G-四链体碱基突变可增强丙型肝炎病毒DNA疫苗的免疫原性

The G4-quadruplex mutation of the core gene enhances the immunogenicity of hepatitis C virus DNA vaccine

目的 探讨丙型肝炎病毒（Hepatitis C Virus,HCV）核心抗原core基因上的G4-四链体（core G4）RNA结构对机体特异性免疫应答的影响。方法 圆二色谱（circular dichroism,CD）检测寡核苷酸链RNA G4（命名为G4R）和突变体G4M（命名为G4RM,在不改变氨基酸密码子的情况下）的G-四链体空间结构;在不改变密码子的情况下采用PCR定点突变的方法把HCV野生型G4-core（DNA）突变为G4Mcore,然后将G4-core和G4M-core基因构建至真核表达质粒pc DNA3.1上（分别称为p G4和pG4M）,免疫印迹（Western blot）分析core基因上G4结构突变后Core蛋白的表达水平。将p G4及pG4M质粒分别用基因导入仪免疫小鼠,检测免疫后小鼠的细胞免疫以及体液免疫水平。结果 CD结果显示寡核苷酸链RNA G4M相比野生型RNA G4结构发生改变,熔解曲线表明G4RM熔解温度低于野生型RNA G4R。Western blot显示在细胞水平及动物水平,pG4M比p G4的Core蛋白表达水平更高（P〈0.05）。动物免疫实验结果表明pG4M免疫后小鼠总IgG及IFN-γ的释放水平增高（P〈0.05）。其中,pG4M免疫组小鼠的IgG水平是p G4组的1.61倍。酶联免疫斑点（Enzyme-linked immunospot,ELISpot）实验中,pG4M免疫后小鼠脾脏细胞IFN-γ的释放水平是p G4的1.39倍。流式实验显示pG4M免疫后小鼠脾脏CD4＋T细胞中IFN-γ产生水平是p G4的1.79倍。结论 本研究首次报道HCV核心抗原core上G-四链体可能抑制其蛋白翻译和免疫应答,core上G-四链体碱基突变可增强翻译水平,并增强其Th1型的细胞免疫应答。核心抗原G-四链体碱基突变可增强HCV疫苗的免疫原性,为研制增强免疫原性的HCV疫苗提供了一种新的策略。

Objective To investigate the effect of G-quadruplex （G4） RNA structure of core of hepatitis C virus （HCV） on the specific immune response. Methods Circular dichroism （CD） was usedto detect the G4 spatial structure of the G4 oligonucleotide chain RNA （named as G4R） and its mutant of G4 （named as G4RM） by G base site-specific mutation.The HCV wild-type core gene G4（DNA） sequence was mutated as G4M-core by PCR site-directed mutagenesis without changing the amino acid codon.Then wild type and mutated core genes were constructed into the eukaryotic expression plasmid pcDNA3.1-Myc, and produced as pcDNA3.1-core-G4-WT （named as pG4） and pcDNA3.1-core-G4-M （named as pG4M）, the expression of core protein was examined by Western blot. The mice were immunized with the pG4 and pG4M plasmids DNA respectively, and their humoral and cellular responses were examined. Results CD results showed that the structure o f G4RM was changed compared to Wild type G4R, and the melting curve analysis showed the melting temperature of GR4M was lower than that of G4R, which indicates that G4RM structure is unstable. Western blot analysis showed that pG4M had much higher protein expression level compared to pG4（P〈0.05）. Analysis of animal immunization showed that pG4M induced increased levels of total IgG and IFN-y compared to pG4（P〈0.05）. The IgG level of the pG4M group was 1.61 times higher than that of the pG4 group. By enz^e-linked immunospot（ELISpot）assay, we found that the release IFN-y level of pG4M was 1.39 times higher than those of pG4. Flow cytometry showed that the intracellular IFN-y production in the splenic CD4＋ T cells was 1.79 times than those of pG4. Conclusion The G-quadmplex structure of HCV core can inhibit its protein translation. The mutation of G-quadruplex of core led to increased Thl-type immune responses. This is the first report demonstrate that HCV core G-quadruplex mutation can enhance its immunogenicity and could be used as a new strategy ofexploring HCV vaccine with enhanced immunogenicity.