Abl interactor 1 promotes tyrosine 296 phosphorylation of mammalian enabled (Mena) by c-Abl kinase

Mammalian Enabled ( Mena) is a mammalian homologue of Drosophila Enabled ( Ena), which genetically interacts with Drosophila Abl tyrosine kinase. The signaling pathway involving c- Abl and Mena ( Ena) is not fully understood. To find molecules that participate in the c- Abl/ Mena pathway, we searched for Mena- binding proteins using a yeast two- hybrid system. We identified Abl interactor 1 ( Abi- 1), which is known to interact with c- Abl, as a binding protein for Mena. Binding analysis revealed that the Ena/ Vasp homology 1 domain of Mena and the polyproline structure of Abi- 1 are necessary for the interaction. The interaction between Mena and Abi- 1 was also observed in a mammalian expression system. Importantly, Abi- 1 dramatically promoted c- Abl-mediated tyrosine phosphorylation of Mena but not other substrates such as c- Cbl. Mutational analysis demonstrated that the phosphorylation site of Mena is Tyr-296. Our results suggest that Abi- 1 regulates c- Abl- mediated phosphorylation of Mena by interacting with both proteins.