The Cellular Antiviral Protein APOBEC3G Interacts with HIV-1 Reverse Transcriptase and Inhibits Its Function during Viral Replication

Abstract

cThe cytidine deaminase APOBEC3G (A3G) exerts a multifaceted antiviral effect against HIV-1 infection. First, A3G was shown to be able to terminate HIV infection by deaminating the cytosine residues to uracil in the minus strand of the viral DNA during reverse transcription. Also, a number of studies have indicated that A3G inhibits HIV-1 reverse transcription by a non-editingmediated mechanism. However, the mechanism by which A3G directly disrupts HIV-1 reverse transcription is not fully understood. In the present study, by using a cell-based coimmunoprecipitation (Co-IP) assay, we detected the direct interaction between A3G and HIV-1 reverse transcriptase (RT) in produced viruses and in the cotransfected cells. The data also suggested that their interaction did not require viral genomic RNA bridging or other viral proteins. Additionally, a deletion analysis showed that the RT-binding region in A3G was located between amino acids 65 and 132. Overexpression of the RT-binding polypeptide A3G 65-132 was able to disrupt the interaction between wild-type A3G and RT, which consequently attenuated the anti-HIV effect of A3G on reverse transcription. Overall, this paper provides evidence for the physical and functional interaction between A3G and HIV-1 RT and demonstrates that this interaction plays an important role in the action of A3G against HIV-1 reverse transcription. Several host proteins have been identified as intrinsic restriction factors because of their ability to inhibit HIV replication and/or dissemination (2, 31, 41, 52). Among them, the apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G; here referred to as A3G) is the one that restricts HIV-1 replication through more than one mechanism (17,32,37,38,40). In the absence of the HIV-1 viral infectivity factor (Vif), A3G is incorporated into progeny viruses through its interaction with the nucleocapsid (NC) domain of the Gag protein and/or viral RNA (1,15,56,63). Once these progeny viruses initiate new infection, the incorporated A3G will deaminate the cytidine to uridine in the viral minus-strand DNA during reverse transcription, resulting in hypermutation in the provirus. As a result, the HIV-1 proviral DNA will be no longer functional or degrade rapidly (21,32,38,64). Additionally, the mutated proviral DNA may produce defective or truncated viral polypeptides that represent a significant source of major histocompatibility complex class I (MHC-I)-restricted epitopes to activate HIV-1-specific CD8 ϩ cytotoxic T lymphocytes (CTLs) (12).Reverse transcription catalyzed by HIV-1 reverse transcriptase (RT) is a critical step for HIV-1 to establish its replication cycle. In infected cells, RT employs tRNA 3Lys and the polypurine tract as primers and converts the viral genomic RNA into doublestranded viral DNA (23). This process is catalyzed by both the DNA polymerase and RNase H activities of RT (23,49). Interestingly, in addition to the deaminase activity, A3G has also been shown to directly inhibit HIV-1 reverse transcription by a non...

Suppression of HIV-1 Infection by APOBEC3 Proteins in Primary Human CD4 + T Cells Is Associated with Inhibition of Processive Reverse Transcription as Well as Excessive Cytidine Deamination

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Murine leukemia virus glycosylated Gag blocks apolipoprotein B editing complex 3 and cytosolic sensor access to the reverse transcription complex

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