半分子转运蛋白ABCG2的肿瘤多药耐药性研究及其应用

肿瘤常对临床上传统使用的多种化学治疗显示其内源性或获得性的药物耐受性即多药耐药性(multidrug resistance,MDR)．这种多药耐药性主要是由一类称为ABC(ATP-binding cassette)转运体蛋白超家族的跨膜蛋白引起的,它们结合并利用水解ATP提供的能量来转运药物,导致肿瘤细胞呈现抗药性．半分子转运蛋白ABCG2是近年来才发现的可归于ABC转运体大家族中的一个新成员,在肠、肝、胎盘和血脑屏障等部位大量表达,与全分子转运蛋白如P-gp (P-glycoprotein)和多药耐药蛋白(multi-drug resistance protein,MRP)相似,可以主动地把具有不同化学结构和作用于细胞内不同靶位点的化疗药物泵出胞外,从而引起肿瘤对多种抗癌药物(包括最新开发的药物)产生抗性．最近的一些十分有趣的研究还表明,ABCG2可能与干细胞分化状态和保护干细胞发育过程中免受周围环境的影响有关,而且还发现,它在侧群骨髓和神经干细胞内大量存在,因此,ABCG2可能在基因治疗中作为选择性的蛋白质标记正受到研究者们的极大关注．同时,ABCG2的单核苷酸多态性影响其结合并转运不同的底物/药物．鉴于ABCG2在肿瘤抗药性研究中的重要性以及它的一些新功能的初步研究表明,对ABCG2的生物学功能和作用机理以及在医学实践中的应用研究必将受到更大的关注．主要阐述了半分子ABC转运蛋白ABCG2的发现、重要的生化特性和生理功能及其相关的新研究进展和问题．     

介导多药耐药的ABC转运蛋白超家族与MTX耐药性的关系研究

细胞耐药性的产生是导致肿瘤化疗失败的重要因素, 尤其是多药耐药是目前研究的一个重点。ABC转运蛋白超家族成员介导药物的外排, 与多药耐药密切相关。为了解该家族成员与MTX耐药的相关性, 进一步探讨MTX的耐药机制, 应用SuperArray基因芯片对MTX耐药前后编码ABC转运蛋白超家族成员的mdr1、mrp1、mrp2、mrp3、mrp5、mrp6和abcg2 7个基因进行检测, 并对MRP1和MRP5蛋白表达进行了验证。结果显示, 与MTX耐药性相关的ABC转运蛋白超家族成员主要为多药耐药相关蛋白, 其中mrp1和mrp5呈现高表达, 并且, 在MTX抗性细胞中, MRP5在mRNA及蛋白水平的表达均明显增强, 提示其在MTX耐药机制中起重要作用, 可能为潜在的药物作用靶点。     

真菌的多向耐药性ABC转运蛋白

真菌的多向耐药性ABC转运蛋白(ATP-binding cassette transporters)是导致多药耐药性和抗真菌药物治疗效果明显下降的主要原因。文章对酿酒酵母(Saccharomyces cerevisiae)和主要致病真菌白色假丝酵母(Candida albicans)、新型隐球酵母(Cryptococcus neoformans)和烟曲霉(Aspergillus fumigatus)中的多向耐药性ABC转运蛋白的种类、药物外排机制以及基因表达调控网络的研究进展作一综述,为深入了解真菌的多向耐药性机制以及探讨克服多向耐药性的策略和提高药效提供参考。     

ABC细胞膜转运蛋白及其介导的细胞多药耐药研究进展

ABC细胞膜转运蛋白是一个能转运多种底物的蛋白质家族,其在宿主对异物的防御机制和肿瘤细胞对抗癌药物的耐药性中发挥重要作用。ABC转运蛋白能将已进人细胞的外源性物质从胞内泵出胞外,是造成肿瘤细胞多药耐药的主要原因,其基因表达水平与细胞内药物浓度和耐药程度密切相关。近年来,肿瘤细胞多药耐药性研究炙手可热。我们简要综述ABC细胞膜转运蛋白的特点、分布、表达及其介导的细胞多药耐药方面的研究进展。     

