Identification of motifs in the fasciclin domains of the transforming growth factor-β-induced matrix protein βig-h3 that interact with the αvβ5 integrin

βig-h3 is a TGF-β-induced matrix protein known to mediate the adhesion of several cell types. In this study, we found that all four of the fas-1 domains in βig-h3 mediate MRC-5 fibroblast adhesion and that this was specifically inhibited by a function-blocking monoclonal antibody specific for the αvβ5 integrin. Using deletion mutants of the fourth fas-1 domain revealed the MRC-5 cell adhesion motif (denoted the YH motif) is located in amino acids 548-614. Experiments with substitution mutants showed that tyrosine 571, histidine 572, and their flanking leucine and isoleucine amino acids, which are all highly conserved in many fas-1 domains, are essential for mediating MRC-5 cell adhesion. A synthetic 18-amino acid peptide encompassing these conserved amino acids could effectively block MRC-5 cell adhesion to βig-h3. Using HEK293 cells stably transfected with the β5 integrin cDNA, we confirmed that the αvβ5 integrin is a functional receptor for the YH motif. In conclusion, we have identified a new αvβ5 integrininteracting motif that is highly conserved in the fas-1 domains of many proteins. This suggests that fas-1 domain-containing proteins may perform their biological functions by interacting with integrins.