Integrins α3β1 and α6β1 are two major laminin receptors expressed on the surface of mammalian cells. Interactions of cells with laminins through these integrins play important roles in cell adhesion, differentiation, motility, and matrix assembly. To determine the binding specificity and affinity of these integrins toward various types of laminins at the level of direct protein-protein interactions, we purified integrins α3β1 and α6β1 from human placenta, and examined their binding to a panel of laminin isoforms, each containing distinct α chains (i.e., laminin-1, laminin-2/4, laminin-5, laminin-8, and laminin-10/11). Integrin α3β1 showed clear specificity for laminin-5 and laminin-10/11, with no significant binding to laminin-1, laminin-2/4, and laminin-8. In contrast, integrin α6β1 showed a broad spectrum of specificity, with apparent binding affinity in the following order: laminin-10/11>laminin-5>laminin-1>laminin-2/4_??_laminin-8. Integrin titration assays demonstrated that laminin-10/11 was the most preferred ligand among the five distinct laminin isoforms for both α3β1 and α6β1 integrins. Given that laminin-10/11 is the major basement membrane component of many adult tissues, the interaction of laminin-10/11 with these integrins should play a central role in the adhesive interactions of epithelial cells with underlying basement membranes.
The Japanese Biochemical Society