A substitution in the pre-S1 promoter region is associated with the viral regulation of hepatitis B virus

Suguru Ogura,Masahiko Tameda,Makoto Ikejiri,Yoshiyuki Takei,Kazushi Sugimoto,Masanobu Usui,Masaaki Ito

doi:10.1186/s12985-019-1169-x

Suguru Ogura, Masahiko Tameda + Show 5 more

Open Access

https://doi.org/10.1186/s12985-019-1169-x

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Journal: Virology journal	Publication Date: May 2, 2019
Citations: 6	License type: open-access

Affiliation: Mie University, Mie University Hospital

Abstract

BackgroundMuch evidence has demonstrated the influence of Hepatitis B virus (HBV) mutations on the clinical course of HBV infection. As large (L) protein plays a crucial role for viral entry, we hypothesized that mutations in the pre-S1 promoter region might affect the expression of L protein and subsequently change the biological characters of virus.MethodsPatients infected with genotype C HBV were enrolled for analysis. HBV DNA sequences were inserted into a TA cloning vector and analyzed. To evaluate the effects of mutations in the pre-S1 promoter region, promoter activity and the expression of mRNA and L protein were analyzed using HepG2 cells.ResultsIn total, 35 patients were enrolled and 13 patients (37.1%) had a single base substitution in the pre-S1 promoter region; the most frequent substitution was a G-to-A substitution at the 2765th base (G2765A) in the Sp1 region. The HBV viral load showed a negative correlation with the substitution ratio of the Sp1 region or G2765A (r = − 0.493 and − 0.473, respectively). Among those with a viral load ≤5.0 log IU/ml, patients with the G2765A substitution showed a significantly lower HBV viral load than those with the wild-type sequence. HepG2 cells transfected with the G2765A substitution vector showed reduced luciferase activity of the pre-S1 promoter, as well as reduced expression of pre-S1 mRNA and L protein. Furthermore, the G2765A substitution greatly reduced the L protein expression level of vector-produced virus particles.ConclusionG2765A substitution in the pre-S1 promoter reduced the expression of L protein and resulted in a low viral load and less severe disease in chronic HBV infections.

Highlights

Much evidence has demonstrated the influence of Hepatitis B virus (HBV) mutations on the clinical course of HBV infection
In this study, we investigated the effects of mutations in the pre-S1 promoter region of HBV on biological characters of virus and prognosis using clinical samples and a cultured cell line
The full genomic sequence of the HBV DNA strain obtained from a patient that had no mutation in the pre-S1 promoter region and that mostly matched with the consensus sequence was determined and deposited into the DNA Data Bank of Japan under accession number LC360507

Summary

Introduction

Much evidence has demonstrated the influence of Hepatitis B virus (HBV) mutations on the clinical course of HBV infection. As large (L) protein plays a crucial role for viral entry, we hypothesized that mutations in the pre-S1 promoter region might affect the expression of L protein and subsequently change the biological characters of virus. According to the World Health Organization, an estimated 257 million people worldwide are currently infected chronically with HBV, and a higher prevalence is found among populations in African and western pacific regions [1]. HBV is a hepatotropic DNA virus that belongs to the Hepadnaviridae family. It contains a partially doublestranded relaxed circular DNA of approximately 3200 nucleotides from which four mRNAs are transcribed, i.e., 0.7-, 2.1-, 2.4-, and 3.5-kb mRNAs. The envelope proteins of HBV consist of, in descending order of size, L protein, M protein, and S protein.

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