Human papillomavirus types 6 and 16 in cooperation with Ha-ras transform secondary rat embryo fibroblasts

Using a focus assay we have shown that the entire human papillomavirus type 16 (HPV-16) genome is capable of cooperating with an activated ras oncogene to transform secondary rat embryo fibroblast (REF) cells as indicated by focus formation of unselected cells. However, this assay failed to detect any similar activity with either the whole HPV-6 genome or with subgenomic fragments. In contrast, transformed colonies appeared when G418 (geneticin)-resistant colonies were selected after cotransfection with activated ras DNA and either the entire HPV-6 genome or subgenomic fragments containing the E6/E7 open reading frames (ORFs) of HPV-6 or HPV-16. The transformation assessment was based on the development of a ras-transformed appearance in G418-resistant colonies. The appearance of this morphology did not imply the ability of transformed cells to produce colonies in semi-solid agarose (anchorage-independent growth), and extended culture for about 10 to 20 population doublings was necessary before transfected cells exhibited anchorage-independent growth. Transformation of REF cells was not observed with the E5 ORF of HPV-16 under the control of an exogenous promoter (the long terminal repeat of Rous sarcoma virus) in cooperation with activated ras DNA. No transformation was observed using an activated myc oncogene with either HPV-6 or HPV-16 DNA.