Structure–function relationship of the TRP channel superfamily

The potential of marine natural products and their synthetic derivatives as drugs targeting ion channels

Ion channels are a type of protein channel that play a vital role in numerous physiological functions by facilitating the passage of ions through cell membranes, thereby enabling ion and electrical signal transmission. As a crucial target for drug action, ion channels have been implicated in various diseases. Many natural products from marine organisms, such as fungi, algae, sponges, and sea cucumber, etc. have been found to have activities related to ion channels for decades. These interesting natural product molecules undoubtedly bring good news for the treatment of neurological and cardiovascular diseases. In this review, 92 marine natural products and their synthetic derivatives with ion channel-related activities that were identified during the period 2000-2024 were systematically reviewed. The synthesis and mechanisms of action of selected compounds were also discussed, aiming to offer insights for the development of drugs targeting ion channels.

Ion channel TRPV2 is critical in enhancing B cell activation and function

The function of transient receptor potential vanilloid (TRPV) cation channels governing B cell activation remains to be explored. We present evidence that TRPV2 is highly expressed in B cells and plays a crucial role in the formation of the B cell immunological synapse and B cell activation. Physiologically, TRPV2 expression level is positively correlated to influenza-specific antibody production and is low in newborns and seniors. Pathologically, a positive correlation is established between TRPV2 expression and the clinical manifestations of systemic lupus erythematosus (SLE) in adult and child SLE patients. Correspondingly, mice with deficient TRPV2 in B cells display impaired antibody responses following immunization. Mechanistically, the pore and N-terminal domains of TRPV2 are crucial for gating cation permeation and executing mechanosensation in B cells upon antigen stimulation. These processes synergistically contribute to membrane potential depolarization and cytoskeleton remodeling within the B cell immunological synapse, fostering efficient B cell activation. Thus, TRPV2 is critical in augmenting B cell activation and function.

Identification of transient receptor potential channel genes from the swimming crab, Portunus Trituberculatus, and their expression profiles under acute temperature stress

BACKGROUND

Temperature is an important environment factor that is critical to the survival and growth of crustaceans. However, the mechanisms by which crustaceans detect changes in temperature are still unclear. The transient receptor potential (TRP) channels are non-selective cation channels well known for properties in temperature sensation. However, comprehensive understandings on TRP channels as well as their temperature sensing functions are still lacking in crustaceans.

RESULTS

In this study, a total of 26 TRP genes were identified in the swimming crab, Portunus trituberculatus, which can be classified into TRPA, TRPC, TRPP, TRPM, TRPML, TRPN and TRPV. Tissue expression analysis revealed a wide distribution of these TRP genes in P. trituberculatus, and antennules, neural tissues, and ovaries were the most commonly expressed tissues. To investigate the responsiveness of TRP genes to the temperature change, 18 TRPs were selected to detect their expression after high and low temperature stress. The results showed that 12 TRPs showed induced gene expression in both high and low temperature groups, while 3 were down-regulated in the low temperature group, and 3 showed no change in expression in either group.

CONCLUSIONS

This study characterized the TRP family genes in P. trituberculatus, and explored their involvement in response to temperature stress. Our results will enhance overall understanding of crustacean TRP channels and their possible functions.

Transient receptor potential (TRP) channels in the Manila clam (Ruditapes philippinarum): Characterization and expression patterns of the TRP gene family under heat stress in Manila clams based on genome-wide identification

In this study, we identified a total of 40 transient receptor potential genes (RpTRP) in Manila clam by genome-wide identification and classified them into four categories (TRPV, TRPA, TRPM, TRPC) based on gene structure and subfamily relationships. The protein length of RpTRP genes ranges from 281 amino acids to 1601 amino acids. Molecular weight and theoretical PI values range from 182.82 kDa to 32.43 kDa, respectively, with PI values between 5.17 and 9.25. By comparing the expression profiles of TRP genes during heat stress in Manila clams at different latitudes, we found that most genes in the TRP gene family were up-regulated in expression during heat challenge. Therefore, we determined that TRP genes have an important role in the heat stress of Manila clams. This work provides a basis for further studies on the molecular mechanisms of TRP-mediated heat tolerance in Manila clam and for explaining differences in heat tolerance in Manila clam at different latitudes through key differential TRP genes at the molecular level.

Improvement of platelet preservation by inhibition of TRPC6

BACKGROUND

The preservation of platelets (PLTs) by room temperature (RT) oscillation limits their shelf life to between 4 and 7 days because of the decrease in PLT function. TRPC6 is a non-selective mechanically sensitive cation channel that has been shown to mediate Ca²⁺ signalling, implying a role in PLT activation during preservation by RT oscillation.

OBJECTIVES

This study was designed to investigate whether inhibition of TRPC6 can improve the RT preservation of PLTs and the possible underlying mechanism.

METHODS

Human PLTs from whole blood were stored at 22 ± 2°C with oscillation in plasma or M-sol (mixture of solutions). BI-749327, a specific TRPC6 inhibitor, was administered throughout the preservation period. PLT distribution width (PDW), mean platelet volume (MPV), maximum platelet aggregation rate (MAR) and average aggregation rate (AAR) were measured. The MTT method was used to assess the relative viability of PLTs. Flow cytometry was used to measure the changes of Ca²⁺ concentration in PLTs and phosphatidylserine (PS) exposure on the PLT surface, and western blotting was used to assess the expression changes of platelet TRPC6 and CD62P proteins.

RESULTS

Compared with the control group, inhibition of TRPC6 with BI-749327 significantly reduced the PDW, MPV and Ca²⁺ concentration, the MAR and AAR were significantly increased, the expression of TRPC6 and CD62P protein was significantly down-regulated in PLTs, and the PS exposure was significantly reduced on the PLT surface. However, these effects were all reversed by activation of TRPC6.

CONCLUSION

Inhibition of TRPC6 improves the quality of PLT preservation by inhibiting the Ca²⁺ signal mediated by TRPC6.

TRPM5 Channel Binds Calcium-Binding Proteins Calmodulin and S100A1

Melastatin transient receptor potential (TRPM) channels belong to one of the most significant subgroups of the transient receptor potential (TRP) channel family. Here, we studied the TRPM5 member, the receptor exposed to calcium-mediated activation, resulting in taste transduction. It is known that most TRP channels are highly modulated through interactions with extracellular and intracellular agents. The binding sites for these ligands are usually located at the intracellular N- and C-termini of the TRP channels, and they can demonstrate the character of an intrinsically disordered protein (IDP), which allows such a region to bind various types of molecules. We explored the N-termini of TRPM5 and found the intracellular regions for calcium-binding proteins (CBPs) the calmodulin (CaM) and calcium-binding protein S1 (S100A1) by in vitro binding assays. Furthermore, molecular docking and molecular dynamics simulations (MDs) of the discovered complexes confirmed their known common binding interface patterns and the uniqueness of the basic residues present in the TRPM binding regions for CaM/S100A1.

