Regulatory volume decrease is actively modulated during the cell cycle

Chloride Channels and Transporters: Roles beyond Classical Cellular Homeostatic pH or Ion Balance in Cancers

Simple Summary

Roles of chloride-associated transporters have been raised in various cancers. Although complicated ion movements, crosstalk among channels/transporters through homeostatic electric regulation, difficulties with experimental implementation such as activity measurement of intracellular location were disturbed to verify the precise modulation of channels/transporters, recently defined cancerous function and communication with tumor microenvironment of chloride channels/transporters should be highlighted beyond classical homeostatic ion balance. Chloride-associated transporters as membrane-associated components of chloride movement, regulations of transmembrane member 16A, calcium-activated chloride channel regulators, transmembrane member 206, chloride intracellular channels, voltage-gated chloride channels, cystic fibrosis transmembrane conductance regulator, voltage-dependent anion channel, volume-regulated anion channel, and chloride-bicarbonate exchangers are discussed.

Abstract

The canonical roles of chloride channels and chloride-associated transporters have been physiologically determined; these roles include the maintenance of membrane potential, pH balance, and volume regulation and subsequent cellular functions such as autophagy and cellular proliferative processes. However, chloride channels/transporters also play other roles, beyond these classical function, in cancerous tissues and under specific conditions. Here, we focused on the chloride channel-associated cancers and present recent advances in understanding the environments of various types of cancer caused by the participation of many chloride channel or transporters families and discuss the challenges and potential targets for cancer treatment. The modulation of chloride channels/transporters might promote new aspect of cancer treatment strategies.

ClC-3/SGK1 regulatory axis enhances the olaparib-induced antitumor effect in human stomach adenocarcinoma

Currently, only a few available targeted drugs are considered to be effective in stomach adenocarcinoma (STAD) treatment. The PARP inhibitor olaparib is a molecularly targeted drug that continues to be investigated in BRCA-mutated tumors. However, in tumors without BRCA gene mutations, particularly in STAD, the effect and molecular mechanism of olaparib are unclear, which largely restricts the use of olaparib in STAD treatment. In this study, the in vitro results showed that olaparib specifically inhibited cell growth and migration, exerting antitumor effect in STAD cell lines. In addition, a ClC-3/SGK1 regulatory axis was identified and validated in STAD cells. We then found that the down-regulation of ClC-3/SGK1 axis attenuated olaparib-induced cell growth and migration inhibition. On the contrary, the up-regulation of ClC-3/SGK1 axis enhanced olaparib-induced cell growth and migration inhibition, and the enhancement effect could be attenuated by SGK1 knockdown. Consistently, the whole-cell recorded chloride current activated by olaparib presented the same variation trend. Next, the clinical data showed that ClC-3 and SGK1 were highly expressed in human STAD tissues and positively correlated (r = 0.276, P = 0.009). Furthermore, high protein expression of both ClC-3 (P = 0.030) and SGK1 (P = 0.006) was associated with poor survival rate in STAD patients, and positive correlations between ClC-3/SGK1 and their downstream molecules in STAD tissues were demonstrated via the GEPIA datasets. Finally, our results suggested that olaparib inhibited the PI3K/AKT pathway in STAD cells, and up-regulation of ClC-3/SGK1 axis enhanced olaparib-induced PI3K/AKT pathway inhibition. The animal experiments indicated that olaparib also exerted antitumor effect in vivo. Altogether, our findings illustrate that olaparib exerts antitumor effect in human STAD, and ClC-3/SGK1 regulatory axis enhances the olaparib-induced antitumor effect. Up-regulation of the ClC-3/SGK1 axis may provide promising therapeutic potential for the clinical application of olaparib in STAD treatment.

The prognostic effects of hyponatremia and hyperchloremia on postoperative NSCLC patients

Electrolytic disorders are common in lung cancer patients. But the association between serum electrolytes levels and survival in patients undergoing lung cancer resections for non-small-cell lung cancer (NSCLC) has been poorly investigated. A retrospective study was conducted on consecutive postoperative NSCLC patients. Pearson's test was used to determine the association between serum sodium and chlorine levels and clinical characteristics, and cox regression and Kaplan-Meier model were applied to analyze risk factors on overall survival. We found that hyponatremia was an independent prognostic factor associated with poor prognosis in NSCLC patients undergoing complete resection (log-rank test, P = 0.004). In addition, we found that hyperchloremia predicted a poor clinical outcome in patients with non-anion-gap (log-rank test, P = 0.011), whereas it predicted a favorable clinical outcome in patients with high-anion-gap (log-rank test, P = 0.002). The serum electrolytes levels may reflect the prognosis of NSCLC patients who receive complete resection. Early detection, monitoring, and management of hyperchloremia and hyponatremia might improve patients' prognosis.

