Fluvastatin exerts an antitumor effect in vemurafenib-resistant melanoma cells.

Although vemurafenib has been shown to improve the overall survival of patients with metastatic melanoma harboring the BRAF V600E mutation, its efficacy is often hampered by drug resistance acquired within a relatively short period through several distinct mechanisms. In the present study, we investigated the effect of fluvastatin as a possible strategy to overcome such acquired resistance using a cultured cell line model. We established vemurafenib-resistant (VR) cells from three BRAF (V600E)-mutated melanoma lines (C32, HMY-1, and SK-MEL-28) and evaluated the mechanism of acquired resistance of VR cells by water-soluble tetrazolium salts assay, western blot, real-time quantitative PCR, and immunofluorescent microscopy. The efficacy of the combination of growth inhibitory effect of vemurafenib and fluvastatin on respective parental and VR cells were assessed by calculating combination index and western blot. IC50 values of three VR cells were ~5-100-fold higher than those for the respective parental cells. The VR cells derived from HMY-1 and SK-MEL-28 showed constitutive activation of AKT kinase, and the specific AKT inhibitor MK-2208 or the PI3K inhibitor wortmannin increased the cellular sensitivity to vemurafenib. Intriguingly, application of a statin-related drug, fluvastatin, also resulted in a synergistic increase of sensitivity to vemurafenib in the VR cells (combination index: 0.73-0.86) probably by alleviating constitutive AKT activation, whereas the same treatment did not notably alter the vemurafenib sensitivity of the parental cells. Our results suggest the possible usefulness of statin-related drugs for overcoming vemurafenib resistance acquired through constitutive activation of the PI3K-AKT axis.

Nucleus accumbens associated 1 is recruited within the promyelocytic leukemia nuclear body through SUMO modification.

Nucleus accumbens associated 1 (NACC1) is a cancer-associated BTB/POZ (pox virus and zinc finger/bric-a-brac tramtrack broad complex) gene, and is involved in several cellular functions in neurons, cancer and stem cells. Some of the BTB/POZ proteins associated with cancer biology are SUMOylated, which appears to play an important role in transcription regulation. We show that NACC1 is SUMOylated on a phylogenetically conserved lysine (K167) out of three consensus SUMOylation motif sites. Amino acid substitution in the SIM sequence (SIM/M) within the BTB/POZ domain partially reduced K167 SUMOylation activity of NACC1. Overexpression of GFP-NACC1 fusion protein leads to formation of discrete nuclear foci similar to promyelocytic leukemia nuclear bodies (PML-NB), which colocalized with SUMO paralogues (SUMO1/2/3). Both NACC1 nuclear body formation and colocalization with SUMO paralogues were completely suppressed in the GFP-NACC1-SIM/M mutant, whereas they were partially maintained in the NACC1 K167R mutant. Confocal immunofluorescence analysis showed that endogenous and exogenous NACC1 proteins colocalized with endogenous PML protein. A pull-down assay revealed that the consensus motifs of the SUMO acceptor site at K167 and the SIM within the BTB/POZ domain were both necessary for efficient binding to PML protein. Our study demonstrates that NACC1 can be modified by SUMO paralogues, and cooperates with PML protein.

Immunohistochemistry for histone h3 lysine 9 methyltransferase and demethylase proteins in human melanomas.

Methylation and demethylation of histone H3 lysine 9 (H3K9) play a role in the transcriptional regulation of several cancer-related genes and are closely associated with malignant tumor behavior. A novel study has recently demonstrated that SETDB1, a member of the H3K9 methyltransferases, accelerates tumor formation significantly in a zebrafish melanoma model. However, the expression of H3K9 methyltransferases including SETDB1 and demethylases has not been systematically examined in samples of human melanoma. Here, we used immunohistochemistry to examine the expression of the H3K9 methyltransferases, EHMT2 and SETDB1, and a H3K9 demethylase, LSD1, in 67 patients with melanoma. Overexpression of EHMT2, SETDB1, and LSD1 was observed in 14 (21%), 38 (57%), and 53 (79%) of the 67 patients, respectively. A significant relationship was observed between overexpression of EHMT2 or SETDB1 and aggressive tumor behavior such as lymph node metastasis and/or distant metastasis (P < 0.05), whereas no significant relationship was evident for LSD1 immunoreactivity. Univariate log-rank tests demonstrated that patients with melanoma overexpressing EHMT2 had a poorer outcome (P < 0.001), whereas overexpression of SETDB1 or LSD1 had no prognostic impact. These results suggest that overexpression of EHMT2 might be a prognostic marker in patients with melanoma.

