title: Cyclin-dependent kinase 5 phosphorylates disabled 1 independently of Reelin signaling.
abstract: Two major signaling pathways that control neuronal positioning during brain development have been uncovered as a result of genetic and biochemical studies on neurological mouse mutants. Mice deficient in Reelin, Disabled 1 (Dab1), or both the very low-density lipoprotein receptor (VLDLR) and the apolipoprotein E receptor 2 (ApoER2) exhibit identical neuroanatomic defects in laminar structures throughout the brain. These proteins function as components of the Reelin signaling pathway. Reelin is a secreted glycoprotein that binds to VLDLR and ApoER2, inducing tyrosine phosphorylation of Dab1, an intracellular adapter protein. Neuronal migration is also regulated by cyclin-dependent kinase 5 (Cdk5) and its activating subunits p35 and p39. Mice deficient in Cdk5, p35, or both p35 and p39 exhibit lamination defects that are similar but not identical to those observed in mice with a defect in the Reelin signaling pathway. Cdk5 phosphorylates proteins that maintain cytoskeletal structures and promote cell motility. To explore the possibility that Cdk5 influences the Reelin pathway, we sought to determine whether Dab1 is a substrate for Cdk5. Here we show that Cdk5 phosphorylates Dab1 on serine 491 in vitro and in vivo, independently of Reelin signaling. We also show that ectopic neurons in Cdk5-deficient mice exhibit reduced levels of Reelin signaling during later stages of cortical development, although Cdk5 is not required for Reelin-induced tyrosine phosphorylation of Dab1. Although the functional significance of Dab1 serine phosphorylation is unclear, our results suggest that there is biochemical cross-talk between two signaling pathways that control cell positioning.
authors.affiliation: Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Lakhu
authors.initials: L
authors.lastname: Keshvara
authors.forename: Susan
authors.initials: S
authors.lastname: Magdaleno
authors.forename: David
authors.initials: D
authors.lastname: Benhayon
authors.forename: Tom
authors.initials: T
authors.lastname: Curran
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001921:Brain / Q000196:embryology / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism*; D002460:Cell Line; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D009474:Neurons / Q000201:enzymology / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000276:immunology / Q000378:metabolism; D000091042:Reelin Protein; D012697:Serine Endopeptidases; D015398:Signal Transduction
chemical_list: D000906:Antibodies; D015816:Cell Adhesion Molecules, Neuronal; C103773:Dab1 protein, mouse; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; D000091042:Reelin Protein; D010768:Phosphoserine; D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; C495906:Cdk5 protein, mouse; D018844:Cyclin-Dependent Kinases; C000717127:RELN protein, human; C000717128:Reln protein, mouse; D012697:Serine Endopeptidases