Single-Cell Analysis of the Impact of Host Cell Heterogeneity on Infection with Foot-and-Mouth Disease Virus

Viral infection and replication are affected by host cell heterogeneity, but the mechanisms underlying the effects remain unclear. Using single-cell analysis, we investigated the effects of host cell heterogeneity, including cell size, inclusion, and cell cycle, on foot-and-mouth disease virus (FMDV) infection (acute and persistent infections) and replication. We detected various viral genome replication levels in FMDV-infected cells. Large cells and cells with a high number of inclusions generated more viral RNA copies and viral protein and a higher proportion of infectious cells than other cells. Additionally, we found that the viral titer was 10- to 100-fold higher in cells in G₂/M than those in other cell cycle phases and identified a strong correlation between cell size, inclusion, and cell cycle heterogeneity, which all affected the infection and replication of FMDV. Furthermore, we demonstrated that host cell heterogeneity influenced the adsorption of FMDV due to differences in the levels of FMDV integrin receptors expression. Collectively, these results further our understanding of the evolution of a virus in a single host cell.IMPORTANCE It is important to understand how host cell heterogeneity affects viral infection and replication. Using single-cell analysis, we found that viral genome replication levels exhibited dramatic variability in foot-and-mouth disease virus (FMDV)-infected cells. We also found a strong correlation between heterogeneity in cell size, inclusion number, and cell cycle status and that all of these characteristics affect the infection and replication of FMDV. Moreover, we found that host cell heterogeneity influenced the viral adsorption as differences in the levels of FMDV integrin receptors' expression. This study provided new ideas for the studies of correlation between FMDV infection mechanisms and host cells.

Methods for cell volume measurement

Volume is an essential characteristic of a cell, and this review describes the main methods of its measurement that have been used in the past several decades. The discussed methods include various implementations of light scattering, estimates based on one or two cell dimensions, surface scanning, fluorescence confocal and transmission slice-by-slice imaging, intracellular volume markers, displacement of extracellular solution, quantitative phase imaging, radioactive methods, and some others. Suitability of these methods to some typical samples and applications is discussed. © 2017 International Society for Advancement of Cytometry.

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.

ClC-3 Chloride Channel Proteins Regulate the Cell Cycle by Up-regulating cyclin D1-CDK4/6 through Suppressing p21/p27 Expression in Nasopharyngeal Carcinoma Cells

It was shown in this study that knockdown of ClC-3 expression by ClC-3 siRNA prevented the activation of hypotonicity-induced chloride currents, and arrested cells at the G0/G1 phase in nasopharyngeal carcinoma CNE-2Z cells. Reconstitution of ClC-3 expression with ClC-3 expression plasmids could rescue the cells from the cell cycle arrest caused by ClC-3 siRNA treatments. Transfection of cells with ClC-3 siRNA decreased the expression of cyclin D1, cyclin dependent kinase 4 and 6, and increased the expression of cyclin dependent kinase inhibitors (CDKIs), p21 and p27. Pretreatments of cells with p21 and p27 siRNAs depleted the inhibitory effects of ClC-3 siRNA on the expression of CDK4 and CDK6, but not on that of cyclin D1, indicating the requirement of p21 and p27 for the inhibitory effects of ClC-3 siRNA on CDK4 and CDK6 expression. ClC-3 siRNA inhibited cells to progress from the G1 phase to the S phase, but pretreatments of cells with p21 and p27 siRNAs abolished the inhibitory effects of ClC-3 siRNA on the cell cycle progress. Our data suggest that ClC-3 may regulate cell cycle transition between G0/G1 and S phases by up-regulation of the expression of CDK4 and CDK6 through suppression of p21 and p27 expression.

Evaluation of the efficacy of peritoneal lavage with distilled water in colorectal cancer surgery: in vitro and in vivo study

BACKGROUND

Peritoneal lavage with distilled water has been performed during colorectal cancer surgery. This study investigated the cytocidal effects of hypotonic shock in vitro and in vivo in colorectal cancer cells.

METHODS

Three human colorectal cancer cell lines, DLD1, HT29, and CACO2, were exposed to distilled water, and morphological changes were observed under a differential interference contrast microscope connected to a high-speed digital video camera. Cell volume changes were assessed using a high-resolution flow cytometer. Re-incubation experiments were performed to investigate the cytocidal effects of distilled water. In the in vivo experiment, cancer cells after hypotonic shock were injected intraperitoneally into mice and the degree of established peritoneal metastasis was subsequently evaluated. The effects of the blockade of Cl(-) channels on these cells during hypotonic shock were also analyzed.

RESULTS

Morphological observations revealed a rapid cell swelling followed by cell rupture. Measurements of cell volume changes showed that mild hypotonic shock induced regulatory volume decrease (RVD) while severe hypotonic shock broke cells into fragments. Re-incubation experiments demonstrated the cytocidal effects of hypotonicity. In vivo experiments revealed the absence of peritoneal dissemination in mice in the distilled water group, and its presence in all mice in the control group. The blockade of Cl(-) channels increased cell volume by inhibiting RVD and enhanced cytocidal effects during mild hypotonic shock.

