Anchorage‐independent growth of primary rat embryo cells is induced by platelet‐derived growth factor and inhibited by type‐beta transforming growth factor

Abstract

Several growth factors implicated in the process of cellular transformation were tested for their ability to induce anchorage‐independent (AI) growth of primary rat embryo (RE) cells. Our results show that in the presence of 10% calf serum, platelet‐derived growth factor (PDGF), 1–30 ng/ml, has the strongest effect of all growth factors tested on Al growth. Type‐β transforming growth factor (TGF‐β), by itself, does not stimulate Al growth, and it inhibits the PDGF‐induced colony formation in a dose‐dependent manner (ED₅₀ ∼ 0.03 ng/ml). Qualitatively similar responses are obtained by using an established line of fibroblasts, NIH 3T3 cells; the principal difference between the response of the primary cells and the established cell line is in colony‐forming efficiency in soft agar culture (15% and 90%, respectively, for growth of colonies > 1,500 μm² diameter in the presence of 10 ng/ml PDGF). Since Al growth has been shown to correlate well with tumorigenicity in vivo, our results suggest that the transforming potential of PDGF in an appropriate responsive cell can be controlled not only through its interaction with its own receptor, but also by the presence of inhibitory factors such as TGF‐β.