Overexpression of centrosomal protein Nlp confers breast carcinoma resistance to paclitaxel

Nlp (ninein-like protein), an important molecule involved in centrosome maturation and spindle formation, plays an important role in tumorigenesis and its abnormal expression was recently observed in human breast and lung cancers. In this study, the correlation between overexpression of Nlp and paclitaxel chemosensitivity was investigated to explore the mechanisms of resistance to paclitaxel and to understand the effect of Nlp upon apoptosis induced by chemotherapeutic agents. Nlp expression vector was stably transfected into breast cancer MCF-7 cells. With Nlp overexpression, the survival rates, cell cycle distributions and apoptosis were analyzed in transfected MCF-7 cells by MTT test and FCM approach. The immunofluorescent assay was employed to detect the changes of microtubule after paclitaxel treatment. Immunoblotting analysis was used to examine expression of centrosomal proteins and apoptosis associated proteins. Subsequently, Nlp expression was retrospectively examined with 55 breast cancer samples derived from paclitaxel treated patients. Interestingly, the survival rates of MCF-7 cells with Nlp overexpressing were higher than that of control after paclitaxel treatment. Nlp overexpression promoted G2-M arrest and attenuated apoptosis induced by paclitaxel, which was coupled with elevated Bcl-2 protein. Nlp expression significantly lessened the microtubule polymerization and bundling elicited by paclitaxel attributing to alteration on the structure or dynamics of β-tubulin but not on its expression. The breast cancer patients with high expression of Nlp were likely resistant to the treatment of paclitaxel, as the response rate in Nlp negative patients was 62.5%, whereas was 58.3 and 15.8% in Nlp (+) and Nlp (++) patients respectively (p = 0.015). Nlp expression was positive correlated with those of Plk1 and PCNA. These findings provide insights into more rational chemotherapeutic regimens in clinical practice, and more effective approaches might be developed through targeting Nlp to increase chemotherapeutic sensitivity.     

Wild-type breast cancer resistance protein (BCRP/ABCG2) is a methotrexate polyglutamate transporter

The existence of an ATP-dependent methotrexate (MTX) efflux mechanism has long been postulated; however, until recently, the molecular components were largely unknown. We have previously demonstrated a role for the ATP-binding cassette transporter breast cancer resistance protein (BCRP) in MTX resistance (Volk et al., Cancer Res., 62: 5035-5040, 2002). Resistance to this antifolate directly correlated with BCRP expression, and was reversible by the BCRP inhibitors fumitremorgin C and GF120918. Here, we provide evidence for BCRP as a MTX-transporter using an in vitro membrane vesicle system. Inside-out membrane vesicles were generated from both drug-selected and stably transfected cell lines expressing either wild-type (Arg482) or mutant (Gly482) variants of BCRP. In the presence of the wild-type variant of BCRP, transport of MTX into vesicles was ATP-dependent, osmotically sensitive, and inhibited by fumitremorgin C. In contrast, no transport was observed in vesicles containing the mutant form of BCRP. Wild-type BCRP appeared to have low affinity, but high capacity, for the transport of MTX, with an estimated K(m) of 680 micro M and a V(max) of 2400 pmol/mg/min. MTX accumulation was greatly decreased by mitoxantrone, a known BCRP substrate, suggesting competition for transport. Furthermore, and in contrast to the multidrug resistance-associated proteins, BCRP also transported significant amounts of polyglutamylated MTX. Although transport gradually decreased as the polyglutamate chain length increased, both MTX-Glu(2) and MTX-Glu(3) were substrates for BCRP. Together, these data demonstrate that BCRP is a MTX and MTX-polyglutamate transporter and reveal a possible mechanism by which it confers resistance.     

