KCP-4 Cells Research Articles

Impaired actin filaments decrease cisplatin sensitivity via dysfunction of volume-sensitive Cl- channels in human epidermoid carcinoma cells.

Cisplatin is a widely used platinum-based anticancer drug in the chemotherapy of numerous human cancers. However, cancer cells acquire resistance to cisplatin. So far, functional loss of volume-sensitive outwardly rectifying (VSOR) Cl- channels has been reported to contribute to cisplatin resistance of cancer cells. Here, we analyzed protein expression patterns of human epidermoid carcinoma KB cells and its cisplatin-resistant KCP-4 cells. Intriguingly, KB cells exhibited higher β-actin expression and clearer actin filaments than KCP-4 cells. The β-actin knockdown in KB cells decreased VSOR Cl- currents and inhibited the regulatory volume decrease (RVD) process after cell swelling. Consistently, KB cells treated with cytochalasin D, which depolymerizes actin filaments, showed smaller VSOR Cl- currents and slower RVD. Cytochalasin D also inhibited cisplatin-triggered apoptosis in KB cells. These results suggest that the disruption of actin filaments cause the dysfunction of VSOR Cl- channels, which elicits resistance to cisplatin in human epidermoid carcinoma cells.

Specific and essential but not sufficient roles of LRRC8A in the activity of volume-sensitive outwardly rectifying anion channel (VSOR)

ABSTRACTThe broadly expressed volume-sensitive outwardly rectifying anion channel (VSOR, also called VRAC) plays essential roles in cell survival and death. Recent findings have suggested that LRRC8A is a core component of VSOR in human cells. In the present study, VSOR currents were found to be largely reduced by siRNA against LRRC8A in mouse C127 cells as well. In contrast, LRRC8A knockdown never affected activities of 4 other types of anion channel activated by acid, Ca2+, patch excision or cAMP. While cisplatin-resistant KCP-4 cells poorly expressed endogenous VSOR activity, molecular expression levels of LRRC8A, LRRC8D and LRRC8E were indistinguishable between VSOR-deficient KCP-4 cells and the parental VSOR-rich KB cells. Furthermore, overexpression of LRRC8A alone or together with LRRC8D or LRRC8E in KCP-4 cells failed to restore VSOR activity. These results show that deficiency of VSOR currents in KCP-4 cells is not due to insufficient expression of the LRRC8A/D/E gene, suggesting an essential involvement of some other factor(s), and indicate that further study is required to better understand the complexities of the molecular determinants of VSOR, including the precise role of LRRC8 proteins.

Factors involved in the cisplatin resistance of KCP-4 human epidermoid carcinoma cells

KCP-4 is a cisplatin-resistant cell line established from human epidermoid carcinoma KB-3-1 cells. Although our previous study revealed that one of the mechanisms for cisplatin resistance in KCP-4 cells is the activation of NF-κB, its high resistance is considered to be induced by multiple mechanisms. In the present study, we explored other factors involved in the development of cisplatin resistance in KCP-4 cells. Since it has been reported that an unknown efflux pump exports cisplatin from KCP-4 cells in an ATP-dependent manner, we examined 48 types of ATP-binding cassette proteins as candidate cisplatin efflux transporters. The mRNA expression levels of ABCA1, ABCA3, ABCA7 and ABCB10 in KCP-4 cells were higher when compared to those in KB-3-1 cells. These expression levels in cisplatin-sensitive revertant KCP-4 cells (KCP-4R cells), were reduced in parallel with the sensitivity of these cells to cisplatin and their intracellular accumulation of cisplatin. Next, we investigated the occurrence of mutations in p53 in KCP-4 cells. We found a heterozygous missense mutation at codon 72 (p.Pro72Arg) in p53 of both KCP-4 and KB-3-1 cells, but the protein expression level of p53 in KCP-4 cells was higher when compared to that in KB-3-1. These results suggest that ABCA1, ABCA3, ABCA7 and ABCB10 are candidate genes for the cisplatin efflux transporter that is involved in the cisplatin resistance of KCP-4 cells, and that the mutation at codon 72 of p53 may contribute to the development of cisplatin resistance.

