Cellular functions of TMEM16/anoctamin

ANO1: central role and clinical significance in non-neoplastic and neoplastic diseases

Anoctamin 1 (ANO1), also known as TMEM16A, is a multifunctional protein that serves as a calcium-activated chloride channel (CaCC). It is ubiquitously expressed across various tissues, including epithelial cells, smooth muscle cells, and neurons, where it is integral to physiological processes such as epithelial secretion, smooth muscle contraction, neural conduction, and cell proliferation and migration. Dysregulation of ANO1 has been linked to the pathogenesis of numerous diseases. Extensive research has established its involvement in non-neoplastic conditions such as asthma, hypertension, and gastrointestinal (GI) dysfunction. Moreover, ANO1 has garnered significant attention for its role in the development and progression of cancers, including head and neck cancer, breast cancer, and lung cancer, where its overexpression correlates with increased tumor growth, metastasis, and poor prognosis. Additionally, ANO1 regulates multiple signaling pathways, including the epidermal growth factor receptor (EGFR) pathway, the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway, and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway, among others. These pathways are pivotal in regulating cell proliferation, migration, and invasion. Given its central role in these processes, ANO1 has emerged as a promising diagnostic biomarker and therapeutic target. Recent advancements in ANO1 research have highlighted its potential in disease diagnosis and treatment. Strategies targeting ANO1, such as small molecule modulators or gene-silencing techniques, have shown preclinical promise in both non-neoplastic and neoplastic diseases. This review explores the latest findings in ANO1 research, focusing on its mechanistic involvement in disease progression, its regulation, and its therapeutic potential. Modulating ANO1 activity may offer novel therapeutic strategies for effectively treating ANO1-associated diseases.

Anoctamins mediate polymodal sensory perception and larval metamorphosis in a non-vertebrate chordate

The ocean represents a complex sensory environment, which acts as a crucible of evolution for polymodal sensory perception. The cellular and molecular bases of polymodal sensory perception in a marine environment remain enigmatic. Here, we use Ca2+ imaging and quantitative behavioral analysis to show that in the tunicate Ciona intestinalis, two members of the evolutionarily conserved anoctamin family (Tmem16E/Ano5 and Tmem16F/Ano6) are required for sensing chemosensory and mechanosensory metamorphic cues. We find that they modulate neuronal excitability and Ca2+ response kinetics in the primary sensory neurons and axial columnar cells of the papillae. Chemogenetic perturbations suggest that Ano5 and Ano6 act downstream of the primary sensory transducer molecules. Using pharmacology, we show that Ano5 and Ano6 cooperate with the inositol 1,4,5-trisphosphate (IP3) receptor and calcium release-activated channels (CRACs) to modulate tail regression. Our results establish Ano5 and Ano6 as players in the zooplanktonic molecular toolkit that controls polymodal sensory perception in aquatic environments.

Multiple cAMP/PKA complexes at the STIM1 ER/PM junction specified by E-Syt1 and E-Syt2 reciprocally gates ANO1 (TMEM16A) via Ca2

ANO1 plays a crucial role in determining numerous physiological functions, including epithelial secretion, yet its regulatory mechanisms remain incompletely understood. Here, we describe a fundamental dynamic regulation of ANO1 surface expression and Ca2+-dependent gating via the cAMP/PKA pathway at the STIM1 ER/PM junctions. At these junctions, STIM1 assembles AC-AKAP-PKA complexes, while E-Syt1 mediates formation of ANO1-VAPA-IRBIT-E-Syt1-AC8-AKAP5-PKA complex, that phosphorylates ANO1 S673, increasing ANO1 Ca2+ affinity. Within these complexes, the Ca2+ and cAMP pathways act synergistically to enhance ANO1 function. By contrast, E-Syt2 dissociates the ANO1-VAPA interaction, forming ANO1-IRBIT-E-Syt2-AC6-AKAP11-PKA complex that phosphorylates ANO1 S221, which markedly reduces ANO1 Ca2+ affinity. The effects of the E-Syts are primarily mediated by their reciprocal regulation of junctional PI(4)P, PI(4,5)P2 and PtdSer. Accordingly, IRBIT deletion in mice impairs receptor-stimulated activation of ANO1 and fluid secretion. These findings should have broad implications for ANO1 roles and functions across various tissues.

Anoctamin-1 is a core component of a mechanosensory anion channel complex in C. elegans

Mechanotransduction channels are widely expressed in both vertebrates and invertebrates, mediating various physiological processes such as touch, hearing and blood-pressure sensing. While previously known mechanotransduction channels in metazoans are primarily cation-selective, we identified Anoctamin-1 (ANOH-1), the C. elegans homolog of mammalian calcium-activated chloride channel ANO1/TMEM16A, as an essential component of a mechanosensory channel complex that contributes to the nose touch mechanosensation in C. elegans. Ectopic expression of either C. elegans or human Anoctamin-1 confers mechanosensitivity to touch-insensitive neurons, suggesting a cell-autonomous role of ANOH-1/ANO1 in mechanotransduction. Additionally, we demonstrated that the mechanosensory function of ANOH-1/ANO1 relies on CIB (calcium- and integrin- binding) proteins. Thus, our results reveal an evolutionarily conserved chloride channel involved in mechanosensory transduction in metazoans, highlighting the importance of anion channels in mechanosensory processes.

