MDR1 Promoter Research Articles

Molecular mechanism of suppression of MDR1 by puerarin fromPueraria lobata viaNF-κB pathway and cAMP-responsive element transcriptional activity-dependent up-regulation of AMP-activated protein kinase in breast cancer MCF-7/adr cells

Multidrug resistance (MDR) is a major obstacle in cancer chemotherapy and its inhibition is an effective way to reverse cancer drug resistance. In the present study, we investigated that puerarin, a natural isoflavonoid from Pueraria lobata, down-regulated MDR1 expression in MCF-7/adriamycin (MCF-7/adr), a human breast MDR cancer cell line. Puerarin treatment significantly inhibited MDR1 expression, MDR1 mRNA and MDR1 promoter activity in MCF-7/adr cells. The suppression of MDR1 was accompanied by partial recovery of intracellular drug accumulation, leading to increased toxicity of adriamycin and fluorescence of rhodamine 123, indicating that puerarin reversed the MDR phenotype by inhibiting the drug efflux function of MDR1. Moreover, nuclear factor kappa-B activity and IkappaB degradation were inhibited by puerarin. Puerarin stimulated AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase and glycogen synthase kinase-3beta phosphorylation, but puerarin decreased cAMP-responsive element-binding protein phosphorylation. The puerarin-induced suppression of MDR1 expression was reduced by AMPK inhibitor (compound C). Furthermore, both MDR1 protein expression and the transcriptional activity of cAMP-responsive element (CRE) were inhibited by puerarin and protein kinase A/CRE inhibitor (H89). Taken together, our results suggested that puerarin down-regulated MDR1 expression via nuclear factor kappa-B and CRE transcriptional activity-dependent up-regulation of AMPK in MCF-7/adr cells.

Glucosylceramide synthase upregulates MDR1 expression in the regulation of cancer drug resistance through cSrc and β-catenin signaling

BackgroundDrug resistance is the outcome of multiple-gene interactions in cancer cells under stress of anticancer agents. MDR1 overexpression is most commonly detected in drug-resistant cancers and accompanied with other gene alterations including enhanced glucosylceramide synthase (GCS). MDR1 encodes for P-glycoprotein that extrudes anticancer drugs. Polymorphisms of MDR1 disrupt the effects of P-glycoprotein antagonists and limit the success of drug resistance reversal in clinical trials. GCS converts ceramide to glucosylceramide, reducing the impact of ceramide-induced apoptosis and increasing glycosphingolipid (GSL) synthesis. Understanding the molecular mechanisms underlying MDR1 overexpression and how it interacts with GCS may find effective approaches to reverse drug resistance.ResultsMDR1 and GCS were coincidently overexpressed in drug-resistant breast, ovary, cervical and colon cancer cells; silencing GCS using a novel mixed-backbone oligonucleotide (MBO-asGCS) sensitized these four drug-resistant cell lines to doxorubicin. This sensitization was correlated with the decreased MDR1 expression and the increased doxorubicin accumulation. Doxorubicin treatment induced GCS and MDR1 expression in tumors, but MBO-asGCS treatment eliminated "in-vivo" growth of drug-resistant tumor (NCI/ADR-RES). MBO-asGCS suppressed the expression of MDR1 with GCS and sensitized NCI/ADR-RES tumor to doxorubicin. The expression of P-glycoprotein and the function of its drug efflux of tumors were decreased by 4 and 8 times after MBO-asGCS treatment, even though this treatment did not have a significant effect on P-glycoprotein in normal small intestine. GCS transient transfection induced MDR1 overexpression and increased P-glycoprotein efflux in dose-dependent fashion in OVCAR-8 cancer cells. GSL profiling, silencing of globotriaosylceramide synthase and assessment of signaling pathway indicated that GCS transfection significantly increased globo series GSLs (globotriaosylceramide Gb3, globotetraosylceramide Gb4) on GSL-enriched microdomain (GEM), activated cSrc kinase, decreased β-catenin phosphorylation, and increased nuclear β-catenin. These consequently increased MDR1 promoter activation and its expression. Conversely, MBO-asGCS treatments decreased globo series GSLs (Gb3, Gb4), cSrc kinase and nuclear β-catenin, and suppressed MDR-1 expression in dose-dependent pattern.ConclusionThis study demonstrates, for the first time, that GCS upregulates MDR1 expression modulating drug resistance of cancer. GSLs, in particular globo series GSLs mediate gene expression of MDR1 through cSrc and β-catenin signaling pathway.