Acid-sensitive outwardly rectifying (ASOR) anion channels in human epithelial cells are highly sensitive to temperature and independent of ClC-3

A novel type of anion channel activated by extracellular acidification, called acid-sensitive outwardly rectifying (ASOR) anion channel, was shown to be involved in acidotoxic necrotic death in human epithelial cells. However, its biophysical property and molecular identity have remained elusive. In human epithelial HeLa cells, here, whole-cell currents of ASOR anion channel were found to be augmented by warm temperature, with a threshold temperature of 32°C. Temperature sensitivity of the conductance was found to be high (with Q 10 of 8.8) in the range of body temperature, suggesting a possible involvement of a non-diffusion-limited process such as a transporter-mediated conduction. In this regard, it is interesting that a Cl(-)/H(+) antiporter ClC-3 has recently been proposed as a candidate for the ASOR channel. However, siRNA-mediated knockdown of hClC-3 failed to suppress ASOR currents in HeLa cells. Also, endogenous ASOR currents in HEK293T cells were not affected by overexpression of human or mouse ClC-3. Furthermore, functional expression of the ASOR channel was virtually absent in the cisplatin-resistant human cancer KCP-4 cell line despite the fact that molecular expression of ClC-3 was indistinguishable between KCP-4 cells and parental cisplatin-sensitive KB-3-1 cells which endogenously exhibit high activity of ASOR anion channels. These results indicate that the ASOR anion channel is highly sensitive to temperature and independent of ClC-3.

Involvement of NF-κB activation in the cisplatin resistance of human epidermoid carcinoma KCP-4 cells

cis-Diamminedichloroplatinum II (cisplatin) is one of the most potent antitumor agents for the treatment of various types of cancer. In spite of its therapeutic usefulness, the intrinsic resistance acquired under continuous treatment limits its benefit in cancer therapy. KCP-4, a cisplatin-resistant cell line, was derived from human epidermoid carcinoma KB-3-1 cells. Since the accumulation of cisplatin in KCP-4 cells is markedly reduced by the presence of an efflux pump, this pump is thought to be related to cisplatin resistance of the KCP-4 cells. However, given that KCP-4 cells are tremendously resistant to cisplatin compared with KB-3-1 cells, it is possible that another mechanism exists. The aim of this study was to investigate whether the activation of nuclear factor-kappa B (NF-κB) contributes to the cisplatin resistance of KCP-4 cells. We used the level of translocated NF-κB into the nucleus, determined by immunoblot analysis, as the indicator of NF-κB activation. The activation level of NF-κB was higher in KCP-4 cells than in KB-3-1 cells. KCP-4 cells were treated with a combination of cisplatin and curcumin, an inhibitor of NF-κB activation, and the cell viabilities were subsequently determined by the MTT assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. In the presence of 10 µmol/l curcumin, we found that the sensitivity of KCP-4 cells to 100 and 300 µmol/l cisplatin was augmented. Additionally, curcumin reduced the activation levels of NF-κB in KCP-4 cells, and suppressed the expression levels of Bcl-2, Bcl-xL and survivin, which are apoptosis-related proteins regulated by NF-κB. Our results suggest that the high cisplatin resistance of KCP-4 cells compared with KB-3-1 cells results from multiple mechanisms other than increased cisplatin efflux, including the activation of NF-κB.

Alterations in the glycoform of cisplatin-resistant human carcinoma cells are caused by defects in the endoplasmic reticulum-associated degradation system

Cisplatin, cis-diamineplatinum-(II) dichloride (CDDP), is one of the most common and valuable chemotherapeutic reagents for various cancers. However, it is well known that tumor cells gain acquired or intrinsic resistance to treatment by this anti-cancer reagent. In spite of extensive efforts using genetic and proteomic approaches, the mechanism underlying CDDP resistance remains unclear. In the present study, we report drastic structural changes in the N-glycans of glycoproteins in CDDP-resistant tumor cells (the KCP-4 cell line obtained from KB-3-1 human carcinoma cells). It was suggested that the CDDP-resistant cells exhibited an increase in one of the high-mannose-type glycans, particularly M8.1. This N-glycan is well known as a tag for the transport of unfolded protein from the endoplasmic reticulum to the lysosome, a process known as endoplasmic reticulum-associated degradation (ERAD) system. The revertant cells (KCP-4R) obtained from the KCP-4 cell line showed almost the same glycoform profile as that of the parental cells, suggesting that N-glycan biosynthesis in tumor cells clearly corresponds to the alteration in the sensitivity against CDDP. Gene expression analysis using a cDNA microarray showed a decrease in the expression of major histocompatibility complex (MHC) proteins in the resistant cells. MHC proteins form a complex with lysosome-degradated proteins and are presented on the cell surface. These results suggest that CDDP tolerance in KCP-4 cells is caused by a defect in the ERAD system.

