Laminin receptors in the integrin family

Abstract

Integrins are membrane receptors, consisting of an alpha and a beta subunit, which are involved in cell adhesion. Their extracellular domain is able to bind to ligands such as laminin which occurs in basement membranes of various kinds of cells. Most of these integrins, with their intracellular domains, interact with the actin-containing cytoskeleton, via linking proteins such as vinculin and talin, while one of them interacts with the keratin filaments, via an as yet unknown linking molecule(s). Among more than eighteen integrins which have been identified to date, integrins alpha 3 beta 1 and alpha 6 beta 1 have been characterized as laminin receptors. They recognize the laminin long arm E8 fragment obtained after elastase digestion of the molecule. The binding requires the presence of divalent cations which bind to specific sites on the integrin alpha subunit. The affinities of the alpha 3 beta 1 and alpha 6 beta 1 integrins for murine and human laminin are different, which is probably depended on the existence of different isoforms of laminin. When cells have adhered to laminin, the alpha 6 beta 1 integrin localizes in focal contacts in which actin microfilaments are anchored to the plasma membrane. Whether another integrin, the alpha 6 beta 4 complex, of epidermal cells is also a laminin receptor has not yet been confirmed. The alpha 6 beta 4 integrin localizes in hemidesmosomes which are attachment structures to the substratum where intermediate (keratin) filaments are anchored.(ABSTRACT TRUNCATED AT 250 WORDS)