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Host and viral determinants of Mx2 antiretroviral activity.

ABSTRACT: Myxovirus resistance 2 (Mx2/MxB) has recently been uncovered as an effector of the anti-HIV-1 activity of type I interferons (IFNs) that inhibits HIV-1 at an early stage postinfection, after reverse transcription but prior to proviral integration into host DNA. The mechanistic details of Mx2 antiviral activity are not yet understood, but a few substitutions in the HIV-1 capsid have been shown to confer resistance to Mx2. Through a combination of in vitro evolution and unbiased mutagenesis, we further map the determinants of sensitivity to Mx2 and reveal that multiple capsid (CA) surfaces define sensitivity to Mx2. Intriguingly, we reveal an unanticipated sensitivity determinant within the C-terminal domain of capsid. We also report that Mx2s derived from multiple primate species share the capacity to potently inhibit HIV-1, whereas selected nonprimate orthologs have no such activity. Like TRIM5?, another CA targeting antiretroviral protein, primate Mx2s exhibit species-dependent variation in antiviral specificity against at least one extant virus and multiple HIV-1 capsid mutants. Using a combination of chimeric Mx2 proteins and evolution-guided approaches, we reveal that a single residue close to the N terminus that has evolved under positive selection can determine antiviral specificity. Thus, the variable N-terminal region can define the spectrum of viruses inhibited by Mx2. Importance: Type I interferons (IFNs) inhibit the replication of most mammalian viruses. IFN stimulation upregulates hundreds of different IFN-stimulated genes (ISGs), but it is often unclear which ISGs are responsible for inhibition of a given virus. Recently, Mx2 was identified as an ISG that contributes to the inhibition of HIV-1 replication by type I IFN. Thus, Mx2 might inhibit HIV-1 replication in patients, and this inhibitory action might have therapeutic potential. The mechanistic details of how Mx2 inhibits HIV-1 are currently unclear, but the HIV-1 capsid protein is the likely viral target. Here, we determine the regions of capsid that specify sensitivity to Mx2. We demonstrate that Mx2 from multiple primates can inhibit HIV-1, whereas Mx2 from other mammals (dogs and sheep) cannot. We also show that primate variants of Mx2 differ in the spectrum of lentiviruses they inhibit and that a single residue in Mx2 can determine this antiviral specificity.

SUBMITTER: Busnadiego I

PROVIDER: S-EPMC4097781 | biostudies-literature | 2014 Jul

REPOSITORIES: biostudies-literature

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Host and viral determinants of Mx2 antiretroviral activity.

Busnadiego Idoia I Kane Melissa M Rihn Suzannah J SJ Preugschas Hannah F HF Hughes Joseph J Blanco-Melo Daniel D Strouvelle Victoria P VP Zang Trinity M TM Willett Brian J BJ Boutell Chris C Bieniasz Paul D PD Wilson Sam J SJ

Journal of virology 20140423 14

Myxovirus resistance 2 (Mx2/MxB) has recently been uncovered as an effector of the anti-HIV-1 activity of type I interferons (IFNs) that inhibits HIV-1 at an early stage postinfection, after reverse transcription but prior to proviral integration into host DNA. The mechanistic details of Mx2 antiviral activity are not yet understood, but a few substitutions in the HIV-1 capsid have been shown to confer resistance to Mx2. Through a combination of in vitro evolution and unbiased mutagenesis, we fu ...[more]

PMID: 24760893

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Project description:BackgroundInterferon-induced cellular proteins play important roles in the host response against viral infection. The Mx family of dynamin-like GTPases, which include MxA and MxB, target a wide variety of viruses. Despite considerable evidence demonstrating the breadth of antiviral activity of MxA, human MxB was only recently discovered to specifically inhibit lentiviruses. Here we assess both host and viral determinants that underlie MxB restriction of HIV-1 infection.ResultsHeterologous expression of MxB in human osteosarcoma cells potently inhibited HIV-1 infection (~12-fold), yet had little to no effect on divergent retroviruses. The anti-HIV effect manifested as a partial block in the formation of 2-long terminal repeat circle DNA and hence nuclear import, and we accordingly found evidence for an additional post-nuclear entry block. A large number of previously characterized capsid mutations, as well as mutations that abrogated integrase activity, counteracted MxB restriction. MxB expression suppressed integration into gene-enriched regions of chromosomes, similar to affects observed previously when cells were depleted for nuclear transport factors such as transportin 3. MxB activity did not require predicted GTPase active site residues or a series of unstructured loops within the stalk domain that confer functional oligomerization to related dynamin family proteins. In contrast, we observed an N-terminal stretch of residues in MxB to harbor key determinants. Protein localization conferred by a nuclear localization signal (NLS) within the N-terminal 25 residues, which was critical, was fully rescuable by a heterologous NLS. Consistent with this observation, a heterologous nuclear export sequence (NES) abolished full-length MxB activity. We additionally mapped sub-regions within amino acids 26-90 that contribute to MxB activity, finding sequences present within residues 27-50 particularly important.ConclusionsMxB inhibits HIV-1 by interfering with minimally two steps of infection, nuclear entry and post-nuclear trafficking and/or integration, without destabilizing the inherent catalytic activity of viral preintegration complexes. Putative MxB GTPase active site residues and stalk domain Loop 4 -- both previously shown to be necessary for MxA function -- were dispensable for MxB antiviral activity. Instead, we highlight subcellular localization and a yet-determined function(s) present in the unique MxB N-terminal region to be required for HIV-1 restriction.

