The 6A1 and 6B1 Integrin Variants Signal Differences in the Tyrosine Phosphorylation of Paxillin and Other Proteins

doi:10.1074/jbc.270.40.23648

The 6A1 and 6B1 Integrin Variants Signal Differences in the Tyrosine Phosphorylation of Paxillin and Other Proteins (*)

From the (1)Deaconess Hospital, Harvard Medical School, Boston, Massachusetts 02115 and
the (2)Department of Anatomy and Cell Biology, State University of New York Health Science Center, Syracuse, New York 13210

** Recipient of an American Cancer Society Faculty Research Award. To whom correspondence should be addressed:
Laboratory of Cancer Biology, Deaconess Hospital, Harvard Medical School, 50 Binney St., Boston, MA 02115.
Tel.: 617-732-9874; Fax: 617-738-9188; mercurio{at}mbcrr.harvard.edu.

Abstract

Integrin receptors can mediate transmembrane signaling in response to ligand binding. To further examine the role of the integrin α subunit in these signaling functions, we assessed the contribution of the α6 cytoplasmic domain variants to the signaling properties of the α6β1 integrin using P388D1 cells that had been transfected with either the α6A or the α6B cDNA. The α6Aβ1 and α6Bβ1 receptors induced marked quantitative differences in the tyrosine phosphorylation of several proteins after binding to laminin. Specifically, the α6A cytoplasmic domain was more effective than the α6B 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 α6Aβ1 integrin-mediated adhesion to laminin than by that of α6Bβ1. 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 α6 transfectants were not evident in response to attachment to other substrates. These findings provide biochemical evidence for functional differences between α subunit cytoplasmic domain variants of the same integrin.

Footnotes

↵^§ Recipient of a U. S. Army Breast Cancer Fellowship.
↵^¶ Established Investigator of the American Heart Association.
↵* This work was supported by National Institutes of Health Grants CA42276 and CA44704 (to A. M. M.) and GM47607 (to C. E. T.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

EHS

Englebreth-Holm-Swarm

PBS

phosphate-buffered saline

FACS

fluorescence-activated cell sorting

PAGE

polyacrylamide gel electrophoresis

mAb

monoclonal antibody.
↵² L. M. Shaw, J.-L. Guan, and A. M. Mercurio, unpublished observations.
- Received April 14, 1995.
- Revision received June 30, 1995.