APOBEC3F的克隆、真核表达及其抗HBV效应的初步研究

目的克隆、体外真核表达载脂蛋白B mRNA编辑酶催化多肽样3F(APOBEC3F)基因并研究其抗病毒效应。方法应用RT-PCR的方法从人PBMC细胞中扩增APOBEC3F基因,构建HA-APOBEC3F融合蛋白真核表达载体pXFA3F,pXFA3F和具有复制能力的1.3倍HBV载体pHBV1.3共转染HepG2细胞,Western印迹检测APOBEC3F融合蛋白在HepG2细胞中的表达,ELISA方法检测细胞培养上清液中的HBsAg和HBeAg水平,实时定量PCR检测HBV相关mRNA水平变化。结果克隆了APOBEC3F基因,其经测序与GeneBank公布序列一致;构建的APOBEC3F真核表达载体pXFA3F经转染可在HepG2细胞中瞬时表达;APOBEC3F可抑制乙型肝炎表面抗原和e抗原的分泌,可使转染细胞内HBV相关mRNA水平下降。结论成功克隆并真核表达了APOBEC3F基因,其在体外具有抗HBV生物学效应。     

HIV-1 Vpr蛋白对C8166细胞毒性研究

目的 利用腺病毒系统研究HIV-1 Vpr蛋白在T细胞来源的C8166细胞内的高表达以及细胞内该蛋白对T细胞毒性.方法 将表达目的 蛋白Vpr的重组腺病毒rAd-vpr和空白载体病毒rAd-vector分别感染对数生长期的C8166细胞,流式细胞术(FCM)检测细胞周期分布、凋亡和坏死.用Hoechst-PI荧光染色观察细胞的凋亡和坏死,JC-1荧光染色测定线粒体膜电势.结果 Annexin V-PI染色及Hoechst-PI染色一致显示HIV-1 Vpr能显著诱导C8166细胞凋亡和坏死;PI细胞周期结果表明HIV-1 Vpr能阻滞C8166细胞于G2期;JC-1荧光染色法测定HIV-1 Vpr致C8166线粒体膜电势下降.结论 细胞内HIV-1 Vpr介导的T细胞毒性包括线粒体功能障碍、细胞周期的G2期阻滞和细胞的死亡.     

HIV-1 Vif与机体内在抗病毒因子APOBEC3G的研究进展

近期研究表明,非允许性细胞中存在的载脂蛋白B mRNA编辑酶催化多肽样蛋白3G(APOBEC3G)是机体内在的抗病毒因子,它在人免疫缺陷病毒(HIV)反转录过程中,使所形成的负链cDNA中的胞嘧啶脱氨,进而降低病毒的感染力.而Vif蛋白可结合APOBEC3G,并激活泛素-蛋白酶体途径,使之降解,拮抗APOBEC3G的抗病毒活性,且二者之间的相互作用还存在种属特异性.Vif与APOBEC3G间的相互作用,为抗HIV药物的研究提供了新靶点.     

表达HIV Vpr细胞株的建立及其促细胞凋亡作用的研究

目的 建立稳定表达人免疫缺陷病毒(HIV)Vpr蛋白的细胞株,观察Vpr蛋白促进感染细胞凋亡的特性,以及Vpr变异后对其致凋亡作用的影响.方法 以携带野生株HIV Vpr基因和突变株HIV vpr-FS基因的质粒分别转染HeLa细胞,建立稳定表达HIV Vpr蛋白的细胞株,以流式细胞仪和细胞内DNA片段分析法检测细胞凋亡效果,观察Vpr蛋白促细胞凋亡的特性,以及两者致凋亡作用的区别.结果 重组质粒pcDNA3.1-vpr和pcDNA3.1-vpr-FS经酶切后均可获得342bp产物,DNA测序结果与目的 基因已知序列完全一致;上述质粒转染的HeLa细胞,RT-PCR检测到目的 基因vpr或vpr-FS的表达,Western blot检测到明显Vpr或Vpr-FS蛋白的表达.流式细胞仪和细胞内DNA片段分析法分别检测细胞凋亡,显示野生株HeLa pcDNA3.1-vpr组的凋亡率明显高于对照组,而变异株HeLa pcDNA3.1-vpr-FS的凋亡率与对照组无明显差别.结论 成功建立了表达HIV Vpr和HIVVpr-FS蛋白的感染细胞株.实验显示HIV Vpr蛋白能促进感染细胞的凋亡,而Vpr蛋白的变异可能使其促进细胞凋亡作用减弱.实验结果为下一步研究提供了基础资料.     