CONCLUSIONS

These results clearly support the efficacy of peritoneal lavage with distilled water during colorectal cancer surgery and suggest that regulating of Cl(-) transport may enhance the cytocidal effects of hypotonic shock.

Volume-sensitive chloride channels are involved in cisplatin treatment of osteosarcoma

Chemotherapy is the most common therapeutic strategy used to treat osteosarcoma. The present study aimed to investigate the effects of functionally activated chloride channels on cisplatin-induced apoptosis of MG-63 human osteosarcoma cells. An MTT assay and flow cytometry were used to detect proliferation and apoptosis of the cells, respectively. Live cell imaging was used to detect volume changes in response to treatment with cisplatin and/or chloride channel blockers. The effects of these treatments on chloride currents were also assayed using the patch-clamp technique. The results of the present study indicate that chloride channel blockers may suppress cisplatin-induced apoptosis. The MG-63 cells cultured with cisplatin demonstrated an apoptotic volume decrease, as well as suppression of cell proliferation; which were reversed by co-treatment with chloride channel blockers. These results suggest that cisplatin may activate chloride channels, and that channel activation is an early signal in the pathways that lead to cisplatin-induced apoptosis and inhibition of proliferation in MG-63 cells. In conclusion, these results indicate that chloride channels have an important role in cisplatin treatment of osteosarcoma.

Functional expression of chloride channels and their roles in the cell cycle and cell proliferation in highly differentiated nasopharyngeal carcinoma cells

We previously demonstrated that the growth of the poorly differentiated nasopharyngeal carcinoma cells (CNE‐2Z) was more dependent on the activities of volume‐activated chloride channels than that of the normal nasopharyngeal epithelial cells (NP69‐SV40T). However, the activities and roles of such volume‐activated chloride channels in highly differentiated nasopharyngeal carcinoma cells (CNE‐1) are not clarified. In this study, it was found that a volume‐activated chloride current and a regulatory volume decrease (RVD) were induced by 47% hypotonic challenges. The current density and the capacity of RVD in the highly differentiated CNE‐1 cells were lower than those in the poorly differentiated CNE‐2Z cells, and higher than those in the normal cells (NP69‐SV40T). The chloride channel blockers, 5‐nitro‐2‐(3‐phenylpropylamino) benzoic acid (NPPB) and tamoxifen inhibited the current and RVD. Depletion of intracellular Cl⁻ abolished the RVD. The chloride channel blockers reversibly inhibited cell proliferation in a concentration‐ and time‐dependent manner, and arrested cells at the G0/G1 phases, but did not change cell viability. The sensitivity of the three cell lines to the chloride channel blockers was different, with the highest in poorly differentiated cells (CNE‐2Z) and the lowest in the normal cells (NP69‐SV40T). ClC‐3 proteins were expressed in the three cells and distributed inside the cells as well as on the cell membrane. In conclusion, the highly differentiated nasopharyngeal carcinoma CNE‐1 cells functionally expressed the volume‐activated chloride channels, which may play important roles in controlling cell proliferation through modulating the cell cycle, and may be associated with cell differentiation. Chloride channels may be a potential target of anticancer therapy.

In this paper, we demonstrated that the volume‐activated chloride channels were involved in regulating CNE‐1 cells proliferation and cell cycle progress. Thus, volume‐activated chloride channels may be a potential target of anticancer therapy.

Aquaporin 2-increased renal cell proliferation is associated with cell volume regulation

We have previously demonstrated that in renal cortical collecting duct cells (RCCD(1)) the expression of the water channel Aquaporin 2 (AQP2) raises the rate of cell proliferation. In this study, we investigated the mechanisms involved in this process, focusing on the putative link between AQP2 expression, cell volume changes, and regulatory volume decrease activity (RVD). Two renal cell lines were used: WT-RCCD(1) (not expressing aquaporins) and AQP2-RCCD(1) (transfected with AQP2). Our results showed that when most RCCD(1) cells are in the G(1)-phase (unsynchronized), the blockage of barium-sensitive K(+) channels implicated in rapid RVD inhibits cell proliferation only in AQP2-RCCD(1) cells. Though cells in the S-phase (synchronized) had a remarkable increase in size, this enhancement was higher and was accompanied by a significant down-regulation in the rapid RVD response only in AQP2-RCCD(1) cells. This decrease in the RVD activity did not correlate with changes in AQP2 function or expression, demonstrating that AQP2-besides increasing water permeability-would play some other role. These observations together with evidence implying a cell-sizing mechanism that shortens the cell cycle of large cells, let us to propose that during nutrient uptake, in early G(1), volume tends to increase but it may be efficiently regulated by an AQP2-dependent mechanism, inducing the rapid activation of RVD channels. This mechanism would be down-regulated when volume needs to be increased in order to proceed into the S-phase. Therefore, during cell cycle, a coordinated modulation of the RVD activity may contribute to accelerate proliferation of cells expressing AQP2.

