Vpu-mediated CD4 down-regulation and degradation is conserved among highly divergent SIV(cpz) strains

Human immunodeficiency virus type 1 (HIV-1) along with simian immunodeficiency viruses from chimpanzees (SIV(cpz)) and three species of Old World monkeys from the genus Cercopithecus have been shown to encode a Vpu protein. To date, the functional characterization of Vpu has been limited to a small number of subtype B and more recently subtype C Vpu proteins. Using a recently developed VpuEGFP reporter system, we have shown that the subtype B and C Vpus are capable of preventing CD4 from being expressed on the cell surface. Using the same reporter system, we report here on the expression and functional analysis of Vpu protein from four SIV(cpz) isolates (CAM13, ANT, TAN1, and GAB1). All four SIV Vpu fusion proteins were efficiently expressed and prevented CD4 expression on the cell surface and induced CD4 degradation. This was surprising as three of the SIV(cpz) Vpu fusion proteins had only one canonical casein kinase II (CK-II) site (CAM13, ANT, TAN1) while previous studies with laboratory adapted HXB2 had indicated that both CK-II sites were required for CD4 degradation. Both ANT and TAN1 Vpu sequences encoded five consecutive negatively charged amino acids residues following the only CKII site (SAIEEDEE for ANT; SGVEEDEE for TAN1). We thus explored the possibility that this stretch of negatively charged amino acids might substitute for the lack of second CK-II site. Substitution of the aspartic acid at position 61 and glutamic acid at position 63 in the SIV(cpz) ANT Vpu within with lysine residues abolished the ability of this protein to down-modulate cell surface expression of CD4. Similarly, change of a serine to an alanine residue following the single consensus CK-II site of the CAM13 Vpu (SGNESDGGEEE) abolished CD4-down-regulation, suggesting that this serine was phosphorylated in the absence of a canonical CK-II site. Our results indicate that the serine was required, suggesting that this serine was phosphorylated by CK-II or possibly another cellular kinase. Taken together, these results show for the first time that Vpu proteins from SIV(cpz) isolates, although quite diverse in sequence and predicted secondary structure from the HIV-1 subtype B protein, are capable of down-regulating CD4, which is one of the major functions of the HIV-1 protein.     

A DEAD box protein facilitates HIV-1 replication as a cellular co-factor of Rev

HIV-1 Rev escorts unspliced viral mRNAs out of the nucleus of infected cells, which allows formation of infectious HIV-1 virions. We have identified a putative DEAD box (Asp-Glu-Ala-Asp) RNA helicase, DDX1, as a cellular co-factor of Rev, through yeast and mammalian two-hybrid systems using the N-terminal motif of Rev as "bait". DDX1 is not a functional homolog of HIV-1 Rev, but down-regulation of DDX1 resulted in an alternative splicing pattern of Rev-responsive element (RRE)-containing mRNA, and attenuation of Gag p24 antigen production from HLfb rev- cells rescued by exogenous Rev. Co-transfection of a DDX1 expression vector with HIV-1 significantly increased viral production. DDX1 binding to Rev, as well as to the RRE, strongly suggest that DDX1 affects Rev function through the Rev-RRE axis. Moreover, down-regulation of DDX1 altered the steady state subcellular distribution of Rev, from nuclear/nucleolar to cytoplasmic dominance. These findings indicate that DDX1 is a critical cellular co-factor for Rev function, which maintains the proper subcellular distribution of this lentiviral regulatory protein. Therefore, alterations in DDX1-Rev interactions could induce HIV-1 persistence and targeting DDX1 may lead to rationally designed and novel anti-HIV-1 strategies and therapeutics.     

Antiviral activity of a Rac GEF inhibitor characterized with a sensitive HIV/SIV fusion assay

A virus-dependent fusion assay was utilized to examine the activity of a panel of HIV-1, -2, and SIV isolates of distinct coreceptor phenotypes. This assay allowed identification of entry inhibitors, and characterization of an antagonist of a Rac guanine nucleotide exchange factor, as an inhibitor of HIV-mediated fusion.     

