Sequence variation upstream of precore translation initiation codon reduces hepatitis B virus e antigen production.
OBJECTIVE
Most South African hepatitis B virus strains harbor point mutations immediately upstream of the precore AUG codon. The aim of this study was to determine their effect on hepatitis B e antigen expression.


METHODS
The hepatitis B virus DNA sequence around the precore region was determined from sera of 45 black South Africans. The South African mutations were introduced into hepatitis B virus dimers of the same genotype, and hepatitis B e antigen was quantified from culture medium of transfected HepG2 or Huh7 cells.


RESULTS
The South African sequence changes were easily detectable in the acute, hepatitis B e antigen-positive phase of infection, suggesting that they were stable traits and were not selected by immune pressure. Triple mutations at the -5, -3, and -2 positions of the AUG codon severely impaired hepatitis B e antigen expression (P < 0.001). The frequent double mutation at the -5 and -2 positions moderately reduced hepatitis B e antigen levels (P < 0.001) to an extent comparable to that of the common core promoter mutations (1762(T)1764(A)). The presence of both South African and core promoter mutations diminished hepatitis B e antigen expression in an additive manner. It is interesting to note that the triple South African mutations enabled core protein translation from precore messenger RNA, which could rescue the replication defect of a hepatitis B virus genome with an ablated core gene.


CONCLUSIONS
We have identified a novel class of hepatitis B e antigen variants with reduced hepatitis B e antigen translation by a ribosomal leaky scanning mechanism. Reduction in hepatitis B e antigen expression may contribute to accelerated seroconversion from hepatitis B e antigen to its antibody in black South Africans infected with hepatitis B virus very early in life.
Liver Research Center, Rhode Island Hospital and Brown Medical School, 55 Claverick Street, Providence, RI 02903, USA.
Sang Hoon
SH
Ahn
Anna
A
Kramvis
Shigenobu
S
Kawai
Hans Christian
HC
Spangenberg
Jisu
J
Li
Gerald
G
Kimbi
Michael
M
Kew
Jack
J
Wands
Shuping
S
Tong
D000293:Adolescent; D000328:Adult; D001483:Base Sequence / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D018387:Codon, Initiator / Q000235:genetics*; D004279:DNA, Viral / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D016679:Genome, Viral; D006509:Hepatitis B / Q000235:genetics; D006513:Hepatitis B e Antigens / Q000096:biosynthesis* / Q000235:genetics*; D006801:Humans; D008297:Male; D017354:Point Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics*; D015534:Trans-Activators / Q000378:metabolism; D014758:Viral Core Proteins / Q000235:genetics*; D054334:Viral Regulatory and Accessory Proteins; D014779:Virus Replication / Q000235:genetics
D018387:Codon, Initiator; D004279:DNA, Viral; D006513:Hepatitis B e Antigens; D011498:Protein Precursors; D015534:Trans-Activators; D014758:Viral Core Proteins; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein