Molecular characterisation of integrin-procollagen C-propeptide interactions

The carboxyl-terminal propeptide of type I procollagen (CPP-I) plays a key role in regulation of collagen fibrillogenesis, and may exert feedback control of collagen biosynthesis. We have previously shown that CPP-I is a ligand for the integrin alpha 2 beta 1 [Weston, S. A., Hulmes, D. J. S., Mould, A. P., Watson, R. B. & Humphries, M. J. (1994) Identification of the integrin alpha 2 beta 1 as a cell surface receptor for the C-propeptide of type I procollagen, J. Biol. Chem. 269, 20982-20986] suggesting that some of the phenotypic effects of C-propeptides may be mediated by adhesion receptors. Here we have extended this work to study the molecular basis of this interaction. We have broadened the ligand range by demonstrating that the C-terminal propeptide of type II procollagen supports alpha 2 beta 1-mediated binding of NHS human fibroblasts in cell attachment assays. Also, we have used function-blacking antibodies in cell attachment and solid-phase binding assays with purified integrin to expand the CPP-I receptor family, showing that integrin alpha 1 beta 1 is also a receptor for CPP-I. Integrin alpha-subunit A-domains are known to be major ligand-binding sites and recombinant alpha 1 and alpha 2 subunit A-domains were able to bind CPP-I. Finally we have shown that peptides corresponding to potential integrin-binding sequences in CPP-I do not mediate integrin--CPP-I adhesion. Taken together, these studies indicate that the interactions between C-propeptides and integrins are more numerous than previously reported, that C-propeptides are a new class of molecule which bind to A-domains, and that the integrin--C-propeptide interaction does not utilise established peptide motifs.