Blocking swelling-activated chloride current inhibits mouse liver cell proliferation

Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206

Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.

A SWELL time to develop the molecular pharmacology of the volume-regulated anion channel (VRAC)

Newly emerging roles of LRRC8 volume-regulated anion channels (VRAC) raise important questions about the therapeutic potential of VRAC in the treatment of epilepsy, type 2 diabetes, and other human diseases. A critical barrier to evaluating whether VRAC represents a viable drug target is the lack of potent and specific small-molecule inhibitors and activators of the channel. Here we review recent progress in developing the molecular pharmacology of VRAC made by screening a library of FDA-approved drugs for novel channel modulators. We discuss the discovery and characterization of cysteinyl leukotriene receptor antagonists Pranlukast and Zafirlukast as novel VRAC inhibitors, and zinc pyrithione (ZPT), which apparently activates VRAC through a reactive oxygen species (ROS)-dependent mechanism. These ongoing efforts set the stage for developing a pharmacological toolkit for probing the integrative physiology, molecular pharmacology, and therapeutic potential of VRAC.

An Update On Proficiency of Voltage-gated Ion Channel Blockers in the Treatment of Inflammation-associated Diseases

Inflammation is the body's mechanism to trigger the immune system, thereby preventing bacteria and viruses from manifesting their toxic effect. Inflammation plays a vital role in regulating inflammatory mediator levels to initiate the wound healing process depending on the nature of the stimuli. This process occurs due to chemical release from white blood cells by elevating blood flow to the site of action, leading to redness and increased body temperature. Currently, there are numerous Non-steroidal anti-inflammatory drugs (NSAIDs) available, but these drugs are reported with adverse effects such as gastric bleeding, progressive kidney damage, and increased risk of heart attacks when prolonged use. For such instances, alternative options need to be adopted. The introduction of voltage-gated ion channel blockers can be a substantial alternative to mask the side effects of these currently available drugs. Chronic inflammatory disorders such as rheumatoid and osteoarthritis, cancer and migraine, etc., can cause dreadful pain, which is often debilitating for the patient. The underlying mechanism for both acute and chronic inflammation involves various complex receptors, different types of cells, receptors, and proteins. The working of voltage-gated sodium and calcium channels is closely linked to both inflammatory and neuropathic pain. Certain drugs such as carbamazepine and gabapentin, which are ion channel blockers, have greater pharmacotherapeutic activity for sodium and calcium channel blockers for the treatment of chronic inflammatory pain states. This review intends to provide brief information on the mechanism of action, latest clinical trials, and applications of these blockers in treating inflammatory conditions.

How Dysregulated Ion Channels and Transporters Take a Hand in Esophageal, Liver, and Colorectal Cancer

Over the last two decades, the understanding of how dysregulated ion channels and transporters are involved in carcinogenesis and tumor growth and progression, including invasiveness and metastasis, has been increasing exponentially. The present review specifies virtually all ion channels and transporters whose faulty expression or regulation contributes to esophageal, hepatocellular, and colorectal cancer. The variety reaches from Ca²⁺, K⁺, Na⁺, and Cl^- channels over divalent metal transporters, Na⁺ or Cl^- coupled Ca²⁺, HCO₃^- and H⁺ exchangers to monocarboxylate carriers and organic anion and cation transporters. In several cases, the underlying mechanisms by which these ion channels/transporters are interwoven with malignancies have been fully or at least partially unveiled. Ca²⁺, Akt/NF-κB, and Ca²⁺- or pH-dependent Wnt/β-catenin signaling emerge as cross points through which ion channels/transporters interfere with gene expression, modulate cell proliferation, trigger epithelial-to-mesenchymal transition, and promote cell motility and metastasis. Also miRs, lncRNAs, and DNA methylation represent potential links between the misexpression of genes encoding for ion channels/transporters, their malfunctioning, and cancer. The knowledge of all these molecular interactions has provided the basis for therapeutic strategies and approaches, some of which will be broached in this review.

Role of ion channels during cell division

Ion channels are transmembrane proteins whose canonical function is the transport of ions across the plasma membrane to regulate cell membrane potential and play an essential role in neural communication, nerve conduction, and muscle contraction. However, over the last few years, non-canonical functions have been identified for many channels, having active roles in phagocytosis, invasiveness, proliferation, among others. The participation of some channels in cell proliferation has raised the question of whether they may play an active role in mitosis. There are several reports showing the participation of channels during interphase, however, the direct participation of ion channels in mitosis has received less attention. In this article, we summarize the current evidence on the participation of ion channels in mitosis. We also summarize some tools that would allow the study of ion channels and cell cycle regulatory molecules in individual cells during mitosis.

Scorpion Toxins and Ion Channels: Potential Applications in Cancer Therapy

Apoptosis, a genetically directed process of cell death, has been studied for many years, and the biochemical mechanisms that surround it are well known and described. There are at least three pathways by which apoptosis occurs, and each pathway depends on extra or intracellular processes for activation. Apoptosis is a vital process, but disturbances in proliferation and cell death rates can lead to the development of diseases like cancer. Several compounds, isolated from scorpion venoms, exhibit inhibitory effects on different cancer cells. Indeed, some of these compounds can differentiate between healthy and cancer cells within the same tissue. During the carcinogenic process, morphological, biochemical, and biological changes occur that enable these compounds to modulate cancer but not healthy cells. This review highlights cancer cell features that enable modulation by scorpion neurotoxins. The properties of the isolated scorpion neurotoxins in cancer cells and the potential uses of these compounds as alternative treatments for cancer are discussed.

NPPB prevents postoperative peritoneal adhesion formation by blocking volume-activated Cl- current

5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) is a non-specific chloride channel blocker. Peritoneal adhesion is an inevitable complication of abdominal surgery and remains an important clinical problem, leading to chronic pain, intestinal obstruction, and female infertility. The aim of this study is to observe the effects of NPPB on peritoneal adhesions and uncover the underlying mechanism. The formation of postoperative peritoneal adhesions was induced by mechanical injury to the peritoneum of rats. MTT assay and wound-healing assay were used to evaluate proliferation and migration of primary cultured adhesion fibroblasts (AFB) respectively. Whole-cell chloride currents were measured using a fully automated patch-clamp workstation. Cell volume changes were monitored by light microscopy and video imaging. Our results demonstrated that NPPB could significantly prevent the formation of peritoneal adhesion in rats and inhibit the proliferation of AFB in a concentration-dependent manner. NPPB also reduced the migration of AFB cells with an IC₅₀ of 53.09 μM. A 47% hypotonic solution successfully activated the I_Cl,vol in AFB cells. The current could be blocked by extracellular treatment with NPPB. Moreover, 100 μM NPPB almost completely eliminated the capacity of regulatory volume decrease (RVD) in these cells. These data indicate that NPPB could prevent the formation of postoperative peritoneal adhesions. The possible mechanism may be through the inhibition of the proliferation and migration of AFB cells by modulating I_Cl,vol and cell volume. These results suggest a potential clinical use of NPPB for preventing the formation of peritoneal adhesions.