HIV-1 Vif与机体内在抗病毒因子APOBEC3G的研究进展

近期研究表明,非允许性细胞中存在的载脂蛋白B mRNA编辑酶催化多肽样蛋白3G(APOBEC3G)是机体内在的抗病毒因子,它在人免疫缺陷病毒(HIV)反转录过程中,使所形成的负链cDNA中的胞嘧啶脱氨,进而降低病毒的感染力。而Vif蛋白可结合APOBEC3G,并激活泛素-蛋白酶体途径,使之降解,拮抗APOBEC3G的抗病毒活性,且二者之间的相互作用还存在种属特异性。Vif与APOBEC3G间的相互作用,为抗HIV药物的研究提供了新靶点。     

HIV-1B’/C重组病毒感染者Vif、Vpr和Vpu特异性细胞免疫应答研究

目的 探讨我国HIV-1 B'/C重组病毒感染者针对HIV-1调节蛋白的细胞免疫反应特征及其与病毒复制控制的关系.方法 以覆盖HIV-1 C亚型Vpr、Vpu和Vif蛋白全长的重叠肽段作为刺激抗原,利用ELISPOT方法检测新疆HIV-1 B'/C重组病毒感染者的特异性细胞免疫反应.使用SIGMAPLOT 10.0和SIGMASTAT 3.5进行统计分析,用双尾t检验比较组间差异,用Spearmam秩相关分析免疫反应与病毒载量及CD4细胞计数的关系.结果 在检测的60名HIV-1 B'/C重组病毒感染者中,能够识别Vif、Vpr和Vpu蛋白产生CIL应答者分别为68%、52%和8%,Vpr和Vif蛋白存在多个强CIL反应的免疫优势区域.研究中还发现针对Vpr、Vif和Vpu蛋白的CTL反应强度和广度与HIV感染者的病毒载量及CD4细胞数量无明显的相关性.结论 HIV-1 Vpr和Vif蛋白包含多个可被机体免疫系统特异性T细胞识别的免疫优势区域.对这些免疫优势区所包含的CIL表位进行鉴定并探讨其在自然感染过程中的作用,对新一代的HIV疫苗设计有重要的参考意义.     

外源性组织型纤溶酶原激活物信号肽突变体增强蛋白质在哺乳细胞中的表达及分泌

目的 比较不同tPA信号肽突变体对目的蛋白表达和分泌水平的影响,优化并筛选通用性外源信号肽序列.方法 通过定点突变技术将人类组织型纤溶酶原激活物（tPA）的信号肽第22位氨基酸由脯氨酸（P）突变为丙氨酸（tPA22P/A）或甘氨酸（tPA22P/G）,并将突变前后的3种信号肽序列分别插入HIV-1 p24基因的N末端,构建不同的p24蛋白表达载体,这些重组表达载体体外瞬时转染人胚肾HEK293T细胞,转染72 h后,通过SDS-PAGE与western blot检测并比较各组培养上清和细胞中p24蛋白的表达水平.结果 成功构建了3个p24蛋白的真核表达载体P24T.tPA、P24T.tPA22P/A和P24T.tPA22P/G,经序列测定证实基因序列和方向与预期相符;重组载体转染293T细胞72 h后均检测到分泌性p24的表达.与P24T.tPA组相比,P24T.tPA22P/A转染组培养上清中和细胞内p24蛋白表达水平分别提高62%和29%,P24T.tPA22P/G转染组分别提高8%和6%.结论 tPA信号肽22位由脯氨酸突变为丙氨酸或甘氨酸,这就提高了目的蛋白的表达和分泌水平,为优化外源蛋白在哺乳细胞中的表达和分泌提供了实验基础.     

