IDENTIFICATION OF INTEGRIN ALPHA-2-BETA-1 AS CELL-SURFACE RECEPTOR FOR THE CARBOXYL-TERMINAL PROPEPTIDE OF TYPE PROCOLLAGEN

The carboxyl-terminal propeptide of procollagen type I (CPP-I) plays a key role in the regulation of collagen fibrillogenesis. In addition, it has been reported that, after cleavage from procollagen, CPP-I exer ts feedback control of collagen biosynthesis. To further elucidate the mechanisms involved in each of these processes, we have investigated the nature of cell surface receptors for CPP-I. CPP-I affinity chromat ography, using detergent extracts of iodinated HT1080 cells and EDTA e lution, resulted in the isolation of two polypeptides of molecular mas s 160 and 110 kDa. Since the migratory behavior of these polypeptides under nonreducing and reducing conditions was characteristic of a subs et of integrin receptors, their reactivity with anti-integrin monoclon al antibodies was tested. Antibodies directed against the alpha 2 and beta 1 subunits specifically immunoprecipitated both CPP-I-binding pol ypeptides, indicating that the CPP-I receptor is the integrin alpha 2 beta 1. CPP-I was found to support the attachment and spreading of HT1 080 cells, demonstrating that it can function as an adhesion protein. Two other approaches supported the identification of alpha 2 beta 1 as the CPP-I receptor. First, antifunctional anti-integrin monoclonal an tibodies directed against the alpha 2 and beta 1 subunits completely a brogated the adhesive activity of CPP-I and, second, highly purified C PP-I bound specifically to alpha 2 beta 1-containing integrin preparat ions in a solid-phase receptor-ligand binding assay. These findings ha ve important implications for the function of fibrillar collagen carbo xyl-terminal propeptides and for the role played by integrins in the r egulation of cellular phenotype.