L1 endocytosis is controlled by a phosphorylation-dephosphorylation cycle stimulated by outside-in signaling by L1.
Dynamic regulation of the cell surface expression of adhesion molecules is an important mechanism for controlling neuronal growth cone motility and guidance. Clathrin-mediated vesicular internalization of L1 via the tyrosine-based endocytosis motif YRSL regulates adhesion and signaling by this Ig superfamily molecule. Here, we present evidence that tyrosine-1176 (Y1176) of the YRSL motif is phosphorylated in vivo. The nonreceptor tyrosine kinase (p60src) is implicated in L1-mediated neurite outgrowth, and we find that p60src phosphorylates Y1176 in vitro. Phosphorylation of Y1176 prevents L1 binding to AP-2, an adaptor required for clathrin-mediated internalization of L1. mAb 74-5H7 recognizes the sequence immediately NH2-terminal to the tyrosine-based motif and binds L1 only when Y1176 is dephosphorylated. 74-5H7 identifies a subset of L1 present at points of cell-cell contact and in vesicle-like structures that colocalize with an endocytosis marker. L1-L1 binding or L1 cross-linking induces a rapid increase in 74-5H7 immunoreactivity. Our data suggest a model in which homophilic binding or L1 cross-linking triggers transient dephosphorylation of the YRSL motif that makes L1 available for endocytosis. Thus, the regulation of L1 endocytosis through dephosphorylation of Y1176 is a critical regulatory point of L1-mediated adhesion and signaling.
Schaefer
Andrew W
AW
Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Kamei
Yoshimasa
Y
Kamiguchi
Hiroyuki
H
Wong
Eric V
EV
Rapoport
Iris
I
Kirchhausen
Tomas
T
Beach
Carol M
CM
Landreth
Gary
G
Lemmon
Sandra K
SK
Lemmon
Vance
V
D033942:Adaptor Proteins, Vesicular Transport; D020816:Amino Acid Motifs; D000818:Animals; D015415:Biomarkers; D001921:Brain / Q000166:cytology; D002352:Carrier Proteins / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002450:Cell Communication; D002478:Cells, Cultured; D002642:Chick Embryo; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D004705:Endocytosis; D005727:Ganglia, Spinal / Q000166:cytology; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D033942:Adaptor Proteins, Vesicular Transport; D015415:Biomarkers; D002352:Carrier Proteins; D015815:Cell Adhesion Molecules; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D019006:Neural Cell Adhesion Molecules; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases