Regulation of the MDR1 promoter by E2F1 and EAPP

Intestinal Flora in Chemotherapy Resistance of Biliary Pancreatic Cancer

Biliary pancreatic malignancy has an occultic onset, a high degree of malignancy, and a poor prognosis. Most clinical patients miss the opportunity for surgical resection of the tumor. Systemic chemotherapy is still one of the important methods for the treatment of biliary pancreatic malignancies. Many chemotherapy regimens are available, but their efficacy is not satisfactory, and the occurrence of chemotherapy resistance is a major reason leading to poor prognosis. With the advancement of studies on intestinal flora, it has been found that intestinal flora is correlated with and plays an important role in chemotherapy resistance. The application of probiotics and other ways to regulate intestinal flora can improve this problem. This paper aims to review and analyze the research progress of intestinal flora in the chemotherapy resistance of biliary pancreatic malignancies to provide new ideas for treatment.

Overcoming ABCB1-mediated multidrug resistance by transcription factor BHLHE40

Multidrug resistance (MDR) hinders treatment efficacy in cancer therapy. One typical mechanism contributing to MDR is the overexpression of permeability-glycoprotein (P-gp) encoded by ATP-binding cassette subfamily B member 1 (ABCB1). Basic helix-loop-helix family member e40 (BHLHE40) is a well-known transcription factor that has pleiotropic effects including the regulation of cancer-related processes. However, whether BHLHE40 regulates MDR is still unknown. Chromatin immunoprecipitation-seq study revealed BHLHE40 occupancy in the promoter of ABCB1 gene. Adriamycin (ADM)-resistant human chronic myeloid leukemia cells (K562/A) and human breast cancer cells (MCF-7/A) were established. BHLHE40 expression was downregulated in the ADM-resistant cell lines. Overexpression of BHLHE40 resensitized resistant cells to ADM, promoted cell apoptosis in vitro and suppressed tumor growth in vivo, whereas BHLHE40 knockdown induced resistance to ADM in parental cells. Moreover, we found that BHLHE40 regulated drug resistance by directly binding to the ABCB1 promoter (-1605 to -1597) and inactivating its transcription. In consistence, the expression of BHLHE40 was negatively correlated with ABCB1 in various cancer cells, while positively with cancer cell chemosensitivity and better prognosis of patients with breast cancer. The study reveals the role of BHLHE40 as a transcriptional suppressor on the expression of ABCB1, major ABC transporter in chemoresistance. The findings extend the function of BHLHE40 in tumor progression and provides a novel mechanism for the reversal of multidrug resistance.

Circular RNAcirc_0076305 Promotes Cisplatin (DDP) Resistance of Non-Small Cell Lung Cancer Cells by Regulating ABCC1 Through miR-186-5p

Background: Lung cancer is a social problem of increasing concern, and non-small cell lung cancer (NSCLC) accounts for 80%-85% incidence of lung cancer. Cisplatin (DDP) is reported as a first-line chemotherapy drug for NSCLC, but the resistance has became a main obstacle for NSCLC treatment. The high level of circular RNA circ_0076305 was related to the DDP resistance in NSCLC. However, the mechanism of circ_0076305 remains unclear in DDP resistance of NSCLC. Materials and Methods: Exosomes were detected by a transmission electron microscope and nanoparticle tracking analysis. The protein levels of CD63, CD81, P-glycoprotein (P-gp), Lung resistance-related protein, and ATP-binding cassette subfamily C member 1 (ABCC1) were examined by Western blot assay. Circ_0076305, microRNA-186-5p (miR-186-5p), and ABCC1 levels were tested by real-time quantitative polymerase chain reaction. DDP resistance was examined by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide assay. The binding relationship between miR-186-5p and circ_0076305 or ABCC1 was predicted by circRNA interactome or starBase, and then verified by dual-luciferase reporter and RNA immunoprecipitation assays. The effect of circ_0076305 on DDP resistance in NSCLC was examined by xenograft tumor model in vivo. Results: Circ_0076305 was increased in NSCLC cell-derived exosomes, DDP-resistant NSCLC tissues and cells. Circ_0076305 knockdown elevated DDP sensitivity in vitro. Mechanically, circ_0076305 enhanced ABCC1 expression through sponging miR-186-5p, thus regulating DDP resistance of NSCLC. Furthermore, circ_0076305 silencing improved DDP sensitivity of NSCLC in vivo. Conclusion: The results from this study disclosed that circ_0076305 knockdown improved DDP sensitivity by the miR-186-5p/ABCC1 axis in NSCLC, hinting a potential circRNA-targeted therapy for NSCLC.

