Evidence that distinct states of the integrin alpha6beta1 interact with laminin 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 a 6 b 1, on mouse eggs and on a 6-transfected cells, interacted with the disintegrin domain of the sperm surface protein ADAM 2 (fertilin b ). In the present study we tested the hypothesis that different states of a 6 b 1 interact with fertilin and laminin, an extracellular matrix ligand for a 6 b 1. Using a 6-transfected cells we found that treatments (e.g., with phorbol myristate acetate or MnCl 2 ) that increased 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 b or with the laminin E8 fragment to bind to eggs. In Ca 2 1 -containing media, fertilin b beads bound to eggs via an interaction mediated by the disintegrin loop of fertilin b and by the a 6 integrin subunit. In Ca 2 1 -containing media, laminin E8 beads did not bind to eggs. Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding. Treatment of eggs with Mn 2 1 dramatically increased laminin E8 bead binding, and inhibited fertilin bead binding. Our results provide the first evidence that different states of an integrin ( a 6 b 1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface