Transforming growth factor-a expression is enhanced in human mammary epithelial cells transformed by an activated c-Ha-ras protooncogene but not by the c-neu protooncogene, and overexpression of the transforming growth factor-a complementary DNA leads to

MCF-1OA cells are a spontaneously immortalized nor-mal human mammary epithelial cell line. MCF-1OA cells were transfected with two expression vector plas-mids containing either a human point-mutated c-Ha-ras protooncogene or the rat c-neu protooncogene. c-Ha-ras-transfected MCE-1OA cells grow as colonies in soft agar, exhibit a 3- to 4-fold increase in their growth rate in serum-free medium, and show a reduced mitogenic response to exogenous epidermal growth factor ([GE) or transforming growth factor-a (TGFa) as compared to MCF-1OA cells. c-Ha-ras-transfected MCF-1OA cells ex-press a 4- to 8-fold increase in TGFa mRNA levels and secrete 4- to 6-fold more TGFa protein as compared to MCF-1OA cells. Addition of either an anti-TGFa neu