Functional and Biochemical Characterization of Hepatitis C Virus (HCV) Particles Produced in a Humanized Liver Mouse Model

Lipoprotein components are crucial factors for hepatitis C virus (HCV) assembly and entry. As hepatoma cells producing cell culture-derived HCV (HCVcc) particles are impaired in some aspects of lipoprotein metabolism, it is of upmost interest to biochemically and functionally characterize the in vivo produced viral particles, particularly regarding how lipoprotein components modulate HCV entry by lipid transfer receptors such as scavenger receptor BI (SR-BI). Sera from HCVcc-infected liver humanized FRG mice were separated by density gradients. Viral subpopulations, termed HCVfrg particles, were characterized for their physical properties, apolipoprotein association, and infectivity. We demonstrate that, in contrast to the widely spread distribution of apolipoproteins across the different HCVcc subpopulations, the most infectious HCVfrg particles are highly enriched in apoE, suggesting that such apolipoprotein enrichment plays a role for entry of in vivo derived infectious particles likely via usage of apolipoprotein receptors. Consistent with this salient feature, we further reveal previously undefined functionalities of SR-BI in promoting entry of in vivo produced HCV. First, unlike HCVcc, SR-BI is a particularly limiting factor for entry of HCVfrg subpopulations of very low density. Second, HCVfrg entry involves SR-BI lipid transfer activity but not its capacity to bind to the viral glycoprotein E2. In conclusion, we demonstrate that composition and biophysical properties of the different subpopulations of in vivo produced HCVfrg particles modulate their levels of infectivity and receptor usage, hereby featuring divergences with in vitro produced HCVcc particles and highlighting the powerfulness of this in vivo model for the functional study of the interplay between HCV and liver components.     

丙型肝炎病毒细胞培养系统研究进展

由于缺少丙型肝炎病毒(HCV)细胞培养系统,因此对其生活周期、感染机制至今仍不十分清楚,严重阻碍了相关治疗药物的研制。HCV复制子仅能在Huh7等极少数细胞中短暂复制且量低。1999年建立了亚基因组复制子,使人们有机会对其进行深入研究,但须人为引入碱基突变。最近建立的全基因组复制子无须引入突变且可形成病毒粒子,是一项重大突破。本文概述了HCV细胞培养系统的研究进展。     

Hepatitis C Virus: Assembly and Release of Virus Particles

Hepatitis C virus is a blood-borne virus that typically establishes a chronic infection in the liver, which often results in cirrhosis and hepatocellular carcinoma. Progress in understanding the complete virus life cycle has been greatly enhanced by the recent availability of a tissue culture system that produces infectious virus progeny. Thus, it is now possible to gain insight into the roles played by viral components in assembly and egress and the cellular pathways that contribute to virion formation. This minireview describes the key determining viral and host factors that are needed to produce infectious virus.     

Biophysical and Ultrastructural Characterization of Adeno-Associated Virus Capsid Uncoating and Genome Release

We describe biophysical and ultrastructural differences in genome release from adeno-associated virus (AAV) capsids packaging wild-type DNA, recombinant single-stranded DNA (ssDNA), or dimeric, self-complementary DNA (scDNA) genomes. Atomic force microscopy and electron microscopy (EM) revealed that AAV particles release packaged genomes and undergo marked changes in capsid morphology upon heating in physiological buffer (pH 7.2). When different AAV capsids packaging ss/scDNA varying in length from 72 to 123% of wild-type DNA (3.4 to 5.8 kb) were incrementally heated, the proportion of uncoated AAV capsids decreased with genome length as observed by EM. Genome release was further characterized by a fluorimetric assay, which demonstrated that acidic pH and high osmotic pressure suppress genome release from AAV particles. In addition, fluorimetric analysis corroborated an inverse correlation between packaged genome length and the temperature needed to induce uncoating. Surprisingly, scAAV vectors required significantly higher temperatures to uncoat than their ssDNA-packaging counterparts. However, externalization of VP1 N termini appears to be unaffected by packaged genome length or self-complementarity. Further analysis by tungsten-shadowing EM revealed striking differences in the morphologies of ssDNA and scDNA genomes upon release from intact capsids. Computational modeling and molecular dynamics simulations suggest that the unusual thermal stability of scAAV vectors might arise from partial base pairing and optimal organization of packaged scDNA. Our work further defines the biophysical mechanisms underlying adeno-associated virus uncoating and genome release.     

