Expression and roles of Cl- channel ClC-5 in cell cycles of myeloid cells

ClC-5 Downregulation Induces Osteosarcoma Cell Apoptosis by Promoting Bax and tBid Complex Formation

Osteosarcoma is the most common malignant bone tumor. Chloride (Cl^-) channels-mediated Cl^- movement plays an important role in regulating the functions of various cancer cells, but its role in osteosarcoma remains unclear. In this study, we found that ClC-5 was increased in osteosarcoma tissues compared with normal bone tissues. Patients with high ClC-5 expression showed poor overall survival relative to those patients with low ClC-5 expression. Higher ClC-5 expression and lower intracellular Cl^- concentration ([Cl^-]_i) were observed in osteosarcoma cells compared with normal osteoblasts. Lowering [Cl^-]_i increased the viability of osteosarcoma cells, which was markedly blocked by ClC-5 downregulation. Knockdown of ClC-5 significantly induced osteosarcoma cell apoptosis and increased the release of cytochrome c from mitochondria to cytosol, concomitantly with cleavage of caspase-9, caspase-3, and PARP. The effect of ClC-5 downregulation on osteosarcoma cell apoptosis and viability was abolished by caspase-3 and caspase-9 inhibitors, but not caspase-8 inhibitor. Furthermore, ClC-5 inhibition promoted Bax translocation from cytosol to mitochondria. Immunoprecipitation showed that ClC-5 interacted with Bax and ClC-5 downregulation enhanced Bax and tBid complex formation. Collectively, we demonstrate that ClC-5 downregulation induces osteosarcoma cell apoptosis via mitochondria-dependent apoptotic pathway activation by promoting Bax and tBid association and subsequent Bax translocation.

Intracellular K+ and water content in human blood lymphocytes during transition from quiescence to proliferation

Many evidence shows that K⁺ ions are required for cell proliferation, however, changes in intracellular K⁺ concentration during transition of cells from quiescence to cycling are insufficiently studied. Here, we show using flame emission assay that a long-term increase in cell K⁺ content per g cell protein is a mandatory factor for transition of quiescent human peripheral blood lymphocytes (PBL) to proliferation induced by phytohemagglutinin, phorbol ester with ionomycin, and anti-CD3 antibodies with interleukin-2 (IL-2). The long-term increase in K⁺ content is associated with IL-2-dependent stage of PBL activation and accompanies the growth of small lymphocytes and their transformation into blasts. Inhibition of PBL proliferation with drugs specific for different steps of G0/G1/S transit prevented both blast-transformation and an increase in K⁺ content per cell protein. Determination of the water content in cells by measuring the density of cells in the Percoll gradient showed that, unlike the K⁺ content, the concentration of K⁺ in cell water remains unchanged, since water and K⁺ change in parallel. Correlation of proliferation with high cell K⁺ and water content has been confirmed by the data obtained in comparative study of PBL and permanently cycling Jurkat cells. Our data suggest that K⁺ is important for successful proliferation as the main intracellular ion that participates in regulation of cell water content during cell transition from quiescence to proliferation. We concluded that high K⁺ content in cells and the associated high water content is a characteristic feature of proliferating cells.

Proliferation-related changes in K+ content in human mesenchymal stem cells

Intracellular monovalent ions have been shown to be important for cell proliferation, however, mechanisms through which ions regulate cell proliferation is not well understood. Ion transporters may be implicated in the intracellular signaling: Na⁺ and Cl⁻ participate in regulation of intracellular pH, transmembrane potential, Ca²⁺ homeostasis. Recently, it is has been suggested that K⁺ may be involved in “the pluripotency signaling network”. Our study has been focused on the relations between K⁺ transport and stem cell proliferation. We compared monovalent cation transport in human mesenchymal stem cells (hMSCs) at different passages and at low and high densities of culture as well as during stress-induced cell cycle arrest and revealed a decline in K⁺ content per cell protein which was associated with accumulation of G1 cells in population and accompanied cell proliferation slowing. It is suggested that cell K⁺ may be important for successful cell proliferation as the main intracellular ion that participates in regulation of cell volume during cell cycle progression. It is proposed that cell K⁺ content as related to cell protein is a physiological marker of stem cell proliferation and may be used as an informative test for assessing the functional status of stem cells in vitro.