ABC转运蛋白的结构与转运机制

腺苷三磷酸结合盒转运蛋白（ATP-binding cassette transponer,ABC转运蛋白）超家族是一组跨膜蛋白,具有ATP结合区域的单向底物转运泵,以主动转运方式完成多种分子的跨膜转运.ABC转运蛋白的一个亚家族与多药抗性（multidrug resistance,MDR）有关,而多药抗性是临床肿瘤化疗中需要解决的主要问题,所以其结构与转运机制一直是研究的热点.最近几年获得了一些高分辨率的ABC转运蛋白的晶体结构,该文将根据ABC转运蛋白的结构的研究进展对其可能的转运机制进行讨论.     

ABC转运蛋白结构及在植物病原真菌中的功能研究进展

ABC (ATP-binding cassette)转运蛋白是最大的膜转运蛋白超家族之一,其主要功能是利用ATP水解产生的能量将底物进行逆浓度梯度运输.所有生物体都含有大量ABC蛋白. ABC蛋白位于细胞的不同空间,如细胞膜、液泡、线粒体和过氧化物酶体.通常,ABC转运蛋白由跨膜结构域(TMD)和核苷酸结合结构域(NBD)组成,分别与底物和ATP结合.NBD执行与ATP结合和水解,是ABC转运蛋白的动力引擎,TMD识别特异性配体.大多数ABC转运蛋白最初是通过研究生物体耐药性而被发现的,包括多效耐药(PDR)和多药耐药(MDR).本文对ABC转运蛋白的结构及作用机制,以及植物病原真菌中ABC转运蛋白功能的研究进展进行综述.     

10种ABC转运蛋白在鼻咽癌顺铂耐药细胞系中的表达

为研究鼻咽癌细胞CNE2中顺铂耐药与10种ABC转运蛋白的关系,分别用顺铂、顺铂+5-氟脲嘧啶来诱导CNE2耐药,在脱药培养2个月后通过MTT法测定细胞的生长曲线及其与顺铂的量效关系和耐药指数,同时,通过荧光定量PCR法检测耐药细胞与敏感细胞中10种ABC转运蛋白mRNA表达的差异,并通过免疫细胞化学法验证．MTT法结果提示,成功诱导出两株分别对顺铂、顺铂+5-氟脲嘧啶耐药的细胞株(分别命名为CNE2/DDP、CNE2/DDP+5Fu),耐药指数分别为2.58和5.31,ABCC2在两株耐药细胞株中表达均上调,分别为2.50和4.08倍,免疫细胞化学法结果表明,ABCC2在两株耐药细胞中表达均增强,同时ABCC2还可在CNE2/DDP+5Fu细胞核中表达．上述结果表明ABCC2在CNE2细胞对顺铂的耐药性中可能发挥着重要的作用．     

多烯类抗生素合成基因簇中ABC转运蛋白研究进展

ABC转运蛋白家族是一个广泛存在于不同生物细胞中且功能保守的膜蛋白亚家族;它们是一类单向底物转运泵,通常以主动转运方式完成多种分子的跨膜转运。随着抗生素合成基因簇相关研究的开展,越来越多的簇内ABC转运蛋白被鉴定出来,对其生物学功能的研究正逐渐成为热点。多烯类抗生素作为一类重要的抗真菌药物,能够有效避免真菌产生耐药性,具有非常重要的临床价值。本文以多烯类抗生素合成基因簇为对象,综述了在其中所发现的ABC转运蛋白的研究进展,综合分析了其结构特性与功能间的关系,并对研究应用进行了展望。     

ABC转运蛋白及其在合成生物学中的应用

ABC转运蛋白(ATP-binding cassette transporter,ABC transporter)作为一种超大膜转运蛋白家族,在大多数生物体中发挥着重要作用。文中从结构特征、转运机制以及生理功能等方面论述了ABC转运蛋白的研究进展,进而着重综述了近些年来ABC转运蛋白在合成生物学领域中的应用,并为今后进一步的研究提出了展望,希望为扩展其应用提供指导。     

