Relationship between interferon therapy and variability in nonstructural gene 5b of hepatitis C virus

The hepatitis C virus (HCV) quasispecies nature in the hypervariable region (HVR) has been reported and found to relate to the effectiveness of interferon (IFN) treatment. However, the quasispecies nature in the nonstructural (NS) 5b region remains to be addressed. To examine this characterization and relationship with IFN therapy, we sequenced six independent HCV clones from each of eight patients. The eight patients were classified as responders or nonresponders to IFN. In the four responders, we found one to three isolates in each of the six clones. In the nonresponders, the six clones consisted of four, five, six, and six isolates, respectively. Compared the (NS) 5b genes of the isolates obtained from the patients with that of the reported hepatitis C virus HC-C2 or HC-J6 isolate the ratio of nonsynonymous to total substitutions ranged from 17.61% to 30.95% in the responders and from 33.11% to 76.47% in the nonresponders. We also compared posttreatment with pretreatment sequences. The average number of varying amino acids ranged from 5.5 to 9.0 in isolates remaining after IFN treatment and from 4.3 to 5.5 in the isolates that disappeared with IFN treatment. Two changed amino acids (glycine to arginine and valine to isoleucine) (compared with the pretreatment clones) were found in the posttreatment clones of one of the responders and one amino acid change (valine to alanine) was found in another responder. These results suggest that the NS5b quasispecies correlates with IFN treatment effectiveness. These results also implied that the heterogeneity in different hierarchical strata has a common impact on IFN treatment, making infected patients resistant to IFN. Our study also provides evidence that HCV elimination and mutation may occur simultaneously during IFN therapy. Received Sept. 19, 1997; accepted Feb. 27, 1998     

The nonstructural 5A protein of hepatitis C virus genotype 1b does not contain an interferon sensitivity-determining region

BACKGROUND: The nonstructural (NS) 5A protein of hepatitis C virus (HCV) has been suggested to contain an interferon (IFN) sensitivity-determining region (ISDR). METHODS: We studied whether the degree of viral decline on day 1 is associated with differences in NS5A amino acid sequences among patients receiving IFN- alpha. RESULTS: Phylogenetic analyses of the full-length protein and of functional domains showed no relationship between the baseline protein sequence and the antiviral response. NS5A quasispecies sequences showed no differences in the number of mutations in the putative ISDR relative to a prototype sequence between responders and nonresponders or according to IFN- alpha antiviral efficacy. No relationship was found between antiviral efficacy at 24 h and the baseline sequence of any NS5A region. Amino acid changes were observed in a few cases at 24 h in both responders and nonresponders, but no consistent pattern of amino acid shifts was observed, ruling out the possibility that IFN- alpha selected IFN-resistant variants. CONCLUSION: Our findings show that there is no ISDR in the HCV genotype 1 NS5A protein and that the NS5A sequence does not influence the capacity of IFN- alpha to block viral replication. The findings do not rule out a role for NS5A in subsequent viral clearance.     

Mutations in nonstructural protein 5A gene and response to interferon in hepatitis C virus genotype 2 infection.

An association has been reported between mutations in the amino acid residues 2209-2248 of the nonstructural protein 5A (NS5A) gene (interferon-sensitivity determining region [ISDR]) and interferon efficacy in hepatitis C virus (HCV)-1b infection. This relationship was analyzed in chronic HCV-2 infection. Forty patients with HCV-2a and 35 with HCV-2b were treated with interferon alfa for 6 months with a total dose of 468 to 860 million units. Pretreatment NS5A sequences were determined by direct sequencing. A higher complete and sustained response rate was observed in HCV-2a than in HCV-2b (70% vs. 34%; P =.003). Serum HCV-RNA levels were lower in complete responders than nonresponders in HCV-2a (P =.049) and HCV-2b (P =. 02). The number of amino acid mutations was greater in complete responders than nonresponders in NS5A2193-2228 (the region corresponding to the ISDR of HCV-1b) alone (P =.049), or NS5A2163-2228 consisting of NS5A2193-2228 plus its upstream region (P =.02) in HCV-2a, but not in HCV-2b. A significant inverse correlation was observed between serum HCV-RNA levels and the number of amino acid mutations in NS5A2193-2228 (P =.003) or NS5A2163-2228 (P =.005) in HCV-2a. With multivariate analysis, the number of substitutions in NS5A was an independent predictor for complete response in HCV-2a (odds ratio: 6.4; P =.03). Interferon efficacy is associated with amino acid variations in the NS5A protein in HCV-2a infection.     

