Regulation of growth inhibitory activity in transformed mouse embryo fibroblasts

Abstract

Treatment of the transformed mouse embryo fibroblast cell line AKR-MCA with 1% N, N-dimethylformamide (DMF) resulted in the restoration of a nontransformed phenotype in these cells. In order to determine if an increase in growth inhibitory peptides might be responsible for these changes in growth properties of the DMF-treated AKR-MCA cells we examined the serum-free conditioned medium for its ability to inhibit the anchorage-independent growth of a human colon carcinoma cell line. The extracellular levels of inhibitory activity were two-fold higher in conditioned medium derived from AKR-MCA cells than in AKR-MCA cells grown in 1% DMF (AKR-MCA/DMF). Fractionation of the crude conditioned medium indicated the presence of an M r 20,000 inhibitory fraction in AKR-MCA/DMF conditioned medium which was reduced in AKR-MCA cells. This M r, 20,000 inhibitory activity was acid and heat stable and sensitive to dithiothreitol and trypsin. In addition to inhibiting the growth of a human colon carcinoma cell line this protein induced colony formation in AKR-2B cells and competed for binding to the transforming growth factor β (TGF-β) receptor. Therefore, this M r, 20,000 inhibitory polypeptide induced by DMF is probably TGF-β. TGF-β was also shown to inhibit the growth of AKR-MCA cells in monolayer culture.