NS5B与HCV负链RNA 3＇末端特异性结合的分析

NS5B是RNA依赖性RNA聚合酶,在病毒RNA合成过程中起到中心催化酶的作用.在大肠杆菌中表达和提纯了GST-NS5B融合蛋白,应用紫外交联试验(UVcross-linking)检测NS5B与丙型肝炎病毒(HCV)负链RNA3＇末端的结合,确定NS5B是否参与HCV负链RNA3＇末端复制体的形成.NS5B可与HCV负链RNA3＇末端发生结合,这种结合存在量效关系,比与正链RNA3＇UTRX区的结合强约10倍,超大量的非同源性RNA和蛋白质不能竞争抑制NS5B与负链RNA3＇末端的结合,证明这种结合存在特异性.结果提示NS5B是HCV负链RNA3＇末端复制体的成分之一.     

丙型肝炎病毒NS5A蛋白的生物学调节作用

丙型肝炎病毒(HCV)是一种正链RNA病毒,基因的编码产物包括10余种结构和非结构蛋白等.NS5A是HCV编码的一种非结构蛋白,在酪蛋白激酶Ⅱ(CK Ⅱ)的催化作用下发生磷酸化修饰.在某些情况下,HCV NS5A的变异与干扰素(IFN)治疗的敏感性有关.NS5A与双链RNA蛋白激酶(PKR)之间的结合不仅与IFN的敏感性有关,而且与感染HCV的细胞发生恶性转化的过程有关.与正常细胞恶性转化有关的机制,还包括NS5A对生长因子受体结合蛋白(Grb2)?接头蛋白、细胞周期及细胞增殖的调节等环节.     

HCV治疗的新方法:RNA依赖的RNA聚合酶抑制剂

丙型肝炎病毒（hepatitis C virus,HCV）感染呈世界流行趋势,50%感染者转变为慢性肝炎,部分发展为肝硬化、肝细胞癌,给人类健康带来了极大危害.目前,没有疫苗研制成功,现有的HCV治疗药物普遍存在局限性,或者有一些药物没有发挥应有的作用.因此,开发新型、安全有效的抗HCV药物成为迫在眉睫的问题.NS5B蛋白是HCV复制的核心物质,具有RNA依赖的RNA聚合酶（RdRp）功能.研发有效的NS5B抑制剂,从而阻断病毒的复制,成为许多科研机构及制药公司的研究热点,有一些NS5B抑制剂已进入临床实验阶段.     

丙型肝炎病毒依赖于RNA的RNA聚合酶(RdRp)研究进展

由于缺乏合适的HCV感染细胞模型,严重制约了HCV复制,特别是HCV复制的关键因子依赖于RNA的RNA聚合酶(RdRp)的研究.对HCV序列比较分析并通过异源表达证明NS5B是HCV复制的RdRp.NS5B C端疏水性氨基酸区域以及NS5B与细胞膜形成复合体等影响NS5B溶解性.在合适的反应条件下NS5B可以多种RNA分子为模板催化RNA复制,特别是能有效复制HCV全长(+)RNA.高浓度GTP激活HCV RdRp活性.NS5B N/C端缺失突变和保守性A、B、C区中的点突变影响RdRp活性,但D区345位精氨酸突变为赖氨酸时RdRp活性明显升高.HCV RdRp的发现及其功能研究为HCV药物研究提供了新型靶标.     

Viperin蛋白可通过影响非结构蛋白与脂筏的关联抑制丙型肝炎病毒复制

目前, 对丙型肝炎病毒( HCV) 感染的患者主要采用以Ⅰ型干扰素为主的治疗方案, 但干扰素抑制病毒的具体机制仍然不详。本研究通过实时聚合酶链反应( PCR) 检测HCV的RNA 水平, 蛋白免疫印迹法检测HCV 非结构蛋白的表达, 以及膜飘浮实验检测非结构蛋白与脂筏的关联性, 探讨干扰素诱导蛋白Viperin 抑制HCV 复制的机制。结果显示, 在体外HCV 亚基因复制子( replicon) 及感染细胞模型中过量表达Viperin 可显著降低细胞内HCV 非结构蛋白的表达及RNA 的水平。膜漂浮实验发现, 过量表达的Viperin 可通过干扰HCV 非结构蛋白NS3、NS5A 与细胞内脂筏膜的关联, 使其对非离子去污剂敏感。进一步研究发现, 与脂筏膜结构组成相关的法尼基合成酶( FPPS) 可通过与Viperin 相互作用, 部分反转Viperin 的抗HCV 复制效应。以上结果提出了一种新的干扰素抗HCV 机制, 即干扰素诱导蛋白Viperin 可通过影响非结构蛋白与脂筏的关联, 干扰HCV 复制复合体的稳定性, 从而抑制HCV 的复制。     

