A 12-O-Tetradecanoylphorbol-13-Acetate (TPA)-Nonproliferative Variant of 3T3 Cells Is Resistant to TPA-Enhanced Gene Amplification

Barsoum and Varshavsky (Proc. Natl. Acad. Sci. U.S.A. 80:5330-5334, 1983) suggest that polypeptide mitogens and the mitogenic tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulate gene amplification by related pathways. I demonstrated that TPA and the polypeptide mitogen fibroblast growth factor (FGF) both increase the frequency of cadmium-resistant variants of Swiss-Webster 3T3 cells. The molecular basis for this phenomenon is the amplification of the metallothionein gene(s). To further characterize the relationship between mitogenesis and gene amplification, I examined the ability of TPA and FGF to increase the frequency of cadmium-resistant colonies in the 3T3 variant cell line 3T3-TNR9. Unlike 3T3 cells, 3T3-TNR9 cells cannot be stimulated by TPA to divide (E. Butler-Gralla and H. R. Herschman, J. Cell. Physiol. 107:59-68, 1981). TPA does not induce an increase in cadmium-resistant colonies of the TPA-nonproliferative 3T3-TNR9, variant, in contrast to its efficacy on 3T3 cells. FGF, a potent mitogen for 3T3-TNR9 cells as well as 3T3 cells, is equally effective for 3T3-TNR9 and 3T3 cells in inducing cadmium-resistant colonies. These data suggest that the pathways of TPA-induced gene amplification and TPA-stimulated mitogenesis share a common step(s). TPA caused transient inhibition of DNA synthesis in both dividing 3T3 and 3T3-TNR9 cells, suggesting that this latter response to TPA is not sufficient to enhance gene amplification.