Permissivity of Primary Human Hepatocytes and Different Hepatoma Cell Lines to Cell Culture Adapted Hepatitis C Virus

Significant progress has been made in Hepatitis C virus (HCV) culture since the JFH1 strain cloning. However, developing efficient and physiologically relevant culture systems for all viral genotypes remains an important goal. In this work, we aimed at producing a high titer JFH1 derived virus to test different hepatic cells’ permissivity. To this end, we performed successive infections and obtained a JFH1 derived virus reaching high titers. Six potential adaptive mutations were identified (I599V in E2, R1373Q and M1611T in NS3, S2364P and C2441S in NS5A and R2523K in NS5B) and the effect of these mutations on HCV replication and infectious particle production was investigated. This cell culture adapted virus enabled us to efficiently infect primary human hepatocytes, as demonstrated using the RFP-NLS-IPS reporter protein and intracellular HCV RNA quantification. However, the induction of a strong type III interferon response in these cells was responsible for HCV inhibition. The disruption of this innate immune response led to a strong infection enhancement and permitted the detection of viral protein expression by western blotting as well as progeny virus production. This cell culture adapted virus also enabled us to easily compare the permissivity of seven hepatoma cell lines. In particular, we demonstrated that HuH-7, HepG2-CD81, PLC/PRF/5 and Hep3B cells were permissive to HCV entry, replication and secretion even if the efficiency was very low in PLC/PRF/5 and Hep3B cells. In contrast, we did not observe any infection of SNU-182, SNU-398 and SNU-449 hepatoma cells. Using iodixanol density gradients, we also demonstrated that the density profiles of HCV particles produced by PLC/PRF/5 and Hep3B cells were different from that of HuH-7 and HepG2-CD81 derived virions. These results will help the development of a physiologically relevant culture system for HCV patient isolates.     

细胞分离戊型肝炎病毒的初步研究

本文报告用2BS细胞分离戊型肝炎病毒(HEV)感染成功的猴肝脏标本中的HEV的初步结果,将2BS细胞长成致密单层,接种已知含有HEV的肝悬液,盲传至第4代,发现在第27天细胞出现了轻微的细胞病变(CPE),随着进一步的传代,细胞病变时间逐渐提前。至第7代时,在第17天就可见到CPE,CPE的主要特征是细胞间隙变宽,透明度降低和轻度细胞破坏,无大片细胞溶解和脱落现象。免疫电镜检查在第5代和第6代细胞培养液中见到很少的27—34nm的病毒颗粒。将第4代至第7代的细胞悬液20ml接种了3只恒河猴,有2只猴在24天和26天出现了典型的ALT升高,待这3只猴恢复正常后一年,再次接种以上细胞悬液20ml,3只猴全部发生了ALT升高,并在胆汁中检查到27—34nm的病毒颗粒,我们初步推测2BS适应的这株病毒很可能是戊型肝炎病毒。     

丙肝病毒全基因组克隆转染细胞体系的初步研究

采用一种含有HCV全基因组和噬菌体T7启动子和终止子序列的载体(pHCV)转染Vero-E6细胞,随后感染高效表达T7 RNA聚合酶的重组痘病毒(vTF7-3),通过vTF7-3的辅助作用,使Vero-E6细胞高效增殖HCV病毒体,建立了一种新的HCV体外细胞培养体系。RT-PCR、荧光定量PCR检测转染细胞裂解液中HCV滴度的结果显示：pHCV转染细胞内HCV基因拷贝达10^7-10^8／mL,同时有HCV正链RNA合成;免疫印迹显示该培养体系中有HCV结构蛋白、非结构蛋白的表达;pHCV转染细胞经透射电镜观察,可见清晰的HCV病毒体,直径在40-50nm。这一新体系的初步建立,为研究HCV的复制机制、制备HCV疫苗和研发抗病毒药物奠定了基础。     

丙肝病毒全基因组克隆转染细胞体系的初步研究

采用一种含有HCV全基因组和噬菌体T7启动子和终止子序列的载体(pHCV)转染Vero-E6细胞,随后感染高效表达T7 RNA聚合酶的重组痘病毒(vTF7-3),通过vTF7-3的辅助作用,使Vero-E6细胞高效增殖HCV病毒体,建立了一种新的HCV体外细胞培养体系.RT-PCR、荧光定量PCR检测转染细胞裂解液中HCV滴度的结果显示pHCV转染细胞内HCV基因拷贝达107-108/mL,同时有HCV正链RNA合成;免疫印迹显示该培养体系中有HCV结构蛋白、非结构蛋白的表达;pHCV转染细胞经透射电镜观察,可见清晰的HCV病毒体,直径在40-50nm.这一新体系的初步建立,为研究HCV的复制机制、制备HCV疫苗和研发抗病毒药物奠定了基础.     