NS5B与HCV负链RNA 3′末端特异性结合的分析

NS5B是RNA依赖性RNA聚合酶，在病毒RNA合成过程中起到中心催化酶的作用，在肠杆菌中表达和提纯了GST－NS5B融合蛋白，应用紫外交联试验（UV cross-linking）检测NS5B与丙型肝炎病毒（HCV）负链RNA3′末端的结合，确定NS5B是否参与HCV负链与HCN负链RNA3′末端复制体的形成。NS5B可与HCV负链RNA3′末端发生结合，这种结合存在量效关系， 比与正链RNA3′UTR X区的结合强约10倍，超大量的非同源性RNA和蛋白质不能竞争抑制S5B与负链RNA3′末端的结合，证明这种结合存在特异性。结果提示NS5B是HCV负链RNA3′末端复制体的成分之一。     

丙型肝炎病毒非结构蛋白5B的研究进展

已知丙型肝炎病毒非结构蛋白(NS5B)具有RNA依赖的RNA聚合酶的功能,负责病毒基因组的复制。通过体外表达及晶体衍射分析,目前对NS5B的三维结构已有了清晰的描述,对顺B催化该病毒基因组复制的分子机制也有了初步了解;对RNA聚合酶抑制物的研究将为人工设计特异性的抗该病毒药物奠定扎实基础。     

丙型肝炎病毒NS5A基因在昆虫细胞中的表达及其分布研究

应用PCR方法从含有丙肝病毒全部非结构蛋白基因的质粒pBAC25中扩增出全长的NS5A基因DNA片段(约1.34kb),PCR扩增NS5A基因片段克隆到转移载体pBlueBacHisA中.重组转移质粒pBlueBacHis5A DNA与野生型杆状病毒(AcNPV)DNA共转染SF-9昆虫细胞,通过空斑纯化获得带有NS5A基因的重组病AcNS5A.对重组病毒基因组DNA进行酶切和PCR鉴定,证实HCV NS5A基因已插入重组病毒基因组中.AcNS5A感染SF-9细胞后,在细胞中表达出一条64kD的蛋白,用Western-blot分析,结果表明这种蛋白与抗HCV HS5A特异性抗体发生强烈反应,说明NS5A基因已在细胞中得到表达,应用免疫荧光技术与免疫组化技术进一步研究NS5A蛋白在昆虫细胞中不同时间的表达情况及其分布,结果表明,NS5A蛋白在AcNS5A重组病毒感染细胞24h后主要分布在细胞质膜上,而在48h后则同时分布于细胞质膜和细胞核内,在72h则完全布满整个细胞,我们认为NS5A蛋白定位于质膜和细胞核中,暗示着在病毒复制过程中NS5A蛋白可能参与病毒RNA在质膜上复制和细胞基因表达的调控.     

HCV NS5A蛋白结构及生物学功能的研究进展

丙型肝炎是丙型肝炎病毒(HCV)感染引起的,是导致肝硬化和肝癌的主要病因。HCV感染已成为严重危害人类健康的社会公共卫生问题。HCV非结构蛋白5A是近年来HCV抑制剂研究的重要靶点及热点,本文对NS5A的三个结构域以及各个结构域在丙肝病毒复制、病毒颗粒组装及释放方面的生物学功能的研究进展进行了综述,为NS5A抑制剂作用机制的研究提供了广泛的思路,有利于对NS5A抑制剂的研制。     

