Fibronectin adsorption and arrangement on copolymer surfaces and their significance in cell adhesion

The adsorption of fibronectin (FN) to (styrene/methyl methacrylate) copolymer surfaces, both sulfonated (hydrophilic) and nonsulfonated (hydrophobic), was studied by means of the radioisotope (125I-FN) and ELISA assays; the latter employed monoclonal antibodies. It was found that the radioiodination-derived isotherms did not follow the Langmuir-type adsorption law within the FN concentration range studied; rather, a quasi-linear FN surface density versus bulk concentration dependence was observed. These isotherms, and our recent ELISA measurements with polyclonal antibodies, allowed us to estimate saturative FN surface densities, which were, within the experimental error, similar on both types of surfaces. This suggested the amount of adsorbed FN to be not responsible for observed differences in leukaemia L1210 cell adhesion (FN-coated sulfonated surfaces are far more pro-adhesive than their nonsulfonated analogues). The presumption that these differences are induced by changes in the FN arrangement was confirmed by the use of monoclonal antibodies directed against distinct FN domains, and by the blocking of alpha5beta1 integrin receptor with the synthetic Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) peptide. The RGD sequence located within the FN cell-binding domain seems to be masked in the structure adopted on nonsulfonated surfaces, which hinders the integrin-ligand interaction.