| Research Abstract |
The following results were obtained to clarify the role of RGD-CAP as the mediator in the interaction of cells and matrix concerning the growth and development of chondrocytes.
(1) A cDNA clone for RGD-CAP (collagen-associated protein containing the RGD sequence) was isolated from chick embryo chondrocyte cDNA library. The deduced amino acid sequence (680 amino acid residues) contained four internal repeat domains and two highly conserved sequences (Hi and H2) in each repeat. The protein contains an integrin recognition site, the RGD motif in the fourth domain of four repetitive structures.
(2) We examined the effect of recombinant chick RGD-CAP on the adhesion of chondrocytes and fibroblasts using RGD-CAP-coated dishes. When rabbit chondrocytes or human fibroblasts were seeded on plastic dishes coated with RGD- CAP, cell adhesion was enhanced compared with control dishes.
(3) RGD-CAP produced a synergistic stimulation of cell adhesion in thepresence of type II or III collagen, and an additive stimulation in the presence of type I or V collagen.
(4) The effect of RGD-CAP on cell adhesion required divalent cations (Mg^<2+> or Mn^<2+>) , and was reduced by EDTA and by the GRGDS peptide.
(5) Monoclonal antibodies to the human integrin alpha1, alpha5, or beta1 subunit but not alpha2, alpha3, or beta2 decreased the RGD-CAP-induced cell adhesion. These findings suggest that RGD-CAP is a novel ligand for integrin alpha1beta1/alpha5beta1, and that a site other than the RGD sequence on RGD-CAP is also involved in cell adhesion.
(6) An RGD-CAP fragment containing two repeating domains was also capable of enhancing efficiently the adhesion of chondrocytes indicating the importance of the repetition of two domains.
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