UHRF1 inhibits MDR1 gene transcription and sensitizes breast cancer cells to anticancer drugs

Overexpression of MDR1 in breast cancer remains a major cause for the failure of chemotherapy. In the present report, we find UHRF1 plays an important role in inhibiting MDR1 promoter activity by directly binding to the MDR1 promoter. Knockdown of UHRF1 activates MDR1 promoter activity and expression, attenuates the binding of UHRF1 and HDAC1 to the MDR1 promoter.Overexpression of UHRF1 in NCI/ADR-RES cells can induce deacetylation of histones H3 and H4 on the MDR1 promoter, which is facilitated by recruitment of HDAC1 to the MDR1 promoter. Loss of histone acetylation is accompanied by loss of binding of the key transcription factor, MyoD, CBP and p300, locking in marked suppression of MDR1, increasing sensitivity of MDR cancer cells to cytotoxic drugs that are transported by P-glycoprotein(P-gp). The inhibition of MDR1 expression by UHRF1 may provide potential ways to overcome multidrug resistance (MDR) in breast cancer treatment.

Increased Nuclear Localization of Transcription Factor Y-Box Binding Protein 1 Accompanied by Up-Regulation of P-Glycoprotein in Breast Cancer Pretreated with Paclitaxel.

Abstract Purpose: The Y-box binding protein 1 (YB-1) regulates expression of P-glycoprotein (P-gp) encoded by the MDR1 gene. There have been no previous studies regarding the involvement of YB-1 in the development of resistance to paclitaxel. The present study was performed to examine how paclitaxel affects the localization and expression of YB-1 in breast cancer.Experimental Design: We evaluated the expression and localization of YB-1 and P-gp in breast cancer tissues obtained from 27 patients before and after treatment with paclitaxel. The effect of paclitaxel on localization of cellular YB-1 was examined by using GFP-YB-1. Interaction of YB-1 with the Y-box motif of the MDR1 promoters was studied by EMSA. The effects of paclitaxel on MDR1 promoter activity were examined by luciferase assay.Results: Of 27 breast cancer tissues treated with paclitaxel, nine (33%) showed translocation of YB-1 from the cytoplasm to the nucleus together with increased expression of P-gp during the course of treatment. Twelve breast cancer tissues (44%) showed neither translocation of YB-1 nor increased expression of P-gp. Nuclear translocation of YB-1 was correlated significantly with increased expression of P-gp (P=0.0037). Confocal analysis indicated that paclitaxel induced nuclear translocation of green fluorescent fused YB-1 in MCF7 cells. Furthermore, binding of YB-1 to the Y-box of MDR1 promoter was increased in response to treatment with paclitaxel. In addition, MDR1 promoter activity was significantly up-regulated by paclitaxel in MCF7 cells (p< 0.001).Conclusions: The results of the present study suggested that YB-1 may be involved in the development of resistance to paclitaxel in breast cancer. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1141.