Identification and characterization of Trpm4 gene involved in regulating Japanese flounder (Paralichthys olivaceus) inflammatory response

The transient receptor potential (TRP) melastatin 4 (TRPM4) is a widely expressed Ca²⁺ -impermeable cation channel involved in modulating inflammatory and immune responses in mammals. However, the role of TRPM4 channel in fish immunity remains unclear. In this report, from a comparative immunological point of view, we identified and characterized a Trpm4 gene from Japanese flounder (Paralichthys olivaceus) and analysed its potential role in regulating the fish inflammatory response. The Japanese flounder Trpm4 gene is expressed in a wide range of tissues and encodes a 1264-amino acid protein which expresses on the cell surface and shares several conserved domains with its mammalian counterparts. In vitro inflammatory challenge and in vivo bacterial infection experiments revealed that Japanese flounder Trpm4 expression was significantly modulated following different immune challenges, indicating the implication of Trpm4 in the fish immune response. Overexpression of TRPM4 significantly attenuated LPS- and poly(I:C)-induced pro-inflammatory cytokine expression in Japanese flounder FG-9307 cells. In contrast, pharmacological inhibition of the endogenous TRPM4 channel activity in Japanese flounder head kidney macrophages resulted in increased pro-inflammatory cytokine expression following LPS and poly(I:C) stimulations. Taken together, these findings indicate that TRPM4 channels may play a conserved role in regulating inflammatory response(s) in fish.

Development of Store-Operated Calcium Entry-Targeted Compounds in Cancer

Store-operated Ca²⁺ entry (SOCE) is the major pathway of Ca²⁺ entry in mammalian cells, and regulates a variety of cellular functions including proliferation, motility, apoptosis, and death. Accumulating evidence has indicated that augmented SOCE is related to the generation and development of cancer, including tumor formation, proliferation, angiogenesis, metastasis, and antitumor immunity. Therefore, the development of compounds targeting SOCE has been proposed as a potential and effective strategy for use in cancer therapy. In this review, we summarize the current research on SOCE inhibitors and blockers, discuss their effects and possible mechanisms of action in cancer therapy, and induce a new perspective on the treatment of cancer.

From High-Throughput Screening to Target Validation: Benzo[d]isothiazoles as Potent and Selective Agonists of Human Transient Receptor Potential Cation Channel Subfamily M Member 5 Possessing In Vivo Gastrointestinal Prokinetic Activity in Rodents

Transient receptor potential cation channel subfamily M member 5 (TRPM5) is a nonselective monovalent cation channel activated by intracellular Ca²⁺ increase. Within the gastrointestinal system, TRPM5 is expressed in the stoma, small intestine, and colon. In the search for a selective agonist of TRPM5 possessing in vivo gastrointestinal prokinetic activity, a high-throughput screening was performed and compound 1 was identified as a promising hit. Hit validation and hit to lead activities led to the discovery of a series of benzo[d]isothiazole derivatives. Among these, compounds 61 and 64 showed nanomolar activity and excellent selectivity (>100-fold) versus related cation channels. The in vivo drug metabolism and pharmacokinetic profile of compound 64 was found to be ideal for a compound acting locally at the intestinal level, with minimal absorption into systemic circulation. Compound 64 was tested in vivo in a mouse motility assay at 100 mg/kg, and demonstrated increased prokinetic activity.

Molecular characterizations and expression profiles of transient receptor potential channels in the brown planthopper, Nilaparvata lugens

Transient receptor potential (TRP) is a superfamily of important cation channels located on the cell membrane. It can regulate almost all sensory modality and control a series of behaviors, including hearing, locomotion, gentle touch, temperature sensation, dry air and food texture detection. The expression profiles of TRP channels have been well documented in the model insect Drosophila melanogaster. However, little is known about the TRP channels of agricultural pests. In this study, we cloned 9 TRP ion channel genes from brown planthopper. Their amino acid sequences are highly conserved with homologues of other insects and have typical TRP channel characteristics: six transmembrane domains (TM1 - TM6) and a pore region between TM5 and TM6. These TRP channels of N. lugens were expressed in all developmental stages and various body parts. The expression levels of almost all TRP channels were relatively higher in adults than nymph stages, and lowest in the eggs. Antenna and abdomen were the main body parts with high expression of these genes. Furthermore, the mRNA levels of these TRP genes were significantly decreased in the third-instar nymphs injected with double-stranded RNA (dsRNA). The survival rate of different TRP dsRNA injected nymphs all exceeded 81%, which was no significant difference compared with the control group. These results suggested that these 9 TRP channels are expressed throughout the body and all ages of the brown planthopper, and are involved in regulating multiple physiological and behavioral processes. The identification of TRP channel genes in this study not only provides a foundation for further exploring the potential roles of TRP channels, but also serves as targets to develop new insecticides for the control of agricultural pests.

Transient receptor potential channels in sensory mechanisms of the lower urinary tract

Disruptions to sensory pathways in the lower urinary tract commonly occur and can give rise to lower urinary tract symptoms (LUTS). The unmet clinical need for treatment of LUTS has stimulated research into the molecular mechanisms that underlie neuronal control of the bladder and transient receptor potential (TRP) channels have emerged as key regulators of the sensory processes that regulate bladder function. TRP channels function as molecular sensors in urothelial cells and afferent nerve fibres and can be considered the origin of bladder sensations. TRP channels in the lower urinary tract contribute to the generation of normal and abnormal bladder sensations through a variety of mechanisms, and have demonstrated potential as targets for the treatment of LUTS in functional disorders of the lower urinary tract.

TRPV4 integrates matrix mechanosensing with Ca2+ signaling to regulate extracellular matrix remodeling

In healthy connective tissues, mechanosensors trigger the generation of Ca²⁺ signals, which enable cells to maintain the structure of the fibrillar collagen matrix through actomyosin contractile forces. Transient receptor potential vanilloid type 4 (TRPV4) is a mechanosensitive Ca²⁺ -permeable channel that, when expressed in cell-matrix adhesions of the plasma membrane, regulates extracellular matrix (ECM) remodeling. In high prevalence disorders such as fibrosis and tumor metastasis, dysregulated matrix remodeling is associated with disruptions of Ca²⁺ homeostasis and TRPV4 function. Here, we consider that ECM polymers transmit cell-activating mechanical signals to TRPV4 in cell adhesions. When activated, TRPV4 regulates fibrillar collagen remodeling, thereby altering the mechanical properties of the ECM. In this review, we integrate functionally connected processes of matrix remodeling to highlight how TRPV4 in cell adhesions and matrix mechanics are reciprocally regulated through Ca²⁺ signaling.

TRPC6 channel and its implications in breast cancer: an overview

TRPC6 channel is widely expressed in most human tissues and participates in a number of physiological processes. TRPC6 belongs to the DAG-activated subfamily of channels, but has also been postulated as a mediator in the store-operated calcium entry pathway. The recent characterization of TRPC6 crystal structure has granted a wonderful tool to finally dissect and understand TRPC6 physiological and biophysical properties. Growing evidences have demonstrated that the pattern of expression of TRPC6 proteins is upregulated in several pathophysiological conditions, including breast cancer. However, the real role of TRPC6 in breast cancer persists still unknown. Here we present the current state of the art concerning the function and significance of TRPC6 in this disease. Future investigations should be focus in the creation and identification of compounds that specifically target the channel to ameliorate TRPC6-related diseases.

