HIV-1 Vif protein is stabilized by AKT-mediated phosphorylation to enhance APOBEC3G degradation

Abstract

HIV-1 virus has to counter anti-viral restriction factors for its successful replication after its entry in the cell. The host-pathogen dynamics operate as soon as HIV-1 interacts with the cell. HIV-1 Vif has been known for its role in degradation of APOBEC3G; a cytosine deaminase which leads to hyper mutations in the viral DNA leading to aberrant viral replication. The cellular proteins regulating the intracellular HIV-1 Vif protein levels can have profound impact on HIV-1 pathogenesis. MDM2 is known to induce degradation of Vif with subsequent effects on APOBEC3G. Here, we have identified AKT/PKB as one of the crucial regulators of HIV-1 Vif protein. The rationale for selecting Vif as a target substrate for AKT was the presence of RMRINT motif in it, which is similar to the AKT phosphorylation motif RxRxxS/T. Immunoprecipitation assay and Kinase assay revealed that AKT and Vif interact strongly with each other and Vif is phosphorylated at T20 position by AKT. This phosphorylation stabilizes HIV-1 Vif while Vif mutant T20A degrades faster. Moreover, use of dominant negative form of AKT (KD-AKT) and AKT inhibitors were found to destabilise Vif and increase its K48-ubiquitination profile. The consequences of this AKT-Vif interplay were also validated on APOBEC3G degradation, a target of Vif. AKT inhibition was found to restore APOBEC3G levels. This process can be interpreted as a strategy used by virus to prevent MDM2 mediated Vif degradation; AKT stabilises Mdm2, which then targets Vif for degradation but at the same time AKT stabilises Vif by phosphorylating it. Thus, AKT mediated stabilization of Vif might compensate for its degradation by MDM2. This study can have significant implications as HIV-1 Tat protein and growth factors like insulin activate PI3-K/AKT Kinase pathway and can potentially affect Vif and APOBEC3G protein levels and hence HIV-1 pathogenesis.