APOBEC3G抗HIV-1作用机制研究进展

APOBEC3G是细胞内新的广谱抗病毒蛋白.它具有胞苷脱氨酶活性,能使病毒负链DNA产生dC→dU高发突变,造成正链DNA G→A突变,使得病毒DNA变成无功能或降解.APO-BEC3G具有广泛的生物学功能,可以限制HIV-1等病毒复制,但HIV-1病毒感染因子Vif能拮抗APOBEC3G抑制病毒活性作用.本文简要综述了APOBEC3G抑制病毒HIV-1作用机制的最新进展.     

胞嘧啶脱氨酶APOBEC3G可能通过G→A突变抑制乙型肝炎病毒的复制

目的研究胞嘧啶脱氨酶APOBEC3G(A3G)对HBV复制的影响及作用机制。方法利用脂质体介导A3G和HBV的真核表达质粒瞬时共转染人肝癌细胞株HepG2,以空载体pcDNA3.1与HBV真核表达质粒共转染为对照,同时转染含增强型绿色荧光蛋白(EGFP)基因的质粒载体以判定转染效率。共转染两天后用荧光定量PCR方法定量细胞内核壳体(core)相关HBV DNA水平,用Western blot检测细胞内A3G和HBcAg的表达,并对细胞内core相关HBV DNA X基因进行PCR扩增、T-A克隆和测序,分析X基因中的碱基突变。结果经EGFP判定的转染效率平均为29%。共转染0.5μgA3G和0.5μgHBV的HepG2细胞内core相关HBV DNA量平均下降为对照的8.9%,共转染2μgA3G和0.5μgHBV的平均下降为对照的0.6%。共转染A3G和HBV表达质粒后,HepG2细胞内HBV的X基因中发生G→A突变的数目明显增多,33个克隆中有9个克隆检测到了16～37个G→A突变,突变总数达254个,而对照的33个克隆中仅有2个克隆各检测到2个G→A突变。进一步的分析发现,共转染A3G后发生的G→A突变大多集中于几个热点区域,突变靶点常在GG二核苷酸中的第一个G上。结论胞嘧啶脱氨酶APOBEC3G可能通过诱导。HBV DNA的X基因发生G→A超突变,抑制HBV在人肝癌细胞HepG2中的复制。     

IFN-α诱导HuH7细胞固有免疫分子APOBEC3G的表达

目的了解IFN-α对HuH7细胞固有免疫分子APOBEC3G表达的影响及其机制。方法HuH7细胞给予不同浓度的IFN-α(0 U/ml、100U/ml、400U/ml、800U/ml and 1200U/ml)刺激,10h后提取细胞总RNA,RT-PCR和实时定量RT-PCR检测HuH7细胞内APOBEC3G的mRNA水平变化,Western blot分析APOBEC3G蛋白水平的表达;分别构建不同长度的含有IRF-E(IFN regulatory factor element)位点的APOBEC3G起始密码上游序列报告质粒、不含IRF-E和IRF-E位点突变的虫荧光素酶报告质粒,报告基因分析IFN-α刺激后APOBEC3G起始密码上游IPF-E位点对APOBEC3G表达的影响。结果IFN-α上调HuH7细胞APOBEC3G mRNA和蛋白水平的表达,并具有剂量依赖的效应。序列分析发现APOBEC3G起始密码上游的-298～-283和-57～-47位碱基分别存在IRF-E和ISRE(IFN stimulated re- sponse element)序列。报告基因分析结果显示,干扰素使含有IRF-E序列的APOBEC3G启动子报告质粒的虫荧光素酶的活性增加6～8倍,而不含IRF-E序列和IRF-E位点突变的报告质粒的虫荧光素酶活性在干扰素刺激后几乎没有变化。结论IFN-α可通过IRF-E位点上调APOBEC3G mRNA和蛋白水平的表达,从而发挥抗病毒效应。     

Function analysis of sequences in human APOBEC3G involved in Vif-mediated degradation