Enhancement of the cytocidal effects of hypotonic solution using a chloride channel blocker in pancreatic cancer cells

BACKGROUND

Tumor cells exfoliated during surgery for pancreatic cancer can cause peritoneal recurrence. Peritoneal lavage with distilled water has been performed during surgery, but there have been no systematic studies for its efficacy and no experimental data demonstrating the cytocidal effects of distilled water on pancreatic cancer cells. This study investigated the cytocidal effects of hypotonic shock and enhancement using chloride channel blocker in pancreatic cancer cells.

METHODS

Three human pancreatic cancer cell lines, KP4-1, PK-1, and PK45-H, were exposed to distilled water, and the resultant morphological changes were observed under a differential interference contrast microscope connected to a high-speed video camera. Analysis of cell volume changes was performed using a high-resolution flow cytometer. To investigate the cytocidal effects of water, re-incubation of cells was performed after exposure to hypotonic solution. Additionally, the effects of 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), a Cl(-) channel blocker, on cells during exposure to hypotonic solution were analyzed.

RESULTS

Video recordings demonstrated that hypotonic shock induced cell swelling followed by cell rupture. Measurement of cell volume changes indicated that severe hypotonicity increased broken fragments of cancer cells within 5 min. Re-incubation experiments demonstrated the cytocidal effects of hypotonic shock. In all cell lines, treatment with NPPB increased cell volume by inhibiting regulatory volume decreases, which are observed during hypotonic shock, and enhanced the cytocidal effects of hypotonic solution.

CONCLUSIONS

These findings support the efficacy of peritoneal lavage with distilled water for pancreatic cancer and suggest that regulation of Cl(-) transport enhances the cytocidal effects of hypotonic shock.

Cell cycle-dependent subcellular distribution of ClC-3 in HeLa cells

Chloride channel-3 (ClC-3) is suggested to be a component and/or a regulator of the volume-activated Cl(-) channel in the plasma membrane. However, ClC-3 is predominantly located inside cells and the role of intracellular ClC-3 in tumor growth is unknown. In this study, we found that the subcellular distribution of endogenous ClC-3 varied in a cell cycle-dependent manner in HeLa cells. During interphase, ClC-3 was distributed throughout the cell and it accumulated at various positions in different stages. In early G1, ClC-3 was mainly located in the nucleus. In middle G1, ClC-3 gathered around the nuclear periphery as a ring. In late G1, ClC-3 moved back into the nucleus, where it remained throughout S phase. In G2, ClC-3 was concentrated in the cytoplasm. When cells progressed from G2 to the prophase of mitosis, ClC-3 from the cytoplasm translocated into the nucleus. During metaphase and anaphase, ClC-3 was distributed throughout the cell except for around the chromosomes and was aggregated at the spindle poles and in between two chromosomes, respectively. ClC-3 was then again concentrated in the nucleus upon the progression from telophase to cytokinesis. These results reveal a cell cycle-dependent change of the subcellular distribution of ClC-3 and strongly suggest that ClC-3 has nucleocytoplasmic shuttling dynamics that may play key regulatory roles during different stages of the cell cycle in tumor cells.

Blockade of chloride ion transport enhances the cytocidal effect of hypotonic solution in gastric cancer cells

BACKGROUND

Cancer cells that are exfoliated into the peritoneal cavity during surgery are viable and have the potential to produce peritoneal recurrence. Although peritoneal lavage with distilled water is applied in some cancer surgeries to kill tumor cells, there is no consensus regarding the optimal methodology and its effects.

METHODS

Three human gastric cancer cell lines, MKN28, MKN45, and Kato-III, were exposed to distilled water, and the resultant morphologic changes were observed using a microscope. Analysis of cell volume changes was performed using a flow cytometer. To investigate the cytocidal effects of the water, re-incubation of the cells was performed after exposing them to hypotonic solution. Additionally, the effects of 5-nitro-2-3-phenylpropylamino)-benzoic acid (NPPB), a Cl(-) channel blocker, and R(+)-[(dihydroindenyl)oxy] alkanoic acid (DIOA), a blocker of the K(+)/Cl(-) co-transporter, on the cells during their exposure to hypotonic solution were analyzed.

RESULTS

After the cells had been exposed to the distilled water, a rapid increase in cell volume occurred followed by cell rupture. In the MKN45 and Kato-III cells, treatment with NPPB increased cell volume by inhibiting regulatory volume decrease and enhanced the cytocidal effects of the hypotonic solution, whereas no such effects were observed in the MKN28 cells. On the other hand, treatment of the MKN28 cells with DIOA inhibited RVD and enhanced the cytocidal effects of hypotonic shock.

CONCLUSION

These findings support the efficacy of peritoneal lavage with distilled water during surgery for gastric cancer and suggest that the regulation of Cl(-) transport enhances the cytocidal effects of hypotonic shock.