IK1 channel activity contributes to cisplatin sensitivity of human epidermoid cancer cells

Cisplatin, a platinum-based drug, is an important weapon against many types of cancer. It induces apoptosis by forming adducts with DNA, although many aspects of its mechanism of action remain to be clarified. Previously, we found a role for the volume-sensitive, outwardly rectifying Cl(-) channel in cisplatin-induced apoptosis. To investigate the possibility that cation channels also have a role in the cellular response to cisplatin, we examined the activity of cation channels in cisplatin-sensitive KB-3-1 (KB) epidermoid cancer cells by the whole cell patch-clamp method. A cation channel in KB cells, activated by hypotonic stress, was identified as the Ca2+-activated, intermediate-conductance K+ (IK1) channel on the basis of its requirement for intracellular Ca2+, its blockage by the blockers clotrimazole and triarylmethane-34, and its suppression by a dominant-negative construct. Activity of this channel was not observed in KCP-4 cells, a cisplatin-resistant cell line derived from KB cells, and its molecular expression, observed by semiquantitative RT-PCR and immunostaining, appeared much reduced. Cell volume measurements confirmed a physiological role for the IK1 channel as a component of the volume-regulatory machinery in KB cells. A possible role of the IK1 channel in cisplatin-induced apoptosis was investigated. It was found that clotrimazole and triarylmethane-34 inhibited a cisplatin-induced decrease in cell viability and increase in caspase-3/7 activity, whereas 1-ethyl-2-benzimidazolinone, an activator of the channel, had the opposite effect. Thus IK1 channel activity appears to mediate, at least in part, the response of KB cells to cisplatin treatment.

Impaired activity of volume‐sensitive Cl− channel is involved in cisplatin resistance of cancer cells

The platinum-based drug cisplatin is a widely used anticancer drug which acts by causing the induction of apoptosis. However, resistance to the drug is a major problem. In this study we show that the KCP-4 human epidermoid cancer cell line, which serves as a model of acquired resistance to cisplatin, has virtually no volume-sensitive, outwardly rectifying (VSOR) chloride channel activity. The VSOR chloride channel's molecular identity has not yet been determined, and semi-quantitative RT-PCR experiments in this study suggested that the channel corresponds to none of three candidate genes. However, because it is known that the channel current plays an essential role in apoptosis, we hypothesized that lack of the current contributes to cisplatin resistance in these cells and that its restoration would reduce resistance. To test this hypothesis, we attempted to restore VSOR chloride current in KCP-4 cells. It was found that treatment with trichostatin A (TSA), a histone deacetylase inhibitor, caused VSOR chloride channel function to be partially restored. Treatment of the cells with both TSA and cisplatin resulted in an increase in caspase-3 activity at 24 h and a decrease in cell viability at 48 h. These effects were blocked by simultaneous treatment of the cells with a VSOR chloride channel blocker. These results indicate that restoration of the channel's functional expression by TSA treatment leads to a decrease in the cisplatin resistance of KCP-4 cells. We thus conclude that impaired activity of the VSOR chloride channel is involved in the cisplatin resistance of KCP-4 cancer cells.

P73 and MDM2 confer the resistance of epidermoid carcinoma to cisplatin by blocking p53

p73 responds to DNA damage and exerts its pro-apoptotic function. However, p73 might contribute to the development of drug-resistance in certain tumor cells. In this study, we found that p73 and MDM2 correlate with cisplatin-resistant phenotype of human epidermoid carcinoma-derived cells. p73 and MDM2 were kept at low levels in the cisplatin-sensitive KB-3-1 cells, whereas p53 was induced to be phosphorylated at Ser-15 in response to cisplatin. In contrast, p73 and MDM2 were expressed at higher levels, and cisplatin-mediated p53 phosphorylation was undetectable in the cisplatin-resistant KCP-4 cells. Enforced expression of p73 in KB-3-1 cells caused an accumulation of unphosphorylated form of p53 and MDM2, and conferred the cisplatin resistance. Collectively, our results suggest that a loss of the cisplatin sensitivity is at least in part due to a lack of cisplatin-induced p53 phosphorylation, and p73 might cooperate with MDM2 to be involved in this process.