Novel TRPV1 Channel Agonists With Faster and More Potent Analgesic Properties Than Capsaicin

The transient receptor potential vanilloid 1 (TRPV1) ion channel is a member of the family of Transient Receptor Potential (TRP) channels that acts as a molecular detector of noxious signals in primary sensory neurons. Activated by capsaicin, heat, voltage and protons, it is also well known for its desensitization, which led to the medical use of topically applied TRPV1 agonist capsaicin for its long-lasting analgesic effects. Here we report three novel small molecules, which were identified using a Structure-Based Virtual Screening for TRPV1 from the ZINC database. The three compounds were tested using electrophysiological assays, which confirmed their capsaicin-like agonist activity. von Frey filaments were used to measure the analgesic effects of the compounds applied topically on tactile allodynia induced by intra-plantar carrageenan. All compounds had anti-nociceptive activity, but two of them showed faster and longer lasting analgesic effects than capsaicin. The present results suggest that TRPV1 agonists different from capsaicin could be used to develop topical analgesics with faster onset and more potent effects.

Exploring the Therapeutic Potential of Membrane Transport Proteins: Focus on Cancer and Chemoresistance

Improving the therapeutic efficacy of conventional anticancer drugs represents the best hope for cancer treatment. However, the shortage of druggable targets and the increasing development of anticancer drug resistance remain significant problems. Recently, membrane transport proteins have emerged as novel therapeutic targets for cancer treatment. These proteins are essential for a plethora of cell functions ranging from cell homeostasis to clinical drug toxicity. Furthermore, their association with carcinogenesis and chemoresistance has opened new vistas for pharmacology-based cancer research. This review provides a comprehensive update of our current knowledge on the functional expression profile of membrane transport proteins in cancer and chemoresistant tumours that may form the basis for new cancer treatment strategies.

How TRPC Channels Modulate Hippocampal Function

Transient receptor potential canonical (TRPC) proteins constitute a group of receptor-operated calcium-permeable nonselective cationic membrane channels of the TRP superfamily. They are largely expressed in the hippocampus and are able to modulate neuronal functions. Accordingly, they have been involved in different hippocampal functions such as learning processes and different types of memories, as well as hippocampal dysfunctions such as seizures. This review covers the mechanisms of activation of these channels, how these channels can modulate neuronal excitability, in particular the after-burst hyperpolarization, and in the persistent activity, how they control synaptic plasticity including pre- and postsynaptic processes and how they can interfere with cell survival and neurogenesis.

TRPCs: Influential Mediators in Skeletal Muscle

Ca²⁺ itself or Ca²⁺-dependent signaling pathways play fundamental roles in various cellular processes from cell growth to death. The most representative example can be found in skeletal muscle cells where a well-timed and adequate supply of Ca²⁺ is required for coordinated Ca²⁺-dependent skeletal muscle functions, such as the interactions of contractile proteins during contraction. Intracellular Ca²⁺ movements between the cytosol and sarcoplasmic reticulum (SR) are strictly regulated to maintain the appropriate Ca²⁺ supply in skeletal muscle cells. Added to intracellular Ca²⁺ movements, the contribution of extracellular Ca²⁺ entry to skeletal muscle functions and its significance have been continuously studied since the early 1990s. Here, studies on the roles of channel proteins that mediate extracellular Ca²⁺ entry into skeletal muscle cells using skeletal myoblasts, myotubes, fibers, tissue, or skeletal muscle-originated cell lines are reviewed with special attention to the proposed functions of transient receptor potential canonical proteins (TRPCs) as store-operated Ca²⁺ entry (SOCE) channels under normal conditions and the potential abnormal properties of TRPCs in muscle diseases such as Duchenne muscular dystrophy (DMD).

Recent Advances in Lipopolysaccharide Recognition Systems

Lipopolysaccharide (LPS), commonly known as endotoxin, is ubiquitous and the most-studied pathogen-associated molecular pattern. A component of Gram-negative bacteria, extracellular LPS is sensed by our immune system via the toll-like receptor (TLR)-4. Given that TLR4 is membrane bound, it recognizes LPS in the extracellular milieu or within endosomes. Whether additional sensors, if any, play a role in LPS recognition within the cytoplasm remained unknown until recently. The last decade has seen an unprecedented unfolding of TLR4-independent LPS sensing pathways. First, transient receptor potential (TRP) channels have been identified as non-TLR membrane-bound sensors of LPS and, second, caspase-4/5 (and caspase-11 in mice) have been established as the cytoplasmic sensors for LPS. Here in this review, we detail the brief history of LPS discovery, followed by the discovery of TLR4, TRP as the membrane-bound sensor, and our current understanding of caspase-4/5/11 as cytoplasmic sensors.

TRPM6 N-Terminal CaM- and S100A1-Binding Domains

Transient receptor potential (TRPs) channels are crucial downstream targets of calcium signalling cascades. They can be modulated either by calcium itself and/or by calcium-binding proteins (CBPs). Intracellular messengers usually interact with binding domains present at the most variable TRP regions-N- and C-cytoplasmic termini. Calmodulin (CaM) is a calcium-dependent cytosolic protein serving as a modulator of most transmembrane receptors. Although CaM-binding domains are widespread within intracellular parts of TRPs, no such binding domain has been characterised at the TRP melastatin member-the transient receptor potential melastatin 6 (TRPM6) channel. Another CBP, the S100 calcium-binding protein A1 (S100A1), is also known for its modulatory activities towards receptors. S100A1 commonly shares a CaM-binding domain. Here, we present the first identified CaM and S100A1 binding sites at the N-terminal of TRPM6. We have confirmed the L520-R535 N-terminal TRPM6 domain as a shared binding site for CaM and S100A1 using biophysical and molecular modelling methods. A specific domain of basic amino acid residues (R526/R531/K532/R535) present at this TRPM6 domain has been identified as crucial to maintain non-covalent interactions with the ligands. Our data unambiguously confirm that CaM and S100A1 share the same binding domain at the TRPM6 N-terminus although the ligand-binding mechanism is different.

Effect of a background Ca2+ entry pathway mediated by TRPC1 on myocardial damage of broilers with induced ascites syndrome

Ascites syndrome (AS) in chickens is associated with profound vascular remodelling and increased pulmonary artery pressure as well as right ventricular hypertrophy. Classical transient receptor potential cation channels (TRPCs) are key regulators of cardiac hypertrophy that act via regulation of calcium influx in mammals. We investigated whether classical transient receptor potential channels in chickens with right ventricular hypertrophy still possess this mechanism for regulating Ca²⁺ flux. Intravenous injection of cellulose particles was successfully used to induce AS in chickens, and tissues were examined 22 days after treatment. The chickens in the test group showed cardiac hypertrophy with oedema of the cardiac muscle and disruption of myofilaments. The right-to-total ventricle weight ratio (RV/TV), the levels of serum aspartate aminotransferase (AST) and creatine kinase (CK) of the test group were significantly higher than in the control group. Intracellular calcium levels were significantly increased in cardiomyocytes from chickens in the test group. Gene expression of TRPC3, TRPC4, TRPC5, TRPC6 and TRPC7 in heart tissues from the test group showed no significant differences compared with controls. However, TRPC1 protein levels, as well as mRNA levels, were down-regulated in the heart muscle of AS chickens (P < 0.05). Although we observed an increase in calcium concentration, the expression of TRPC1 decreased in cardiac cells. We hypothesized that an increase in intracellular free calcium concentration could inversely regulate calcium channel expression. RESEARCH HIGHLIGHTS Intracellular Ca²⁺ levels were increased in the myocardium of AS broilers. Expression of TRPC1, which mediates calcium influx, was decreased in the myocardium of AS broilers. The relationship between intracellular Ca²⁺ levels and expression of TRPC1 requires further study.