The Tmem16a chloride channel is required for mucin maturation after secretion from goblet-like cells in the Xenopus tropicalis tadpole skin

The TMEM16A chloride channel is proposed as a therapeutic target in cystic fibrosis, where activation of this ion channel might restore airway surface hydration and mitigate respiratory symptoms. While TMEM16A is associated with increased mucin production under stimulated or pro-inflammatory conditions, its role in baseline mucin production, secretion and/or maturation is less well understood. Here, we use the Xenopus tadpole skin mucociliary surface as a model of human upper airway epithelium to study Tmem16a function in mucus production. We found that Xenopus tropicalis Tmem16a is present at the apical membrane surface of tadpole skin small secretory cells that express canonical markers of mammalian "goblet cells" such as Foxa1 and spdef. X. tropicalis Tmem16a functions as a voltage-gated, calcium-activated chloride channel when transfected into mammalian cells in culture. Depletion of Tmem16a from the tadpole skin results in dysregulated mucin maturation post-secretion, with secreted mucins having a disrupted molecular size distribution and altered morphology assessed by sucrose gradient centrifugation and electron microscopy, respectively. Our results show that in the Xenopus tadpole skin, Tmem16a is necessary for normal mucus barrier formation and demonstrate the utility of this model system to discover new biology relevant to human mucosal biology in health and disease.

The ion channel Anoctamin 10/TMEM16K coordinates organ morphogenesis across scales in the urochordate notochord

During embryonic development, tissues and organs are gradually shaped into their functional morphologies through a series of spatiotemporally tightly orchestrated cell behaviors. A highly conserved organ shape across metazoans is the epithelial tube. Tube morphogenesis is a complex multistep process of carefully choreographed cell behaviors such as convergent extension, cell elongation, and lumen formation. The identity of the signaling molecules that coordinate these intricate morphogenetic steps remains elusive. The notochord is an essential tubular organ present in the embryonic midline region of all members of the chordate phylum. Here, using genome editing, pharmacology and quantitative imaging in the early chordate Ciona intestinalis we show that Ano10/Tmem16k, a member of the evolutionarily ancient family of transmembrane proteins called Anoctamin/TMEM16 is essential for convergent extension, lumen expansion, and connection during notochord morphogenesis. We find that Ano10/Tmem16k works in concert with the plasma membrane (PM) localized Na+/Ca2+ exchanger (NCX) and the endoplasmic reticulum (ER) residing SERCA, RyR, and IP3R proteins to establish developmental stage specific Ca2+ signaling molecular modules that regulate notochord morphogenesis and Ca2+ dynamics. In addition, we find that the highly conserved Ca2+ sensors calmodulin (CaM) and Ca2+/calmodulin-dependent protein kinase (CaMK) show an Ano10/Tmem16k-dependent subcellular localization. Their pharmacological inhibition leads to convergent extension, tubulogenesis defects, and deranged Ca2+ dynamics, suggesting that Ano10/Tmem16k is involved in both the "encoding" and "decoding" of developmental Ca2+ signals. Furthermore, Ano10/Tmem16k mediates cytoskeletal reorganization during notochord morphogenesis, likely by altering the localization of 2 important cytoskeletal regulators, the small GTPase Ras homolog family member A (RhoA) and the actin binding protein Cofilin. Finally, we use electrophysiological recordings and a scramblase assay in tissue culture to demonstrate that Ano10/Tmem16k likely acts as an ion channel but not as a phospholipid scramblase. Our results establish Ano10/Tmem16k as a novel player in the prevertebrate molecular toolkit that controls organ morphogenesis across scales.

WNK kinase, ion channels and arachidonic acid metabolites choreographically execute endothelium-dependent vasodilation

The smooth muscle-walled blood vessels control blood pressure. The vessel lumen is lined by an endothelial cell (ECs) layer, interconnected to the surrounding smooth muscle cells (SMCs) by myoendothelial gap junctions. Gap junctions also maintain homo-cellular ECs-ECs and SMCs-SMCs connections. This gap junction network nearly equalises both cells' membrane potential and cytosolic ionic composition, whether in resting or stimulated conditions. When acetylcholine (ACh) activates ECs M3 receptors, a complex signalling cascade involving second messengers and ion channels is triggered to induce vasodilation.

In or out of the groove? Mechanisms of lipid scrambling by TMEM16 proteins

Phospholipid scramblases mediate the rapid movement of lipids between membrane leaflets, a key step in establishing and maintaining membrane homeostasis of the membranes of all eukaryotic cells and their organelles. Thus, impairment of lipid scrambling can lead to a variety of pathologies. How scramblases catalyzed the transbilayer movement of lipids remains poorly understood. Despite the availability of direct structural information on three unrelated families of scramblases, the TMEM16s, the Xkrs, and ATG-9, a unifying mechanism has failed to emerge thus far. Among these, the most extensively studied and best understood are the Ca2+ activated TMEM16s, which comprise ion channels and/or scramblases. Early work supported the view that these proteins provided a hydrophilic, membrane-exposed groove through which the lipid headgroups could permeate. However, structural, and functional experiments have since challenged this mechanism, leading to the proposal that the TMEM16s distort and thin the membrane near the groove to facilitate lipid scrambling. Here, we review our understanding of the structural and mechanistic underpinnings of lipid scrambling by the TMEM16s and discuss how the different proposals account for the various experimental observations.

Insights into the function and regulation of the calcium-activated chloride channel TMEM16A

The TMEM16A channel, a member of the TMEM16 protein family comprising chloride (Cl-) channels and lipid scramblases, is activated by the free intracellular Ca2+ increments produced by inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release after GqPCRs or Ca2+ entry through cationic channels. It is a ubiquitous transmembrane protein that participates in multiple physiological functions essential to mammals' lives. TMEM16A structure contains two identical 10-segment monomers joined at their transmembrane segment 10. Each monomer harbours one independent hourglass-shaped pore gated by Ca2+ ligation to an orthosteric site adjacent to the pore and controlled by two gates. The orthosteric site is created by assembling negatively charged glutamate side chains near the pore´s cytosolic end. When empty, this site generates an electrostatic barrier that controls channel rectification. In addition, an isoleucine-triad forms a hydrophobic gate at the boundary of the cytosolic vestibule and the inner side of the neck. When the cytosolic Ca2+ rises, one or two Ca2+ ions bind to the orthosteric site in a voltage (V)-dependent manner, thus neutralising the electrostatic barrier and triggering an allosteric gating mechanism propagating via transmembrane segment 6 to the hydrophobic gate. These coordinated events lead to pore opening, allowing the Cl- flux to ensure the physiological response. The Ca2+-dependent function of TMEM16A is highly regulated. Anions with higher permeability than Cl- facilitate V dependence by increasing the Ca2+ sensitivity, intracellular protons can replace Ca2+ and induce channel opening, and phosphatidylinositol 4,5-bisphosphate bound to four cytosolic sites likely maintains Ca2+ sensitivity. Additional regulation is afforded by cytosolic proteins, most likely by phosphorylation and protein-protein interaction mechanisms.

