title: dNTP pool modulation dynamics by SAMHD1 protein in monocyte-derived macrophages.
abstract: BACKGROUND
  SAMHD1 degrades deoxyribonucleotides (dNTPs), suppressing viral DNA synthesis in macrophages. Recently, viral protein X (Vpx) of HIV-2/SIVsm was shown to target SAMHD1 for proteosomal degradation and led to elevation of dNTP levels, which in turn accelerated proviral DNA synthesis of lentiviruses in macrophages.
  
  
  RESULTS
  We investigated both time-dependent and quantitative interplays between SAMHD1 level and dNTP concentrations during multiple exposures of Vpx in macrophages. The following were observed. First, SAMHD1 level was rapidly reduced by Vpx + VLP to undetectable levels by Western blot analysis. Recovery of SAMHD1 was very slow with less than 3% of the normal macrophage level detected at day 6 post Vpx treatment and only ~30% recovered at day 14. Second, dGTP, dCTP and dTTP levels peaked at day 1 post Vpx treatment, whereas dATP peaked at day 2. However, all dNTPs rapidly decreased starting at day 3, while SAMHD1 level was below the level of detection. Third, when Vpx pretreated macrophages were re-exposed to a second Vpx treatment at day 7, we observed dNTP elevation that had faster kinetics than the first Vpx + VLP treatment. Moreover, we performed a short kinetic analysis of the second Vpx treatment to find that dATP and dGTP levels peaked at 8 hours post secondary VLP treatment. dGTP peak was consistently higher than the primary, whereas peak dATP concentration was basically equivalent to the first Vpx + VLP treatment. Lastly, HIV-1 replication kinetics were faster in macrophages treated after the secondary Vpx treatments when compared to the initial single Vpx treatment.
  
  
  CONCLUSIONS
  This study reveals that a very low level of SAMHD1 sufficiently modulates the normally low dNTP levels in macrophages and proposes potential diverse mechanisms of Vpx-mediated dNTP regulation in macrophages.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Hollenbaugh
authors.forename: Sijia
authors.initials: S
authors.lastname: Tao
authors.forename: Gina M
authors.initials: GM
authors.lastname: Lenzi
authors.forename: Sulryung
authors.initials: S
authors.lastname: Ryu
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Kim
authors.forename: Felipe
authors.initials: F
authors.lastname: Diaz-Griffero
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Schinazi
authors.forename: Baek
authors.initials: B
authors.lastname: Kim
mesh_terms: D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000494:pharmacology; D015497:HIV-1 / Q000235:genetics; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D009000:Monocytes / Q000166:cytology*; D020559:Monomeric GTP-Binding Proteins / Q000032:analysis*; D009711:Nucleotides / Q000032:analysis*; D000076106:SAM Domain and HD Domain-Containing Protein 1; D053719:Tandem Mass Spectrometry; D054334:Viral Regulatory and Accessory Proteins / Q000494:pharmacology; D014771:Virion / Q000502:physiology; D000093542:Gemcitabine
chemical_list: D009711:Nucleotides; C074286:VPX protein, Human immunodeficiency virus 2; C513059:VPX protein, Simian immunodeficiency virus; D054334:Viral Regulatory and Accessory Proteins; D003841:Deoxycytidine; D000076106:SAM Domain and HD Domain-Containing Protein 1; C484280:SAMHD1 protein, human; D020559:Monomeric GTP-Binding Proteins; D000093542:Gemcitabine