Cell biology of HIV-1 Nef and Vpr

在本研究中，我们详细地阐述了HIV-1 Nef的作用机制以及HIV-1 Vpr强大的诱导细胞凋亡的能力。据报道，HIV-1 Nef通过调节病毒颗粒来增强病毒的感染性。我们发现，在没有Nef的情况下产生的HIV-1病毒粒子在病毒进入和DNA合成过程中是有缺陷的。HIV-1Nef对HIV-L有效进入细胞的要求是生产细胞依赖的，PxxP和RR结构域都是增强病毒进入所必需的，这表明Nef与细胞因子(S)的另一种相互作用参与了病毒进入过程。已有研究表明，病毒感染性、Nef与病毒粒子的融合、下调MHC-I等重要功能都与HIV-1Nef的N末端部分相对应。我们通过对Nef第20个氨基酸的点突变分析表明，Nef诱导的MHC-I下调在功能上与其病毒粒子的掺入、病毒感染性的增强和CD4的下调是分离的。有报道称VPR具有诱导细胞凋亡的作用，也有报道称VPR具有抗凋亡作用。为了确定HIV-1VPR是否是细胞凋亡的诱导剂，我们分析了感染HIV-1/VSV假型病毒的细胞。该系统不需要选择产生VPR的细胞，因此可以直接监测细胞的凋亡。结果表明，HIV-1VPR是一种强烈的细胞凋亡诱导剂，而VPR没有表现出明显的抗凋亡作用。综上所述，我们对HIV-1Nef和VPR的生物学认识取得了很大进展。更清楚的是，对HIV-1 Nef和Vpr在体内的功能还需要详细的研究。

In this study, we have demonstrated the detaild action mechanisms of HIV-1 Nef and the strong apoptosis-inducing ability of HIV-1 Vpr.HIV-1 Nef has been reported to act via modulation of viral particles to enhance virus infectivity. We showed that HIV-1 virions produced in the absence of Nef are defective for the processes of virus entry and DNA synthesis. Requirement of HIV-1 Nef for efficient entry of HIV-l into cells was producer cell-dependent The PxxP and RR domains were both dispensable for enhanced viral entry, thus suggesting that another interaction of Nef with a cellular factor(s) is involved in the process of viral entry. It has been reported that various important functions such as the viral infectivity, incorporation of Nef into virions, and down-regulation of MHC-I are mapped to the N-terminal portion of HIV-1 Nef. We showed, by the analysis of point mutants regarding 20th amino acid of the Nef, that Nef-induced MHC-I down-regulation is functionally dissociated from its virion incorporation, enhancement of viral infectivity, and CD4 down-regulation.It is controversial about the regulation of apoptosis by Vpr. Some report that Vpr induces apoptosis, and others that Vpr shows anti-apoptotic function. To determine whether HIV-1 Vpr is an inducer of apoptosis, we analyzed the cells infected with HIV-1/VSV pseudotype virus. This system does not require the selection of cells producing Vpr, and thus it is possible to directly monitor the apoptosis in cells. We showed by this system that HIV- 1 Vpr is a strong inducer of apoptosis, and that Vpr displays no detectable anti-apoptotic action.In conclusion, we have made great progress in understanding the biology of HIV-1 Nef and Vpr. It is much clearer that the detaild studies on the functions in vivo of HIV-1 Nef and Vpr is required.