Enhanced nucleotide excision repair in cisplatin resistant human KB carcinoma cells

We previously reported that enhanced active efflux of cisplatin and increased GSH level were observed in KCP-4 cells. In the present study, KCP-4 cells were found to be cross-resistant to ultraviolet (UV) compared with parental KB-3-1 cells. Enhanced nucleotide excision repair (NER) was verified by time-dependent repair of UV-induced DNA damage. In addition, the amount of platinum bound to DNA after exposure to cisplatin decreased in a time-dependent manner in KCP-4 cells and this was reversed by aphidicolin, a DNA polymerase inhibitor. In stationary phase cultures, aphidicolin increased the sensitivity of KCP-4 cells to cisplatin. The expression of xeroderma pigmentosum complementation group F (XPF), an endonuclease involved in NER, was upregulated in KCP-4 cells. In KCP-4 cells the expression of hMSH6, one of the mismatch repair (MMR) factors, was decreased compared to parental KB-3-1 and revertant KCP-4R cells. However, KCP-4 cells were cross-resistant to oxaliplatin, and microsatellite instability was not observed in them. These findings suggest that the enhanced NER activity for DNA damage caused by cisplatin may be involved in cisplatin resistance in KCP-4 cells.

An enhanced active efflux of CPT-11 and SN-38 in cisplatin-resistant human KB carcinoma cells

Cisplatin-resistant KCP-4 cells were 12.4- and 31.6-fold more resistant to CPT-11 and SN-38 than parental KB-3-1 cells, respectively. We studied the mechanism of cross-resistance to CPT-11 and SN-38. Our previous study showed that multidrug resistance protein (MRP), canalicular multispecific organic anion transporter (cMOAT) and P-glycoprotein (P-gp) were not expressed in KCP-4 cells (Chen, Z.-S. et al., Exp. Cell Res., 240 (1998) 312–320, and Chuman, Y. et al., Biochem. Biophys. Res. Commun., 226 (1996) 158–165). The accumulation of both CPT-11 and SN-38 in KCP-4 cells was lower than that in KB-3-1 cells. The ATP-dependent efflux of CPT-11 and SN-38 from KCP-4 cells was enhanced compared with that from KB-3-1 cells. DNA topoisomerase (topo) I expression, topo I activity, topo I-mediated cleavable complex, and the sensitivity to SN-38 of DNA topo I in KCP-4 were similar to those in KB-3-1 cells. Furthermore, the conversion of CPT-11 to SN-38 in the two cell lines was also similar. The transport of LTC 4 in KCP-4 membrane vesicles was competitively inhibited by bis-(glutathionato)-platinum (II) (GS-Pt), CPT-11 and SN-38. These findings suggested that an unknown transporter distinct from P-gp, MRP or cMOAT is expressed in KCP-4 cells and transports CPT-11 and SN-38.

An Active Efflux System for Heavy Metals in Cisplatin-Resistant Human KB Carcinoma Cells

The mechanism for cisplatin resistance in cisplatin-resistant KCP-4 cells was studied. Although multidrug resistance-associated protein (MRP) was not detected in KCP-4 cells, the cells were more resistant to heavy metals than multidrug-resistant C-A120 cells that overexpressed MRP. KCP-4 cells expressed metallothionein, but it was scarcely involved in cisplatin resistance in these cells. KCP-4 cells did not express canalicular multispecific organic anion transporter (cMOAT). The glutathione(GSH) level was 4.7-fold higher in KCP-4 cells than in KB-3-1 cells. When the GSH level in KCP-4 cells was decreased by treating the cells with buthionine sulfoximine and nitrofurantoin, the accumulation of and sensitivity to cispaltin in the cells were increased. C-A120 cells were only 3.0-fold more resistant to cisplatin than KB-3-1 cells and this resistance was not affected by the increased glutathione level. The accumulation of platinum in C-A120 and KCP-4 cells was 68.5 and 20.4% of that in KB-3-1 cells, respectively, while the intracellular levels of antimony potassium tartrate in C-A120 and KCP-4 cells were 13.2 and 9.9% of that in KB-3-1 cells, respectively. The ATP-dependent efflux of antimony was enhanced in both C-A120 and KCP-4 cells. These results, taken together, suggest an efflux pump for heavy metals different from MRP and cMOAT is involved in cisplatin resistance in KCP-4 cells.