Effect of MDR1 gene promoter methylation in patients with ulcerative colitis

Altered MDR1 expression and/or function contribute to the pathogenesis of inflammatory bowel disease (IBD). DNA methylation was shown as an important mechanism in gene silencing. We investigated DNA methylation of the MDR1 gene in ulcerative colitis (UC) and its relation to MDR1 C3435T genotypes. Eighty-three UC patients were enrolled. Methylation of MDR1 promoter was determined by methylation specific polymerase (MSP) for rectal inflammatory mucosa from all patients and normal terminal ileum from 17 patients. Promoter methylation of MDR1 gene was also quantified by digital densitographic analysis following MSP. MDR1 methylation was detected in 51 (61.4%) out of 83 patients in rectal inflammatory mucosa. Mean methylation level of MDR1 gene in rectal inflammatory mucosa was significantly higher than in normal terminal ileum (p=0.021). MDR1 methylation occurred more frequently in total colitis, and total+left side colitis, compared to rectal colitis (p=0.001, 0.013, respectively). Higher methylation levels were also associated with chronic continuous type (p=0.034) and earlier onset of disease (p=0.038). The 3435 CC+CT genotype of MDR1 was associated with more than 6-fold increased risk of MDR1 methylation, especially in UC patients with 9 years and shorter duration. Both frequency and level of MDR1 methylation were higher in UC onset at younger or in middle age with the same genotype. MDR1 methylation frequently occurred in inflammatory rectal mucosa from UC patients and was influenced by MDR1 C3435T polymorphism, especially in patients with shorter duration and younger onset.

Correlation Between MDR1 Methylation Status in the Promoter Region and MDR1 Genetic Polymorphism in 194 Healthy Chinese Han subjects

To investigate the correlation between the methylation status in the MDR1 promoter region and the MDR1 genetic polymorphism. A total of 194 unrelated subjects (105 men and 89 women) with a median age of 26 years were enrolled in this study. DNA was extracted and PCR-RFLP was performed for C1236T, C3435T and G2677T/A polymorphism genotyping. The combined bisulfite restriction analysis (COBRA) method was also performed to determine DNA methylation levels in the MDR1 promoter region. Genotype frequencies for the variants SNPs were assessed for deviation from Hardy-Weinberg equilibrium using the chi2 test. Nonparametric tests including Kruskal-Wallis method and the Mann-Whitney U test were used to compare the DNA methylation levels between different genotypes. The allelic frequency distribution of the C1236T, C3435T and G2677T/A was found to be in good agreement with previous reports. Our study revealed significant correlation between different genotypes of C3435T and G2677T/A, but there is no significant difference between the different genotypes of C1236T. A correlation between MDR1 genetic polymorphisms C3435T and G2677T/A, as well as haplotypes derived from C1236T, G2677T/A and C3435T, with methylation status of MDR1 promoter region was found in this study. Further investigations are needed to explore the molecular mechanism and clinical significance of this correlation.

Cantharidin reverses multidrug resistance of human hepatoma HepG2/ADM cells via down-regulation of P-glycoprotein expression

Multidrug resistance (MDR) is a serious obstacle encountered in cancer treatment. In this study, we established an in vitro multiple drug resistant HepG2 cell line (HepG2/ADM), and characterized its MDR. This model was used to screen potential candidate chemosensitisers from over 200 purified naturally occurring compounds extracted from plants and animals. Cantharidin was found to have a significant reversal on MDR in our model. Further, our results showed that Cantharidin could significantly inhibit P-gp (P-glycoprotein) expression, mRNA transcription, as well as MDR1 promoter activity. These results suggest that Cantharidin is a novel and potent MDR reversal agent and may be a potential adjunctive agent for tumor chemotherapy.

Rexinoids Modulate Steroid and Xenobiotic Receptor Activity by Increasing Its Protein Turnover in a Calpain-dependent Manner

