Interaction of Disabled-1 and the GTPase activating protein Dab2IP in mouse brain

The Reelin signaling pathway controls neuronal positioning during mammalian brain development by binding to the very low density lipoprotein receptor and apolipoprotein E receptor-2, and signaling through the intracellular adapter protein Disabled-1 (Dab1). To identify new components in the Reelin signaling pathway, we used a yeast two-hybrid screen to select Dab1-interacting proteins. Here, we report the characterization of a new mouse Dab1-interacting protein that is orthologous to rat Dab2IP, a Ras-GTPase activating protein previously shown to bind to Dab2/DOC. The interaction of Dab1 and Dab2IP was confirmed in biochemical assays and by co-immunoprecipitation from brain lysates. The site of interaction between Dab1 and Dab2IP was narrowed to the Dab1-PTB domain and the NPxY motif in Dab2IP. The deduced amino acid sequence of mouse Dab2IP encompasses 1,208 residues containing several protein interaction motifs as well as a Ras-like GAP-related domain. Northern blot analysis revealed at least two isoforms of Dab2IP mRNA in the brain, both of which exhibited increased expression during development. In situ hybridization analyses indicated that Dab2IP mRNA is diffusely expressed throughout the developing and the adult brain. Using a polyclonal antiserum specific for Dab2IP, we observed protein expression in the soma and processes of neurons in a variety of brain structures, including the developing cerebral cortex. Our findings suggest that Dab2IP may function as a downstream effector in the Reelin signaling pathway that influences Ras signaling during brain development.