Rat primary embryo fibroblast cells suppress transformation by the E6 and E7 genes of human papillomavirus type 16 in somatic hybrid cells.

The E6 and E7 genes of human papillomavirus type 16 (HPV-16) transform established lines of rat cells but not rat cells in primary culture irrespective of the expression of the two genes. The reason for this difference between the susceptibilities of cell lines and primary cells was examined by using hybrid cells obtained by somatic cell fusion of rat cell lines transformed by the E6 and E7 genes of HPV-16 and freshly isolated rat embryo fibroblast cells. In these hybrid cells, transformed phenotypes, including colony formation in soft agar, saturation density, and tumorigenicity in nude mice, were suppressed, whereas hybrid cells between E6/E7-transformed cell lines and normal rat cell lines retained these transformed phenotypes. RNA analysis showed that the E6 and E7 genes were transcribed in both types of hybrid cells. These results suggest that primary rat cells possess intracellular functions that cause posttranscriptional suppression of induction of the transformed phenotypes by the E6 and E7 genes of HPV-16.