Functional analysis of the interaction of the human immunodeficiency virus type 1 Rev nuclear export signal with its cofactors

Human immunodeficiency virus type 1 (HIV-1) Rev-mediated nuclear export of viral RNAs involves the interaction of its leucine-rich nuclear export sequence (NES) with nuclear cofactors. In yeast two-hybrid screens of a human lymph node derived cDNA expression library, we identified the human nucleoporin Nup98 as a highly specific and potent interactor of the Rev NES. Using an extensive panel of nuclear export positive and negative mutants of the functionally homologous NESs of the HIV-1 Rev, human T cell leukemia virus type 1 (HTLV-1) Rex, and equine infectious anemia virus (EIAV) Rev proteins, physiologically significant interaction of hNup98 with the various NESs was demonstrated. Missense mutations in the yeast nuclear export factor Crm1p that abrogated Rev NES interaction with the XXFG repeat-containing nucleoporin, Rab/hRIP, had minimal effects on the interaction of GLFG repeat-containing hNup98. Functional analysis of Nup98 domains required for nuclear localization demonstrated that the entire ORF was required for efficient incorporation into the nuclear envelope. A putative nuclear localization signal was identified downstream of the GLFG repeat region. Whereas overexpression of both full-length Nup98 and the amino-terminal GLFG repeat region, but not the unique carboxy-terminal region, induced significant suppression of HIV unspliced RNA export, lower levels of exogenous Nup98 expression resulted in a relatively modest increase in unspliced RNA export. These results suggest a physiological role for hNup98 in modulating Rev-dependent RNA export during HIV infection.     

Insulin-like growth factor II mRNA binding protein 1 modulates Rev-dependent human immunodeficiency virus type 1 RNA expression

Human immunodeficiency virus type 1 (HIV-1) needs to overcome cellular counter mechanisms such as to successfully propagate itself. Results of our recent studies show that overexpression of insulin-like growth factor II mRNA binding protein 1 (IMP1) inhibits production of infectious HIV-1 particles through adversely affecting virus maturation. Here, we report that IMP1 interacts with HIV-1 Rev protein and its ectopic expression causes relocation of Rev from the nucleus to the cytoplasm. In accordance with this observation, ectopic expression of IMP1 severely diminishes Rev-dependent expression of CAT enzyme and disturbs HIV-1 RNA expression by causing accumulation of the multiple spliced viral RNA. Results of mutagenesis analysis further reveal that the KH4 domain represents the key element of IMP1 in modulating HIV-1 RNA expression. Taken together, these data suggest, in addition to hampering virus assembly, that IMP1 also has an effect on Rev-dependent viral RNA expression.     

Stable complex formation between HIV Rev and the nucleosome assembly protein, NAP1, affects Rev function

The Rev protein of HIV-1 is essential for HIV-1 proliferation due to its role in exporting viral RNA from the nucleus. We used a modified version of tandem affinity purification (TAP) tagging to identify proteins interacting with HIV-1 Rev in human cells and discovered a prominent interaction between Rev and nucleosome assembly protein 1 (Nap1). This interaction was also observed by specific retention of Nap1 from human cell lysates on a Rev affinity column. Nap1 was found to bind Rev through the Rev arginine-rich domain and altered the oligomerization state of Rev in vitro. Overexpression of Nap1 stimulated the ability of Rev to export RNA, reduced the nucleolar localization of Rev, and affected Rev nuclear import rates. The results suggest that Nap-1 may influence Rev function by increasing the availability of Rev.     