HCV非结构蛋白5A对HIV长末端重复序列影响的初步探讨

目的本研究拟探讨HCV非结构蛋白5A(NS5A)对HIV长末端重复序列(long terminal repeat,LTR)影响,从而为HCV对HIV的影响提供实验依据。方法将构建的LTR启动子驱动的荧光素酶(Luc)报告基因表达质粒(pGL3-LTR-Luc)和含HCV NS5A基因的表达质粒pCNS5A共转染肝癌细胞株(Huh7细胞),采用免疫细胞化学技术、Western Blot及逆转录聚合酶链反应检测HCV NS5A蛋白及mRNA的表达;本实验分三组,将质粒pGL3-LTR-Luc(空白组)、质粒pRc/CMV+pGL3-LTR-Luc(对照组)、质粒pCNS5A+pGL3-LTR-Luc(实验组)分别转染Huh7细胞,48 h后收集细胞,采用Luc活性检测LTR的活性,以观察HCV NS5A对LTR的调控影响。所得荧光活性值以均数±标准差表示,采用Levene's方差齐性检验,多组间比较采用单因素方差分析,两两比较行LSD-t检验。结果转染pcNS5A质粒的Huh7细胞质经RT-PCR及Western Blot检测,HCV NS5A mRNA及蛋白在细胞中获得表达。方差分析结果提示LTR荧光活性在三组间有明显的差异(F=7.876,P=0.002),进一步比较各组间的差异,结果提示共转染质粒pcNS5A+pGL3-LTR-Luc组的Huh7细胞中Luc相对活性(22 476±4471)明显高于单转染pGL3-LTR-Luc组(15 887±3039,P=0.002)及共转染质粒pRc/CMV+pGL3-LTR-Luc组(16 321±4162,P=0.008),差异有统计学意义。结论表达HCV NS5A的质粒pCNS5A成功转染至Huh7细胞;HCV NS5A蛋白能激活HIV LTR,提示HCV NS5A可能为HCV促进HIV复制的分子机制之一。     

SUMOylation of nonstructural 5A protein regulates hepatitis C virus replication

Viruses exploit cellular SUMOylation machinery to favour their own propagation. We show that NS5A is a target protein of small ubiquitin‐like modifier (SUMO) and is SUMOylated at lysine residue 348. We demonstrated that SUMOylation increased protein stability of NS5A by inhibiting ubiquitylation, and SUMOylation was also required for protein interaction with NS5B. These data imply that SUMO modification may contribute to HCV replication. Indeed, silencing of UBC9 impaired HCV replication in Jc1‐infected cells, and HCV replication level was also significantly reduced in SUMO‐defective subgenomic replicon cells. Taken together, these data indicate that HCV replication is regulated by SUMO modification of NS5A protein. We provide evidence for the first time that HCV exploits host cellular SUMO modification system to favour its own replication.     

丙型肝炎病毒非结构蛋白5A反式激活基因4的克隆化研究

目的 丙型肝炎病毒(HCV)非结构蛋白5A(NS5A)病毒蛋白反式激活作用的新的靶基因NS5ATP4的基因序列的确立及基因克隆化研究。方法 依据我室构建的NS5A反式激活基因差异表达的cDNA消减文库，利用生物信息学技术获得新基因NS5ATP4的编码序列，对其可能的氨基酸序列进行分析比较，并对其基因利用多聚酶链反应技术(PCR)进行克隆化研究。结果 发现了HCVNS5A反式激活作用的新的靶基因NS5ATP4。结论 这一发现，为阐明HCVV NS5A蛋白的反式激活作用及其机制，开辟了新的研究方向。     

Mutagenic effect of ribavirin on hepatitis C nonstructural 5B quasispecies in vitro and during antiviral therapy

