Abstract
Background : SAMHD1 is a nuclear protein that blocks lentiviral infection before reverse transcription inmacrophages and dendritic cells. The viral accessory protein Vpx overcomes the SAMHD1-mediated lentiviral blockby inducing its proteasomal degradation.Results : Here, we identified the nuclear localization signal (NLS) of SAMHD1, and studied its contribution torestriction of HIV-1 and SIVmac. By studying the cellular distribution of different SAMHD1 variants, we mapped thenuclear localization of SAMHD1 to residues11KRPR14. Mutagenesis of these residues changed the cellulardistribution of SAMHD1 from the nucleus to the cytoplasm. SAMHD1 mutants that lost nuclear localizationrestricted HIV-1 and SIV as potently as the wild type protein. Interestingly, SAMHD1 mutants that localized to thecytoplasm were not degraded by nuclear Vpx alleles. Therefore, nuclear Vpx alleles require nuclear localization ofSAMHD1 in order to induce its degradation. In agreement, SIVmac viruses encoding Vpx did not overcome therestriction imposed by the cytoplasmic variants of SAMHD1.Conclusions : We mapped the NLS of SAMHD1 to residues11KRPR14and studied the contribution of SAMHD1nuclear localization to restriction of HIV-1 and SIV. These experiments demonstrate that cytoplasmic variants ofSAMHD1 potently block lentiviral infection and are resistant to Vpx-mediated degradation. The nuclear Vpx allelesstudied here are only capable of degrading a nuclearly localized SAMHD1 suggesting that Vpx-mediateddegradation of SAMHD1 is initiated in the nucleus.