1.A.17.1.1
The plasma membrane Ca² -activated chloride (ICl_Ca) channel, TMEM16A (Anoctamin 1a; ANO1a; ANO1, DOG1, ORAOV2, TAOS2) (Huang et al., 2012; Chen et al. 2011). The mouse orthologue (Q8BHY3), TMEM16A (956aas), is localized to the apical membranes of epithelia as well as intracellular membranes in many cell types. Knockout mice show diminished rhythmic contraction of gastric smooth muscle (Huang et al., 2009). ANO1 is also required for normal tracheal development (Ousingsawat et al., 2009). Expression is upregulated by epidermal growth factor (Mroz and Keely, 2012). Novel 5-substituted benzyloxy-2-arylbenzofuran-3-carboxylic acids are inhibitors (Kumar et al., 2012). TMEM16A channels contribute to the myogenic response in cerebral arteries (Bulley et al., 2012). Membrane stretch activates arterial myocyte TMEM16A channels, leading to membrane depolarization and vasoconstriction. A local Ca²⁺  signal generated by nonselective cation channels stimulates TMEM16A channels to induce myogenic constriction (Bulley et al., 2012).  Ca²⁺/calmodulin activates bicarbonate (anion) transport (Jung et al. 2012).  The protein exists in the membrane as a homodimer where the cytoplasmic N-terminus functions in dimerization (Tien et al. 2013).  TMSs 5-6 of the 8 TMSs may comprise parts of the pore-loop that controls Cl^- conductance (Adomaviciene et al. 2013).  ANO1 confers ICl_Ca in retinal neurons and acts as an intrinsic regulator of the presynaptic membrane potential during synaptic transmission (Jeon et al. 2013).  TMEM16A may be a primary driver of the "Grow" (tumor proliferation) or "Go"(metastasis) model for cancer progression, in which TMEM16A expression acts to balance tumor proliferation and metastasis via its promoter methylation (Shiwarski et al. 2014).  Regulation of TMEM16A/16B by Ca²⁺ is mediated by preassociated apo-calmodulin (Yang et al. 2014) as well as CaMKIIδ (Gui et al. 2015).  Because the Cl^- channel is the only active ion-selective conductance with a reversal potential that lies within the dynamic range of spiral ganglion neurons (SGN) action potentials, developmental alteration of [Cl^-], and hence the equilibrium potential for Cl^- (ECl), transforms the pre- to the post-hearing phenotype (Zhang et al. 2015).  Four basic residues involved in ion selectivity and pore blocker sensitivity have been identified (Peters et al. 2015).  Channel activity is required for mucus secretion induced by interleukin-13 (Lin et al. 2015; Zhang et al. 2015). Ano1 may interact cooperatively with TrpV1 (TC# 1.A.4.2.1) to form a thermal sensor (Kanazawa and Matsumoto 2014). Inhibitors have been described (Boedtkjer et al. 2015).  The first intracellular loop serves as a Ca²⁺ binding site and includes D439, E444 and E447 (Pang et al. 2015).  It is inhibited by various 4-Aryl-2-amino thiazoles at concentrations as low as 1 mμM (Piechowicz et al. 2016).  ANO1 and TRPC6 (1.A.4.1.5) are present in the same macromolecular complex and localize in close spatial proximity in the myocyte plasma membrane.  TRPC6 channels probably generate a local intracellular Ca²⁺ signal that activates nearby ANO1 channels in myocytes to stimulate vasoconstriction (Wang et al. 2016).  ANO1 transports bicarbonate which functions in the regulation of pancreatic acinar cell pH (Han et al. 2016).  TMEM16A contains two ion conduction pores that are independently activated by Ca²⁺ binding to sites that are embedded within the transmembrane part of each subunit (Lim et al. 2016).  Interactions between the carboxy- terminus and the first intracellular loop in the TMEM16A homo-dimer regulate channel activity (Scudieri et al. 2016).  A STAT6-TMEM16A-ERK1/2 signal pathway and TMEM16A channel activity are required for the Interleukin-13 (IL-13)-induced TMEM16A-mediated mucus production (Qin et al. 2016). Angiotensin II elicits a TMEM16A-mediated current, and TMEM16A participates in Ang II-induced basilar constriction via the RhoA/ROCK signaling pathway (Li et al. 2016). 2-acylamino-cycloalkylthiophene-3-carboxylic acid arylamides (AACTs) are inhibitors of TMEM16A, and 48 synthesized analogs (10ab-10bw) of the original AACT compound (10aa) have been synthesized and studied.  