Human APOBEC3G (hA3G) has been identified as an anti-HIV cellular factor. As a counter measure, the HIV-1 protein Vif causes the degradation of hA3G by binding to it and directing it to the cellular proteasome. In this work, we have used hA3G deletion mutants to map the region in hA3G required for its degradation by Vif to hA3G amino acids 105-245, the linker region between the two zinc coordination motifs. A small fragment of hA3G containing only amino acids 105-245 will undergo Vif-induced degradation. However, while amino acids 105-156 of hA3G are required for Vif interaction with hA3G, they are not themselves sufficient for hA3G degradation, a process that further requires amino acids 157-245. While expression of hA3G fragments 1-156 or 157-384 (but not 246-384) can dominantly inhibit the Vif-mediated degradation of full-length hA3G, only the N-terminal fragment inhibits the Vif/hA3G interaction. Inhibition of hA3G degradation by the C-terminal hA3G fragment 157-384 appears to be related to its ability to prevent the polyubiquitination of hA3G induced by Vif, a process that is required for Vif-mediated proteosomal degradation of hA3G. Non-permissive cells stably expressing hA3G 1-156 or hA3G 157-384 are able to inhibit the replication of wild-type HIV-1, thereby verifying the inhibitory effect of these fragments upon Vif-mediated hA3G degradation and suggesting their potential in anti-HIV-1 therapy.     

Expression of human immunodeficiency virus type 1 vif and vpr mRNAs is Rev-dependent and regulated by splicing.

We have analyzed the structure and expression of the HIV-1 vif and vpr mRNAs. The results revealed that the predominant vif and vpr mRNAs belong to the intermediate size class of HIV-1 mRNAs and that their expression is dependent on the presence of Rev protein. In addition, low levels of a small multiply spliced vpr mRNA were produced by HIV-1. cDNA cloning and expression of vpr cDNAs in eucaryotic cells revealed that high levels of Vpr were produced only from the intermediate-size mRNA in the presence of Rev. Thus, as demonstrated for the viral structural proteins, expression of Vif and Vpr is regulated by Rev. The arrangement of the splice sites and the Rev-RRE interaction are responsible for the regulation of viral expression, and especially for the switching from an early stage, producing only or primarily Tat, Rev, and Nef from multiply spliced mRNAs, to a late stage, leading to the production of Gag, Pol, Env, Vpu, Vif, and Vpr from unspliced and partially spliced mRNAs.     

Functional analysis of the two cytidine deaminase domains in APOBEC3G

Human APOBEC3G (hA3G), a cytidine deaminase with two cytidine deaminase domains (CDs), has been identified as an anti-HIV-1 host factor. Although the two CDs of hA3G have been extensively characterized, there is still debate on the role of the CDs in the biological function of hA3G. In this work, we constructed three hA3G mutants CD1-1, CD2-2 and CD2-1, which contain duplicate CD1 domain, duplicate CD2 domain and position switched CD domain respectively, and investigated the effect of CD domain replacement or switch upon virion encapsidation, Vif-mediated degradation, deamination and antiviral activity of hA3G. The results showed that the two CD domains were functionally equivalent in virion encapsidation and the interaction with HIV-1 Vif of hA3G, whereas CD domain switch or replacement greatly affected the sensitivity to Vif induced degradation, editing and antiviral activity of hA3G. Although the CD2 domain was shown to possess the deamination activity, CD2-2 incorporated efficiently into HIV-1 was unable to mutate viral cDNA, suggesting that CD1 also involved in the enzymatic function. Interestingly, CD2-1 retained considerable deamination activity with a different sequence preference. Taken together, our results suggest that CD domain may play a structural role in virion encapsidation and Vif-mediated degradation of hA3G, and coordination of the two CD domains is required for its editing and antiviral activity.     