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 role of anoctamin 1 in liver disease

Liver diseases include all types of viral hepatitis, alcoholic liver disease (ALD), nonalcoholic fatty liver disease (NAFLD), cirrhosis, liver failure (LF) and hepatocellular carcinoma (HCC). Liver disease is now one of the leading causes of disease and death worldwide, which compels us to better understand the mechanisms involved in the development of liver diseases. Anoctamin 1 (ANO1), a calcium-activated chloride channel (CaCC), plays an important role in epithelial cell secretion, proliferation and migration. ANO1 plays a key role in transcriptional regulation as well as in many signalling pathways. It is involved in the genesis, development, progression and/or metastasis of several tumours and other diseases including liver diseases. This paper reviews the role and molecular mechanisms of ANO1 in the development of various liver diseases, aiming to provide a reference for further research on the role of ANO1 in liver diseases and to contribute to the improvement of therapeutic strategies for liver diseases by regulating ANO1.

Lifting the veils on transmembrane proteins: Potential anticancer targets

Cancer, as a prevalent cause of mortality, poses a substantial global health burden and hinders efforts to enhance life expectancy. Nevertheless, the prognosis of patients with malignant tumors remains discouraging, owing to the lack of specific diagnostic and therapeutic targets. Therefore, the development of early diagnostic indicators and novel therapeutic drugs for the prevention and treatment of cancer is essential. Transmembrane proteins (TMEMs) are a class of proteins that can span the phospholipid bilayer and are stably anchored. They are associated with fibrotic diseases, neurodegenerative diseases, autoimmune diseases, developmental disorders, and cancer. It has been found that the expression levels of TMEMs were elevated or reduced in cancer cells, exerting pro/anticancer effects. These aberrant expression levels have also been linked to the prognostic and clinicopathological features of diverse tumors. In this review, the structures, functions, and roles of TMEMs in cancer were discussed, and the scientific perspectives were described. This review also explored the potential of TMEMs as tumor drug candidates from the perspective of targeted therapies, and the challenges that need to be overcome in a wide range of preclinical and clinical anticancer research were summarized.

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.

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.

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.

Researches of calcium-activated chloride channel ANO1 intervening amyotrophic lateral sclerosis progression by activating EGFR and CaMKII signaling

BACKGROUND

ANO1 is closely correlated with the activation of EGFR and CaMKII, while EGFR and CaMKII show low activation in amyotrophic lateral sclerosis (ALS) models. Therefore, we designed experiments to verify that ANO1 may play a protective role on motor neurons in ALS by activating EGFR and CaMKII.

METHODS

The expression changes of ANO1, EGFR, CaMKII, pEGFR, and pCaMKII, cell survival status, and apoptosis were studied by western blot, real-time quantitative PCR, immunofluorescence, immunohistochemistry, CCK-8, and flow cytometry. The role of ANO1 in the ALS model by activating EGFR and CaMKII was studied by applying corresponding activators, inhibitors, gene silencing, and overexpression.

RESULTS

In hSOD1G93A transgenic animals and cell lines, low expression of ANO1 and low activation of EGFR and CaMKII were identified. ANO1 expression decreased gradually with the progression of ALS. Overexpression of ANO1 in the hSOD1G93A cell line and primary neurons of hSOD1G93A transgenic mice increased cell viability and decreased cell apoptosis. After the application of ANO1 inhibitor CaCC-inhA01 in hSOD1G93A cell line and primary neurons of hSOD1G93A transgenic mice, EGFR activator EGF and CaMKII activator Carbachol, increased cell viability and reduced cell apoptosis. After ANO1 was overexpressed in the hSOD1G93A cell line and primary neurons of hSOD1G93A transgenic mice, EGFR inhibitor AEE788 and CaMKII inhibitor KN93 decreased cell viability and increased cell apoptosis.

CONCLUSIONS

Our results suggest that ANO1 plays an important role in the survival of ALS motor neurons. ANO1 can increase cell activity and reduce apoptosis by activating EGFR and CaMKII signals.

Identification of a druggable pocket of the calcium-activated chloride channel TMEM16A in its open state

The calcium-activated chloride channel TMEM16A is a potential drug target to treat hypertension, secretory diarrhea, and several cancers. However, all reported TMEM16A structures are either closed or desensitized, and direct inhibition of the open state by drug molecules lacks a reliable structural basis. Therefore, revealing the druggable pocket of TMEM16A exposed in the open state is important for understanding protein-ligand interactions and facilitating rational drug design. Here, we reconstructed the calcium-activated open conformation of TMEM16A using an enhanced sampling algorithm and segmental modeling. Furthermore, we identified an open state druggable pocket and screened a potent TMEM16A inhibitor, etoposide, which is a derivative of a traditional herbal monomer. Molecular simulations and site-directed mutagenesis showed that etoposide binds to the open state of TMEM16A, thereby blocking the ion conductance pore of the channel. Finally, we demonstrated that etoposide can target TMEM16A to inhibit the proliferation of prostate cancer PC-3 cells. Together, these findings provide a deep understanding of the TMEM16A open state at an atomic level and identify pockets for the design of novel inhibitors with broad applications in chloride channel biology, biophysics, and medicinal chemistry.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Analysis of inhibitors of the anoctamin-1 chloride channel (transmembrane member 16A, TMEM16A) reveals indirect mechanisms involving alterations in calcium signalling

BACKGROUND AND PURPOSE

Pharmacological inhibitors of TMEM16A (ANO1), a Ca²⁺ -activated Cl^- channel, are important tools of research and possible therapeutic agents acting on smooth muscle, airway epithelia and cancer cells. We tested a panel of TMEM16A inhibitors, including CaCC_inh -A01, niclosamide, MONNA, Ani9 and niflumic acid, to evaluate their possible effect on intracellular Ca²⁺ .