胆固醇流出调节蛋白与胆固醇逆向转运

高密度脂蛋白（ＨＤＬ）能从外周细胞摄取我余胆固醇并运输至肝脏排出,防止其在血管壁沉积。外周细胞内胆固醇流向ＨＤＬ的机制一直是人们积极探索但尚未弄清的问题。新近发表在《Ｎａｔｕｒｅ Ｇｅｎｅｔｉｃｓ》上的三篇论文在这个环节上取得了重大突破,他们通过对Ｔａｎｇｉｅｒ病的研究,发现由ＡＴＰ－ｂｉｎｄｉｎｇ－ｃａｓｓｅｔｔｅ ｔｒａｎｓｐｏｒｔｅｒ １基因编码的胆固醇流出调节蛋白（ｃｈｏｌｅｓｔｅｒｏｌ－     

The Involvement of Sphingolipids in Multidrug Resistance

Administration of most chemotherapeutic agents eventually results in the onset of apoptosis, despite the agents' variety in structure and molecular targets. Ceramide, the central molecule in cellular glycosphingolipid metabolism, has recently been identified as an important mediator of this process. Indeed, one of the events elicited by application of many cytotoxic drugs is an accumulation of this lipid. Treatment failure in cancer chemotherapy is largely attributable to multidrug resistance, in which tumor cells are typically cross-resistant to multiple chemotherapeutic agents. Different cellular mechanisms underlying this phenomenon have been described. Of these the drug efflux pump activity of P-glycoprotein and the multidrug resistance-associated proteins are the most extensively studied examples. Recently, an increased cellular capacity for ceramide glycosylation has been recognized as a novel multidrug resistance mechanism. Indeed, virtually all multidrug-resistant cells exhibit a deviating sphingolipid composition, most typically, increased levels of glucosylceramide. On the other hand, several direct molecular interactions between sphingolipids and drug efflux proteins have been described. Therefore, in addition to a role in the multidrug resistance phenotype by which ceramide accumulation and, thus, the onset of apoptosis are prevented, an indirect role for sphingolipids might be envisaged, by which the activity of these efflux proteins is modulated. In this review, we present an overview of the current understanding of the interesting relations that exist between sphingolipid metabolism and multidrug resistance. Received: 16 June 2000/Revised: 16 August 2000     

Modulation of Multidrug Resistance in Cancer Cells by Liposome Encapsulated Doxorubicin

Abstract

A major problem in the chemotherapy of solid tumors and hematologic malignancies is the intrinsic as well as acquired cross resistance to multiple chemotherapeutic agents. Recently, this type of multidrug resistance has been related to a gene, MDR1, and its gene product, p-glycoprotein, which functions as the efflux pump, prevents accumulation of drugs and alters their cytotoxicity. Many drug-resistant human tumors express the MDR1 gene and MDR1 RNA levels are elevated in many cancers that have not responded to chemotherapy. The same persistent observation has been made in recurrent tumors who have responded initially to chemotherapy.

Doxorubicin is one of the most important anticancer agent having significant single agent activity in a variety of cancer types and is now the cornerstone of some widely used combination regimens. Despite the clinical effectiveness of the drug, doxorubicin resistance that arises in malignant cells following repeated courses of treatment is the major problem in the clinical management of neoplastic diseases. Recently, extensive studies have demonstrated that liposome encapsulated doxorubicin effectively modulates the multidrug resistance phenotype in cancer cells by altering the function of p-glycoprotein. This modulation of MDR phenotype by liposomes has been demonstrated in vitro in human breast cancer cells, ovarian cancer cells, human promyelocytic leukemia cells and in human colon cancer cells and in vivo in transgenic mice transfected with a functional MDR1 gene. It appears liposomes can play an effective role as a new modality of treatment for human cancers which have become refractory to chemotherapy. An exciting area of research which soon will emerge will exploit the different binding sites on p-glycoprotein by using combination of liposomes with other pharmacological modulators of MDR to impart maximal overcoming of multidrug resistance in cancer patients.     

