An Aurora Kinase-Dependent Role for Vif in Regulating HIV-1-Induced Cell-Cell Fusion

Viral infectivity factor (Vif) is an HIV-1 accessory protein best known for its counteraction of APOBEC3 enzymes, interferon-inducible host defenses against viral infection, as well as PPP2R5A-E, which are regulatory subunits of the PP2A cellular phosphatase holoenzyme, resulting in striking Vif-dependent phosphoproteome remodeling. One reported consequence of this remodeling is hyperphosphorylation of several Aurora kinase substrates in HIV-1 infected cells, which is reversed when Vif-deficient virus is used. We previously showed that infection of T cells with Vif-deficient HIV-1 results in significantly accelerated formation of syncytia compared to wild-type HIV-1 infection. More recently, others have shown that application of Aurora kinase B inhibitors during HIV-1 infection in T cells also results in a similar hyperfusogenic phenotype. Both effects were specific to Env-driven cell-cell fusion, and did not influence virus infectivity. We thus hypothesized that Vifs influence on the rate of HIV-1-induced cell-cell fusion was mediated by Aurora kinase activity. To start testing this hypothesis, we have evaluated the effects of a small panel of Aurora kinase inhibitors on HIV-1-induced cell-cell fusion in the presence or absence of Vif. Our results replicate the previously documented increase in cell-cell fusion in the absence of Vif, as well as the increase in cell-cell fusion observed upon inhibition of Aurora kinase B in the presence of Vif. Critically, we now present evidence that Vif deletion significantly blunts the impact of Aurora kinase inhibition on cell-cell fusion, supporting our hypothesis that Vif-mediated regulation of cell-cell fusion depends on Aurora kinase signaling dysregulation, likely because of PPP2R5A-E degradation. Further, we document that the cell-cell fusion regulator downstream of Aurora kinase signaling is likely Ezrin, which we have previously shown to prevent excess HIV-1-induced syncytium formation when in its phosphorylated (activated) state. Taken together, these findings establish a Vif, Aurora kinase, and Ezrin-dependent mechanistic framework for the regulation of HIV-1-induced cell-cell fusion in infected T cells which likely helps preserve optimal cell-to-cell virus transmission.