The Volume-Regulated Anion Channel LRRC8/VRAC Is Dispensable for Cell Proliferation and Migration

Cells possess the capability to adjust their volume for various physiological processes, presumably including cell proliferation and migration. The volume-regulated anion channel (VRAC), formed by LRRC8 heteromers, is critically involved in regulatory volume decrease of vertebrate cells. The VRAC has also been proposed to play a role in cell cycle progression and cellular motility. Indeed, recent reports corroborated this notion, with potentially important implications for the VRAC in cancer progression. In the present study, we examined the role of VRAC during cell proliferation and migration in several cell types, including C2C12 myoblasts, human colon cancer HCT116 cells, and U251 and U87 glioblastoma cells. Surprisingly, neither pharmacological inhibition of VRAC with 4-[(2-Butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid (DCPIB), carbenoxolone or 5-nitro-2-(3-phenylpropyl-amino)benzoic acid (NPPB), nor siRNA-mediated knockdown or gene knockout of the essential VRAC subunit LRRC8A affected cell growth and motility in any of the investigated cell lines. Additionally, we found no effect of the VRAC inhibition using siRNA treatment or DCPIB on PI3K/Akt signaling in glioblastoma cells. In summary, our work suggests that VRAC is dispensable for cell proliferation or migration.

Cell Volume-Activated and Volume-Correlated Anion Channels in Mammalian Cells: Their Biophysical, Molecular, and Pharmacological Properties

There are a number of mammalian anion channel types associated with cell volume changes. These channel types are classified into two groups: volume-activated anion channels (VAACs) and volume-correlated anion channels (VCACs). VAACs can be directly activated by cell swelling and include the volume-sensitive outwardly rectifying anion channel (VSOR), which is also called the volume-regulated anion channel; the maxi-anion channel (MAC or Maxi-Cl); and the voltage-gated anion channel, chloride channel (ClC)-2. VCACs can be facultatively implicated in, although not directly activated by, cell volume changes and include the cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, the Ca²⁺-activated Cl^- channel (CaCC), and the acid-sensitive (or acid-stimulated) outwardly rectifying anion channel. This article describes the phenotypical properties and activation mechanisms of both groups of anion channels, including accumulating pieces of information on the basis of recent molecular understanding. To that end, this review also highlights the molecular identities of both anion channel groups; in addition to the molecular identities of ClC-2 and CFTR, those of CaCC, VSOR, and Maxi-Cl were recently identified by applying genome-wide approaches. In the last section of this review, the most up-to-date information on the pharmacological properties of both anion channel groups, especially their half-maximal inhibitory concentrations (IC₅₀ values) and voltage-dependent blocking, is summarized particularly from the standpoint of pharmacological distinctions among them. Future physiologic and pharmacological studies are definitely warranted for therapeutic targeting of dysfunction of VAACs and VCACs.

A 30-year journey from volume-regulated anion currents to molecular structure of the LRRC8 channel

Strange et al. review recent advances in our understanding of the molecular and structural basis of volume-regulated anion channel function within the framework of classical biophysical and physiological studies.

The swelling-activated anion channel VRAC has fascinated and frustrated physiologists since it was first described in 1988. Multiple laboratories have defined VRAC’s biophysical properties and have shown that it plays a central role in cell volume regulation and possibly other fundamental physiological processes. However, confusion and intense controversy surrounding the channel’s molecular identity greatly hindered progress in the field for >15 yr. A major breakthrough came in 2014 with the demonstration that VRAC is a heteromeric channel encoded by five members of the Lrrc8 gene family, Lrrc8A–E. A mere 4 yr later, four laboratories described cryo-EM structures of LRRC8A homomeric channels. As the melee of structure/function and physiology studies begins, it is critical that this work be framed by a clear understanding of VRAC biophysics, regulation, and cellular physiology as well as by the field’s past confusion and controversies. That understanding is essential for the design and interpretation of structure/function studies, studies of VRAC physiology, and studies aimed at addressing the vexing problem of how the channel detects cell volume changes. In this review we discuss key aspects of VRAC biophysics, regulation, and function and integrate these into our emerging understanding of LRRC8 protein structure/function.

Ion Channels in Cancer: Are Cancer Hallmarks Oncochannelopathies?

Genomic instability is a primary cause and fundamental feature of human cancer. However, all cancer cell genotypes generally translate into several common pathophysiological features, often referred to as cancer hallmarks. Although nowadays the catalog of cancer hallmarks is quite broad, the most common and obvious of them are 1) uncontrolled proliferation, 2) resistance to programmed cell death (apoptosis), 3) tissue invasion and metastasis, and 4) sustained angiogenesis. Among the genes affected by cancer, those encoding ion channels are present. Membrane proteins responsible for signaling within cell and among cells, for coupling of extracellular events with intracellular responses, and for maintaining intracellular ionic homeostasis ion channels contribute to various extents to pathophysiological features of each cancer hallmark. Moreover, tight association of these hallmarks with ion channel dysfunction gives a good reason to classify them as special type of channelopathies, namely oncochannelopathies. Although the relation of cancer hallmarks to ion channel dysfunction differs from classical definition of channelopathies, as disease states causally linked with inherited mutations of ion channel genes that alter channel's biophysical properties, in a broader context of the disease state, to which pathogenesis ion channels essentially contribute, such classification seems absolutely appropriate. In this review the authors provide arguments to substantiate such point of view.