BACKGROUND AND AIMS: Addition of ribavirin to interferon alfa treatment has substantially increased sustained virologic response rates in patients with chronic hepatitis C (CHC). Ribavirin acts as an RNA virus mutagen in vitro, thereby leading to error catastrophe. However, data in CHC are controversial. METHODS: The nonstructural (NS) 5B quasi-species heterogeneity was analyzed in Huh7 cells harboring a subgenomic hepatitis C virus (HCV) replicon system treated with ribavirin or levovirin. Accordingly, NS5B quasi-species were studied in 14 patients with CHC who received ribavirin alone or combined with pegylated interferon alfa both at baseline and during the first weeks of therapy. Analysis of NS3 quasi-species served as control. RESULTS: Cultivation of HCV replicon cells with ribavirin led to higher NS5B mutational frequencies compared with levovirin-treated or untreated cells (P < .05). Patients receiving ribavirin monotherapy showed higher overall mutational frequencies within NS3 and NS5B during therapy as compared with baseline (P < .01). Proportions of ribavirin-specific G-to-A and C-to-T transitions increased (P < .01). Paired analysis confirmed significant mean increases of mutational frequencies of approximately 5%. Ribavirin serum concentrations were positively correlated with mutational frequency changes (P < .05). In patients receiving combination therapy, a decrease of NS5B mutational frequencies ( approximately 10%) and lower proportions of G-to-A and T-to-C mutations (P < .01) were detectable. CONCLUSIONS: Ribavirin, but not its L-enantiomer levovirin, is a mutagen in HCV replicon cells. In patients with CHC, ribavirin monotherapy exhibits a moderate mutagenic effect early during therapy that is not detectable in combination with pegylated interferon alfa.     

Number and position of mutations in the interferon (IFN) sensitivity-determining region of the gene for nonstructural protein 5A correlate with IFN efficacy in hepatitis C virus genotype 1b infection

To explore the relationship between responses to interferon (IFN) and the mutation patterns in the IFN sensitivity-determining region (ISDR; amino acid positions 2209-2248) in the NS5A gene of hepatitis C virus genotype 1b, a cohort of 334 patients was analyzed. The number of mutations in the ISDR was higher in patients with sustained response (SR) than in patients with transient or no response (P<.001). Patients with viruses mutated at positions 2209 (P=.02), 2216 (P=.01), or 2227 (P=.02) more frequently experienced SR than did those without these mutations. Mutation occurred most frequently at position 2218, where the presence of cysteine was significantly associated with SR. Thus, the mutation pattern in the ISDR affects the virologic response to IFN and reflects different influences on the function of the NS5A protein. ISDR sequence analysis would allow the prediction of clinical IFN efficacy in individual patients.     

Variability of the nonstructural 5A protein of hepatitis C virus type 3a isolates and relation to interferon sensitivity

The nonstructural 5A (NS5A) protein of hepatitis C virus (HCV) genotype 1 is thought to interact with several cellular proteins, including the double-stranded RNA-dependent protein kinase (PKR) induced by interferon (IFN). The PKR-binding domain (PKR-BD; aa 2209-2274), including the IFN sensitivity-determining region (aa 2209-2248) and other regions, could be linked to IFN resistance. Thus, the entire NS5A sequence of 27 isolates of HCV genotype 3a was investigated in relation to the clinical response to IFN. The NS5A 3a protein presented a low variability with some specific variable regions. Differential analysis between IFN-resistant and -sensitive isolates identified 5 regions in NS5A, 2 of them inside the PKR-BD and another around the variable 3 region. However, using the yeast growth suppression assay, no interaction was found between 5 resistant NS5A 3a proteins and PKR. Some amino acid changes of the NS5A protein of genotype 3a seemed to relate to IFN resistance independently of the PKR pathway.     

Sequence variation in hepatitis C virus nonstructural protein 5A predicts clinical outcome of pegylated interferon/ribavirin combination therapy