Indole Curcumin Reverses Multidrug Resistance by Reducing the Expression of ABCB1 and COX2 in Induced Multidrug Resistant Human Lung Cancer Cells

Background:

Drug resistance by the cancer cells towards current chemotherapeutic approaches poses a great challenge. In the present study, an indole analogue of a well-known plant derived anticancer molecule, curcumin, was tested for its Multidrug Resistance (MDR) reversing potential in induced multi drug resistant A549 cell line.

Materials and Methods:

Human lung cancer cell line A549 was made Multidrug Resistant (MDR) by prolonged treatment with low dosage of Docetaxel, an established anticancer drug. The MDR induction was confirmed by morphological evidence, Hoechst 33342 staining, MTT assay, Rhodamine123 staining and RT-PCR of ABCB1 gene. Protein expression studies were carried out using western blotting technique

Results and Discussions:

The induced MDR A549 cells exhibited significant increase in the gene expression of ABCB1 gene at the transcriptional level. Retention and efflux studies with Pglycoprotein (P-gp) substrate Rh123 indicated that indole curcumin inhibited P-gp mediated efflux of Rhodamine. Furthermore, treatment of MDR A549 cells with indole curcumin showed downregulation of gene expression of ABCB1 and COX 2. This was also confirmed from the decreased protein expression of COX 2.

Conclusion:

The results of the present study indicate that indole curcumin reverses multi drug resistance by downregulating the expression of ABCB1 and COX 2 genes. Thus, indole curcumin may act as a potent modulator for ABCB1 and COX 2 mediated MDR in lung cancer.

10-Phenyltriazoyl Artemisinin is a Novel P-glycoprotein Inhibitor that Suppresses the Overexpression and Function of P-glycoprotein

Background:

The effect of drugs on ATP-binding cassette transporters, especially permeabilityglycoprotein (P-gp), is an important consideration during new anti-cancer drug development.

Objective:

In this context, the effects of a newly synthesized artemisinin derivative, 10-(4-phenyl-1H-1,2,3- triazol)-artemisinin (5a), were evaluated on P-gp expression and function.

Methods:

Reverse transcript polymerase chain reaction and immunoblotting techniques were used to determine the effect of 5a on P-gp expression in LS174T cells. In addition, the ability of 5a to work as either a substrate or an inhibitor of P-gp was investigated through different methods.

Results:

The results revealed that 5a acts as a novel P-gp inhibitor that dually suppresses the overexpression and function of P-glycoprotein. Co-treatment of LS174T cell line, human colon adenocarcinoma cell line, with 5a and paclitaxel recovered the anticancer effect of paclitaxel by controlling the acquired drug resistance pathway. The overexpression of P-gp induced by rifampin and paclitaxel in a colorectal cell line was suppressed by 5a which could be a novel inhibitory substrate inhibiting the transport of paclitaxel by P-gp.

Conclusion:

The results revealed that 5a can be classified as a type B P-gp inhibitor (with both substrate and inhibitor activities) with an additional function of suppressing P-gp overexpression. The results might be clinically useful in the development of anticancer drugs against cancers with multidrug resistance.

