Requirement of conditioned medium or a high concentration of serum for anchorage-independent growth of adenovirus type 12 E1a-transformed rat cells (HY1).

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Abstract
Adenovirus type 12 (Ad12) Ela-transformed rat cells (HY1) grew in methocel medium containing 9% fetal calf serum (FCS), but the frequency of colony formation was very low (the order of 10-4). The addition of conditioned medium or a high concentration of serum (20% FCS) to the methocel medium accelerated colony formation, and plating efficiency increased 10- to 100-fold. In contrast, in stationary culture, HY1 cells grew well even in 1%-FCS medium. These results indicate that HY1 cells require high concentrations of growth factors for anchorage-independent growth. The effects of conditioned medium or FCS also were demonstrated in several transformed cell lines induced by transfection of combined sets of Ad12-transforming genes (E1a, E1b and E4). These growth behaviors suggest that the first step in cell transformation with adenovirus 12 is the acquisition of responsiveness to growth factors in methocel culture, which must be the function of the Ad12-E1a gene products. The function of the other two Ad12-transforming genes was discussed.