Bcl-xL mediates therapeutic resistance of a mesenchymal breast cancer cell subpopulation

The transition from an epithelial to a mesenchymal phenotype (EMT) confers increased invasiveness and clonogenic potential to tumor cells. We used a breast epithelium-derived cell culture model to evaluate the impact of EMT on the cellular sensitivity towards chemotherapeutics and apoptotic stimuli. Cells that had passed through an EMT acquired resistance towards chemotherapeutics and death ligands. Mechanistically, we found that the levels of the apoptosis inhibitor Bcl-xL were strongly enhanced in mesenchymal versus epithelial cells, whereas the pro-apoptotic proteins Bim and Puma were diminished. Clinical samples from breast cancer showed enhanced Bcl-xL staining in cells that had dispersed into the desmoplastic stroma, as compared to cells that were part of large tumor cell aggregates, suggesting increased Bcl-xL expression when cells invade the stroma. Bcl-xL was necessary for apoptotic resistance in mesenchymal cells, and its expression was sufficient to confer such resistance to epithelial cells. To antagonize Bcl-xL, BH3-mimetics were used. They successfully interfered with the proliferation and survival of mesenchymal cells, and also inhibited the growth of xenograft tumors raised from the mesenchymal subpopulation. We conclude that enhanced Bcl-xL levels confer resistance to cells upon EMT, and that Bcl-xL represents a promising target for therapy directed against invasive cancer cells.     

Overexpression of Snail accelerates adriamycin induction of multidrug resistance in breast cancer cells

In addition to several molecular and morphologic changes, epithelial-mesenchymal transition (EMT) cells also show variation in sensitivity to chemotherapeutics agents. The aim of this study was to investigate whether overexpression of Snail in MCF-7 cells is associated with facilitated acquisition of P-gp mediated multidrug resistance (MDR). The results demonstrated that over-expression of Snail indeed resulted in slight enhancement of adriamycin-induced MDR in MCF-7/Snail cells without detectable increase of P-gp. However, in the longer term, MCF-7 cells overexpressing Snail were prone to be resistant to adriamycin, in this case with increased expression of P-gp. These results provide evidence that a strategy involving Snail inhibition may be a useful and promising therapeutic aspect in modulating MDR.     

托瑞米芬逆转乳腺癌耐药蛋白介导的多药耐药机制

目的 探讨托瑞米芬逆转乳腺癌耐药蛋白(BCRP)介导的多药耐药机制。方法 通过基因扩增,构建分别由BCRP启动子和巨细胞病毒(CMV)启动子启动表达BCRP的重组质粒pcDNA3-Promoter-BCRP和作为对照的质粒pcDNA3-CMV-BCRP,将其分别转染雌激素受体α（ERα）阳性的MCF-7和ERα阴性的MDA-MB-231乳腺癌细胞系,建立由BCRP启动子和CMV启动子启动表达BCRP的4种耐药细胞系MCF-7/Promoter-BCRP、MCF-7/CMV-BCRP、MDA-MB-231/PromoterBCRP和MDA-MB-231/CMV-BCRP。在耐药细胞培养基中加入托瑞米芬,通过逆转录聚合酶链反应(RT-PCR)、Western blot、外排实验以及细胞毒性实验观察托瑞米芬对不同细胞系的耐药逆转效果。结果与空白对照组（未加药物）相比,托瑞米芬以剂量依赖方式抑制BCRP mRNA的表达,0.1、1和10 μmol/L托瑞米芬处理组MCF-7/Promoter-BCRP细胞中BCRP mRNA的表达水平分别下调29.5％(P＜0.05)、68.1％ (P＜0.01)和97.4％(P＜0.01);MCF-7/Promoter-BCRP细胞经托瑞米芬和17β-雌二醇联合处理后,细胞中BCRP mRNA的相对表达水平为64.2％±1.3％,明显高于托瑞米芬单独处理组(3.8％±0.2％,P＜0.01)。托瑞米芬对各组细胞系中BCRP蛋白表达的调控作用与mRNA相似。经托瑞米芬处理后,MCF-7/Promoter-BCRP细胞内米托蒽醌的荧光强度显著增强,外排米托蒽醌的能力降低了 47.3％ (P ＜0.05);经托瑞米芬和17β-雌二醇联合处理后,MCF-7/Promoter-BCRP细胞内米托蒽醌的荧光强度明显低于托瑞米芬单独处理组,外排米托蒽醌的能力升高了61.5％。托瑞米芬可有效逆转MCF-7/Promoter-BCRP细胞对米托蒽醌的耐药性。上述作用在MCF-7/CMV-BCRP、MDA-MB-231/Promoter-BCRP和MDA-MB-231/CMV-BCRP细胞中未能体现。结论 托瑞米芬可能通过ERot的介导与BCRP启动子上游调控序列中的ERE结合,负性调节BCRP的表达,抑制BCRP蛋白的功能,在体外有效逆转BCRP介导的多药耐药。     