Downregulation of Leucine-Rich Repeat-Containing 8A Limits Proliferation and Increases Sensitivity of Glioblastoma to Temozolomide and Carmustine

Background

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Ubiquitously expressed volume-regulated anion channels (VRAC) are thought to play a role in cell proliferation, migration, and apoptosis. VRAC are heteromeric channel complexes assembled from proteins belonging to the leucine-rich repeat-containing 8A (LRRC8A through E), among which LRRC8A plays an indispensable role. In the present work, we used an RNAi approach to test potential significance of VRAC and LRRC8A in GBM survival and sensitivity to chemotherapeutic agents.

Methods

Primary GBM cells were derived from a human surgical tissue sample. LRRC8A expression was determined with quantitative RT-PCR and downregulated using siRNA. The effects of LRRC8A knockdown on GBM cell viability, proliferation, and sensitivity to chemotherapeutic agents were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and Coulter counter assays. Cell cycle progression was further explored using fluorescence-activated cell sorting analysis of propidium iodide-stained cells.

Results

Temozolomide (TMZ), carmustine, and cisplatin reduced GBM cell survival with the IC₅₀ values of ~1,250, 320, and 30 µM, respectively. Two of three tested gene-specific siRNA constructs, siLRRC8A_3 and siLRRC8A_6, downregulated LRRC8A expression by >80% and significantly reduced GBM cell numbers. The most potent siLRRC8A_3 itself reduced viable cell numbers by ≥50%, and significantly increased toxicity of the sub-IC₅₀ concentrations of TMZ (570 µM) and carmustine (167 µM). In contrast, the effects of siLRRC8A_3 and cisplatin (32 µM) were not additive, most likely because cisplatin uptake is VRAC-dependent. The results obtained in primary GBM cells were qualitatively recapitulated in U251 human GBM cell line.

Conclusion

Downregulation of LRRC8A expression reduces GBM cell proliferation and increases sensitivity to the clinically used TMZ and carmustine. These findings indicate that VRAC represents a potential target for the treatment of GBM, alone or in combination with the current standard-of-care.

Study on the role of transient receptor potential C6 channels in esophageal squamous cell carcinoma radiosensitivity

Background

To study the effect of transient receptor potential C6 (TRPC6) channels on esophageal squamous cell carcinoma (ESCC) cell lines Eca109 cell cycle and to confirm whether TRPC6 channel is candidate radiosensitivity in vitro and in vivo.

Methods

We chose Eca109 cell line with a strong TRPC6 channels expression. Cell cycle was investigated after TRPC6 channel inhibitor SKF96365 treated with a 5 µM concentration. According to the results of cell cycle, radiation was performed. CCK-8 test was used to test the cell proliferation. Then we performed the same study in vivo. Total of 40 male nude mice were randomly divided into four groups as follows: SKF96365, radio, combined radio-SKF96365 and control. In SKF96365 group, 20 mg/kg 5 µM SKF96365 was injected into the abdominal cavity of the nude mice at day 5-11. In radiation group, the nude mice received radiotherapy 2 Gy per day at day 7-11. In combined radio-SKF96365 group, 20 mg/kg 5 µM SKF96365 was injected into the abdominal cavity of the nude mice at day 5-11 and 2 Gy radiotherapy was delivered to the tumor site at day 7-11. In control group, nude mice were injected saline into the abdominal cavity at day 5-11. General states of health were observed, the tumor size in volume was measured with calipers two times every week. Six weeks after seeding, mice were sacrificed by neck-break. The tumor size was measured in volume with caliper and in weigh with scale.

Results

Treatment with SKF96365 substantially increased the percentage of Eca109 cells in the G2/M phase and reduced that in G0/G1 phase in a time-dependent manner. Most of the cells (85.26%), 24 h after SKF96365 treatment were arrested in the G2/M phase. CCK-8 test showed that Eca109 ESCC cells received both SKF96365 and radiation showed the worst ability of cell proliferation. The same result was obtained in vivo. Nude mice received combined radio-SKF96365 showed the smallest tumor size and volume.

Conclusions

TRPC6 plays an important role in development of esophageal cancer, and SKF96365 may increase the sensitivity of radiotherapy. TRPC6 may become a new radiotherapy target in esophageal cancer.

ClC5 Decreases the Sensitivity of Multiple Myeloma Cells to Bortezomib via Promoting Prosurvival Autophagy

Resistance to bortezomib (BZ) is the major problem that largely limits its clinical application in multiple myeloma treatment. In the current study, we investigated whether ClC5, a member of the chloride channel family, is involved in this process. The MTT assay showed that BZ treatment decreased cell viability in three multiple myeloma cell lines (ARH77, U266, and SKO-007), with IC₅₀ values of 2.83, 4.37, and 1.91 nM, respectively. Moreover, BZ increased the conversion of LC3B-I to LC3B-II and expressions of beclin-1 and ATG5, concomitantly with a decreased p62 expression. Pharmacological inhibition of autophagy with 3-MA facilitated cell death in response to BZ treatment. Additionally, BZ increased ClC5 protein expression in ARH77, U266, and SKO-007 cells. Knockdown of ClC5 with small interfering RNA sensitized cells to BZ treatment, and upregulation of ClC5 induced chemoresistance to BZ. Furthermore, ClC5 downregulation promoted BZ-induced LC3B-I to LC3B-II conversion and beclin-1 expression, whereas overexpression of ClC5 showed the opposite results in ARH77 cells. Finally, BZ induced dephosphorylation of AKT and mTOR, which was significantly attenuated by ClC5 inhibition. However, ClC5 upregulation further enhanced AKT and mTOR dephosphorylation induced by BZ. Our study demonstrates that ClC5 induces chemoresistance of multiple myeloma cells to BZ via increasing prosurvival autophagy by inhibiting the AKT–mTOR pathway. These data suggest that ClC5 may play a critical role in future multiple myeloma treatment strategies.

