Direct repression of anoctamin 1 (ANO1) gene transcription by Gli proteins

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.

Capsaicin as an amphipathic modulator of NaV1.5 mechanosensitivity

SCN5A-encoded Na_V1.5 is a voltage-gated Na⁺ channel that drives the electrical excitability of cardiac myocytes and contributes to slow waves of the human gastrointestinal smooth muscle cells. Na_V1.5 is mechanosensitive: mechanical force modulates several facets of Na_V1.5’s voltage-gated function, and some Na_V1.5 channelopathies are associated with abnormal Na_V1.5 mechanosensitivity (MS). A class of membrane-active drugs, known as amphiphiles, therapeutically target Na_V1.5’s voltage-gated function and produce off-target effects including alteration of MS. Amphiphiles may provide a novel option for therapeutic modulation of Na_V1.5’s mechanosensitive operation. To more selectively target Na_V1.5 MS, we searched for a membrane-partitioning amphipathic agent that would inhibit MS with minimal closed-state inhibition of voltage-gated currents. Among the amphiphiles tested, we selected capsaicin for further study. We used two methods to assess the effects of capsaicin on Na_V1.5 MS: (1) membrane suction in cell-attached macroscopic patches and (2) fluid shear stress on whole cells. We tested the effect of capsaicin on Na_V1.5 MS by examining macro-patch and whole-cell Na⁺ current parameters with and without force. Capsaicin abolished the pressure- and shear-mediated peak current increase and acceleration; and the mechanosensitive shifts in the voltage-dependence of activation (shear) and inactivation (pressure and shear). Exploring the recovery from inactivation and use-dependent entry into inactivation, we found divergent stimulus-dependent effects that could potentiate or mitigate the effect of capsaicin, suggesting that mechanical stimuli may differentially modulate Na_V1.5 MS. We conclude that selective modulation of Na_V1.5 MS makes capsaicin a promising candidate for therapeutic interventions targeting MS.

Roles, molecular mechanisms, and signaling pathways of TMEMs in neurological diseases

Transmembrane protein family members (TMEMs) span the entire lipid bilayer and act as channels that allow the transport of specific substances through biofilms. The functions of most TMEMs are unexplored. Numerous studies have shown that TMEMs are involved in the pathophysiological processes of various nervous system diseases, but the specific mechanisms of TMEMs in the pathogenesis of diseases remain unclear. In this review, we discuss the expression, physiological functions, and molecular mechanisms of TMEMs in brain tumors, psychiatric disorders, abnormal motor activity, cobblestone lissencephaly, neuropathic pain, traumatic brain injury, and other disorders of the nervous system. Additionally, we propose that TMEMs may be used as prognostic markers and potential therapeutic targets in patients with various neurological diseases.

Genome-wide analysis of 944 133 individuals provides insights into the etiology of haemorrhoidal disease

OBJECTIVE

Haemorrhoidal disease (HEM) affects a large and silently suffering fraction of the population but its aetiology, including suspected genetic predisposition, is poorly understood. We report the first genome-wide association study (GWAS) meta-analysis to identify genetic risk factors for HEM to date.

DESIGN

We conducted a GWAS meta-analysis of 218 920 patients with HEM and 725 213 controls of European ancestry. Using GWAS summary statistics, we performed multiple genetic correlation analyses between HEM and other traits as well as calculated HEM polygenic risk scores (PRS) and evaluated their translational potential in independent datasets. Using functional annotation of GWAS results, we identified HEM candidate genes, which differential expression and coexpression in HEM tissues were evaluated employing RNA-seq analyses. The localisation of expressed proteins at selected loci was investigated by immunohistochemistry.

RESULTS

We demonstrate modest heritability and genetic correlation of HEM with several other diseases from the GI, neuroaffective and cardiovascular domains. HEM PRS validated in 180 435 individuals from independent datasets allowed the identification of those at risk and correlated with younger age of onset and recurrent surgery. We identified 102 independent HEM risk loci harbouring genes whose expression is enriched in blood vessels and GI tissues, and in pathways associated with smooth muscles, epithelial and endothelial development and morphogenesis. Network transcriptomic analyses highlighted HEM gene coexpression modules that are relevant to the development and integrity of the musculoskeletal and epidermal systems, and the organisation of the extracellular matrix.

CONCLUSION

HEM has a genetic component that predisposes to smooth muscle, epithelial and connective tissue dysfunction.