BCL2 and BCLxL are key determinants of resistance to antitubulin chemotherapeutics in melanoma cells.

Malignant melanoma is refractory to various chemotherapeutics including antitubulin agents such as paclitaxel. Previous studies have suggested a link between ßIII-tubulin overexpression and paclitaxel resistance through alterations in the properties of the mitotic spindle. We found that paclitaxel treatment induced temporary mitotic arrest in 7 melanoma cell lines irrespective of the ßIII-tubulin level, suggesting that ßIII-tubulin had no significant influence on spindle properties. On the other hand, the amount of BCL2, an anti-apoptotic protein, was well correlated with paclitaxel resistance. Treatment of the paclitaxel-resistant cell lines with ABT-737, an inhibitor of BCL2 and BCLxL, or simultaneous knock-down of BCL2 and BCLxL dramatically increased the cells' sensitivity, while knock-down of MCL1, another member of the BCL2 family, had only a minimal effect. Our results suggest that the paclitaxel sensitivity of melanoma cells is attributable to apoptosis susceptibility rather than a change in spindle properties and that BCL2 and BCLxL play a pivotal role in the former.

Correlation of dysfunction of nonmuscle myosin IIA with increased induction of Cyp1a1 in Hepa-1 cells.

The aryl hydrocarbon receptor (AhR) is one of the best known ligand-activated transcription factors and it induces Cyp1a1 transcription by binding with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Recent focus has been on the relationship of AhR with signaling pathways that modulate cell shape and migration. In nonmuscle cells, nonmuscle myosin II is one of the key determinants of cell morphology, but it has not been investigated whether its function is related to Cyp1a1 induction. In this study, we observed that (-)-blebbistatin, which is a specific inhibitor of nonmuscle myosin II, increased the level of CYP1A1-mRNA in Hepa-1 cells. Comparison of (-)-blebbistatin with (+)-blebbistatin, which is an inactive enantiomer, indicated that the increase of CYP1A1-mRNA was due to nonmuscle myosin II inhibition. Subsequent knockdown experiments observed that reduction of nonmuscle myosin IIA, which is only an isoform of nonmuscle myosin II expressed in Hepa-1 cells, was related to the enhancement of TCDD-dependent Cyp1a1 induction. Moreover, chromatin immunoprecipitation assay indicated that the increase of Cyp1a1 induction was the result of transcriptional activation due to increased binding of AhR and RNA polymerase II to the enhancer and proximal promoter regions of Cyp1a1, respectively. These findings provide a new insight into the correlation between the function of nonmuscle myosin II and gene induction.

DUSP4 Inactivation Leads to Reduced Extracellular Signal‒Regulated Kinase Activity through Upregulation of DUSP6 in Melanoma Cells.

A subset of dual-specificity phosphatases is a major negative regulator of MAPKs, and their involvement in tumorigenesis remains controversial. Among them, DUSP4 is reported to preferentially dephosphorylate extracellular signal‒regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase over p38. In this study, we aimed to identify a possible role of DUSP4 in melanoma genesis. An examination of large-scale public data on gene expression and dependency revealed a considerably high DUSP4 expression and dependency of the melanoma cell lines compared with those of other tumor cell lines, which was not apparent for the other 24 dual-specificity phosphatases genes encoded in the human genome. Using two melanoma lines, we confirmed that DUSP4 depletion impaired cell growth without notably inducing apoptosis. Interestingly, immunoblotting and kinase translocation reporter data revealed that DUSP4 depletion induces a decrease in ERK1/2 phosphorylation but barely affects c-Jun N-terminal kinase phosphorylation, suggesting that neither ERK nor c-Jun N-terminal kinase is a direct target of DUSP4 in our experimental setting. Notably, DUSP4 depletion led to an increase in DUSP6 level, possibly through a post-transcriptional process, and DUSP6 knockout almost eliminated the DUSP4-depletion effect on cell growth and ERK activity. Our findings suggest that DUSP4 plays a role in maintaining a high ERK1/2 activity by negatively regulating DUSP6 and thus contributes to the survival and growth of melanoma cells.

