Requirement of Caprine Arthritis Encephalitis VirusvifGene forin VivoReplication

Replication of human immunodeficiency virus type 1 (HIV-1) in primary blood lymphocytes, certain T-cell lines (nonpermissive cells), and most likely in vivo is highly dependent on the virally encoded Vif protein.Evidence suggests that Vif acts late in the viral life cycle during assembly, budding, and/or maturation to counteract the antiviral activity of the CEM15 protein and possibly other antiviral factors. Because HIV-1 virions produced in the absence of Vif are severely restricted at a postentry, preintegration step of infection, it is presumed that such virions differ from wild-type virions in some way. In the present study, we established a protocol for producing large quantities of vif-deficient HIV-1 (HIV-1/⌬vif) from an acute infection of nonpermissive T cells and performed a thorough examination of the defect in these virions. Aside from the expected lack of Vif, we observed no apparent abnormalities in the packaging, modification, processing, or function of proteins in ⌬vif virions. In addition, we found no consistent defect in the ability of ⌬vif virions to perform intravirion reverse transcription under a variety of assay conditions, suggesting that the reverse transcription complexes in these particles can behave normally under cell-free conditions. Consistent with this finding, neither the placement of the primer tRNA 3 Lys nor its ability to promote reverse transcription in an in vitro assay was affected by a lack of Vif. Based on the inability of this comprehensive analysis to uncover molecular defects in ⌬vif virions, we speculate that such defects are likely to be subtle and/or rare.

mentioning

confidence: 96%

Comprehensive Investigation of the Molecular Defect in vif -Deficient Human Immunodeficiency Virus Type 1 Virions

Gaddis

Chertova

Sheehy

et al. 2003

“…The Vif protein, which modulates viral infectivity (8,11,13,15,19,27,32,40,45,53,56,57,(60)(61)(62) and pathogenicity (7,19,20,24,25,35), is present in nearly all lentiviruses, including human immunodeficiency virus type 1 (HIV-1). It is believed to act during the late stages of virus assembly by enabling the establishment of integrated provirus in new target cells.…”

mentioning

confidence: 99%

“…For example, Jurkat, CEM-SS, and SupT1 cells do not require Vif for HIV-1 replication (permissive cells); for H9 cells, CEM cells, and primary blood-derived monocytes, however, Vif is essential (nonpermissive cells). In the case of nonhuman lentiviruses, primary blood-derived monocytes derived from the appropriate animals fail to support the replication of Vif mutant viruses (10,19,45,61). Cell fusion experiments with permissive and nonpermissive cells have indicated that the nonpermissive phenotype is dominant (36,52), leading to the concept that there exist specific cellular factors that act as inhibitors of lentiviral replication and which Vif must overcome (36,52).…”

mentioning

confidence: 99%

Influence of Primate Lentiviral Vif and Proteasome Inhibitors on Human Immunodeficiency Virus Type 1 Virion Packaging of APOBEC3G

Liu

Luo

et al. 2004

131

122

The Vif protein of human immunodeficiency virus type 1 (HIV-1) is essential for viral evasion of the host antiviral protein APOBEC3G, also known as CEM15. Vif mutant but not wild-type HIV-1 viruses produced in the presence of APOBEC3G have been shown to undergo hypermutations in newly synthesized viral DNA upon infection of target cells, presumably resulting from C-to-U modification during minus-strand viral DNA synthesis. We now report that HIV-1 Vif could induce rapid degradation of human APOBEC3G that was blocked by the proteasome inhibitor MG132. The efficiency of Vif-induced downregulation of APOBEC3G expression depended on the level of Vif expression. A single amino acid substitution in the conserved SLQXLA motif reduced Vif function. Vif proteins from distantly related primate lentiviruses such as SIVagm were unable to suppress the antiviral activity of human APOBEC3G or the packaging of APOBEC3G into HIV-1 Vif mutant virions, due to a lack of interaction with human APOBEC3G. In the presence of the proteasome inhibitor MG132, virion-associated Vif increased dramatically. However, increased virion packaging of Vif did not prevent virion packaging of APOBEC3G when proteasome function was impaired, and the infectivity of these virions was significantly reduced. These results suggest that Vif function is required during virus assembly to remove APOBEC3G from packaging into released virions. Once packaged, virion-associated Vif could not efficiently block the antiviral activity of APOBEC3G.

“…For example, Jurkat and SupT1 cells do not require Vif for HIV-1 replication; for H9 cells and primary blood-derived monocytes (PBMCs), however, Vif is essential. In the case of nonhuman lentiviruses, PBMCs derived from the appropriate animals fail to support the replication of vif mutant viruses (14,33,42). This finding has led to the concept that specific cellular factors exist which act as inhibitors of lentiviral replication and which Vif must overcome (26,37).…”

mentioning

confidence: 99%

Association of Human Immunodeficiency Virus Type 1 Vif with RNA and Its Role in Reverse Transcription

Dettenhofer

Cen

Carlson

et al. 2000

100

108

The vif gene of human immunodeficiency virus type 1 (HIV-1) is essential for viral replication, although the functional target of Vif remains elusive. HIV-1 vif mutant virions derived from nonpermissive H9 cells displayed no significant differences in the amount, ratio, or integrity of their protein composition relative to an isogenic wild-type virion. The amounts of the virion-associated viral genomic RNA and tRNA 3Lys were additionally present at normal levels in vif mutant virions. We demonstrate that Vif associates with RNA in vitro as well as with viral genomic RNA in virus-infected cells. A functionally conserved lentivirus Vif motif was found in the double-stranded RNA binding domain of Xenopus laevis, Xlrbpa. The natural intravirion reverse transcriptase products were markedly reduced in vif mutant virions. Moreover, purified vif mutant genomic RNA-primer tRNA complexes displayed severe defects in the initiation of reverse transcription with recombinant reverse transcriptase. These data point to a novel role for Vif in the regulation of efficient reverse transcription through modulation of the virion nucleic acid components.