Characterization of the ATP-Dependent LTC4Transporter in Cisplatin-Resistant Human KB Cells

An active efflux pump forcis-diamminedichloroplatinum(II) (cisplatin) has been identified in cisplatin-resistant KCP-4 cells isolated from human epidermoid carcinoma KB-3-1 cells. The adenosine triphosphate(ATP)-dependent transport of leukotriene C4(LTC4), an endogenous substrate for the glutathione S-conjugate export pump(GS-X pump), has been found in membrane vesicles prepared from KCP-4 cells. Multidrug resistance-associated protein (MRP) has also been identified as an ATP-dependent LTC4transporter. To examine whether the GS-X pump expressed in KCP-4 cells is MRP, we investigated the expression of MRP in KCP-4 cells and compared the LTC4transporting activity of GS-X pump expressed in KCP-4 cells with that of MRP. The level ofMRPgene expression in KCP-4 cells was low and similar to that in KB-3-1 cells. MRP was not detected in membrane vesicles prepared from KB-3-1 and KCP-4 cells by immunoblot analysis. The ATP-dependent transport of LTC4in KCP-4 and C-A120 vesicles showed saturable kinetics with an apparent Km of 0.18 μM and 0.25 μM, respectively. [3H]LTC4transport in KCP-4 vesicles was more inhibited by 2,4-dinitrophenyl-S-glutathione(DNP-SG), bis-(glutathionato)-platinum(II) (GS-platinum) complex and glutathione disulfide(GS-SG) and less by LTD4compared with that in C-A120 vesicles. The character of the LTC4transporter expressed in KCP-4 vesicles is similar but not identical to that of MRP. Our results suggest that a glutathione S-conjugate export pump which is different from MRP exists in cisplatin-resistant KCP-4 cells.

Adenosine Triphosphate-Dependent Transport of Leukotriene C4 by Membrane Vesicles Prepared From Cisplatin-Resistant Human Epidermoid Carcinoma Tumor Cells

Cisplatin accumulation is decreased in many cisplatin-resistant cells. An active efflux pump for cisplatin exists in cisplatin-resistant human epidermoid carcinoma cells (called KB cells). A previous study has suggested that the adenosine triphosphate (ATP)-dependent glutathione S-conjugate export pump (GS-X pump), which exports the bis-(glutathionato)-platinum (II) (GS-platinum) complex, could contribute to cellular resistance to cisplatin. In this study, we examined whether the active efflux pump for cisplatin in the cisplatin-resistant KB cells is the GS-X pump and tested its activity by using an endogenous substrate, [3H]leukotriene C4 ([3H]LTC4). Membrane vesicles were prepared from KB-3-1 (clone from parental KB cells) cells and from cisplatin-resistant KCP-4 (a mutant clone derived from KB-3-1 cells) cells. Using a filtration technique, we measured the uptake and transport of [3H]LTC4, a substrate for the GS-X pump, into membrane vesicles at 37 degrees C. The uptake of [3H]LTC4 in the membrane vesicles from both the KB-3-1 and KCP-4 cells was ATP-dependent. In contrast, the ATP-dependent transport of [3H]LTC4 was observed only in KCP-4 membrane vesicles but not in KB-3-1 membrane vesicles. The ATP-dependent transport was vanadate sensitive and was inhibited by GS-platinum complex but only marginally by cisplatin and glutathione and not by vincristine or verapamil. The nucleotide triphosphates, guanosine triphosphate, cytidine triphosphate, uridine triphosphate, and deoxythymidine triphosphate could be substituted for ATP but were less efficient. A nonhydrolyzable ATP analogue, adenosine 5'-(beta,gamma-methylene) triphosphate, was not effective. The transport of LTC4 in membrane vesicles prepared from KCP-4 cells was facilitated by an ATP-dependent pump that appeared very similar to the GS-X pump. Our study suggests that the GS-X pump is involved in the decreased accumulation of cisplatin in KCP-4 cells.