Expression of multidrug-resistance associated proteins in human retinoblastoma treated by primary enucleation

AIM

To reveal the expression of multidrug-resistance associated proteins: glutathione-S-transferase π (GSTπ), P-glycoprotein (P-gp) and vault protein lung resistance protein (LRP) in retinoblastoma (RB) without any conservative treatment before primary enucleation and to correlate this expression with histopathological tumor features.

METHODS

A total of 42 specimens of RB undergone primary enucleation were selected for the research. Sections from the formalin-fixed, paraffin-embedded specimens were stained with HE and immunohistochemistry to detect the expression of GSTπ, P-gp and LRP.

RESULTS

GSTπ was expressed in 39/42 (92.86%) RBs and in 9/9 (100%) well-differentiated RBs. P-gp/GSTπ was found in 30 (71.42%) of 42 RBs. Totally 9 (21.43%) tumors were well differentiated and 33 (78.57%) were poorly differentiated. Totally 15 (35.71%) eyes had optic nerve (ON) tumor invasion, 36 (85.71%) had choroidal tumor invasion, and 14 (33.33%) had simultaneous choroidal and ON invasion. There was no statistically significant relationship between P-gp, GSTπ, LRP positivity and the degree of ocular layer tumor invasion and ON tumor invasion (P>0.05).

CONCLUSION

RB intrinsically expresses GSTπ, P-gp and LRP. GSTπ expression is positive in 100% well-differentiation ones, so in which way it is correlated with differentiation. But the other two proteins expressions are not related to tumor differentiation and to the degree of tumor invasion. GSTπ may be a new target of chemotherapy in RB.

LncRNA NEAT1 contributes to paclitaxel resistance of ovarian cancer cells by regulating ZEB1 expression via miR-194

Background

Chemoresistance is one of the major obstacles for cancer therapy in the clinic. Nuclear paraspeckle assembly transcript 1 (NEAT1) has been reported as an oncogene in most malignancies such as lung cancer, esophageal cancer, and gastric cancer. This study is designed to investigate the function of NEAT1 in paclitaxel (PTX) resistance of ovarian cancer and its potential molecular mechanism.

Patients and methods

The expressions of NEAT1 and miR-194 in ovarian cancer tissues and cells were estimated by quantitative real-time polymerase chain reaction (qRT-PCR). MTT, flow cytometry, and Western blot assays were used to assess the effect of NEAT1 on PTX resistance in PTX-resistant ovarian cancer cells. Luciferase reporter assay was applied to examine the association between NEAT1, zinc finger E-box-binding homeobox 1 (ZEB1) and miR-194. Xenograft tumor model was established to confirm the biological role of NEAT1 in PTX resistance of ovarian cancer in vivo.

Results

NEAT1 was upregulated, and miR-194 was downregulated in PTX-resistant ovarian cancer tissues and cells. Functionally, NEAT1 knockdown enhanced cell sensitivity to PTX via promoting PTX-induced apoptosis in vitro. NEAT1 was identified as a molecular sponge of miR-194 to upregulate ZEB1 expression. Mechanistically, NEAT1-knockdown-induced PTX sensitivity was mediated by miR-194/ZEB1 axis. Moreover, NEAT1 knockdown improved PTX sensitivity of ovarian cancer in vivo.

Conclusion

NEAT1 contributed to PTX resistance of ovarian cancer cells at least partly through upregulating ZEB1 expression by sponging miR-194, elucidating a novel regulatory pathway of chemoresistance in PTX-resistant ovarian cancer cells and providing a possible long noncoding RNA (lncRNA)-targeted therapy for ovarian cancer.