GLI1/GLI2 functional interplay is required to control Hedgehog/GLI targets gene expression

The Hedgehog-regulated transcription factors GLI1 and GLI2 play overlapping roles in development and disease; however, the mechanisms underlying their interplay remain elusive. We report for the first time that GLI1 and GLI2 physically and functionally interact in cancer cells. GLI1 and GLI2 were shown to co-immunoprecipitate in PANC1 pancreatic cancer cells and RMS13 rhabdomyosarcoma cells. Mapping analysis demonstrated that the zinc finger domains of both proteins are required for their heteromerization. RNAi knockdown of either GLI1 or GLI2 inhibited expression of many well-characterized GLI target genes (BCL2, MYCN, PTCH2, IL7 and CCND1) in PANC1 cells, whereas PTCH1 expression was only inhibited by GLI1 depletion. qPCR screening of a large set of putative canonical and non-canonical Hedgehog/GLI targets identified further genes (e.g. E2F1, BMP1, CDK2) strongly down-regulated by GLI1 and/or GLI2 depletion in PANC1 cells, and demonstrated that ANO1, AQP1 and SOCS1 are up-regulated by knockdown of either GLI1 or GLI2. Chromatin immunoprecipitation showed that GLI1 and GLI2 occupied the same regions at the BCL2, MYCN and CCND1 promoters. Furthermore, depletion of GLI1 inhibited GLI2 occupancy at these promoters, suggesting that GLI1/GLI2 interaction is required for the recruitment of GLI2 to these sites. Together, these findings indicate that GLI1 and GLI2 co-ordinately regulate the transcription of some genes, and provide mechanistic insight into the roles of GLI proteins in carcinogenesis.

Another twist to the GLI code

The canonical Hedgehog (Hh) signalling pathway is essential for vertebrate development and its uncontrolled activation is a common occurrence in human cancers. Hh signalling converges in the modification of a family of transcription factors, GLI1, GLI2 and GLI3, to orchestrate a cell type and context-specific transcriptional response. Despite binding to very similar responsive elements, the GLI family members can exert diverse and even opposing functions. A recent article by Tolosa et al. (Biochem. J. 477, 3131-3145, 2020) reveals an unexpected layer of complexity, through physical and functional interaction between GLI1 and GLI2. This commentary discusses the biological significance of the findings and incorporates them into an updated 'GLI code'.

Calcium-Activated Chloride Channel ANO1/TMEM16A: Regulation of Expression and Signaling

Anoctamin-1 (ANO1), also known as TMEM16A, is the most studied member of anoctamin family of calcium-activated chloride channels with diverse cellular functions. ANO1 controls multiple cell functions including cell proliferation, survival, migration, contraction, secretion, and neuronal excitation. This review summarizes the current knowledge of the cellular mechanisms governing the regulation of ANO1 expression and of ANO1-mediated intracellular signaling. This includes the stimuli and mechanisms controlling ANO1 expression, agonists and processes that activate ANO1, and signal transduction mediated by ANO1. The major conclusion is that this field is poorly understood, remains highly controversial, and requires extensive and rigorous further investigation.

Prototypical pacemaker neurons interact with the resident microbiota

Pacemaker neurons exert control over neuronal circuit function by their intrinsic ability to generate rhythmic bursts of action potential. Recent work has identified rhythmic gut contractions in human, mice, and hydra to be dependent on both neurons and the resident microbiota. However, little is known about the evolutionary origin of these neurons and their interaction with microbes. In this study, we identified and functionally characterized prototypical ANO/SCN/TRPM ion channel-expressing pacemaker cells in the basal metazoan Hydra by using a combination of single-cell transcriptomics, immunochemistry, and functional experiments. Unexpectedly, these prototypical pacemaker neurons express a rich set of immune-related genes mediating their interaction with the microbial environment. Furthermore, functional experiments gave a strong support to a model of the evolutionary emergence of pacemaker cells as neurons using components of innate immunity to interact with the microbial environment and ion channels to generate rhythmic contractions.

Differential phosphorylation determines the repressor and activator potencies of GLI1 proteins and their efficiency in modulating the HPV life cycle

The Sonic Hedgehog (Shh) signalling pathway plays multiple roles during embryonic development and under pathological conditions. Although the core components of the Shh pathway are conserved, the regulation of signal transduction varies significantly among species and cell types. Protein kinases Ulk3 and Pka are involved in the Shh pathway as modulators of the activities of Gli transcription factors, which are the nuclear mediators of the signal. Here, we investigate the regulation and activities of two GLI1 isoforms, full-length GLI1 (GLI1FL) and GLI1ΔN. The latter protein lacks the first 128 amino acids including the conserved phosphorylation cluster and the binding motif for SUFU, the key regulator of GLI activity. Both GLI1 isoforms are co-expressed in all human cell lines analysed and possess similar DNA binding activity. ULK3 potentiates the transcriptional activity of both GLI1 proteins, whereas PKA inhibits the activity of GLI1ΔN, but not GLI1FL. In addition to its well-established role as a transcriptional activator, GLI1FL acts as a repressor by inhibiting transcription from the early promoters of human papillomavirus type 18 (HPV18). Additionally, compared to GLI1ΔN, GLI1FL is a more potent suppressor of replication of several HPV types. Altogether, our data show that the N-terminal part of GLI1FL is crucial for the realization of its full potential as a transcriptional regulator.

The multifaceted role of TMEM16A in cancer

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