Hepatitis C core and nonstructural 3 proteins trigger toll-like receptor 2-mediated pathways and inflammatory activation

BACKGROUND AND AIMS: Recent evidence suggests that toll-like receptors (TLRs) recognize certain viruses. We reported that hepatitis C virus (HCV) core and nonstructural 3 (NS3) proteins activate inflammatory pathways in monocytes. The aim of this study was to investigate the role of TLRs in innate immune cell activation by core and NS3 proteins. METHODS: Human monocytes, human embryonic kidney cells transfected with TLR2, and peritoneal macrophages from TLR2, MyD88 knockout, and wild-type mice were studied to determine intracellular signaling and proinflammatory cytokine induction by HCV proteins. RESULTS: HCV core and NS3 proteins triggered inflammatory cell activation via the pattern recognition receptor TLR2 and failed to activate macrophages from TLR2 or MyD88-deficient mice. HCV core and NS3 induced interleukin (IL)-1 receptor-associated kinase (IRAK) activity, phosphorylation of p38, extracellular regulated (ERK), and c-jun N-terminal (JNK) kinases and induced AP-1 activation. Activation of nuclear factor-kappaB by core and NS3 was associated with increased IkappaBalpha phosphorylation. TLR2-mediated cell activation was dependent on the conformation of core and NS3 proteins and required sequences in the regions of aa 2-122 in core and aa 1450-1643 in NS3. Although cellular uptake of core and NS3 proteins was independent of TLR2 expression, cell activation required TLR2. HCV core protein and TLR2 showed intracellular colocalization. The hyper-elevated TNF-alpha induction by TLR2 ligands in monocytes of HCV-infected patients was not due to increased TLR2 expression. CONCLUSIONS: HCV core and NS3 proteins trigger inflammatory pathways via TLR2 that may affect viral recognition and contribute to activation of the innate immune system.     

Hepatitis C virus proteins do not directly trigger fibrogenic events in cultured human liver myofibroblasts

Summary. Although liver fibrosis is the major complication of hepatitis C virus (HCV) infection, the mechanisms of fibrogenesis in this setting are not completely understood. The aim of this study was to test the direct effect of HCV proteins on signalling- and fibrosis-related events in cultured human liver myofibroblasts, the effector cells of liver fibrogenesis. Cultured myofibroblasts were exposed to recombinant HCV core, a structural protein, and nonstructural proteins (NS) 3, NS 4 and NS 5. HCV proteins did not significantly increase DNA synthesis in myofibroblasts. We then examined if these proteins affected early signalling events. None of the HCV proteins affected the phosphorylation of the mitogen activated protein kinases/extracellular regulated kinases 1 and 2, or of the phosphatidylinositol 3-kinase target, Akt. HCV proteins had also no effect on intracellular calcium concentration. In other experiments, fibrogenesis-related parameters were measured. None of the HCV proteins had any effect on the secretion of type I collagen, tissue inhibitor of matrix metalloproteinases type 1, gelatinase or urokinase. Alpha-smooth muscle actin expression was also not modified. In summary, our experiments do not support a direct effect of these HCV proteins on fibrogenic cells.     

Post-translational modifications of hepatitis C viral proteins and their biological significance

Replication of hepatitis C virus(HCV)depends on the interaction of viral proteins with various host cellular proteins and signalling pathways.Similar to cellular proteins,post-translational modifications(PTMs)of HCV proteins are essential for proper protein function and regulation,thus,directly affecting viral life cycle and the generation of infectious virus particles.Cleavage of the HCV polyprotein by cellular and viral proteases into more than 10 proteins represents an early protein modification step after translation of the HCV positivestranded RNA genome.The key modifications include the regulated intramembranous proteolytic cleavage of core protein,disulfide bond formation of core,glycosylation of HCV envelope proteins E1 and E2,methylation of nonstructural protein 3(NS3),biotinylation of NS4A,ubiquitination of NS5B and phosphorylation of core and NS5B.Other modifications like ubiquitination of core and palmitoylation of core and NS4B proteins have been reported as well.For some modifications such as phosphorylation of NS3 and NS5A and acetylation of NS3,we have limited understanding of their effects on HCV replication and pathogenesis while the impact of other modifications is far from clear.In this review,we summarize the available information on PTMs of HCV proteins and discuss their relevance to HCV replication and pathogenesis.     

