TRANSFORMING GROWTH FACTOR-ALPHA EXPRESSION PRODUCES ONLY MORPHOLOGICAL TRANSFORMANTS OF DIPLOID HUMAN FIBROBLASTS

Transforming growth factor-alpha (TGF-alpha) is a potent mitogen for a variety of epithelial and mesenchymal cells and is commonly expressed in many human tumors and tumor cell lines. Frequently, this creates a potential autocrine circuit for growth stimulation in these cells; ho wever, this is occurring in a background of other mutation-generated e vents. To determine the significance of the TGF-alpha circuit alone, w e expressed the human TGF-alpha cDNA in a diploid human foreskin fibro blast strain, 7-25, under the control of the cytomegalovirus immediate early promoter-enhancer region and screened transfectants for TGF-alp ha expression by Northern analysis and by immunoprecipitation. Partial ly processed forms (M(r) 24,000 and 20,000) of the recombinant TGF-alp ha were observed in cell lysates and a Mr 5500 fully processed form wa s secreted by the fibroblasts into the media. TGF-alpha-expressing clo nes showed an altered morphology and an increased saturation density ( 1.4- to 2.1-fold) but did not exhibit anchorage-independent growth in soft agarose or the ability to form tumors in nude mice. Additionally, expression of recombinant TGF-alpha did not extend the lifespan of th ese fibroblast clones. Scatchard analysis revealed approximately 10(5) epidermal growth factor (EGF) receptors on the surface of these human fibroblasts, indicating that the failure of TGF-alpha expression to s trongly transform these cells is not due to low EGF receptor levels. T hese data suggest that cell type plays an important role in determinin g the transforming ability of TGF-alpha.