ABSTRACT
APOBEC3 proteins are cytidine deaminases which help defend cells against retroviral infections. One antiviral mechanism involves deaminating dC residues in minus-strand DNA during reverse transcription, resulting in G-to-A mutations in the coding strand. We investigated the effects of mouse APOBEC3 (mA3) and human APOBEC3G (hA3G) upon Moloney murine leukemia virus (MLV). We find that mA3 inactivates MLV but is significantly less effective against MLV than is hA3G. In contrast, mA3 is as potent against human immunodeficiency virus type 1 (HIV-1, lacking the protective Vif protein) as is hA3G. The two APOBEC3 proteins are packaged to similar extents in MLV particles. Dose-response profiles imply that a single APOBEC3 molecule (or oligomer) is sufficient to inactivate an MLV particle. The inactivation of MLV by mA3 and hA3G is accompanied by relatively small reductions in the amount of viral DNA in infected cells. Although hA3G induces significant levels of G-to-A mutations in both MLV and HIV DNAs, and mA3 induces these mutations in HIV DNA, no such mutations were detected in DNA synthesized by MLV inactivated by mA3. Thus, MLV has apparently evolved to partially resist the antiviral effects of mA3 and to totally resist the ability of mA3 to induce G-to-A mutation in viral DNA. Unlike the resistance of HIV-1 and human T-cell leukemia virus type 1 to hA3G, the resistance of MLV to mA3 is not mediated by the exclusion of APOBEC from the virus particle. The nature of its resistance and the mechanism of inactivation of MLV by mA3 are completely unknown.
Subject(s)
Cytidine Deaminase/metabolism , Cytosine Deaminase/metabolism , DNA, Viral/genetics , Moloney murine leukemia virus/metabolism , Virus Inactivation , APOBEC Deaminases , Animals , Base Sequence , Cell Line , Cytidine Deaminase/genetics , Cytosine Deaminase/genetics , DNA Primers/genetics , Humans , Immunoblotting , Mice , Molecular Sequence Data , Moloney murine leukemia virus/genetics , Mutation/genetics , Sequence Analysis, DNAABSTRACT
Human T cell leukemia virus type 1 (HTLV-1) has evolved a remarkable strategy to thwart the antiviral effects of the cellular cytidine deaminase APOBEC3G (hA3G). HTLV-1 infects T lymphocytes in vivo, where, like HIV-1, it is likely to encounter hA3G. HIV-1 counteracts the innate antiviral activity of hA3G by producing an accessory protein, Vif, which hastens the degradation of hA3G. In contrast, HTLV-1 does not encode a Vif homologue; instead, HTLV-1 has evolved a cis-acting mechanism to prevent hA3G restriction. We demonstrate here that a peptide motif in the C terminus of the HTLV-1 nucleocapsid (NC) domain inhibits hA3G packaging into nascent virions. Mutation of amino acids within this region resulted in increased levels of hA3G incorporation into virions and increased susceptibility to hA3G restriction. Elements within the C-terminal extension of the NC domain are highly conserved among the primate T cell leukemia viruses, but this extension is absent in all other retroviral NC proteins.
Subject(s)
Human T-lymphotropic virus 1/drug effects , Human T-lymphotropic virus 1/physiology , Nucleocapsid/chemistry , Nucleocapsid/metabolism , Nucleoside Deaminases/pharmacology , Repressor Proteins/pharmacology , APOBEC-3G Deaminase , Amino Acid Motifs , Amino Acid Sequence , Conserved Sequence , Cytidine Deaminase , Gene Products, gag/chemistry , Gene Products, gag/metabolism , Gene Products, vif/chemistry , Gene Products, vif/metabolism , HIV-1 , HeLa Cells , Humans , Molecular Sequence Data , Mutant Proteins/metabolism , Nucleocapsid/drug effects , Peptides/chemistry , Protein Structure, Tertiary/drug effects , Virus Assembly/drug effects , Virus Replication/drug effects , vif Gene Products, Human Immunodeficiency VirusABSTRACT
A single-cycle infection assay with recombinant viral vectors was developed to study human T cell leukemia virus type I (HTLV-I) replication and its inhibition by antiviral agents. The susceptibility of HTLV-I to 6 nucleoside reverse-transcriptase inhibitors was examined. HTLV-I replication was inhibited by tenofovir, abacavir, lamivudine, zalcitabine, stavudine, and zidovudine.