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; however, this is occurring in a background of other mutation-generated events. To determine the significance of the TGF-alpha circuit alone, we expressed the human TGF-alpha cDNA in a diploid human foreskin fibroblast strain, 7-25, under the control of the cytomegalovirus immediate early promoter-enhancer region and screened transfectants for TGF-alpha expression by Northern analysis and by immunoprecipitation. Partially processed forms (M(r) 24,000 and 20,000) of the recombinant TGF-alpha were observed in cell lysates and a M(r) 5500 fully processed form was secreted by the fibroblasts into the media. TGF-alpha-expressing clones showed an altered morphology and an increased saturation density (1.4- to 2.1-fold) but did not exhibit anchor-age-dependent 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 these 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 strongly transform these cells is not due to low EGF receptor levels. These data suggest that cell type plays an important role in determining the transforming ability of TGF-alpha.