance. Therefore, multi-drug combination chemotherapy is popular in lung cancer treatment. This study found that tracheloside (TCS) was a novel inhibitor of TMEM16A which was specific high expressed in lung cancer tissues. TCS concentration dependently inhibited TMEM16A with an IC₅₀ of 3.09 ± 0.21 μM. It inhibited lung cancer cells proliferation, migration, and induced cells apoptosis targeting TMEM16A. In addition, molecular docking combined with site-directed mutagenesis confirmed that the binding sites of TCS to TMEM16A were S387, E623, E624. Subsequently, multi-target combined drug administration was conducted based on the different drug targets of TCS and doxorubicin (DOX). Both in vitro and in vivo experiments indicated that the combined administration of low concentration of TCS and DOX achieved satisfactory anticancer effect, and it offset the side effects caused by high concentration of DOX. Therefore, TCS is a safe and efficient anticancer lead compound which can enhance the effect of DOX.

TMEM16A Plays an Insignificant Role in Myocardium Remodeling but May Promote Angiogenesis of Heart During Pressure-overload

Background: Cardiac hypertrophy (CH) occurs with an increase in myocardium mass as an adaptive compensation to increased stress. Prolonged CH causes decompensated heart failure (HF). Enhanced angiogenesis by vascular endothelial growth factor (VEGF) is observed in hypertrophied hearts; impaired angiogenesis by angiotensin II (AngII) is observed in failing hearts. Angiogenesis is executed by vascular endothelial cells (ECs). Abnormal Ca²⁺ homeostasis is a hallmark feature of hypertrophied and failing hearts. Ca²⁺-activated chloride channel transmembrane protein 16A (TMEM16A) is expressed in cardiomyocytes and ECs but its role in heart under stress remains unknown.

Methods: Pressure-overload-induced CH and HF mouse models were established. Echocardiography was performed to evaluate cardiac parameters. Quantitative real-time PCR, traditional and simple western assays were used to quantify molecular expression. Whole-cell patch-clamp experiments were used to detect TMEM16A current (I_TMEM16A) and action potential duration (APD) of cardiomyocytes. VEGF and AngII were used separately in ECs culture to simulate enhanced or impaired angiogenesis, respectively. TMEM16A low-expressed and over-expressed ECs were obtained by siRNA or lentivirus transfection. Wound healing, tube formation and ECs spheroids sprouting assays were performed to assess migration and angiogenesis.

Results: Neither TMEM16A molecular expression levels nor whole-cell I_TMEM16A density varied significantly during the development of CH and HF. I_TMEM16A comprises transient outward current, but doesn’t account for APD prolongation in hypertrophied or failing cardiomyocytes. In cultured ECs, TMEM16A knockdown inhibited migration and angiogenesis, TMEM16A overexpression showed opposite result. Promotion of migration and angiogenesis by VEGF was decreased in TMEM16A low-expressed ECs but was increased in TMEM16A over-expressed ECs. Inhibition of migration and angiogenesis by AngII was enhanced in TMEM16A low-expressed ECs but was attenuated in TMEM16A over-expressed ECs.

Conclusion: TMEM16A contributes insignificantly in myocardium remodeling during pressure-overload. TMEM16A is a positive regulator of migration and angiogenesis under normal condition or simulated stress. TMEM16A may become a new target for upregulation of angiogenesis in ischemic disorders like ischemic heart disease.

TMEM16A blockers T16Ainh-A01 and benzbromarone do not modulate the regulation of sweating and cutaneous vasodilatation in humans in vivo

NEW FINDINGS

What is the central question of this study? Do transmembrane member 16A (TMEM16A) blockers modulate the activation of heat loss responses of sweating and cutaneous vasodilatation? What are the main finding and its importance? Relative to the vehicle control site, TMEM16A blockers T16Ainh-A01 and benzbromarone had no effect on sweat rate or cutaneous vascular conductance during whole-body heating inducing a 1.1 ± 0.1°C increase in core temperature above baseline resting levels. These results suggest that TMEM16A blockers T16Ainh-A01 and benzbromarone do not modulate the regulation of sweating and cutaneous vasodilatation during whole-body heat stress.