Hepatitis C virus expression suppresses interferon signaling by degrading STAT1

BACKGROUND & AIMS: The molecular mechanisms by which hepatitis C virus (HCV) antagonizes the antiviral actions of interferon (IFN) have not been fully characterized. Specifically, how HCV proteins impact on IFN signaling components has yet to be elucidated. We used an HCV cell-based expression model to examine the interaction between HCV protein expression and host type I IFN signaling components in the Jak-STAT kinase pathway. METHODS: Full-length HCV and HCV subgenomic constructs corresponding to structural and each of the nonstructural proteins were transiently transfected into Huh-T7 cells. HCV expression was monitored by an HCV core antigen enzyme-linked immunosorbent assay. STAT1, P-STAT1, and HCV protein expression was investigated with immunoprecipitation and Western blots. RESULTS: Overexpression and small interfering RNA studies showed that STAT1 was indispensable for control of HCV expression. STAT1 and P-STAT1 expression were markedly reduced in HCV-transfected cells. Full-length HCV, HCV core/E1/E2, and NS3-4A were each associated with decreased STAT1 expression, which was attributable to proteasome-dependent degradation of STAT1. HCV core, but not HCV E1, E2, NS3, NS4, or NS5, bound to STAT1. STAT2 expression was not affected by HCV. CONCLUSIONS: HCV expression selectively degrades STAT1 and reduces P-STAT1 accumulation in the nucleus in a proteasome-dependent manner. HCV core protein binds STAT1, suggesting that this viral protein is associated with STAT1 degradation. STAT1 plays an indispensable role in innate antiviral immunity against HCV expression. In turn, HCV subverts the Jak-STAT kinase by selectively inducing STAT1 degradation.     

丙型肝炎病毒非结构蛋白NS5A反式激活基因NS5A-TP9启动子序列的确定及转录活性的鉴定

目的：阐明丙型肝炎病毒(HCV)非结构蛋白NS5A(NS5A)反式激活基因NS5A-TP9表达的调控机制。方法：选取NS5A-TP9基因翻译起始密码子ATG上游661bp的基因组DNA序列作为启动子序列，应用聚合酶链反应(PCR)技术，以肝母细胞瘤细胞系HepG2基因组DNA为模板，扩增该启动子DNA片段，将其克隆至pCAT3中，构建pCAT3-NS5A-TP9-promoter报告基因表达载体，以该质粒转染HepG2细胞，用酶联免疫吸附法(ELISA)检测报告基因编码产物氯霉素乙酰转移酶(CAT)的表达活性。结果：发现质粒pCAT3-NS5A-TP9-promoter具有指导报告基因CAT转录表达的启动子活性，CAT的吸光度(A值)是缺乏启动子序列对照质粒pCAT3的13．9倍。结论：本研究克隆的启动子DNA序列具有指导下游基因转录的启动子活性，这一结果为研究新基因NS5A-TP9转录表达的调节机制，进一步阐明丙型肝炎病毒非结构蛋白NS5A的作用机制奠定了基础。     

Loading of mechanical pressure activates mitogen-activated protein kinase and early immediate gene in intestinal epithelial cells

Intestinal mucosa is continuously exposed to mechanical forces. We examined whether pressure loading activates mitogen-activated protein kinase (MAPK) and expression of early immediate genes in intestinal epithelial cells. Pressure was applied to IEC18 cells by helium gas in a culture flask and pressure-induced cell proliferation was examined. The expression of early immediate genes, MAPK activity, and activation of nuclear factor activator protein-1 (AP-1) were also examined. Pressures significantly promoted cell proliferation with peak effect at 80 mm Hg. Pretreatment with either a protein kinase C inhibitor or tyrosine kinase inhibitors, but not calcium chelating agents significantly inhibited cell proliferation promoted by pressure. Early inductions of c-myc and c-fos proteins, increased activity of MAPK, and activation of AP-1 were observed by pressure loading. Our study showed that intestinal mucosal cell proliferation is promoted by mechanical pressure and various intracellular signaling pathways are involved in the process.     

新基因TAHCCP1编码蛋白对NS3TP6基因启动子转录活性的调节

目的探讨丙型肝炎病毒（HCV）核心蛋白反式激活基因TAHCCP1编码蛋白对NS3TP6启动子转录活性的调节。方法以我室前期克隆的TAHCCP1基因表达谱芯片结果为基础,利用生物信息学方法确定NS3TP6基因的启动子区域（NS3TP6-p）,聚合酶链反应（PCR）扩增并克隆至真核报告载体pCAT3-basic中,构建重组报告质粒pCAT3-NS3TP6-p;以该质粒单独或与pcDNA3．1（-）-TAHCCP1共转染肝癌细胞系HepG2细胞,用酶联免疫吸附法（ELISA）检测氯霉素乙酰转移酶（CAT）的表达活性;观察细胞中表达的TAHCCP1蛋白对NS3TP6启动子转录活性的调节。结果构建的重组表达载体pCAT3-NS3TP6-P在HepG2细胞中能够启动报告基因CAT表达,表明克隆的NS3TP6启动子有指导下游基因转录表达的活性;共转染实验中pCAT3-NS3TP6-p与pcDNA3．1（-）-TAHCCP1组CAT的表达活性是对照组的3．1倍,说明TAHCCP1蛋白能够在转录水平反式激活NS3TP6基因启动子活性。结论本实验验证了基因芯片的实验结果准确性,进一步完善了新基因TAHCCP1的生物学功能,为深入理解HCV核心蛋白的反式激活调节机制提供了新的依据。     