Protein and chemotherapy profiling of extracellular vesicles harvested from therapeutic induced senescent triple negative breast cancer cells

Triple negative breast cancer (TNBC) is an aggressive subtype with relatively poor clinical outcomes and limited treatment options. Chemotherapy, while killing cancer cells, can result in the generation of highly chemoresistant therapeutic induced senescent (TIS) cells that potentially form stem cell niches resulting in metastases. Intriguingly, senescent cells release significantly more extracellular vesicles (EVs) than non-senescent cells. Our aim was to profile EVs harvested from TIS TNBC cells compared with control cells to identify a potential mechanism by which TIS TNBC cells maintain survival in the face of chemotherapy. TIS was induced and confirmed in Cal51 TNBC cells using the chemotherapeutic paclitaxel (PTX) (Taxol). Mass spectrometry (MS) analysis of EVs harvested from TIS compared with control Cal51 cells was performed using Ingenuity Pathway Analysis and InnateDB programs. We demonstrate that TIS Cal51 cells treated with 75 nM PTX for 7 days became senescent (senescence-associated β-galactosidase (SA-β-Gal) positive, Ki67-negative, increased p21 and p16, G2/M cell cycle arrest) and released significantly more EVs (P=0.0002) and exosomes (P=0.0007) than non-senescent control cells. Moreover, TIS cells displayed an increased expression of the multidrug resistance protein 1/p-glycoprotein. MS analysis demonstrated that EVs derived from senescent Cal51 cells contained 142 proteins with a significant increased fold change compared with control EVs. Key proteins included ATPases, annexins, tubulins, integrins, Rabs and insoluble senescence-associated secretory phenotype (SASP) factors. A fluorescent analogue of PTX (Flutax-2) allowed appreciation of the removal of chemotherapy in EVs from senescent cells. Treatment of TIS cells with the exosome biogenesis inhibitor GW4869 resulted in reduced SA-β-Gal staining (P=0.04). In summary, this study demonstrates that TIS cells release significantly more EVs compared with control cells, containing chemotherapy and key proteins involved in cell proliferation, ATP depletion, apoptosis and the SASP. These findings may partially explain why cancer senescent cells remain viable despite chemotherapeutic challenge.

The miR-491-3p/Sp3/ABCB1 axis attenuates multidrug resistance of hepatocellular carcinoma

As one of main obstacles in the treatment and prognosis of hepatocellular carcinoma (HCC), multidrug resistance (MDR) is usually associated with the overexpression of the drug efflux pump P-glycoprotein (P-gp/ABCB1) which is responsible for reducing the intracellular concentration of chemotherapeutic agents. In current work, we discovered the novel role of miR-491-3p in ABCB1-mediated multidrug resistance in HCC and revealed the underlying mechanism in which miR-491-3p downregulated the expression of ABCB1 and its transcription factor Sp3 by directly targeting their 3'-UTR. Moreover, overexpressing ABCB1 or Sp3 reversed the sensitivity to chemotherapeutics in Hep3B cells induced by miR-491-3p, confirming miR-491-3p/Sp3/ABCB1 regulatory loop plays an important role in enhancing the drugs sensitivity of HCC. Meanwhile, the discovery of that the expression level of miR-491-3p was inversely correlated with that of ABCB1 and Sp3 in HCC cell lines and clinical samples pointed out the possibility of miR-491-3p in clinical use. In summary, our results reveal a pivotal role of miR-491-3p in the regulation of MDR in HCC, and suggest the potential application of miR-491-3p as a therapeutic strategy for modulating MDR in cancer cells.

A preliminary study on epigenetic regulation of Acanthopanax senticosus in leukemia cell lines

Conventional chemotherapy for leukemia inevitably causes systemic toxicity. Acanthopanax senticosus, a naturally occurring herb used in traditional Chinese medicine, has been found to be a multipotent bioflavonoid with great potential in the prevention and treatment of malignant diseases. However, the mechanism underlying the action of A. senticosus in epigenetic regulation is poorly understood. In the study described here, we focused on the efficacy of A. senticosus in inducing apoptosis of leukemia cells and a possible mechanism. By evaluating the inhibition ratio and morphologic changes, we found that A. senticosus can inhibit growth and induce apoptosis of human leukemia HL-60 and HL60/ADM cells in a dose- and time-dependent manner. Furthermore, A. senticosus induced Fas ligand (FasL) expression and blocked the cell cycle in S phase. In addition, A. senticosus exhibited a potential for inhibition of histone deacetylase (HADC), which contributes to histone acetylation. It possibly resulted in the promotion of the expression of FasL. It is suggested that A. senticosus could be recognized as a new HDAC inhibitor which was able to reactivate aberrantly silenced genes. We discuss the clinical aspects of using A. senticosus for treatment of leukemia.