ABC Transporters in Dynamic Macromolecular Assemblies

ATP-binding cassette (ABC) transporters constitute one of the largest families of integral membrane proteins, including importers, exporters, channels, receptors, and mechanotransducers, which fulfill a plethora of cellular tasks. ABC transporters are involved in nutrient uptake, hormone and xenobiotic secretion, ion and lipid homeostasis, antibiotic and multidrug resistance, and immunity, thus making them prime candidates for cellular regulation and pharmacological intervention. In recent years, numerous various structures of ABC transporters have been determined by X-ray crystallography or cryogenic electron microscopy. Structural and functional studies revealed that various auxiliary domains play key roles for the subcellular localization of ABC transporters and recruitment of regulatory factors. In this regard, the ABC transporter associated with antigen processing TAP stands out. In the endoplasmic reticulum membrane, TAP assembles the peptide-loading complex, which serves as a central checkpoint in adaptive immunity. Here, we discuss the various aspects of auxiliary domains for ABC transporter function with a particular emphasis on the structure of the peptide-loading complex, which is crucial for antigen presentation in adaptive immunity.     

拟南芥中ABC转运蛋白的研究进展

物质运输系统是植物和环境间相互作用的方法之一,受膜上接合的转运蛋白的控制.植物中数量最多的膜转运蛋白是接合ATP的盒式蛋白,简称ABC蛋白.通过核基困BLAST同源序列查询,在拟南芥中发现了60个开放阅读框架（ORFs）编码ABC转运蛋白,在编码的60个蛋白上发现有89个ABC结构域.     

Regulation of Biotransformation Systems and ABC Transporters by Benznidazole in HepG2 Cells: Involvement of Pregnane X-Receptor

Background

Benznidazole (BZL) is the only antichagasic drug available in most endemic countries. Its effect on the expression and activity of drug-metabolizing and transporter proteins has not been studied yet.

Methodology/Principal Findings

Expression and activity of P-glycoprotein (P-gp), Multidrug resistance-associated protein 2 (MRP2), Cytochrome P450 3A4 (CYP3A4), and Glutathione S-transferase (GST) were evaluated in HepG2 cells after treatment with BZL. Expression was estimated by immunoblotting and real time PCR. P-gp and MRP2 activities were estimated using model substrates rhodamine 123 and dinitrophenyl-S-glutathione (DNP-SG), respectively. CYP3A4 and GST activities were evaluated through their abilities to convert proluciferin into luciferin and 1-chloro-2,4-dinitrobenzene into DNP-SG, respectively. BZL (200 µM) increased the expression (protein and mRNA) of P-gp, MRP2, CYP3A4, and GSTπ class. A concomitant enhancement of activity was observed for all these proteins, except for CYP3A4, which exhibited a decreased activity. To elucidate if pregnane X receptor (PXR) mediates BZL response, its expression was knocked down with a specific siRNA. In this condition, the effect of BZL on P-gp, MRP2, CYP3A4, and GSTπ protein up-regulation was completely abolished. Consistent with this, BZL was able to activate PXR, as detected by reporter gene assay. Additional studies, using transporter inhibitors and P-gp-knock down cells, demonstrated that P-gp is involved in BZL extrusion. Pre-treatment of HepG2 cells with BZL increased its own efflux, as a consequence of P-gp up-regulation.

Conclusions/Significance

Modifications in the activity of biotransformation and transport systems by BZL may alter the pharmacokinetics and efficiency of drugs that are substrates of these systems, including BZL itself.     

Overview: ABC Transporters and Human Disease

ABC transporters are found in all known organisms, and approximately 1,100 different transporters belonging to this family have been described in the literature. The family is defined by homology within the ATP-binding cassette (ABC) region, which extends outside of the more typical Walker motifs found in all ATP-binding proteins. Most family members also contain transmembrane domains involved in recognition of substrates, which are transported across, into, and out of cell membranes, but some members utilize ABCs as engines to regulate ion channels. There are approximately 50 known ABC transporters in the human, and there are currently 13 genetic diseases associated with defects in 14 of these transporters. The most common genetic disease conditions include cystic fibrosis, Stargardt disease, age-related macular degeneration, adrenoleukodystrophy, Tangier disease, Dubin–Johnson syndrome and progressive familial intrahepatic cholestasis. At least 8 members of this family are involved in the transport of a variety of amphipathic compounds, including anticancer drugs, and some appear to contribute to the resistance of cancer cells to chemotherapy.