Expression of the recently discovered human restriction factor SAMHD1 is responsible for the infection block imposed to lentiviruses such as HIV-1, HIV-2 and SIVmac by primary macrophages, dendritic cells and resting CD4+ T-cells. SAMHD1 blocks lentiviral infection by preventing the occurrence of reverse transcription. The viral accessory protein Vpx, contained in SIVmac and HIV-2 particles, overcomes the SAMHD1 reverse transcription block by inducing SAMHD1 degradation. SAMHD1 is a dGTP-regulated deoxynucleotide triphosphohydrolase that decreases the cellular levels of triphosphodeoxynucleotides (dNTPs). The dramatic decrease in dNTP levels in macrophages, dendritic cells and CD4+ resting T cells correlates with the inability of lentiviruses to undergo reverse transcription;therefore, SAMHD1 prevents lentiviral reverse transcription by depletion of dNTP levels. Interestingly, cycling and non-cycling cells express SAMHD1;however, SAMHD1's antiviral activity is only observed in non-cycling cells. Our preliminary findings correlate the lentiviral restriction phenotype observed in non-cycling cells with the phosphorylation state of SAMHD1.These results strongly suggested that phosphorylation regulates the antiviral activity of SAMHD1;therefore, this proposal will test the hypothesis that phosphorylation of SAMHD1 induces a conformational change that closes the active site of SAMHD1 domain resulting in an enzymatically and antivirally inactive SAMHD1 protein. The following specific aims will be used to address this hypothesis.
Aim1 will explore the role of SAMHD1 phosphorylation in retroviral restriction. For this purpose, we will study restriction of SAMHD1 proteins where the phosphorylatable residues are replaced by either a phosphomimetic or non-phosphorylatable residue.
This aim will also explore the nature of the kinase involved in the phosphorylation of SAMHD1.
Aim 2 will explore the ability of Vpx to modulate SAMHD1 antiviral and enzymatic activities before SAMHD1 degradation.
Aim 3 will explore the regulation of the antiviral and enzymatic activity of SAMHD1. Specifically, this aim will test the notion that SAMHD1 is regulated by a ball-and-chain mechanism. Overall, this proposal will establish phosphorylation as a new framework for understanding the antiviral properties of SAMHD1. Understanding the regulation of SAMHD1 is instrumental for the development of novel anti-HIV-1 vaccine strategies since overcoming SAMHD1 increases the adaptive immune response during infection of dendritic cells and macrophages. In addition, macrophages represent one of the most resilient HIV-1 reservoirs, so understanding the regulation of SAMHD1 antiviral properties could provide novel insides for the elimination of HIV-1 reservoirs.

Public Health Relevance

SAMHD1 is a restriction factor that blocks HIV-1 infection in macrophages and dendritic cells. However, SAMHD1 only blocks HIV-1 infection in non-cycling cells. This work will attempt to understand the regulation of SAMHD1 in both cycling and non-cycling cells. Understanding this regulation will be instrumental for the development of novel anti-HIV-1 vaccine strategies since overcoming SAMHD1 increases the adaptive immune response during HIV-1 infection of macrophages and dendritic cells.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
High Priority, Short Term Project Award (R56)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Sharma, Opendra K
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Albert Einstein College of Medicine
Schools of Medicine
United States
Zip Code
Schulte, Bianca; Selyutina, Anastasia; Opp, Silvana et al. (2018) Localization to detergent-resistant membranes and HIV-1 core entry inhibition correlate with HIV-1 restriction by SERINC5. Virology 515:52-65
Martinez-Lopez, Alicia; Martin-Fernandez, Marta; Buta, Sofija et al. (2018) SAMHD1 deficient human monocytes autonomously trigger type I interferon. Mol Immunol 101:450-460
Opp, Silvana; Fricke, Thomas; Shepard, Caitlin et al. (2017) The small-molecule 3G11 inhibits HIV-1 reverse transcription. Chem Biol Drug Des 89:608-618
Chen, Nan-Yu; Zhou, Lihong; Gane, Paul J et al. (2016) HIV-1 capsid is involved in post-nuclear entry steps. Retrovirology 13:28
White, Tommy E; Brandariz-Nuñez, Alberto; Han, Kyudong et al. (2016) Modulation of LINE-1 Retrotransposition by a Human SAMHD1 Polymorphism. Virol Rep 6:53-60
Fricke, Thomas; Diaz-Griffero, Felipe (2016) HIV-1 Capsid Stabilization Assay. Methods Mol Biol 1354:39-47
Campbell, Edward M; Weingart, Jared; Sette, Paola et al. (2016) TRIM5?-Mediated Ubiquitin Chain Conjugation Is Required for Inhibition of HIV-1 Reverse Transcription and Capsid Destabilization. J Virol 90:1849-57
Opp, Silvana; Vieira, Daniel A S A; Schulte, Bianca et al. (2016) MxB Is Not Responsible for the Blocking of HIV-1 Infection Observed in Alpha Interferon-Treated Cells. J Virol 90:3056-64
Bhattacharya, Akash; Wang, Zhonghua; White, Tommy et al. (2016) Effects of T592 phosphomimetic mutations on tetramer stability and dNTPase activity of SAMHD1 can not explain the retroviral restriction defect. Sci Rep 6:31353
Schulte, Bianca; Buffone, Cindy; Opp, Silvana et al. (2015) Restriction of HIV-1 Requires the N-Terminal Region of MxB as a Capsid-Binding Motif but Not as a Nuclear Localization Signal. J Virol 89:8599-610

Showing the most recent 10 out of 15 publications