Spatiotemporal Expression of EAPP Modulates Neuronal Apoptosis and Reactive Astrogliosis After Spinal Cord Injury

E2F-associated phosphoprotein (EAPP) is a novel E2F binding protein that interacts with the activating members of the E2F transcription factors family and involved in various biological processes. However, the expression and function of EAPP in central nervous system (CNS) are still unknown. In this study, we performed an acute spinal cord injury (SCI) model in adult rats, we found that EAPP protein levels were significantly increased and reached a peak at day 3, and then gradually returned to normal level at day 14 after spinal cord injury and we observed that the expression of EAPP is enhanced in the gray and white matter. Spatially, increased levels of EAPP were striking in neurons and astrocytes. Moreover, colocalization of EAPP/active caspase-3 was detected in neurons, and colocalization of EAPP/proliferating cell nuclear antigen (PCNA) was detected in astrocytes after spinal cord injury. These results indicated that EAPP might play an important role in neuronal apoptosis and reactive astrogliosis. Furthermore in vitro, EAPP depletion by siRNA inhibited astrocyte proliferation, migration and CDK4/cyclinD1 expression. Meanwhile, EAPP knockdown also reduce neuronal apoptosis and cell cycle related proteins. Which indicated that EAPP might integrate cell cycle progression and play a crucial role in cell proliferation and apoptosis. Taken together, we speculated that EAPP was involved in biochemical and physiological responses after SCI.

MicroRNA-186 induces sensitivity of ovarian cancer cells to paclitaxel and cisplatin by targeting ABCB1

Background

Recent studies have shown that microRNAs may regulate the ABCB1 gene (ATP-binding cassette, sub-family B [MDR/TAP], member 1). Computational programs have predicted that the 3’-untranslated region (3’-UTR) of ABCB1 contains a potential miRNA-binding site for miR-186. Here, we investigated the role of miR-186 in sensitizing ovarian cancer cells to paclitaxel and cisplatin.

Results

Human ovarian carcinoma cell lines OVCAR3, A2780, A2780/DDP, and A2780/Taxol were exposed to paclitaxel or cisplatin with or without miR-186 transfection, and cell viability was determined by MTT assay. Reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis were used to assess the MDR1, GST-π, and MRP1 expression levels. Dual-luciferase reporter assay was used to reveal the correlation between miR-186 and ABCB1. Lower miR-186 while higher MDR1 and GST-π mRNA expression levels were found in the A2780/Taxol and A2780/DDP cells than in the A2780 cells. After miR-186 transfection, all the cell lines showed increased sensitivity to paclitaxel and cisplatin. MiR-186 transfection induced apoptosis while anti-miR-186 transfection reduced apoptosis. The dual-luciferase reporter assay verified that that miR-186 combined with the 3’-untranslated region (UTR) of ABCB1. MDR1 and GST-π mRNA and protein expression levels were downregulated after transfection with miR-186 but upregulated following anti-miR-186 transfection compared to the mock and negative control cancer cells; however, the MRP1 expression levels did not significantly differ among the groups.

Conclusion

Our results are the first to demonstrate that miR-186 may sensitize ovarian cancer cell to paclitaxel and cisplatin by targeting ABCB1 and modulating the expression of GST-π.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-015-0207-6) contains supplementary material, which is available to authorized users.

MicroRNA-133b targets glutathione S-transferase π expression to increase ovarian cancer cell sensitivity to chemotherapy drugs

Background

Accumulating studies reveal that aberrant microRNA (miRNA) expression can affect the development of chemotherapy drug resistance by modulating the expression of relevant target proteins. The aim of this study was to investigate the role of miR-133b in the development of drug resistance in ovarian cancer cells.

