Lack of fibronectin‐binding plasma membrane proteins may explain defective pericellular matrix formation in transformed fibroblasts and fibrosarcoma cells

Affinity of iodinated fibronectin (Fn) and its defined proteolytic fragments to electrophoretically separated polypeptides of normal and malignant cells was studied in an overlay assay. Cellular 125 I‐Fn and a major 125 I‐Fn fragment (M r 120,000 ‐ 140,000), containing the cell‐binding site, revealed in fibroblasts M r 170,000, M r 140,000, and M r 47,000 Fn‐binding polypeptides of which the first two could also be found in the plasma membrane preparations. Binding of 125 I‐Fns to M r 170,000 and M r 140,000 polypeptides was inhibited by the synthetic peptide Arg‐Gly‐Asp‐Ser and to all 3 polypeptides by Fns and M r 120,000‐140,000 fibronectin fragment. Both fibrosarcoma cells and SV40‐virus‐transformed fibroblasts appeared to lack the M r 140,000 Fn‐binding polypeptide. Binding was similar when Fn from normal fibroblasts or fibrosarcoma cells was used in the assay, while plasma 125 I‐Fn had weaker affinity towards the M r 140,000 polypeptide. Instead, proteolytic Fn‐fragments, lacking the cell binding site, did not bind to any proteins in the assay. Radioactive cell‐surface labelling showed differences in the corresponding surface polypeptide profiles of normal and malignant cells. The results suggest that the failure of pericellular matrix deposition in malignant cells could be due to either defective surface exposition or defective binding property of the Fn‐receptor‐like polypeptides.