Ion channel signaling influences cellular proliferation and phagocyte activity during axolotl tail regeneration

Little is known about the potential for ion channels to regulate cellular behaviors during tissue regeneration. Here, we utilized an amphibian tail regeneration assay coupled with a chemical genetic screen to identify ion channel antagonists that altered critical cellular processes during regeneration. Inhibition of multiple ion channels either partially (anoctamin1/Tmem16a, anoctamin2/Tmem16b, KV2.1, KV2.2, L-type CaV channels and H/K ATPases) or completely (GlyR, GABAAR, KV1.5 and SERCA pumps) inhibited tail regeneration. Partial inhibition of tail regeneration by blocking the calcium activated chloride channels, anoctamin1&2, was associated with a reduction of cellular proliferation in tail muscle and mesenchymal regions. Inhibition of anoctamin 1/2 also altered the post-amputation transcriptional response of p44/42 MAPK signaling pathway genes, including decreased expression of erk1/erk2. We also found that complete inhibition via voltage gated K+ channel blockade was associated with diminished phagocyte recruitment to the amputation site. The identification of H+ pumps as required for axolotl tail regeneration supports findings in Xenopus and Planaria models, and more generally, the conservation of ion channels as regulators of tissue regeneration. This study provides a preliminary framework for an in-depth investigation of the mechanistic role of ion channels and their potential involvement in regulating cellular proliferation and other processes essential to wound healing, appendage regeneration, and tissue repair.

LRRC8A channels support TNFα-induced superoxide production by Nox1 which is required for receptor endocytosis

Leucine Rich Repeat Containing 8A (LRRC8A) is a required component of volume-regulated anion channels (VRACs). In vascular smooth muscle cells, tumor necrosis factor-α (TNFα) activates VRAC via type 1 TNFα receptors (TNFR1), and this requires superoxide (O₂^•-) production by NADPH oxidase 1 (Nox1). VRAC inhibitors suppress the inflammatory response to TNFα by an unknown mechanism. We hypothesized that LRRC8A directly supports Nox1 activity, providing a link between VRAC current and inflammatory signaling. VRAC inhibition by 4-(2-butyl-6,7-dichlor-2-cyclopentylindan-1-on-5-yl) oxobutyric acid (DCPIB) impaired NF-κB activation by TNFα. LRRC8A siRNA reduced the magnitude of VRAC and inhibited TNFα-induced NF-κB activation, iNOS and VCAM expression, and proliferation of VSMCs. Signaling steps disrupted by both siLRRC8A and DCPIB included; extracellular O₂^•- production by Nox1, c-Jun N-terminal kinase (JNK) phosphorylation and endocytosis of TNFR1. Extracellular superoxide dismutase, but not catalase, selectively inhibited TNFR1 endocytosis and JNK phosphorylation. Thus, O₂^•- is the critical extracellular oxidant for TNFR signal transduction. Reducing JNK expression (siJNK) increased extracellular O₂^•- suggesting that JNK provides important negative feedback regulation to Nox1 at the plasma membrane. LRRC8A co-localized by immunostaining, and co-immunoprecipitated with, both Nox1 and its p22phox subunit. LRRC8A is a component of the Nox1 signaling complex. It is required for extracellular O₂^•- production, which is in turn essential for TNFR1 endocytosis. These data are the first to provide a molecular mechanism for the potent anti-proliferative and anti-inflammatory effects of VRAC inhibition.

Role of volume-regulated and calcium-activated anion channels in cell volume homeostasis, cancer and drug resistance

Volume-regulated channels for anions (VRAC) / organic osmolytes (VSOAC) play essential roles in cell volume regulation and other cellular functions, e.g. proliferation, cell migration and apoptosis. LRRC8A, which belongs to the leucine rich-repeat containing protein family, was recently shown to be an essential component of both VRAC and VSOAC. Reduced VRAC and VSOAC activities are seen in drug resistant cancer cells. ANO1 is a calcium-activated chloride channel expressed on the plasma membrane of e.g., secretory epithelia. ANO1 is amplified and highly expressed in a large number of carcinomas. The gene, encoding for ANO1, maps to a region on chromosome 11 (11q13) that is frequently amplified in cancer cells. Knockdown of ANO1 impairs cell proliferation and cell migration in several cancer cells. Below we summarize the basic biophysical properties of VRAC, VSOAC and ANO1 and their most important cellular functions as well as their role in cancer and drug resistance.

Bioelectrical regulation of cell cycle and the planarian model system

Cell cycle regulation through the manipulation of endogenous membrane potentials offers tremendous opportunities to control cellular processes during tissue repair and cancer formation. However, the molecular mechanisms by which biophysical signals modulate the cell cycle remain underappreciated and poorly understood. Cells in complex organisms generate and maintain a constant voltage gradient across the plasma membrane known as the transmembrane potential. This potential, generated through the combined efforts of various ion transporters, pumps and channels, is known to drive a wide range of cellular processes such as cellular proliferation, migration and tissue regeneration while its deregulation can lead to tumorigenesis. These cellular regulatory events, coordinated by ionic flow, correspond to a new and exciting field termed molecular bioelectricity. We aim to present a brief discussion on the biophysical machinery involving membrane potential and the mechanisms mediating cell cycle progression and cancer transformation. Furthermore, we present the planarian Schmidtea mediterranea as a tractable model system for understanding principles behind molecular bioelectricity at both the cellular and organismal level. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

CLC-3 channels in cancer (review)

Ion channels are involved in regulating cell proliferation and apoptosis (programed cell death). Since increased cellular proliferation and inhibition of apoptosis are characteristic features of tumorigenesis, targeting ion channels is a promising strategy for treating cancer. CLC-3 is a member of the voltage-gated chloride channel superfamily and is expressed in many cancer cells. In the plasma membrane, CLC-3 functions as a chloride channel and is associated with cell proliferation and apoptosis. CLC-3 is also located in intracellular compartments, contributing to their acidity, which increases sequestration of drugs and leads to chemotherapy drug resistance. In this review, we summarize the recent findings concerning the involvement of CLC-3 in cancer and explore its potential in cancer therapy.

Functions of volume-sensitive and calcium-activated chloride channels

The review describes molecular and functional properties of the volume regulated anion channel and Ca(2+)-dependent Cl(-) channels belonging to the anoctamin family with emphasis on physiological importance of these channels in regulation of cell volume, cell migration, cell proliferation, and programmed cell death. Finally, we discuss the role of Cl(-) channels in various diseases.