ABSTRACT

Animal and in vitro studies suggest that transmembrane member 16A (TMEM16A), a Ca²⁺ -activated Cl^- channel, contributes to regulating eccrine sweating. However, direct evidence supporting this possibility in humans is lacking. We assessed the hypothesis that TMEM16A blockers attenuate sweating during whole-body heating in humans. Additionally, we assessed the associated changes in the heat loss response of cutaneous vasodilatation to determine if a functional role of TMEM16A may exist. Twelve young (24 ± 2 years) adults (six females) underwent whole-body heating using a water-perfused suit to raise core temperature 1.1 ± 0.1°C above baseline. Sweat rate and cutaneous vascular conductance (normalized to maximal conductance via administration of sodium nitroprusside) were evaluated continuously at four forearm skin sites treated continuously by intradermal microdialysis with (1) lactated Ringer's solution (control), (2) 5% dimethyl sulfoxide (DMSO) serving as a vehicle control, or (3) TMEM16A blockers 1 mM T16Ainh-A01 or 2 mM benzbromarone dissolved in 5% DMSO solution. All drugs were administered continuously via intradermal microdialysis. Whole-body heating increased core temperature progressively and this was paralleled by an increase in sweat rate and cutaneous vascular conductance at all skin sites. However, sweat rate (all P > 0.318) and cutaneous vascular conductance (all P ≥ 0.073) did not differ between the vehicle control site relative to the TMEM16A blocker-treated sites. Collectively, our findings indicate that TMEM16A blockers T16Ainh-A01 and benzbromarone do not modulate the regulation of sweating and cutaneous vasodilatation during whole-body heating in young adults in vivo.

Inhibition mechanism of the chloride channel TMEM16A by the pore blocker 1PBC

TMEM16A, a calcium-activated chloride channel involved in multiple cellular processes, is a proposed target for diseases such as hypertension, asthma, and cystic fibrosis. Despite these therapeutic promises, its pharmacology remains poorly understood. Here, we present a cryo-EM structure of TMEM16A in complex with the channel blocker 1PBC and a detailed functional analysis of its inhibition mechanism. A pocket located external to the neck region of the hourglass-shaped pore is responsible for open-channel block by 1PBC and presumably also by its structural analogs. The binding of the blocker stabilizes an open-like conformation of the channel that involves a rearrangement of several pore helices. The expansion of the outer pore enhances blocker sensitivity and enables 1PBC to bind at a site within the transmembrane electric field. Our results define the mechanism of inhibition and gating and will facilitate the design of new, potent TMEM16A modulators.

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.

Intestinal secretory mechanisms and diarrhea

One of the primary functions of the intestinal epithelium is to transport fluid and electrolytes to and from the luminal contents. Under normal circumstances, absorptive and secretory processes are tightly regulated such that absorption predominates, thereby enabling conservation of the large volumes of water that pass through the intestine each day. However, in conditions of secretory diarrhea, this balance becomes dysregulated, so that fluid secretion, driven primarily by Cl- secretion, overwhelms absorptive capacity, leading to increased loss of water in the stool. Secretory diarrheas are common and include those induced by pathogenic bacteria and viruses, allergens, and disruptions to bile acid homeostasis, or as a side effect of many drugs. Here, we review the cellular and molecular mechanisms by which Cl- and fluid secretion in the intestine are regulated, how these mechanisms become dysregulated in conditions of secretory diarrhea, currently available and emerging therapeutic approaches, and how new strategies to exploit intestinal secretory mechanisms are successfully being used in the treatment of constipation.

Zafirlukast inhibits the growth of lung adenocarcinoma via inhibiting TMEM16A channel activity

Lung cancer has the highest mortality among cancers worldwide due to its high incidence and lack of the effective cures. We have previously demonstrated that the membrane ion channel TMEM16A is a potential drug target for the treatment of lung adenocarcinoma and have identified a pocket of inhibitor binding that provides the basis for screening promising new inhibitors. However, conventional drug discovery strategies are lengthy and costly, and the unpredictable side effects lead to a high failure rate in drug development. Therefore, finding new therapeutic directions for already marketed drugs may be a feasible strategy to obtain safe and effective therapeutic drugs. Here, we screened a library of over 1400 Food and Drug Administration-approved drugs through virtual screening and activity testing. We identified a drug candidate, Zafirlukast (ZAF), clinically approved for the treatment of asthma, that could inhibit the TMEM16A channel in a concentration-dependent manner. Molecular dynamics simulations and site-directed mutagenesis experiments showed that ZAF can bind to S387/N533/R535 in the nonselective inhibitor binding pocket, thereby blocking the channel pore. Furthermore, we demonstrate ZAF can target TMEM16A channel to inhibit the proliferation and migration of lung adenocarcinoma LA795 cells. In vivo experiments showed that ZAF can significantly inhibit lung adenocarcinoma tumor growth in mice. Taken together, we identified ZAF as a novel TMEM16A channel inhibitor with excellent anticancer activity, and as such, it represents a promising candidate for future preclinical and clinical studies.