ClC-3 is a main component of background chloride channels activated under isotonic conditions by autocrine ATP in nasopharyngeal carcinoma cells

In this study, the activation mechanisms of the background chloride current and the role of the current in maintaining of basal cell volume were investigated in human nasopharyngeal carcinoma CNE-2Z cells. Under isotonic conditions, a background chloride current was recorded by the patch clamp technique. The current presented the properties similar to those of the volume-activated chloride current in the same cell line and was inhibited by chloride channel blockers or by cell shrinkage induced by hypertonic challenges. Extracellular applications of reactive blue 2, a purinergic receptor antagonist, suppressed the background chloride current in a concentration-dependent manner under isotonic conditions. Depletion of extracellular ATP with apyrase or inhibition of ATP release from cells by gadolinium chloride decreased the background current. Extracellular applications of micromolar concentrations of ATP activated a chloride current which was inhibited by chloride channel blockers and hypertonic solutions. Extracellular ATP could also reverse the action of gadolinium chloride. Transfection of CNE-2Z cells with ClC-3 siRNA knocked down expression of ClC-3 proteins, attenuated the background chloride current and prevented activation of the ATP-induced current. Furthermore, knockdown of ClC-3 expression or exposures of cells to ATP (10 mM), the chloride channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and tamoxifen, or reactive blue 2 increased cell volume under isotonic conditions. The results suggest that ClC-3 protein may be a main component of background chloride channels which can be activated under isotonic conditions by autocrine/paracrine ATP through purinergic receptor pathways; the background current is involved in maintenance of basal cell volume.

Cell volume homeostatic mechanisms: effectors and signalling pathways

Cell volume homeostasis and its fine-tuning to the specific physiological context at any given moment are processes fundamental to normal cell function. The understanding of cell volume regulation owes much to August Krogh, yet has advanced greatly over the last decades. In this review, we outline the historical context of studies of cell volume regulation, focusing on the lineage started by Krogh, Bodil Schmidt-Nielsen, Hans-Henrik Ussing, and their students. The early work was focused on understanding the functional behaviour, kinetics and thermodynamics of the volume-regulatory ion transport mechanisms. Later work addressed the mechanisms through which cellular signalling pathways regulate the volume regulatory effectors or flux pathways. These studies were facilitated by the molecular identification of most of the relevant channels and transporters, and more recently also by the increased understanding of their structures. Finally, much current research in the field focuses on the most up- and downstream components of these paths: how cells sense changes in cell volume, and how cell volume changes in turn regulate cell function under physiological and pathophysiological conditions.

Gap junctions favor normal rat kidney epithelial cell adaptation to chronic hypertonicity

Upon hypertonic stress most often resulting from high salinity, cells need to balance their osmotic pressure by accumulating neutral osmolytes called compatible osmolytes like betaine, myo-inositol, and taurine. However, the massive uptake of compatible osmolytes is a slow process compared with other defense mechanisms related to oxidative or heat stress. This is especially critical for cycling cells as they have to double their volume while keeping a hospitable intracellular environment for the molecular machineries. Here we propose that clustered cells can accelerate the supply of compatible osmolytes to cycling cells via the transit, mediated by gap junctions, of compatible osmolytes from arrested to cycling cells. Both experimental results in epithelial normal rat kidney cells and theoretical estimations show that gap junctions indeed play a key role in cell adaptation to chronic hypertonicity. These results can provide basis for a better understanding of the functions of gap junctions in osmoregulation not only for the kidney but also for many other epithelia. In addition to this, we suggest that cancer cells that do not communicate via gap junctions poorly cope with hypertonic environments thus explaining the rare occurrence of cancer coming from the kidney medulla.

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.

Monovalent ions control proliferation of Ehrlich Lettre ascites cells

Channels and transporters of monovalent ions are increasingly suggested as putative anticarcinogenic targets. However, the mechanisms involved in modulation of proliferation by monovalent ions are poorly understood. Here, we investigated the role of K+, Na+, and Cl− ions for the proliferation of Ehrlich Lettre ascites (ELA) cells. We measured the intracellular concentration of each ion in G0, G1, and S phases of the cell cycle following synchronization by serum starvation and release. We show that intracellular concentrations and content of Na+ and Cl− were reduced in the G0–G1 phase transition, followed by an increased content of both ions in S phase concomitant with water uptake. The effect of substituting extracellular monovalent ions was investigated by bromodeoxyuridine incorporation and showed marked reduction after Na+ and Cl− substitution. In spectrofluorometric measurements with the pH-sensitive dye BCECF, substitution of Na+ was observed to upregulate the activity of the Na+/H+ exchanger NHE1 as well as of Na+-independent acid extrusion mechanisms, facilitating intracellular pH (pHi) recovery after acid loading and increasing pHi. Results using the potential sensitive dye DiBaC4( 3 ) showed a reduced Cl− conductance in S compared with G1 followed by transmembrane potential ( Em) hyperpolarization in S. Cl− substitution by impermeable anions strongly inhibited proliferation and increased free, intracellular Ca2+ ([Ca2+]i), whereas a more permeable anion had little effect. Western blots showed reduced chloride intracellular channel CLIC1 and chloride channel ClC-2 expression in the plasma membrane in S compared with G1. Our results suggest that Na+ regulates ELA cell proliferation by regulating intracellular pH while Cl− may regulate proliferation by fine-tuning of Em in S phase and altered Ca2+ signaling.