The steroid and xenobiotic receptor SXR (human pregnane X receptor) is a nuclear receptor that plays a key role in the body's detoxification response by regulating genes involved in drug metabolism and transport. SXR ligands include a wide range of compounds, which induce transcription of SXR target genes via activation of a heterodimeric transcription factor consisting of SXR and the related nuclear receptor retinoid X receptor (RXR). We investigated the effect of RXR-selective ligands, rexinoids, on SXR/RXR activity. In agreement with previous reports, we found that rexinoids are weak activators of SXR, but we also found that they can antagonize SXR activation by the potent SXR agonist rifampicin. This antagonism included suppression of rifampicin-induced expression of SXR target genes, as well as reduced binding of SXR/RXR to SXR response elements both in vivo and in vitro. Interestingly, two rexinoids, bexarotene (LGD1069/Targretin) and LG100268, caused a rapid and sustained decrease in the protein levels of both SXR and RXR. The decrease in SXR level was due to an enhanced rate of protein degradation and was dependent on calpain activity, as opposed to rexinoid-induced RXR degradation, which is mediated via the proteasome. Thus, we have demonstrated a novel, rexinoid-modulated mechanism regulating SXR protein stability, which may explain why rexinoids are only weak activators of SXR/RXR-mediated transcription, despite reports that they bind to SXR with high affinity. We suggest that the ability of rexinoids to induce degradation of both SXR and RXR, in combination with competition for binding to SXR, can also explain why rexinoids antagonize the activation of SXR by drugs like rifampicin.

Activation of β‐catenin signalling by GSK‐3 inhibition increases p‐glycoprotein expression in brain endothelial cells

This study investigates involvement of beta-catenin signalling in regulation of p-glycoprotein (p-gp) expression in endothelial cells derived from brain vasculature. Pharmacological interventions that enhance or that block beta-catenin signalling were applied to primary rat brain endothelial cells and to immortalized human brain endothelial cells, hCMEC/D3, nuclear translocation of beta-catenin being determined by immunocytochemistry and by western blot analysis to confirm effectiveness of the manipulations. Using the specific glycogen synthase kinase-3 (GSK-3) inhibitor 6-bromoindirubin-3'-oxime enhanced beta-catenin and increased p-gp expression including activating the MDR1 promoter. These increases were accompanied by increases in p-gp-mediated efflux capability as observed from alterations in intracellular fluorescent calcein accumulation detected by flow cytometry. Similar increases in p-gp expression were noted with other GSK-3 inhibitors, i.e. 1-azakenpaullone or LiCl. Application of Wnt agonist [2-amino-4-(3,4-(methylenedioxy) benzylamino)-6-(3-methoxyphenyl)pyrimidine] also enhanced beta-catenin and increased transcript and protein levels of p-gp. By contrast, down-regulating the pathway using Dickkopf-1 or quercetin decreased p-gp expression. Similar changes were observed with multidrug resistance protein 4 and breast cancer resistance protein, both known to be present at the blood-brain barrier. These results suggest that regulation of p-gp and other multidrug efflux transporters in brain vasculature can be influenced by beta-catenin signalling.

Mutations in the multi‐drug resistance regulator MRR1, followed by loss of heterozygosity, are the main cause of MDR1 overexpression in fluconazole‐resistant Candida albicans strains

Overexpression of the MDR1 gene, encoding a multi-drug efflux pump of the major facilitator superfamily, is a major cause of resistance to the widely used antifungal agent fluconazole and other toxic substances in the fungal pathogen Candida albicans. We found that all tested clinical and in vitro generated C. albicans strains that had become fluconazole-resistant by constitutive MDR1 upregulation contained mutations in the MRR1 gene, which encodes a transcription factor that controls MDR1 expression. Introduction of the mutated alleles into a drug-susceptible C. albicans strain resulted in activation of the MDR1 promoter and multi-drug resistance, confirming that the amino acid substitutions in Mrr1p were gain-of-function mutations that rendered the transcription factor constitutively active. The majority of the MDR1 overexpressing strains had become homozygous for the mutated MRR1 alleles, demonstrating that the increased resistance level conferred by two gain-of-function alleles provides sufficient advantage to select for the loss of heterozygosity in the presence of fluconazole both in vitro and within the human host during therapy. Loss of heterozygosity usually occurred by mitotic recombination between the two chromosome 3 homologues on which MRR1 is located, but evidence for complete loss of one chromosome and duplication of the chromosome containing the mutated MRR1 allele was also obtained in two in vitro generated fluconazole-resistant strains. These results demonstrate that gain-of-function mutations in MRR1 are the major, if not the sole, mechanism of MDR1 overexpression in fluconazole-resistant strains and that this transcription factor plays a central role in the development of drug resistance in C. albicans.

