Transforming but not immortalizing oncogenes activate the transcription factor PEA1

The transcription factor PEA1 (a homologue of AP1 and c‐jun) is highly active in several fibroblast cell lines, compared to its low activity in a myeloma and an embryo‐carcinoma (EC) cell line. Serum components are essential to attain these high levels of PEA1 activity in fibroblasts. This serum requirement is abrogated by transformation with the oncogenes c‐Ha‐ras, v‐src and polyoma middle T (Py‐MT) but not by immortalization with polyoma large T (Py‐LT), v‐myc, c‐myc or SV40 large T (SV40T). Expression in myeloma cells of the same transforming oncogenes, as well as v‐mos and c‐fos, activates PEA1, whereas expression of the same immortalizing oncogenes and EIA does not. These results suggest that a common target for transforming oncogenes is PEA1. Serum components have no effect on PEA1 activity in the myeloma and EC cell lines. In contrast, retinoic acid treatment of F9 EC cells augments PEA1 activity. These results suggest that transforming oncogene expression compensates for the absence of cell type‐specific factors which are required to activate PEA1. Activation of PEA1 may lead to altered transcription of a set of transformation‐related genes.