The Tudor domain protein Spindlin1 is involved in intrinsic antiviral defense against incoming hepatitis B Virus and herpes simplex virus type 1.

Aurélie Ducroux,Shirine Benhenda,Monsef Benkirane,Lise Rivière,O John Semmes,Christine Neuveut,Aleem Siddiqui

doi:10.1371/journal.ppat.1004343

Abstract

Hepatitis B virus infection (HBV) is a major risk factor for the development of hepatocellular carcinoma. HBV replicates from a covalently closed circular DNA (cccDNA) that remains as an episome within the nucleus of infected cells and serves as a template for the transcription of HBV RNAs. The regulatory protein HBx has been shown to be essential for cccDNA transcription in the context of infection. Here we identified Spindlin1, a cellular Tudor-domain protein, as an HBx interacting partner. We further demonstrated that Spindlin1 is recruited to the cccDNA and inhibits its transcription in the context of infection. Spindlin1 knockdown induced an increase in HBV transcription and in histone H4K4 trimethylation at the cccDNA, suggesting that Spindlin1 impacts on epigenetic regulation. Spindlin1-induced transcriptional inhibition was greater for the HBV virus deficient for the expression of HBx than for the HBV WT virus, suggesting that HBx counteracts Spindlin1 repression. Importantly, we showed that the repressive role of Spindlin1 is not limited to HBV transcription but also extends to other DNA virus that replicate within the nucleus such as Herpes Simplex Virus type 1 (HSV-1). Taken together our results identify Spindlin1 as a critical component of the intrinsic antiviral defense and shed new light on the function of HBx in HBV infection.

Highlights

Despite the existence of an effective preventive vaccine, hepatitis B virus infection remains a major health problem
Since Hepatitis B virus infection (HBV) transcriptional activation by HBx relies on the modulation of histones post-translational modifications, we further studied whether Spindlin1 is involved in HBV transcriptional regulation [10,13]
The ability of HBx to interact with Spindlin1 was first confirmed by immunoprecipitation assay using cellular extract from HEK293 cells transfected with His-Myc-Spindlin1 (His-mycSpin1) and HA-HBx vectors (Figure 1A)

Summary

Introduction

Despite the existence of an effective preventive vaccine, hepatitis B virus infection remains a major health problem. Chronic HBV infection affects 350 million people worldwide who are at high risk of developing liver diseases including cirrhosis and hepatocellular carcinoma (HCC) [1]. HBV is a prototypical member of the hepadnavirus family of DNA viruses that preferentially target hepatocytes and share the particularity to replicate their genome via an RNA intermediate. The virion consists of a 3.2 kb partially double stranded relaxed circular DNA (RC-DNA). RC-DNA is delivered into the nucleus and converted into a covalently closed circular DNA (cccDNA) that serves as the template for transcription of all viral RNAs including the pregenomic RNA (pgRNA). PgRNA is encapsidated in the cytoplasm and retrotranscribed into RC-DNA. Capsids containing RC-DNA are either enveloped at the endoplasmic reticulum and released from the cell or are recycled to the nucleus and contribute to the amplification of cccDNA

Methods

Results

Conclusion