Mechanism of the pharmacokinetic interaction between methotrexate and benzimidazoles: potential role for breast cancer resistance protein in clinical drug-drug interactions

The antifolate drug methotrexate (MTX) is transported by breast cancer resistance protein (BCRP; ABCG2) and multidrug resistance-associated protein1-4 (MRP1-4; ABCC1-4). In cancer patients, coadministration of benzimidazoles and MTX can result in profound MTX-induced toxicity coinciding with an increase in the serum concentrations of MTX and its main metabolite 7-hydroxymethotrexate. We hypothesized that benzimidazoles interfere with the clearance of MTX and/or 7-hydroxymethotrexate by inhibition of the ATP-binding cassette drug transporters BCRP and/or MRP2, two transporters known to transport MTX and located in apical membranes of epithelia involved in drug disposition. First, we investigated the mechanism of interaction between benzimidazoles (pantoprazole and omeprazole) and MTX in vitro in membrane vesicles from Sf9 cells infected with a baculovirus containing human BCRP or human MRP2 cDNA. In Sf9-BCRP vesicles, pantoprazole and omeprazole inhibited MTX transport (IC50 13 microm and 36 microm, respectively). In Sf9-MRP2 vesicles, pantoprazole did not inhibit MTX transport and at high concentrations (1 mm), it even stimulated MTX transport 1.6-fold. Secondly, we studied the transport of pantoprazole in MDCKII monolayers transfected with mouse Bcrp1 or human MRP2. Pantoprazole was actively transported by Bcrp1 but not by MRP2. Finally, the mechanism of the interaction was studied in vivo using Bcrp1-/- mice and wild-type mice. Both in wild-type mice pretreated with pantoprazole to inhibit Bcrp1 and in Bcrp1-/- mice that lack Bcrp1, the clearance of i.v. MTX was decreased significantly 1.8- to 1.9-fold compared with the clearance of i.v. MTX in wild-type mice. The conclusion is as follows: benzimidazoles differentially affect transport of MTX mediated by BCRP and MRP2. Competition for BCRP may explain the clinical interaction between MTX and benzimidazoles.     

PKD2 mediates multi-drug resistance in breast cancer cells through modulation of P-glycoprotein expression

Multi-drug resistance (MDR) represents a major obstacle for chemotherapeutic treatment of a wide variety of human cancers. Increased expression of drug efflux pumps, such as the P-glycoprotein (P-gp) have been linked to development of MDR. Herein, we have identified protein kinase D isoform 2 (PKD2) as an important regulator of MDR and P-gp expression in paclitaxel-treated breast cancer cell lines. PKD2 was expressed with the highest phosphorylated activation status in the MDA-MB-231 cell line. MDA-MB-231 cells were also found to exhibit the highest level of resistance to an array of chemotherapeutic drugs. To further characterize the relationship between PKD2 activation and MDR, we next focused on the effects of the chemotherapeutic agent paclitaxel in MDA-MB-231 cells. Treatment with paclitaxel was shown to induce both PKD2 phosphorylation and P-gp expression in a time-dependent manner. Importantly, shRNA-mediated knockdown of PKD2 in MDA-MB-231 cells resulted in a significant decrease in resistance to paclitaxel, evident as significant decreases in both the IC₅₀ value and the resistance index (RI). Concurrent with the decrease in drug resistance, paclitaxel-induced expression of P-gp was also significantly reduced in PKD knockdown cells. These results indicate that PKD2 is required for paclitaxel-induced MDR and expression of P-gp. Therefore, modulation of PKD2 activity represents an attractive therapeutic strategy for improvement of the clinical effectiveness of chemotherapy.     

