Macrophages and dendritic cells have key roles in viral infections, providing virus reservoirs that frequently resist anti-viral therapies and linkin innate virus detection to anti-viral adaptive immune responses. Human immunodeficiency virus 1 (HIV-1) fails to transduce dendritic cells and has a reduced ability to transduce macrophages, due to a potent early post-entry restriction preventing accumulation of viral cDNA. The restriction is to a large extent mediated by cellular SAMHD1 protein, mutations in which lead to Aicardi Goutieres Syndrome (AGS), an autoimmune disease associated with activation of the innate immune response thought to be provoked by endogenous nucleic acids. Importantly, SAMHD1 is targeted for degradation by the Vpx protein of HIV-2/SIVsm viruses, consistent with its key role in inhibiting primate lentivirus infection. These findings indicate that SAMHD1 mediates potent and relevant restriction in key cell types that orchestrate the immune response to HIV infection, and hence could determine long-term outcomes of antiviral therapies. We propose to elucidate the cellular and molecular mechanisms that control and mediate the restriction of HIV infection by SAMHD1. Experiments in aim 1 will define the functional organization of the SAMHD1 protein in the context of viral and cell-based assays, and assess the relationship between virologic and cellular functions of SAMHD1. Experiments in aim 2 will assess how SAMHD1 interferes with HIV-1 cDNA synthesis. Our data suggest that SAMHD1 deoxynucleoside triphosphate triphosphohydrolase (dNTPase) catalytic activity is regulated in cels, as is the case with other cellular enzymes, and per se is not sufficient to restrict HIV infection. Hence, SAMHD1 catalytic activity under restrictive vs non-restrictive conditions will be characterized and the possible importance of SAMHD1 proximity to the RTC for the restriction to occur will be assessed.
In aim 3, a combination of biochemical/proteomic/reverse genetic approaches will be used to identify cellular proteins and post-translational modifications that control SAMHD1 function. Experiments in aim 4 wil characterize developmental profiles of SAMHD1-mediated inhibition of HIV-1 infection in myeloid cells during their in vitro differentiation from CD34+ progenitor cells, and the possible involvement of SAMHD1 in early post-entry blocks of HIV-1 infection in non-myeloid cells. The relative importance of SAMHD1 co-factors, identified in aim 3, in primary myeloid cels wil also be assessed. The knowledge gained from our studies could lead to the conception of new strategies to improve the immune response to HIV and/or prevent formation of long-lived HIV reservoirs in tissue macrophages, by manipulating the SAMHD1 pathway.

Public Health Relevance

Cellular SAMHD1 protein inhibits HIV-1 infection of certain blood cells termed macrophages and dendritic cells, which cells play key roles in AIDS pathogenesis by providing virus reservoirs and orchestrating immune response to HIV-1 infection. The main goal of the proposed research is to understand precisely how SAMHD1 inhibits HIV-1 infection of these cells. This is expected to identify potential attractive new targts for therapeutic intervention, and suggest strategies to better protect these cells from HIV infection.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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AIDS Molecular and Cellular Biology Study Section (AMCB)
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Sharma, Opendra K
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Case Western Reserve University
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Yan, Junpeng; Shun, Ming-Chieh; Hao, Caili et al. (2018) HIV-1 Vpr Reprograms CLR4DCAF1 E3 Ubiquitin Ligase to Antagonize Exonuclease 1-Mediated Restriction of HIV-1 Infection. MBio 9:
Zhou, Xiaohong; DeLucia, Maria; Hao, Caili et al. (2017) HIV-1 Vpr protein directly loads helicase-like transcription factor (HLTF) onto the CRL4-DCAF1 E3 ubiquitin ligase. J Biol Chem 292:21117-21127
Hrecka, Kasia; Hao, Caili; Shun, Ming-Chieh et al. (2016) HIV-1 and HIV-2 exhibit divergent interactions with HLTF and UNG2 DNA repair proteins. Proc Natl Acad Sci U S A 113:E3921-30
Li, Wei; Xin, Baozhong; Yan, Junpeng et al. (2015) SAMHD1 Gene Mutations Are Associated with Cerebral Large-Artery Atherosclerosis. Biomed Res Int 2015:739586
Yan, Junpeng; Hao, Caili; DeLucia, Maria et al. (2015) CyclinA2-Cyclin-dependent Kinase Regulates SAMHD1 Protein Phosphohydrolase Domain. J Biol Chem 290:13279-92
Westmoreland, Susan V; Converse, A Peter; Hrecka, Kasia et al. (2014) SIV vpx is essential for macrophage infection but not for development of AIDS. PLoS One 9:e84463
Fregoso, Oliver I; Ahn, Jinwoo; Wang, Chuanping et al. (2013) Evolutionary toggling of Vpx/Vpr specificity results in divergent recognition of the restriction factor SAMHD1. PLoS Pathog 9:e1003496
Yan, Junpeng; Kaur, Sarabpreet; DeLucia, Maria et al. (2013) Tetramerization of SAMHD1 is required for biological activity and inhibition of HIV infection. J Biol Chem 288:10406-17
Ji, Xiaoyun; Wu, Ying; Yan, Junpeng et al. (2013) Mechanism of allosteric activation of SAMHD1 by dGTP. Nat Struct Mol Biol 20:1304-9