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.

The K-Cl cotransporter KCC3 as an independent prognostic factor in human esophageal squamous cell carcinoma

The objectives of the present study were to investigate the role of K–Cl cotransporter 3 (KCC3) in the regulation of cellular invasion and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC). Immunohistochemical analysis performed on 70 primary tumor samples obtained from ESCC patients showed that KCC3 was primarily found in the cytoplasm of carcinoma cells. Although the expression of KCC3 in the main tumor (MT) was related to several clinicopathological features, such as the pT and pN categories, it had no prognostic impact. KCC3 expression scores were compared between the MT and cancer nest (CN), and the survival rate of patients with a CN > MT score was lower than that of patients with a CN ≤ MT score. In addition, the survival rate of patients in whom KCC3 was expressed in the invasive front of tumor was lower than that of the patients without it. Furthermore, multivariate analysis demonstrated that the expression of KCC3 in the invasive front was one of the most important independent prognostic factors. The depletion of KCC3 using siRNAs inhibited cell migration and invasion in human ESCC cell lines. These results suggest that the expression of KCC3 in ESCC may affect cellular invasion and be related to a worse prognosis in patients with ESCC.

Role of the Na+/K+/2Cl- cotransporter NKCC1 in cell cycle progression in human esophageal squamous cell carcinoma

AIM: To investigate the role of Na⁺/K⁺/2Cl^- cotransporter 1 (NKCC1) in the regulation of genes involved in cell cycle progression and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC).

METHODS: An immunohistochemical analysis was performed on 68 primary tumor samples obtained from ESCC patients that underwent esophagectomy. NKCC1 expression in human ESCC cell lines was analyzed by Western blotting. Knockdown experiments were conducted using NKCC1 small interfering RNA, and the effects on cell cycle progression were analyzed. The gene expression profiles of cells were analyzed by microarray analysis.

RESULTS: Immunohistochemical staining showed that NKCC1 was primarily found in the cytoplasm of carcinoma cells and that its expression was related to the histological degree of differentiation of SCC. NKCC1 was highly expressed in KYSE170 cells. Depletion of NKCC1 in these cells inhibited cell proliferation via G₂/M phase arrest. Microarray analysis identified 2527 genes with altered expression levels in NKCC1depleted KYSE170. Pathway analysis showed that the top-ranked canonical pathway was the G₂/M DNA damage checkpoint regulation pathway, which involves MAD2L1, DTL, BLM, CDC20, BRCA1, and E2F5.

CONCLUSION: These results suggest that the expression of NKCC1 in ESCC may affect the G₂/M checkpoint and may be related to the degree of histological differentiation of SCCs. We have provided a deeper understanding of the role of NKCC1 as a mediator and/or a biomarker in ESCC.

Enhancement of tubulin polymerization by Cl(-)-induced blockade of intrinsic GTPase

In growing neurite of neuronal cells, it is suggested that α/β-tubulin heterodimers assemble to form microtubule, and assembly of microtubule promotes neurite elongation. On the other hand, recent studies reveal importance of intracellular Cl(-) in regulation of various cellular functions such as cell cycle progression, differentiation, cell migration, and elongation of neurite in neuronal cells. In this study, we investigated effects of Cl(-) on in vitro tubulin polymerization. We found that efficiency of in vitro tubulin polymerization (the number of microtubule) was higher (3 to 5-fold) in Cl(-)-containing solutions than that in Cl(-)-free solutions containing Br(-) or NO(3)(-). On the other hand, GTPase activity of tubulin was lower (2/3-fold) in Cl(-)-containing solutions than that in Cl(-)-free solutions containing Br(-) or NO(3)(-). Efficiency of in vitro tubulin polymerization in solutions containing a non-hydrolyzable analogue of GTP (GpCpp) instead of GTP was much higher than that in the presence of GTP. Effects of replacement of GTP with GpCpp on in vitro tubulin polymerization was weaker in Cl(-) solutions (10-fold increases) than that in Br(-) or NO(3)(-) solutions (20-fold increases), although the efficiency of in vitro tubulin polymerization in Cl(-) solutions containing GpCpp was still higher than that in Br(-) or NO(3)(-) solutions containing GpCpp. Our results suggest that a part of stimulatory effects of Cl(-) on in vitro tubulin polymerization is mediated via an inhibitory effect on GTPase activity of tubulin, although Cl(-) would also regulate in vitro tubulin polymerization by factors other than an inhibitory effect on GTPase activity.