EXPERIMENTAL APPROACH

We recorded cytosolic Ca²⁺ increase elicited with UTP, ionomycin or IP₃ uncaging.

KEY RESULTS

Unexpectedly, we found that all compounds, except for Ani9, markedly decreased intracellular Ca²⁺ elevation induced by stimuli acting on intracellular Ca²⁺ stores. These effects were similarly observed in cells with and without TMEM16A expression. We investigated in more detail the mechanism of action of niclosamide and CaCC_inh -A01. Acute addition of niclosamide directly increased intracellular Ca²⁺ , an activity consistent with inhibition of the SERCA pump. In contrast to niclosamide, CaCC_inh -A01 did not elevate intracellular Ca²⁺ , thus implying a different mechanism of action, possibly a block of inositol triphosphate receptors.

CONCLUSIONS AND IMPLICATIONS

Most TMEM16A inhibitors are endowed with indirect effects mediated by alteration of intracellular Ca²⁺ handling, which may in part preclude their use as TMEM16A research tools.

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.

ANO4 Expression Is a Potential Prognostic Biomarker in Non-Metastasized Clear Cell Renal Cell Carcinoma

Background: Over the past decade, transcriptome profiling has elucidated many pivotal pathways involved in oncogenesis. However, a detailed comprehensive map of tumorigenesis remains an enigma to solve. Propelled research has been devoted to investigating the molecular drivers of clear cell renal cell carcinoma (ccRCC). To add another piece to the puzzle, we evaluated the role of anoctamin 4 (ANO4) expression as a potential prognostic biomarker in non-metastasized ccRCC. Methods: A total of 422 ccRCC patients with the corresponding ANO4 expression and clinicopathological data were obtained from The Cancer Genome Atlas Program (TCGA). Differential expression across several clinicopathological variables was performed. The Kaplan-Meier method was used to assess the impact of ANO4 expression on the overall survival (OS), progression-free interval (PFI), disease-free interval (DFI), and disease-specific survival (DSS). Univariate and multivariate Cox logistic regression analyses were conducted to identify independent factors modulating the aforementioned outcomes. Gene set enrichment analysis (GSEA) was used to discern a set of molecular mechanisms involved in the prognostic signature. Tumor immune microenvironment was estimated using xCell. Results: ANO4 expression was upregulated in tumor samples compared to normal kidney tissue. Albeit the latter finding, low ANO4 expression is associated with advanced clinicopathological variables such as tumor grade, stage, and pT. In addition, low ANO4 expression is linked to shorter OS, PFI, and DSS. Multivariate Cox logistic regression analysis identified ANO4 expression as an independent prognostic variable in OS (HR: 1.686, 95% CI: 1.120-2.540, p = 0.012), PFI (HR: 1.727, 95% CI: 1.103-2.704, p = 0.017), and DSS (HR: 2.688, 95% CI: 1.465-4.934, p = 0.001). GSEA identified the following pathways to be enriched within the low ANO4 expression group: epithelial-mesenchymal transition, G2-M checkpoint, E2F targets, estrogen response, apical junction, glycolysis, hypoxia, coagulation, KRAS, complement, p53, myogenesis, and TNF-α signaling via NF-κB pathways. ANO4 expression correlates significantly with monocyte (ρ = -0.1429, p = 0.0033) and mast cell (ρ = 0.1598, p = 0.001) infiltration. Conclusions: In the presented work, low ANO4 expression is portrayed as a potential poor prognostic factor in non-metastasized ccRCC. Further experimental studies should be directed to shed new light on the exact molecular mechanisms involved.

Pharmacological modulation of chloride channels as a therapeutic strategy for neurological disorders

Chloride homeostasis is critical in the physiological functions of the central nervous system (CNS). Its concentration is precisely regulated by multiple ion-transporting proteins such as chloride channels and transporters that are widely distributed in the brain cells, including neurons and glia. Unlike ion transporters, chloride channels provide rapid responses to efficiently regulate ion flux. Some of chloride channels are also permeable to selected organic anions such as glutamate and γ-aminobutyric acid, suggesting neuroexcitatory and neuroinhibitory functions while gating. Dysregulated chloride channels are implicated in neurological disorders, e.g., ischemia and neuroinflammation. Modulation of chloride homeostasis through chloride channels has been suggested as a potential therapeutic approach for neurological disorders. The drug design for CNS diseases is challenging because it requires the therapeutics to traverse the blood-brain-barrier. Small molecules are a well-established modality with better cell permeability due to their lower molecular weight and flexibility for structure optimization compared to biologics. In this article, we describe the important roles of chloride homeostasis in each type of brain cells and introduce selected chloride channels identified in the CNS. We then discuss the contribution of their dysregulations towards the pathogenesis of neurological disorders, emphasizing the potential of targeting chloride channels as a therapeutic strategy for CNS disease treatment. Along with this literature survey, we summarize the small molecules that modulate chloride channels and propose the potential strategy of optimizing existing drugs to brain-penetrants to support future CNS drug discovery.