Correction: Involvement of C-terminal truncation mutation of kinesin-5 in resistance to kinesin-5 inhibitor.

[This corrects the article DOI: 10.1371/journal.pone.0209296.].

Downregulation of miR-138 is associated with overexpression of human telomerase reverse transcriptase protein in human anaplastic thyroid carcinoma cell lines.

Alterations of several microRNA (miRNA) have been linked to cancer development and its biology. To search for unique miRNA that might play a role in the development of anaplastic thyroid carcinoma (ATC), we examined the expression of multiple miRNA and their functional effects on target genes in human thyroid carcinoma cell lines. We quantitatively evaluated the expression of multiple miRNA in 10 ATC and five papillary thyroid carcinoma (PTC) cell lines, as well as primary tumors from 11 thyroid carcinoma patients (three ATC and eight PTC), using the stem-loop-mediated reverse transcription real-time polymerase chain reaction method. We also examined the target gene specificity of unique miRNA that showed differences in expression between ATC and PTC cell lines. One miRNA, miR-138, was significantly downregulated in ATC cell lines in comparison with PTC (P < 0.01). Eleven miRNA (including miR-138) potentially targeting the human telomerase reverse transcriptase (hTERT) gene were totally downregulated in both ATC and PTC cell lines in comparison with normal thyroid tissues. A tendency for an inverse correlation between miR-138 and hTERT protein expression was observed in the thyroid cancer cell lines, although this failed to reach significance (r = -0.392, P = 0.148). We demonstrated that overexpression of miR-138 induced a reduction in hTERT protein expression, and confirmed target specificity between miR-138 and the hTERT 3'-untranslated region by luciferase reporter assay. These results suggest that loss of miR-138 expression may partially contribute to the gain of hTERT protein expression in ATC, and that further multiple miRNA targeting hTERT mRNA might be involved in the development of thyroid carcinoma.

Epigenetic modification is involved in aberrant expression of class III beta-tubulin, TUBB3, in ovarian cancer cells.

Aberrant expression of class III beta-tubulin, TUBB3, has been reported to be one of the important mechanisms responsible for taxane resistance in diverse human malignancies. We investigated aberrant TUBB3 expression and its epigenetic modification in 66 primary tumors and 3 cell lines (OVCAR-3, JHOC-5 and JHOC-8) of ovarian cancers. Overexpression of TUBB3 protein was observed in 56 (85%) of the 66 ovarian cancers, and was significantly associated with aggressive tumor behavior (advanced stage, presence of ascites, suboptimal cytoreduction at surgery and presence of lymph node metastasis) (P<0.05). Responses to treatment with a demethylating agent (5-aza-2'-deoxycytidine, 5-Aza-CdR) and a histone deacetylase inhibitor (4-phenylbutyric acid, PBA) differed among the ovarian cancer cell lines. In 2 cell lines with weak expression of TUBB3 protein (OVCAR-3 and JHOC-8), TUBB3 induction was independently induced by treatment with 5-Aza-CdR (JHOC-8) or PBA (OVCAR-3), while neither agent markedly altered TUBB3 mRNA/protein expression in a strongly TUBB3-expressing cell line (JHOC-5). A CpG island within intron 1 was hypermethylated in 1 cell line (JHOC-8) that expressed TUBB3 weakly and required 5-Aza-CdR treatment for gene expression. A CpG island of another cell line showing faint expression of TUBB3 protein (OVCAR-3), in which a significant gain of TUBB3 expression was induced by treatment with PBA but not with 5-Aza-CdR, was hypomethylated, similarly to a cell line (JHOC-5) showing constitutive expression of TUBB3. We evaluated methylation status in this region in 14 primary tumors using methylation-specific PCR, but there was no significant relationship with TUBB3 immunoreactivity. These findings suggest that aberrant expression of TUBB3 protein might be associated with aggressive behavior of ovarian cancers, and that epigenetic modulation (DNA methylation and chromatin acetylation) might be partly involved in TUBB3 expression.

