SAMHD1 restricts the replication of human immunodeficiency virus type 1 by depleting the intracellular pool of deoxynucleoside triphosphates

Abstract

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.

Effect of Ribonucleotides Embedded in a DNA Template on HIV-1 Reverse Transcription Kinetics and Fidelity

“…1 clearly demonstrates that the rNMP-mediated pausing disappears when HIV-1 RT synthesizes DNA at a fast rate with elevated dNTP concentrations. In fact, we and others recently reported that the limited dNTP pool found in macrophages is due to the expression of host restriction factor, SAMHD1, which is a dNTP triphosphohydrolase (5,45). Indeed, we also reported that HIV-2 and some SIVs encode an accessory protein, Vpx, that antagonizes the anti-viral function of SAMHD1 by proteasomal degradation.…”

“…Previously, we have shown that dNTP levels in macrophage are lower than the K m values of RT (4,50). However, Vpx-mediated degradation of SAMHD1 elevates dNTP levels above the K m values of RT (5,50), accelerating proviral DNA synthesis (46). Therefore, we further envision that Vpx-induced dNTP elevation in the non-dividing target cell types enables RTs to effectively overcome the rNMP-induced pausing as shown in Fig.…”

“…Indeed, we also reported that HIV-2 and some SIVs encode an accessory protein, Vpx, that antagonizes the anti-viral function of SAMHD1 by proteasomal degradation. This led to the elevation of cellular dNTPs in macrophages (5,46), dendritic cells (47), and resting T cells (48,49), which ultimately rescued the delayed reverse transcription process. Previously, we have shown that dNTP levels in macrophage are lower than the K m values of RT (4,50).…”

“…Activated CD4 ϩ T cells, which are dividing cells, contain high levels of dNTPs (1-16 M) as compared with terminally differentiated macrophages (20 -40 nM) (3,4). Recently, we and others reported that the low dNTP pool in macrophages is partially due to active hydrolysis of cellular dNTPs by SAMHD1, a cellular dNTP triphosphohydrolase (5,6). Although the dNTP pools differ considerably, both cell types have similarly high concentrations of ribonucleoside triphosphates (rNTPs) 2 (4).…”

The dNTP triphosphohydrolase activity of SAMHD1 persists during S-phase when the enzyme is phosphorylated at T592

“…It has been intensively investigated as a host restriction factor that, in quiescent/differentiated cells, limits HIV-1 and other viral infections by lowering cellular dNTP concentrations under a threshold critical for the synthesis of viral DNA [6]. …”