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Semiquantitative evaluation of fibronectin adsorption on unmodified and sulfonated polystyrene, as related to cell adhesion.

The process of human fibronectin (FN) adsorption on nonsulfonated and sulfonated polystyrene surfaces was studied in relation to mechanisms of L1210 cell adhesion. Radioisotope assays directed towards FN, as well as ELISA measurements of adsorbed FN and bovine serum albumin (BSA) were carried out. (125)I radioisotope assays led to linear FN adsorption isotherms. When combined to ELISA measurements for FN, they revealed the multilayer adsorption. Results indicated a large difference in the saturating first-layer surface density of FN adsorbed on sulfonated and nonsulfonated polystyrene surfaces: significantly (ca. factor of 5) less FN molecules are necessary to complete a monolayer on sulfonated than on nonsulfonated polystyrene. This suggests an unfolded conformation of FN on sulfonated polystyrene, and a more compact one on the nonsulfonated polymer. Significant conformational changes of FN are also indicated by the following: (1) early phase of cell adhesion to FN adsorbed on sulfonated polystyrene surfaces is significantly (ca. factor of 6) higher than to FN on nonsulfonated surfaces, and in the former case adhesion proceeds mostly via alpha(5)beta(1) integrins; (2) RGD, the crucial fragment within central cell binding domain, seems to be partially hidden in the protein structure adopted on nonsulfonated surfaces; (3) patterns of F-actin organization differ in cells adhering to FN on sulfonated and nonsulfonated surfaces. The ELISA study directed against BSA (this protein always present on the surface after the adsorption of FN), showed the importance of "free area," uncovered by both proteins, which influence the cell adhesion processes.