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.

Chloride channels involve in hydrogen peroxide-induced apoptosis of PC12 cells

Chloride channel activity is one of the critical factors responsible for cell apoptotic volume decrease (AVD). However, the roles of chloride channels in apoptosis have not been fully understood. In the current study, we assessed the role of chloride channels in hydrogen peroxide (H(2)O(2))-induced apoptosis of pheochromocytoma cells (PC12). Extracellular application of H(2)O(2) activated a chloride current and induced cell volume decrease in a few minutes. Incubation of cells with H(2)O(2) elevated significantly the membrane permeability to the DNA dye Hoechst 33258 in 1h and induced apoptosis of most PC12 cells tested in 24h. The chloride channel blocker NPPB (5-nitro-2-(3-phenylpropylamino)-benzoate) prevented appearance of H(2)O(2)-induced high membrane permeability and cell shrinkage, suppressed H(2)O(2)-activated chloride currents and protected PC12 cells from apoptosis induced by H(2)O(2). The results suggest that chloride channels may contribute to H(2)O(2)-induced apoptosis by ways of elevation of membrane permeability and AVD in PC12 cells.

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.

Suppression of ClC-3 channel expression reduces migration of nasopharyngeal carcinoma cells

Recent studies suggest that chloride (Cl-) channels regulate tumor cell migration. In this report, we have used antisense oligonucleotides specific for ClC-3, the most likely molecular candidate for the volume-activated Cl- channel, to investigate the role of ClC-3 in the migration of nasopharyngeal carcinoma cells (CNE-2Z) in vitro. We found that suppression of ClC-3 expression inhibited the migration of CNE-2Z cells in a concentration-dependent manner. Whole-cell patch-clamp recordings and image analysis further demonstrated that ClC-3 suppression inhibited the volume-activated Cl- current (I(Cl,vol)) and regulatory volume decrease (RVD) of CNE-2Z cells. The expression of ClC-3 positively correlated with cell migration, I(Cl,vol) and RVD. These results strongly suggest that ClC-3 is a component or regulator of the volume-activated Cl- channel. ClC-3 may regulate CNE-2Z cell migration by modulating cell volume. ClC-3 may be a new target for cancer therapies.

Involvement of regulatory volume decrease in the migration of nasopharyngeal carcinoma cells

The transwell chamber migration assay and CCD digital camera imaging techniques were used to investigate the relationship between regulatory volume decrease (RVD) and cell migration in nasopharyngeal carcinoma cells (CNE-2Z cells). Both migrated and non-migrated CNE-2Z cells, when swollen by 47% hypotonic solution, exhibited RVD which was inhibited by extracellular application of chloride channel blockers adenosine 5'-triphosphate (ATP), 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and tamoxifen. However, RVD rate in migrated CNE-2Z cells was bigger than that of non-migrated cells and the sensitivity of migrated cells to NPPB and tamoxifen was higher than that of non-migrated cells. ATP, NPPB and tamoxifen also inhibited migration of CNE-2Z cells. The inhibition of migration was positively correlated to the blockage of RVD, with a correlation coefficient (r) = 0.99, suggesting a functional relationship between RVD and cell migration. We conclude that RVD is involved in cell migration and RVD may play an important role in migratory process in CNE-2Z cells.

Characterization of regulatory volume behavior by fluorescence quenching in human corneal epithelial cells

An in-depth understanding of the mechanisms underlying regulatory volume behavior in corneal epithelial cells has been in part hampered by the lack of adequate methodology for characterizing this phenomenon. Accordingly, we developed a novel approach to characterize time-dependent changes in relative cell volume induced by anisosmotic challenges in calcein-loaded SV40-immortalized human corneal epithelial (HCE) cells with a fluorescence microplate analyzer. During a hypertonic challenge, cells shrank rapidly, followed by a temperature-dependent regulatory volume increase (RVI), tau(c) = 19 min. In contrast, a hypotonic challenge induced a rapid (tau(c) = 2.5 min) regulatory volume decrease (RVD). Temperature decline from 37 to 24 degrees C reduced RVI by 59%, but did not affect RVD. Bumetanide (50 microM), ouabain (1 mM), DIDS (1 mM), EIPA (100 microM), or Na(+)-free solution reduced the RVI by 60, 61, 39, 32, and 69%, respectively. K+, Cl- channel and K(+)-Cl(-) cotransporter (KCC) inhibition obtained with either 4-AP (1 mM), DIDS (1 mM), DIOA (100 microM), high K+ (20 mM) or Cl(-)-free solution, suppressed RVD by 42, 47, 34, 52 and 58%, respectively. KCC activity also affects steady-state cell volume, since its inhibition or stimulation induced relative volume alterations under isotonic conditions. Taken together, K+ and Cl- channels in parallel with KCC activity are important mediators of RVD, whereas RVI is temperature-dependent and is essentially mediated by the Na(+)-K(+)-2Cl(-) cotransporter (Na(+)-K(+)-2Cl(-)) and the Na(+)-K(+) pump. Inhibition of K+ and Cl- channels and KCC but not Na(+)-K(+)-2Cl(-) affect steady-state cell volume under isotonic conditions. This is the first report that KCC activity is required for HCE cell volume regulation and maintenance of steady-state cell volume.