Methods

We examined the levels of miR-133b expression in ovarian carcinoma tissues and the human ovarian carcinoma cell lines (A2780, A2780/DDP and A2780/Taxol, respectively). We determined the cell viability of these cell lines treated with cisplatin or paclitaxel in the presence or absence of miR-133b or anti-miR-133b transfection using the MTT assay. Reverse transcription polymerase chain reaction and Western blotting were used to assess the mRNA and protein expression levels of two drug-resistance-related genes: glutathione S-transferase (GST)-π and multidrug resistance protein 1 (MDR1). The dual-luciferase reporter assay was used to detect the promoter activity of GST-π in the presence and absence of miR-133b.

Results

The expression of miR-133b was significantly lower in primary resistant ovarian carcinomas than in the chemotherapy-sensitive carcinomas (P<0.05), and the same results were found in primary resistant ovarian cell lines (A2780/Taxol and A2780/DDP) compared to the chemotherapy-sensitive cell line (A2780; P<0.05). Following miR-133b transfection, four cell lines showed increased sensitivity to paclitaxel and cisplatin, while anti-miR-133b transfection reduced cell sensitivity to paclitaxel and cisplatin. Dual-luciferase reporter assay showed that miR-133b interacted with the 3′-untranslated region of GST-π. Compared to controls, the mRNA and protein levels of MDR1 and GST-π were downregulated after miR-133b transfection and upregulated after anti-miR-133b transfection.

Conclusion

MicroRNA-133b may reduce ovarian cancer drug resistance by silencing the expression of the drug-resistance-related proteins, GST-π and MDR1. In future, the combination of miR-133b with chemotherapy agents may prevent the development of drug resistance in ovarian cancers.

Pulmonary expression of CYP2A13 and ABCB1 is regulated by FOXA2, and their genetic interaction is associated with lung cancer

Inhaled xenobiotics such as tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone are mainly metabolized by phase I oxidase cytochrome P450, family 2, subfamily A, polypeptide 13 (CYP2A13), phase II conjugate UDP glucuronosyltransferase 2 family, polypeptide B17 (UGT2B17), and phase III transporter ATP-binding cassette, subfamily B (MDR/TAP), member 1 (ABCB1), with genetic polymorphisms implicated in lung cancer. Their genetic interaction and pulmonary expression regulation are largely unknown. We analyzed joint association for CYP2A13 and ABCB1 polymorphisms in 2 independent lung cancer case populations (669 and 566 patients) and 1 common control population (749 subjects), and characterized the trans-acting function of the lung development-related transcription factor forkhead box A2 (FOXA2). We undertook FOXA2 overexpression and down-regulation in lung epithelial cell lines, analyzed functional impact on the transactivation of CYP2A13, UGT2B17, and ABCB1, and measured correlation for their expressions in lung tissues. We found a substantial reduction in cancer risk (OR 0.39; 95% CI 0.25-0.61; Pinteraction = 0.029) associated with combined genotypes for CYP2A13 R257C and a functionary regulatory variant in the cis element of ABCB1 synergistically targeted by GATA binding protein 6 and FOXA2. Genetic manipulation of FOXA2 consistently influenced its binding to and transactivation of the promoters of CYP2A13, UGT2B17, and ABCB1, whose mRNA and protein expressions were all consistently correlated with those of FOXA2 in both tumorous and normal lung tissues. We therefore establish FOXA2 as a core transcriptional modulator for pulmonary xenobiotic metabolic pathways and uncover an etiologically relevant interaction between CYP2A13 and ABCB1, furthering our understanding of expression and function of the xenobiotic metabolism system.

