RGD-CAP (beta ig-h3) enhances the spreading of chondrocytes and fibroblasts via integrin alpha(1)beta(1)

In previous studies, RGD-CAP (collagen-associated protein containing the RG D sequence) isolated from a collagen fiber-rich fraction of pig cartilage w as found to be orthologous to human beta ig-h3, which is synthesized by lun g adenocarcinoma cells in response to transforming growth factor-beta. In t he present study, we examined the effect of recombinant chick RGD-CAP on th e spreading of chondrocytes and fibroblasts using RGD-CAP-coated dishes, Wh en rabbit articular chondrocytes, chick embryonic sternal chondrocytes, rab bit peritoneal fibroblasts or human MRCS fibroblasts were seeded on plastic dishes coated with RGD-CAP, cell spreading was enhanced compared with that on control dishes (bovine serum albumin- or beta-galactosidase-coated dish es). The effect of RGD-CAP on the cell spreading required divalent cations (Mg2+ or Mn2+), and was reduced by EDTA. Monoclonal antibodies (mAbs) to th e human integrin alpha(1) or beta(1) subunit, but not to the alpha(2), alph a(3), alpha(5) or beta(2) subunits, suppressed the RGD-CAP-induced spreadin g of human MRCS fibroblasts. In a parallel experiment, the mAb to the alpha (5) subunit, but not the mAb to the alpha(1) subunit, suppressed fibronecti n-induced spreading of these cells. These findings suggest that RGD-CAP is a novel ligand for integrin alpha(1)beta(1) that dose not bind to the RGD m otif. Accordingly, an RGD-CAP fragment, which carries a deletion in the C-t erminal region containing the RGD motif, was still capable of stimulating c ell spreading. (C) 1999 Elsevier Science B.V. All rights reserved.