CELLULAR AND VIRAL TRANS-ACTING FACTORS MODULATE N-MYC2 PROMOTER ACTIVITY IN WOODCHUCK LIVER-TUMORS

Activation of the N-myc2 oncogene by integration of woodchuck hepatiti s virus (WHV) DNA is a central event in woodchuck liver oncogenesis, I n this study, we have evaluated the influence of several cellular and viral tr ans-acting factors and mediators of inflammation on N-myc2 pr omoter activity in hepatoma cell lines, Ets oncoproteins, including Et s1, Ets2 and PEA3 efficiently activated a chimeric N-myc2 promoter/luc iferase reporter gene, By electrophoretic mobility shift assays, we sh ow that Ets1 and Ets2 proteins can efficiently bind two consensus Ets sites located within a 59 bp sequence upstream of the N-myc2 transcrip tion start site, Site-directed mutagenesis of these Ets-binding motifs abolished transactivation of the N-myc2 promoter by Ets proteins, Add ition of interleukin-6 (IL-6) induced a weak but reproducible activati on of the N-myc2 promoter, while IL-1 was ineffective, We further show that the N-myc2 promoter can be transactivated by the hepadnavirus X protein, and that distal promoter sequences are required for both IL-6 and X responsiveness, Similar effects of these factors were observed in the context of the N-myc2 promoter activated by WHV cis-regulatory elements, In view of the high-level expression of the N-myc2 oncogene in most woodchuck liver tumors, the Ets oncoproteins, inflammation-ass ociated cytokine IL-6 and the viral X transactivator might play import ant roles in hepadnavirus-associated tumorigenesis.