title: Nuclear targeting by the growth factor midkine.
abstract: Ligand-receptor internalization has been traditionally regarded as part of the cellular desensitization system. Low-density lipoprotein receptor-related protein (LRP) is a large endocytosis receptor with a diverse array of ligands. We recently showed that LRP binds heparin-binding growth factor midkine. Here we demonstrate that LRP mediates nuclear targeting by midkine and that the nuclear targeting is biologically important. Exogenous midkine reached the nucleus, where intact midkine was detected, within 20 min. Midkine was not internalized in LRP-deficient cells, whereas transfection of an LRP expression vector restored midkine internalization and subsequent nuclear translocation. Internalized midkine in the cytoplasm bound to nucleolin, a nucleocytoplasmic shuttle protein. The midkine-binding sites were mapped to acidic stretches in the N-terminal domain of nucleolin. When the nuclear localization signal located next to the acidic stretches was deleted, we found that the mutant nucleolin not only accumulated in the cytoplasm but also suppressed the nuclear translocation of midkine. By using cells that overexpressed the mutant nucleolin, we further demonstrated that the nuclear targeting was necessary for the full activity of midkine in the promotion of cell survival. This study therefore reveals a novel role of LRP in intracellular signaling by its ligand and the importance of nucleolin in this process.
authors.affiliation: Department of Biochemistry, Nagoya University School of Medicine, Showa-ku, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Shibata
authors.forename: Takashi
authors.initials: T
authors.lastname: Muramatsu
authors.forename: Makoto
authors.initials: M
authors.lastname: Hirai
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Inui
authors.forename: Terutoshi
authors.initials: T
authors.lastname: Kimura
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Saito
authors.forename: Lynn M
authors.initials: LM
authors.lastname: McCormick
authors.forename: Guojun
authors.initials: G
authors.lastname: Bu
authors.forename: Kenji
authors.initials: K
authors.lastname: Kadomatsu
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D016207:Cytokines; D003593:Cytoplasm / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D026563:LDL-Receptor Related Protein-Associated Protein / Q000378:metabolism; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D000078792:Midkine; D016297:Mutagenesis, Site-Directed; D009414:Nerve Growth Factors / Q000378:metabolism*; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D000097796:Nucleolin
chemical_list: D002352:Carrier Proteins; D016207:Cytokines; D026563:LDL-Receptor Related Protein-Associated Protein; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D000078792:Midkine; D009414:Nerve Growth Factors; D019913:Nuclear Localization Signals; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D000097796:Nucleolin