Quercetin stimulates NGF-induced neurite outgrowth in PC12 cells via activation of Na(+)/K(+)/2Cl(-) cotransporter

We have recently reported that Na(+)/K(+)/2Cl(-) cotransporter isoform 1 (NKCC1) plays an essential role in nerve growth factor (NGF)-induced neurite outgrowth in PC12D cells. On the other hand, it has been reported that dietary flavonoids, such as quercetin, apigenin, and luteolin, stimulate various ion transporters. In the present report, we investigated the effect of quercetin, a flavonoid, on NGF-induced neurite outgrowth in PC12 cells (the parental strain of PC12D cells). Quercetin stimulated the NGF-induced neurite outgrowth in a dose-dependent manner. Knockdown of NKCC1 by RNAi methods abolished the stimulatory effect of flavonoid. Quercetin stimulated NKCC1 activity (measured as bumetanide-sensitive (86)Rb influx) without any increase in the expression level of NKCC1 protein. The stimulatory effect of quercetin on neurite outgrowth was dependent upon extracellular Cl(-). These observations indicate that quercetin stimulates the NGF-induced neurite outgrowth via an increase in Cl(-) incorporation into the intracellular space by activating NKCC1 in PC12 cell.

The role of glutathione S-transferase P in signaling pathways and S-glutathionylation in cancer

Glutathione S-transferase P is abundantly expressed in some mammalian tissues, particularly those associated with malignancies. While the enzyme can catalyze thioether bond formation between some electrophilic chemicals and GSH, novel nondetoxification functions are now ascribed to it. This review summarizes recent material that implicates GSTP in mediating S-glutathionylation of specific clusters of target proteins and in reactions that define a negative regulatory role in some kinase pathways through ligand or protein:protein interactions. It is becoming apparent that GSTP participates in the maintenance of cellular redox homeostasis through a number of convergent and divergent mechanisms. Moreover, drug platforms that have GSTP as a target have produced some interesting preclinical and clinical candidates.

Diazeniumdiolate mediated nitrosative stress alters nitric oxide homeostasis through intracellular calcium and S-glutathionylation of nitric oxide synthetase

BACKGROUND

PABA/NO is a diazeniumdiolate that acts as a direct nitrogen monoxide (NO) donor and is in development as an anticancer drug. Its mechanism of action and effect on cells is not yet fully understood.

METHODOLOGY/PRINCIPAL FINDINGS

We used HPLC and mass spectrometry to identify a primary nitroaromatic glutathione metabolite of PABA/NO and used fluorescent assays to characterize drug effects on calcium and NO homeostasis, relating these to endothelial nitric oxide synthase (eNOS) activity. Unexpectedly, the glutathione conjugate was found to be a competitive inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) presumably at the same site as thapsigargin, increasing intracellular Ca2+ release and causing auto-regulation of eNOS through S-glutathionylation.

CONCLUSIONS/SIGNIFICANCE

The initial direct release of NO after PABA/NO was followed by an eNOS-mediated generation of NO as a consequence of drug-induced increase in Ca2+ flux and calmodulin (CaM) activation. PABA/NO has a unique dual mechanism of action with direct intracellular NO generation combined with metabolite driven regulation of eNOS activation.