Inhibit multidrug resistance and induce apoptosis by using glycocholic acid and epirubicin

Cancer-cell resistance to chemotherapy limits the efficacy of cancer treatment. The primary mechanisms of multidrug resistance (MDR) are “pump” and “non-pump” resistance. We evaluated the effects and mechanisms of glycocholic acid (GC), a bile acid, on inhibiting pump and non-pump resistance, and increasing the chemosensitivity of epirubicin in human colon adenocarcinoma Caco-2 cells and rat intestine. GC increased the cytotoxicity of epirubicin, significantly increased the intracellular accumulation of epirubicin in Caco-2 cells and the absorption of epirubicin in rat small intestine, and intensified epirubicin-induced apoptosis. GC and epirubicin significantly reduced mRNA expression levels of human intestinal MDR1, MDR-associated protein (MRP)1, and MRP2; downregulated the MDR1 promoter region; suppressed the mRNA expression of Bcl-2; induced the mRNA expression of Bax; and significantly increased the Bax-to-Bcl-2 ratio and the mRNA levels of p53, caspase-9 and -3. This suggests that GC- and epirubicin-induced apoptosis was mediated through the mitochondrial pathway. We conclude that simultaneous suppression of pump and non-pump resistance dramatically increased the chemosensitivity of epirubicin. A combination of anticancer drugs with GC can control MDR via a mechanism that involves modulating P-gp and MRPs as well as regulating apoptosis-related pathways.

Rifampicin induces MDR1 expression in Candida albicans

Overexpression of efflux pumps such as MDR1 has been identified as an important mechanism contributing to fluconazole resistance in Candida albicans. This phenomenon is frequently observed in fluconazole-resistant strains isolated from AIDS patients treated with various pharmaceuticals. Therefore, we hypothesized that some of these compounds might influence the expression of genes responsible for fluconazole resistance. We examined a variety of clinically relevant compounds for their in vitro effects on MDR1 expression with a C. albicans reporter strain containing a transcriptional fusion of the MDR1 promoter (MDR1P) with the gfp gene. Activation of the MDR1 promoter and subsequent green fluorescent protein production was determined by fluorescence microscopy and flow cytometry. Additionally, MDR1 transcription was confirmed and quantified by RT-PCR analysis, followed by Mdr1p detection by western blot. Finally, the effect of a selected agent on resistance to fluconazole was tested by chequerboard titration of both substances. Of 15 compounds tested, only rifampicin induced a rapid and dose-dependent increase in MDR1 expression (up to 122-fold induction), whereas structurally related molecules such as rifabutin and rifamycin were not active. Induction of MDR1 expression upon rifampicin exposure was also observed in 10 blood culture isolates. In contrast, rifampicin exposure did not markedly affect the expression of the transporters CDR1 and CDR2. Increased MDR1 expression was accompanied by elevated MICs for fluconazole after exposure of C. albicans to rifampicin, whereas Mdr1p expression was only moderately induced. Out of the compounds examined, only rifampicin specifically induced MDR1 expression in all C. albicans strains tested. Rifampicin may play a general role in signal transduction or another means of modulation of gene expression in C. albicans.