Phosphatidylinositol 4,5-Bisphosphate and Cholesterol Regulators of the Calcium-Activated Chloride Channels TMEM16A and TMEM16B

Chloride fluxes through homo-dimeric calcium-activated channels TMEM16A and TMEM16B are critical to blood pressure, gastrointestinal motility, hormone, fluid and electrolyte secretion, pain sensation, sensory transduction, and neuronal and muscle excitability. Their gating depends on the voltage-dependent binding of two intracellular calcium ions to a high-affinity site formed by acidic residues from α-helices 6-8 in each monomer. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), a low-abundant lipid of the inner leaflet, supports TMEM16A function; it allows TMEM16A to evade the down-regulation induced by calcium, poly-L-lysine, or PI(4,5)P2 5-phosphatase. In stark contrast, adding or removing PI(4,5)P2 diminishes or increases TMEM16B function, respectively. PI(4,5)P2-binding sites on TMEM16A, and presumably on TMEM16B, are on the cytosolic side of α-helices 3-5, opposite the calcium-binding sites. This modular structure suggested that PI(4,5)P2 and calcium cooperate to maintain the conductive state in TMEM16A. Cholesterol, the second-largest constituent of the plasma membrane, also regulates TMEM16A though the mechanism, functional outcomes, binding site(s), and effects on TMEM16A and TMEM16B remain unknown.

Pharmacological potentiators of the calcium signaling cascade identified by high-throughput screening

Pharmacological modulators of the Ca²⁺ signaling cascade are important research tools and may translate into novel therapeutic strategies for a series of human diseases. We carried out a screening of a maximally diverse chemical library using the Ca²⁺-sensitive Cl^- channel TMEM16A as a functional readout. We found compounds that were able to potentiate UTP-dependent TMEM16A activation. Mechanism of action of these compounds was investigated by a panel of assays that looked at intracellular Ca²⁺ mobilization triggered by extracellular agonists or by caged-IP₃ photolysis, PIP₂ breakdown by phospholipase C, and ion channel activity on nuclear membrane. One compound appears as a selective potentiator of inositol triphosphate receptor type 1 (ITPR1) with a possible application for some forms of spinocerebellar ataxia. A second compound is instead a potentiator of the P2RY2 purinergic receptor, an activity that could promote fluid secretion in dry eye and chronic obstructive respiratory diseases.

Ion channels as a therapeutic target for renal fibrosis

Renal ion channel transport and electrolyte disturbances play an important role in the process of functional impairment and fibrosis in the kidney. It is well known that there are limited effective drugs for the treatment of renal fibrosis, and since a large number of ion channels are involved in the renal fibrosis process, understanding the mechanisms of ion channel transport and the complex network of signaling cascades between them is essential to identify potential therapeutic approaches to slow down renal fibrosis. This review summarizes the current work of ion channels in renal fibrosis. We pay close attention to the effect of cystic fibrosis transmembrane conductance regulator (CFTR), transmembrane Member 16A (TMEM16A) and other Cl− channel mediated signaling pathways and ion concentrations on fibrosis, as well as the various complex mechanisms for the action of Ca2+ handling channels including Ca2+-release-activated Ca2+ channel (CRAC), purinergic receptor, and transient receptor potential (TRP) channels. Furthermore, we also focus on the contribution of Na+ transport such as epithelial sodium channel (ENaC), Na+, K+-ATPase, Na+-H+ exchangers, and K+ channels like Ca2+-activated K+ channels, voltage-dependent K+ channel, ATP-sensitive K+ channels on renal fibrosis. Proposed potential therapeutic approaches through further dissection of these mechanisms may provide new therapeutic opportunities to reduce the burden of chronic kidney disease.

Evolutionary history of metazoan TMEM16 family

Most of Transmembrane protein 16 (TMEM16) proteins function as either a Ca²⁺-activated Cl^- channel (CaCC) or phospholipid scramblase (CaPLSase) and play diverse physiological roles. It is well conserved in eukaryotes; however, the origin and evolution of different subfamilies in Metazoa are not yet understood. To uncover the evolutionary history of the TMEM16 family, we analyzed 398 proteins from 74 invertebrate species using evolutionary genomics. We found that the TMEM16C-F and J subfamilies are vertebrate-specific, but the TMEM16A/B, G, H, and K subfamilies are ancient and present in many, but not all metazoan species. The most ancient subfamilies in Metazoa, TMEM16L and M, are only maintained in limited species. TMEM16N and O are Cnidaria- and Ecdysozoa-specific subfamilies, respectively, and Ctenophora, Xenacoelomorpha, and Rotifera contain species-specific proteins. We also identified TMEM16 genes that are closely linked together in the genome, suggesting that they have been generated via recent gene duplication. The anoctamin domain structures of invertebrate-specific TMEM16 proteins predicted by AlphaFold2 contain conserved Ca²⁺-binding motifs and permeation pathways with either narrow or wide inner gates. The inner gate distance of TMEM16 protein may have frequently switched during metazoan evolution, and thus determined the function of the protein as either CaCC or CaPLSase. These results demonstrate that TMEM16 family has evolved by gene gain and loss in metazoans, and the genes have been generally under purifying selection to maintain protein structures and physiological functions.

Pivotal roles for membrane phospholipids in axonal degeneration

Membrane phospholipids are critical components of several signaling pathways. Maintained in a variety of asymmetric distributions, their trafficking across the membrane can be induced by intra-, extra-, and intercellular events. A familiar example is the externalization of phosphatidylserine from the inner leaflet to the outer leaflet in apoptosis, inducing phagocytosis of the soma. Recently, it has been recognized that phospholipids in the axonal membrane may be a signal for axonal degeneration, regeneration, or other processes. This review focuses on key recent developments and areas for ongoing investigations. KEY FACTS: Phosphatidylserine externalization propagates along an axon after axonal injury and is delayed in the Wallerian degeneration slow (Wld^S) mutant. The ATP8A2 flippase mutant has spontaneous axonal degeneration. Microdomains of axonal degeneration in spheroid bodies have differential externalization of phosphatidylserine and phosphatidylethanolamine. Phospholipid trafficking could represent a mechanism for coordinated axonal degeneration and elimination, i.e. axoptosis, analogous to apoptosis of the cell body.

