Unusual activation of the integrated preS1 promoter of woodchuck hepatitis virus in a liver tumour

Abstract

We have analysed abnormal virus RNAs produced from integrated woodchuck hepatitis virus (WHV) sequences in two woodchuck liver tumours. Analysis of cDNA clones revealed that these transcripts consisted of rearranged, virus-specific RNAs encoding the WHV surface antigens. In one tumour, transcription was driven by the major preS2/S promoter and terminated at a cryptic poly(A) signal in the 5' end of the P gene, giving rise to a truncated version of the normal viral S message. In contrast, the integrated preS2/S promoter remained silent in the second tumour. The start sites of two abundant WHV transcripts encoding the large and middle surface proteins were localized about 100 bp upstream and 300 bp downstream of the preS1 translation initiation codon, corresponding to minor start sites of the normal surface protein mRNAs in chronically infected liver. Thus, the preS1 promoter, a weak promoter in episomal replicative forms of the virus, was activated in the integrated state in this tumour. Our results indicate that alternative usage of the preS1 or the preS2/S promoter in the integrated state may yield differential production of the three virus surface proteins in woodchuck liver tumours.