A role of chondroitin sulfate glycosaminoglycan binding site in α4β1 integrin-mediated melanoma cell adhesion

We have previously reported that alpha(4) beta(1) (but not alpha(5) beta(1)) integrin-mediated melanoma cell adhesion is inhibited by removal of cell surface chondroitin sulfate glycosaminoglycan (CSGAG), suggesting that melanoma chondroitin sulfate proteoglycan plays a role in modulating the adhesive function of alpha(4) beta(1) integrin, In the current study, we demonstrated that alpha(4) beta(1) integrin binds to CSGAG, We have identified a peptide from within a, integrin termed SG1 (KKEKDIMKKTI) that binds to cell surface melanoma chondroitin sulfate proteoglycan, indicating that SG1 represents a CSGAG binding site within the alpha(4) integrin subunit, Soluble SG1 inhibits alpha(4) beta(1) integrin-mediated human melanoma cell adhesion to CS1. Polyclonal antibody generated against the peptide inhibits melanoma cell adhesion to CS1, and the inhibition is reversed by Mn2+ and an activating monoclonal antibody anti-beta(1) (8A2). Additionally, pretreatment of cells with anti-SG1 IgG inhibits the expression of the monoclonal antibody 15/7 epitope in the presence of soluble CS1 peptide, suggesting that anti-SG1 IgG prevents ligand binding by alpha(4) beta(1) integrin, These results demon strate that alpha(4) beta(1) integrin interacts directly with CSGAG through SG1 site, and that this site can affect the ligand binding properties of the integrin.