Lack of P-Glycoprotein Expression by Low-Dose Fractionated Radiation Results from Loss of Nuclear Factor-κB and NF-Y Activation in Oral Carcinoma Cells

Multidrug resistance (MDR) is associated with the overproduction of the 170-kDa transmembrane protein P-glycoprotein (MDR1) caused by transcriptional activation. However, the activity of the MDR1 promoter in response to different doses of ionizing radiation has not been investigated. In this study, two squamous cell carcinoma oral cavity cell lines, T-167 and T-409, were exposed to either a standard clinical dose of 2 Gy or low-dose fractionated radiation therapy (LDFRT), delivered as 0.5 Gy in four fractions. MDR1 gene expression and degree of cell death were assessed. Clinically relevant 2-Gy dose of radiation resulted in increased expression of MDR1 by reverse transcription-PCR and luciferase reporter assays in both cell lines (T-167 and T-409), whereas LDFRT did not. LDFRT caused enhanced apoptosis when compared with the 2-Gy dose in T-167 and T-409 cells as assessed by terminal nucleotidyl transferase-mediated nick end labeling (TUNEL) assays. Transcription of the MDR1 gene is regulated by numerous transcription factors, which include nuclear factor-kappaB (NF-kappaB), NF-Y, SP1, YB1, MEF1 (MDR1 promoter-enhancing factor 1), p53, and NF-R1. Interestingly, 2 Gy robustly induced both NF-kappaB and NF-Y in T-167 and T-409 cells, but did not show induction when exposed to LDFRT. Silencing the expression of the DNA binding subunit of NF-kappaB, p50, by small interfering RNA vector resulted in a decrease of MDR1 function by rhodamine 123 efflux assay in T167 cells exposed to 2 Gy. Together, these results provide evidence for the lack of induction of P-glycoprotein expression by LDFRT, which has important implications in combinatorial cancer therapy, including the use of LDFRT as an adjuvant for chemotherapy.

Genomic variation at the MDR1 promoter and P-glycoprotein expression and activity in AML patients

Sequence variation at the proximal MDR1 promoter of 72 patients with acute myeloid leukemia (AML) was investigated and its association with P-glycoprotein (Pgp) expression and activity using flow cytometry were analyzed. Two variants were found: −129T/C and a non-described A/T substitution at position +68 of intron 1 in one patient. Three different genotypes were identified for single nucleotide polymorphism (SNP) −129T/C: 60 patients TT, 11 individuals TC, and 1 CC. No significant association was found between SNP variants and Pgp activity and expression, at protein level. Our data also suggested that an evaluation of MDR1 promoter polymorphisms is of uncertain prognostic value.

ΔNp73α regulates MDR1 expression by inhibiting p53 function

The p73 protein is a transcription factor and member of the p53 protein family that expresses as a complex variety of isoforms. DeltaNp73alpha is an N-terminally truncated isoform of p73. We found that DeltaNp73 protein is upregulated in human gastric carcinoma suggesting that DeltaNp73 may play an oncogenic role in these tumors. Although it has been shown that DeltaNp73alpha inhibits apoptosis and counteracts the effect of chemotherapeutic drugs, the underlying mechanism by which this p73 isoform contributes to chemotherapeutic drug response remains to be explored. We found that DeltaNp73alpha upregulates MDR1 mRNA and p-glycoprotein (p-gp), which is involved in chemotherapeutic drug transport. This p-gp upregulation was accompanied by increased p-gp functional activity in gastric cancer cells. Our data suggest that upregulation of MDR1 by DeltaNp73alpha is mediated by interaction with p53 at the MDR1 promoter.

Construction of double suicide genes system controlled by MDR1 promoter with targeted expression in drug-resistant glioma cells

The multiple drug resistance protein (MDR1) is frequently overexpressed in human glioma. The aim of this study is to clone the MDR1 promoter from C6/ADR, construct the double suicide genes expressive vector controlled by MDR1 promoter, and explore its targeted expression in C6/ADR cells. MDR1 promoter from C6/ADR genomic DNA, which was linked with T vector, was amplified by using Polymerase chain reaction (PCR). After cut by NdeI and HindIII, MDR1 promoter was cloned into pcDNA3-TK (thymidine kinase) plasmid. The cytosine deaminase (CD) gene from pcDNA3-CD-TK plasmid was directly cloned into the above vector to construct pcDNA3-MDR1-promoter-CD-TK vector. Then this vector was transfected into C6 and C6/ADR cells respectively by liposome. After selection by G418, the tumor cell lines were stably established. Then these cell lines were examined through PCR and RT-PCR to respectively detect the integration and expression of TK and CD genes. The results showed the length and sequence of MDR1 promoter amplified by PCR were confirmed by DNA sequencing. The pcDNA3-MDR1-promoter-CD-TK expression vectors were constructed successfully. PCR indicated the double suicide genes were integrated into C6 and C6/ADR cells. RT-PCR revealed that CD and TK genes expressed in C6/ADR/CD-TK cells, whereas not in C6/CD-TK cells. In conclusions, construction of expressive vector containing double suicide genes controlled by MDR1 promoter with targeted expression in C6/ADR will provide a sound basis for targeted gene therapy for multidrug resistance (MDR) glioma.