Hepatitis C virus NS4 protein impairs the Th1 polarization of immature dendritic cells

Summary. Dendritic cells (DCs) in chronic hepatitis C patients display impaired function, although the details remain unclear. To investigate the hepatitis C virus (HCV) protein that has the most impact on DC function, we compared five recombinant proteins and seven HCV protein genes in modulating DC phenotype and function. Immature DCs (iDCs) were established from healthy donor peripheral blood monocytes with granulocyte–macrophage colony stimulating factor (GM‐CSF) and IL‐4. Lipopolysaccharide was used to establish mature DCs (mDCs). Cells were then pulsed with HCV recombinant proteins or transfected with HCV plasmids and subsequently assayed for cell surface marker expression by flow cytometry. For cytokine and proliferative T‐cell response analysis, DCs were cultured with autologous CD4 T cells and tuberculin purified protein derivative (PPD). Mean fluorescent intensity of CD86 was reduced in HCV protein‐pulsed iDCs. Proliferative T‐cell responses and Th1 cytokine concentrations were reduced with HCV nonstructural proteins (NS), particularly with HCV NS4. HCV nonstructural proteins, particularly NS4, change the iDC phenotype and reduce antigen‐specific T‐cell stimulatory function with Th1 cytokine reductions.     

丙型肝炎病毒NS4B对LO2肝细胞细胞周期及cyclin D1表达的影响

目的研究丙型肝炎病毒非结构蛋白4B对LO2肝细胞细胞周期和cyclinD1表达的影响，探讨HCVNS4B在HCV致病中的可能机制。方法利用脂质体介导将空白载体PCXN2及重组质粒PCXN2-NS4B转染入LO2肝细胞，G418筛选，RT-PCR法鉴定质粒转染成功。MTT法检测细胞生长并绘制生长曲线，观察NS4B对肝细胞生长的影响；流式细胞仪检测细胞周期；免疫组化法检测细胞cyclinD1的表达。结果NS4B成功转染入LO2细胞；转染的NS4B可促进肝细胞的生长；转染PcxN2-NS4B细胞的S期、G2／M期较转染PCXN2细胞增加，两组比较差异有显著性（P〈0．05）；转染NS4B的细胞cyclinD1表达较转染空白载体组增强，两组比较差异有显著性（P〈0．01）。结论 HCVNS4B可能通过调节某些基因转录与表达，促进DNA合成，干扰肝细胞周期，促进肝细胞增殖。     

丙型肝炎病毒非结构蛋白质5A抑制Hepcidin基因表达并促进肝细胞内铁储留

目的 探讨丙型肝炎病毒(HCV)非结构蛋白质5A (NS5A)对Hepcidin基因表达的影响. 方法 用含HCV NS5A基因的表达质粒pcNS5A瞬时转染QSG7701细胞,采用逆转录-聚合酶链反应及Western blot试验观察HCV NS5A和Hepcidin的mRNA转录水平及蛋白质表达水平,铁染色后观察细胞内铁储留情况.检测数据的多组间比较行单因素方差分析,两两比较行LSD-t检验.结果 转染pcNS5A质粒细胞内有HCV NS5A的mRNA和蛋白的表达,未转染质粒组和转染空白质粒pRc/CMV组细胞内无HCV NS5A的mRNA和蛋白的表达.未转染质粒组、转染pRc/CMV质粒组和转染pcNS5A质粒组细胞的Hepcidin mRNA相对表达量分别为0.711±0.049、0.718±0.052和0.264±0.030,转染pcNS5A组Hepcidin mRNA表达低于未转染质粒组和转染pRc/CMV质粒组(t值分别为- 13.523和- 13.045,P值均＜0.01).转染pcNS5A质粒组细胞Hepcidin蛋白表达较未转染质粒组及转染pRc/CMV质粒组下降,且随着转染pcNS5A质粒剂量的增加,Hepcidin蛋白表达下降更明显.铁染色结果显示,转染pcNS5A质粒细胞内铁较转染pRC/CMV质粒细胞和未转染质粒细胞高.结论 HCV NS5A蛋白能抑制Hepidin的mRNA和蛋白质表达,并引起细胞内铁的储留增加.