title: HNK-1 glyco-epitope regulates the stability of the glutamate receptor subunit GluR2 on the neuronal cell surface.
abstract: HNK-1 (human natural killer-1) glyco-epitope, a sulfated glucuronic acid attached to N-acetyllactosamine on the nonreducing termini of glycans, is highly expressed in the nervous system. Our previous report showed that mice lacking a glucuronyltransferase (GlcAT-P), a key enzyme for biosynthesis of the HNK-1 epitope, showed reduced long term potentiation at hippocampal CA1 synapses. In this study, we identified an alpha-amino-3-hydroxy-5-methylisoxazole propionate (AMPA)-type glutamate receptor subunit, GluR2, which directly contributes to excitatory synaptic transmission and synaptic plasticity, as a novel HNK-1 carrier molecule. We demonstrated that the HNK-1 epitope is specifically expressed on the N-linked glycan(s) on GluR2 among the glutamate receptors tested, and the glycan structure, including HNK-1 on GluR2, was determined using liquid chromatography-tandem mass spectrometry. As for the function of HNK-1 on GluR2, we found that the GluR2 not carrying HNK-1 was dramatically endocytosed and expressed less on the cell surface compared with GluR2 carrying HNK-1 in both cultured hippocampal neurons and heterologous cells. These results suggest that HNK-1 stabilizes GluR2 on neuronal surface membranes and regulates the number of surface AMPA receptors. Moreover, we showed that the expression of the HNK-1 epitope enhanced the interaction between GluR2 and N-cadherin, which has important roles in AMPA receptor trafficking. Our findings suggest that the HNK-1 epitope on GluR2 regulates cell surface stability of GluR2 by modulating the interaction with N-cadherin.
authors.affiliation: Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Ippei
authors.initials: I
authors.lastname: Morita
authors.forename: Shinako
authors.initials: S
authors.lastname: Kakuda
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: Satsuki
authors.initials: S
authors.lastname: Itoh
authors.forename: Nana
authors.initials: N
authors.lastname: Kawasaki
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Kizuka
authors.forename: Toshisuke
authors.initials: T
authors.lastname: Kawasaki
authors.forename: Shogo
authors.initials: S
authors.lastname: Oka
mesh_terms: D000818:Animals; D018959:CD57 Antigens / Q000502:physiology*; D015820:Cadherins / Q000378:metabolism*; D000939:Epitopes; D006624:Hippocampus / Q000166:cytology; D051379:Mice; D009474:Neurons / Q000737:chemistry*; D055550:Protein Stability; D021381:Protein Transport; D018091:Receptors, AMPA / Q000737:chemistry* / Q000378:metabolism; D017470:Receptors, Glutamate / Q000737:chemistry
chemical_list: D018959:CD57 Antigens; D015820:Cadherins; D000939:Epitopes; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; C104722:glutamate receptor ionotropic, AMPA 2