Tumour promoter induces proliferation of 3T6 cells in serum-free medium, as do polypeptide growth factors

The potent tumour promoter agent 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induces multiple rounds of 3T6 cell replication in completely serum-free medium. The maximal effect is elicited at 100 ng/ml, is further enhanced by adding insulin, and is comparable to that of the polypeptide's epidermal growth factor (EGF), insulin, and fibroblast-derived growth factor. The results support the proposition that TPA acts as a mitogen via mechanisms akin to those used by polypeptide growth factors.