Interferon regulatory factor 3 is a key regulation factor for inducing the expression of SAMHD1 in antiviral innate immunity

Shen Yang,Fei Gao,Zhiyong Ma,Xuchen Zheng,Yuan Zhan,Yifeng Jiang,Lingxue Yu,Guangzhi Tong,Qinfeng Huang,Yanjun Zhou,Wu Tong,Liwei Li

doi:10.1038/srep29665

Shen Yang, Fei Gao + Show 10 more

Open Access

https://doi.org/10.1038/srep29665

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Abstract

SAMHD1 is a type I interferon (IFN) inducible host innate immunity restriction factor that inhibits an early step of the viral life cycle. The underlying mechanisms of SAMHD1 transcriptional regulation remains elusive. Here, we report that inducing SAMHD1 upregulation is part of an early intrinsic immune response via TLR3 and RIG-I/MDA5 agonists that ultimately induce the nuclear translocation of the interferon regulation factor 3 (IRF3) protein. Further studies show that IRF3 plays a major role in upregulating endogenous SAMHD1 expression in a mechanism that is independent of the classical IFN-induced JAK-STAT pathway. Both overexpression and activation of IRF3 enhanced the SAMHD1 promoter luciferase activity, and activated IRF3 was necessary for upregulating SAMHD1 expression in a type I IFN cascade. We also show that the SAMHD1 promoter is a direct target of IRF3 and an IRF3 binding site is sufficient to render this promoter responsive to stimulation. Collectively, these findings indicate that upregulation of endogenous SAMHD1 expression is attributed to the phosphorylation and nuclear translocation of IRF3 and we suggest that type I IFN induction and induced SAMHD1 expression are coordinated.

Highlights

Human sterile alpha motif and HD domain 1 (SAMHD1) is induced by IL-12/IL-18 in monocyte-derived macrophages (MDM), and by TNF-αin lung fibroblasts[17,18]
Previous studies showed that the levels of endogenous SAMHD1 protein in TCR-activated CD4+ T cells, monocytes, macrophages, dendritic cells (DCs), resting CD4+ T lymphocytes, and THP-1 cells were unaffected by type I IFN treatment[15,16], while SAMHD1 protein levels significantly increased in HeLa cells and HEK293 cells treated with IFN-α(Fig. 1A–D) or with IFN-β15
Upregulation of SAMHD1 expression induced by HP-porcine reproductive and respiratory syndrome virus (PRRSV) was not inhibited in porcine alveolar macrophages (PAMs) treated with IFN alpha-IFNAR-IN-1 (Fig. 2E). These results indicate that SAMHD1 expression is upregulated by HP-PRRSV in the infection of PAMs, which is different from what was observed in MARC-145 cells, and type I IFN production is not required for the induction of SAMHD1 expression in porcine macrophages infected with HP-PRRSV

Summary

Introduction

Human SAMHD1 is induced by IL-12/IL-18 in monocyte-derived macrophages (MDM), and by TNF-αin lung fibroblasts[17,18]. The type I interferon signaling network initiates an antiviral response through host pattern recognition receptors (PRRs) which recognize pathogen-associated molecular patterns (PAMPs)[21,27,28]. Recognition of PAMPs by PRRs, such as Toll-like receptors (TLR3, TLR4, TLR7/8, TLR9) and the RIG-I-like receptor families (RIG-I and MDA5)[29,30,31,32], with downstream signaling through IRF3, IRF7, and NF-κB leading to type I IFN production. Phosphorylated STAT1 and STAT2 work together with interferon regulatory factor 9 (IRF9) and translocate into the nucleus, resulting in the expression of IFN-stimulated genes (ISGs), which modulate the host immune responses[25,33]. We show that the TLR3 and RIG-I/MDA5 pathways participate in the regulation of SAMHD1 expression and find that IRF3 phosphorylation and nuclear translocation are critical aspects of SAMHD1 upregulation after IFN-αtreatment and virus infection

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