Nucleotide change of codon 38 in the X gene of hepatitis B virus genotype C is associated with an increased risk of hepatocellular carcinoma
Introduction
Hepatitis B virus (HBV) infection is a major global health problem, and more than 350 million people in the world are chronic carriers of the virus [1], [2]. A significant number of these carriers suffer from either liver failure or hepatocellular carcinoma (HCC) at the late stage of the disease [3], [4].
Currently, HBV has been classified into eight genotypes (types A–H) with distinct geographic distributions [5], [6]. HBV genotypes B and C are prevalent in Japan [7], and previous studies have suggested that genotype C is associated with more active hepatitis [8], [9], more advanced liver disease [10], and higher prevalence of HCC than genotype B [11], [12].
The HBV genomic DNA is 3.2 kb in length and contains four partially overlapping open reading frames: preC/C, P, preS/S, and X gene. The X gene product, HBx, plays an essential role in viral replication [13], [14]. HBx also modifies several cellular pathways [15], [16], [17] and, as a result, has been shown to induce cell transformation leading to HCC in a select strain of transgenic mice [18].
Nucleotide changes may occur throughout the genome during the course of HBV infection. Previous reports have suggested that nucleotide changes in HBV might be related to the development of severe fulminant hepatitis [19], [20], and might reflect the attempt of the virus to adjust itself to the immune response of the host [21], [22]. Researchers have also suggested that basal core promoter (BCP) mutations (A–T at nucleotide 1762 and G–A at nucleotide 1764) increase the risk of HCC development [23], [24].
To further explore the relationship between nucleotide changes in HBV and the development of HCC, we examined the nucleotide sequence of the X gene and precore region obtained from the sera of patients infected with HBV genotype C.
Section snippets
Patients
We collected sera from 91 consecutive patients with HBV-related HCC (HCC patients) who visited the outpatient clinics at the University of Tokyo Hospital and the University of Okayama Hospital in Japan between 1994 and 2004. We also collected sera from 87 patients with HBV-related chronic liver disease (CLD patients) who visited the outpatient clinics at the University of Tokyo Hospital, the University of Chiba Hospital, and the University of Okayama Hospital in Japan. Both groups of patients
Nucleotide changes in the X gene and precore region (Cohort A, n = 75)
The clinical features of the patients in Cohort A are shown in Table 2. The proportion of those with cirrhosis was higher in HCC patients in comparison with CLD patients, whereas the viral load, positive rate of HBeAg, serum albumin level, and platelet count were lower.
The deduced amino acid change from proline to serine at codon 38 in HBx (codon-38 change) was found in 19 of 39 (48.7%) patients with HCC, but in only 5 of 36 (13.9%) patients with CLD (P = 0.001; Fig. 1). In all cases, the amino
Discussion
Orito et al. showed that the HBV genotypes B and C are prevalent in Japan, with more than 80% of cases being genotype C [7]. Therefore, we examined the nucleotide sequence of the X gene in genotype C and identified a single nucleotide change (codon-38 change) that was preferentially found in HCC patients of different study cohorts.
BCP mutations (A–T at nucleotide 1762 and G–A at nucleotide 1764) have been found to increase the risk of HCC development, and precore mutation (G–A at nucleotide
Acknowledgements
This work was supported in part by Health and Labor Sciences Research Grants for Research on Hepatitis from the Ministry of Health, Labor, and Welfare of Japan, and by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, and Technology of Japan.
References (39)
- et al.
Comparison of serum hepatitis B surface antigen (HBsAg) and serum anticore with tissue HBsAg and hepatitis B core antigen (HBcAg)
Gastroenterology
(1978) - et al.
Global control of hepatitis B virus infection
Lancet Infect Dis
(2002) - et al.
Hepatocellular carcinoma and hepatitis B virus. A prospective study of 22,707 men in Taiwan
Lancet
(1981) - et al.
Geographic distribution of hepatitis B virus (HBV) genotype in patients with chronic HBV infection in Japan
Hepatology
(2001) - et al.
Viral genotype and hepatitis B virus DNA levels are correlated with histological liver damage in HBeAg-negative chronic hepatitis B virus infection
Am J Gastroenterol
(2002) - et al.
Hepatitis B genotypes correlate with clinical outcomes in patients with chronic hepatitis B
Gastroenterology
(2000) - et al.
X-gene product antagonizes the p53-mediated inhibition of hepatitis B virus replication through regulation of the pregenomic/core promoter
J Biol Chem
(1995) Pathogenesis of hepatitis B virus-related hepatocellular carcinoma: old and new paradigms
Gastroenterology
(2004)- et al.
Naturally occurring variants of hepatitis B virus
Adv Virus Res
(1999) - et al.
Basal core promoter mutations of hepatitis B virus increase the risk of hepatocellular carcinoma in hepatitis B carriers
Gastroenterology
(2003)