Roles of volume-activated Cl- currents and regulatory volume decrease in the cell cycle and proliferation in nasopharyngeal carcinoma cells

OBJECTIVES

Previously it has been shown, that the volume-activated plasma membrane chloride channel is associated with regulatory volume decrease (RVD) of cells and may play an important role in control of cell proliferation. We have demonstrated that both expression of the channel and RVD capacity are actively regulated in the cell cycle. In this study, we aimed to further study the role of the volume-activated chloride current and RVD in cell cycle progression and overall in cell proliferation.

MATERIALS AND METHODS

Whole-cell currents, RVD, cell cycle distribution, cell proliferation and cell viability were measured or detected with the patch-clamp technique, the cell image analysis technique, flow cytometry, the MTT assay and the trypan blue assay respectively, in nasopharyngeal carcinoma cells (CNE-2Z cells).

RESULTS

The Cl- channel blockers, 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and tamoxifen, inhibit the volume-activated chloride current, RVD and proliferation of CNE-2Z cells in a dose-dependent manner. Analysis of relationships between the current, RVD and cell proliferation showed that both the current and RVD were positively correlated with cell proliferation. NPPB (100 microM) and tamoxifen (20 microM) did not significantly induce cell death, but inhibited cell proliferation, implying that the blockers may inhibit cell proliferation by affecting cell cycle progression. This was verified by the observation that tamoxifen (20 microM) and NPPB (100 microM) inhibited cell cycle progress and arrested cells at the G0/G1 phase boundary.

CONCLUSIONS

Activity of the volume-activated chloride channel is one of the important factors that regulate the passage of cells through the G1 restriction point and that the Cl- current associated with RVD plays an important role in cell proliferation.

Cytoplasmic volume condensation is an integral part of mitosis

Cell growth and osmotic volume regulation are undoubtedly linked to the progression of the cell cycle as with each division, a newly generated cell must compensate for loss of half of its volume to its sister cell. The extent to which size influences cell cycle decisions, however, is controversial in mammalian cells. Further, a mechanism by which cells can monitor and therefore regulate their size has not been fully elucidated. Despite an ongoing debate, there have been few studies which directly address the question in single cell real-time experiments. In this study we used fluorescent time-lapse imaging to quantitatively assess volume in individual spontaneously dividing cells throughout the cell cycle. Together with biophysical studies, these establish that the efflux of salt and water brings about a condensation of cytoplasmic volume as glioma cells progress through mitosis. As cells undergo this pre-mitotic condensation (PMC) they approach a preferred cell volume preceding each division. This is functionally linked to chromatin condensation, suggesting that PMC plays an integral role in mitosis.

Cancer cell cycle modulated by a functional coupling between sigma-1 receptors and Cl- channels

The sigma-1 receptor is an intracellular protein characterized as a tumor biomarker whose function remains mysterious. We demonstrate herein for the first time that highly selective sigma ligands inhibit volume-regulated chloride channels (VRCC) in small cell lung cancer and T-leukemia cells. Sigma ligands and VRCC blockers provoked a cell cycle arrest underlined by p27 accumulation. In stably sigma-1 receptor-transfected HEK cells, the proliferation rate was significantly lowered by sigma ligands when compared with control cells. Sigma ligands produced a strong inhibition of VRCC in HEK-transfected cells but not in control HEK. Surprisingly, the activation rate of VRCC was dramatically delayed in HEK-transfected cells in the absence of ligands, indicating that sigma-1 receptors per se modulate cell regulating volume processes in physiological conditions. Volume measurements in hypotonic conditions revealed indeed that the regulatory volume decrease was delayed in HEK-transfected cells and virtually abolished in the presence of igmesine in both HEK-transfected and T-leukemic cells. Moreover, HEK-transfected cells showed a significant resistance to staurosporine-induced apoptosis volume decrease, indicating that sigma-1 receptors protect cancer cells from apoptosis. Altogether, our results show for the first time that sigma-1 receptors modulate "cell destiny" through VRCC and cell volume regulation.

