Spatial Restriction of α4 Integrin Phosphorylation Regulates Lamellipodial Stability and α4β1-Dependent Cell Migration

Integrins coordinate spatial signaling events essential for cell polarity and directed migration. Such signals from α4 integrins regulate cell migration in development and in leukocyte trafficking. Here, we report that efficient α4-mediated migration requires spatial control of α4 phosphorylation by protein kinase A, and hence localized inhibition of binding of the signaling adaptor, paxillin, to the integrin. In migrating cells, phosphorylated α4 accumulated along the leading edge. Blocking α4 phosphorylation by mutagenesis or by inhibition of protein kinase A drastically reduced α4-dependent migration and lamellipodial stability. α4 phosphorylation blocks paxillin binding in vitro; we now find that paxillin and phospho-α4 were in distinct clusters at the leading edge of migrating cells, whereas unphosphorylated α4 and paxillin colocalized along the lateral edges of those cells. Furthermore, enforced paxillin association with α4 inhibits migration and reduced lamellipodial stability. These results show that topographically specific integrin phosphorylation can control cell migration and polarization by spatial segregation of adaptor protein binding.