Role of SAMHD1 nuclear localization in restriction of HIV-1 and SIVmac.
BACKGROUND
SAMHD1 is a nuclear protein that blocks lentiviral infection before reverse transcription in macrophages and dendritic cells. The viral accessory protein Vpx overcomes the SAMHD1-mediated lentiviral block by inducing its proteasomal degradation.


RESULTS
Here, we identified the nuclear localization signal (NLS) of SAMHD1, and studied its contribution to restriction of HIV-1 and SIVmac. By studying the cellular distribution of different SAMHD1 variants, we mapped the nuclear localization of SAMHD1 to residues 11KRPR14. Mutagenesis of these residues changed the cellular distribution of SAMHD1 from the nucleus to the cytoplasm. SAMHD1 mutants that lost nuclear localization restricted HIV-1 and SIV as potently as the wild type protein. Interestingly, SAMHD1 mutants that localized to the cytoplasm were not degraded by nuclear Vpx alleles. Therefore, nuclear Vpx alleles require nuclear localization of SAMHD1 in order to induce its degradation. In agreement, SIVmac viruses encoding Vpx did not overcome the restriction imposed by the cytoplasmic variants of SAMHD1.


CONCLUSIONS
We mapped the NLS of SAMHD1 to residues 11KRPR14 and studied the contribution of SAMHD1 nuclear localization to restriction of HIV-1 and SIV. These experiments demonstrate that cytoplasmic variants of SAMHD1 potently block lentiviral infection and are resistant to Vpx-mediated degradation. The nuclear Vpx alleles studied here are only capable of degrading a nuclearly localized SAMHD1 suggesting that Vpx-mediated degradation of SAMHD1 is initiated in the nucleus.
Department of Microbiology and Immunology, Albert Einstein College of Medicine Bronx, Bronx, NY 10461, USA.
Alberto
A
Brandariz-Nuñez
Jose Carlos
JC
Valle-Casuso
Tommy E
TE
White
Nadine
N
Laguette
Monsef
M
Benkirane
Jurgen
J
Brojatsch
Felipe
F
Diaz-Griffero
D000163:Acquired Immunodeficiency Syndrome / Q000821:virology; D021581:Active Transport, Cell Nucleus; D000483:Alleles; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D003593:Cytoplasm / Q000378:metabolism / Q000821:virology; D015658:HIV Infections / Q000821:virology; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D006367:HeLa Cells; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D019913:Nuclear Localization Signals / Q000378:metabolism*; D059748:Proteolysis; D015183:Restriction Mapping; D048348:Reverse Transcription; D000076106:SAM Domain and HD Domain-Containing Protein 1; D015302:Simian Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D020298:U937 Cells; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000378:metabolism
D019913:Nuclear Localization Signals; C513059:VPX protein, Simian immunodeficiency virus; D054334:Viral Regulatory and Accessory Proteins; D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D020559:Monomeric GTP-Binding Proteins