The Studies On The Mechanisms That Host Restriction Factor APOBEC3F Inhibit HIV-1

The causeof AIDS was identified as a retrovirus and wassubsequently named the human immunodeficiency virustype 1 (HIV-1). In the global response to HIV to date, development andimplementation of effective antiretroviral therapy (ART)have been the premier accomplishments.Despite the advances inHIV treatment, there continues to be considerable variation inHIV disease progression. Studies of thisgroup of viruses have progressed from basic characterizationto an intricate and deep understanding of howthey interact with their hosts.Cellular proteins (host factors) called "restriction factors" can serve as powerfulblockades to HIV replication, but the virus possesses elaboratestrategies to circumvent these barriers.These HIV restriction and counter-restriction mechanisms suggest strategies for new thera peuticinter-ventions.APOBEC3 proteins are a family of cytidine deaminase that exhibits antiretroviral activity against HIV-1 by different mechanisms. Among these proteins, APOBEC3G and APOBEC3F have the most potent anti-HIV-1 activities.The packaging of APOBEC3F into viral particles requires a mechanism that confers this promiscuity.In this report, we present data that the incorporation of APOBEC3F into HIV-1 requires sequencesbetween the two zinc coordination motifs of APOBEC3F (amino acids 104-156). By the same time, delection mumtant analysis of Gag reveal that nucleocapsid sequence in Gag is necessary for the interaction of APOBEC3F with Gag.As a main restriction factors to HIV-1, APOBEC3F displays similar phenotypes to those of APOBEC3G in reducing the accumulation of HIV-1 reverse transcription products and preventing provira DNA formation, but there are obvious distinctions of mechanism between the two proteins.Mutagenesis studies of Gag NC reveal that the basic amino acid residues between the two zinc coordination motifs and in N-terminal are important determinants for the incorporation of both APOBEC3F and APOBEC3G.The competition of APOBEC3F and APOBEC3G in incorporation shows that the mechanism of interaction between APOBEC3F/G and NC for incorporation is similar.Although the antiviral of APOBEC3 family is clearly linked to their deamiases mechanism activity, increasing evidence suggest that APOBEC3s also exert antiviral activity by other mechanisms. Because the actions of APOBEC3Fare to inhibit HIV-1 reverse transcription,a characterization of the mechanisms by which APOBEC3Ftargets RT and inhibits its function is of considerable interest, as itmay provide a novel insight into the mechanisms underlying theantiviral effect of APOBEC3F.In the present study, by using a cell-based coimmunoprecipitation (Co-IP) assay, we detected the direct interaction betweenAPOBEC3F and HIV-1 reverse transcriptase (RT) in produced viruses.Additionally, a deletion analysis showed that the RT-binding region in APOBEC3F was located between amino acids 104 and 156. Overexpression of the RT-binding polypeptidewas able to inhibit HIV-1 replication.The Thumb domain of RT is also required for its interaction with APOBEC3F.Because virion packaging is required for APOBEC3F antiviral activity, a critical action of Vif is toexclude APOBEC3F from virions in order to protect viral replication.This is achieved bydegradation-dependent and/or independent mechanism in the viral producer cells.Here, we identify a critical determinant of APOBEC3F susceptibility to HIV-1 Vif by comparing APOBEC3F with the closely related APOBEC3C. Using chimeras between these orthologs as well as single-domain studies, weconfirm that Vif recognizes the CTD ofAPOBEC3F. Through structural system in construction of C-terminal APOBEC3F residueswith Vif residues, we identifythe critical amino acid residuedeterminant of this interaction.By mutagenesis and Co-IP analysis, the effect of the amino acid residues for the interaction between APOBEC3F and Vif were confirmed.