The most potent compound (10bm), which contains an unusual bromodifluoroacetamide at the thiophene 2-position, had an IC50 ~ 30 nM (Truong et al. 2017).  Ano1 plays a role in asthma (Wang et al. 2017). The E143A mutant showed reduced sensitivity to Ca²⁺ but not to high temperatures, whereas the E705V mutant exhibited reduced sensitivity to both Ca²⁺ and noxious heat (Choi et al. 2018). Voltage modulation of TMEM16A involves voltage-dependent occupancy of calcium- and anion-binding site(s) within the membrane electric field as well as a voltage-dependent conformational change intrinsic to the channel protein. These gating modalities all critically depend on the sixth transmembrane segment (Peters et al. 2018). TMEM16A in myocytes plays a major functional role in contraction (Mohanakumar et al. 2018). Bile acids activate TMEM16A and thereby increase cholangiocyte fluid secretion (Li et al. 2018). TMEM16A participates in H₂O₂-induced apoptosis via modulation of mitochondrial membrane permeability (Zeng et al. 2018). Glioma-associate oncogene proteins, Gli1 and Gli2, bind to the promoter and repress ANO1 transcription, dependent on Gli binding to a site close to the ANO1 transcriptional start site (Mazzone et al. 2019). Clarithromycin suppresses IL-13-induced goblet cell metaplasia via the TMEM16A-dependent pathway in guinea pig airway epithelial cells (Hara et al. 2019).  TMEM16A is involved in gastric emptying, and TMEM16A inhibition may be effective in treating disorders of accelerated gastric emptying, such as dumping syndrome (Cil et al. 2019).  Phosphatidylinositol (4,5)-bisphosphate (PIP2) regulates TMEM16A channel activation and desensitization by binding to a binding site, possibly at the cytosolic interface of TMSs 3-5. The ion-conducting pore of TMEM16A consists of two functionally distinct modules: a Ca²⁺-binding module formed by TMSs 6-8 and a PIP2-binding regulatory module formed by TMs 3-5, which mediate channel activation and desensitization, respectively (Sui et al. 2020). TMEM16A plays a dual role in LPS-induced intestinal epithelial barrier dysfunction (Sui et al. 2020). Hepatocyte TMEM16A plays a role in nonalcoholic fatty liver disease (NAFLD), and its deletion retards NAFLD progression by ameliorating hepatic glucose metabolic disorder (Guo et al. 2020). Hepatocyte TMEM16A interacts with vesicle-associated membrane protein 3 (VAMP3) to induce its degradation, suppressing the formation of the VAMP3/syntaxin 4 and VAMP3/synaptosome-associated protein 23 complexes (see TC# 1.F.1.1.5). This leads to impairment of hepatic glucose transporter 2 (GLUT2) translocation and glucose uptake (Guo et al. 2020). TMEM16A is a potential biomarker for Lung Cancer (Hu et al. 2019). Allosteric modulation of alternatively spliced Ca²⁺-activated Cl^- channels, TMEM16A by PI(4,5)P2 and CaMKII (TC# 8.A.104.1.11) has been demonstrated (Ko et al. 2020). Signaling through the interleukin-4 and interleukin-13 receptor complexes regulates cholangiocyte TMEM16A expression and biliary secretion (Dutta et al. 2020). A second Ca²⁺ binding site allosterically controls TMEM16A activation (Le and Yang 2020). A long noncoding RNA (lncRNA), ANO1-AS2, downregulates the ANO1 gene by interacting with the ANO1 gene promoter, which can influence sperm motility and morphology (Saberiyan et al. 2020). Ano1 plays an important role in generating urethral tone (Drumm et al. 2021). Human TMEM16A shows increated expression in many cancers (Chen et al. 2021). TMEM16A is inhibitied by liquiritigenin (Kato et al. 2021) and is activated by the natural product canthaxanthin which  promotes gastrointestinal contraction (Ji et al. 2020). TMEM16A ameliorates vascular remodeling by suppressing autophagy via inhibiting Bcl-2-p62 complex formation. It regulates the four-way interaction between p62 (P37198; TC# 1.I.1.1.3), Bcl-2 (TC# 1.A.21.1.10), Beclin-1 (BECN1 or GT197; Q144570; TC# 9.A.15.2.1), and VPS34 (phosphatidylinositol 3-kinase, PI 3-kinase, PIK3C3), and coordinately prevents vascular autophagy and remodeling (Lv et al. 2020). A small molecule inhibitor of TMEM16A (2-bromodifluoroacetylamino-5,6,7,8-tetrahydro-4H-cyclohepta[b]thiophene-3-carbox ylic acid o-tolylamide) blocks