Involvement of CtBP1 in the transcriptional activation of the MDR1 gene in human multidrug resistant cancer cells

Drug resistance caused by overexpression of P-glycoprotein (P-gp), the MDR1 ( ABCB1) gene product, limits the therapeutic outcome. Expression of MDR1 can be induced by divergent stimuli, and involves a number of transcriptional factors. We found that the expression of CtBP1 (C-terminal-binding protein 1), a transcriptional co-regulator, was increased (∼4-fold) in human multidrug resistant (MDR) cancer cell lines, NCI/ADR-RES and A2780/DX, as compared to their sensitive counterparts. Silencing of CtBP1 expression by RNAi decreased the MDR1 mRNA and P-gp. Knockdown of CtBP1 also enhanced the sensitivity of MDR cells to chemotherapeutic drugs that are transported by P-gp and increased intracellular drug accumulation. In a reporter gene assay, co-transfection of MDR1 promoter constructs with a CtBP1 expression vector resulted in a ∼2–4-fold induction of MDR1 promoter activity. CtBP1 appeared to contribute to the activation of MDR1 transcription through directly interacting with the MDR1 promoter, as evidenced by its physical binding to the promoter region of the MDR1 gene in chromatin immunoprecipitation and electromobility shift assays. Histone modifications at the MDR1 promoter, such as mono-methylation, di-methylation, and acetylation of histone H3, were not found to be affected by silencing of CtBP1 expression. Our results reveal a novel role for CtBP1 as an activator of MDR1 gene transcription, and suggest that CtBP1 might be one of the key transcription factors involved in the induction of MDR1 gene. Therefore, CtBP1 may represent a potentially new target for inhibiting drug resistance mediated by overexpression of the MDR1 gene.

Phosphorylation of RNA Helicase A by DNA-Dependent Protein Kinase Is Indispensable for Expression of the MDR1 Gene Product P-Glycoprotein in Multidrug-Resistant Human Leukemia Cells

Development of multidrug resistance (MDR) in cancer frequently involves overexpression of the MDR1 gene product P-glycoprotein (P-gp), a drug transporter which severely impedes the efficacy of chemotherapy. Because intensive efforts to identify therapeutics that reverse MDR by inhibiting the drug transport activity of P-gp have not yet met with success, we have focused on the alternative strategy of targeting MDR1 promoter activation to knockdown P-gp expression in cancer cells. We recently identified RNA helicase A (RHA) inhibition as a rational strategy to downregulate P-gp in leukemia cells by showing that RHA RNAi knockdown abrogated P-gp expression in MDR variants of human leukemia HL-60 cells. In that report, we also demonstrated that RHA activated the MDR1 promoter in the MDR variant cells but not in the drug-sensitive counterpart. This led us to hypothesize that P-gp induction by RHA required cooperation with another factor present only in the MDR variants. Here, we identify the RHA cooperating factor as DNA-PK catalytic subunit (cs), and we show that DNA-PKcs resides with RHA at the MDR1 promoter in a multiprotein complex. Furthermore, targeted DNA-PKcs inhibition abrogated P-gp expression in the MDR variant cells. We demonstrate that constitutive multisite RHA phosphorylation producing retarded migration in SDS-PAGE is catalyzed by DNA-PKcs in the MDR variants, and does not occur in the parental cells, which are DNA-PKcs deficient. The indispensable role played by DNA-PK in P-gp overexpression in MDR leukemia cells in this report identifies targeted DNA-PK inhibition as a rational strategy to reverse drug resistance in cancer.

