ADHESIVE INTERACTION OF HEMATOPOIETIC PROGENITOR-CELL MEMBRANE WITH THE RGD DOMAIN OF FIBRONECTIN

The binding of two cloned hemopoietic progenitor cell lines, B6Sut (mu ltipotential) and FDCP-1 (bipotential) to dishes coated with fibronect in or its chymotryptic fragments was studied by labeling the cells wit h Cr-51 or [S-35]methionine. Intact fibronectin molecule and its 120 k Da fragment, containing the Arg-Gly-Asp (RGD) sequence motif, as well as a synthetic RGD-containing peptide Peptite 2000 all bound progenito r cells. However, the 40 or 45 kDa fragments, containing the heparin-b inding and CS-1 domains, failed to bind the cells in a comparable magn itude. 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 I-125 and subjected to affinity chromatography using a matrix to which the 120 kDa fragment of fibrone ctin was covalently bound. Specific competitive elution with RGD yield ed two bands with molecular masses of 160 and 1 10 kDa, corresponding, respectively, to those of alpha5 and beta1 chains of integrin molecul e. Western blotting of whole-cell-lysate proteins with a monospecific, polyclonal serum specific for vertebrate beta1 integrins identified a beta1 integrin in these cells. Thus, it appears that an interaction i nvolving alpha5beta1 integrin with 120 kDa fragment of fibronectin may be involved between hemopoietic progenitor cells and the fibronectin component of extracellular matrix.