Isolation and Characterization of ras‐Transfected BALB/3T3 Clone Showing Morphological Transformation by 12‐O‐Tetradecanoyl‐phorbol‐13‐acetate

The transformation frequency of mouse BALB/3T3 cells was significantly enhanced after transfection with an activated ras oncogene (v‐Ha‐ras) followed by treatment with a tumor promoter, 12‐O‐tetradecanoyl‐phorbol‐13‐acetate (TPA), suggesting that the ras oncogene acted as an initiator in two‐stage carcinogenesis. A cell clone (Bhas42) containing the ras oncogene was isolated from the ras‐transfected BALB/3T3 cells. Bhas42 cells were flat and showed contact inhibition, but the addition of TPA to quiescent Bhas42 cultures resulted in a dramatic change of cell morphology to spindle shape, doubling of the cell population, and increased DNA synthesis.