Low-voltage-activated T-type Ca2+ channel inhibitors as new tools in the treatment of glioblastoma: the role of endostatin

Ca(2+) plays a key role in intracellular signaling and controls various cellular processes such as proliferation, differentiation, cell growth, death, and apoptosis. Aberrant changes in intracellular Ca(2+) levels can promote undesired cell proliferation and migration and are therefore associated with certain tumor types. Many research groups have suggested a potential role for voltage-gated Ca(2+) channels in the regulation of tumor growth and progression, particularly T-type channels due to their unique biophysical properties. T-type channels are expressed in normal tissues throughout the body and in different types of tumors such as breast carcinoma, retinoblastoma, neuroblastoma, and glioma. It has been demonstrated that increased functional expression of the α1 subunit of T-type channels plays a role in the abnormal proliferation of glioblastoma cells. As such, siRNA-mediated knockdown of the expression of the α1 subunit of T-type channels decreases the proliferation of these cells. Moreover, pharmacological blockade of T-type channels significantly decreases tumor growth. In this review, we focus on the use of T-type channel blockers for the potential treatment of cancers, particularly highly proliferative tumors such as glioblastoma. We conclude that T-type channel blockers such as endostatin can serve as a potential therapeutic tool for tumors whose proliferation depends on increased T-type channel expression.

Cell volume regulation in epithelial physiology and cancer

The physiological function of epithelia is transport of ions, nutrients, and fluid either in secretory or absorptive direction. All of these processes are closely related to cell volume changes, which are thus an integrated part of epithelial function. Transepithelial transport and cell volume regulation both rely on the spatially and temporally coordinated function of ion channels and transporters. In healthy epithelia, specific ion channels/transporters localize to the luminal and basolateral membranes, contributing to functional epithelial polarity. In pathophysiological processes such as cancer, transepithelial and cell volume regulatory ion transport are dys-regulated. Furthermore, epithelial architecture and coordinated ion transport function are lost, cell survival/death balance is altered, and new interactions with the stroma arise, all contributing to drug resistance. Since altered expression of ion transporters and channels is now recognized as one of the hallmarks of cancer, it is timely to consider this especially for epithelia. Epithelial cells are highly proliferative and epithelial cancers, carcinomas, account for about 90% of all cancers. In this review we will focus on ion transporters and channels with key physiological functions in epithelia and known roles in the development of cancer in these tissues. Their roles in cell survival, cell cycle progression, and development of drug resistance in epithelial cancers will be discussed.

Expression patterns of As-ClC gene of Artemia sinica in early development and under salinity stress

As-ClC (chloride channels protein from Artemia sinica), a member from the chloride channels protein family, is a α-helical membrane protein predicted to traverse the cell membrane 11 times. It is important for several physiological functions such as cell volume regulation, cell proliferation, growth and differentiation. In this paper, the complete cDNA sequence of As-CIC was cloned from A. sinica for the first time using RACE technology. The expression pattern and location of the As-CIC gene was investigated in different stages of the embryonic development by means of quantitative real-time PCR and in situ hybridization (ISH) assay. As-CLC was distributed throughout the whole body in cells of different embryonic development of A. sinica as shown by ISH. There was a low expression level of the As-ClC gene after 0 h and a higher expression level after 15 and 40 h when the embryo entered the next growth period and the environmental salinity changed. At adult stage, the As-ClC maintained a high expression level. The results of the real-time PCR assay showed an increasing trend of As-ClC transcripts with increasing salinity. The expression of As-ClC was higher in the control group (28) than in the experimental group except at a salinity of 200 PSU. It indicated that As-ClC functions as salinity-stress-related gene, probably participated in cell volume regulation and osmotic regulation during the early embryonic development of A. sinica.

Inhibition of glioblastoma and enhancement of survival via the use of mibefradil in conjunction with radiosurgery

OBJECT

The survival of patients with high-grade gliomas remains unfavorable. Mibefradil, a T-type calcium channel inhibitor capable of synchronizing dividing cells at the G1 phase, has demonstrated potential benefit in conjunction with chemotherapeutic agents for gliomas in in vitro studies. In vivo study of mibefradil and radiosurgery is lacking. The authors used an intracranial C6 glioma model in rats to study tumor response to mibefradil and radiosurgery.

METHODS

Two weeks after implantation of C6 cells into the animals, each rat underwent MRI every 2 weeks thereafter for 8 weeks. After tumor was confirmed on MRI, the rats were randomly assigned to one of the experimental groups. Tumor volumes were measured on MR images. Experimental Group 1 received 30 mg/kg of mibefradil intraperitoneally 3 times a day for 1 week starting on postoperative day (POD) 15; Group 2 received 8 Gy of cranial radiation via radiosurgery delivered on POD 15; Group 3 underwent radiosurgery on POD 15, followed by 1 week of mibefradil; and Group 4 received mibefradil on POD 15 for 1 week, followed by radiosurgery sometime from POD 15 to POD 22. Twenty-seven glioma-bearing rats were analyzed. Survival was compared between groups using Kaplan-Meier methodology.

RESULTS

Median survival in Groups 1, 2, 3, and 4 was 35, 31, 43, and 52 days, respectively (p = 0.036, log-rank test). Two animals in Group 4 survived to POD 60, which is twice the expected survival of untreated animals in this model. Analysis of variance and a post hoc test indicated no tumor volume differences on PODs 15 and 29. However, significant volume differences were found on POD 43; mean tumor volumes for Groups 1, 2, 3, and 4 were 250, 266, 167, and 34 mm(3), respectively (p = 0.046, ANOVA). A Cox proportional hazards regression test showed survival was associated with tumor volume on POD 29 (p = 0.001) rather than on POD 15 (p = 0.162). In vitro assays demonstrated an appreciable and dose-dependent increase in apoptosis between 2- and 7-μM concentrations of mibefradil.

CONCLUSIONS

Mibefradil response is schedule dependent and enhances survival and reduces glioblastoma when combined with ionizing radiation.

Swelling activated Cl- channels in microglia: Biophysics, pharmacology and role in glutamate release

Microglia have a swelling-activated Cl- current (which we call IClswell), and while some of its biophysical properties and functional roles have been elucidated, its molecular identity is unknown. To relate this current to cell functions and determine whether it is regulated by mechanisms other than cell swelling, it is important to establish both biophysical and pharmacological fingerprints. Here, we used rat microglia and a cell line derived from them (MLS-9) to study biophysical, regulatory and pharmacological properties of IClswell. The whole-cell current was activated in response to a hypo-osmotic bath solution, but not by voltage, and was time-independent during long voltage steps. The halide selectivity sequence was I->Br->Cl- (Eisenman sequence I) and importantly, the excitatory amino acid, glutamate was permeant. Current activation required internal ATP, and was not affected by the guanine nucleotides, GTPS or GDPS, or physiological levels of internal Mg2+. The same current was activated by a low intracellular ionic strength solution without an osmotic gradient. IClswell was reversibly inhibited by known Cl- channel blockers (NPPB, flufenamic acid, glibenclamide, DCPIB), and by the glutamate release inhibitor, riluzole. Cell swelling evoked glutamate release from primary microglia and MLS-9 cells, and this was inhibited by the blockers (above), and by IAA-94, but not by tamoxifen or the Na+/K+/Cl- symport inhibitor, bumetanide. Together, these results confirm the similarity of IClswell in the two cell types, and point to a role for this channel in inflammation-mediated glutamate release in the CNS.

