Abstract
BackgroundHIV-1 viral infectivity factor (Vif) is an essential accessory protein for HIV-1 replication. The predominant function of Vif is to counteract Apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G, A3G), a potent host restriction factor that inhibits HIV-1 replication. Vif mediates the proteasomal degradation of A3G and inhibits A3G translation, thus diminishing the pool of A3G that is available to be packaged into budding virion. Although Vif is robust in degrading A3G, the protection provided against A3G is not absolute. Clinical and laboratory evidence have shown that A3G is not completely excluded from HIV-1 viral particles during HIV-1 replication. It remains unclear why the viral samples are still infectious when A3G has been packaged into the virions.ResultsIn this study, we provide evidence that Vif continues to protect HIV-1 from the deleterious effects of A3G, even after packaging of A3G has occurred. When equal amounts of A3G were packaged into budding virions, the virus expressing functional Vif was more infectious and incurred fewer G to A hypermutations in the second round of infection compared to Vif-deficient virus. A Vif mutant with a defect in viral packaging showed a reduced ability to protect the HIV-1 genome from G to A hypermutations.ConclusionOur data suggest that even packaged A3G is still under the tyranny of Vif. Our work brings to light an additional caveat for any therapy that hopes to exploit the Vif-A3G axis. The ideal strategy would not only enhance A3G viral packaging, but also reduce HIV-1 Vif viral encapsidation.
Highlights
HIV-1 viral infectivity factor (Vif) is an essential accessory protein for HIV-1 replication
Antiviral activity of A3G is less potent against wild-type virus compared to Vif-deficient virus HIV-1 Vif counteracts A3G antiviral function by mediating its degradation, which leads to the exclusion of A3G from budding viral particles
The amount of A3G in the virion from 20 μg A3G/HXB2N sample was more than 4 μg A3G/HXB2NΔVif sample (169% vs 100%). The infectivity of the former virus was much higher than the one of 4 μg A3G/HXB2NΔVif sample (Figure 1 lane 5 vs lane 7). These data suggest that wild-type HIV-1 circumvents A3G antiviral function more efficiently than Vif-deficient virus, and Vif may have an additional ability to overcome A3G even after A3G has been packaged into viral particles
Summary
HIV-1 viral infectivity factor (Vif) is an essential accessory protein for HIV-1 replication. The predominant function of Vif is to counteract Apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G, A3G), a potent host restriction factor that inhibits HIV-1 replication. Clinical and laboratory evidence have shown that A3G is not completely excluded from HIV-1 viral particles during HIV-1 replication It remains unclear why the viral samples are still infectious when A3G has been packaged into the virions. The general consensus is that Vif orchestrates proteasomal degradation of A3G, preventing its packaging into the budding virion [10,11,12,13,14,15,16]. While Vif-mediated degradation of A3G is the well-recognized mechanism by which Vif rescues HIV-1, it has been proposed that Vif prevents A3G viral packaging through inhibiting A3G translation [15,22] or another unknown mechanism [23]
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