title: NMDA receptor-dependent recruitment of calnexin to the neuronal plasma membrane.
abstract: Calnexin is a molecular chaperone that resides in the endoplasmic reticulum and participates in the folding and assembly of nascent proteins. In the present study, calnexin was found in both synaptic and non-synaptic membrane components of rat brain tissue. Immunohistochemical staining of mouse hippocampal sections revealed the presence of calnexin in the neuronal cell soma, as well as dendrite-enriched regions. Staining of permeabilized cultured rat hippocampal neurons with anti-calnexin antibody produced intense staining throughout the cytoplasm of the cell body and dendrites. In non-permeabilized cells, calnexin was found on the surface of the cell body and dendrites. To further confirm the surface localization of calnexin, cell surface proteins were selectively labeled with a membrane-impermeable biotinylation reagent. Calnexin and other plasma membrane proteins including N-methyl-D-aspartate (NMDA) receptor and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor were biotinylated, and the amount of calnexin on the plasma membrane markedly increased after NMDA receptor activation. These results suggest that a significant fraction of calnexin localizes to the neuronal cell membrane, and that this recruitment is regulated in an NMDA receptor-dependent manner. Moreover, immunoisolation of vesicles revealed co-localization of the AMPA receptor subunit, GluA2, and calnexin in post-endoplasmic reticulum intracellular membrane components. These findings provide support for the hypothesis that calnexin may play a role in NMDA receptor-dependent neuronal functions.
authors.affiliation: Department of Biochemistry, Kitasato University School of Medicine, Sagamihara, Kanagawa 252-0374, Japan. mitakura@med.kitasato-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Itakura
authors.forename: Jun
authors.initials: J
authors.lastname: Tsujimura
authors.forename: Saori
authors.initials: S
authors.lastname: Yamamori
authors.forename: Taro
authors.initials: T
authors.lastname: Ohkido
authors.forename: Masami
authors.initials: M
authors.lastname: Takahashi
mesh_terms: D000818:Animals; D037281:Calnexin / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D018091:Receptors, AMPA / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013570:Synaptic Membranes / Q000378:metabolism
chemical_list: D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D037281:Calnexin; C104722:glutamate receptor ionotropic, AMPA 2
keywords: Calnexin; Chaperone; Endoplasmic reticulum; Hippocampal neurons; NMDA receptor