A BIOCHEMICAL-CHARACTERIZATION OF THE BINDING OF OSTEOPONTIN TO INTEGRINS ALPHA(V)BETA(1) AND ALPHA(V)BETA(5)

Osteopontin (OPN) is an extracellular matrix protein that binds to integrin alpha(v) beta(3), Here we demonstrate that two other integrins, alpha(v) beta(1) and alpha(v) beta(5), are also receptors for OPN. Human embryonic kidney 293 cells adhere to human recombinant osteopontin (glutathione S-transferase-osteopontin; GST-OPN) using integrin alpha(v) beta(5). When the 293 cells are transfected with the beta(5) subunit, they can also adhere to GST-OPN using integrin alpha(v) beta(5). Divalent cations regulate the binding of GST-OPN to both alpha(v) beta(1) and alpha(v) beta(5). Mg2+ and Mn2+ support the binding of GST-OPN to these integrins but Ca2+ does not, The highest affinity is observed in Mn2+, In the presence of this ion, the affinity of GST-OPN for alpha(v) beta(1), is 18 nM and the affinity for gp, is 48 nM, The antibody 8A2, which is an agonist for beta(1), promotes the adhesion of 293 cells to GST-OPN even when Ca2+ is present. This observation suggests that cellular events could modulate the affinity of alpha(v) beta(1) for OPN, Collectively, these findings prove that integrins alpha(v) beta(1), alpha(v) beta(3) and alpha(v) beta(5) have similar affinity for OPN. Therefore, all three integrins must be considered when evaluating the biological affects of OPN.