The establishment of two paclitaxel‐resistant prostate cancer cell lines and the mechanisms of paclitaxel resistance with two cell lines

Although paclitaxel is used for hormone-resistant prostate cancer, relapse definitely occurs later. Details of the molecular mechanism responsible for paclitaxel- resistance remain unclear. We established paclitaxel-resistant cells, DU145-TxR and PC-3-TxR from parent DU145 and PC-3. To characterize these cells, we examined cross-resistance to other anticancer drugs. Expression of several potential genes that had been related to drug-resistance was compared with parent cells by RT-PCR and Western blotting. Methylation analysis of multiple drug resistance (MDR1) promoter was carried out using bisulfite-modified DNA from cell lines. Knockdown experiments using small interfering RNA (siRNA) were also performed to confirm responsibility of drug-resistance. Finally, cDNA microarray was performed to quantify gene expression in PC-3 and PC-3-TxR cells. The IC(50) for paclitaxel in DU145-TxR and PC-3-TxR was 34.0- and 43.4-fold higher than that in both parent cells, respectively. Both cells showed cross-resistance to some drugs, but not to VP-16 and cisplatin. Methylation analysis revealed that methylated CpG sites of MDR1 promoter in DU145 and PC-3 cells were demethylated in DU145-TxR cells, but not in PC-3-TxR cells. Knockdown of P-glycoprotein (P-gp), which was up-regulated in resistant cells, by MDR-1 siRNA restored paclitaxel sensitivity in DU145-TxR but not in PC-3-TxR, indicating that up-regulation of P-gp was not always main cause of paclitaxel-resistance. Microarray analysis identified 201 (1.34%) up-regulated genes and 218 (1.45%) out of screened genes in PC-3-TxR. Our data will provide molecular mechanisms of paclitaxel-resistance and be useful for screening target genes to diagnose paclitaxel sensitivity.

Differential modulation of nuclear texture, histone acetylation, and MDR1 gene expression in human drug-sensitive and -resistant OV1 cell lines

Image cytometric study of pathological specimens or cell lines has suggested that epigenetic mechanisms are likely to play a major role in determining chromatin patterns evaluable through nuclear texture analysis. We previously reported that nuclear textural changes observed in the OV1-VCR etoposide-resistant ovarian carcinoma cell line were associated with an increased acetylated histone H4 level. In this study we analyzed the effects of treatments with the HDAC inhibitor trichostatin A (TSA) or with nickel subsulfide on histone H4 acetylation, nuclear texture, and MDR1 gene expression in drug-sensitive IGROV1 and drug-resistant OV1-VCR cell lines. In IGROV1 cells, TSA induced an increase in acetylated H4 level associated with a chromatin textural decondensation and an increase in MDR1 gene expression. In OV1-VCR cells, a similar increase in H4 acetylation was observed, but nuclear texture or MDR1 gene expression remained unchanged. ChIP analysis revealed that MDR1 gene expression remained stable in TSA-treated OV1-VCR cells despite a localized increase in H4 acetylation at the promoter level. Analysis of the methylation status of MDR1 promoter showed an increase in DNA methylation at 3 specific sites in OV1-VCR cells, that could participate to TSA low responsiveness in these cells. Treatment with nickel subsulfide induced a decrease in H4 acetylation without any effect on nuclear texture characteristics in both cell lines. In OV1-VCR cells, nickel subsulfide induced a significant down-regulation of the MDR1 gene expression. These results indicate that modulation of histone H4 acetylation level can be associated with up- or down-regulation of the MDR1 gene in OV1 cells. However, this modulation does not always result in chromatin pattern alterations and these data emphasize the complexity of chromatin texture regulation in tumor cells.