The effects of serum and phorbol ester tumor promoter on ornithine decarboxylase activity in Swiss 3T3 cells.

Addition of the tumor promotor 12-O-tetradecanoyl phorbol-13-acetate (TPA) to serum-deprived mouse 3T3 cells resulted in an increase in ornithine decarboxylase activity which is maximal at 3 h and declined thereafter. Addition of serum to these same cells resulted in an ornithine decarboxylase (ODC) response which was identical to the TPA-induced response at 3 h but continued to increase to a maximum at 6 h. A variant line of 3T3 cells, which possessed phorbol ester receptors, failed to increase its ODC in response to TPA. Also, the early component of the serum-induced ODC response was markedly diminished. These data suggest that phorbol ester tumor promoters may induce an early component of a more extensive ODC response, and that a component of serum may act through the same pathway as the phorbol esters.