Normal human fibroblasts immortalized by introduction of human papillomavirus type 16 (HPV-16) E6-E7 genes

This report demonstrates that normal human fibroblasts can be immortalized by the introduction of HPV-16 E6-E7 genes. We designed zinc-inducible expression plasmids with HPV-16 E6, E7 or both. Each plasmid was introduced into normal human fibroblasts (TIG-3 cells) using lipofection methods. Only transfectants with the HPV-16 E6-E7 zinc-inducible expression plasmid, which were cultured in medium supplemented with 100 microM ZnSO4, overcame crisis and could be cultured over 200 population doubling levels (PDLs). These cell lines showed the reactivation of telomerase after crisis, and morphological alterations were also observed.