Evidence for a newly discovered cellular anti-HIV-1 phenotype

Simon, Jillian N.; Gaddis, Nathan; Fouchier, Ron A. M.; Malim, Michael H.

doi:10.1038/3987

Cited by 248 publications

(184 citation statements)

References 36 publications

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“…This discovery traces back to original observations that deletion of the HIV-1 vpu gene results in a 5-10-fold 4 The abbreviation used is: SIV, simian immunodeficiency virus. decrease in virus release from infected T cells without impairing the expression of other viral proteins (33).…”

Section: Restriction By Particle Tethering: Bst-2/tetherin Integral Mmentioning

confidence: 97%

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The Restriction Factors of Human Immunodeficiency Virus

Harris

Hultquist

Evans

2012

Journal of Biological Chemistry

244

255

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Cellular proteins called "restriction factors" can serve as powerful blockades to HIV replication, but the virus possesses elaborate strategies to circumvent these barriers. First, we discuss general hallmarks of a restriction factor. Second, we review how the viral Vif protein protects the viral genome from lethal levels of cDNA deamination by promoting APOBEC3 protein degradation; how the viral Vpu, Env, and Nef proteins facilitate internalization and degradation of the virus-tethering protein BST-2/tetherin; and how the viral Vpx protein prevents the premature termination of reverse transcription by degrading the dNTPase SAMHD1. These HIV restriction and counter-restriction mechanisms suggest strategies for new therapeutic interventions. Restriction Factor HallmarksRestriction factors have at least four defining characteristics (see Fig. 1A). First and foremost, a restriction factor must directly and dominantly cause a significant decrease in HIV infectivity. This is often determined by cotransfecting cell lines such as HEK293 and HeLa with a molecular clone of the virus, with or without a plasmid expressing the restriction factor, and measuring the amount and infectivity of virus recovered in the cell culture medium after 1-2 days of incubation. Such assays are ideally done over a range of restriction factor expression, with the highest levels often imposing log-scale drops in viral infectivity (see Fig. 1B). This "single-cycle" assay for viral replication is useful for testing the impact of viral mutations and/or restriction factor variations.Second, if a restriction factor is a true threat to viral replication, then the predecessors of HIV invariably evolved an equally potent counter-restriction mechanism that still exists in the present day virus. For instance, titrating a counter-restriction factor into the aforementioned single-cycle infectivity experiment can result in a full recovery of viral infectivity despite the presence of an active restriction factor (Fig. 1B). Viruses lacking these various countermeasures are able to replicate in some, but not all, cell types depending on the expression level of the relevant restriction factor. Cell lines that support replication are termed "permissive," and those that do not are termed "nonpermissive." This life/death dichotomy has been elegantly exploited to identify several restriction factors and their corresponding viral antagonists.Third, because the interactions between restriction and counter-restriction factors occur through direct protein-protein interactions, the restriction factor often shows signatures of rapid evolution. In general, mutations are maintained in a population only if they confer a selective advantage. If a host species experiences iterative rounds of pathogenic pressure, altered variants of host restriction factors that are no longer susceptible to the pathogen's counteraction mechanism are selected. Over evolutionary time, this results in an overabundance of amino acid substitution mutations in these genes relative to non-amino acid...

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Section: Restriction By Particle Tethering: Bst-2/tetherin Integral Mmentioning

confidence: 97%

“…23). An excellent recent example is provided by studies on nat- ural simian immunodeficiency virus (SIV) 4 infection of four African green monkey (SIV agm ) subspecies (24). As expected, the Vif protein of each SIV agm strain degrades the APOBEC3G protein of its respective host.…”

Section: Restriction By Hypermutation: Apobec3 Dna Deaminasesmentioning

confidence: 99%

The Restriction Factors of Human Immunodeficiency Virus

Harris

Hultquist

Evans

2012

Journal of Biological Chemistry

244

255

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“…It was shown that the propagation of HIV-1 strains lacking the accessory protein Vif is suppressed in a number of nonpermissive cells and that this block was due to expression of the cytidine deaminase APOBEC3G (A3G). 7,8 Further studies revealed that A3G induces massive C3 U deamination of single stranded retroviral DNA, resulting in DNA degradation or lethal G3 A hypermutation. [9][10][11] Interestingly, A3G can also interfere with the HBV life cycle in cotransfected cells.…”

