Evidence that distinct states of the integrin alpha 6 beta 1 interact withlaminin and an ADAM

Integrins can exist in different functional states with low or high binding capacity for particular ligands. We previously provided evidence that the integrin alpha 6 beta 1, on mouse eggs and on alpha 6-transfected cells, in teracted with the disintegrin domain of the sperm surface protein ADAM 2 (f ertilin beta). In the present study we tested the hypothesis that different states of alpha 6 beta 1 interact with fertilin and laminin, an extracellu lar matrix ligand for alpha 6 beta 1. Using alpha 6-transfected cells we fo und that treatments (e.g., with phorbol myristate acetate or MnCl2) that in creased adhesion to laminin inhibited sperm binding. Conversely, treatments that inhibited laminin adhesion increased sperm binding. Next, we compared the ability of fluorescent beads coated with either fertilin beta or with the laminin E8 fragment to bind to eggs. In Ca2+-containing media, fertilin beta beads bound to eggs via an interaction mediated by the disintegrin lo op of fertilin beta and by the alpha 6 integrin subunit, In Ca2+-containing media, laminin E8 beads did not bind to eggs. Treatment of eggs with phorb ol myristate acetate or with the actin disrupting agent, latrunculin A, inh ibited fertilin bead binding, but did not induce laminin E8 bead binding. T reatment of eggs with Mn2+ dramatically increased laminin E8 bead binding, and inhibited fertilin bead binding. Our results provide the first evidence that different states of an integrin (alpha 6 beta 1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).