Identification of trichlormethiazide as a Mdr1a/b gene expression enhancer via a dual secretion-based promoter assay

Transporters of the ATP-binding cassette (ABC) family such as MDR1 play a pivotal role in persistence of brain homeostasis by contributing to the strict permeability properties of the blood–brain barrier. This barrier on one hand compromises treatment of central nervous system diseases by restricting access of drugs; on the other hand, an impaired or altered function of barrier building cells has been described in neurological disorders. The latter might contribute to increased vulnerability of the brain under pathological conditions or even enforce pathogenesis. Here, we present a novel approach for a systematic examination of drug impact on Mdr1 gene expression by establishing a dual reporter gene assay for the murine upstream core promoters of Mdr1a and b. We validated the time-resolved assay in comparison with single reporter gene constructs and applied it to analyze effects of a Food and Drug Administration (FDA)-approved drug library consisting of 627 substances. The chemo-preventive synthetic dithiolethione oltipraz was reidentified with our assay as an already known inducer of Mdr1 gene expression. Together with two newly characterized modifiers – gemcitabine and trichlormethiazide – we prove our findings in a blood–brain barrier culture model as well as in wild-type and Mdr1 knockout mice. In sum, we could demonstrate that our dual reporter gene assay delivers results, which also persist in the living animal and consequently is applicable for further analysis and prediction of Mdr1 regulation in vivo.

Overexpression of E2F1 in human gastric carcinoma is involved in anti-cancer drug resistance

Background

Routine chemotherapy often cannot achieve good therapeutic effects because of multidrug resistance (MDR). MDR is frequently caused by the elevated expression of the MDR1 gene encoding P-glycoprotein (P-gp). E2F1 is a frequently overexpressed protein in human tumor cells that increases the activity of the MDR1 promoter, resulting in higher P-gp levels. The upregulation of P-gp might contribute to the survival of tumor cells during chemotherapy. E2F1 confers anticancer drug resistance; however, we speculate whether E2F1 affects MDR through other pathways. This study investigated the possible involvement of E2F1 in anticancer drug resistance of gastric carcinoma in vitro and in vivo.

Methods

A cisplatin-resistant SGC7901/DDP gastric cancer cell line with stable overexpression of E2F1 was established. Protein expression levels of E2F1, MDR1, MRP, TAp73, GAX, ZEB1, and ZEB2 were detected by western blotting. The influence of overexpression of E2F1 on anticancer drug resistance was assessed by measuring IC50 of SGC7901/DDP cells to cisplatin, doxorubicin, and 5-fluorouracil, as well as the rate of doxorubicin efflux, apoptosis, and cell cycle progression detected by flow cytometry. We determined the in vivo effects of E2F1-overexpression on tumor size in nude mice, and apoptotic cells in tumor tissues were detected by deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling and hematoxylin and eosin staining.

Results

The SGC7901/DDP gastric cancer cell line stably overexpressing E2F1 exhibited significantly inhibited sensitivity to cisplatin, doxorubicin, and 5-fluorouracil. Flow cytometry confirmed that the percentage of apoptotic cells decreased after E2F1 upregulation, and that upregulation of E2F1 potentiated S phase arrest of the cell cycle. Furthermore, upregulation of E2F1 significantly decreased intracellular accumulation of doxorubicin. Western blot revealed that E2F1 upregulation suppressed expression of GAX, and increased the expression of MDR1, MRP, ZEB1, TAp73, and ZEB2.

Conclusions

Overexpression of E2F1 promotes the development of MDR in gastric carcinoma, suggesting that E2F1 may represent an efficacious target for gastric cancer therapy.

Regulation of the human ABCB10 gene by E2F transcription factors

Here, we report for the first time a functional study of transcriptional regulation of the human ABCB10 gene. We cloned a functional promoter sequence, and then showed that E2F2, E2F3 and E2F4 can activate transcription from the ABCB10 promoter. We identified sites responsible for this activation and confirmed direct binding of E2F4 to these sites in EMSA and ChIP assays. Finally, by silencing the expression of E2F factors we demonstrated their importance in maintenance of the basal ABCB10 expression. This study provides important atypical examples of E2F4 being a transcriptional activator rather than repressor as well as directly binding to a promoter and regulating it through an alternative and classical DNA consensus response element sequences. It also provides a mechanistic link between E2F4 and ABCB10, both of which are involved in the same physiological phenomena: erythroid lineage differentiation and maturation as well as protection against cardiomyocyte cell death.

microRNA 490-3P enhances the drug-resistance of human ovarian cancer cells

BACKGROUND

MicroRNAs (miRNAs) are non-coding, single-stranded small RNAs that regulate gene expression negatively, which is involved in fundamental cellular processes. In this study, we investigated the role of miR-490-3P in the development of drug resistance in ovarian cancer cells.

