Regulation of Mitogen-activated Protein Kinase Activation by the Cytoplasmic Domain of the α6 Integrin Subunit*
- From the Department of Medicine (GI Division), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215
Abstract
We examined the possibility that the α6A and α6B cytoplasmic domain variants of the α6β1 integrin differentially activate p42 and p44 mitogen-activated protein (MAP) kinases. P388D1 macrophages that express equivalent surface levels of either the α6Aβ1 or α6Bβ1 integrin were used to examine this issue. Adhesion to laminin-1 mediated by the α6Aβ1 integrin triggered activation of a substantial fraction of total p42 and p44 MAP kinases as assessed using a mobility shift assay, immunoblot analysis with a phosphospecific MAP kinase antibody, and an immune complex kinase assay. In contrast, ligation of the α6Bβ1 integrin did not trigger significant MAP kinase activation. These data were confirmed by antibody clustering of the α6β1 integrins. Both the α6Aβ1 and α6Bβ1 integrins were capable of activating the p70 ribosomal S6 kinase and this activation, unlike MAP kinase activation, is dependent on phosphoinositide 3-OH kinase. Activation of MAP kinase by α6β1 requires both Ras and protein kinase C activity. A functional correlate for differential activation of MAP kinase was provided by the findings that the α6Aβ1 transfectants migrated significantly better on laminin than the α6Bβ1transfectants and this migration was dependent on MAP kinase activity based on the use of the MAP kinase kinase (MEK1) inhibitor PD98059. Our findings demonstrate that the α6β1 integrin can activate MAP kinase, that this activation is regulated by the cytoplasmic domain of the α6 subunit, and that it relates to α6β1-mediated migration.
Footnotes
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↵* This work was supported by National Institutes of Health Grant AI39264 (to A. M. M.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Beth Israel Deaconess Medical Center, Dana 601, Harvard Medical School, 330 Brookline Ave., Boston, MA 02215. Tel.: 617-667-7714; Fax: 617-975-5071; E-mail:amercuri{at}bidmc.harvard.edu.
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↵1 The abbreviations used are: ERK, extracellular-signal regulated kinase; MAP, mitogen-activated protein; S6K, p70 ribosomal S6 kinase; MBP, myelin basic protein; FAK, focal adhesion kinase; PKC, protein kinase C; mAb, monoclonal antibody; Ab, antibody; PAGE, polyacrylamide gel electrophoresis; HA, hemagglutinin.
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↵2 J. Wei and L. M. Shaw, unpublished results.
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- Received December 17, 1997.
- The American Society for Biochemistry and Molecular Biology, Inc.