The antiparasitic agent ivermectin induces chloride-dependent membrane hyperpolarization and cell death in leukemia cells

To identify known drugs with previously unrecognized anticancer activity, we compiled and screened a library of such compounds to identify agents cytotoxic to leukemia cells. From these screens, we identified ivermectin, a derivative of avermectin B1 that is licensed for the treatment of the parasitic infections, strongyloidiasis and onchocerciasis, but is also effective against other worm infestations. As a potential antileukemic agent, ivermectin induced cell death at low micromolar concentrations in acute myeloid leukemia cell lines and primary patient samples preferentially over normal hematopoietic cells. Ivermectin also delayed tumor growth in 3 independent mouse models of leukemia at concentrations that appear pharmacologically achievable. As an antiparasitic, ivermectin binds and activates chloride ion channels in nematodes, so we tested the effects of ivermectin on chloride flux in leukemia cells. Ivermectin increased intracellular chloride ion concentrations and cell size in leukemia cells. Chloride influx was accompanied by plasma membrane hyperpolarization, but did not change mitochondrial membrane potential. Ivermectin also increased reactive oxygen species generation that was functionally important for ivermectin-induced cell death. Finally, ivermectin synergized with cytarabine and daunorubicin that also increase reactive oxygen species production. Thus, given its known toxicology and pharmacology, ivermectin could be rapidly advanced into clinical trial for leukemia.

ClC chloride channels in tooth germ and odontoblast-like MDPC-23 cells

OBJECTIVE

To detect expression of ClC chloride channel mRNA in tooth germ and odontoblasts, and explore the affect of chloride channel function on cell proliferation and cell cycle.

DESIGN

We extracted total RNA of tooth germ from newborn C57BL mice and mouse odontoblast-like cells (MDPC-23), then detected mRNA expression of chloride channel genes Clcn1-7 with RT-PCR. We used chloride channel blocker 5-nitro-2-(3- phenylpropylamino)benzoic acid (NPPB) to interfere with chloride channel function of MDPC-23 cells. Cell proliferation rate and cell cycle were detected with MTT assay and flow cytometry, respectively. Student's t-test was used to determine statistical significance between control and treatment groups.

RESULTS

The mRNA of Clcn1-7 chloride channel genes was expressed in tooth germ of newborn mice. Clcn3, Clcn5 and Clcn7 mRNAs were expressed in MDPC-23 cells. NPPB slowed down the proliferation rate of MDPC-23 cells from day 2 to day 4 (P<0.01), and also changed the proportion of cell cycle phase. Comparing to the control, the proportion of G2/M phase cells reduced from 3.93+/-2.62% to 0.54+/-0.25% (P<0.05). The ratio of G1/G2 increased from 1.86+/-0.01 to 1.95+/-0.02 (P<0.05).

CONCLUSIONS

There is abundant chloride channel gene expression in tooth germ. Some of these chloride channels may regulate tooth development through effects on cell proliferation and cell cycle signal pathway.

Dimethyl sulfoxide effects on hERG channels expressed in HEK293 cells

INTRODUCTION

Dimethyl sulfoxide (DMSO) is widely used as a solvent to facilitate formulation of test substances in cell perfusion solutions. However, DMSO concentration in bath (extracellular) solution is usually limited to 0.1-0.3% to avoid DMSO-induced changes in cell morphology and membrane properties due to elevation of osmolality. The purpose of this study was to examine whether DMSO-induced hyperosmotic effects on hERG expressing cells could be compensated by adding an equivalent amount of DMSO in pipette (intracellular) solution, to investigate DMSO effects on hERG channels, and to determine the impact of DMSO on the potency of hERG channel blockers.

METHOD

Whole-cell patch clamp method was used to record hERG currents in HEK293 cells. DMSO at concentrations of 0.1% to 2% was applied to bath and pipette solutions. Various voltage protocols were used to examine DMSO effects on hERG channel properties and to evaluate DMSO impacts on the potency of terfenadine and E-4031.

RESULTS

When DMSO was added simultaneously in bath and pipette solutions, normal cell morphology and the proper current recording conditions could be maintained with application of up to 2% DMSO. DMSO slightly shifted the current-voltage relationship, activation curve, and inactivation curve of the hERG channel to more positive voltages. DMSO had little effect on the concentration-response relationship of hERG channel blockers we assessed. The IC50 for terfenadine and E-4031 were not significantly changed in the presence of 0.3, 0.5, 1 and 2% DMSO.