Involvement of C-terminal truncation mutation of kinesin-5 in resistance to kinesin-5 inhibitor.

Cultured cells easily develop resistance to kinesin-5 inhibitors (K5Is) often by overexpressing a related motor protein, kinesin-12/KIF15, or by acquiring mutations in the N-terminal motor domain of kinesin-5/KIF11 itself. We aimed to identify novel mechanisms responsible for resistance to S-trityl L-cysteine (STLC), one of the K5Is, using human osteosarcoma cell lines. Among six lines examined, U-2OS and HOS survived chronic STLC treatment and gave rise to resistant cells with IC50s at least 10-fold higher than those of the respective parental lines. Depletion of KIF15 largely eliminated the acquired K5I resistance in both cases, consistent with the proposed notion that KIF15 is indispensable for it. In contrast to the KIF11-independent property of the cells derived from HOS, those derived from U-2OS still required KIF11 for their growth and, intriguingly, expressed a C-terminal truncated variant of KIF11 resulting from a frame shift mutation (S1017fs). All of the isolated clones harbored the same mutation, suggesting its clonal expansion in the cell population due to the growth advantage during chronic STLC treatment. Transgenic expression of KIF11S1017fs in the parental U-2OS cells, as well as in HeLa cells, conferred a moderate but reproducible STLC resistance, probably owing to STLC-resistant localization of the mutant KIF11 on mitotic spindle. Our observations indicate that both KIF15 and the C-terminal-truncated KIF11 contributes to the STLC resistance of the U-2OS derived cells.

Carnosic acid, an inducer of NAD(P)H quinone oxidoreductase 1, enhances the cytotoxicity of ß-lapachone in melanoma cell lines.

NAD(P)H quinone oxidoreductase 1 (NQO1)-dependent antitumor drugs such as ß-lapachone (ß-lap) are attractive candidates for cancer chemotherapy because several tumors exhibit higher expression of NQO1 than adjacent tissues. Although the association between NQO1 and ß-lap has been elucidated, the effects of a NQO1-inducer and ß-lap used in combination remain to be clarified. It has previously been reported that melanoma cell lines have detectable levels of NQO1 expression and are sensitive to NQO1-dependent drugs such as 17-allylamino-17-demethoxygeldanamycin. The present study was conducted to investigate the involvement of NQO1 in ß-lap-mediated toxicity and the utility of combination treatment with a NQO1-inducer and ß-lap in malignant melanoma cell lines. Decreased expression or inhibition of NQO1 caused these cell lines to become less sensitive to ß-lap, indicating a requirement of NQO1 activity for ß-lap-mediated toxicity. Of note was that carnosic acid (CA), a compound extracted from rosemary, was able to induce further expression of NQO1 through NF-E2 related factor 2 (NRF2) stabilization, thus significantly enhancing the cytotoxicity of ß-lap in all of the melanoma cell lines tested. Taken together, the data presented in the current study indicated that the NRF2-NQO1 axis may have potential value as a therapeutic target in malignant melanoma to improve the rate of clinical response to NQO1-dependent antitumor drugs.

Dynamic Phenotypic Transition of Breast Cancer Cells In Vitro Revealed by Self-floating Cell Culture.

