Identification of CrkL-SH3 binding proteins from embryonic murine brain: implications for Reelin signaling during brain development.

The Crk and Crk-like (CrkL) adaptor proteins play important roles in numerous signaling pathways, bridging tyrosine kinase substrates to downstream signaling effectors by virtue of their phosphotyrosine-binding SH2 domains and their effector-binding SH3 domains. Critical to understanding the diverse roles of Crk/CrkL is the identification of tissue- and signal-specific tyrosine phosphorylated substrates to which they are recruited and the tissue-specific effector proteins they chaperone into signaling complexes. Crk and CrkL are known biochemically and genetically to be essential mediators of Reelin/Disabled-1 (Dab1) signaling, which governs proper mammalian brain development. Multimeric Reelin clusters its receptors as well as the receptor-bound intracellular scaffolding protein Dab1. Clustering induces Fyn/Src-dependent Dab1 tyrosine phosphorylation, which recruits Crk/CrkL and SH3-bound effectors. Previously, 21 Crk/CrkL-SH3 binding proteins were identified from diverse cell types. We present here the proteomic identification of 101 CrkL-SH3 binding proteins from embryonic murine brain. The identified proteins are enriched in the Crk/CrkL-SH3 binding motif and signaling activities regulating cell adhesion and motility. These results suggest Reelin-induced Dab1 tyrosine phosphorylation may generate a multifaceted signaling scaffold containing a rich array of Crk/CrkL-SH3 binding effectors and may explain a growing diversity of cellular activities suggested to be influenced by Reelin/Dab1 signaling.