Volume-sensitive chloride channels are involved in maintenance of basal cell volume in human acute lymphoblastic leukemia cells

Chloride channels are expressed ubiquitously in different cells. However, the activation and roles of volume-activated chloride channels under normal isotonic conditions are not clarified, especially in lymphatic cells. In this study, the activation of basal and volume-activated chloride currents and their roles in maintenance of basal cell volume under isotonic conditions were investigated in human acute lymphoblastic leukemia Molt4 cells. The patch-clamp technique and time-lapse image analysis were employed to record whole-cell currents and cell volume changes. Under isotonic conditions, a basal chloride current was recorded. The current was weakly outward-rectified and volume-sensitive and was not inactivated obviously in the observation period. A 47% hypertonic bath solution and the chloride channel blockers NPPB and tamoxifen suppressed the current. Exposure of cells to 47% hypotonic bath solution activated further the basal current. The hypotonicity-activated current possessed properties similar to those of the basal current and was inhibited by NPPB, tamoxifen, ATP and hypertonic bath solution. Furthermore, extracellular hypotonic challenges swelled the cells and induced a regulatory volume decrease (RVD). Extracellular applications of NPPB, tamoxifen and ATP swelled the cells under isotonic conditions and inhibited the RVD induced by hypotonic cell swelling. The results suggest that some volume-activated chloride channels are activated under isotonic conditions, resulting in the appearance of the basal chloride current, which plays an important role in the maintenance of basal cell volume in lymphoblastic leukemia cells. Chloride channels can be activated further to induce a regulatory volume recovery when cells are swollen.

Effects of Tween 80 on volume-regulated chloride channel and cell proliferation in rat basilar artery smooth muscle cell

Objectives

We have previously found that volume-regulated chloride current (VRCC) is involved in cell cycle progression and cell proliferation. This study was to examine the effect of Tween 80, a nonionic surfactant, on VRCC and cell proliferation in rat basilar artery smooth muscle cells (BASMCs).

Methods

VRCC was recorded using a whole-cell patch clamp. Cell proliferation and cell cycle were determined by CCK-8, cell count and flow cytometry.

Key findings

The results showed that endothelin-1 promotes cell cycle transition from the G0/G1 phase to the S phase and significantly increases VRCC in BASMCs. The effect of Tween 80 on VRCC is reversible and concentration dependent. However, this chemical has no effect on the calcium-activated chloride channel. Tween 80 also concentration-dependently inhibits BASMCs proliferation and arrests cells in the G1/S checkpoint. The antiproliferative effect is paralleled with the inhibitory effect on VRCC.

Conclutision

Our study demonstrates that the inhibitory effect of Tween 80 on VRCC contributes importantly to arrest of the cell cycle and prevention of cell proliferation.

ClC-3 chloride channels are essential for cell proliferation and cell cycle progression in nasopharyngeal carcinoma cells

ClC-3, a gene encoding a candidate protein for volume-activated chloride (C(-)) channels, may be involved in tumor development. Herein we report a study using an antisense "knock-down" strategy to investigate the mechanism by which ClC-3 affects cell proliferation in nasopharyngeal carcinoma CNE-2Z cells. With immunoblots and MTT assays we demonstrated that the expression of ClC-3 was cell cycle dependent and in a similar concentration-dependent manner, an antisense oligonucleotide specific for ClC-3 inhibited ClC-3 protein expression and cell proliferation. The expression level of ClC-3 correlated with cell proliferation. Moreover, in the cells exposed to a ClC-3 antisense oligonucleotide, the cloning efficiency was inhibited, and cells were arrested in the S phase. The ClC-3 antisense oligonucleotide inhibited the volume-activated C(-) current (I(Cl,vol)) and the regulatory volume decrease (RVD) in a concentration-dependent manner. Additionally, the I(Cl,vol) or RVD was positively correlated with cell proliferation in the treated cells. In conclusion, ClC-3 is involved in cell proliferation and cell cycle progression through a mechanism involving modulation of I(Cl,vol) and RVD. CIC-3 may represent a therapeutic target in human cancer.

Regulation of proliferation and membrane potential by chloride currents in rat pulmonary artery smooth muscle cells

Pulmonary artery smooth muscle cell (PASMC) proliferation contributes to increased pulmonary vascular resistance and pulmonary hypertension. Because proliferation depends on membrane potential (V(m)) and because V(m) is, in part, determined by Cl(-) currents (I(Cl)), we examined the effects of I(Cl) inhibition with 4,4;-diisothiocyanatostilbene-2,2;-disulfonic acid (DIDS) on cultured rat PASMCs. DIDS (30 mumol/L) reduced cell numbers, decreased 5-bromodeoxyuridine incorporation and delayed cell cycle progression. I(Cl) inhibition with 5-Nitro-2-(3-phenylpropylamino) benzoic acid (100 mumol/L) also reduced cell numbers of cultured rat PASMCs. To test the possible involvement of I(Cl) in the regulation of PASMC proliferation, we measured V(m) and I(Cl) in both cultured (proliferating) and acutely dissociated (nonproliferating) rat PASMCs. V(m) (-39.3+/-1.4 mV) was close to the equilibrium potential of Cl(-) (-39 mV) in proliferating PASMCs but differed from equilibrium potential of Cl(-) in acutely dissociated cells (-45.3+/-0.9 mV). DIDS and substitution of extracellular Cl(-) with I(-) induced V(m) hyperpolarization in proliferating but not nonproliferating PASMCs. Consistent with V(m) recordings, DIDS-sensitive baseline and swelling-activated (Ca(2+)-independent) I(Cl)s, recorded with low Ca(2+) (<1 nmol/L) pipette solutions, were approximately 5-fold greater in proliferating than in nonproliferating PASMCs. By contrast, Ca(2+)-activated I(Cl) did not differ between proliferating and nonproliferating PASMCs. Ca(2+)-independent I(Cl)s were also increased in proliferating PASMCs acutely dissociated from rats exposed to hypoxia (10% O(2); 7 days). These findings are consistent with the conclusion that I(Cl)s regulate proliferation of PASMCs and suggest that selective I(Cl) inhibition may be useful in treating pulmonary hypertension.

