[Show abstract][Hide abstract] ABSTRACT: The expression of certain HLA class I alleles, including HLA-B*27 and HLA-B*57, is associated with better control of HIV-1 infection, but the mechanisms responsible are not fully understood. We sought evidence that pressure from the human restriction factor TRIM5α (hTRIM5α) could contribute to viral control. The hTRIM5α sensitivity of viruses from both HLA-B*57+ and HLA-B*27+ patients who spontaneously controlled viral replication, but not viruses from viremic patients expressing these alleles, was significantly greater than that of viruses from patients not expressing these protective HLA-B alleles. Overall, a significant negative correlation between hTRIM5α sensitivity and viral load was observed. In HLA-B*57+ patients, the T242N mutation in the HLA-B*57-restricted TW10 CTL epitope was strongly associated with hTRIM5α sensitivity. In HLA-B*27+ controllers, hTRIM5α sensitivity was associated with a significant reduction in emergence of key CTL mutations. In several patients, viral evolution to avoid hTRIM5α sensitivity was observed, but could be associated with reduced viral replicative capacity. Thus, in individuals expressing protective HLA-B alleles, the combined pressures exerted by CTL, hTRIM5α and capsid structural constraints can prevent viral escape both by impeding the selection of necessary resistance/compensatory mutations, and forcing the selection of escape mutations that increase hTRIM5α sensitivity or impair viral replicative capacity.
[Show abstract][Hide abstract] ABSTRACT: Because uncoating of the capsid is linked to reverse transcription, modifications that delay this process lead to the persistence in the cytoplasm of capsids susceptible to recognition by the human restriction factor TRIM5α (hTRIM5α). It is unknown, however, if increasing the time available for capsid-hTRIM5α interactions would actually render viruses more sensitive to hTRIM5α.
Viral sensitivity to hTRIM5α was evaluated by comparing their replication in human U373-X4 cells in which hTRIM5α activity had or had not been inhibited by overexpression of human TRIM5γ. No differences were observed comparing wild-type HIV-1 and variants carrying mutations in reverse transcriptase or the central polypurine tract that delayed the completion of reverse transcription. In addition, the effect of delaying the onset of reverse transcription for several hours by treating target cells with nevirapine was evaluated using viral isolates with different sensitivities to hTRIM5α. Delaying reverse transcription led to a time-dependent loss in viral infectivity that was increased by inhibiting capsid-cyclophilin A interactions, but did not result in increased viral sensitivity to hTRIM5α, regardless of their intrinsic sensitivity to this restriction factor.
Consistent with prior studies, the HIV-1 capsid can be targeted for destruction by hTRIM5α, but different strains display considerable variability in their sensitivity to this restriction factor. Capsids can also be lost more slowly through a TRIM5α-independent process that is accelerated when capsid-cyclophilin A interactions are inhibited, an effect that may reflect changes in the intrinsic stability of the capsid. Blocking the onset or delaying reverse transcription does not, however, increase viral sensitivity to hTRIM5α, indicating that the recognition of the capsids by hTRIM5α is completed rapidly following entry into the cytoplasm, as previously observed for the simian restriction factors TRIM-Cyp and rhesus TRIM5α.
PLoS ONE 01/2013; 8(1):e52434. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although laboratory-adapted HIV-1 strains are largely resistant to the human restriction factor TRIM5α (hTRIM5α), we have recently shown that some viruses carrying capsid (CA) sequences from clinical isolates can be more sensitive to this restriction factor. In this study we evaluated the contribution to this phenotype of CA mutations known to be associated with escape from cytotoxic T lymphocyte (CTL) responses. Recombinant viruses carrying HIV-1 CA sequences from NL4-3 and three different clinical isolates were prepared, along with variants in which mutations associated with CTL resistance were modified by site-directed mutagenesis, and the infectivities of these viruses in target cells expressing hTRIM5α and cells in which TRIM5α activity had been inhibited by overexpression of TRIM5γ were compared. For both hTRIM5α-sensitive viruses studied, CTL-associated mutations were found to be responsible for this phenotype. Both CTL resistance mutations occurring within HLA-restricted CA epitopes and compensatory mutations occurring outside CTL epitopes influenced hTRIM5α sensitivity, and mutations associated with CTL resistance selected in prior hosts can contribute to this effect. The impact of CTL resistance mutations on hTRIM5α sensitivity was context dependent, because mutations shown to be responsible for the TRIM5α-sensitive phenotype in viruses from one patient could have little or no impact on this parameter when introduced into another virus. No fixed relationship between changes in hTRIM5α sensitivity and infectivity was discernible in our studies. Taken together, these findings suggest that CTL mutations may influence HIV-1 replication by modifying both viral infectivity and sensitivity to TRIM5α.
Journal of Virology 09/2011; 85(22):11846-54. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: TRIM5α is a restriction factor that can block an early step in the retroviral life cycle by recognizing and causing the disassembly of incoming viral capsids, thereby preventing the completion of reverse transcription. Numerous other isoforms of human TRIM5 exist, and isoforms lacking a C-terminal SPRY domain can inhibit the activity of TRIM5α. Thus, TRIM5α activity in a given cell type could be dependent on the relative proportions of TRIM5 isoforms expressed, but little information concerning the relative expression of TRIM5 isoforms in human cells is available. In this study, we demonstrate that mRNAs coding for TRIM5α represent only 50% of total TRIM5 transcripts in human cell lines, CD4(+) T cells, and macrophages. Transcripts coding for, in order of abundance, TRIM5ι (TRIM5-iota), a previously uncharacterized isoform, TRIM5γ, TRIM5δ, and TRIM5κ are also present. Like TRIM5γ and TRIM5δ, TRIM5ι and TRIM5κ do not inhibit HIV-1 replication, but both have dominant-negative activity against TRIM5α. Specific knockdown of TRIM5ι increases TRIM5α activity in human U373-X4 cells, indicating that physiological levels of expression of truncated TRIM5 isoforms in human cells can reduce the activity of TRIM5α.
Journal of Virology 06/2011; 85(15):7828-35. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: HIV-1 infectivity is strongly restricted by TRIM5α from certain primate species but has been described as being only marginally susceptible to human TRIM5α. In this study, we evaluated the effects of the modulation of human TRIM5α activity (pretreatment of target cells with alpha interferon, expression of a pre-miRNA targeting TRIM5α, and/or overexpression of TRIM5γ), the inhibition of cyclophilin A (CypA)-CA interactions, and the expression of different allelic variants of human TRIM5α on the infectivity of a series of recombinant viruses carrying different patient-derived Gag-protease sequences. We show that HIV-1 displays virus-specific differences in its sensitivity to human TRIM5α and in its sensitivity to different TRIM5α alleles. The effect of inhibiting CypA-CA interactions is also strain specific, and blocking these interactions can either inhibit or improve viral infectivity, depending on the isolate studied. The inhibition of CypA-CA interactions also modulates viral sensitivity to human TRIM5α. In the absence of CypA-CA interactions, most viruses displayed increased sensitivity to the inhibitory effects of TRIM5α on viral replication, but one isolate showed a paradoxical decrease in sensitivity to TRIM5α. Taken together, these findings support a model in which three interlinked factors--capsid sequence, CypA levels, and TRIM5α--interact to determine capsid stability and therefore viral infectivity.
Journal of Virology 11/2010; 84(21):11010-9. · 5.08 Impact Factor