Growth Dependence of Human Papillomavirus 16 DNA‐positive Cervical Cancer Cell Lines and Human Papillomavirus 16‐Transformed Human and Rat Cells on the Viral Oncoproteins

The dependence on human papillomavirus (HPV) Oncoproteins of the growth of cervical cancer cell lines [C4‐1, HeLa (both containing HPV 18 DNA), CaSki and SiHa (both containing HPV 16 DNA)], HPV 16‐transformed human embryonic kidney cells, and HPV 16‐transformed rat brain and 3Y1 cells was examined by using antisense RNA approaches. The cells were transfected with plasmids expressing RNA antisense to the HPV 16 or 18 open reading frames E6E7, together with plasmids expressing the hygromycin B resistance gene, and drug‐resistant colonies were scored three weeks later. In all the human cell lines, the efficiency of colony formation was lowered by RNA antisense to the resident HPV type. Some of the rat cell lines responded to the antisense plasmids, but some did not. From a nonresponding rat tumor line (3Y1HP‐1T), cell clones with various levels of E7 protein were isolated after transaction with the antisense plasmid, and were examined for anchorageindependent growth in soft agar. The colonies formed by the clones with lower E7 levels tended to be smaller and fewer than those formed by the clones with higher E7 levels. These findings strongly suggest that some of the transformed or cancer phenotypes of cells in vitro are dependent, even after extensive passages and malignant changes, on expression of the oncoproteins of the resident HPV.