title: Activation of a Dab1/CrkL/C3G/Rap1 pathway in Reelin-stimulated neurons.
abstract: During brain development, many neurons migrate long distances before settling and differentiating. These migrations are coordinated to ensure normal development. The secreted protein Reelin controls the locations of many types of neurons, and its absence causes the classic "Reeler" phenotype. Reelin action requires tyrosine phosphorylation of the intracellular protein Dab1 by Src-family kinases. However, little is known about signaling pathways downstream of Dab1. Here, we identify several proteins in embryonic brain extract that bind to tyrosine-phosphorylated, but not non-phosphorylated, Dab1. Of these, the Crk-family proteins (CrkL, CrkI, and CrkII ), bind significant quantities of Dab1 when embryonic cortical neurons are exposed to Reelin. CrkL binding to Dab1 involves two tyrosine phosphorylation sites, Y220 and 232, that are critical for proper positioning of migrating cortical plate neurons. CrkL also binds C3G, an exchange factor (GEF) for the small GTPase Rap1 that is activated in other systems by tyrosine phosphorylation. We report that Reelin stimulates tyrosine phosphorylation of C3G and activates Rap1. C3G and Rap1 regulate adhesion of fibroblasts and other cell types. Regulation of Crk/CrkL, C3G, and Rap1 by Reelin may be involved in coordinating neuron migrations during brain development.
authors.affiliation: Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA. jcooper@fhcrc.org
authors.forename: Bryan A
authors.initials: BA
authors.lastname: Ballif
authors.forename: Lionel
authors.initials: L
authors.lastname: Arnaud
authors.forename: William T
authors.initials: WT
authors.lastname: Arthur
authors.forename: Deborah
authors.initials: D
authors.lastname: Guris
authors.forename: Akira
authors.initials: A
authors.lastname: Imamoto
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Cooper
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D016367:Baculoviridae; D015153:Blotting, Western; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D016326:Extracellular Matrix Proteins / Q000378:metabolism* / Q000494:pharmacology; D005822:Genetic Vectors; D020735:Guanine Nucleotide-Releasing Factor 2 / Q000378:metabolism*; D013058:Mass Spectrometry; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D000091042:Reelin Protein; D012697:Serine Endopeptidases; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C082869:CRKL protein; D015816:Cell Adhesion Molecules, Neuronal; C103773:Dab1 protein, mouse; D016326:Extracellular Matrix Proteins; D020735:Guanine Nucleotide-Releasing Factor 2; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D000091042:Reelin Protein; C000717128:Reln protein, mouse; D012697:Serine Endopeptidases; D020827:rap1 GTP-Binding Proteins