BACKGROUND: Breast tumor heterogeneity leads to phenotypic diversity, such as tumor-initiating and metastatic properties and drug sensitivity. MATERIALS AND METHODS: We found that a self-floating cell (SFC) culture enriches a drug-resistant subpopulation in a HER2-positive breast cancer cell line. SFCs were analyzed for cancer stem cell markers, gene expression profiles, and sensitivity for anticancer drugs. RESULTS: SFCs expressed cancer stem cell markers, such as aldehyde dehydrogenase (ALDH) activity and elevated HER2 autophosphorylation. Gene expression profiles of SFCs showed a dramatic difference compared to those of parental or forced floating cells. SFCs also expressed CD133, a marker of drug resistance, and resisted cytotoxic drugs by drug efflux transporters. In contrast, HER2 kinase inhibitors efficiently reduced SFC viability. CONCLUSION: SFCs enrich drug-resistant subpopulations even in vitro and might reflect the highly plastic nature of breast cancer cells even in vitro.

Bcl-2/Bcl-xL inhibitor ABT-737 sensitizes pancreatic ductal adenocarcinoma to paclitaxel-induced cell death.

Pancreatic ductal adenocarcinoma (PDA) is an aggressive malignant disease that is resistant to various chemotherapeutic agents and commonly relapses. Efficient elimination of metastasized PDA is critical for a positive post-surgical treatment outcome. The present study analyzed the effect of the B-cell lymphoma-2 (Bcl-2)/B-cell lymphoma extra-large (Bcl-xL) inhibitor, ABT-737, on paclitaxel-induced PDA cell death. A total of 8 PDA cell lines were subjected to immunoblotting to compare the expression of Bcl-2/Bcl-xL and other factors associated with taxane resistance, including myeloid cell leukemia 1 and ßIII-tubulin (TUBB3). The viability of PDA cells was analyzed following treatment with paclitaxel alone or a combination treatment with ABT-737 and paclitaxel. Treatment with the ABT-737/paclitaxel combination induced PDA cell death at a lower concentration of paclitaxel compared with paclitaxel alone. In addition, the viable cell population at the saturation point of paclitaxel was also decreased by co-treatment with ABT-737. ABT-737 lowered the half maximal inhibitory concentration (IC50) by >2-fold in PDA cells with high Bcl-2/Bcl-xL expression, but not in PDA cells with low Bcl-2/Bcl-xL expression and high TUBB3 expression. Knockdown of Bcl-xL lowered the IC50 of paclitaxel, but knockdown of TUBB3 did not. ABT-737 sensitized PDA to paclitaxel-induced cell death, and Bcl-xL expression was a key determinant of its sensitivity. ABT-737 is potential candidate for combination chemotherapy of PDA with high Bcl-xL expression levels.

Hyaluronic acid enhances cell migration and invasion via the YAP1/TAZ-RHAMM axis in malignant pleural mesothelioma.

Most malignant mesotheliomas (MPMs) frequently show activated forms of Yes-associated protein 1 (YAP1) and transcriptional co-activator with PDZ-binding motif (TAZ), which transcriptionally regulates the receptor for hyaluronic acid-mediated motility (RHAMM). As RHAMM is involved in cell migration and invasion in various tumors, we speculated that hyaluronic acid (HA) in pleural fluid might affect the progression of mesothelioma by stimulating cell migration and invasion through RHAMM. The level of RHAMM expression was decreased by YAP1/TAZ knockdown, and conversely increased by forced expression of the active form of YAP1, suggesting that RHAMM was regulated by YAP1/TAZ in MPM cells. Cell migration and invasion were also decreased by YAP1/TAZ or RHAMM knockdown. Notably, HA treatment increased cell motility and invasion, and this was abolished by RHAMM knockdown, suggesting that HA may augment local progression of MPM cells via RHAMM. Furthermore, treatment with fluvastatin, which regulates RHAMM transcription by modulating YAP1/TAZ activity, decreased the motility and invasion of MPM cells. Collectively, these data suggest that HA is an "unfavorable" factor because it promotes malignancy in mesothelioma and that the YAP1/TAZ-RHAMM axis may have potential value as a therapeutic target for inhibition of disease progression in MPM.

Paclitaxel-induced aberrant mitosis and mitotic slippage efficiently lead to proliferative death irrespective of canonical apoptosis and p53.

