Stably Expressed APOBEC3F Has Negligible Antiviral Activity

Abstract

APOBEC3F (A3F) is a member of the family of cytidine deaminases that is often coexpressed with APOBEC3G (A3G) in cells susceptible to HIV infection. A3F has been shown to have strong antiviral activity in transient-expression studies, and together with A3G, it is considered the most potent cytidine deaminase targeting HIV. Previous analyses suggested that the antiviral properties of A3F can be dissociated from its catalytic deaminase activity. We were able to confirm the deaminase-independent antiviral activity of exogenously expressed A3F; however, we also noted that exogenous expression was associated with very high A3F mRNA and protein levels. In analogy to our previous study of A3G, we produced stable HeLa cell lines constitutively expressing wild-type or deaminase-defective A3F at levels that were more in line with the levels of endogenous A3F in H9 cells. A3F expressed in stable HeLa cells was packaged into Vif-deficient viral particles with an efficiency similar to that of A3G and was properly targeted to the viral nucleoprotein complex. Surprisingly, however, neither wild-type nor deaminase-defective A3F inhibited HIV-1 infectivity. These results imply that the antiviral activity of endogenous A3F is negligible compared to that of A3G.

HIV-1 and HIV-2 Vif Interact with Human APOBEC3 Proteins Using Completely Different Determinants

“…The viruses produced in the presence of either the VPGϾ3A or the WAWϾ3A mutant did not have severely reduced infectivity, strongly suggesting that the levels of A3F and A3H in CEM2n cells are too low to significantly inhibit HIV-1 in a single cycle of replication. These data agree with previously published results from us and other investigators indicating that A3G expression is sufficient to substantially inhibit HIV-1 replication in T cell lines, while A3F does not exert a strong antiviral effect in early infections (41,54) but can inhibit an A3G-specific Vif mutant in multiple cycles of replication (41). However, results from another study suggest that A3F levels in CEM2n cells are sufficient to inhibit HIV-1 replication (53).…”

Biochemical Analysis of Hypermutation by the Deoxycytidine Deaminase APOBEC3A

“…This has implications for other Apo3 family members that prefer to deaminate 5Ј-TC motifs. Apo3F has been shown to have negligible ability to restrict HIV when stably expressed (68) and supports the notion that the mutations induced by deamination of 5Ј-TC motifs could be ineffective.…”

Anti-APOBEC3G Activity of HIV-1 Vif Protein Is Attenuated in Elite Controllers

“…At the least, we found that Vifinduced intracellular degradation of APOBEC3G could be one of the possible mechanisms of attenuated Vif function in EC. Although we did not evaluate Vif's interactions with other APOB EC3G proteins, the intrinsic potencies of other APOBEC3 proteins (such as APOBEC3DE/3F/3H) appear to be lower than those of APOBEC3G (46,(72)(73)(74)(75). Moreover, we did not observe interpatient differences in Vif-mediated infectivity in control experiments where the APOBEC3G expression plasmid was not delivered into 293 T cells (data not shown).…”