Identification of motifs for cell adhesion within the repeated domains of transforming growth factor-β-induced gene, βig-h3

βig-h3 is a transforming growth factor-β-inducible cell adhesion molecule that has four characteristic homologous repeated domains. We made recombinant βig-h3 proteins, which were highly active in mediating human corneal epithelial (HCE) cell adhesion and spreading. The 2nd and the 4th repeated domains were sufficient to mediate HCE cell adhesion. A sequence analysis showed that aspartic acid (Asp) and isoleucine (Ile) of the 2nd and the 4th domains are highly conserved in many fasciclin 1 homologous (fas-1) domains. Substitution mutational study identified these two amino acids are essential for cell adhesion. Synthetic peptides containing Asp and Ile, NKDIL and EPDIM derived from the 2nd and the 4th domains, respectively, almost completely blocked cell adhesion mediated by not only wild type βig-h3 but also each of the 2nd and the 4th domains. These peptides alone were fully active in mediating cell adhesion. In addition, we demonstrated the functional receptor for βig-h3 is α₃β₁ integrin. These results, therefore, establish the essential motifs within the 2nd and the 4th domains of βig-h3, which interact with α₃β₁ integrin to mediate HCE cell adhesion to βig-h3 and suggest that other proteins containing Asp-Ile in their fas-1 domains could possibly function as cell adhesion molecules.