Microbiology
Elimination of Aicardi–Goutières syndrome protein SAMHD1 activates cellular innate immunity and suppresses SARS-CoV-2 replication
The lack of antiviral innate immune responses during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections is characterized by limited production of interferons (IFNs). One protein associated with Aicardi–Goutières syndrome, SAMHD1, has been shown to negatively regulate the IFN-1 signaling pathway. However, it is unclear whether elevated IFN signaling associated with genetic loss of SAMHD1 would affect SARS-CoV-2 replication. In this study, we established in vitro tissue culture model systems for SARS-CoV-2 and human coronavirus OC43 infections in which SAMHD1 protein expression was absent as a result of CRISPR–Cas9 gene KO or lentiviral viral protein X–mediated proteosomal degradation.Enhanced enzyme kinetics of reverse transcriptase variants cloned from animals infected with SIVmac239 lacking viral protein X
HIV Type 1 (HIV-1) and simian immunodeficiency virus (SIV) display differential replication kinetics in macrophages. This is because high expression levels of the active host deoxynucleotide triphosphohydrolase sterile α motif domain and histidine-aspartate domain–containing protein 1 (SAMHD1) deplete intracellular dNTPs, which restrict HIV-1 reverse transcription, and result in a restrictive infection in this myeloid cell type. Some SIVs overcome SAMHD1 restriction using viral protein X (Vpx), a viral accessory protein that induces proteasomal degradation of SAMHD1, increasing cellular dNTP concentrations and enabling efficient proviral DNA synthesis.Viral protein X reduces the incorporation of mutagenic noncanonical rNTPs during lentivirus reverse transcription in macrophages
Unlike activated CD4+ T cells, nondividing macrophages have an extremely small dNTP pool, which restricts HIV-1 reverse transcription. However, rNTPs are equally abundant in both of these cell types and reach much higher concentrations than dNTPs. The greater difference in concentration between dNTPs and rNTPs in macrophages results in frequent misincorporation of noncanonical rNTPs during HIV-1 reverse transcription. Here, we tested whether the highly abundant SAM domain– and HD domain–containing protein 1 (SAMHD1) deoxynucleoside triphosphorylase in macrophages is responsible for frequent rNTP incorporation during HIV-1 reverse transcription.Interplay of ancestral non-primate lentiviruses with the virus-restricting SAMHD1 proteins of their hosts
Lentiviruses infect both dividing CD4+ T cells and nondividing myeloid cells, and the infected myeloid cells serve as long-living viral reservoirs. Host sterile alpha motif– and histidine-aspartate domain–containing protein 1 (SAMHD1) kinetically restricts reverse transcription of primate lentiviruses, including human immunodeficiency virus, type 1 (HIV-1) and simian immunodeficiency virus (SIV), in nondividing myeloid cells. SAMHD1 enforces this restriction through its dNTP triphosphohydrolase (dNTPase) activity that depletes cellular dNTPs.A CRISPR/Cas9 approach reveals that the polymerase activity of DNA polymerase β is dispensable for HIV-1 infection in dividing and nondividing cells
Retrovirus integration into the host genome relies on several host enzymes, potentially including DNA polymerase β (Pol β). However, whether human Pol β is essential for lentivirus replication in human cells is unclear. Here, we abolished DNA polymerase β (Pol β) expression by targeting its DNA polymerase domain with CRISPR/Cas9 in human monocytic THP-1 cells to investigate the role of Pol β in HIV-1 transduction in both dividing and nondividing macrophage stages of THP-1 cells. Pol β–knock-out was confirmed by enhanced sensitivity to methyl methanesulfonate-induced DNA damage.