HIV-1 Vif protein blocks the cytidine deaminase activity of B-cell specific AID in E. coli by a similar mechanism of action

HIV-1 Vif protein protects viral replication in non-permissive cells by inducing degradation of APOBEC3G via ubiquitination and proteasomal pathway, although new studies indicate a putative role in Vif's direct inhibition of APOBEC3G. APOBEC3G is member of a homologous family of proteins with cytidine deaminase activity expressed with characteristic tissue specificity, that in humans consist of APOBEC1, APOBEC2, APOBEC3A-H, APOBEC4 and the activation-induced deaminase (AID), a B lymphoid protein necessary for somatic hypermutation, gene conversion and class switch recombination. In this work we show that Vif can counteract AID's activity in E. coli in absence of specific eukaryotic co-factors necessary for AID induced somatic hypermutation, gene conversion and to stimulate class switch recombination in B-cells. We show that AID inhibition is mediated by a direct protein-protein interaction via unique amino acid D118 an homologous mutant responsible for the species-specific restriction of HIV-1 Vif protein existent for APOBEC3G. These results raise the hypothesis that Vif related proteins can act as a broad inhibitor of deaminase activity. Moreover as AID and Vif evolved in different cellular environments, these results may indicate that Vif related proteins might mimic cellular factors that interact with a structural conserved domain of cytidine deaminases during evolution.     

HIV-1 Vpr对细胞周期的影响和致凋亡作用的研究

目的 研究人免疫缺陷病毒1型(HIV-1)的vpr基因和不同变异株对宿主细胞周期和凋亡的影响,以及其致细胞周期变化和致细胞凋亡机制的两者间的可能关系.方法 将14个带有不同变异位点的中国感染者HIV-1 upr片段分别连入pcDNA3.1(+)真核表达载体,构建重组质粒.将这些重组质粒电转染Jurkat细胞,并设立保守株vpr基因转染细胞、突变株vpr-Fs基因转染细胞、空载体转染细胞和未转染细胞作为对照.经G418选择培养及RT-PCR检测目的基因转染成功后,PI染色,流式细胞仪检测被转染细胞的细胞周期分布和细胞凋亡.结果 流式细胞仪检测上述14个带有不同变异位点的HIV-1 vpr基因片段的Jurkat细胞,发现转染保守片段HIV-1 vpr的Jurkat细胞,其细胞周期出现G_2期阻滞和细胞凋亡率明显升高,但转染vpr C端截断的vpr-Fs片段的细胞、空载体peDNA3.1(+)转染细胞和未转染的Jurkat细胞无此现象.转染了,HIV-1 vpr基因序列相对应的Vpr蛋白中含有70V、85P、86G、94G突变的片段,较vpr保守片段其致感染细胞G_2期阻滞和凋亡的能力明显下降,且Vpr蛋白的AE亚型致细胞周期阻滞和致凋亡能力较其他亚型普遍为低.初步发现vpr诱导G2期阻滞百分比越高其所致凋亡率越高.结论 HIV-I vpr基因有明显的致感染细胞G_2周期阻滞和致细胞凋亡的作用,但vpr C端截断的vpr-Fs片段无此功能.首次发现中国感染者HIV-1 vpr基因表达蛋白的70V、85P、86G、94G位点突变能使其致感染细胞G_2期阻滞和凋亡的能力下降,Vpr的AE亚型致细胞周期阻滞和凋亡能力较其他亚型普遍为低.对14个变异片段的分析显示vpr诱导G_2期阻滞的程度与其致凋亡水平可能相关,提示两者的发生机制可能有一定的关联.本研究为进一步探讨HIV-1致病机制和探索可能的基因干预措施打下基础.     

Human APOBEC3B is a potent inhibitor of HIV-1 infectivity and is resistant to HIV-1 Vif

