Regulation of mitogen-activated protein kinase activation by the cytoplasmic domain of the α6 integrin subunit

We examined the possibility that the alpha(6A) and alpha(6B) cytoplasmic domain variants of the alpha(6) beta(1) integrin differentially activate p42 and p44 mitogen-activated protein (MAP) kinases, P388D1 macrophages that express equivalent surface levels of either the alpha(6A)beta(1) or alpha(6B)beta(1) integrin were used to examine this issue. Adhesion to laminin-1 mediated by the alpha(6A)beta(1) 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 alpha(6B)beta(1) integrin did not trigger significant MAP kinase activation, These data were confirmed by antibody clustering of the alpha(6) beta(1) integrins, Both the alpha(6A)beta(1) and alpha(6B)beta(1) 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 alpha(6) beta(1) requires both Pas and protein kinase C activity, A functional correlate for differential activation of MAP kinase was provided by the findings that the alpha(6A)beta(1) transfectants migrated significantly better on laminin than the alpha(6B)beta(1) transfectants 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 alpha(6) beta(1) integrin can activate MAP kinase, that this activation is regulated by the cytoplasmic domain of the alpha(6) subunit, and that it relates to alpha(6) beta(1)-mediated migration.