Synthesis and expression of the fibroblast fibronectin receptor in human monocytes

Human monocytes adhere to fibronectin, but the receptor (or receptors) mediating this interaction has not been clearly identified. To examine the nature of this receptor, human monocytes were obtained by counter-current elutriation and were found to adhere to immobilized fibronectin but not to vitronectin or von Willebrand factor. Antibodies and peptides were used to determine whether monocyte adherence to immobilized fibronectin was mediated by a receptor similar to that which mediates the adherence of fibroblasts to fibronectin. Antibodies against both the α and β subunits of the fibroblast fibronectin receptor (VLA-5) inhibited monocyte adherence to fibronectin. These antibodies immunoprecipitated two surface proteins from monocytes that migrated at 140 and 120 kD under nonreducing conditions. Surface proteins with identical apparent molecular weights were immunoprecipitated from surface-labeled MG-63 cells, a fibroblast-like cell line. A synthetic peptide containing the Arg-Gly-Asp-Ser (RGDS) sequence also inhibited monocyte adherence to fibronectin. cDNA hybridization experiments revealed the presence of mRNA for both the α and β subunits of the fibroblast fibronectin receptor in human monocytes. We conclude that circulating monocytes express a fibronectin receptor that is structurally and functionally very similar, if not identical, to the fibronectin receptor in adherent fibroblasts, and that this receptor mediates monocyte adherence to immobilized fibronectin.