Poster abstracts

Poster number 36 submitted by Zhihua Qin

The dNTPase activity of SAMHD1 is required for its suppression of innate immune responses in differentiated monocytic cells

Zhihua Qin, Serena Bonifati, Corine St. Gelais, Tai-Wei Li, Sun-Hee Kim (The Ohio State University, Center for Retrovirus Research, Center for RNA Biology, Columbus, OH), Bijan Mahboubi, Baek Kim (Emory University School of Medicine, Center for Drug Discovery, Department of Pediatrics, Atlanta, GA), Li Wu (The Ohio State University, Center for Retrovirus Research, Center for RNA Biology, Columbus, OH)

Abstract:
Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a deoxynucleoside triphosphohydrolase (dNTPase) with a nuclear localization signal (NLS). We reported that SAMHD1 suppresses innate immune responses to viral infection and inflammatory stimuli by inhibiting the NF-𝑘B and type I interferon (IFN-I) pathways. However, whether the dNTPase activity and nuclear localization of SAMHD1 are required for its suppression of innate immunity remains unknown. To address this question, we compared monocytic U937 cell lines stably expressing wild-type (WT) SAMHD1 or mutants defective for dNTPase activity (HD/RN) or nuclear localization (mNLS). Expression of WT SAMHD1 in differentiated U937 cells significantly inhibited mRNA levels of TNF-a and IL-6 induced by lipopolysaccharide (LPS) treatment, as well as IFN-a, IFN-b and TNF-a mRNA levels induced by Sendai virus (SeV) infection. In contrast, expression of the HD/RN mutant did not show the inhibition. Consistent results were also observed in SAMHD1-knockout THP-1 cells after re-expressing the HD/RN mutant, suggesting that the dNTPase activity of SAMHD1 is required for suppressing NF-𝑘B activation and IFN-I induction by inflammatory stimuli or viral infection. However, expression of the mNLS mutant or WT SAMHD1 similarly reduced TNF-a or IFN-b mRNA levels in LPS-treated or SeV-infected U937 cells, suggesting that cytoplasmic SAMHD1 inhibits innate immune responses to inflammatory stimuli and viral infection. Our data demonstrated that the dNTPase activity, but not nuclear localization of SAMHD1, is required for its suppression of innate immune responses in differentiated monocytic cells. This study further defines the role and mechanism of SAMHD1 in suppressing innate immunity.

Keywords: SAMHD1, innate immune responses, dNTPase