An unresolved question is how HIV‐1 achieves efficient replication in terminally differentiated macrophages despite the restriction factor SAMHD1. We reveal inducible changes in expression of cell cycle‐associated proteins including MCM2 and cyclins A, E, D1/D3 in macrophages, without evidence for DNA synthesis or mitosis. These changes are induced by activation of the Raf/MEK/ERK kinase cascade, culminating in upregulation of CDK1 with subsequent SAMHD1 T592 phosphorylation and deactivation of its antiviral activity. HIV infection is limited to these G1‐like phase macrophages at the single‐cell level. Depletion of SAMHD1 in macrophages decouples the association between infection and expression of cell cycle‐associated proteins, with terminally differentiated macrophages becoming highly susceptible to HIV‐1. We observe both embryo‐derived and monocyte‐derived tissue‐resident macrophages in a G1‐like phase at frequencies approaching 20%, suggesting how macrophages sustain HIV‐1 replication in vivo. Finally, we reveal a SAMHD1‐dependent antiretroviral activity of histone deacetylase inhibitors acting via p53 activation. These data provide a basis for host‐directed therapeutic approaches aimed at limiting HIV‐1 burden in macrophages that may contribute to curative interventions.

Productive replication of human papillomaviruses (HPV) is restricted to the uppermost layers of the differentiating epithelia. How HPV ensures an adequate supply of cellular substrates for viral DNA synthesis in a differentiating environment is unclear. Here, we demonstrate that HPV31 positive cells exhibit increased dNTP pools and levels of RRM2, a component of the ribonucleotide reductase (RNR) complex, which is required for de novo synthesis of dNTPs. RRM2 depletion blocks productive replication, suggesting RRM2 provides dNTPs for viral DNA synthesis in differentiating cells. We demonstrate that HPV31 regulates RRM2 levels through expression of E7 and activation of the ATR-Chk1-E2F1 DNA damage response, which is essential to combat replication stress upon entry into S-phase, as well as for productive replication. Our findings suggest a novel way in which viral DNA synthesis is regulated through activation of ATR and Chk1 and highlight an intriguing new virus/host interaction utilized for viral replication.

The latent HIV-1 reservoir primarily resides in resting CD4؉ T cells which are a heterogeneous population composed of both naive (T N ) and memory cells. In HIV-1-infected individuals, viral DNA has been detected in both naive and memory CD4 ؉ T cell subsets although the frequency of HIV-1 DNA is typically higher in memory cells, particularly in the central memory (T CM ) cell subset. T N and T CM cells are distinct cell populations distinguished by many phenotypic and physiological differences. In this study, we used a primary cell model of HIV-1 latency that utilizes direct infection of highly purified T N and T CM cells to address differences in the establishment and reversal of HIV-1 latency. Consistent with what is seen in vivo, we found that HIV-1 infected T N cells less efficiently than T CM cells. However, when the infected T N cells were treated with latency-reversing agents, including anti-CD3/CD28 antibodies, phorbol myristate acetate/phytohemagglutinin, and prostratin, as much (if not more) extracellular virion-associated HIV-1 RNA was produced per infected T N cell as per infected T CM cell. There were no major differences in the genomic distribution of HIV-1 integration sites between T N and T CM cells that accounted for these observed differences. We observed decay of the latent HIV-1 cells in both T cell subsets after exposure to each of the latency-reversing agents. Collectively, these data highlight significant differences in the establishment and reversal of HIV-1 latency in T N and T CM CD4؉ T cells and suggest that each subset should be independently studied in preclinical and clinical studies. IMPORTANCE The latent HIV-1 reservoir is frequently described as residing within resting memory CD4؉ T cells. This is largely due to the consistent finding that memory CD4 ؉ T cells, specifically the central (T CM )

In this study, we report that the tetraspanin CD81 enhances HIV-1 reverse transcription in HIV-1-infected cells. This is enabled by the direct interaction of CD81 with the deoxynucleoside triphosphate phosphohydrolase SAMHD1. This interaction prevents the endosomal accumulation and favours the proteasome-dependent degradation of SAMHD1. Consequently, CD81 depletion results in SAMHD1 increased expression, decreasing the availability of deoxynucleoside triphosphates (dNTP) and thus HIV-1 reverse transcription. Conversely, CD81 overexpression, but not the expression of a CD81 C-term deletion mutant, increases cellular dNTP content and HIV-1 reverse transcription. Our results demonstrate that the interaction of CD81 with SAMHD1 controls the metabolic rate of HIV-1 replication by tuning the availability of building blocks for reverse transcription, i.e. dNTPs. Together with its role in HIV-1 entry and budding into host cells, the data herein indicate that HIV-1 uses CD81 as a rheostat that controls different stages of the infection.