Incomplete transformation of rat cells by a small fragment of adenovirus 12 DNA

Rat cells (3Y1) were transformed by the Bpa-H fragment (4.5%, the left end) of adenovirus 12 (Ad 12) DNA, cloned, and transformed cell lines (HY1 to HY7 cells) were established. Most of the sequence of the BpaI-H fragment of Ad 12 DNA was present in HY1 and HY2 cells. The properties of HY (HY1, HY2, HY7), GY1 (a rat cell line transformed by the HindIII-G fragment of Ad 12 DNA), CY1 (a rat cell line transformed by the EcoRI-C fragment), and WY3 (a rat cell line transformed by the whole Ad 12 DNA) cells were examined. The morphology and the growth in Eagle's minimal essential medium with 10% fetal calf serum of HY1, HY5, and HY7 cells were similar of CY1 cells, showing the transformed phenotype. However, the following properties of HY1, HY5, and HY7 cells were intermediate between transformed and untransformed cells: (1) the growth in Eagle's medium with 2% fetal calf serum; (2) the colony formation in soft agar culture; (3) cellular DNA synthesis in Methocel medium; (4) the tumor growth after transplantation of HY1, HY2, and HY7 cells into rats. Ad 12 T antigens were not detected in HY cells by immunofluorescence. Viral antigen could not be detected in the HY cell extract by complement fixation test. These results indicate that HY cells are incomplete in the transformed phenotype. The significance of incomplete transformation is discussed.