The pharmacology of the TMEM16A channel: therapeutic opportunities

The TMEM16A Ca²⁺-gated Cl^- channel is involved in a variety of vital physiological functions and may be targeted pharmacologically for therapeutic benefit in diseases such as hypertension, stroke, and cystic fibrosis (CF). The determination of the TMEM16A structure and high-throughput screening efforts, alongside ex vivo and in vivo animal studies and clinical investigations, are hastening our understanding of the physiology and pharmacology of this channel. Here, we offer a critical analysis of recent developments in TMEM16A pharmacology and reflect on the therapeutic opportunities provided by this target.

ANO1: More Than Just Calcium-Activated Chloride Channel in Cancer

ANO1, a calcium-activated chloride channel (CACC), is also known as transmembrane protein 16A (TMEM16A). It plays a vital role in the occurrence, development, metastasis, proliferation, and apoptosis of various malignant tumors. This article reviews the mechanism of ANO1 involved in the replication, proliferation, invasion and apoptosis of various malignant tumors. Various molecules and Stimuli control the expression of ANO1, and the regulatory mechanism of ANO1 is different in tumor cells. To explore the mechanism of ANO1 overexpression and activation of tumor cells by studying the different effects of ANO1. Current studies have shown that ANO1 expression is controlled by 11q13 gene amplification and may also exert cell-specific effects through its interconnected protein network, phosphorylation of different kinases, and signaling pathways. At the same time, ANO1 also resists tumor apoptosis and promotes tumor immune escape. ANO1 can be used as a promising biomarker for detecting certain malignant tumors. Further studies on the channels and the mechanism of protein activity of ANO1 are needed. Finally, the latest inhibitors of ANO1 are summarized, which provides the research direction for the tumor-promoting mechanism of ANO1.

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.

Anoctamin 1 controls bone resorption by coupling Cl- channel activation with RANKL-RANK signaling transduction

Osteoclast over-activation leads to bone loss and chloride homeostasis is fundamental importance for osteoclast function. The calcium-activated chloride channel Anoctamin 1 (also known as TMEM16A) is an important chloride channel involved in many physiological processes. However, its role in osteoclast remains unresolved. Here, we identified the existence of Anoctamin 1 in osteoclast and show that its expression positively correlates with osteoclast activity. Osteoclast-specific Anoctamin 1 knockout mice exhibit increased bone mass and decreased bone resorption. Mechanistically, Anoctamin 1 deletion increases intracellular Cl^- concentration, decreases H⁺ secretion and reduces bone resorption. Notably, Anoctamin 1 physically interacts with RANK and this interaction is dependent upon Anoctamin 1 channel activity, jointly promoting RANKL-induced downstream signaling pathways. Anoctamin 1 protein levels are substantially increased in osteoporosis patients and this closely correlates with osteoclast activity. Finally, Anoctamin 1 deletion significantly alleviates ovariectomy induced osteoporosis. These results collectively establish Anoctamin 1 as an essential regulator in osteoclast function and suggest a potential therapeutic target for osteoporosis.

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.

Purple Corn Extract Improves Benign Prostatic Hyperplasia by Regulating Prostate Cell Proliferation and Apoptosis

Purple corn (Zea mays L.), utilized as a natural pigment in food production and processing, has been used to treat obesity, cystitis, and urinary tract infections. However, no reports of its use for benign prostatic hyperplasia (BPH) exist. Purple corn extract (PCE) contains anthocyanins, particularly cyanidin-3-O-glucoside, which have various pharmacological characteristics. Therefore, this study sought to elucidate the ameliorative effect of PCE on BPH in dihydrotestosterone (DHT)-stimulated WPMY-1 cells and testosterone propionate (TP)-induced rats. Expression levels of the upregulated androgen receptor (AR) and its related genes in DHT-stimulated WPMY-1 cells were reduced by PCE, and proapoptotic gene expression increased by modulating the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling cascade. PCE reduced the weight of the enlarged prostate by inhibiting the androgen/AR signaling-related markers. Histological variations in the prostate epithelium caused by TP injection were restored by PCE. Thus, PCE alleviates BPH by modulating prostate cell proliferation and apoptosis.

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.

Introduction of a Cys360Tyr Mutation in ANO5 Creates a Mouse Model for Gnathodiaphyseal Dysplasia

Gnathodiaphyseal dysplasia (GDD) is a rare autosomal dominant genetic disease characterized by the osteosclerosis of tubular bones and the formation of cemento-osseous lesions in mandibles. Although genetic mutations for GDD have been identified in the ANO5/TMEM16E gene, the cellular and molecular mechanisms behind the pathogenesis of GDD remain unclear. Here, we generated the first knock-in mouse model for GDD with the expression of human mutation p.Cys360Tyr in ANO5. Homozygous Ano5 knock-in mice (Ano5^KI/KI ) replicated GDD-like skeletal features, including massive jawbones, bowing tibia, bone fragility, sclerosis, and cortical thickening of the femoral and tibial diaphysis. Serum alkaline phosphatase (ALP) levels were elevated in Ano5^KI/KI mice as in GDD patients with p.Cys360Tyr mutation. Calvaria-derived Ano5^KI/KI osteoblast cultures showed increased osteoblastogenesis, including hypermineralized bone matrix and enhanced bone formation-related factors expression. Interestingly, Ano5^KI/KI bone marrow-derived macrophage cultures showed decreased osteoclastogenesis, and Ano5^KI/KI osteoclasts exhibited disrupted actin ring formation, which may be associated with some signaling pathways. In conclusion, this new mouse model may facilitate elucidation of the pathogenesis of GDD and shed more light on its treatment. © 2021 American Society for Bone and Mineral Research (ASBMR).