Ligands Exert Biased Activity to Regulate Sigma 1 Receptor Interactions With Cationic TRPA1, TRPV1, and TRPM8 Channels

The sigma 1 receptor (σ1R) and the mu-opioid receptor (MOR) regulate the transient receptor potential (TRP) V1 calcium channel. A series of proteins are involved in the cross-regulation between MORs and calcium channels like the glutamate N-methyl-D-aspartate receptor (NMDAR), including the histidine triad nucleotide-binding protein 1 (HINT1), calmodulin (CaM), and the σ1R. Thus, we assessed whether similar mechanisms also apply to the neural TRP ankyrin member 1 (TRPA1), TRP vanilloid member 1 (TRPV1), and TRP melastatin member 8 (TRPM8). Our results indicate that σ1R and CaM bound directly to cytosolic regions of these TRPs, and this binding increased in the presence of calcium. By contrast, the association of HINT1 with these TRPs was moderately dependent on calcium. The σ1R always competed with CaM for binding to the TRPs, except for its binding to the TRPA1 C-terminal where σ1R binding cooperated with that of CaM. However, σ1R dampened HINT1 binding to the TRPA1 N-terminal. When the effect of σ1R ligands was addressed, the σ1R agonists PRE084 and pregnenolone sulfate enhanced the association of the σ1R with the TRPM8 N-terminal and TRPV1 C-terminal in the presence of physiological calcium, as seen for the σ1R-NMDAR interactions. However, these agonists dampened σ1R binding to the TRPA1 and TRPV1 N-terminal domains, and also to the TRPA1 C-terminal, as seen for σ1R-binding immunoglobulin protein (BiP) interactions in the endoplasmic reticulum (ER). By contrast, the σ1R antagonists progesterone and S1RA reduced the association of σ1R with TRPA1 and TRPV1 C-terminal regions, as seen for the σ1R-NMDAR interactions. Conversely, they enhanced the σ1R interaction with the TRPA1 N-terminal, as seen for σ1R-BiP interactions, whereas they barely affected the association of σ1R with the TRPV1 N-terminal. Thus, depending on the calcium channel and the cytosolic region examined, the σ1R agonists pregnenolone sulfate and PRE084 opposed or collaborated with the σ1R antagonists progesterone and S1RA to disrupt or promote such interactions. Through the use of cloned cytosolic regions of selected TRP calcium channels, we were able to demonstrate that σ1R ligands exhibit biased activity to regulate particular σ1R interactions with other proteins. Since σ1Rs are implicated in essential physiological processes, exploiting such ligand biases may represent a means to develop more selective and efficacious pharmacological interventions.

Reduced transient receptor potential vanilloid 2 expression in alveolar macrophages causes COPD in mice through impaired phagocytic activity

Background

Defective phagocytosis in alveolar macrophages is associated with chronic obstructive pulmonary disease (COPD). Transient receptor potential cation channel subfamily V member 2 (TRPV2), a type of nonselective cation channel pertinent to diverse physiological functions, regulates macrophage phagocytosis. However, the role of TRPV2 in COPD remains poorly understood. Here, we explored the role of TRPV2 in the development of COPD.

Methods

Macrophage TRPV2 expression and phagocytosis function were measured in MH-S cells (a murine alveolar macrophage cell line) and a cigarette smoke exposure mouse model.

Results

TRPV2 expression and phagocytosis function were reduced when MH-S cells were exposed to cigarette smoke extract (CSE). TRPV2 knockdown by siRNA decreased phagocytosis in MH-S cells. Consistently, TRPV2 expression was reduced in alveolar macrophages prepared from bronchoalveolar lavage samples of mice which were exposed to cigarette smoke for 2 months. In addition, the alveolar space was progressively enlarged during development in TRPV2 knockout (TRPV2KO) mice. Moreover, exposure to cigarette smoke for 2 months significantly induced alveolar space enlargement in TRPV2KO mice, but not in wild-type (WT) mice. The phagocytic function of alveolar macrophages from TRPV2KO mice was reduced, compared with macrophages from WT mice.

Conclusions

TRPV2 expression is profoundly downregulated in alveolar macrophages at early time points of cigarette smoke exposure. Reduced TRPV2-mediated phagocytic function renders the lung susceptible to cigarette smoke-induced alveolar space enlargement. TRPV2 may provide a therapeutic target for COPD induced by cigarette smoke.

Electronic supplementary material

The online version of this article (10.1186/s12890-019-0821-y) contains supplementary material, which is available to authorized users.

TRPC-mediated Ca2+ signaling and control of cellular functions

Canonical members of the TRP superfamily of ion channels have long been recognized as key elements of Ca²⁺ handling in a plethora of cell types. The emerging role of TRPC channels in human physiopathology has generated considerable interest in their pharmacological targeting, which requires detailed understanding of their molecular function. Although consent has been reached that receptor-phospholipase C (PLC) pathways and generation of lipid mediators constitute the prominent upstream signaling process that governs channel activity, multimodal sensing features of TRPC complexes have been demonstrated repeatedly. Downstream signaling by TRPC channels is similarly complex and involves the generation of local and global cellular Ca²⁺ rises, which are well-defined in space and time to govern specific cellular functions. These TRPC-mediated Ca²⁺ signals rely in part on Ca²⁺ permeation through the channels, but are essentially complemented by secondary mechanisms such as Ca²⁺ mobilization from storage sites and Na⁺/Ca²⁺ exchange, which involve coordinated interaction with signaling partners. Consequently, the control of cell functions by TRPC molecules is critically determined by dynamic assembly and subcellular targeting of the TRPC complexes. The very recent availability of high-resolution structure information on TRPC channel complexes has paved the way towards a comprehensive understanding of signal transduction by TRPC channels. Here, we summarize current concepts of cation permeation in TRPC complexes, TRPC-mediated shaping of cellular Ca²⁺ signals and the associated control of specific cell functions.

Store-operated calcium entry in thrombosis and thrombo-inflammation

Cytosolic free calcium (Ca²⁺) is a second messenger regulating a wide variety of functions in blood cells, including adhesion, activation, proliferation and migration. Store-operated Ca²⁺ entry (SOCE), triggered by depletion of Ca²⁺ from the endoplasmic reticulum, provides a main mechanism of regulated Ca²⁺ influx in blood cells. SOCE is mediated and regulated by isoforms of the ion channel proteins ORAI and TRP, and the transmembrane Ca²⁺ sensors stromal interaction molecules (STIMs), respectively. This report provides an overview of the (patho)physiological importance of SOCE in blood cells implicated in thrombosis and thrombo-inflammation, i.e. platelets and immune cells. We also discuss the physiological consequences of dysregulated SOCE in platelets and immune cells and the potential of SOCE inhibition as a therapeutic option to prevent or treat arterial thrombosis as well as thrombo-inflammatory disease states such as ischemic stroke.

