Polyoma virus transformation of rat kidney fibroblasts results in loss of requirement for insulin and retinoic acid.

Cloned cells of the rat kidney fibroblast line designated NRK-49F, which requires epidermal growth factor (EGF), fibronectin, insulin, and retinoic acid for rapid multiplication in serum-free culture, were transformed by polyoma virus. Cells from two independent transformation events were isolated and cloned, as were cells from two corresponding control untransformed cultures not treated with virus. Tests in serum-free culture showed that the two transformed subclones required EGF and fibronectin but not insulin or retinoic acid for rapid multiplication, whereas the two control subclones retained the requirements for all four factors. Although EGF at 10 to 50 ng/ml stimulated the multiplication of all four subclones, EGF at 500 ng/ml strongly inhibited multiplication of the two transformed subclones but not the two control subclones.