Calcium signalling and cancer cell growth

Cancer is caused by defects in the mechanisms underlying cell proliferation and cell death. Calcium ions are central to both phenomena, serving as major signalling agents with spatial localization, magnitude and temporal characteristics of calcium signals ultimately determining cell's fate. There are four primary compartments: extracellular space, cytoplasm, endoplasmic reticulum and mitochondria that participate in the cellular Ca2+ circulation. They are separated by own membranes incorporating divers Ca2(+)-handling proteins whose concerted action provides for Ca2+ signals with the spatial and temporal characteristics necessary to account for specific cellular response. The transformation of a normal cell into a cancer cell is associated with a major re-arrangement of Ca2+ pumps, Na/Ca exchangers and Ca2+ channels, which leads to the enhanced proliferation and impaired ability to die. In the present chapter we examine what changes in Ca+ signalling and the mechanisms that support it underlie the passage from normal to pathological cell growth and death control. Understanding this changes and identifying molecular players involved provides new prospects for cancers treatment.

Cell cycle-dependent activity of the volume- and Ca2+-activated anion currents in Ehrlich lettre ascites cells

Recent evidence implicates the volume-regulated anion current (VRAC) and other anion currents in control or modulation of cell cycle progression; however, the precise involvement of anion channels in this process is unclear. Here, Cl- currents in Ehrlich Lettre Ascites (ELA) cells were monitored during cell cycle progression, under three conditions: (i) after osmotic swelling (i.e., VRAC), (ii) after an increase in the free intracellular Ca2+ concentration (i.e., the Ca2+-activated Cl- current, CaCC), and (iii) under steady-state isotonic conditions. The maximal swelling-activated VRAC current decreased in G1 and increased in early S phase, compared to that in G0. The isotonic steady-state current, which seems to be predominantly VRAC, also decreased in G1, and increased again in early S phase, to a level similar to that in G0. In contrast, the maximal CaCC current (500 nM free Ca2+ in the pipette), was unaltered from G0 to G1, but decreased in early S phase. A novel high-affinity anion channel inhibitor, the acidic di-aryl-urea NS3728, which inhibited both VRAC and CaCC, attenuated ELA cell growth, suggesting a possible mechanistic link between cell cycle progression and cell cycle-dependent changes in the capacity for conductive Cl- transport. It is suggested that in ELA cells, entrance into the S phase requires an increase in VRAC activity and/or an increased potential for regulatory volume decrease (RVD), and at the same time a decrease in CaCC magnitude.

Monitoring Cl− Movement in Single Cells Exposed to Hypotonic Solution

Self-referencing ion--selective electrodes (ISEs), made with Chloride Ionophore I-Cocktail A (Fluka), were positioned 1-3 microm from human embryonic kidney cells (tsA201a) and used to record chloride flux during a sustained hyposmotic challenge. The ISE response was close to Nernstian when comparing potentials (VN) measured in 100 and 10 mM NaCl (deltaVN = 57 +/- 2 mV), but was slightly greater than ideal when comparing 1 and 10 mM NaCl (deltaVN = 70 +/- 3 mV). The response was also linear in the presence of 1 mM glutamate, gluconate, or acetate, 10 microM tamoxifen, or 0.1, 1, or 10 mM HEPES at pH 7.0. The ISE was approximately 3 orders of magnitude more selective for Cl- over glutamate or gluconate but less than 2 orders of magnitude move selective for Clover bicarbonate, acetate, citrate or thiosulfate. As a result this ISE is best described as an anion sensor. The ISE was 'poisoned' by 50 microM 5-nitro-2-(3phenylpropyl-amino)-benzoic acid (NPPB), but not by tamoxifen. An outward anion efflux was recorded from cells challenged with hypotonic (250 +/- 5 mOsm) solution. The increase in efflux peaked 7-8 min before decreasing, consistent with regulatory volume decreases observed in separate experiments using a similar osmotic protocol. This anion efflux was blocked by 10 microM tamoxifen. These results establish the feasibility of using the modulation of electrochemical, anion-selective, electrodes to monitor anions and, in this case, chloride movement during volume regulatory events. The approach provides a real-time measure of anion movement during regulated volume decrease at the single-cell level.

Volume-regulated Cl- channels in human pleural mesothelioma cells

Anion channels in human mesothelial and mesothelioma cell lines were characterized by patch-clamp and biomolecular approaches. We found an outwardly rectifying anionic current which was inactivated at positive voltages and inhibited by extracellular adenosine 5'-triphosphate (ATP). Mesothelial and mesothelioma cells behaved differently concerning current inactivation properties. Inactivation is more pronounced and has a steeper onset in mesothelial cells. Different reversal potentials, in asymmetrical Cl(-) solutions, that could be attributed to a different selectivity of the channel, have been observed in the two cell lines. Mesothelioma cell single-channel analysis indicates that the number of the same active anion channel (3-4 pS) increased under hypoosmotic conditions. Immunocytochemistry experiments showed the presence of ICln protein in the cytosol and in the plasma membrane. Western blot analysis revealed an increase of ICln in the membrane under hypotonic conditions, an event possibly related to the activation of Cl(-) channels.