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confidence: 99%

APOBEC-mediated interference with hepadnavirus production

et al. 2005

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APOBEC3G is a cellular cytidine deaminase displaying broad antiretroviral activity. Recently, it was shown that APOBEC3G can also suppress hepatitis B virus (HBV) production in human hepatoma cells. In the present study, we characterized the mechanisms of APO-BEC-mediated antiviral activity against HBV and related hepadnaviruses. We show that human APOBEC3G blocks HBV production in mammalian and nonmammalian cells and is active against duck HBV as well. Early steps of viral morphogenesis, including RNA and protein synthesis, binding of pregenomic RNA to core protein, and self-assembly of viral core protein, were unaffected. However, APOBEC3G rendered HBV core protein-associated full-length pregenomic RNA nuclease-sensitive. Ongoing reverse-transcription in capsids that had escaped the block in morphogenesis was not significantly inhibited. The antiviral effect was not modulated by abrogating or enhancing expression of the accessory HBV X protein, suggesting that HBV X protein does not represent a functional homologue to the HIV vif protein. Furthermore, human APOBEC3F but not rat APOBEC1 inhibited HBV DNA production. Viral RNA and low-level DNA produced in the presence of APOBEC3F or rat APOBEC1 occasionally displayed mutations, but the majority of clones were wild-type. In conclusion, APOBEC3G and APOBEC3F but not rat APOBEC1 can downregulate the production of replication-competent hepadnaviral nucleocapsids. In contrast to HIV and other retroviruses, however, APOBEC3G/3F-mediated editing of nucleic acids does not seem to represent an effective innate defense mechanism for hepadnaviruses. H epadnaviruses are a group of small enveloped DNA viruses with a narrow host range and a relative tropism for the liver. Hepatitis B virus (HBV), the prototypic member of the hepadnavirus family, is a major cause of liver disease worldwide, ranging from acute and chronic hepatitis to cirrhosis and hepatocellular carcinoma. 1,2 Other members of the family include the duck hepatitis B virus (DHBV) and the woodchuck hepatitis virus. 3,4 Hepadnaviral replication involves reverse-transcription of a pregenomic RNA (pgRNA) intermediate inside nucleocapsids, which are formed by 180 or 240 core protein subunits. Inside the capsid, the viral polymerase converts pgRNA into minus-strand DNA, which in turn is completed to a double-stranded, relaxed circular DNA molecule. 5,6 This life cycle places HBV into the large family of retroelements, which all require reverse-transcription of an RNA intermediate.Recently, a cellular defense mechanism targeting a wide range of retroviruses was identified. It was shown that the propagation of HIV-1 strains lacking the accessory protein Vif is suppressed in a number of nonpermissive cells and that this block was due to expression of the cytidine deaminase APOBEC3G (A3G). 7,8 Further studies revealed that A3G induces massive C3 U deamination of single stranded retroviral DNA, resulting in DNA degradation or lethal G3 A hypermutation. [9][10][11] Interestingly, A3G can also interfere with the HBV life c...

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“…Several reports (9,10,12,(14)(15)(16)(17)(18)(19) have shown that mutations in the recently defined HCCH motif impair Vif function. In one report (19), Vif C114 (amino acid numbering used hereafter refers to the HIV-1 HXB2 Vif sequence) was proposed to constitute part of a cysteine protease active site involved in gp41 processing.…”

mentioning

confidence: 99%

Zinc binding to the HCCH motif of HIV-1 virion infectivity factor induces a conformational change that mediates protein–protein interactions

Paul

Cui

Maynard

2006

Proc. Natl. Acad. Sci. U.S.A.

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Virion infectivity factor (Vif) is an accessory protein encoded by HIV-1 and is critical for viral infection of the host CD4 ؉ T cell population. Vif induces ubiquitination and subsequent degradation of Apo3G, a cytosolic cytidine deaminase that otherwise targets the retroviral genome. Interaction of Vif with the cellular Cullin5-based E3 ubiquitin ligase requires a conserved BC box and upstream residues that are part of the conserved H-(Xaa)5-C-(Xaa)17-18-C-(Xaa)3-5-H (HCCH) motif. The HCCH motif is involved in stabilizing the Vif-Cullin 5 interaction, but the exact role of the conserved His and Cys residues remains elusive. In this report, we find that full-length HIV-1 Vif, as well as a HCCH peptide, is capable of binding to zinc with high specificity. Zinc binding induces a conformational change that leads to the formation of large protein aggregates. EDTA reversed aggregation and regenerated the apoprotein conformation. Cysteine modification studies with the HCCH peptide suggest that C114 is critical for stabilizing the fold of the apopeptide, and that C133 is located in a solvent-exposed region with no definite secondary structure. Selective alkylation of C133 reduced metal-binding specificity of the HCCH peptide, allowing cobalt to bind with rates comparable to that with zinc. This study demonstrates that the HCCH motif of HIV-1 Vif is a unique metal-binding domain capable of mediating protein-protein interactions in the presence of zinc and adds to a growing list of examples in which metal ion binding induces protein misfolding and/or aggregation.aggregation ͉ cullin ubiquitin ligase ͉ metal-binding protein

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Evidence for a newly discovered cellular anti-HIV-1 phenotype

Cited by 248 publications

References 36 publications

The Restriction Factors of Human Immunodeficiency Virus

The Restriction Factors of Human Immunodeficiency Virus

APOBEC-mediated interference with hepadnavirus production

Zinc binding to the HCCH motif of HIV-1 virion infectivity factor induces a conformational change that mediates protein–protein interactions

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