title: Interactions between the L1 cell adhesion molecule and ezrin support traction-force generation and can be regulated by tyrosine phosphorylation.
abstract: An Ig superfamily cell-adhesion molecule, L1, forms an adhesion complex at the cell membrane containing both signaling molecules and cytoskeletal proteins. This complex mediates the transduction of extracellular signals and generates actin-mediated traction forces, both of which support axon outgrowth. The L1 cytoplasmic region binds ezrin, an adapter protein that interacts with the actin cytoskeleton. In this study, we analyzed L1-ezrin interactions in detail, assessed their role in generating traction forces by L1, and identified potential regulatory mechanisms controlling ezrin-L1 interactions. The FERM domain of ezrin binds to the juxtamembrane region of L1, demonstrated by yeast two-hybrid interaction traps and protein binding analyses in vitro. A lysine-to-leucine substitution in this domain of L1 (K1147L) shows reduced binding to the ezrin FERM domain. Additionally, in ND7 cells, the K1147L mutation inhibits retrograde movement of L1 on the cell surface that has been linked to the generation of the traction forces necessary for axon growth. A membrane-permeable peptide consisting of the juxtamembrane region of L1 that can disrupt endogenous L1-ezrin interactions inhibits neurite extension of cerebellar cells on L1 substrates. Moreover, the L1-ezrin interactions can be modulated by tyrosine phosphorylation of the L1 cytoplasmic region, namely, Y1151, possibly through Src-family kinases. Replacement of this tyrosine together with Y1176 with either aspartate or phenylalanine changes ezrin binding and alters colocalization with ezrin in ND7 cells. Collectively, these data suggest that L1-ezrin interactions mediated by the L1 juxtamembrane region are involved in traction-force generation and can be regulated by the phosphorylation of L1.
authors.affiliation: Department of Psychiatry, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sakurai
authors.forename: Orlando D
authors.initials: OD
authors.lastname: Gil
authors.forename: John D
authors.initials: JD
authors.lastname: Whittard
authors.forename: Mihaela
authors.initials: M
authors.lastname: Gazdoiu
authors.forename: Todd
authors.initials: T
authors.lastname: Joseph
authors.forename: James
authors.initials: J
authors.lastname: Wu
authors.forename: Adam
authors.initials: A
authors.lastname: Waksman
authors.forename: Deanna L
authors.initials: DL
authors.lastname: Benson
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Salton
authors.forename: Dan P
authors.initials: DP
authors.lastname: Felsenfeld
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism* / Q000502:physiology; D003599:Cytoskeleton / Q000502:physiology; D005110:Extracellular Space / Q000502:physiology; D006801:Humans; D051379:Mice; D039842:Neural Cell Adhesion Molecule L1 / Q000378:metabolism* / Q000502:physiology; D016501:Neurites / Q000502:physiology; D010766:Phosphorylation / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism*; D000099149:Ezrin
chemical_list: D003598:Cytoskeletal Proteins; D039842:Neural Cell Adhesion Molecule L1; D014443:Tyrosine; D000099149:Ezrin