Deciphering the Interactions of SARS-CoV-2 Proteins with Human Ion Channels Using Machine-Learning-Based Methods

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is accountable for the protracted COVID-19 pandemic. Its high transmission rate and pathogenicity led to health emergencies and economic crisis. Recent studies pertaining to the understanding of the molecular pathogenesis of SARS-CoV-2 infection exhibited the indispensable role of ion channels in viral infection inside the host. Moreover, machine learning (ML)-based algorithms are providing a higher accuracy for host-SARS-CoV-2 protein–protein interactions (PPIs). In this study, PPIs of SARS-CoV-2 proteins with human ion channels (HICs) were trained on the PPI-MetaGO algorithm. PPI networks (PPINs) and a signaling pathway map of HICs with SARS-CoV-2 proteins were generated. Additionally, various U.S. food and drug administration (FDA)-approved drugs interacting with the potential HICs were identified. The PPIs were predicted with 82.71% accuracy, 84.09% precision, 84.09% sensitivity, 0.89 AUC-ROC, 65.17% Matthews correlation coefficient score (MCC) and 84.09% F1 score. Several host pathways were found to be altered, including calcium signaling and taste transduction pathway. Potential HICs could serve as an initial set to the experimentalists for further validation. The study also reinforces the drug repurposing approach for the development of host directed antiviral drugs that may provide a better therapeutic management strategy for infection caused by SARS-CoV-2.

Scramblases as Regulators of Proteolytic ADAM Function

Proteolytic ectodomain release is a key mechanism for regulating the function of many cell surface proteins. The sheddases ADAM10 and ADAM17 are the best-characterized members of the family of transmembrane disintegrin-like metalloproteinase. Constitutive proteolytic activities are low but can be abruptly upregulated via inside-out signaling triggered by diverse activating events. Emerging evidence indicates that the plasma membrane itself must be assigned a dominant role in upregulation of sheddase function. Data are discussed that tentatively identify phospholipid scramblases as central players during these events. We propose that scramblase-dependent externalization of the negatively charged phospholipid phosphatidylserine (PS) plays an important role in the final activation step of ADAM10 and ADAM17. In this manuscript, we summarize the current knowledge on the interplay of cell membrane changes, PS exposure, and proteolytic activity of transmembrane proteases as well as the potential consequences in the context of immune response, infection, and cancer. The novel concept that scramblases regulate the action of ADAM-proteases may be extendable to other functional proteins that act at the cell surface.

Molecular dynamics simulation of TMEM16A channel: Linking structure with gating

TMEM16A, the calcium-activated chloride channel, is broadly expressed and plays pivotal roles in diverse physiological processes. To understand the structural and functional relationships of TMEM16A, it is necessary to fully clarify the structural basis of the gating of the TMEM16A channel. Herein, we performed the protein electrostatic analysis and molecular dynamics simulation on the TMEM16A in the presence and absence of Ca²⁺. Data showed that the separation of TM4 and TM6 causes pore expansion, and Q646 may be a key residue for the formation of π-helix in the middle segment of TM6. Moreover, E705 was found to form a group of H-bond interactions with D554/K588/K645 below the hydrophobic gate to stabilize the closed conformation of the pore in the Ca²⁺-free state. Interestingly, in the Ca²⁺ bound state, the E705 side chain swings 100^o to serve as Ca²⁺-binding coordination and released K645. K645 is closer to the hydrophobic gate in the calcium-bound state, which facilitates the provision of electrostatic forces for chloride ions as the ions pass through the hydrophobic gate. Our findings provide the structural-based insights to understanding the mechanisms of gating of TMEM16A.

Polymodal Control of TMEM16x Channels and Scramblases

The TMEM16A/anoctamin-1 calcium-activated chloride channel (CaCC) contributes to a range of vital functions, such as the control of vascular tone and epithelial ion transport. The channel is a founding member of a family of 10 proteins (TMEM16x) with varied functions; some members (i.e., TMEM16A and TMEM16B) serve as CaCCs, while others are lipid scramblases, combine channel and scramblase function, or perform additional cellular roles. TMEM16x proteins are typically activated by agonist-induced Ca2+ release evoked by Gq-protein-coupled receptor (GqPCR) activation; thus, TMEM16x proteins link Ca2+-signalling with cell electrical activity and/or lipid transport. Recent studies demonstrate that a range of other cellular factors—including plasmalemmal lipids, pH, hypoxia, ATP and auxiliary proteins—also control the activity of the TMEM16A channel and its paralogues, suggesting that the TMEM16x proteins are effectively polymodal sensors of cellular homeostasis. Here, we review the molecular pathophysiology, structural biology, and mechanisms of regulation of TMEM16x proteins by multiple cellular factors.

Reciprocal Relationship between Ca2+ Signaling and Ca2+-Gated Ion Channels as a Potential Target for Drug Discovery

Cellular Ca²⁺ signaling functions as one of the most common second messengers of various signal transduction pathways in cells and mediates a number of physiological roles in a cell-type dependent manner. Ca²⁺ signaling also regulates more general and fundamental cellular activities, including cell proliferation and apoptosis. Among ion channels, Ca²⁺-permeable channels in the plasma membrane as well as endo- and sarcoplasmic reticulum membranes play important roles in Ca²⁺ signaling by directly contributing to the influx of Ca²⁺ from extracellular spaces or its release from storage sites, respectively. Furthermore, Ca²⁺-gated ion channels in the plasma membrane often crosstalk reciprocally with Ca²⁺ signals and are central to the regulation of cellular functions. This review focuses on the physiological and pharmacological impact of i) Ca²⁺-gated ion channels as an apparatus for the conversion of cellular Ca²⁺ signals to intercellularly propagative electrical signals and ii) the opposite feedback regulation of Ca²⁺ signaling by Ca²⁺-gated ion channel activities in excitable and non-excitable cells.

BVES is a novel interactor of ANO5 and regulates myoblast differentiation

BACKGROUND

Anoctamin 5 (ANO5) is a membrane protein belonging to the TMEM16/Anoctamin family and its deficiency leads to the development of limb girdle muscular dystrophy R12 (LGMDR12). However, little has been known about the interactome of ANO5 and its cellular functions.