HCV NS5B蛋白对HCV RNA的模板特异性研究

在大肠杆菌菌株BL21(DE3)中表达并纯化HCV的依赖于RNA的RNA多聚酶(RNA-dependent RNA polymerase,RdRp,NS5B蛋白).以HCV正、负链RNA 3′末端的序列为模板,体外研究NS5B蛋白催化的RNA合成.结果显示,正链RNA在体外不能指导RNA合成,而负链RNA模板可以产生一条全长的正链RNA产物,表明NS5B对负链RNA具有模板特异性.NS5B对负链RNA的特异性在模板竞争性实验中得到进一步证实,正链RNA的存在和竞争对以负链为模板的RNA合成没有影响.这样,就合理解释了在HCV RNA复制时正链RNA的数量远比负链RNA多这一问题.同时,本实验的结果也为进一步研究病毒或其它细胞因子参与以正链RNA为模板进行的RNA合成,以及有关负链RNA模板特性的研究奠定了基础.     

Interactions between viral nonstructural proteins and host protein hVAP-33 mediate the formation of hepatitis C virus RNA replication complex on lipid raft

The lipid raft membrane has been shown to be the site of hepatitis C virus (HCV) RNA replication. The mechanism of formation of the replication complex is not clear. We show here that the formation of the HCV RNA replication complex on lipid raft (detergent-resistant membranes) requires interactions among the HCV nonstructural (NS) proteins and may be initiated by the precursor of NS4B, which has the intrinsic property of anchoring to lipid raft membrane. In hepatocyte cell lines containing an HCV RNA replicon, most of the other NS proteins, including NS5A, NS5B, and NS3, were also localized to the detergent-resistant membranes. However, when individually expressed, only NS4B was associated exclusively with lipid raft. In contrast, NS5B and NS3 were localized to detergent-sensitive membrane and cytosolic fractions, respectively. NS5A was localized to both detergent-sensitive and -resistant membrane fractions. Furthermore, we show that a cellular vesicle membrane transport protein named hVAP-33 (the human homologue of the 33-kDa vesicle-associated membrane protein-associated protein), which binds to both NS5A and NS5B, plays a critical role in the formation of HCV replication complex. The hVAP-33 protein is partially associated with the detergent-resistant membrane fraction. The expression of dominant-negative mutants and small interfering RNA of hVAP-33 in HCV replicon cells resulted in the relocation of NS5B from detergent-resistant to detergent-sensitive membranes. Correspondingly, the amounts of both HCV RNA and proteins in the cells were reduced, indicating that hVAP-33 is critical for the formation of HCV replication complex and RNA replication. These results indicate that protein-protein interactions among the various HCV NS proteins and hVAP-33 are important for the formation of HCV replication complex.     

Protein kinase C-related kinase 2 regulates hepatitis C virus RNA polymerase function by phosphorylation

The hepatitis C virus (HCV) NS5B protein is the viral RNA-dependent RNA polymerase required for replication of the HCV RNA genome. We have identified a peptide that most closely resembles a short region of the protein kinase C-related kinase 2 (PRK2) by screening of a random 12-mer peptide library displayed on the surface of the M13 bacteriophage with NS5B proteins immobilized on microwell plates. Competitive phage enzyme-linked immunosorbent assay with a synthetic peptide showed that the phage clone displaying this peptide could bind HCV RNA polymerase with a high affinity. Coimmunoprecipitation and colocalization studies demonstrated in vivo interaction of NS5B with PRK2. In vitro kinase assays demonstrated that PRK2 specifically phosphorylates NS5B by interaction with the N-terminal finger domain of NS5B (amino acids 1-187). Consistent with the in vitro NS5B-phosphorylating activity of PRK2, we detected the phosphorylated form of NS5B by metabolic cell labeling. Furthermore, HCV NS5B immunoprecipitated from HCV subgenomic replicon cells was specifically recognized by an antiphosphoserine antibody. Knock-down of the endogenous PRK2 expression using a PRK2-specific small interfering RNA inhibited HCV RNA replication. In contrast, PRK2 overexpression, which was accompanied by an increase of in the level of its active form, dramatically enhanced HCV RNA replication. Altogether, our results indicate that HCV RNA replication is regulated by NS5B phosphorylation by PRK2.     