vascular smooth muscle contraction and lowers blood pressure in spontaneously hypertensive rats (Cil et al. 2021). Evodiamine and rutecarpine are TMEM16A inhibitors (Zhao et al. 2021). Cepharanthine is a selective ANO1 inhibitor with potential for lung adenocarcinoma therapy (Zhang et al. 2021). Benzophenanthridine alkaloids suppress lung adenocarcinoma by blocking TMEM16A Ca²⁺-activated Cl^- channels (Zhang et al. 2020). The diverse roles of TMEM16A Ca²⁺-activated Cl^- channels in inflammation have been described (Bai et al. 2021). TMEM16A-mediated breast cancer metastasis has been described in which ROCK1 increases TMEM16A channel activity via moesin phosphorylation.  An increase in TMEM16A channel activity promotes cell migration and invasion (Luo et al. 2021). Four Ca²⁺ sensing sites in TMEM16A have been identfied, and the activation properties of TMEM16A by them has been discussed (Ji et al. 2021). Blockade of TMEM16A protects against renal fibrosis by reducing the intracellular Cl^- concentration (Li et al. 2021). The TMEM16A/anoctamin 1 inhibitor T16Ainh-A01 reverses monocrotaline-induced rat pulmonary arterial hypertension (Xie et al. 2020). The role of TMEM16A/ERK/NK-1 signaling in dorsal root ganglia neurons in the development of neuropathic pain induced by spared nerve injury has been studied (Chen et al. 2021). Elevated ANO1 (DOG1) expression is frequent in colorectal cancer and is linked to molecular alterations (Jansen et al. 2022). ANO1 plays a role in the occurrence, development, metastasis, proliferation, and apoptosis of various malignant tumors. Guo et al. 2022 reviewed the mechanism of ANO1 involved in the replication, proliferation, invasion and apoptosis of various malignant tumors. Procyanidin (PC) is an efficacious and selective inhibitor of TMEM16A with an IC50 of 10.6 +/- 0.6 muM. The precise sites (D383, R535, and E624) of electrostatic interactions between PC and TMEM16A are known (Li et al. 2022). TMEM16A is a Ca²⁺activated Cl^- channel that plays critical roles in regulating vascular tone, sensory signal transduction, and mucosal secretion. TMEM16A activation also requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) (Tembo et al. 2022). TMEM16A may promote angiogenesis of the heart during pressure-overload (Zhang et al. 2022), and it is an immunohistochemical marker of acinic cell carcinoma (Fiorentino et al. 2022). The progress in understanding solute carrier SLC families in nonalcoholic fatty liver disease has been reviewed (Tang et al. 2022). Arctigenin attenuates vascular inflammation induced by high salt through the TMEM16A/ESM1/VCAM-1 pathway (Zeng et al. 2022). Biologics that inactivate Na_v1.7 channels have the potential to reduce arthritis pain over a protracted period of time (Reid et al. 2022). Allicin, containing thiosulfinate moieties, inhibits TMEM16A) ion channel activity (Bai et al. 2023). TMEM16A) plays a role in pulmonary hypertension (Yuan et al. 2023). Chloride channels in biliary epithelial cells provide the driving force for biliary secretion. Norursodeoxycholic acid (norUDCA) potently stimulated chloride currents in mouse large cholangiocytes, which was blocked by siRNA silencing and pharmacological inhibition of TMEM16A (Truong et al. 2023). TMEM16A partners with mTOR to influence pathways of cell survival, proliferation, and migration in cholangiocarcinoma (Kulkarni et al. 2023). Analysis of inhibitors of TMEM16A revealed indirect mechanisms involving alterations in calcium signalling (Genovese et al. 2023).  Dysregulation of TMEM16A impairs oviductal transport of embryos (Ning et al. 2023). TMEM16A may be a target for cancer treatment (Li et al. 2023). Vasodilators activate TMEM16A in endothelial cells to reduce blood pressure (Mata-Daboin et al. 2023). Tubular TMEM16A promotes tubulointerstitial fibrosis by suppressing PGC-1alpha-mediated mitochondrial homeostasis in diabetic kidney disease (Ji et al. 2023).  The TMEM16A channel is a potential therapeutic target for vascular diseases (Al-Hosni et al. 2024).  Extracellular glucose and dysfunctional insulin receptor signaling independently upregulate arterial smooth muscle TMEM16A expression (Raghavan et al. 2024).