Inhibition of Hepatitis B virus replication by SAMHD1

https://doi.org/10.1016/j.bbrc.2014.07.023Get rights and content

Highlights

  • SAMHD1 expression is detectable in four liver cell lines.

  • SAMHD1 inhibits HBV replication in SMMC-7721 and BEL-7402 cells.

  • SAMHD1 HD/AA with no dNTPase activity blocks HBV replication in liver cells.

  • HBV replication reduces SAMHD1 expression in HepG2 cells.

  • IFN-α induces SAMHD1 expression in liver cells.

Abstract

Sterile alpha motif and HD-domain containing protein 1 (SAMHD1) is a newly identified intracellular antiviral factor. By depleting the dNTPs pool of host cells to a low level that cannot support the efficient synthesis of viral cDNA, it restricts replication of some retroviruses. As a DNA virus, Hepatitis B virus (HBV) experiences a process of reverse transcription in its life cycle akin to that of retroviruses. However, whether SAMHD1 can restrict HBV replication in liver cells is unknown. Here, we reported that SAMHD1 expression was detectable in four liver cell lines. Exogenous expression of SAMHD1 in SMMC-7721 cells restrained HBV replication. Similarly, SAMHD1 impeded HBV replication in another liver cell line, BEL-7402. Remarkably, the catalytically inactive mutant, SAMHD1 HD/AA also hampered HBV replication. Additionally, HBV replication reduced SAMHD1 expression in HepG2 cells. Moreover, it was found that IFN-α induced expression of SAMHD1 in liver cells. Together, these findings suggested that IFN-α-inducible SAMHD1 inhibited HBV replication in liver cells.

Introduction

Hosts have evolved diverse mechanisms to defend themselves against viral infection. Intrinsic immunity mediated by constitutively expressed restriction factors is the recently recognized way to block viral replication, which is somewhat different from the conventional innate immunity [1]. In 2011, Sterile alpha motif and HD-domain containing protein 1 (SAMHD1) was identified as a novel intracellular antiviral factor in intrinsic immunity [2], [3], [4]. By depleting the deoxynucleoside triphosphates (dNTPs) pool of host cells to a low level that cannot support the efficient synthesis of viral cDNA, SAMHD1 restricts replication of Human immunodeficiency virus type 1 (HIV-1) [5], [6], [7]. Besides HIV-1, SAMHD1 has been found to inhibit replication of other retroviruses [8], [9], [10]. Recent studies further demonstrated SAMHD1 restricted DNA viruses in non-dividing myeloid cells by limiting DNA replication [11], [12].

Hepatitis B virus is a DNA virus whose infection accounts for approximately 1 million deaths per year from cirrhosis, liver failure and hepatocellular carcinoma (HCC) [13]. As a nonretroviral virus, HBV experiences a process of reverse transcription in its life cycle akin to that of lentiviruses [14]. SAMHD1 was found to be expressed in human liver [15]. However, whether HBV replication can be inhibited by human SAMHD1 in hepatocytes is unknown.

In the present study, we examined the role of SAMHD1 in HBV replication in liver cells. We found IFN-α-inducible SAMHD1 could inhibit HBV replication in liver cells without depleting intracellular dNTPs.

Section snippets

Plasmids

pHBVwt, which contained HBV1.3L (replication-competent overlength 1.3-fold HBV), and its mutant pHBV ΔX (HBx defective) were generous gifts from Dr. James Ou (University of Southern California), and had been described previously [16]. pcDNA3.1-HA-SAMHD1wt (pSAMHD1wt) and pcDNA3.1-HA-SAMHD1 HD/AA (pSAMHD1 HD/AA) were kind gifts from Dr. Klaus Strebel (National Institutes of Health). pRL-TK (Promega) was used to correct for transfection efficiency and luciferase activities were measured using

SAMHD1 expression is detectable in four liver cell lines

To investigate whether SAMHD1 restricted HBV replication in liver cells, we firstly detected endogenous expression of SAMHD1 in four liver cell lines: HepG2, LO2, BEL-7402, SMMC-7721. BEL-7402 cells transiently expressing exogenous SAMHD1 was regarded as a positive control for SAMHD1 expression. As showed in Fig. 1A, SAMHD1 expression was detectable in all four liver cell lines using Western blot whilst it was over-expressed in transfected BEL-7402 cells. These results were further confirmed by

Discussion

It has been well known that SAMHD1 restricts replication of retroviruses [8], [9], [10]. Recent studies showed SAMHD1 also blocked replication of two double stranded DNA viruses, vaccinia virus and herpes simplex virus 1, by depleting dNTPs in non-dividing myeloid cells [11], [12]. Here we provided evidence that SAMHD1 inhibited replication of HBV, another DNA virus, in liver cells. Remarkably, the catalytically inactive mutant, SAMHD1 HD/AA also hampered HBV replication, suggesting SAMHD1 had

Acknowledgments

We would like to thank Dr. James Ou (University of Southern California) and Dr. Klaus Strebel (National Institutes of Health) who kindly provided reagents used in this study. We also thank Dake Huang and Cuiping Ren (Anhui Medical University) for their technical help. This work was supported by grants from National Undergraduate Training Programs for Innovation and Entrepreneurship-China (No. 201310366009 to Zhangming Chen), National Natural Science Foundation of China (Nos. 81173074 and

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    These authors contributed equally to this work.

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