Integrin α4β1-dependent T cell migration requires both phosphorylation and dephosphorylation of the α4 cytoplasmic domain to regulate the reversible binding of paxillin

alpha(4) integrins mediate increased cell migration and decreased cell spreading because the alpha(4) cytoplasmic domain ( tail) binds tightly to paxillin, a signaling adaptor protein. Paxillin binding to the alpha(4) tail is blocked by alpha(4) phosphorylation at Ser(988). To establish the biological role of alpha(4) phosphorylation, we reconstituted alpha(4)-deficient Jurkat T cells with phosphorylation-mimicking (alpha(4)(S988D)) or non-phosphorylatable (alpha(4)(S988A)) mutants. alpha(4)(S988D) disrupted paxillin binding and also inhibited cell migration and promoted cell spreading. In contrast, the non-phosphorylatable alpha(4)( S988A) resulted in a further reduction in cell spreading; however, this mutation led to an unexpected suppression of cell migration. The suppression of cell migration by alpha(4)( S988A) was ascribable to enhanced alpha(4)-paxillin association, because enforced association by an alpha(4)-paxillin fusion led to a phenotype similar to that of the non-phosphorylatable alpha(4)(S988A) mutant. These data establish that optimal alpha(4)-mediated cell migration requires both phosphorylation and dephosphorylation of the alpha(4) cytoplasmic domain to regulate the reversible binding of paxillin.