Ion Channels in Pulmonary Hypertension: A Therapeutic Interest?

Pulmonary arterial hypertension (PAH) is a multifactorial and severe disease without curative therapies. PAH pathobiology involves altered pulmonary arterial tone, endothelial dysfunction, distal pulmonary vessel remodeling, and inflammation, which could all depend on ion channel activities (K⁺, Ca²⁺, Na⁺ and Cl^-). This review focuses on ion channels in the pulmonary vasculature and discusses their pathophysiological contribution to PAH as well as their therapeutic potential in PAH.

Activation of TRPC1 Channel by Metabotropic Glutamate Receptor mGluR5 Modulates Synaptic Plasticity and Spatial Working Memory

Group I metabotropic glutamate receptors, in particular mGluR5, have been implicated in various forms of synaptic plasticity that are believed to underlie declarative memory. We observed that mGluR5 specifically activated a channel containing TRPC1, an isoform of the canonical family of transient receptor potential (TRPC) channels highly expressed in CA1-3 regions of the hippocampus. TRPC1 is able to form tetrameric complexes with TRPC4 and/or TRPC5 isoforms. TRPC1/4/5 complexes have recently been involved in the efficiency of synaptic transmission in the hippocampus. We therefore used a mouse model devoid of TRPC1 expression to investigate the involvement of mGluR5-TRPC1 pathway in synaptic plasticity and memory formation. Trpc1^-/- mice showed alterations in spatial working memory and fear conditioning. Activation of mGluR increased synaptic excitability in neurons from WT but not from Trpc1^-/- mice. LTP triggered by a theta burst could not maintain over time in brain slices from Trpc1^-/- mice. mGluR-induced LTD was also impaired in these mice. Finally, acute inhibition of TRPC1 by Pico145 on isolated neurons or on brain slices mimicked the genetic depletion of Trpc1 and inhibited mGluR-induced entry of cations and subsequent effects on synaptic plasticity, excluding developmental or compensatory mechanisms in Trpc1^-/- mice. In summary, our results indicate that TRPC1 plays a role in synaptic plasticity and spatial working memory processes.

TRP Channels as Sensors of Bacterial Endotoxins

The cellular and systemic effects induced by bacterial lipopolysaccharides (LPS) have been solely attributed to the activation of the Toll-like receptor 4 (TLR4) signalling cascade. However, recent studies have shown that LPS activates several members of the Transient Receptor Potential (TRP) family of cation channels. Indeed, LPS induces activation of the broadly-tuned chemosensor TRPA1 in sensory neurons in a TLR4-independent manner, and genetic ablation of this channel reduced mouse pain and inflammatory responses triggered by LPS and the gustatory-mediated avoidance to LPS in fruit flies. LPS was also shown to activate TRPV4 channels in airway epithelial cells, an effect leading to an immediate production of bactericidal nitric oxide and to an increase in ciliary beat frequency. In this review, we discuss the role of TRP channels as sensors of bacterial endotoxins, and therefore, as crucial players in the timely detection of invading gram-negative bacteria.

Establishing life is a calcium-dependent TRiP: Transient receptor potential channels in reproduction

Calcium plays a key role in many different steps of the reproduction process, from germ cell maturation to placental development. However, the exact function and regulation of calcium throughout subsequent reproductive events remains rather enigmatic. Successful pregnancy requires the establishment of a complex dialogue between the implanting embryo and the endometrium. On the one hand, endometrial cell will undergo massive changes to support an implanting embryo, including stromal cell decidualization. On the other hand, trophoblast cells from the trophectoderm surrounding the inner cell mass will differentiate and acquire new functions such as hormone secretion, invasion and migration. The need for calcium in the different gestational processes implicates the presence of specialized ion channels to regulate calcium homeostasis. The superfamily of transient receptor potential (TRP) channels is a class of calcium permeable ion channels that is involved in the transformation of extracellular stimuli into the influx of calcium, inducing and coordinating underlying signaling pathways. Although the necessity of calcium throughout reproduction cannot be negated, the expression and functionality of TRP channels throughout gestation remains elusive. This review provides an overview of the current evidence regarding the expression and function of TRP channels in reproduction.

Regulation of Pain and Itch by TRP Channels

Nociception is an important physiological process that detects harmful signals and results in pain perception. In this review, we discuss important experimental evidence involving some TRP ion channels as molecular sensors of chemical, thermal, and mechanical noxious stimuli to evoke the pain and itch sensations. Among them are the TRPA1 channel, members of the vanilloid subfamily (TRPV1, TRPV3, and TRPV4), and finally members of the melastatin group (TRPM2, TRPM3, and TRPM8). Given that pain and itch are pro-survival, evolutionarily-honed protective mechanisms, care has to be exercised when developing inhibitory/modulatory compounds targeting specific pain/itch-TRPs so that physiological protective mechanisms are not disabled to a degree that stimulus-mediated injury can occur. Such events have impeded the development of safe and effective TRPV1-modulating compounds and have diverted substantial resources. A beneficial outcome can be readily accomplished via simple dosing strategies, and also by incorporating medicinal chemistry design features during compound design and synthesis. Beyond clinical use, where compounds that target more than one channel might have a place and possibly have advantageous features, highly specific and high-potency compounds will be helpful in mechanistic discovery at the structure-function level.

Schwann cell TRPA1 mediates neuroinflammation that sustains macrophage-dependent neuropathic pain in mice

It is known that transient receptor potential ankyrin 1 (TRPA1) channels, expressed by nociceptors, contribute to neuropathic pain. Here we show that TRPA1 is also expressed in Schwann cells. We found that in mice with partial sciatic nerve ligation, TRPA1 silencing in nociceptors attenuated mechanical allodynia, without affecting macrophage infiltration and oxidative stress, whereas TRPA1 silencing in Schwann cells reduced both allodynia and neuroinflammation. Activation of Schwann cell TRPA1 evoked NADPH oxidase 1 (NOX1)-dependent H2O2 release, and silencing or blocking Schwann cell NOX1 attenuated nerve injury-induced macrophage infiltration, oxidative stress and allodynia. Furthermore, the NOX2-dependent oxidative burst, produced by macrophages recruited to the perineural space activated the TRPA1-NOX1 pathway in Schwann cells, but not TRPA1 in nociceptors. Schwann cell TRPA1 generates a spatially constrained gradient of oxidative stress, which maintains macrophage infiltration to the injured nerve, and sends paracrine signals to activate TRPA1 of ensheathed nociceptors to sustain mechanical allodynia.

Disrupted Ionic Homeostasis in Ischemic Stroke and New Therapeutic Targets

BACKGROUND

Stroke is a leading cause of long-term disability. All neuroprotectants targeting excitotoxicity have failed to become stroke medications. In order to explore and identify new therapeutic targets for stroke, we here reviewed present studies of ionic transporters and channels that are involved in ischemic brain damage.

METHOD

We surveyed recent literature from animal experiments and clinical reports in the databases of PubMed and Elsevier ScienceDirect to analyze ionic mechanisms underlying ischemic cell damage and suggest promising ideas for stroke therapy.

