Adhesive interaction of hemopoietic progenitor cell membrane with the RGD domain of fibronectin

Abstract

The binding of two cloned hemopoietic progenitor cell lines, B6Sut (multipotential) and FDCP-1 (bipotential) to dishes coated with fibronectin or its chymotryptic fragments was studied by labeling the cells with 51Cr or [ 35S]methionine. Intact fibronectin molecule and its 120 kDa fragment, containing the Arg-Gly-Asp (RGD) sequence motif, as well as a synthetic RGD-containing peptide Peptite 2000 all bound progenitor cells. However, the 40 or 45 kDa fragments, containing the heparin-binding and CS-1 domains, failed to bind the cells in a comparable magnitude. The binding of intact fibronectin and its 120 kDa fragment was inhibited in a dose-dependent fashion with increasing concentration of RGD-containing Gly-Arg-Gly-Asp-Ser peptide, but not with Gly-Arg-Gly-Glu-Ser control peptide that does not contain the RGD sequence motif. To explore the nature of the receptor for this fragment of fibronectin, membrane proteins were labeled with 125I and subjected to affinity chromatography using a matrix to which the 120 kDa fragment of fibronectin was covalently bound. Specific competitive elution with RGD yielded two bands with molecular masses of 160 and 110 kDa, corresponding, respectively, to those of α5 and β1 chains of integrin molecule. Western blotting of whole-cell-lysate proteins with a monospecific, polyclonal serum specific for vertebrate β1 integrins identified a β1 integrin in these cells. Thus, it appears that an interaction involving α5β1 integrin with 120 kDa fragment of fibronectin may be involved between hemopoietic progenitor cells and the fibronectin component of extracellular matrix.