Tumor promoters increase the synthesis of a 32,000-dalton protein in BALB/c 3T3 cells.

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Abstract
The effect of 12-O-tetradecanoylphorbol 13-acetate (TPA), a potent tumor promoter, on the synthesis of proteins in BALB/c 3T3 mouse fibroblasts was studied. When [35S]methionine-labeled proteins synthesized after the addition of TPA were analyzed by 1- or 2-dimensional polyacrylamide gel electrophoresis, the increased synthesis of a 32,000-dalton protein (designated p32) was noted as one of the earliest changes. The synthesis of p32 increased approximately 2-fold witin 2 h at a promoter concentration of 20 ng/ml. Phorbol 12, 13-didecanoate, another potent tumor promoter, showed the same effect as TPA whereas 4-O-methyl-TPA, which has little promoting activity, did not enhance the synthesis of p32 at the same concentration but did effect a slight increase at 1 .mu.g/ml. p32 differed immunologically from a major excreted protein discovered by Gottesman. The increased rate of the synthesis of p32 was considered to be regulated at the transcriptional level because the increase in synthesis of p32 was inhibited by actinomycin D, and TPA-treated cells contained a higher level of translatable mRNA coding for p32 than did control cells. A possible relationship between the increase in p32 synthesis and transformation is discussed.