While the human antiretroviral defense factors APOBEC3F and APOBEC3G are potent inhibitors of the replication of HIV-1 mutants lacking a functional vif gene, the Vif protein expressed by wild-type HIV-1 blocks the function of both host cell proteins. Here, we report that a third human protein, APOBEC3B, is able to suppress the infectivity of both Vif-deficient and wild-type HIV-1 with equal efficiency. APOBEC3B, which shows approximately 58% sequence identity to both APOBEC3F and APOBEC3G, shares the ability of these other human proteins to bind the nucleocapsid domain of HIV-1 Gag specifically and to thereby package into progeny virion particles. However, APOBEC3B differs from APOBEC3F and APOBEC3G in that it is unable to bind to HIV-1 Vif in co-expressing cells and is therefore efficiently packaged into HIV-1 virions regardless of Vif expression. Unfortunately, APOBEC3B also differs from APOBEC3F and APOBEC3G in that it is not normally expressed in the lymphoid cells that serve as targets for HIV-1 infection. These studies therefore raise the possibility that activation of the endogenous APOBEC3B gene in primary human lymphoid cells could form a novel and effective strategy for inhibition of HIV-1 replication in vivo.     

HIV-1 Vif promotes the formation of high molecular mass APOBEC3G complexes

HIV-1 Vif inhibits the antiviral activity of APOBEC3G (APO3G) by inducing proteasomal degradation. Here, we studied the effects of Vif on APO3G in vitro. In this system, Vif did not cause APO3G degradation. Instead, Vif induced changes in APO3G that affected immunoprecipitation of the native protein. This effect required wt Vif and was reversed by heat denaturation of APO3G. Sucrose gradient analysis demonstrated that wt Vif induced the gradual transition of APO3G translated in vitro or expressed in HeLa cells from a low molecular mass conformation to puromycin-sensitive high molecular mass (HMM) complexes. In the absence of Vif or the presence of biologically inactive Vif APO3G failed to form HMM complexes. Our results expose a novel function of Vif that promotes the assembly of APO3G into presumably packaging-incompetent HMM complexes and may explain how Vif can overcome the APO3G-imposed block to HIV replication under conditions of no or inefficient APO3G degradation.     

Antiviral roles of APOBEC proteins against HIV-1 and suppression by Vif

Apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like (APOBEC) proteins are members of a protein family sharing the common characteristic of cytidine deaminase activity. The antiviral activity of APOBEC3G and APOBEC3F has been studied more extensively than that of the other members of this family. The antiviral activity of APOBEC3B and APOBEC3DE has also been described. Studies of other APOBEC proteins have not revealed any antiviral activities against HIV-1; however, further investigation is required. In the absence of human immunodeficiency virus type 1 (HIV-1) virion infectivity factor (Vif), APOBEC3G and APOBEC3F are incorporated into HIV-1 virions and hypermutate the viral genomic DNA by their cytidine deaminase activity. HIV-1 Vif protein suppresses the antiviral role of APOBEC proteins by several mechanisms that lead to inhibition of incorporation of APOBEC3G/3F into HIV-1 virions. The detailed mechanisms involved in the suppression of APOBEC proteins by Vif are still being elucidated. Novel studies in which as yet undefined aspects of the suppression of APOBEC proteins are investigated could reveal important and potentially exploitable information for addressing HIV-1 infection in humans.     

Complementary function of the two catalytic domains of APOBEC3G

The HIV-1 viral accessory protein Vif prevents the encapsidation of the antiviral cellular cytidine deaminases APOBEC3F and APOBEC3G by inducing their proteasomal degradation. In the absence of Vif, APOBEC3G is encapsidated and blocks virus replication by deaminating cytosines of the viral cDNA. APOBEC3G encapsidation has been recently shown to depend on the viral nucleocapsid protein; however, the role of RNA remains unclear. Using APOBEC3G deletion and point mutants, we mapped the encapsidation determinant to the Zn(2+) coordination residues of the N-terminal catalytic domain (CD1). Notably, these residues were also required for RNA binding. Mutations in the two aromatic residues of CD1 but not CD2, which are conserved in cytidine deaminase core domains and are required for RNA binding, prevented encapsidation into HIV-1, HTLV-I and MLV. The Zn(2+) coordination residues of the C-terminal catalytic domain (CD2) were not required for encapsidation but were essential for cytidine deaminase activity and the antiviral effect. These findings suggest a model in which CD1 mediates encapsidation and RNA binding while CD2 mediates cytidine deaminase activity. Interestingly, HTLV-I was relatively resistant to the antiviral effects of encapsidated APOBEC3G.