The primate lentivirus auxiliary protein Vpx counteracts an unknown restriction factor that renders human dendritic and myeloid cells largely refractory to HIV-1 infection. Here we identify SAMHD1 as this restriction factor. SAMHD1 is a protein involved in Aicardi-Goutières syndrome, a genetic encephalopathy with symptoms mimicking congenital viral infection, that has been proposed to act as a negative regulator of the interferon response. We show that Vpx induces proteasomal degradation of SAMHD1. Silencing of SAMHD1 in non-permissive cell lines alleviates HIV-1 restriction and is associated with a significant accumulation of viral DNA in infected cells. Concurrently, overexpression of SAMHD1 in sensitive cells inhibits HIV-1 infection. The putative phosphohydrolase activity of SAMHD1 is probably required for HIV-1 restriction. Vpx-mediated relief of restriction is abolished in SAMHD1-negative cells. Finally, silencing of SAMHD1 markedly increases the susceptibility of monocytic-derived dendritic cells to infection. Our results demonstrate that SAMHD1 is an antiretroviral protein expressed in cells of the myeloid lineage that inhibits an early step of the viral life cycle.
SAMHD1 restricts human immunodeficiency virus-1 (HIV-1) infection of dendritic and other myeloid cells at an early stage in the replication cycle. SIVsm/HIV-2 lineage viruses counteract SAMHD1-mediated restriction by encoding Vpx, a virion-packaged accessory protein that targets SAMHD1 for degradation. We show that SAMHD1 restricts HIV-1 infection of monocyte-derived macrophages (MDM) by hydrolyzing the cellular deoxynucleotide triphosphates (dNTP), reducing their level to below that required for the synthesis of the viral genomic DNA. Vpx prevented the SAMHD1-mediated decrease in dNTP. The restriction was partially alleviated in MDM by the addition of exogenous deoxynucleosides. HIV-1 with a V148I mutation in reverse transcriptase that lowers its affinity for dNTP was particularly sensitive to SAMHD1-mediated restriction. Nucleotide starvation could serve as a mechanism to protect cells from infection by a wide variety of infectious agents that replicate through a DNA intermediate.
MicroRNAs (miRNAs) are single-stranded noncoding RNAs of 19 to 25 nucleotides that function as gene regulators and as a host cell defense against both RNA and DNA viruses. We provide evidence for a physiological role of the miRNA-silencing machinery in controlling HIV-1 replication. Type III RNAses Dicer and Drosha, responsible for miRNA processing, inhibited virus replication both in peripheral blood mononuclear cells from HIV-1-infected donors and in latently infected cells. In turn, HIV-1 actively suppressed the expression of the polycistronic miRNA cluster miR-17/92. This suppression was found to be required for efficient viral replication and was dependent on the histone acetyltransferase Tat cofactor PCAF. Our results highlight the involvement of the miRNA-silencing pathway in HIV-1 replication and latency.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.