Adhesion-promoting factor from embryonic fibroblasts for normal liver epithelial cells.

In the present study we show that adhesion of normal rat liver epithelial cells (RL34) to substratum coated with type I collagen (collagen substratum) is promoted by a factor involved in 80% ammonium sulfate precipitated proteins from serum-free conditioned medium (PCM) of rat embryo fibroblasts. Adhesion of RL34 cells to collagen substratum was promoted dose dependently by whole PCM and the maximum effects on adhesion could be achieved by 200 micrograms/ml whole PCM. Kinetics studies with 100 micrograms/ml whole PCM showed that adhesion proceeded very slowly, taking 16 h to reach a plateau. Adhesion-promoting activity in whole PCM was sensitive to treatments with trypsin, acid, and heat but stable to dithiothreitol treatment. Further purification of whole PCM was performed using a combination of chromatography on blue Sepharose column, gel filtration column and heparin Sepharose column. The partially purified proteins, referred to as heparin PCM, are not bound or only weakly bound to heparin under physiological ion strength and pH, and the apparent molecular weight (Mr) range is estimated to be 40,000 to 60,000 from gel filtration chromatography and SDS-polyacrylamide gel electrophoresis. When whole PCM or heparin PCM was used for coating on plastic or collagen substratum, they no longer exerted the promoting activity.