Endogenous Hepatitis C Virus Homolog Fragments in European Rabbit and Hare Genomes Replicate in Cell Culture

Endogenous retroviruses, non-retroviral RNA viruses and DNA viruses have been found in the mammalian genomes. The origin of Hepatitis C virus (HCV), the major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma in humans, remains unclear since its discovery. Here we show that fragments homologous to HCV structural and non-structural (NS) proteins present in the European rabbit (Oryctolagus cuniculus) and hare (Lepus europaeus) genomes replicate in bovine cell cultures. The HCV genomic homolog fragments were demonstrated by RT-PCR, PCR, mass spectrometry, and replication in bovine cell cultures by immunofluorescence assay (IFA) and immunogold electron microscopy (IEM) using specific MAbs for HCV NS3, NS4A, and NS5 proteins. These findings may lead to novel research approaches on the HCV origin, genesis, evolution and diversity.     

Mutational Analysis of Hepatitis C Virus NS5B in the Subgenomic Replicon Cell Culture

The hepatitis C virus (HCV) NS5B is an RNA-dependent RNA polymerase (RdRP), a central catalytic enzyme of HCV RNA replication. We previously identified five novel residues of NS5B in a JK-1 isolate indispensable for RdRP activity in vitro (Qin, W., Yamashita, T., Shirota, Y., Lin, Y., Wei, W., and Murakami, S. (2001) Hepatology 33, 728-737). We addressed the role of these residues in HCV RNA replication using a HCV replicon system derived from an M1LE isolate (Kishine, H., Sugiyama, K., Hijikata, M., Kato, N., Takahashi, H., Noshi, T., Nio, Y., Hosaka, M., Miyanari, Y., and Shimotohno, K. (2002) Biochem. Biophys. Res. Commun. 293, 993-999). The five residues of NS5B in M1LE were found to be critical for HCV replication in vivo and also indispensable for RdRP activity in vitro along with purified bacterial recombinant proteins. We also found a chimeric replicon of JK-1 and M1LE in which only the NS5B sequence derived from JK-1 could not replicate in Huh-7 cells. The residues responsible for the phenomenon were mapped by several chimeric and substituted forms of NS5B M1LE and/or JK-1 isolates in the HCV RNA replicon. Two residues, amino acids 220 and 288, were critical, and two residues, amino acids 213 and 231, were important for efficient HCV replication. Mutant JK-1 NS5B harboring all four residues of M1LE was replication-competent in the chimeric replicon and was as efficient as the original M1LE replicon. By comparing the replication competence in vivo and RdRP activity in vitro with various chimeric and mutated versions of NS5B, the HCV replication ability was found to correlate well with the RdRP activity. However, heat- and dilution-sensitive NS5Bs exhibiting weaker RdRP activity in vitro were found to be replication-incompetent, suggesting that HCV replication requires RdRP activity higher than a certain critical threshold.     

Hepatitis C Virus Hypervariable Region 1 Variants Presented on Hepatitis B Virus Capsid-Like Particles Induce Cross-Neutralizing Antibodies

Hepatitis C virus (HCV) infection is still a serious global health burden. Despite improved therapeutic options, a preventative vaccine would be desirable especially in undeveloped countries. Traditionally, highly conserved epitopes are targets for antibody-based prophylactic vaccines. In HCV-infected patients, however, neutralizing antibodies are primarily directed against hypervariable region I (HVRI) in the envelope protein E2. HVRI is the most variable region of HCV, and this heterogeneity contributes to viral persistence and has thus far prevented the development of an effective HVRI-based vaccine. The primary goal of an antibody-based HCV vaccine should therefore be the induction of cross-reactive HVRI antibodies. In this study we approached this problem by presenting selected cross-reactive HVRI variants in a highly symmetric repeated array on capsid-like particles (CLPs). SplitCore CLPs, a novel particulate antigen presentation system derived from the HBV core protein, were used to deliberately manipulate the orientation of HVRI and therefore enable the presentation of conserved parts of HVRI. These HVRI-CLPs induced high titers of cross-reactive antibodies, including neutralizing antibodies. The combination of only four HVRI CLPs was sufficient to induce antibodies cross-reactive with 81 of 326 (24.8%) naturally occurring HVRI peptides. Most importantly, HVRI CLPs with AS03 as an adjuvant induced antibodies with a 10-fold increase in neutralizing capability. These antibodies were able to neutralize infectious HCVcc isolates and 4 of 19 (21%) patient-derived HCVpp isolates. Taken together, these results demonstrate that the induction of at least partially cross-neutralizing antibodies is possible. This approach might be useful for the development of a prophylactic HCV vaccine and should also be adaptable to other highly variable viruses.     