乳腺癌耐药蛋白在乳腺癌组织中的表达及与预后关系

目的研究乳腺癌耐药蛋白（Breast cancer resistance protein,BCRP）在乳腺癌组织中的表达,评估其在乳腺癌预后中的作用。方法采用免疫组织化学方法（Immunohistochemistry,IHC）检测47例手术切除的乳腺癌组织中BCRP的表达,并分析其与临床、病理特征的关系及对预后的影响。结果（1）BCRP在乳腺癌组织中的阳性表达率为55．3％（26／47例）,其中高表达者13例（27．7％）;（2）激素受体阳性者BCRP表达水平明显高于激素受体阴性者（P〈0．05）,BCRP表达与月经状况、肿瘤大小、腋淋巴结转移和组织分级均无关（P〉0．05）;（3）Kaplan—Meier生存分析结果表明BCRP和无病生存期相关（P〈0．05）,但和总生存期无关（P〉0．05）;（4）Cox单因素分析显示肿瘤大小和BCRP表达与无病生存期明显相关（P〈0．05）,而肿瘤大小和总生存期也明显相关（P〈0．05）;在多因素分析中BCRP表达仅和无病生存期明显相关,此外腋淋巴结转移与无病生存期和总生存期均明显相关（P〈0．05）。结论BCRP在乳腺癌组织中具有较高的表达水平,但与乳腺癌患者预后无关。     

Overexpression of ABCB4 contributes to acquired doxorubicin resistance in breast cancer cells in vitro

Purpose

Doxorubicin is one of the most active agents in the first-line therapy for metastatic breast cancer, but its utility is partially limited by the frequent emergence of doxorubicin resistance. In this study, we aimed to investigate the role of ATP-binding cassette sub-family B, member 4 (ABCB4) in acquired doxorubicin resistance in breast cancer cells, as well as its potential mechanism.

Methods

In doxorubicin-sensitive and -resistant breast cancer cell lines MCF-7 and MDA-MB-231, the expression levels of ABCB4 were detected using real-time quantitative PCR and Western blot analysis, the DNA methylation and histone acetylation status of ABCB4 gene were investigated by bisulfite-sequencing PCR (BSP) and chromatin immunoprecipitation (ChIP) assays, and the doxorubicin sensitivity and intracellular doxorubicin accumulation were observed using cell cytotoxicity assay and flow cytometry. In Madin–Darby Canine Kidney (MDCKII) cells, In vitro transport assay was used to assess the ABCB4-mediated transport of doxorubicin.

Results

ABCB4 was overexpressed in doxorubicin-resistant breast cancer cells compared to their doxorubicin-sensitive counterparts, which was associated with reduced DNA methylation as well as increased histone acetylation at the ABCB4 promoter. ABCB4 could actively pump doxorubicin out of the cells, and knockdown of ABCB4 increased doxorubicin sensitivity and intracellular accumulation in doxorubicin-resistant breast cancer cells.

Conclusions

Our results indicate that ABCB4 is overexpressed in breast cancer cells with acquired doxorubicin resistance, which could be attributed, at least partially, to the epigenetic modifications of ABCB4 gene. ABCB4 mediates the efflux transport of doxorubicin, and contributes to the acquired resistance of doxorubicin in breast cancer cells.

     

A steroid-binding protein mediates estrogen-dependent inhibition of growth of MCF-7 breast cancer cells

We have described two different proteins that mediate MCF-7 cell growth inhibition (1). One is estrogen-dependent and is a heterodimer consisting of a heavy (54 kDa) and light (29 kDa) chain. This protein is distinct from cortisol-binding globulin (CBG), sex hormone-binding protein (SBP or SHBG) and albumin (HSA). It may be fetal steroid binding protein (FSBP). The other is not estrogen dependent, but may be related to the estrogen-dependent protein. Since these are large proteins they must be acting at the level of the plasma membrane, not traditional intracellular estrogen receptors, and inhibit MCF-7 cell growth.     

