SAMHD1 Impairs HIV-1 Gene Expression and Negatively Modulates Reactivation of Viral Latency in CD4 ⁺ T Cells

Abstract

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) restricts human immunodeficiency virus type 1 (HIV-1) replication in nondividing cells by degrading intracellular deoxynucleoside triphosphates (dNTPs). SAMHD1 is highly expressed in resting CD4 T cells, which are important for the HIV-1 reservoir and viral latency; however, whether SAMHD1 affects HIV-1 latency is unknown. Recombinant SAMHD1 binds HIV-1 DNA or RNA fragments , but the function of this binding remains unclear. Here we investigate the effect of SAMHD1 on HIV-1 gene expression and reactivation of viral latency. We found that endogenous SAMHD1 impaired HIV-1 long terminal repeat (LTR) activity in monocytic THP-1 cells and HIV-1 reactivation in latently infected primary CD4 T cells. Overexpression of wild-type (WT) SAMHD1 suppressed HIV-1 LTR-driven gene expression at a transcriptional level. Tat coexpression abrogated SAMHD1-mediated suppression of HIV-1 LTR-driven luciferase expression. SAMHD1 overexpression also suppressed the LTR activity of human T-cell leukemia virus type 1 (HTLV-1), but not that of murine leukemia virus (MLV), suggesting specific suppression of retroviral LTR-driven gene expression. WT SAMHD1 bound to proviral DNA and impaired reactivation of HIV-1 gene expression in latently infected J-Lat cells. In contrast, a nonphosphorylated mutant (T592A) and a dNTP triphosphohydrolase (dNTPase) inactive mutant (H206D R207N [HD/RN]) of SAMHD1 failed to efficiently suppress HIV-1 LTR-driven gene expression and reactivation of latent virus. Purified recombinant WT SAMHD1, but not the T592A and HD/RN mutants, bound to fragments of the HIV-1 LTR These findings suggest that SAMHD1-mediated suppression of HIV-1 LTR-driven gene expression potentially regulates viral latency in CD4 T cells. A critical barrier to developing a cure for HIV-1 infection is the long-lived viral reservoir that exists in resting CD4 T cells, the main targets of HIV-1. The viral reservoir is maintained through a variety of mechanisms, including regulation of the HIV-1 LTR promoter. The host protein SAMHD1 restricts HIV-1 replication in nondividing cells, but its role in HIV-1 latency remains unknown. Here we report a new function of SAMHD1 in regulating HIV-1 latency. We found that SAMHD1 suppressed HIV-1 LTR promoter-driven gene expression and reactivation of viral latency in cell lines and primary CD4 T cells. Furthermore, SAMHD1 bound to the HIV-1 LTR and in a latently infected CD4 T-cell line, suggesting that the binding may negatively modulate reactivation of HIV-1 latency. Our findings indicate a novel role for SAMHD1 in regulating HIV-1 latency, which enhances our understanding of the mechanisms regulating proviral gene expression in CD4 T cells.

Fingolimod inhibits multiple stages of the HIV-1 life cycle

“…Phosphorylated SAMHD1 is the inactive form of the restriction factor, thus, our observation of decreased levels of pSAMHD1 concomitant with maintenance of the total SAMHD1 availability indicates increased relative expression of the active form of this antiviral factor. SAMHD1 was first shown to restrict HIV-1 in myeloid and dendritic cells [ 51 ] and was recently demonstrated to have an analogous role in macrophages [ 73 – 75 ] and CD4 T cells [ 76 – 78 ]. In CD4 T cells, a cyclin-binding motif on SAMHD1 is required for its restriction of HIV [ 79 ] and its regulation by cell-cycle associated proteins including cyclins or Cyclin-Dependent Kinases (CDKs) has been demonstrated [ 54 , 80 ].…”

The Polar Region of the HIV-1 Envelope Protein Determines Viral Fusion and Infectivity by Stabilizing the gp120-gp41 Association

“…After cells were washed with staining buffer and stained with fluorescein isothiocyanate (FITC)-conjugated anti-human IgG (Fc specific) (F9512, 1:100; Sigma-Aldrich) for 30 min, the cells were washed and resuspended with staining buffer and then detected using a Guava EasyCyte flow cytometer (Guava Technologies). The flow cytometry data were analyzed with FlowJo software (version 10; Tree Star) as described previously (40).…”

SAMHD1 Suppression of Antiviral Immune Responses

“…Conversely, it is plausible that SAMHD1mediated HIV-1 restriction prevents activation of innate and adaptive immune responses, indicating competition between cell-autonomous virus control and viral replication. A recent study reported that SAMHD1-mediated suppression of HIV-1 gene expression negatively affects reactivation of viral latency in CD4 + T cells, suggesting a novel role for SAMHD1 in regulating HIV-1 latency [112]. The function of SAMHD1 in anti-viral immune regulation is complex and connected to multi-cellular pathways.…”