Plasmodium berghei-infection induces volume-regulated anion channel-like activity in human hepatoma cells

Parasite infection can lead to alterations in the permeability of host plasma membranes. Presented here is the first demonstration that this phenomenon occurs in Plasmodium-infected liver cells. Using the whole-cell patch-clamp technique, volume-regulated anion channel (VRAC) activity was characterized in Huh-7 cells (a human hepatoma cell line) before and after infection with Plasmodium berghei. Consistent with the presence of VRACs, hypotonic bath solution induced large ion currents in Huh-7 cells that rectified outwardly, reversed close to the equilibrium potential for Cl^- and were inhibited by tamoxifen, clomiphene, mefloquine and 5-nitro-2, 3-(phenylpropylamino)-benzoic acid (NPPB), with IC₅₀ values of 4 ± 1, 4 ± 2, 2 ± 1 and 52 ± 12 μM respectively. In isotonic conditions, initial current recordings measured in uninfected and immature (24 h post invasion) parasite-infected Huh-7 cells were similar (with conductances of 14 ± 3 versus 19 ± 5 pS/pF). However, in mature (48–72 h post invasion) parasite-infected Huh-7 cells there was a sevenfold increase in currents (with a conductance of 98 ± 16 pS/pF). The elevated currents observed in the latter are consistent with VRAC-like activity and the possible reasons for their activation are discussed.

Physiology of cell volume regulation in vertebrates

The ability to control cell volume is pivotal for cell function. Cell volume perturbation elicits a wide array of signaling events, leading to protective (e.g., cytoskeletal rearrangement) and adaptive (e.g., altered expression of osmolyte transporters and heat shock proteins) measures and, in most cases, activation of volume regulatory osmolyte transport. After acute swelling, cell volume is regulated by the process of regulatory volume decrease (RVD), which involves the activation of KCl cotransport and of channels mediating K(+), Cl(-), and taurine efflux. Conversely, after acute shrinkage, cell volume is regulated by the process of regulatory volume increase (RVI), which is mediated primarily by Na(+)/H(+) exchange, Na(+)-K(+)-2Cl(-) cotransport, and Na(+) channels. Here, we review in detail the current knowledge regarding the molecular identity of these transport pathways and their regulation by, e.g., membrane deformation, ionic strength, Ca(2+), protein kinases and phosphatases, cytoskeletal elements, GTP binding proteins, lipid mediators, and reactive oxygen species, upon changes in cell volume. We also discuss the nature of the upstream elements in volume sensing in vertebrate organisms. Importantly, cell volume impacts on a wide array of physiological processes, including transepithelial transport; cell migration, proliferation, and death; and changes in cell volume function as specific signals regulating these processes. A discussion of this issue concludes the review.

Cell volume regulation: physiology and pathophysiology

Cell volume perturbation initiates a wide array of intracellular signalling cascades, leading to protective and adaptive events and, in most cases, activation of volume-regulatory osmolyte transport, water loss, and hence restoration of cell volume and cellular function. Cell volume is challenged not only under physiological conditions, e.g. following accumulation of nutrients, during epithelial absorption/secretion processes, following hormonal/autocrine stimulation, and during induction of apoptosis, but also under pathophysiological conditions, e.g. hypoxia, ischaemia and hyponatremia/hypernatremia. On the other hand, it has recently become clear that an increase or reduction in cell volume can also serve as a specific signal in the regulation of physiological processes such as transepithelial transport, cell migration, proliferation and death. Although the mechanisms by which cell volume perturbations are sensed are still far from clear, significant progress has been made with respect to the nature of the sensors, transducers and effectors that convert a change in cell volume into a physiological response. In the present review, we summarize recent major developments in the field, and emphasize the relationship between cell volume regulation and organism physiology/pathophysiology.

ClC3 is a critical regulator of the cell cycle in normal and malignant glial cells

Although most brain cells are postmitotic, small populations of progenitor or stem cells can divide throughout life. These cells are believed to be the most likely source for primary brain malignancies including gliomas. Such tumors share many common features with nonmalignant glial cells but, because of their insidious growth, form cancers that are typically incurable. In studying the growth regulation of these tumors, we recently discovered that glioma cell division is preceded by a cytoplasmic condensation that we called premitotic condensation (PMC). PMC represents an obligatory step in cell replication and is linked to chromatin condensation. If perturbed, the time required to complete a division is significantly prolonged. We now show that PMC is a feature shared more commonly among normal and malignant cells and that the reduction of cell volume is accomplished by Cl(-) efflux through ClC3 Cl(-) channels. Patch-clamp electrophysiology demonstrated a significant upregulation of chloride currents at M phase of the cell cycle. Colocalization studies and coimmunoprecipitation experiments showed the channel on the plasma membrane and at the mitotic spindle. To demonstrate a mechanistic role for ClC3 in PMC, we knocked down ClC3 expression using short hairpin RNA constructs. This resulted in a significant reduction of chloride currents at M phase that was associated with a decrease in the rate of PMC and a similar impairment of DNA condensation. These data suggest that PMC is an integral part of cell division and is dependent on ClC3 channel function.

Silence of ClC-3 chloride channel inhibits cell proliferation and the cell cycle via G/S phase arrest in rat basilar arterial smooth muscle cells

OBJECTIVES

Previously, we have found that the ClC-3 chloride channel is involved in endothelin-1 (ET-1)-induced rat aortic smooth muscle cell proliferation. The present study was to investigate the role of ClC-3 in cell cycle progression/distribution and the underlying mechanisms of proliferation.

MATERIALS AND METHODS

Small interference RNA (siRNA) is used to silence ClC-3 expression. Cell proliferation, cell cycle distribution and protein expression were measured or detected with cell counting, bromodeoxyuridine (BrdU) incorporation, Western blot and flow cytometric assays respectively.

