Growth inhibitory factor diffusing from chick embryo fibroblasts

Density-dependent inhibition (DDI) of growth is assumed to be the result of diffusion in the medium of growth inhibitory molecules. In this work, we demonstrate the presence of inhibitory molecules (IDFc: chicken inhibitory diffusible factor) in the medium of chick embryo fibroblasts (CEF) cultures. IDFc partially purified by Bio-Gel P150 chromatography followed by reverse phase FPLC. The dose-response curve showed that 250 ng/ml IDFc inhibited 50% DNA synthesis. IDFc was also able to inhibit the growth of sparse cultures of CEF; this inhibition was reversible. IDFc was unable to prevent the DNA synthesis in cells transformed by v-src gene expression. These results suggest that IDFc is involved in the DDI of CEF growth.