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Potent drugs such as cyclosporine have provided effective probes of signal transduction pathways and, as well, of human immunodeficiency virus type 1 (HIV-1) replication mechanisms. Recently, it was reported that As[sub 2]O[sub 3], a drug used to treat acute promyelocytic leukemia (PML), stimulates HIV-1 replication. We found that As[sub 2]O[sub 3] accelerates the kinetics of a spreading HIV-1 infection in human T cells and increases the number of cells bearing HIV-1 provirus after a single round of infection. The stimulatory effect occurred after membrane fusion and resulted in increased steady-state levels of newly synthesized viral cDNA. Stimulation was independent of HIV-1 env and most viral accessory genes, and As[sub 2]O[sub 3] had no detectable effects on viral expression postintegration or virion assembly. Murine leukemia virus (MLV) transduction was enhanced by As[sub 2]O[sub 3] to the same extent as HIV-1 transduction, but As[sub 2]O[sub 3] had no additional effect on Fv1 restriction. In contrast, As[sub 2] the stimulatory effect of As[sub 2]O[sub 3]. As[sub 2]O[sub 3] caused cell death in uninfected cells at the same concentrations which stimulate HIV-1 replication. Among four additional apoptosis-inducing agents, a boost in HIV-1 infectivity was observed only with carbonyl cyanide m-chlorophenylhydrazone, a compound which, like As[sub 2]O[sub 3], disrupts the mitochondrial transmembrane potential. In summary, As[sub 2]O[sub 3] stimulates retroviral reverse transcription, perhaps via effects on mitochondria, and provides a useful tool for characterizing Ref1. [ABSTRACT FROM AUTHOR]

Tripartite motif-containing protein 5 (TRIM5) restricts human immunodeficiency virus type 1 (HIV-1) in a species-specific manner by uncoating viral particles while activating early innate responses. Although the contribution of TRIM5 proteins to cellular immunity has not yet been studied, their interactions with the incoming viral capsid and the cellular proteasome led us to hypothesize a role for them. Here, we investigate whether the expression of two nonhuman TRIM5 orthologs, rhesus TRIM5α (RhT5) and TRIM-cyclophilin A (TCyp), both of which are potent restrictors of HIV-1, could enhance immune recognition of infected cells by CD8+ T cells. We illustrate how TRIM5 restriction improves CD8+ T-cell-mediated HIV-1 inhibition. Moreover, when TRIM5 activity was blocked by the nonimmunosuppressive analog of cyclosporine (CsA), sarcosine-3(4-methylbenzoate)- CsA (SmBz-CsA), we found a significant reduction in CD107a/MIP-1β expression in HIV-1-specific CDCD8+ T cells. This finding underscores the direct link between TRIM5 restriction and activation of CD8+ T-cell responses. Interestingly, cells expressing RhT5 induced stronger CD8+ T-cell responses through the specific recognition of the HIV-1 capsid by the immune system. The underlying mechanism of this process may involve TRIM5-specific capsid recruitment to cellular proteasomes and increase peptide availability for loading and presentation of HLA class I antigens. In summary, we identified a novel function for nonhuman TRIM5 variants in cellular immunity. We hypothesize that TRIM5 can couple innate viral sensing and CD8+ T-cell activation to increase species barriers against retrovirus infection. [ABSTRACT FROM AUTHOR]

CD8+ T cells are major players in antiviral immunity against human immunodeficiency virus type 1 (HIV-1) through recognition of viral epitopes presented on the surface of infected cells. However, the early events involving HIV-1 epitope presentation to CD8+ T cells remain poorly understood but are nonetheless crucial for the rapid clearance of virus-infected cells. Here, we comprehensively studied the kinetics of antigen presentation of two protective epitopes, KF11Gag and KK10Gag, restricted by HLA alleles B*57:01 and B*27:05, respectively, and compared these to KY9Pol and VL9Vpr epitopes in a single cycle of HIV-1 replication. We consistently demonstrate differences in epitope presentation kinetics, with very early presentation, within 3 h postinfection, for the protective KF11Gag, KK10Gag epitopes, and KY9Pol but only late presentation for VL9Vpr. We show that this early presentation relies on the antigen being presented from incoming viral particles and is correlated with rapid CD8+ T cell activation and clearance of virus-infected cells. Additionally, our data indicate a dose-response dependency between the levels of CD8+ T cell activation and the amount of virus inoculum. These data reflect a proof of principle emphasizing the importance of identifying early-presented viral epitopes for rapid elimination of HIV-1-infected cells. [ABSTRACT FROM AUTHOR]