HIV-1 Gag、Tat、Rev和Nef蛋白特异性的免疫应答

目的：探讨中国HIV／AIDS患者HIV—1 Gag、Tat、Rev和Nef蛋白特异性CTL应答的特征。方法：应用覆盖HIV-1 B、C亚型Gag、Tat、Rev和Nef蛋白的220个肽段作为抗原，通过ELISPOT方法俭测HIV／AIDS患者HIV特异性CTL应答。结果：无沦HIV—1 B亚型还是HIV-1C亚型所构建肽库的应答强度和频率，主要集中在Gag和Nef蛋白，Tat和Rev蛋白也有不同程度的应答。HIV—1 B、C亚型间应答比较，整体应答强度大致相同，但免疫优势区间存在着一定的差异，B亚型Gagp24亚蛋白的288～313氨基酸区应答最强，而C亚型Gagp24亚蛋白的155～181氨基酸区应答最强；两个亚型免疫优势区应答频率最高的都是Nef蛋白106～143氨基酸区(48．1％)。结论：中国人群CTL应答多集中在Gag和Nef蛋白，B、C业型间略有差异且存在交叉识别，这对设计针对中国人群的HIV疫苗是有重要的意义。     

Differential incorporation of uracil DNA glycosylase UNG2 into HIV-1, HIV-2, and SIV(MAC) viral particles

We have previously reported that the host uracil DNA glycosylase UNG2 enzyme is incorporated into HIV-1 virions via a specific association with the viral integrase (IN) domain of Gag-Pol precursor. In this study, we investigated whether UNG2 was packaged into two phylogenetically closely related primate lentiviruses, HIV-2(ROD) and SIV(MAC239). We demonstrated by GST-pull-down and coprecipitation assays that INs from HIV-1, HIV-2(ROD), and SIV(MAC239) associated with UNG2, although the interaction of UNG2 with HIV-2(ROD) IN and SIV(MAC239) IN was less strong than with HIV-1 IN. We then showed by Western blotting that highly purified HIV-2 and SIV(MAC) viral particles did not incorporate host UNG2, contrasting with the presence of UNG2 in HIV-1 viral particles. Finally, we showed that HIV-1/SIV chimeric viruses in which residues 6 to 202 of HIV-1 IN were replaced by the SIV counterpart were impaired for packaging of UNG2, indicating that the incorporation of host UNG2 into viral particles is the hallmark of the HIV-1 strain. Moreover, we found that HIV-1/SIV IN chimeric viruses were deficient for viral propagation.     

Mapping of determinants involved in the stimulation of HIV-1 expression by Sam68

Control of HIV-1 RNA processing is central to the replication of the virus. Previously, we demonstrated that the cellular protein Sam68 enhances HIV-1 structural protein expression and RNA 3′ end processing. In this report, we show that Sam68 interacts with unspliced HIV-1 RNA and that other members of the STAR/GSG protein family also promote viral RNA 3′ end processing. We define a portion of the GSG domain (Sam 97-255) as sufficient for enhancement of Rev-dependent expression. In contrast to Sam68, Sam 97-255 increases unspliced RNA processing only in the presence of Rev in 293T cells. In a different cell line, Sam 97-255 enhances HIV-1 gene expression without enhancing RNA 3′ end processing, suggesting that stimulation of 3′ end processing is not required for enhancement of HIV-1 gene expression. Overall, these results indicate that Sam68 and the mutants described affect the composition of the viral RNP to enhance viral protein synthesis.     

中国HIV-1 CRF01_AE流行株结构基因和调节/辅助基因DNA疫苗的构建和免疫原性研究

目的 构建表达gag-env融合基因和tat-rev-integrase(c-holf)-vif-nef融合基因的DNA疫苗,并评价其免疫原性.方法 按人源密码子使用频率对AE2f株的gag、env、tat、rev、integrase、vif和nef基因序列进行优化,构建真核表达质粒.用Western blot法验证体外表达情况;用ELISPOT法检测小鼠的细胞免疫反应.结果 限制性酶切及DNA测序结果表明两个融合基因质粒构建正确,可以表达相应的融合蛋白.ELISPOT结果显示,Gag-Env特异性的T细胞反应强度为(3010±566)SFC/10~6脾细胞;Tat-Rev-Integrase(C-half)-Vif-Nef融合蛋白特异性的T细胞反应为(948±737)SFC/10~6脾细胞,均显著高于空载体组.结论 构建的表达HIV-1 CRF01_AE流行株gag-env融合基因和tat-rev-integrase(c-half)-vif-nef融合基因的DNA疫苗可以正确表达所编码的融合蛋白并有效地激活机体的T细胞免疫反应.     

