The E7 open reading frame of human papillomavirus type 16 encodes a transforming gene

Prior analysis of bovine papillomavirus has identified two genes, E5 and E6, which induce morphologic transformation of certain established cells. To study the transforming genes of human papillomavirus (HPV) type 16, the HPV type most commonly associated with cervical carcinoma, we examined subgenomic viral DNAs under control of a retroviral long terminal repeat for their capacity to induce cellular transformation of NIH 3T3 cells. Plasmids carrying the entire viral early region, the E6 and E7 (E6/E7) open reading frames (ORFs), or the E2,E4, and E5 (E2-E5) ORFs induced a very low frequency of focal transformation (0.4-1.7 ffu/micrograms DNA). In contrast, the plasmids with the entire early region of E6/E7, when selected by co-transfection with a transformation independent marker (neoR), induced anchorage independent growth with high efficiency. Cells selected after co-transfection with the marker gene and the E2-E5 plasmid grew much less efficiently in agar. Mutational analysis of the E6/E7 plasmid indicated that E7 was the gene primarily responsible for inducing anchorage independent growth. E7 gene therefore represents a third class of PV transforming gene. These results correlate with E7 (along with E6) being selectively retained and expressed in HPV associated cervical carcinomas and cell lines.