The alpha 6A beta 1 and alpha 6B beta 1 integrin variants signal differences in the tyrosine phosphorylation of paxillin and other proteins.

Leslie M Shaw,Arthur M Mercurio,Christopher E Turner

doi:10.1074/jbc.270.40.23648

Abstract

Integrin receptors can mediate transmembrane signaling in response to ligand binding. To further examine the role of the integrin alpha subunit in these signaling functions, we assessed the contribution of the alpha 6 cytoplasmic domain variants to the signaling properties of the alpha 6 beta 1 integrin using P388D1 cells that had been transfected with either the alpha 6A or the alpha 6B cDNA. The alpha 6A beta 1 and alpha 6B beta 1 receptors induced marked quantitative differences in the tyrosine phosphorylation of several proteins after binding to laminin. Specifically, the alpha 6A cytoplasmic domain was more effective than the alpha 6B cytoplasmic domain in inducing the tyrosine phosphorylation of three major proteins (molecular mass, 120, 110, and 76 kDa). In addition to these proteins, we also observed that the tyrosine phosphorylation of the cytoskeletal protein paxillin was increased significantly more by alpha 6A beta 1 integrin-mediated adhesion to laminin than by that of alpha 6B beta 1. This differential pattern of tyrosine phosphorylation induction does not appear to be a secondary event initiated by cell shape changes. Also, differences in tyrosine phosphorylation in the alpha 6 transfectants were not evident in response to attachment to other substrates. These findings provide biochemical evidence for functional differences between alpha subunit cytoplasmic domain variants of the same integrin.

Highlights

The ability of integrins to function as transmembrane signaling receptors has been well-established
This possibility was supported by our previous functional data that demonstrated that the ␣6A␤1 and ␣6B␤1 integrin receptors, which are identical except for the sequence of the ␣6 cytoplasmic domain [8, 9], differed in their ability to promote cell migration on EHS1 laminin
We investigated the possibility that the ␣6A␤1 and ␣6B␤1 receptors induce either qualitative or quantitative differences in tyrosine phosphorylation in response to laminin attachment and that such differences contribute to the distinct functional properties of these receptors

Summary

Introduction

The ability of integrins to function as transmembrane signaling receptors has been well-established (reviewed in Refs. 1–3). Integrin cytoplasmic domains do not contain intrinsic kinase motifs [4], it is assumed that these domains associate either directly or indirectly with other proteins to affect signaling functions In this connection, a role for ␤ subunit cytoplasmic domains in the activation of tyrosine kinase signaling has been reported. We addressed the question of whether the cytoplasmic domain of the ␣6 subunit contributes to tyrosine kinase-mediated signaling by the ␣6␤1 integrin This possibility was supported by our previous functional data that demonstrated that the ␣6A␤1 and ␣6B␤1 integrin receptors, which are identical except for the sequence of the ␣6 cytoplasmic domain [8, 9], differed in their ability to promote cell migration on EHS1 laminin. Our findings are significant because they are the first to attribute differences in the regulation of integrin-dependent tyrosine phosphorylation to ␣ subunit cytoplasmic domain variants

Methods

Results

Conclusion