METHODS

The human ovarian carcinoma cell line A2780 and A2780/Taxol were exposed to paclitaxel in the presence or absence of microRNA 490-3P transfection, after which cell viability were performed by CCK-8 assay. Reverse transcription polymerase chain reaction (RT-PCR) and western blotting were used to assess the mRNA and protein expression levels of GST-π, MDR1 or P-gp.

RESULTS

Our results showed higher miR-490-3P mRNA expression level in A2780/Taxol cells than in A2780 cells (p < 0.05). Following miR-490-3P transfection, both A2780 and A2780/Taxol cells showed decreased sensitivity to paclitaxel. The mRNA expression levels of MDR1, GST-π (p < 0.05) and protein expression levels of P-gp, GST-π were up-regulated [corrected] after miR-490-3P transfection in comparison to mock and negative control cancer cells.

CONCLUSION

Our results demonstrate for the first time that microRNA 490-3P may be involved in the development of drug resistance in ovarian cancer.

Expression of P-glycoprotein in human retinoblastoma and its clinical significance

Retinoblastoma is the most common malignant intraocular tumor of childhood. Drug resistance and relapses are major problems with chemotherapy, which is regarded as the mainstay of globe preserving treatment in retinoblastoma. P-glycoprotein (P-gp) expression has been reported to be associated with chemoresistance and poor prognosis in various malignancies. We analyzed P-gp expression in retinoblastoma specimens, enucleated either primarily or after neoadjuvant chemotherapy by immunohistochemistry and immunoblotting, and correlated with the histopathological findings. Variables were statistically analyzed by Fischer's exact and chi-square tests. Tumor tissues were collected from enucleated eyes of 24 children. Fifteen of these were primarily enucleated (group I), and nine (group II) had received chemotherapy prior to enucleation. P-gp was expressed in 4/15 (26.7 %) eyes in group I and in 5/9 (55.6 %) eyes in group II. P-gp was highly expressed in group II as compared to group I. There was no correlation between P-gp expression and tumor differentiation, invasion, or laterality. In conclusion, there was markedly high expression of P-gp in eyes with retinoblastoma enucleated after chemotherapy. This may possibly play a role in chemoresistance or it may be that chemotherapy might have induced high expression. These findings may have important implications for the treatment of retinoblastoma patients but need further prospective investigations in a larger patient population.

Sinomenine sensitizes multidrug-resistant colon cancer cells (Caco-2) to doxorubicin by downregulation of MDR-1 expression

Chemoresistance in multidrug-resistant (MDR) cells over expressing P-glycoprotein (P-gp) encoded by the MDR1 gene, is a major obstacle to successful chemotherapy for colorectal cancer. Previous studies have indicated that sinomenine can enhance the absorption of various P-gp substrates. In the present study, we investigated the effect of sinomenine on the chemoresistance in colon cancer cells and explored the underlying mechanism. We developed multidrug-resistant Caco-2 (MDR-Caco-2) cells by exposure of Caco-2 cells to increasing concentrations of doxorubicin. We identified overexpression of COX-2 and MDR-1 genes as well as activation of the NF-κB signal pathway in MDR-Caco-2 cells. Importantly, we found that sinomenine enhances the sensitivity of MDR-Caco-2 cells towards doxorubicin by downregulating MDR-1 and COX-2 expression through inhibition of the NF-κB signaling pathway. These findings provide a new potential strategy for the reversal of P-gp-mediated anticancer drug resistance.