Mechanical Stress Modulates Calcium-Activated-Chloride Currents in Differentiating Lens Cells

During accommodation, the lens changes focus by altering its shape following contraction and relaxation of the ciliary muscle. At the cellular level, these changes in shape may be accompanied by fluid flow in and out of individual lens cells. We tested the hypothesis that some of this flow might be directly modulated by pressure-activated channels. In particular, we used the whole cell patch clamp technique to test whether calcium-activated-chloride channels (CaCCs) expressed in differentiating lens cells are activated by mechanical stimulation. Our results show that mechanical stress, produced by focally perfusing the lens cell at a constant rate, caused a significant increase in a chloride current that could be fully reversed by stopping perfusion. The time course of activation and recovery from activation of the flow-induced current occurred rapidly over a time frame similar to that of accommodation. The flow-induced current could be inhibited by the TMEM16A specific CaCC blocker, Ani9, suggesting that the affected current was predominantly due to TMEM16A chloride channels. The mechanism of action of mechanical stress did not appear to involve calcium influx through other mechanosensitive ion channels since removal of calcium from the bath solution failed to block the flow-induced chloride current. In conclusion, our results suggest that CaCCs in the lens can be rapidly and reversibly modulated by mechanical stress, consistent with their participation in regulation of volume in this organ.

Enterotoxigenic Escherichia coli Heat-Stable Toxin and Ebola Virus Delta Peptide: Similarities and Differences

Enterotoxigenic Escherichia coli (ETEC) STb toxin exhibits striking structural similarity to Ebola virus (EBOV) delta peptide. Both ETEC and EBOV delta peptide are enterotoxins. Comparison of the structural and functional similarities and differences of these two toxins illuminates features that are important in induction of pathogenesis by a bacterial and viral pathogen.

Positive modulation of the TMEM16B mediated currents by TRPV4 antagonist

Calcium-activated chloride channels (CaCCs) play important roles in many physiological processes and their malfunction is implicated in diverse pathologies such as cancer, asthma, and hypertension. TMEM16A and TMEM16B proteins are the structural components of the CaCCs. Recent studies in cell cultures and animal models have demonstrated that pharmacological inhibition of CaCCs could be helpful in the treatment of some diseases, however, there are few specific modulators of these channels. CaCCs and Transient Receptor Potential Vanilloid-4 (TRPV4) channels are co-expressed in some tissues where they functionally interact. TRPV4 is activated by different stimuli and forms a calcium permeable channel that is activated by GSK1016790A and antagonized by GSK2193874. Here we report that GSK2193874 enhances the chloride currents mediated by TMEM16B expressed in HEK cells at nanomolar concentrations and that GSK1016790A enhances native CaCCs of Xenopus oocytes. Thus, these compounds may be used as a tool for the study of CaCCs, TRPV4 and their interactions.

Chloride transport modulators as drug candidates

Chloride transport across cell membranes is broadly involved in epithelial fluid transport, cell volume and pH regulation, muscle contraction, membrane excitability, and organellar acidification. The human genome encodes at least 53 chloride-transporting proteins with expression in cell plasma or intracellular membranes, which include chloride channels, exchangers, and cotransporters, some having broad anion specificity. Loss-of-function mutations in chloride transporters cause a wide variety of human diseases, including cystic fibrosis, secretory diarrhea, kidney stones, salt-wasting nephropathy, myotonia, osteopetrosis, hearing loss, and goiter. Although impactful advances have been made in the past decade in drug treatment of cystic fibrosis using small molecule modulators of the defective cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel, other chloride channels and solute carrier proteins (SLCs) represent relatively underexplored target classes for drug discovery. New opportunities have emerged for the development of chloride transport modulators as potential therapeutics for secretory diarrheas, constipation, dry eye disorders, kidney stones, polycystic kidney disease, hypertension, and osteoporosis. Approaches to chloride transport-targeted drug discovery are reviewed herein, with focus on chloride channel and exchanger classes in which recent preclinical advances have been made in the identification of small molecule modulators and in proof of concept testing in experimental animal models.

