Reduced transcription and progeny virus production of hepatitis B virus containing an 8-bp deletion in basic core promoter

We have demonstrated previously the presence of an 8-bp deletion mutant, sp anning from nt. 1768 to nt. 1775 in the basic core promoter region of hepat itis B virus (HBV) in patients with anti-HBe positive asymptomatic phase be fore developing acute exacerbation after immunosuppressive treatment. The t ranscription and progeny virus production activities of the mutant were exa mined by transfection of the recombinant plasmid [pUC De1(2)] containing th e head-to-tail dimer DNA of the mutant into HepG2 cells. The amounts of hep atitis B surface antigen (HBsAg) and HBe antigens secreted into the culture medium were markedly reduced. Southern blotting of DNAs extracted from the culture medium also showed reduced mutant activity to produce progeny viru s. Northern blotting and RNase protection assay of RNAs extracted from tran sfected cells demonstrated that the transcription of both precore mRNA and pregenome RNA was reduced significantly compared to that of wild-type HBV. The promoter activity examined by transfection of the CAT plasmid containin g deletion mutant DNA was much lower than that of wild type. Cotransfection experiments, however, of the CAT plasmid containing wild-type DNA with pUC De1(2) reduced CAT activity induced by wildtype, suggesting that truncated X protein produced by the mutant does not possess a sufficient transactiva ting activity. Gel shift assay using HepG2 nuclear extract and a probe cont aining four TA-rich regions in CP and various competitors suggested that th e lack of the third TA-rich region was responsible for the transcription re duction of precore mRNA and pregenome RNA. The possible mechanisms are disc ussed. J. Med. Virol. 61:15-22, 2000. (C) 2000 Wiley-Liss, Inc.