RESULTS

Dysfunction of ionic transporters and disrupted ionic homeostasis are most early changes that underlie ischemic brain injury, thus receiving sustained attention in translational stroke research. The Na⁺/K⁺-ATPase, Na⁺/Ca²⁺ Exchanger, ionotropic glutamate receptor, acid-sensing ion channels (ASICs), sulfonylurea receptor isoform 1 (SUR1)-regulated NC_Ca-ATP channels, and transient receptor potential (TRP) channels are critically involved in ischemia-induced cellular degenerating processes such as cytotoxic edema, excitotoxicity, necrosis, apoptosis, and autophagic cell death. Some ionic transporters/channels also act as signalosomes to regulate cell death signaling. For acute stroke treatment, glutamate-mediated excitotoxicity must be interfered within 2 hours after stroke. The SUR1-regulated NC_Ca-ATP channels, Na⁺/K⁺-ATPase, ASICs, and TRP channels have a much longer therapeutic window, providing new therapeutic targets for developing feasible pharmacological treatments toward acute ischemic stroke.

CONCLUSION

The next generation of stroke therapy can apply a polypharmacology strategy for which drugs are designed to target multiple ion transporters/channels or their interaction with neurotoxic signaling pathways. But a successful translation of neuroprotectants relies on in-depth analyses of cell death mechanisms and suitable animal models resembling human stroke.

Role of TRPM7 in Cancer: Potential as Molecular Biomarker and Therapeutic Target

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a ubiquitously expressed ion channel with intrinsic kinase activity. Molecular and electrophysiological analyses of the structure and activity of TRPM7 have revealed functional coupling of its channel and kinase activity. Studies have indicated the important roles of TRPM7 channel-kinase in fundamental cellular processes, physiological responses, and embryonic development. Accumulating evidence has shown that TRPM7 is aberrantly expressed and/or activated in human diseases including cancer. TRPM7 plays a variety of functional roles in cancer cells including survival, cell cycle progression, proliferation, growth, migration, invasion, and epithelial-mesenchymal transition (EMT). Data from a study using mouse xenograft of human cancer show that TRPM7 is required for tumor growth and metastasis. The aberrant expression of TRPM7 and its genetic mutations/polymorphisms have been identified in various types of carcinoma. Chemical modulators of TRPM7 channel produced inhibition of proliferation, growth, migration, invasion, invadosome formation, and markers of EMT in cancer cells. Taken together, these studies suggest the potential value of exploiting TRPM7 channel-kinase as a molecular biomarker and therapeutic target in human malignancies.

Ion channels or aquaporins as novel molecular targets in gastric cancer

Gastric cancer (GC) is a common disease with few effective treatment choices and poor prognosis, and has the second-highest mortality rates among all cancers worldwide. Dysregulation and/or malfunction of ion channels or aquaporins (AQPs) are common in various human cancers. Furthermore, ion channels are involved in numerous important aspects of the tumor aggressive phonotype, such as proliferation, cell cycle, apoptosis, motility, migration, and invasion. Indeed, by localizing in the plasma membrane, ion channels or AQPs can sense and respond to extracellular environment changes; thus, they play a crucial role in cell signaling and cancer progression. These findings have expanded a new area of pharmaceutical exploration for various types of cancer, including GC. The involvement of multiple ion channels, such as voltage-gated potassium and sodium channels, intracellular chloride channels, ‘transient receptor potential’ channels, and AQPs, which have been shown to facilitate the pathogenesis of other tumors, also plays a role in GC. In this review, an overview of ion channel and aquaporin expression and function in carcinogenesis of GC is presented. Studies of ion channels or AQPs will advance our understanding of the molecular genesis of GC and may identify novel and effective targets for the clinical application of GC.

Identification and Expression Analysis of the Complete Family of Zebrafish pkd Genes

Polycystic kidney disease (PKD) proteins are trans-membrane proteins that have crucial roles in many aspects of vertebrate development and physiology, including the development of many organs as well as left–right patterning and taste. They can be divided into structurally-distinct PKD1-like and PKD2-like proteins and usually one PKD1-like protein forms a heteromeric polycystin complex with a PKD2-like protein. For example, PKD1 forms a complex with PKD2 and mutations in either of these proteins cause Autosomal Dominant Polycystic Kidney Disease (ADPKD), which is the most frequent potentially-lethal single-gene disorder in humans. Here, we identify the complete family of pkd genes in zebrafish and other teleosts. We describe the genomic locations and sequences of all seven genes: pkd1, pkd1b, pkd1l1, pkd1l2a, pkd1l2b, pkd2, and pkd2l1. pkd1l2a/pkd1l2b are likely to be ohnologs of pkd1l2, preserved from the whole genome duplication that occurred at the base of the teleosts. However, in contrast to mammals and cartilaginous and holostei fish, teleosts lack pkd2l2, and pkdrej genes, suggesting that these have been lost in the teleost lineage. In addition, teleost, and holostei fish have only a partial pkd1l3 sequence, suggesting that this gene may be in the process of being lost in the ray-finned fish lineage. We also provide the first comprehensive description of the expression of zebrafish pkd genes during development. In most structures we detect expression of one pkd1-like gene and one pkd2-like gene, consistent with these genes encoding a heteromeric protein complex. For example, we found that pkd2 and pkd1l1 are expressed in Kupffer's vesicle and pkd1 and pkd2 are expressed in the developing pronephros. In the spinal cord, we show that pkd1l2a and pkd2l1 are co-expressed in KA cells. We also identify potential co-expression of pkd1b and pkd2 in the floor-plate. Interestingly, and in contrast to mouse, we observe expression of all seven pkd genes in regions that may correspond to taste receptors. Taken together, these results provide a crucial catalog of pkd genes in an important model system for elucidating cell and developmental processes and modeling human diseases and the most comprehensive analysis of embryonic pkd gene expression in any vertebrate.

Side chain flexibility and coupling between the S4-S5 linker and the TRP domain in thermo-sensitive TRP channels: Insights from protein modeling

The transient receptor potential (TRP) superfamily is subdivided into several subfamilies on the basis of sequence similarity, which is highly heterogeneous but shows a molecular architecture that resembles the one present in members of the Kv channel superfamily. Because of this diversity, they produce a large variety of channels with different gating and permeability properties. Elucidation of these particular features necessarily requires comparative studies based on structural and functional data. The present study aims to compilate, analyze, and determine, in a coherent way, the relationship between intrinsic side-chain flexibility and the allosteric coupling in members of the TRPV, TRPM, and TRPC families. Based on the recently determined structures of TRPV1 and TRPV2, we have generated protein models for single subunits of TRPV5, TRPM8, and TRPC5 channels. With these models, we focused our attention on the apparently crucial role of the GP dipeptide at the center of the S4-S5 linker and discussed its role in the interaction with the TRP domain, specifically with the highly-conserved Trp during this coupling. Our analysis suggests an important role of the S4-S5L flexibility in the thermosensitivity, where heat-activated channels possess rigid S4-S5 linkers, whereas cold-activated channels have flexible ones. Finally, we also present evidence of the key interaction between the conserved Trp residue of the TRP box and of several residues in the S4-S5L, importantly the central Pro. Proteins 2017; 85:630-646. © 2016 Wiley Periodicals, Inc.

Endocannabinoid system and anticancer properties of cannabinoids

Cannabinoids impact human body by binding to cannabinoids receptors (CB1 and CB2). The two main phytocannabinoids are Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC interacts with CB1 receptors occurring in central nervous system and is responsible for psychoactive properties of marijuana. CBD has low affinity to CB1 receptor, has no psychoactive characteristics and its medical applications can be wider. CB receptors are part of a complex machinery involved in regulation of many physiological processes – endocannabinoid system. Cannabinoids have found some applications in palliative medicine, but there are many reports concerning their anticancer affects. Agonists of CB1 receptors stimulate accumulation of ceramides in cancer cells, stress of endoplasmic reticulum (ER stress) and, in turn, apoptosis. Effects of cannabinoids showing low affinity to CB receptors is mediated probably by induction of reactive oxygen species production.  Knowledge of antitumor activity of cannabinoids is still based only on preclinical studies and there is a necessity to conduct more experiments to assess the real potential of these compounds.

TRP channels in calcium homeostasis: from hormonal control to structure-function relationship of TRPV5 and TRPV6

Maintaining plasma calcium levels within a narrow range is of vital importance for many physiological functions. Therefore, calcium transport processes in the intestine, bone and kidney are tightly regulated to fine-tune the rate of absorption, storage and excretion. The TRPV5 and TRPV6 calcium channels are viewed as the gatekeepers of epithelial calcium transport. Several calciotropic hormones control the channels at the level of transcription, membrane expression, and function. Recent technological advances have provided the first near-atomic resolution structural models of several TRPV channels, allowing insight into their architecture. While this field is still in its infancy, it has increased our understanding of molecular channel regulation and holds great promise for future structure-function studies of these ion channels. This review will summarize the mechanisms that control the systemic calcium balance, as well as extrapolate structural views to the molecular functioning of TRPV5/6 channels in epithelial calcium transport.

Channels and Volume Changes in the Life and Death of the Cell

Volume changes deviating from original cell volume represent a major challenge for cellular homeostasis. Cell volume may be altered either by variations in the external osmolarity or by disturbances in the transmembrane ion gradients that generate an osmotic imbalance. Cells respond to anisotonicity-induced volume changes by active regulatory mechanisms that modify the intracellular/extracellular concentrations of K(+), Cl(-), Na(+), and organic osmolytes in the direction necessary to reestablish the osmotic equilibrium. Corrective osmolyte fluxes permeate across channels that have a relevant role in cell volume regulation. Channels also participate as causal actors in necrotic swelling and apoptotic volume decrease. This is an overview of the types of channels involved in either corrective or pathologic changes in cell volume. The review also underlines the contribution of transient receptor potential (TRP) channels, notably TRPV4, in volume regulation after swelling and describes the role of other TRPs in volume changes linked to apoptosis and necrosis. Lastly we discuss findings showing that multimers derived from LRRC8A (leucine-rich repeat containing 8A) gene are structural components of the volume-regulated Cl(-) channel (VRAC), and we underline the intriguing possibility that different heteromer combinations comprise channels with different intrinsic properties that allow permeation of the heterogenous group of molecules acting as organic osmolytes.

Store-operated CRAC channel inhibitors: opportunities and challenges

Aberrant Ca(2+) release-activated Ca(2+) (CRAC) channel activity has been implicated in a number of human disorders, including immunodeficiency, autoimmunity, occlusive vascular diseases and cancer, thus placing CRAC channels among the important targets for the treatment of these disorders. We briefly summarize herein the molecular basis and activation mechanism of CRAC channel and focus on discussing several pharmacological inhibitors of CRAC channels with respect to their biological activity, mechanisms of action and selectivity over other types of Ca(2+) channel in different types of cells.

Role of TRP ion channels in cancer and tumorigenesis

Transient receptor potential (TRP) channels are recently identified proteins that form a versatile family of ion channels, the majority of which are calcium permeable and exhibit complex regulatory patterns with sensitivity to multiple environmental factors. While this sensitivity has captured early attention, leading to recognition of TRP channels as environmental and chemical sensors, many later studies concentrated on the regulation of intracellular calcium by TRP channels. Due to mutations, dysregulation of ion channel gating or expression levels, normal spatiotemporal patterns of local Ca(2+) distribution become distorted. This causes deregulation of downstream effectors sensitive to changes in Ca(2+) homeostasis that, in turn, promotes pathophysiological cancer hallmarks, such as enhanced survival, proliferation and invasion. These observations give rise to the appreciation of the important contributions that TRP channels make to many cellular processes controlling cell fate and positioning these channels as important players in cancer regulation. This review discusses the accumulated scientific knowledge focused on TRP channel involvement in regulation of cell fate in various transformed tissues.

Increased expression of transient receptor potential canonical 6 (TRPC6) in differentiating human megakaryocytes

Members of the transient receptor potential (TRP) family of cation conducting channels are found in several tissues and cell types where they have different physiological functions. The canonical TRP channel 6 (TRPC6) is present on the platelet membrane and appears to participate in calcium influx during platelet activation. However, limited information is available on the importance of TRPC channels in megakaryocytes (MKs), the precursor cells of platelets. We determined the mRNA and protein expression of TRPC family members and investigated the role of TRPC6 for proliferation and differentiation of human MKs derived from CD34+ progenitor cells. TRPC6 transcripts were highly expressed during the differentiation of MKs and TRPC6 protein was detectable in MK cytoplasm by confocal staining. TRPC6 channel activity was modulated by pharmacological approaches using flufenamic acid (FFA) for activation and SKF96365 for inhibition. Upon FFA stimulation in MKs, an increase in intracellular calcium was observed, which was blocked by SKF96365 at 10 µM concentration. Incubation of MKs with SKF96365 resulted in a reduction in thrombopoietin-stimulated cell proliferation. Our results suggest a role of TRPC6 in calcium homeostasis during MK development, particularly for cell proliferation.

Regulation of calcium channels in smooth muscle: new insights into the role of myosin light chain kinase

Smooth muscle myosin light chain kinase (MLCK) plays a crucial role in artery contraction, which regulates blood pressure and blood flow distribution. In addition to this role, MLCK contributes to Ca(2+) flux regulation in vascular smooth muscle (VSM) and in non-muscle cells, where cytoskeleton has been suggested to help Ca(2+) channels trafficking. This conclusion is based on the use of pharmacological inhibitors of MLCK and molecular and cellular techniques developed to down-regulate the enzyme. Dissimilarities have been observed between cells and whole tissues, as well as between large conductance and small resistance arteries. A differential expression in MLCK and ion channels (either voltage-dependent Ca(2+) channels or non-selective cationic channels) could account for these observations, and is in line with the functional properties of the arteries. A potential involvement of MLCK in the pathways modulating Ca(2+) entry in VSM is described in the present review.