Cinobufagin Exerts Anticancer Activity in Oral Squamous Cell Carcinoma Cells through Downregulation of ANO1

Anoctamin1 (ANO1), a calcium-activated chloride channel, is frequently overexpressed in several cancers, including oral squamous cell carcinoma (OSCC). OSCC is a highly aggressive cancer and the most common oral malignancy. ANO1 has been proposed as a potential candidate for targeted anticancer therapy. In this study, we performed a cell-based screening to identify novel regulators leading to the downregulation of ANO1, and discovered cinobufagin, which downregulated ANO1 expression in oral squamous cell carcinoma CAL-27 cells. ANO1 protein levels were significantly reduced by cinobufagin in a dose-dependent manner with an IC₅₀ value of ~26 nM. Unlike previous ANO1 inhibitors, short-term (≤10 min) exposure to cinobufagin did not alter ANO1 chloride channel activity and ANO1-dependent intestinal smooth muscle contraction, whereas long-term (24 h) exposure to cinobufagin significantly reduced phosphorylation of STAT3 and mRNA expression of ANO1 in CAL-27 cells. Notably, cinobufagin inhibited cell proliferation of CAL-27 cells expressing high levels of ANO1 more potently than that of ANO1 knockout CAL-27 cells. In addition, cinobufagin significantly reduced cell migration and induced caspase-3 activation and PARP cleavage in CAL-27 cells. These results suggest that downregulation of ANO1 by cinobufagin is a potential mechanism for the anticancer effect of cinobufagin in OSCC.

Evidence for tetrodotoxin-resistant spontaneous myogenic contractions of mouse isolated stomach that are dependent on acetylcholine

Background and Purpose

Gastric pacemaker cells, interstitial cells of Cajal (ICC), are believed to initiate myogenic (non‐neuronal) contractions. These become damaged in gastroparesis, associated with dysrhythmic electrical activity and nausea. We utilised mouse isolated stomach to model myogenic contractions and investigate their origin and actions of interstitial cells of Cajal modulators.

Experimental Approach

Intraluminal pressure was recorded following distension with a physiological volume; tone, contraction amplitude and frequency were quantified. Compounds were bath applied.

Key Results

The stomach exhibited regular large amplitude contractions (median amplitude 9.0 [4.7–14.8] cmH₂O, frequency 2.9 [2.5–3.4] c.p.m; n = 20), appearing to progress aborally. Tetrodotoxin (TTX, 10⁻⁶ M) had no effect on tone, frequency or amplitude but blocked responses to nerve stimulation. ω‐conotoxin GVIA (10⁻⁷ M) ± TTX was without effect on baseline motility. In the presence of TTX, (1) atropine (10⁻¹⁰–10⁻⁶ M) reduced contraction amplitude and frequency in a concentration‐related manner (pIC₅₀ 7.5 ± 0.3 M for amplitude), (2) CaCC channel (previously ANO1) inhibitors MONNA and CaCCinh‐A01 reduced contraction amplitude (significant at 10⁻⁵, 10⁻⁴ M respectively) and frequency (significant at 10⁻⁵ M), and (3), neostigmine (10⁻⁵ M) evoked a large, variable, increase in contraction amplitude, reduced by atropine (10⁻⁸–10⁻⁶ M) but unaffected (exploratory study) by the H1 receptor antagonist mepyramine (10⁻⁶ M).

Conclusions and Implications

The distended mouse stomach exhibited myogenic contractions, resistant to blockade of neural activity by TTX. In the presence of TTX, these contractions were prevented or reduced by compounds blocking interstitial cells of Cajal activity or by atropine and enhanced by neostigmine (antagonised by atropine), suggesting involvement of non‐neuronal ACh in their regulation.

Cepharanthine, a novel selective ANO1 inhibitor with potential for lung adenocarcinoma therapy

Anoctamin-1 (ANO1), also known as transmembrane protein 16A (TMEM16A), is identified as a Ca²⁺-activated Cl^- channel that is expressed in many organs and tissues. It is involved in numerous major physiological functions and especially in tumor growth. By screening 530 natural compounds, we identified cepharanthine as a potent blocker of ANO1 channels with an IC₅₀ of 11.2 ± 0.9 μM and E_max of 92.7 ± 1.7%. The Lys³⁸⁴, Arg⁵³⁵, Thr⁵³⁹, and Glu⁶²⁴ in ANO1 are critical for the inhibitory effect of cepharanthine. Similar to its effect on ANO1, cepharanthine inhibits ANO2, the closest analog of TMEM16A. In contrast, up to 30 μM of cepharanthine showed limited inhibitory effects on recombinant ANO6 and bestrophin-1-encoded Ca²⁺-activated Cl^- currents, but it showed no effects on endogenous volume-regulated anion currents (VRAC). Cepharanthine could also potently suppress endogenous ANO1 currents, significantly inhibit cell proliferation and migration, and induce apoptosis in LA795 lung adenocarcinoma cells. Moreover, animal experiments have shown that cepharanthine can dramatically inhibit the growth of xenograft tumors in mice. The high specificity provided by cepharanthine could be an important foundation for future studies of the physiological role of ANO1 channels, and these findings may reveal a new mechanism of its anticancer effect.