Nucleocytoplasmic transport of luciferase gene mRNA requires CRM1/Exportin1 and RanGTPase

Human immunodeficiency virus type 1 Rev (regulator of the expression of the virion) protein was shown to reduce the expression level of the co-transfected luciferase reporter gene (luc+) introduced to monitor transfection efficiency. We studied the mechanism of the inhibitory Rev effect. The effect, caused by nuclear retention of luc+ mRNA, was reversed if rev had a point mutation that makes its nuclear export signal (NES) unable to associate with cellular transport factors. The Rev NES receptor CRM1 (chromosome region maintenance 1)-specific inhibitor, leptomycin B, blocked luc+ mRNA export. This finding was also supported by the overexpression of ΔCAN, another specific CRM1 inhibitor that caused inhibition of luciferase gene expression. Experiments involving tsBN2 cells, which have a temperature-sensitive RCC1 (regulator of chromosome condensation 1) allele, demonstrated that luc+ expression required generation of the GTP-bound form of RanGTPase (RanGTP) by RCC1. The constitutive transport element (CTE)-mediated nuclear export of luc+ mRNA was found to also depend upon RanGTP. Nuclear export of luc+ mRNA is thus suggested to involve CRM1 and RanGTP, which Rev employs to transport viral mRNA. The Rev effect is therefore considered to involve competition between two molecules for common transport factors.     

Functional Variability of Rev Response Element in HIV-1 Primary Isolates

We have previously studied sequence heterogeneity of HIV-1 Rev response element (RRE), and showed uneven variations in different stem–loops of both primary sequence and secondary structure. Here we studied the functional variation of RRE clones from a set of 10 primary isolates, and demonstrated a variation in the function of these RRE clones on the expression of Gag proteins from a truncated HIV-1 genome. The difference in Gag level was, in part, if not exclusively, resulted from the differential efficiency of RNA transport and enhancing of translation. These data suggested that variation of HIV-1 RRE may play a role in regulation of viral replication rate in HIV-1 primary isolates.     

Rev1 is essential in generating G to C transversions downstream of the Ung2 pathway but not the Msh2+Ung2 hybrid pathway

Somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin (Ig) genes are initiated by the enzymatic deamination of cytosine (C) to uracil (U). Uracil‐DNA‐glycosylase (Ung2) converts uracils into apyrimidinic (AP) sites, which is essential for the generation of transversions (TVs) at G/C basepairs during SHM and for efficient DNA break formation during CSR. Besides Ung2, the mismatch repair protein Msh2 and the translesion synthesis (TLS) DNA polymerase (Pol) Rev1 are implicated in SHM and CSR. To further unravel the role of Rev1, we studied WT, Rev1‐deficient, Msh2‐deficient, and Rev1, Msh2 double‐deficient B cells. Loss of Rev1 only slightly reduced CSR. During SHM G/C to C/G TVs are generated in both Ung2‐ and Ung+Msh2‐dependent fashions. We found that Rev1 is essential for the Msh2‐independent generation of these TVs downstream of Ung2‐induced AP sites. In the Ung+Msh2 hybrid pathway, Rev1 is not essential and can be substituted by an alternative TLS Pol, especially when Rev1 is lacking.     

