Binding and cross-linking of rabbit fibronectin by rabbit hepatocytes in suspension

Fibronectin purified from rabbit plasma was radioiodinated, and its interaction with rabbit hepatocytes in suspension was studied. Iodinated fibronectin interacted in a time-dependent fashion reaching plateau at 3 h. The interaction was greater in the presence of calcium than in the presence of magnesium or EDTA. Saturation occurred at about 140 nM fibronectin with about 1,400,000 molecules bound per cell. The interaction could be inhibited by unlabeled fibronectin or fibrinogen but not by the tetrapeptide Arg-Gly-Asp-Ser or by albumin, transferrin, or fetuin. About 50% of the bound iodinated fibronectin was incorporated, in a calcium-dependent fashion, into cross-linked high molecular weight complexes at the cell surface through a mechanism consistent with a cellular transglutaminase-mediated reaction. Iodinated fibronectin which could be displaced from the cell was monomeric in nature, while the cell-associated material remained in high molecular weight complexes. The role of the interaction is currently under investigation, but it is possible that the binding may promote cellular adhesion or facilitate intercellular interaction.