丙型肝炎病毒细胞和动物模型的研究进展

丙型肝炎病毒(HCV)是造成慢性肝炎、肝硬化及肝癌的重要病因之一,目前全世界约1.7亿人感染HCV.HCV的自然宿主范围很窄,由于缺少有效的HCV细胞培养系统和小动物模型,人们对其生活周期、作用机制等仍不是很清楚,从而严重阻碍了HCV疫苗及治疗药物的开发与研制.我们简要综述了近几年在HCV细胞和动物模型方面的进展,同时...     

丙型肝炎病毒体外培养系统研究进展

由于缺少丙型肝炎病毒（HCV）的细胞培养系统和小动物模型,因此对其生活周期、作用机制至今仍不是很清楚,从而严重阻碍了丙型肝炎疫苗及相关治疗药物的开发与研制。一直以来,人们研究的HCV体外培养细胞模型包括感染模型和转染模型两种,感染模型由于原代肝细胞培养问题未能解决而难以成功,而转染模型的发展可喜。但是HCV复制子只能在极少数细胞中短暂复制,且产生的病毒量很低。1999年建立了亚基因组复制子,使人们有机会对其进行深入研究,但须人为引入碱基突变。最近建立的全基因复制子不需要引入突变即形成病毒粒子,是一项重大突破。概述了HCV体外培养系统的研究进展。     

Hepatitis C Virus Infection in Phenotypically Distinct Huh7 Cell Lines

In 2005, the first robust hepatitis C virus (HCV) infectious cell culture system was developed based on the HCV genotype 2a JFH-1 molecular clone and the human-derived hepatoma cell line Huh7. Although much effort has been made to dissect and expand the repertoire of JFH-1-derived clones, less attention has been given to the host cell despite the intriguing facts that thus far only Huh7 cells have been found to be highly permissive for HCV infection and furthermore only a limited number of Huh7 cell lines/stocks appear to be fully permissive. As such, we compiled a panel of Huh7 lines from disparate sources and evaluated their permissiveness for HCV infection. We found that although Huh7 lines from different laboratories do vary in morphology and cell growth, the majority (8 out of 9) were highly permissive for infection, as demonstrated by robust HCV RNA and de novo infectious virion production following infection. While HCV RNA levels achieved in the 8 permissive cell lines were relatively equivalent, three Huh7 lines demonstrated higher infectious virion production suggesting these cell lines more efficiently support post-replication event(s) in the viral life cycle. Consistent with previous studies, the single Huh7 line found to be relatively resistant to infection demonstrated a block in HCV entry. These studies not only suggest that the majority of Huh7 cell lines in different laboratories are in fact highly permissive for HCV infection, but also identify phenotypically distinct Huh7 lines, which may facilitate studies investigating the cellular determinants of HCV infection.     

酿酒酵母表达的rHBcAg颗粒的纯化和鉴定及其透射电镜观察

乙肝核心抗原(HBcAg)蛋白基因(C基因)在酿酒酵母中表达,表达产物经过分离和Sepharose CL-4B柱子的初步纯化。产物经SDS-PAGE和Western blotting鉴定为一分子量约21.5kDa的多肽。再经蔗糖密度梯度超离心和CsCl等密度梯度超离心等过程而被纯化。分管收集的超离心纯化产物经ELISA抗原活性检测和密度分析,可知ELISA反应强度较高的收集管中的颗粒密度主要分布在1.27g/mL和1.40 g/mL两个峰值处。将rHBcAg抗原活性最高的收集管合并,再经TEM观察,发现酵母表达的rHBcAg蛋白(核心蛋白)能自主装配成大小不同的两种核心颗粒,大颗粒直径约为30.1±2.4 nm,小颗粒直径约为21.5±3.3 nm。这表明,酿酒酵母表达的rHBcAg颗粒具有大小不同的二态性,其生物学意义还未明了,需进一步研究和探讨。