SOCE and cancer: Recent progress and new perspectives

Ca²⁺ acts as a universal and versatile second messenger in the regulation of a myriad of biological processes, including cell proliferation, differentiation, migration and apoptosis. Store‐operated Ca²⁺ entry (SOCE) mediated by ORAI and the stromal interaction molecule (STIM) constitutes one of the major routes of calcium entry in nonexcitable cells, in which the depletion of intracellular Ca²⁺ stores triggers activation of the endoplasmic reticulum (ER)‐resident Ca²⁺ sensor protein STIM to gate and open the ORAI Ca²⁺ channels in the plasma membrane (PM). Accumulating evidence indicates that SOCE plays critical roles in cancer cell proliferation, metastasis and tumor neovascularization, as well as in antitumor immunity. We summarize herein the recent advances in our understanding of the function of SOCE in various types of tumor cells, vascular endothelial cells and cells of the immune system. Finally, the therapeutic potential of SOCE inhibitors in the treatment of cancer is also discussed.

Comparative sequence analysis suggests a conserved gating mechanism for TRP channels

The transient receptor potential (TRP) channel superfamily plays a central role in transducing diverse sensory stimuli in eukaryotes. Although dissimilar in sequence and domain organization, all known TRP channels act as polymodal cellular sensors and form tetrameric assemblies similar to those of their distant relatives, the voltage-gated potassium (Kv) channels. Here, we investigated the related questions of whether the allosteric mechanism underlying polymodal gating is common to all TRP channels, and how this mechanism differs from that underpinning Kv channel voltage sensitivity. To provide insight into these questions, we performed comparative sequence analysis on large, comprehensive ensembles of TRP and Kv channel sequences, contextualizing the patterns of conservation and correlation observed in the TRP channel sequences in light of the well-studied Kv channels. We report sequence features that are specific to TRP channels and, based on insight from recent TRPV1 structures, we suggest a model of TRP channel gating that differs substantially from the one mediating voltage sensitivity in Kv channels. The common mechanism underlying polymodal gating involves the displacement of a defect in the H-bond network of S6 that changes the orientation of the pore-lining residues at the hydrophobic gate.

TRP ion channels in thermosensation, thermoregulation and metabolism

In humans, the TRP superfamily of cation channels includes 27 related molecules that respond to a remarkable variety of chemical and physical stimuli. While physiological roles for many TRP channels remain unknown, over the past years several have been shown to function as molecular sensors in organisms ranging from yeast to humans. In particular, TRP channels are now known to constitute important components of sensory systems, where they participate in the detection or transduction of osmotic, mechanical, thermal, or chemosensory stimuli. We here summarize our current understanding of the role individual members of this versatile receptor family play in thermosensation and thermoregulation, and also touch upon their immerging role in metabolic control.

The TRPA1 channel in inflammatory and neuropathic pain and migraine

The transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily of channels, is primarily localized to a subpopulation of primary sensory neurons of the trigeminal, vagal, and dorsal root ganglia. This subset of nociceptors produces and releases the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), which mediate neurogenic inflammatory responses. TRPA1 is activated by a number of exogenous compounds, including molecules of botanical origin, environmental irritants, and medicines. However, the most prominent feature of TRPA1 resides in its unique sensitivity for large series of reactive byproducts of oxidative and nitrative stress. Here, the role of TRPA1 in models of different types of pain, including inflammatory and neuropathic pain and migraine, is summarized. Specific attention is paid to TRPA1 as the main contributing mechanism to the transition of mechanical and cold hypersensitivity from an acute to a chronic condition and as the primary transducing pathway by which oxidative/nitrative stress produces acute nociception, allodynia, and hyperalgesia. A series of migraine triggers or medicines have been reported to modulate TRPA1 activity and the ensuing CGRP release. Thus, TRPA1 antagonists may be beneficial in the treatment of inflammatory and neuropathic pain and migraine.

A novel PKD2L1 C-terminal domain critical for trimerization and channel function

As a transient receptor potential (TRP) superfamily member, polycystic kidney disease 2-like-1 (PKD2L1) is also called TRPP3 and has similar membrane topology as voltage-gated cation channels. PKD2L1 is involved in hedgehog signaling, intestinal development, and sour tasting. PKD2L1 and PKD1L3 form heterotetramers with 3:1 stoichiometry. C-terminal coiled-coil-2 (CC2) domain (G699-W743) of PKD2L1 was reported to be important for its trimerization but independent studies showed that CC2 does not affect PKD2L1 channel function. It thus remains unclear how PKD2L1 proteins oligomerize into a functional channel. By SDS-PAGE, blue native PAGE and mutagenesis we here identified a novel C-terminal domain called C1 (K575-T622) involved in stronger homotrimerization than the non-overlapping CC2, and found that the PKD2L1 N-terminus is critical for dimerization. By electrophysiology and Xenopus oocyte expression, we found that C1, but not CC2, is critical for PKD2L1 channel function. Our co-immunoprecipitation and dynamic light scattering experiments further supported involvement of C1 in trimerization. Further, C1 acted as a blocking peptide that inhibits PKD2L1 trimerization as well as PKD2L1 and PKD2L1/PKD1L3 channel function. Thus, our study identified C1 as the first PKD2L1 domain essential for both PKD2L1 trimerization and channel function, and suggest that PKD2L1 and PKD2L1/PKD1L3 channels share the PKD2L1 trimerization process.

Copper-induced activation of TRP channels promotes extracellular calcium entry, activation of CaMs and CDPKs, copper entry and membrane depolarization in Ulva compressa

In order to identify channels involved in membrane depolarization, Ulva compressa was incubated with agonists of TRP channels C5, A1 and V1, and the level of intracellular calcium was detected. Agonists of TRPC5, A1 and V1 induced increases in intracellular calcium at 4, 9, and 11 min of exposure, respectively, and antagonists of TRPC5, A1, and V1 corresponding to SKF-96365 (SKF), HC-030031 (HC), and capsazepin (CPZ), respectively, inhibited calcium increases indicating that functional TRPs exist in U. compressa. In addition, copper excess induced increases in intracellular calcium at 4, 9, and 12 min which were inhibited by SKF, HC, and CPZ, respectively, indicating that copper activate TRPC5, A1, and V1 channels. Moreover, copper-induced calcium increases were inhibited by EGTA, a non-permeable calcium chelating agent, but not by thapsigargin, an inhibitor of endoplasmic reticulum (ER) calcium ATPase, indicating that activation of TRPs leads to extracellular calcium entry. Furthermore, copper-induced calcium increases were not inhibited by W-7, an inhibitor of CaMs, and staurosporine, an inhibitor of CDPKs, indicating that extracellular calcium entry did not require activation of CaMs and CDPKs. In addition, copper induced membrane depolarization events at 4, 8, and 11 min and these events were inhibited by SKF, HC, CPZ, and bathocuproine, a specific copper chelating agent, indicating that copper entry through TRP channels leads to membrane depolarization. Moreover, membrane depolarization events were inhibited by W-7 and staurosporine, indicating that activation of CaMs and CDPKs is required to allow copper entry through TRPs. Interestingly, copper-induced calcium increases and depolarization events were light-dependent and were inhibited by DCMU, an inhibitor of photosystem II, and ATP-γ-S, a non-hydrolizable analog of ATP, suggesting that ATP derived from photosynthesis is required to activate TRPs. Thus, light-dependent copper-induced activation TRPC5, A1 and V1 promotes extracellular calcium entry leading to activation of CaMs and CDPKs which, in turn, promotes copper entry through TRP channels and membrane depolarization.