RESULTS

In this study, we exploited a proximal labeling approach to identify the interacting proteins of ANO5 in C2C12 myoblasts stably expressing ANO5 tagged with BioID2. Mass spectrometry identified 41 unique proteins including BVES and POPDC3 specifically from ANO5-BioID2 samples, but not from BioID2 fused with ANO6 or MG53. The interaction between ANO5 and BVES was further confirmed by co-immunoprecipitation (Co-IP), and the N-terminus of ANO5 mediated the interaction with the C-terminus of BVES. ANO5 and BVES were co-localized in muscle cells and enriched at the endoplasmic reticulum (ER) membrane. Genome editing-mediated ANO5 or BVES disruption significantly suppressed C2C12 myoblast differentiation with little impact on proliferation.

CONCLUSIONS

Taken together, these data suggest that BVES is a novel interacting protein of ANO5, involved in regulation of muscle differentiation.

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.

Gating and Regulatory Mechanisms of TMEM16 Ion Channels and Scramblases

The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated ion channels and Ca2+-activated phospholipid scramblases (CaPLSases) that passively flip-flop phospholipids between the two leaflets of the membrane bilayer. Owing to their diverse functions, TMEM16 proteins have been implicated in various human diseases, including asthma, cancer, bleeding disorders, muscular dystrophy, arthritis, epilepsy, dystonia, ataxia, and viral infection. To understand TMEM16 proteins in health and disease, it is critical to decipher their molecular mechanisms of activation gating and regulation. Structural, biophysical, and computational characterizations over the past decade have greatly advanced the molecular understanding of TMEM16 proteins. In this review, we summarize major structural features of the TMEM16 proteins with a focus on regulatory mechanisms and gating.

TMEM16A protein: calcium binding site and its activation mechanism

TMEM16A mediates calcium-activated transmembrane flow of chloride ion and a variety of physiological functions. The binding of cytoplasmic calcium ions of TMEM16A and the consequent conformational changes of it are the key issues to explore the relationship between its structure and function. In recent years, researchers have explored this issue through electrophysiological experiment, structure resolving, molecular dynamic simulation and other methods. The structures of TMEM16 family members resolved by cryo-Electron microscopy (cryo-EM) and X-ray crystallization provide the primarily basis for the investigation of the molecular mechanism of TMEM16A. However, the binding and activation mechanism of calcium ions in TMEM16A are still unclear and controversial. This review discusses four Ca2+ sensing sites of TMEM16A and analyze activation properties of TMEM16A by them, which will help to understand the structure-function relationship of TMEM16A and throw light on the molecular design targeting TMEM16A channel.

TMEM16A, a Homoharringtonine Receptor, as a Potential Endogenic Target for Lung Cancer Treatment

Lung cancer has the highest rate of incidence and mortality among all cancers. Most chemotherapeutic drugs used to treat lung cancer cause serious side effects and are susceptible to drug resistance. Therefore, exploring novel therapeutic targets for lung cancer is important. In this study, we evaluated the potential of TMEM16A as a drug target for lung cancer. Homoharringtonine (HHT) was identified as a novel natural product inhibitor of TMEM16A. Patch-clamp experiments showed that HHT inhibited TMEM16A activity in a concentration-dependent manner. HHT significantly inhibited the proliferation and migration of lung cancer cells with high TMEM16A expression but did not affect the growth of normal lung cells in the absence of TMEM16A expression. In vivo experiments showed that HHT inhibited the growth of lung tumors in mice and did not reduce their body weight. Finally, the molecular mechanism through which HHT inhibits lung cancer was explored by western blotting. The findings showed that HHT has the potential to regulate TMEM16A activity both in vitro and in vivo and could be a new lead compound for the development of anti-lung-cancer drugs.

The diverse roles of TMEM16A Ca2+-activated Cl- channels in inflammation

Background

Transmembrane protein 16A (TMEM16A) Ca²⁺-activated Cl^- channels have diverse physiological functions, such as epithelial secretion of Cl^- and fluid and sensation of pain. Recent studies have demonstrated that TMEM16A contributes to the pathogenesis of infectious and non-infectious inflammatory diseases. However, the role of TMEM16A in inflammation has not been clearly elucidated.

Aim of review

In this review, we aimed to provide comprehensive information regarding the roles of TMEM16A in inflammation by summarizing the mechanisms underlying TMEM16A expression and activation under inflammatory conditions, in addition to exploring the diverse inflammatory signaling pathways activated by TMEM16A. This review attempts to develop the idea that TMEM16A plays a diverse role in inflammatory processes and contributes to inflammatory diseases in a cellular environment-dependent manner.

Key scientific concepts of review

Multiple inflammatory mediators, including cytokines (e.g., interleukin (IL)-4, IL-13, IL-6), histamine, bradykinin, and ATP/UTP, as well as bacterial and viral infections, promote TMEM16A expression and/or activity under inflammatory conditions. In addition, TMEM16A activates diverse inflammatory signaling pathways, including the IP₃R-mediated Ca²⁺ signaling pathway, the NF-κB signaling pathway, and the ERK signaling pathway, and contributes to the pathogenesis of many inflammatory diseases. These diseases include airway inflammatory diseases, lipopolysaccharide-induced intestinal epithelial barrier dysfunction, acute pancreatitis, and steatohepatitis. TMEM16A also plays multiple roles in inflammatory processes by increasing vascular permeability and leukocyte adhesion, promoting inflammatory cytokine release, and sensing inflammation-induced pain. Furthermore, TMEM16A plays its diverse pathological roles in different inflammatory diseases depending on the disease severity, proliferating status of the cells, and its interacting partners. We herein propose cellular environment-dependent mechanisms that explain the diverse roles of TMEM16A in inflammation.