RESULTS

ET-1-induced rat basilar vascular smooth muscle cell (BASMC) proliferation was parallel to a significant increase in endogenous expression of ClC-3 protein. Silence of ClC-3 by siRNA inhibited expression of ClC-3 protein, prevented an increase in BrdU incorporation and cell number induced by ET-1. Silence of ClC-3 also caused cell cycle arrest in G(0)/G(1) phase and prevented the cells' progression from G(1) to S phase. Knockdown of ClC-3 potently inhibited cyclin D1 and cyclin E expression and increased cyclin-dependent kinase inhibitors (CDKIs) p27(KIP) and p21(CIP) expression. Furthermore, ClC-3 knockdown significantly attenuated phosphorylation of Akt and glycogen synthase kinase-3beta (GSK-3beta) induced by ET-1.

CONCLUSION

Silence of ClC-3 protein effectively suppressed phosphorylation of the Akt/GSK-3beta signal pathway, resulting in down-regulation of cyclin D1 and cyclin E, and up-regulation of p27(KIP) and p21(CIP). In these BASMCs, integrated effects lead to cell cycle G(1)/S arrest and inhibition of cell proliferation.

T-type Ca2+ channel blockers suppress the growth of human cancer cells

In order to further clarify the role of T-type Ca(2+) channels in cell proliferation, we have measured the growth inhibition of human cancer cells by using our potent T-type Ca(2+) channel blockers. As a result, KYS05090, a most potent T-type Ca(2+) channel blocker, was found to be as potent as doxorubicin against some human cancer cells without acute toxicity. Therefore, this letter provides the biological results that T-type calcium channel is important in regulating the important cellular phenotype transition leading to cell proliferation, and thus novel T-type Ca(2+) channel blocker presents new prospects for cancer treatment.

Mammalian cells change volume during mitosis

Using single cell-imaging methods we have found that the volume of adherent cells grown in culture decreases as the cells rounds when it enters mitosis. A minimal volume is reached at metaphase. Rapid volume recovery initiates before abscission as cells make the transition from metaphase to cytokinesis. These volume changes are simultaneous with the rapid surface area decrease and recovery observed in mitotic cells [1].

Small-conductance Cl- channels contribute to volume regulation and phagocytosis in microglia

The shape and volume of microglia (brain immune cells) change when they activate during brain inflammation and become migratory and phagocytic. Swollen rat microglia express a large Cl(-) current (I(Clswell)), whose biophysical properties and functional roles are poorly understood and whose molecular identity is unknown. We constructed a fingerprint of useful biophysical properties for comparison with I(Clswell) in other cell types and with cloned Cl(-) channels. The microglial I(Clswell) was rapidly activated by cell swelling but not by voltage, and showed no time-dependence during voltage-clamp steps. Like I(Clswell) in many cell types, the halide selectivity sequence was I(-) > Br(-) > Cl(-) > F(-). However, it differed in lacking inactivation, even at +100 mV with high extracellular Mg(2+), and in having a much lower single-channel conductance: 1-3 pS. Based on these fundamental differences, the microglia channel is apparently a different gene product than the more common intermediate-conductance I(Clswell). Microglia express several candidate genes, with relative mRNA expression levels of: CLIC1 > ClC3 > I(Cln) > or = ClC2 > Best2 > Best1 > or = Best3 > Best4. Using a pharmacological toolbox, we show that all drugs that reduced the microglia current (NPPB, IAA-94, flufenamic acid and DIOA) increased the resting cell volume in isotonic solution and inhibited the regulatory volume decrease that followed cell swelling in hypotonic solution. Both channel blockers tested (NPPB and flufenamic acid) dose-dependently inhibited microglia phagocytosis of E. coli bacteria. Because I(Clswell) is involved in microglia functions that involve shape and volume changes, it is potentially important for controlling their ability to migrate to damage sites and phagocytose dead cells and debris.

Involvement of chloride channels in TGF-beta1-induced apoptosis of human bronchial epithelial cells

Widespread damage of airway epithelium and defective epithelial repair are hallmarks of chronic asthma. Growth factors and cytokines spatially and temporally regulate epithelial shedding and repair. Within this context, a key function is exerted by transforming growth factor (TGF)-beta. Recent growing evidence suggests that chloride (Cl(-)) channels are critical to cell apoptosis. We examined the effects of TGF-beta1 on Cl(-) channel expression and activity and its relationship with apoptosis in human bronchial epithelial cells (HBECs). The small interfering RNA (siRNA) approach was used to investigate the potential role of CLC-3, a member of the volume-regulated Cl(-) channel family, in apoptosis of HBECs. TGF-beta1 significantly induced HBEC apoptosis, which paralleled to a significant decrease in the endogenous expression of CLC-3 protein and mRNA transcripts. Outward rectifying and voltage-dependent CLC-3-like Cl(-) currents in HBECs were diminished by TGF-beta1. siRNA for CLC-3 abolished Cl(-) current and enhanced TGF-beta1-induced cell apoptosis. Overexpression of CLC-3 in HBECs inhibited TGF-beta1-induced cell apoptosis. Bcl-2 was also downregulated after TGF-beta stimulation. TGF-beta1-induced cell apoptosis was suppressed in Bcl-2-transfected HBECs. Our data demonstrate that CLC-3-like voltage-gated chloride channels play a critical role in TGF-beta-induced apoptosis of human airway epithelial cells.

Injury-induced neurogenesis in Bax-deficient mice: evidence for regulation by voltage-gated potassium channels

Adult neural stem and progenitor cells may help remodel the brain in response to injury. The pro-apoptotic molecule Bax has recently been identified as a key player in adult neural stem cell survival. In Bax-deficient mice that have undergone traumatic brain injury, we find increased numbers of neural progenitor cells in the dentate gyrus and improved remodeling of the hippocampus. Exogenous potassium chloride mimics spreading depression (SD)-like events in vitro, and Bax-deficient neural stem cells proliferate in response to these events more robustly than wild-type neural stem cells. Selective potassium channel blockers interrupt SD-mediated stimulation of stem cells. In addition, the potassium channel Kv4.1 is expressed within neural stem and progenitor cells in the dentate gyrus and is increased in Bax-deficiency. These data suggest that the neuroprotection observed after injury in Bax-deficiency may be due to increased neurogenesis via activation of the Kv4 family of potassium channels.