人类免疫缺陷病毒Ⅰ型和丙型肝炎病毒核酸联合检测试剂的评价

目的 了解人类免疫缺陷病毒Ⅰ型（HIV-1）和丙型肝炎病毒（HCV）核酸联合检测试剂检测的敏感性、特异性以及检测中国不同亚型样品的适应性。方法 用酶联免疫试剂对来自于不同地区的HIV感染者或可疑感染者献血员样品进行HIV抗体和HCV抗体检测。对HIV抗体阳性者进行抗体确证。用HIV-1和HCV核酸联合检测试剂对样品进行检测，对初次检测阳性者，用HIV RNA和HCV RNA鉴别试剂单独检测，区分是HIV RNA阳性或是HCV RNA阳性。结果 74份HIV和HCV抗体均阳性的样品，HIV／HCV RNA检测也为阳性，5份HIV和HCV抗体均阴性的样品，HIV／HCV RNA检测也为阴性；84份HIV抗体确证为阳性的样品，有82份检测为HIVRNA阳性，7份HIV抗体阴性的样品检测均为HIV RNA阴性，12份HIV抗体不确定的样品，有6份检测为HIV RNA阳性；81份HCV抗体阳性样品中有70份检测为HCV RNA阳性，22份HCV抗体阴性样品中有18份检测为HCV RNA阴性，4份检测为HCV RNA阳性。结论 该试剂的灵敏度较高，尤其在HCV抗体阴性样品中检出HCV RNA阳性者。因此，可用于献血员筛查，减少窗口期的传播。     

HIV/AIDS患者CCR5、CXCR4的表达与疾病进展的关系

目的　了解HIV AIDS患者淋巴细胞表面第二受体CCR5、CXCR4的表达 ,分析其与疾病进展的关系 ,探讨HIV感染的免疫基础。方法　收集 33例HIV AIDS患者及 13例健康对照的抗凝全血 ,用流式细胞仪检测第二受体CCR5、CXCR4的表达 ,并分析第二受体表达与病毒载量、CD4 + T淋巴细胞绝对值及T淋巴细胞活化 (HLA DR+ CD38+ )的相关性。结果　艾滋病组CD4 + 、CD8+ T淋巴细胞表面CCR5表达高于无症状HIV 1感染组及健康对照 (P <0 .0 0 1) ;艾滋病组CD8+ T淋巴细胞表面CXCR4表达低于健康对照 (P <0 .0 1)。HIV AIDS患者CD4 + 、CD8+ T淋巴细胞表面CCR5的表达与病毒载量明显正相关 (P <0 .0 1) ;与CD4 + T淋巴细胞绝对值明显负相关 (P <0 .0 1) ,与T淋巴细胞活化(HLA DR+ CD38+ )水平明显正相关 (P <0 .0 0 1)。结论　HIV 1感染者第二受体CCR5的表达与机体对HIV的免疫反应及疾病进展密切相关。     

慢性HIV/AIDS患者T淋巴细胞凋亡与疾病进展关系的研究

目的 探讨慢性未经抗病毒治疗的HIV/AIDS患者T淋巴细胞及各亚群凋亡与疾病进展的相关性.方法 以36例慢性未经抗病毒治疗的HIV/AIDS患者为研究对象,根据CD4细胞计数分为3组:<200个/μl组,200～350个/μl组,>350个/μl组,同时选取16例健康志愿者作对照,分离外周血单核细胞(PBMC)后,采用CD45RO及CD27标记T细胞亚群,Annexin V标记细胞凋亡,用流式细胞仪检测各项指标.其中4例患者及4例健康志愿者的PBMC在体外培养,比较分析体外培养0、3、6、12、24 h不同时间点T细胞凋亡的变化情况.结果 (1)HIV/AIDS患者CD4~+、CD8~+T细胞及各亚群上Annexin V表达百分比均显著高于健康人(P<0.05),但3组患者之间比较差异无统计学意义(P>0.05);(2)HIV/AIDS患者CD4~+、CD8~+T细胞及各业群上Annexin V表达百分比与CD4~+T细胞计数及病毒载显均无显著相关性(P>0.05);(3)随着体外细胞培养时间的延长,HIV/AIDS患者CD4~+T细胞的凋亡及死亡细胞百分比均显著高于健康人(P<0.05),并且HIV/AIDS患者CD4~+T细胞较CD8~+T细胞更易发生凋亡和死亡.结论 HIV/AIDS患者的T细胞凋亡水平显著高于健康人,并且CD4~+T细胞较CD8~+T细胞更易发生凋亡和死亡,但是T细胞凋亡水平与HIV的疾病进展程度并没有相关性.     