Project description:BackgroundThe authors examined associations between structural characteristics and HIV disease management among a geographically diverse sample of behaviorally and perinatally HIV-infected adolescents and young adults in the United States.MethodsThe sample included 1891 adolescents and young adults living with HIV (27.8% perinatally infected; 72.2% behaviorally infected) who were linked to care through 20 Adolescent Medicine Trials Network for HIV/AIDS Interventions Units. All completed audio computer-assisted self-interview surveys. Chart abstraction or blood draw provided viral load data. Geographic-level variables were extracted from the United States Census Bureau (e.g., socioeconomic disadvantage, percent of Black and Latino households, percent rural) and Esri Crime (e.g., global crime index) databases as Zip Code Tabulation Areas. AIDSVu data (e.g., prevalence of HIV among youth) were extracted at the county-level. Using HLM v.7, the authors conducted means-as-outcomes random effects multi-level models to examine the association between structural-level and individual-level factors and (1) being on antiretroviral therapy (ART) currently; (2) being on ART for at least 6 months; (3) missed HIV care appointments (not having missed any vs. having missed one or more appointments) over the past 12 months; and (4) viral suppression (defined by the corresponding assay cutoff for the lower limit of viral load at each participating site which denoted nondetectability vs. detectability).ResultsFrequencies for the 4 primary outcomes were as follows: current ART use (n = 1120, 59.23%); ART use for ≥6 months (n = 861, 45.53%); at least one missed HIV care appointment (n = 936, 49.50); and viral suppression (n = 577, 30.51%). After adjusting for individual-level factors, youth living in more disadvantaged areas (defined by a composite score derived from 2010 Census indicators including percent poverty, percent receiving public assistance, percent of female, single-headed households, percent unemployment, and percent of people with less than a high school degree) were less likely to report current ART use (OR: 0.85, 95% CI: 0.72-1.00, p = .05). Among current ART users, living in more disadvantaged areas was associated with greater likelihood of having used ART for ≥6 months. Participants living in counties with greater HIV prevalence among 13-24 year olds were more likely to report current ART use (OR: 1.32, 95% CI: 1.05-1.65, p = .02), ≥6 months ART use (OR: 1.32, 95% CI: 1.05-1.65, p = .02), and to be virally suppressed (OR: 1.50, 95% CI: 1.20-1.87, p = .001); however, youth in these areas were also more likely to report missed medical appointments (OR: 1.32, 95% CI: 1.07-1.63, p = .008).ConclusionsThe findings underscore the multi-level and structural factors associated with ART use, missed HIV care appointments, and viral suppression for adolescents and young adults in the United States. Consideration of these factors is strongly recommended in future intervention, clinical practice, and policy research that seek to understand the contextual influences on individuals' health behaviors.

Project description:BackgroundRefugees and host nationals who accessed antiretroviral therapy (ART) in a remote refugee camp in Kakuma, Kenya (2011-2013) were compared on outcome measures that included viral suppression and adherence to ART.MethodsThis study used a repeated cross-sectional design (Round One and Round Two). All adults (?18 years) receiving care from the refugee camp clinic and taking antiretroviral therapy (ART) for ?30 days were invited to participate. Adherence was measured by self-report and monthly pharmacy refills. Whole blood was measured on dried blood spots. HIV-1 RNA was quantified and treatment failures were submitted for drug resistance testing. A remedial intervention was implemented in response to baseline testing. The primary outcome was viral load <5000 copies/mL. The two study rounds took place in 2011-2013.ResultsAmong eligible adults, 86% (73/85) of refugees and 84% (86/102) of Kenyan host nationals participated in the Round One survey; 60% (44/73) and 58% (50/86) of Round One participants were recruited for Round Two follow-up viral load testing. In Round One, refugees were older than host nationals (median age 36 years, interquartile range, IQR 31, 41 vs 32 years, IQR 27, 38); the groups had similar time on ART (median 147 weeks, IQR 38, 64 vs 139 weeks, IQR 39, 225). There was weak evidence for a difference between proportions of refugees and host nationals who were virologically suppressed (<5000 copies/mL) after 25 weeks on ART (58% vs 43%, p?=?0.10) and no difference in the proportions suppressed at Round Two (74% vs 70%, p?=?0.66). Mean adherence within each group in Round One was similar. Refugee status was not associated with viral suppression in multivariable analysis (adjusted odds ratio: 1.69, 95% CI 0.79, 3.57; p?=?0.17). Among those not suppressed at either timepoint, 69% (9/13) exhibited resistance mutations.ConclusionsVirologic outcomes among refugees and host nationals were similar but unacceptably low. Slight improvements were observed after a remedial intervention. Virologic monitoring was important for identifying an underperforming ART program in a remote facility that serves refugees alongside host nationals. This work highlights the importance of careful laboratory monitoring of vulnerable populations accessing ART in remote settings.

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Host and viral determinants of Mx2 antiretroviral activity.

Publications

Host and viral determinants of Mx2 antiretroviral activity.

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