Transcriptional regulation of proto-oncogene expression by epidermal growth factor, transforming growth factor beta 1, and triiodothyronine in MDA-468 cells.

We have examined the epidermal growth factor (EGF) dependence of the transcription of different proto-oncogenes, using cultured human mammary carcinoma MDA-468 cells and a nuclear run-on transcription assay. We found that the stimulation of MDA-468 cells with EGF regulates moderately and to different extents the transcription of the EGF-receptor(R) and c-erbB-2 proto-oncogenes. In contrast, the transcription of other proto-oncogenes, including c-myc, c-H-ras, and c-fps, was unchanged. Furthermore, we provide evidence that transforming growth factor beta 1 (TGF-beta 1) selectively and to different degrees modulates the EGF-dependent transcription of EGF-R and c-erbB-2 genes. In this study, we also discovered that T3 (triiodothyronine) exerts synergistic control on the action of EGF alone or in association with TGF-beta 1, on EGF-R and c-erbB-2 gene transcription. Moreover, we established that within 6 h after the addition of EGF, cytoplasmic EGF-R mRNA levels are increased several-fold and that this accumulation is enhanced by the presence of TGF-beta 1 and/or T3. The results described here are consistent with the hypothesis that a complex program of cooperative interactions among EGF-, TGF-beta 1-, and T3-generated signals at the transcriptional level may mediate, at least in part, the combined actions of EGF, TGF-beta 1, and T3 in target cells.