以Rev依赖性凋亡增强HIV-1gp160的抗原性

目的　检测Rev(HIV的调控基因 )依赖性肿瘤坏死因子受体 (TNFR 1)和gp16 0双重表达质粒pDM12 8 TNFR 1(pT12 8)的凋亡诱导功能。方法　采用基因枪转导及流式细胞仪检测新质粒的表达功能。结果　新结构具有特异的选择性表达作用。当Rev存在时 ,能间接表达TNFR 1,明显诱导HeLa细胞凋亡 ,使绿荧光细胞百分率非常显著地低于阴性对照 (P <0 .0 1)。等质量转染时 ,TNFR 1表达量少于Hup6 0TNFR 1的pDC30 2 (pT6 0 ) ,故间接表达不及单纯pT6 0的直接表达 ,绿荧光细胞百分率显著高于pT6 0转染组 (P <0 .0 1)。培养 40h ,才有明显杀伤功能并接近单纯pT6 0 ,差异无显著性 (P>0 .0 1)。单纯pT12 8不能直接表达TNFR 1,绿荧光细胞百分率非常显著地高于单纯pT6 0转染组 (P<0 .0 1) ,接近阴性对照 ,培养 40h时差异无显著性 (P >0 .0 1)。当AD8或pMD +pRnv存在并表达Rev时 ,pT12 8均能表达TNFR 1,杀伤HeLa细胞 ,绿荧光细胞百分率非常显著地低于阴性对照 (P <0 .0 1)。pT12 8与pRev或AD8转染人正常的角质生成细胞时 ,能表达TNFR 1,诱导细胞凋亡。培养 72h后 ,阴性对照和单纯pT12 8组的绿荧光角质生成细胞数皆显著地超过pT12 8+pRev和pT12 8+pAD8组 (P <0 .0 1)。结论　pT12 8可调控的凋亡诱导保证了HIVDNA疫苗足量的抗原表     

中国HIV-1 B'/C亚型感染者对异体病毒中和作用与疾病进展关系研究

目的 探讨中国HIV-1 B'/C亚型感染者对异体病毒中和作用与疾病进展的关系.方法 根据CD4 T淋巴细胞数量和有尤临床症状将HIV-1 B'/C亚型感染者分为HIV慢性感染组和AIDS组.将HIV-1感染者血清稀释(1/10～1/320)后,与在基因结构特点上同源性很低的3株HIV-1作用,以检测其中和作用.同时以正常人血清加病毒悬液为对照孔,能够抑制对照孔50%病毒复制的血清为中和作用阳性.将某个HIV-1感染者血浆能够中和异体病毒的个数占3个异体病毒的百分率定义为HIV-1感染者中和异体病毒的宽度;将某个HIV-1感染者血浆中和3个异体病毒抗体滴度的几何平均滴度定义为HIV-1感染者中和异体病毒的强度.结果 HIV-1慢性感染组与AIDS组之间中和异体病毒的宽度和强度差异有统计学意义,HIV-1慢性感染组显著高于AIDS组.HIV-1慢性感染组中和异体病毒的宽度和强度与病毒载量呈正相关,而AIDS组巾和异体病毒的宽度和强度与病毒载量没有显著的相关性.HIV-1慢性感染组和AIDS组中和异体病毒的宽度和强度与CD4 T淋巴细胞数均没有显著的相关性.结论 中国HIV-1B'/C亚型感染者不同疾病进展阶段针对异体病毒中和作用能力不同,HIV慢性感染组显著高于AIDS组,当疾病进展到AIDS期时,失去对异体病毒的中和作用,提示针对异体病毒的中和抗体与疾病进程有关.