ABSTRACT
The role of transforming growth factors in transformation has been difficult to assess because transformed cells produce in culture a number of factors that interact in complex ways. Furthermore, it remained unclear whether induction of transformation is a specific property of the transforming growth factors, or whether constitutive production of any other mitogen by cells is sufficient to induce transformation. It is well known that the epithelial surfaces of the body, such as in the alimentary tract, are the sites of constant cell renewal. Work from Gregory’s laboratory demonstrated the identity of human epidermal growth factor (EGF) and urogastrone, a hormone able to inhibit gastric acid secretion, and also provided the primary amino acid sequence of the human form of this growth factor. Early observations showed that some retrovirally transformed fibroblasts displayed a strongly reduced number of EGF-binding sites at their surface. Neoplastic transformation of cells by carcinogens also results in the elaboration of growth factors.