A substantial proportion of hepatitis C virus (HCV)-1b-infected patients still do not respond to interferon-based therapy. This study aims to explore a predictive marker for the ultimate virological response of HCV-1b-infected patients treated with pegylated interferon/ribavirin (PEG-IFN/RBV) combination therapy. Nonstructural protein 5A (NS5A) sequences of HCV in the pretreated sera of 45 patients infected with HCV-1b were analyzed. The mean number of mutations in the variable region 3 (V3) plus its upstream flanking region of NS5A (amino acid 2334-2379), referred to as IFN/RBV resistance-determining region (IRRDR), was significantly higher for HCV isolates obtained from patients who later achieved sustained virological response (SVR) by PEG-IFN/RBV than for those in patients undergoing non-SVR. The receiver operating characteristic curve analysis estimated six mutations in IRRDR as the optimal threshold for SVR prediction. Indeed, 16 (76%) of 21 SVR, but only 2 (8%) of 24 non-SVR, had HCV with six or more mutations in IRRDR (IRRDR > or = 6) (P < 0.0001). All of 18 patients infected with HCV of IRRDR of 6 or greater examined showed a significant (> or =1 log) reduction or disappearance of serum HCV core antigen titers within 24 hours after initial dose of PEG-IFN/RBV, whereas 10 (37%) of 27 patients with HCV of IRRDR of 5 or less did (P < 0.0001). The positive predictive value of IRRDR of 6 or greater for SVR was 89% (16/18; P = 0.0007), with its negative predictive value for non-SVR being 81% (22/27; P = 0.0008). CONCLUSION: A high degree (> or =6) of sequence variation in IRRDR would be a useful marker for predicting SVR, whereas a less diverse (< or =5) IRRDR sequence predicts non-SVR.     

丙型肝炎病毒非结构蛋白5a对细胞周期的影响

丙型肝炎病毒(HCV)感染是慢性肝炎、肝硬化的主要病因之一，并与肝细胞癌的发生关系非常密切。但HCV导致原发性肝细胞癌的机制，特别是其基因产物(结构蛋白和非结构蛋白)在致癌中的作用仍不清楚。HCV非结构蛋白5a(NS5a)能激活多种转录因子，并与细胞内因子结合，影响其功能，导致细胞增殖分化异常，可能与原发性肝细胞癌的发生有关。为进     

丙型肝炎病毒非结构蛋白HS5A反式激活基因HS5ATP6的克隆化研究

目的 应用抑制性消减杂交(SSH)技术及生物信息学技术(bioinformatics)筛选并克隆丙型肝炎病毒(HCV)非结构蛋白5A(NS5A)反式激活新型靶基因。方法 以HCVNS5A表达质粒PcDNA3．1(-)-NS5A转染HepG2细胞，以空载体pcDNA3．1(-)为平行对照，提取mRNA并进行抑制性消减杂交分析。对于所获基因片段序列分析表明，其中之一为新型基因片段，与GenBank中注册的已知功能基因序列没有同源性，利用表达序列标签(EST)序列的搜索和比对，进行电子拼接，根据基因起始密码子的KOZ2ak规则和终止密码子下游保守的多聚腺苷酸信号序列，确定新型基因序列。结果 从HePG2细胞提取总RNA，以逆转录多聚酶链反应(RT-PCR)技术扩增获得该新基因的全长序列，并测序证实，命名为NS5ATP6，在GenBatk中注册，注册号为AF529367。Ns5ATP6基因的编码序列全长为1572个核苷酸(nt)，编码产物由524个氨基酸残基(aa)组成。结论 HCVNS5A反式激活新型靶基因NS5ATP6的筛选与克隆，为进一步研究HCVNS5A反式激活作用的分子生物学机制和探索新型治疗技术奠定基础。     

丙型肝炎病毒非结构蛋白NS3反式激活基因1的克隆化研究

目的 应用抑制性消减杂交技术(SSH)及生物信息学技术(bioinformatics)筛选并克隆丙型肝炎病毒非结构蛋白3(NS3)反式激活新型靶基因，进一步阐明HCV感染相关疾病的发病机制。方法 以HCVNS3蛋白表达质粒pcDNA3．1(-)-NS3转染HepG2细胞，以空载体pcDNA3．1(-)为平行对照，提取mRNA并进行抑制性消减杂交分析。并应用分子生物学技术，结合生物信息学技术，克隆HCVNS3反式激活作用的新的靶基因。结果 对于所获基因片段序列分析表明，其中之一为新型基因片段。从HepG2细胞提取总RNA，以逆转录多聚酶链反应(RT—PCR)技术扩增获得该新基因的全长序列，并测序证实，因其可以被NS3蛋白反式激活，故命名为NS3TP1，已在GenBank中注册，注册号为AYll6969。NS3评1基因的编码序列全长为1932个核昔酸(nt)，编码产物由眺个氨基酸残基(aa)组成。结论 HCVNS3是一种典型的病毒基因组编码的具有反式激活作用的蛋白，HCVNS3反式激活作用的新靶基因的发现，为进一步研究HCVNS3蛋白反式激活作用的分子生物学机制和探索新型治疗技术奠定基础。