Spindle poisons elicit various cellular responses following metaphase arrest, but how they relate to long-term clonogenicity has remained unclear. We prepared several HeLa lines in which the canonical apoptosis pathway was attenuated, and compared their acute responses to paclitaxel, as well as long-term fate, with the parental line. Three-nanomolar paclitaxel induced brief metaphase arrest (<5 h) often followed by aberrant mitosis, and about 90% of the cells of each line had lost their clonogenicity after 48 h of the treatment. A combination of the same concentration of paclitaxel with the kinesin-5 inhibitor, S-trityl-L-cysteine (STLC), at 1 µM led to much longer arrest (∼20 h) and predominance of subsequent line-specific responses: mitochondrial outer membrane permeabilization (MOMP) in the apoptosis-prone line, or mitotic slippage without obvious MOMP in the apoptosis-reluctant lines. In spite of this, combination with STLC did not lead to a marked difference in clonogenicity between the apoptosis-prone and -reluctant lines, and intriguingly resulted in slightly better clonogenicity than that of cells treated with 3 nM paclitaxel alone. This indicates that changes in the short-term response within 3 possible scenarios - acute MOMP, mitotic slippage or aberrant mitosis - has only a weak impact on clonogenicity. Our results suggest that once cells have committed to slippage or aberrant mitosis they eventually undergo proliferative death irrespective of canonical apoptosis or p53 function. Consistent with this, cells with irregular DNA contents originating from mitotic slippage or aberrant mitosis were mostly eliminated from the population within several rounds of division after the drug treatment.

NAD(P)H dehydrogenase, quinone 1 (NQO1), protects melanin-producing cells from cytotoxicity of rhododendrol.

Rhododendrol (RD) is a potent tyrosinase inhibitor that is metabolized to RD-quinone by tyrosinase, which may underlie the cytotoxicity of RD and leukoderma of the skin that may result. We have examined how forced expression of the NAD(P)H quinone dehydrogenase, quinone 1 (NQO1), a major quinone-reducing enzyme in cytosol, affects the survival of RD-treated cells. We found that treatment of the mouse melanoma cell line B16BL6 or normal human melanocytes with carnosic acid, a transcriptional inducer of the NQO1 gene, notably suppressed the cell killing effect of RD. This effect was mostly abolished by ES936, a highly specific NQO1 inhibitor. Moreover, conditional overexpression of the human NQO1 transgene in B16BL6 led to an expression-dependent increase of cell survival after RD treatment. Our results suggest that NQO1 attenuates the cytotoxicity of RD and/or its metabolites.

NAD(P)H:Quinone Oxidoreductase-1 Expression Sensitizes Malignant Melanoma Cells to the HSP90 Inhibitor 17-AAG.

The KEAP1-NRF2 pathway regulates cellular redox homeostasis by transcriptional induction of genes associated with antioxidant synthesis and detoxification in response to oxidative stress. Previously, we reported that KEAP1 mutation elicits constitutive NRF2 activation and resistance to cisplatin (CDDP) and dacarbazine (DTIC) in human melanomas. The present study was conducted to clarify whether an HSP90 inhibitor, 17-AAG, efficiently eliminates melanoma with KEAP1 mutation, as the NRF2 target gene, NQO1, is a key enzyme in 17-AAG bioactivation. In melanoma and non-small cell lung carcinoma cell lines with or without KEAP1 mutations, NQO1 expression and 17-AAG sensitivity are inversely correlated. NQO1 is highly expressed in normal melanocytes and in several melanoma cell lines despite the presence of wild-type KEAP1, and the NQO1 expression is dependent on NRF2 activation. Because either CDDP or DTIC produces reactive oxygen species that activate NRF2, we determined whether these agents would sensitize NQO1-low melanoma cells to 17-AAG. Synergistic cytotoxicity of the 17-AAG and CDDP combination was detected in four out of five NQO1-low cell lines, but not in the cell line with KEAP1 mutation. These data indicate that 17-AAG could be a potential chemotherapeutic agent for melanoma with KEAP1 mutation or NQO1 expression.

Protein kinase Ctheta activity is involved in the 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced signal transduction pathway leading to apoptosis in L-MAT, a human lymphoblastic T-cell line.

