The effect of the G1888A mutation of subgenotype A1 of hepatitis B virus on the translation of the core protein.

A distinctive characteristic of subgenotype A1 of hepatitis B virus is G1888A in the precore region. This transition introduces an out-of-frame AUG, creating an overlapping upstream open reading frame (uORF), terminating five nucleotides downstream from the core AUG. This uORF can potentially be translated into a seven amino acid peptide. In addition to stabilizing the encapsidation signal by forming a base pair with T1871, this mutation may affect translation of the core protein. The aim of this study was to use reporter constructs to determine whether G1888A had any modulating effect on core protein translation. The complete core gene with part of the precore of subgenotype A1 was cloned into the amino terminal of a green fluorescent protein (GFP) plasmid. Core/GFP fusion protein expression was measured using flow cytometry following transfection of Huh 7 cells. The introduction of uORF resulted in an 18.75% reduction of core gene expression. When the suboptimal Kozak sequence of the 1888 AUG was replaced with an optimal one, this reduction was enhanced (64.84%). By increasing the distance between the stop of the overlapping uORF and the core AUG, by a minimum of 15 nucleotides, core/GFP expression was almost doubled, indicating that stalling of ribosomes at the stop of the uORF may be interfering with initiation at the core AUG through steric hindrance. Our findings indicate that the G1888A mutation, may interfere with initiation at the downstream 1901 core AUG, decreasing core protein translation. This decrease may account for the relatively low viral loads seen in individuals infected with subgenotype A1.

249ser p53 mutation in the serum of black southern African patients with hepatocellular carcinoma.

BACKGROUND AND AIMS: A specific mutation at codon 249 of the p53 tumor suppressor gene (guanine to thymine; arginine to serine [249(serine)p53]) is present in the cell-free plasma of 30-47% of patients with hepatocellular carcinoma (HCC) in regions with uniformly high levels of dietary exposure to the fungal toxin, aflatoxin B(1). No information is available from other regions. We therefore examined cell-free serum from HCC patients in southern Africa, where aflatoxin B(1) exposure ranges from very high to low levels. METHODS: DNA extracted from the serum of 158 black African patients with HCC was amplified by the polymerase chain reaction assay using primers specific for exon 7 of the p53 gene, and submitted to endonuclease cleavage with HaeIII to identify the 249(serine)p53 mutation. The presence of the mutation was confirmed by nucleotide sequencing. RESULTS: The specific mutation was detected in 18% of the patients, giving an odds ratio for HCC in those with the mutation of 13.3 (95% confidence limits 1.8; 100.2). Surprisingly, the mutation was present equally often in rural and urban patients, despite presumed levels of aflatoxin B(1) exposure in the latter being much lower. No correlation was found with the presence of hepatitis B virus infection or the age, sex or tribe of the patients. CONCLUSIONS: The 249(serine)p53 mutation is found less often in the serum of patients with HCC in a region with variable levels of exposure to aflatoxin B(1) than in those with uniformly high levels of exposure, but the mutation does occur in black Africans with presumed lower levels of exposure to the fungal toxin.

Integration of hepatitis B virus DNA into chromosomal DNA during acute hepatitis B.

AIM: To examine the serum from black African patients with acute hepatitis B to ascertain if integrants of viral DNA can be detected in fragments of cellular DNA leaking from damaged hepatocytes into the circulation. METHODS: DNA was extracted from the sera of five patients with uncomplicated acute hepatitis B and one with fulminant disease. Two subgenomic PCRs designed to amplify the complete genome of HBV were used and the resulting amplicons were cloned and sequenced. RESULTS: HBV and chromosomal DNA were amplified from the sera of all the patients. In one patient with uncomplicated disease, HBV DNA was integrated into host chromosome 7 q11.23 in the WBSCR1 gene. The viral DNA comprised 200 nucleotides covering the S and X genes in opposite orientation, with a 1 169 nucleotide deletion. The right virus/host junction was situated at nucleotide 1,774 in the cohesive overlap region of the viral genome, at a preferred topoisomerase I cleavage motif. The chromosomal DNA was not rearranged. The patient made a full recovery and seroconverted to anti-HBs- and anti-HBe-positivity. Neither HBV nor chromosomal DNA could be amplified from his serum at that time. CONCLUSION: Integration of viral DNA into chromosomal DNA may occur rarely during acute hepatitis B and, with clonal propagation of the integrant, might play a role in hepatocarcinogenesis.

Distinctive sequence characteristics of subgenotype A1 isolates of hepatitis B virus from South Africa.

Phylogenetic analysis of hepatitis B virus (HBV) has led to its classification into eight genotypes, A to H. The dominant genotype in South Africa is genotype A, which consists of two subgenotypes, A1 and A2. Subgenotype A1 (previously subgroup A') predominates over subgenotype A2 (previously subgroup A minus A'). The complete genome of HBV isolated from 18 asymptomatic carriers of the virus and five acute hepatitis B patients was amplified; the resulting amplicons were cloned and sequenced. All acute hepatitis isolates belonged to subgenotype A1 and had no distinguishing mutations relative to the isolates from asymptomatic carriers, which had a distribution of ten subgenotype A1, two subgenotype A2 and six genotype D. The presence of the previously described amino acid residues that distinguish subgenotype A1 (subgroup A') from the remainder of genotype A in the S and polymerase genes was confirmed. Moreover, the large number of subgenotype A1 isolates sequenced allowed identification in the other open reading frames of additional nucleotide and amino acid changes that are characteristic of subgenotype A1. In particular, nucleotide mutations at positions 1809-1812 that alter the Kozak sequence of the precore/core open reading frame, and A(1888) in the precore region, were found exclusively in subgenotype A1 isolates. Unique sequence alterations of the transcriptional regulatory elements were also found in subgenotype A1 isolates. The mean nucleotide divergence of subgenotype A1 was greater than that of subgenotype A2, suggesting that this subgenotype has been endemic for a longer time in the South African black population than had subgenotype A2.