Woodchuck hepatitis virus enhancer I and enhancer II are both involved in N-myc2 activation in woodchuck liver tumors.
Direct activation of the N-myc2 oncogene by insertion of woodchuck hepatitis virus (WHV) DNA is a major oncogenic step in woodchuck hepatocarcinogenesis. We previously reported that WHV enhancer II (We2), which controls expression of the core/pregenome RNA, can also activate the N-myc2 promoter in hepatoma cell lines. To better define the integrated WHV regulatory sequences responsible for N-myc2 promoter activation in woodchuck liver tumors, we analyzed the structure and enhancer activity of a single viral integrant found at the win locus in tumor 2260T1 and mapping approximately 175 kb 3' of N-myc2. This viral insert was made of 11 concatemerized WHV fragments, 5 of which overlapped with We2 sequences and 1 with WHV sequence homologous to that of hepatitis B virus enhancer I (We1). In transient transfection assays in hepatoma-derived cells, the We2 activator was found to be fully effective only when inserted in close proximity to the N-myc2 promoter whereas the We1 element by itself was apparently devoid of activity. In contrast, the 2260T1 viral insert exhibited a potent enhancer capacity that depended both on multimerized We2 and on We1 sequences. In a survey of different woodchuck hepatomas, both elements were commonly found within integrated viral sequences involved in long-range N-myc2 activation.
Flajolet
M
M
Unité de Recombinaison et Expression Génétique, INSERM U163, Institut Pasteur, 75724 Paris Cedex 15, France.
Tiollais
P
P
Buendia
M A
MA
Fourel
G
G
D000818:Animals; D004742:Enhancer Elements, Genetic; D015972:Gene Expression Regulation, Neoplastic; D016259:Genes, myc; D017919:Hepatitis B Virus, Woodchuck / Q000235:genetics*; D008113:Liver Neoplasms / Q000235:genetics*; D008392:Marmota