Human VAP-B is involved in hepatitis C virus replication through interaction with NS5A and NS5B

The hepatitis C virus (HCV) nonstructural protein (NS) 5A is a phosphoprotein that associates with various cellular proteins and participates in the replication of the HCV genome. Human vesicle-associated membrane protein-associated protein (VAP) subtype A (VAP-A) is known to be a host factor essential for HCV replication by binding to both NS5A and NS5B. To obtain more information on the NS5A protein in HCV replication, we screened human brain and liver libraries by a yeast two-hybrid system using NS5A as bait and identified VAP-B as an NS5A-binding protein. Immunoprecipitation and mutation analyses revealed that VAP-B binds to both NS5A and NS5B in mammalian cells and forms homo- and heterodimers with VAP-A. VAP-A interacts with VAP-B through the transmembrane domain. NS5A interacts with the coiled-coil domain of VAP-B via 70 residues in the N-terminal and 341 to 344 amino acids in the C-terminal polyproline cluster region. NS5A was colocalized with VAP-B in the endoplasmic reticulum and Golgi apparatus. The specific antibody to VAP-B suppressed HCV RNA replication in a cell-free assay. Overexpression of VAP-B, but not of a mutant lacking its transmembrane domain, enhanced the expression of NS5A and NS5B and the replication of HCV RNA in Huh-7 cells harboring a subgenomic replicon. In the HCV replicon cells, the knockdown of endogenous VAP-B by small interfering RNA decreased expression of NS5B, but not of NS5A. These results suggest that VAP-B, in addition to VAP-A, plays an important role in the replication of the HCV genome.     

Anti-hepatitis C virus activity of tamoxifen reveals the functional association of estrogen receptor with viral RNA polymerase NS5B

Hepatitis C virus (HCV) is a major causative agent of hepatocellular carcinoma. HCV genome replication occurs in the replication complex (RC) around the endoplasmic reticulum membrane. However, the mechanisms regulating the HCV RC remain widely unknown. Here, we used a chemical biology approach to show that estrogen receptor (ESR) is functionally associated with HCV replication. We found that tamoxifen suppressed HCV genome replication. Part of ESRalpha resided on the endoplasmic reticulum membranes and interacted with HCV RNA polymerase NS5B. RNA interference-mediated knockdown of endogenous ESRalpha reduced HCV replication. Mechanistic analysis suggested that ESRalpha promoted NS5B association with the RC and that tamoxifen abrogated NS5B-RC association. Thus, ESRalpha regulated the presence of NS5B in the RC and stimulated HCV replication. Moreover, the ability of ESRalpha to regulate NS5B was suggested to serve as a potential novel target for anti-HCV therapeutics.     

Cyclophilin B is a functional regulator of hepatitis C virus RNA polymerase

Viruses depend on host-derived factors for their efficient genome replication. Here, we demonstrate that a cellular peptidyl-prolyl cis-trans isomerase (PPIase), cyclophilin B (CyPB), is critical for the efficient replication of the hepatitis C virus (HCV) genome. CyPB interacted with the HCV RNA polymerase NS5B to directly stimulate its RNA binding activity. Both the RNA interference (RNAi)-mediated reduction of endogenous CyPB expression and the induced loss of NS5B binding to CyPB decreased the levels of HCV replication. Thus, CyPB functions as a stimulatory regulator of NS5B in HCV replication machinery. This regulation mechanism for viral replication identifies CyPB as a target for antiviral therapeutic strategies.     

The C-terminal transmembrane domain of hepatitis C virus (HCV) RNA polymerase is essential for HCV replication in vivo

Hepatitis C virus (HCV) RNA replication is dependent on the enzymatic activities of the viral RNA-dependent RNA polymerase NS5B, which is a membrane-anchored protein. Recombinant NS5B lacking the C-terminal transmembrane domain (21 amino acids) is enzymatically active. To address the role of this domain in HCV replication in vivo, we introduced a series of mutations into the NS5B of an HCV subgenomic replicon and examined the replication capabilities of the resultant mutants by a colony formation assay. Replicons lacking the transmembrane domain did not yield any colonies. Furthermore, when Huh-7 cells harboring the HCV subgenomic replicon were treated with a synthetic peptide consisting of the NS5B transmembrane domain fused to the antennapedia peptide, the membrane association of NS5B was completely disrupted. Correspondingly, the HCV RNA titer was reduced by approximately 50%. A scrambled peptide used as a control did not have any effects. These findings suggest that the membrane association of NS5B facilitates HCV RNA synthesis. However, a related transmembrane domain derived from bovine viral diarrhea virus could not replace the HCV NS5B transmembrane segment. This finding suggests that the C-terminal 21 amino acids not only have a membrane-anchoring function but also may perform additional functions for RNA synthesis in vivo.     

