EphA4 Induces the Phosphorylation of an Intracellular Adaptor Protein Dab1 via Src Family Kinases

Dab1 is an intracellular adaptor protein essential for brain formation during development. Tyrosine phosphorylation in Dab1 plays important roles in neuronal migration, dendrite development, and synapse formation by affecting several downstream pathways. Reelin is the best-known extracellular protein that induces Dab1 phosphorylation. However, whether other upstream molecule(s) contribute to Dab1 phosphorylation remains largely unknown. Here, we found that EphA4, a member of the Eph family of receptor-type tyrosine kinases, induced Dab1 phosphorylation when co-expressed in cultured cells. Tyrosine residues phosphorylated by EphA4 were the same as those phosphorylated by Reelin in neurons. The autophosphorylation of EphA4 was necessary for Dab1 phosphorylation. We also found that EphA4-induced Dab1 phosphorylation was mediated by the activation of the Src family tyrosine kinases. Interestingly, Dab1 phosphorylation was not observed when EphA4 was activated by ephrin-A5 in cultured cortical neurons, suggesting that Dab1 is localized in a different compartment in them. EphA4-induced Dab1 phosphorylation may occur under limited and/or pathological conditions in the brain.