The aromatic hydrocarbon receptor (AhR)-dependent pathway involved in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced immunotoxicity has been studied extensively, but the AhR-independent molecular mechanism has not. In previous studies we found that the AhR is not expressed in L-MAT, a human lymphoblastic T-cell line. In this report, we provide the following evidence that the protein kinase C (PKC)theta activity is functionally involved in the AhR-independent signal transduction mechanism that participates in the TCDD-induced L-MAT cell apoptosis. First, only rottlerin, a novel PKC (nPKC)-selective inhibitor, blocked the apoptosis completely, in a dose-dependent manner. Second, PKCtheta was the major nPKC isoform (compared to PKCdelta) expressed in the L-MAT cell line. Third, a cell-permeable myristoylated PKCtheta pseudosubstrate peptide inhibitor also blocked the apoptosis completely, in a dose-dependent manner. Fourth, both rottlerin and myristoylated PKCtheta pseudosubstrate peptide inhibitor completely inhibited PKCtheta kinase activity in vitro at doses that effectively blocked TCDD-induced L-MAT cell apoptosis. TCDD treatment induced a time-dependent activation of nPKC kinase activity in L-MAT cells, and moreover, TCDD induced a translocation of PKCtheta from the cytosolic fraction to the particulate fraction in L-MAT cells. Finally, transient over-expression of a dominant negative PKCtheta (a kinase-dead mutant, K/R 409) in L-MAT cells conferred significant protection against TCDD-induced apoptosis.

Blockade by SB203580 of Cyp1a1 induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin, and the possible mechanism: possible involvement of the p38 mitogen-activated protein kinase pathway in shuttling of Ah receptor overexpressed in COS-7 cells.

A transiently overexpressed aryl hydrocarbon receptor (AhR) became translocated into the nucleus of COS-7 cells without treatment with any ligand, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin. This spontaneous AhR translocation into the nucleus was reduced by pretreatment of the recipient cells with the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580. Immunofluorescent microscopic analysis revealed that SB203580 treatment increased the fluorescence intensity of AhR within the cytoplasm. An analogue compound, SB202474, which does not inhibit p38 MAP kinase, did not reduce AhR translocation into the nucleus. Moreover, a reporter gene assay showed that the AhR spontaneously translocated into the nucleus activated reporter gene transcription and that SB203580 suppressed its transcriptional activity. From these data we conclude that the p38 MAP kinase pathway is involved in determining AhR cellular localization in COS-7 cells overexpressing AhR.

Loss of HOXD10 expression induced by upregulation of miR-10b accelerates the migration and invasion activities of ovarian cancer cells.

Small and large non-coding RNAs (ncRNAs) contribute to the acquisition of aggressive tumor behavior in diverse human malignancies. Two types of ncRNAs, miRNA­10b (miR-10b) and homemobox (HOX) transcript antisense RNA (HOTAIR), can suppress the translation of the HOXD10 gene, an mRNA encoding a transcriptional repressor that inhibits the expression of cell migration/invasion-associated genes. Using epithelial ovarian cancer cell lines and primary tumors, we investigated whether miR­10b and/or HOTAIR can regulate the expression of HOXD10, and whether it permits gain of pro­metastatic gene products, matrix metallopeptidase 14 (MMP14) and ras homolog family member C (RHOC). Overexpression of miR-10b induced a decrease in HOXD10 protein expression, and upregulated the migration and invasion abilities in ovarian cancer cell lines (P<0.05). In these cells, a significant increase of MMP14 and RHOC protein was observed. No significant upregulation of the HOXD10 protein was observed in cells with the treatment of HOTAIR-siRNA. Positive signals for HOXD10 and MMP14 proteins were observed in 47 (69%) and 25 (37%) of 68 patients with epithelial ovarian cancers. An inverse correlation between HOXD10 and MMP14 immunoreactivities was observed (P<0.05), and miR-10b expression was also inversely correlated with HOXD10 protein expression (P<0.05). These results suggested that downregulation of HOXD10 expression by miR-10b overexpression may induce an increase of pro-metastatic gene products, such as MMP14 and RHOC, and contribute to the acquisition of metastatic phenotypes in epithelial ovarian cancer cells.