Direct interaction between alpha-actinin and hepatitis C virus NS5B

It has been suggested that cellular proteins are involved in hepatitis C virus (HCV) RNA replication. By using the yeast two-hybrid system, we isolated seven cDNA clones encoding proteins interacting with HCV RNA polymerase (NS5B) from a human liver cDNA library. For one of these, alpha-actinin, we confirmed the interaction by coimmunoprecipitation, immunofluorescent staining and confocal microscopic analysis. Experiments with deletion mutants showed that domains NS5B(84-95), NS5B(466-478), and alpha-actinin(621-733) are responsible for the interaction. Studies of the HCV subgenomic replicon system with small interference RNA indicate that alpha-actinin is essential for HCV RNA replication. Our results suggest alpha-actinin may be a component of the HCV replication complex.     

Effect of hepatitis C virus (HCV) NS5B-nucleolin interaction on HCV replication with HCV subgenomic replicon

We previously reported that nucleolin, a representative nucleolar marker, interacts with nonstructural protein 5B (NS5B) of hepatitis C virus (HCV) through two independent regions of NS5B, amino acids 208 to 214 and 500 to 506. We also showed that truncated nucleolin that harbors the NS5B-binding region inhibited the RNA-dependent RNA polymerase activity of NS5B in vitro, suggesting that nucleolin may be involved in HCV replication. To address this question, we focused on NS5B amino acids 208 to 214. We constructed one alanine-substituted clustered mutant (CM) replicon, in which all the amino acids in this region were changed to alanine, as well as seven different point mutant (PM) replicons, each of which harbored an alanine substitution at one of the amino acids in the region. After transfection into Huh7 cells, the CM replicon and the PM replicon containing NS5B W208A could not replicate, whereas the remaining PM replicons were able to replicate. In vivo immunoprecipitation also showed that the W208 residue of NS5B was essential for its interaction with nucleolin, strongly suggesting that this interaction is essential for HCV replication. To gain further insight into the role of nucleolin in HCV replication, we utilized the small interfering RNA (siRNA) technique to investigate the knockdown effect of nucleolin on HCV replication. Cotransfection of replicon RNA and nucleolin siRNA into Huh7 cells moderately inhibited HCV replication, although suppression of nucleolin did not affect cell proliferation. Taken together, our findings strongly suggest that nucleolin is a host component that interacts with HCV NS5B and is indispensable for HCV replication.     

Inhibition of hepatitis C virus RNA replication by 2'-modified nucleoside analogs

The RNA-dependent RNA polymerase (NS5B) of hepatitis C virus (HCV) is essential for the replication of viral RNA and thus constitutes a valid target for the chemotherapeutic intervention of HCV infection. In this report, we describe the identification of 2'-substituted nucleosides as inhibitors of HCV replication. The 5'-triphosphates of 2'-C-methyladenosine and 2'-O-methylcytidine are found to inhibit NS5B-catalyzed RNA synthesis in vitro, in a manner that is competitive with substrate nucleoside triphosphate. NS5B is able to incorporate either nucleotide analog into RNA as determined with gel-based incorporation assays but is impaired in its ability to extend the incorporated analog by addition of the next nucleotide. In a subgenomic replicon cell line, 2-C-methyladenosine and 2'-O-methylcytidine inhibit HCV RNA replication. The 5'-triphosphates of both nucleosides are detected intracellularly following addition of the nucleosides to the media. However, significantly higher concentrations of 2'-C-methyladenosine triphosphate than 2'-O-methylcytidine triphosphate are detected, consistent with the greater potency of 2'-C-methyladenosine in the replicon assay, despite similar inhibition of NS5B by the triphosphates in the in vitro enzyme assays. Thus, the 2'-modifications of natural substrate nucleosides transform these molecules into potent inhibitors of HCV replication.