The New Mechanisms Of The Interaction Between HIV-1and Host Anti-viral Factors

Ongoing research on the mutual effects of HIV-1 accessory proteins and host antiviral agents is an extremely important field for HIV-1/AIDS investigation, and the clarification of the interplay between them is crucial to properly understanding the pathogenetic mechanism of HIV-1 and to developing effective therapeutic strategies for HIV-1/AIDS. APOBEC3G(A3G) is one of the most important innate immunol antiHIV-1 agents, whose activity of inhibiting virus replication could be curbed by HIV-1 Vif protein. In this study, we found that another HIV-1 accessory protein, Vpr, also possesses the functional relationship with A3 G, so extensive research has been carried out to the details of their interaction.We firstly performed a computer-based prediction based on the PRISM(protein interactions by structural matching) algorithm which suggested that Vpr could interact directly with A3 G, and this in vivo interaction was confirmed later by using the coimmunoprecipitation(Co-IP) method. Further study was focused on revealing the potential implication of the interaction between Vpr and A3 G. The results showed that Vpr could reduce the virion encapsidation of A3 G to inhibit the anti-HIV-1 activity of it and thus to enhance viral replication. Subsequent experiments showed that Vpr significantly down-regulated the expression of A3 G, which was reflected at the protein level rather than transcription, and then we proved that this down-regulation was due to the Vpr binding protein(Vpr BP)-mediated proteasomal degradation. Last, experiments with Vpr mutant were used to confirm further that the reduction of A3 G encapsidation associated with Vpr was due to Vpr’s degradation-inducing activity.Our findings highlight the versatility of Vpr by unveiling the hostile relationship between Vpr and A3 G. In addition, the observation that A3 G is targeted to the proteasomal degradation pathway through different E3 ligase complexes, namely by Vpr in addition to Vif, implicates the existence of crosstalk between different HIV-1-host ubiquitin ligase complex systems. To obtain more accurate details of hostile interaction between HIV-1 accessory proteins and cellular antiviral agents, future investigations and more concentrated efforts should be dedicated to systematic research rather than isolated investment.As another kind of important HIV-1 restriction factor, Tetherin is located in the cellular membrane system, and almost all the efforts so far have been put into the study of how Tetherin exerts its “tethering” activity to inhibit the release and transmission of HIV-1 particles. However, our previous research concentrated on the antagonism between Vpu and Tetherin present us with a repeatable experimental result, that is Tetherin might have the ability to regulate the replication of intracellular HIV-1 which has never been reported before. This phenomenon intrigued us and systematic studies have been carried out to probe the regulating mechanism of Tetherin on HIV-1 replication.First of all, we found that the ectopic expression of Tetherin could up-regulate significantly the single-cycle replication of HIV-1 pseudo-virus infection which held an interesting appearance that, when low dose of Tetherin was expressed, the up-regulating effect was remarkable, whereas the influence of high dose of Tetherin was moderate. Furthermore, the transcription of HIV-1 genome was proved to be increased by lowlevel Tetherin. The results above were subsequently extended by knocking down endogenous Tetherin with the outcomes coincident with ectopic experiments. Then luciferase reporter gene assay showed that Tetherin could activate the HIV-1 LTR, which was testified afterwards to be dependent on the NF-κB transcription factor binding site of LTR. Finally, the up-regulation of HIV-1 replication induced by Tetherin was shown convincingly to be correlated with cellular NF-κB signaling.Our results show that Tetherin could enhance the replication of HIV-1 genome by stimulating HIV-1 LTR through activating NF-κB pathway. This capacity of Tetherin might be another potential function besides restraining HIV-1 particles release. Tetherin, a kind of type I interferon-inducible protein, could be expressed endogenously at a very low level in many cell types including some major HIV-1 targets, so we hypothesize that the activity of Tetherin in up-regulating the replication of HIV-1 genome through NF-κB cascade could reactivate HIV-1 latency, by which the host immune system is capable of recognizing and implementing the process of eliminating latent HIV-1. In contrast, when HIV-1 is in productive status, Tetherin with high protein level induced by the enriched IFN-I switches its dominant role from increasing HIV-1 replication to inhibiting the release of newly budded virions. From this perspective, the ability of Tetherin in boosting HIV-1 genome replication can be viewed as another manifestation of its anti-HIV-1 activity.