DISCUSSION

Our results demonstrate that changes in cell morphology induced by extracellular DMSO can be prevented by application of DMSO in pipette solution. By utilizing this approach, we successfully performed hERG current recordings using bath solution containing up to 2% DMSO. DMSO-induced shifts of the voltage-dependence of hERG channel gating had little impact on the potency of hERG channel blockers.

Furosemide, a Blocker of Na+/K+/2Cl− Cotransporter, Diminishes Proliferation of Poorly Differentiated Human Gastric Cancer Cells by Affecting G0/G1 State

Furosemide, a blocker of Na(+)/K(+)/2Cl(-) cotransporter (NKCC), is often used as a diuretic to improve edema, ascites, and pleural effusion of patients with cancers. The aim of the present study was to investigate whether an NKCC blocker affects cancer cell growth. If so, we would clarify the mechanism of this action. We found that poorly differentiated gastric adenocarcinoma cells (MKN45) expressed the mRNA of NKCC1 three times higher than moderately differentiated ones (MKN28) and that the NKCC in MKN45 showed higher activity than that in MKN28. A cell proliferation assay indicates that furosemide significantly inhibited cell growth in MKN45 cells, but not in MKN28 cells. Using flow cytometrical analysis, we found that the exposure to furosemide brought MKN45 cells to spend more time at the G(0)/G(1) phase, but not MKN28 cells. Based on these observations, we indicate that furosemide diminishes cell growth by delaying the G(1)-S phase progression in poorly differentiated gastric adenocarcinoma cells, which show high expression and activity of NKCC, but not in moderately differentiated gastric adenocarcinoma cells with low expression and NKCC activity.

Ion Channels and Cancer

Membrane ion channels are essential for cell proliferation and appear to have a role in the development of cancer. This has initially been demonstrated for potassium channels and is meanwhile also suggested for other cation channels and Cl- channels. For some of these channels, like voltage-gated ether à go-go and Ca2+-dependent potassium channels as well as calcium and chloride channels, a cell cycle-dependent function has been demonstrated. Along with other membrane conductances, these channels control the membrane voltage and Ca2+ signaling in proliferating cells. Homeostatic parameters, such as the intracellular ion concentration, cytosolic pH and cell volume, are also governed by the activity of ion channels. Thus it will be an essential task for future studies to unravel cell cycle-specific effects of ion channels and non-specific homeostatic functions. When studying the role of ion channels in cancer cells, it is indispensable to choose experimental conditions that come close to the in vivo situation. Thus, environmental parameters, such as low oxygen pressure, acidosis and exposure to serum proteins, have to be taken into account. In order to achieve clinical application, more studies on the original cancer tissue are required, and improved animal models. Finally, it will be essential to generate more potent and specific inhibitors of ion channels to overcome the shortcomings of some of the current approaches.

Immunoglobulin G subclasses and prolactin (PRL) isoforms in macroprolactinemia due to anti-PRL autoantibodies

Although macroprolactinemia due to antiprolactin (anti-PRL) autoantibodies is not uncommon among hyperprolactinemic patients, the pathogenesis of such macroprolactinemia is still unknown. We examined IgG subclasses of anti-PRL autoantibodies by enzyme immunoassay, and PRL phosphorylation and isoforms by Western blotting, mass spectrometry, and two-dimensional electrophoresis in six patients with anti-PRL autoantibodies and in 29 controls. PRL-specific IgG subclasses in patients with anti-PRL autoantibodies were heterogeneous, but five of six patients showed IgG4 predominance, which is known to be produced by chronic antigen stimulation. Western blot and mass spectrometric analyses revealed that human pituitary PRL was phosphorylated at serine 194 and serine 163, whereas serine 163 in serum PRL was dephosphorylated. On two-dimensional electrophoresis, serum PRL mainly consisted of isoform with isoelectric point (pI) 6.58 in control hyperprolactinemic patients, whereas acidic isoforms (pIs 6.43 and 6.29) were also observed in patients with anti-PRL autoantibodies. Our data first demonstrate that human pituitary PRL is serine phosphorylated and partially dephosphorylated in serum, and suggest that the acidic isoforms may give rise to chronic antigen stimulation in patients with anti-PRL autoantibodies.