Guanylate binding proteins (GBPs) are an interferon (IFN)-inducible subfamily of guanosine triphosphatases (GTPases) with well-established activity against intracellular bacteria and parasites. Here we show that GBP5 potently restricts HIV-1 and other retroviruses. GBP5 is expressed in the primary target cells of HIV-1, where it impairs viral infectivity by interfering with the processing and virion incorporation of the viral envelope glycoprotein (Env). GBP5 levels in macrophages determine and inversely correlate with infectious HIV-1 yield over several orders of magnitude, which may explain the high donor variability in macrophage susceptibility to HIV. Antiviral activity requires Golgi localization of GBP5, but not its GTPase activity. Start codon mutations in the accessory vpu gene from macrophage-tropic HIV-1 strains conferred partial resistance to GBP5 inhibition by increasing Env expression. Our results identify GBP5 as an antiviral effector of the IFN response and may explain the increased frequency of defective vpu genes in primary HIV-1 strains.

SUMMARY Most simian immunodeficiency viruses use their Nef protein to antagonize the host restriction factor tetherin. A deletion in human tetherin confers Nef resistance, representing a hurdle to successful zoonotic transmission. HIV-1 group M evolved to utilize the viral protein U (Vpu) to counteract tetherin. Although HIV-1 group O has spread epidemically in humans, it has not evolved a Vpu-based tetherin antagonism. Here we show that HIV-1 group O Nef targets a region adjacent to this deletion to inhibit transport of human tetherin to the cell surface, enhances virion release, and increases viral resistance to inhibition by interferon-α. The Nef protein of the inferred common ancestor of group O viruses is also active against human tetherin. Thus, Nef-mediated antagonism of human tetherin evolved prior to the spread of HIV-1 group O and likely facilitated secondary virus transmission. Our results may explain the epidemic spread of HIV-1 group O.

BackgroundKnown antiretroviral restriction factors are encoded by genes that are under positive selection pressure, induced during HIV-1 infection, up-regulated by interferons, and/or interact with viral proteins. To identify potential novel restriction factors, we performed genome-wide scans for human genes sharing molecular and evolutionary signatures of known restriction factors and tested the anti-HIV-1 activity of the most promising candidates.ResultsOur analyses identified 30 human genes that share characteristics of known restriction factors. Functional analyses of 27 of these candidates showed that over-expression of a strikingly high proportion of them significantly inhibited HIV-1 without causing cytotoxic effects. Five factors (APOL1, APOL6, CD164, TNFRSF10A, TNFRSF10D) suppressed infectious HIV-1 production in transfected 293T cells by >90% and six additional candidates (FCGR3A, CD3E, OAS1, GBP5, SPN, IFI16) achieved this when the virus was lacking intact accessory vpr, vpu and nef genes. Unexpectedly, over-expression of two factors (IL1A, SP110) significantly increased infectious HIV-1 production. Mechanistic studies suggest that the newly identified potential restriction factors act at different steps of the viral replication cycle, including proviral transcription and production of viral proteins. Finally, we confirmed that mRNA expression of most of these candidate restriction factors in primary CD4+ T cells is significantly increased by type I interferons.ConclusionsA limited number of human genes share multiple characteristics of genes encoding for known restriction factors. Most of them display anti-retroviral activity in transient transfection assays and are expressed in primary CD4+ T cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-015-0165-5) contains supplementary material, which is available to authorized users.

No abstract

Antibody fragments, especially single-chain Fv fragments, have been established for the generation of immunoliposomes for targeted drug delivery in cancer therapy and other applications. Bispecific immunoliposomes should be useful for dual targeting addressing inter- and intratumoral heterogeneity of tumor antigen expression. Here, we established a protocol to generate dual-targeted immunoliposomes using genetically engineered scFv molecules recognizing two different tumor-associated antigens, EGFR and CEA (CEACAM5), applying a step-wise insertion of antibody-coupled micelles into preformed PEGylated liposomes. The dual-targeted immunoliposomes retained binding activity for both antigens and combined the selectivity of both antibodies within one liposome. Thus, these dual-targeted immunoliposomes should be suitable to deliver therapeutic payloads to tumor cells expressing EGFR or CEA, or both antigens