The restriction factors Fv1 and TRIM5 α provide dominant blocks to retroviral infection, targeting incoming capsids at a postentry, preintegration step. They both restrict N-tropic murine leukemia virus with similar specificity yet act at different points in the viral life cycle. TRIM5 α-restricted virus is usually unable to reverse transcribe, whereas Fv1-restricted virus reverse transcribes normally. Here we investigate the relationship between these two restriction factors by expressing Fv1 alleles in human cells. We demonstrate that Fv1 is able to compete with TRIM5 α for virus before reverse transcription. In human cells expressing Fv1b, N-tropic restricted virus becomes less infectious but reverse transcribes more efficiently, indicating competition between the two antiviral molecules and protection of the virus from TRIM5 α by Fv1. Our findings suggest that, like TRIM5 α, Fv1 interacts with virus before reverse transcription, but the consequences of this interaction are not realized until a later stage of the life cycle. We also demonstrate that Fv1 is functionally independent of TRIM5 α when expressed in human cells. [ABSTRACT FROM AUTHOR]

Restriction of murine leukemia virus (MLV) was examined in cells from a range of mammals. All nonmurine restrictions were saturable blocks to N-tropic MLV infection, and several were prior to reverse transcription. We demonstrate restriction in cells from bat and show that if we express the murine restriction factor Fv1 in human cells, then Fv1, not the human host, defines the stage at which infection is blocked. [ABSTRACT FROM AUTHOR]

Unlabelled: Tripartite motif-containing protein 5 (TRIM5) restricts human immunodeficiency virus type 1 (HIV-1) in a species-specific manner by uncoating viral particles while activating early innate responses. Although the contribution of TRIM5 proteins to cellular immunity has not yet been studied, their interactions with the incoming viral capsid and the cellular proteasome led us to hypothesize a role for them. Here, we investigate whether the expression of two nonhuman TRIM5 orthologs, rhesus TRIM5α (RhT5) and TRIM-cyclophilin A (TCyp), both of which are potent restrictors of HIV-1, could enhance immune recognition of infected cells by CD8(+) T cells. We illustrate how TRIM5 restriction improves CD8(+) T-cell-mediated HIV-1 inhibition. Moreover, when TRIM5 activity was blocked by the nonimmunosuppressive analog of cyclosporine (CsA), sarcosine-3(4-methylbenzoate)-CsA (SmBz-CsA), we found a significant reduction in CD107a/MIP-1β expression in HIV-1-specific CD8(+) T cells. This finding underscores the direct link between TRIM5 restriction and activation of CD8(+) T-cell responses. Interestingly, cells expressing RhT5 induced stronger CD8(+) T-cell responses through the specific recognition of the HIV-1 capsid by the immune system. The underlying mechanism of this process may involve TRIM5-specific capsid recruitment to cellular proteasomes and increase peptide availability for loading and presentation of HLA class I antigens. In summary, we identified a novel function for nonhuman TRIM5 variants in cellular immunity. We hypothesize that TRIM5 can couple innate viral sensing and CD8(+) T-cell activation to increase species barriers against retrovirus infection., Importance: New therapeutics to tackle HIV-1 infection should aim to combine rapid innate viral sensing and cellular immune recognition. Such strategies could prevent seeding of the viral reservoir and the immune damage that occurs during acute infection. The nonhuman TRIM5 variants, rhesus TRIM5α (RhT5) and TRIM-cyclophilin A (TCyp), are attractive candidates owing to their potency in sensing HIV-1 and blocking its activity. Here, we show that expression of RhT5 and TCyp in HIV-1-infected cells improves CD8(+) T-cell-mediated inhibition through the direct activation of HIV-1-specific CD8(+) T-cell responses. We found that the potency in CD8(+) activation was stronger for RhT5 variants and capsid-specific CD8(+) T cells in a mechanism that relies on TRIM5-dependent particle recruitment to cellular proteasomes. This novel mechanism couples innate viral sensing with cellular immunity in a single protein and could be exploited to develop innovative therapeutics for control of HIV-1 infection., (Copyright © 2016 Jimenez-Moyano et al.)

CD8(+) T cells are major players in antiviral immunity against human immunodeficiency virus type 1 (HIV-1) through recognition of viral epitopes presented on the surface of infected cells. However, the early events involving HIV-1 epitope presentation to CD8(+) T cells remain poorly understood but are nonetheless crucial for the rapid clearance of virus-infected cells. Here, we comprehensively studied the kinetics of antigen presentation of two protective epitopes, KF11Gag and KK10Gag, restricted by HLA alleles B*57:01 and B*27:05, respectively, and compared these to KY9Pol and VL9Vpr epitopes in a single cycle of HIV-1 replication. We consistently demonstrate differences in epitope presentation kinetics, with very early presentation, within 3 h postinfection, for the protective KF11Gag, KK10Gag epitopes, and KY9Pol but only late presentation for VL9Vpr. We show that this early presentation relies on the antigen being presented from incoming viral particles and is correlated with rapid CD8(+) T cell activation and clearance of virus-infected cells. Additionally, our data indicate a dose-response dependency between the levels of CD8(+) T cell activation and the amount of virus inoculum. These data reflect a proof of principle emphasizing the importance of identifying early-presented viral epitopes for rapid elimination of HIV-1-infected cells.