Sarcoma growth factor and other transforming peptides produced by human cells: interactions with membrane receptors

Transforming growth factors (TGFs) stimulate cells to divide in monolayer cultures and to form colonies that grow progressively in soft agar. TGFs are a family of polypeptide hormones that, in vitro, confer on fibroblasts and epithelial cells properties associated with the transformed phenotype. They have been isolated from the supernatant fluids of several human and animal carcinoma and sarcoma cells. TGFs interact with epidermal growth factor (EGF) membrane receptors. They are not detectable in culture fluids from cells that contain high numbers of free EGF cell membrane receptors. One TGF is sarcoma growth factor (SGF), which is released by murine sarcoma virus-transformed cells. Studies have shown EGF and SGF to be two distinct growth factors despite the fact that SGF exerts its effects by specifically interacting with EGF receptors. Addition of SGF to normal indicator cells results in expression of the transformed phenotype. The effects of SGF are reversible; the cells resume their normal growth pattern when the growth factor is removed. Three different human tumor cell lines in culture, a rhabdomyosarcoma, a bronchogenic carcinoma, and a metastatic melanoma, release TGFs that also confer the transformed phenotype on normal fibroblasts. One would expect that, as research into this area continues, new TGFs and their interaction with different specific cell membrane receptors will be described.