Vpx overcomes a SAMHD1-independent block to HIV reverse transcription that is specific to resting CD4 T cells

Abstract

Early after entry into monocytes, macrophages, dendritic cells, and resting CD4 T cells, HIV encounters a block, limiting reverse transcription (RT) of the incoming viral RNA genome. In this context, dNTP triphosphohydrolase SAM domain and HD domain-containing protein 1 (SAMHD1) has been identified as a restriction factor, lowering the concentration of dNTP substrates to limit RT. The accessory lentiviral protein X (Vpx) proteins from the major simian immunodeficiency virus of rhesus macaque, sooty mangabey, and HIV-2 (SIVsmm/ SIVmac/HIV-2) lineage packaged into virions target SAMHD1 for proteasomal degradation, increase intracellular dNTP pools, and facilitate HIV cDNA synthesis. We find that virion-packaged Vpx proteins from a second SIV lineage, SIV of red-capped mangabeys or mandrills (SIVrcm/mnd-2), increased HIV infection in resting CD4 T cells, but not in macrophages, and, unexpectedly, acted in the absence of SAMHD1 degradation, dNTP pool elevation, or changes in SAMHD1 phosphorylation. Vpx rcm/mnd-2 virion incorporation resulted in a dramatic increase of HIV-1 RT intermediates and viral cDNA in infected resting CD4 T cells. These analyses also revealed a barrier limiting HIV-1 infection of resting CD4 T cells at the level of nuclear import. Single amino acid changes in the SAMHD1-degrading Vpx mac239 allowed it to enhance early postentry steps in a Vpx rcm/mnd-2-like fashion. Moreover, Vpx enhanced HIV-1 infection of SAMHD1-deficient resting CD4 T cells of a patient with AicardiGoutières syndrome. These results indicate that Vpx, in addition to SAMHD1, overcomes a previously unappreciated restriction for lentiviruses at the level of RT that acts independently of dNTP concentrations and is specific to resting CD4 T cells.

Potent Inhibition of HIV-1 Replication in Resting CD4 T Cells by Resveratrol and Pterostilbene

“…On the basis of the ability of resting T cells to be productively infected, SAMHD1 fails to lower dNTP levels to below those required for RT to function, though its kinetics are markedly decreased; thus, the combination of SAMHD1 and inhibition of RNR is required to lower the amount of dNTPs to a level that RT is unable to function at all. A recent paper on Vpx has suggested that Vpx additionally enhances HIV infection by an SAMHD1/dNTPindependent mechanism (89). While this additional mechanism may be operating in our system, the restoration of dNTP levels by Vpx would appear to be necessary to overcome resveratrol and pterostilbene inhibition.…”

CD4+T Cell Subsets and Pathways to HIV Latency

“…65 For example, T cell activation has been shown to enhance the efficiency of reverse transcription since it is associated with low expression of the restriction factor SAMHD1 and increased availability of nucleotides. [77][78][79] T cell activation will also influence integration site selection by reorganizing general chromatin organization and localization of transcriptionally active open chromatin to the nuclear periphery near nucleoporin structures. [80][81][82][83] That antigen receptor-driven T cell activation influences HIV infection is supported by observations showing that superantigens increase susceptibility of CD4 + T cells to HIV infection 84 and that in vitro and in vivo T cells specific for tetanus toxoid, Candida albicans, 85 adenovirus, 86 HSV-2, 86 TB, 87 and HIV [88][89][90] are preferentially infected.…”

SAMHD1 Phosphorylation Coordinates the Anti-HIV-1 Response by Diverse Interferons and Tyrosine Kinase Inhibition

“…Whether restriction factors other than SAMHD1 were at play in our studies is unclear, though plausible. In fact, a recent study showed that SIV Vpx of red-capped mangabeys and mandrills (SIVrcm/mnd-2) enhances HIV-1 infection specifically in resting CD4 + T cells in a SAMHD1- and dNTP pool-independent manner and led the authors to suggest the existence of an unknown restriction factor ( 47 ).…”