Overexpression of ROCK in human breast cancer cells: Evidence that ROCK activity mediates intracellular membrane traffic of lysosomes

Small GTPase Rho and its downstream effectors, ROCK family of Rho-associated serine-threonine kinases, are thought to participate in cell morphology, motility, and tumor progression through regulating the rearrangement of actin cytoskeleton. Here we present evidence that transfection of human breast cancer cells with cDNA encoding a dominant active mutant of ROCK causes dispersal of lysosomal vesicles throughout the cytoplasm without perturbing the machinery of the endocytic pathway. The intracellular distribution of lysosomes and endocytosed transferrin, an early endosomal marker, were further assessed by confocal immunofluorescence microscopy. In the active ROCK transfected cells the lysosomal proteins, cathepsin D, LIMPII, and LAMP1, were found throughout the cytoplasm in dispersed small vesicles, which were accessible to the endocytosed Texas Red-labeled transferrin. 3D-image analysis of lysosomal distribution in the active ROCK transfectants revealed abundant punctate signals in the peripheral region of the basal plasma membrane. Cells expressing vector alone did not exhibit these alterations. Wortmannin, a phosphatidylinositol 3-kinase inhibitor, induced LIMPII-positive/ transferrin negative large vacuoles in the perinuclear region, and disappearence of the dispersed small vesicular structures. To our knowledge, this is the first evidence that increasing ROCK expression contributes to selective cellular dispersion of lysosomes in invasive breast cancer cells.     

子宫颈癌中乳腺癌耐药蛋白mRNA的表达及其临床意义

目的 研究乳腺癌耐药蛋白（BCRP）mRNA在子宫颈癌中的表达及临床意义.方法 实时定量PCR检测12例正常子宫颈组织和47例子宫颈癌组织中BCRP mRNA的表达,并分析其与临床因素间的关系.结果 BCRPmRNA在正常子宫颈组织中低表达,相对表达值为0.19±0.17,在癌组织中高表达,相对表达值为0.59±0.26,两种组织间表达差异有统计学意义（P＜ 0.001）.子宫颈癌患者不同临床病理特征之间BCRPmRNA表达差异无统计学意义（P＞0.05）.结论 BCRP mRNA在子宫颈癌中高表达,可能参与了子宫颈癌原发性耐药的形成,并且BCRP mRNA表达的检测可能对临床选择化疗方案有一定的指导意义.     

Overexpression of betaPix-a in human breast cancer tissues

Pak interacting exchange factor (betaPix) is a recently cloned protein that contains a multidomain with many potential binding sites and is known to be involved in the regulation of Cdc42/Rac GTPases and Pak kinase activity. These domains of betaPix appear to play a critical role in the regulation of the cytoskeletal organization. The overexpression of betaPix enhances the activation of p38, which is thought to be an important downstream effector of the Rho GTPase family (Rac, Cdc42), which are involved in increased membrane ruffling and cell motility. This increase of cell mobility is an important feature of cancer invasion. We examined the expression of betaPix-a in human breast cancer tissues and adjacent normal tissues obtained from 39 breast cancer patients. Immunoblot analysis and RT-PCR revealed that betaPix-a expression was significantly increased in 37 of the 39 breast cancer tissues (94.9%) versus normal breast tissues. Immunohistochemical analysis showed that breast cancer tissues have consistently stronger immunoreactivity to betaPix-a antibodies than normal tissues. betaPix-a overexpression was inversely associated with extensive intraductal component (P<0.001). In conclusion, betaPix-a expression was found to be higher in human breast cancer tissues than in normal breast tissues, which implies a role for betaPix-a in human breast tumorigenesis. We suggest that betaPix-a may be a useful marker of malignant disease in the breast.