title: Regulated internalization of NMDA receptors drives PKD1-mediated suppression of the activity of residual cell-surface NMDA receptors.
abstract: BACKGROUND
  Constitutive and regulated internalization of cell surface proteins has been extensively investigated. The regulated internalization has been characterized as a principal mechanism for removing cell-surface receptors from the plasma membrane, and signaling to downstream targets of receptors. However, so far it is still not known whether the functional properties of remaining (non-internalized) receptor/channels may be regulated by internalization of the same class of receptor/channels. The N-methyl-D-aspartate receptor (NMDAR) is a principal subtype of glutamate-gated ion channel and plays key roles in neuronal plasticity and memory functions. NMDARs are well-known to undergo two types of regulated internalization - homologous and heterologous, which can be induced by high NMDA/glycine and DHPG, respectively. In the present work, we investigated effects of regulated NMDAR internalization on the activity of residual cell-surface NMDARs and neuronal functions.
  
  
  RESULTS
  In electrophysiological experiments we discovered that the regulated internalization of NMDARs not only reduced the number of cell surface NMDARs but also caused an inhibition of the activity of remaining (non-internalized) surface NMDARs. In biochemical experiments we identified that this functional inhibition of remaining surface NMDARs was mediated by increased serine phosphorylation of surface NMDARs, resulting from the activation of protein kinase D1 (PKD1). Knockdown of PKD1 did not affect NMDAR internalization but prevented the phosphorylation and inhibition of remaining surface NMDARs and NMDAR-mediated synaptic functions.
  
  
  CONCLUSIONS
  These data demonstrate a novel concept that regulated internalization of cell surface NMDARs not only reduces the number of NMDARs on the cell surface but also causes an inhibition of the activity of remaining surface NMDARs through intracellular signaling pathway(s). Furthermore, modulating the activity of remaining surface receptors may be an effective approach for treating receptor internalization-induced changes in neuronal functions of the CNS.
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. fangxiaoqian.ch@gmail.com.
authors.forename: Xiao-Qian
authors.initials: XQ
authors.lastname: Fang
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. haifa.qiao@med.fsu.edu.
authors.forename: Haifa
authors.initials: H
authors.lastname: Qiao
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. bradley.groveman@nih.gov.
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Groveman
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. doc.shfeng@gmail.com.
authors.forename: Shuang
authors.initials: S
authors.lastname: Feng
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. melpflueger@yahoo.com.
authors.forename: Melissa
authors.initials: M
authors.lastname: Pflueger
authors.affiliation: Faculty of Dentistry, University of Toronto, Toronto, M5G 1G6, Canada. xinw@sccp.sc.edu.
authors.forename: Wen-Kuan
authors.initials: WK
authors.lastname: Xin
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. alikutub@yahoo.com.
authors.forename: Mohammad K
authors.initials: MK
authors.lastname: Ali
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. suelinyu1@hotmail.com.
authors.forename: Shuang-Xiu
authors.initials: SX
authors.lastname: Lin
authors.affiliation: Faculty of Dentistry, University of Toronto, Toronto, M5G 1G6, Canada. jindong.xu09@gmail.com.
authors.forename: Jindong
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. florian.duclot@med.fsu.edu.
authors.forename: Florian
authors.initials: F
authors.lastname: Duclot
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. mohamed.kabbaj@med.fsu.edu.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Kabbaj
authors.affiliation: Department of Neurology, 1st Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, PR China. ww20040723@163.com.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Neurology, 1st Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, PR China. ding-xs@139.com.|BenQ Neurological Institute, Nanjing Medical University, Nanjing, 210021, PR China. ding-xs@139.com.
authors.forename: Xin-Sheng
authors.initials: XS
authors.lastname: Ding
authors.affiliation: Department of Neurosurgery, The University of Texas Medical School at Houston Vivian L. Smith, Houston, TX, 77030, USA. Teresa.SantiagoSim@uth.tmc.edu.
authors.forename: Teresa
authors.initials: T
authors.lastname: Santiago-Sim
authors.affiliation: Department of Physiology and Neurobiology, Medical College of Soochow University, Suzhou, 215123, China. jiangxinghong@suda.edu.cn.
authors.forename: Xing-Hong
authors.initials: XH
authors.lastname: Jiang
authors.affiliation: Program in Neuroscience and Mental Health, Hospital for Sick Children, University of Toronto, Toronto, M5G 1X8, Canada. mike.salter@utoronto.ca.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Salter
authors.affiliation: Department of Biomedical Sciences, Florida State University, Tallahassee, FL, 32306, USA. yuxianminyu1981@hotmail.com.|Faculty of Dentistry, University of Toronto, Toronto, M5G 1G6, Canada. yuxianminyu1981@hotmail.com.|BenQ Neurological Institute, Nanjing Medical University, Nanjing, 210021, PR China. yuxianminyu1981@hotmail.com.|Department of Physiology and Neurobiology, Medical College of Soochow University, Suzhou, 215123, China. yuxianminyu1981@hotmail.com.
authors.forename: Xian-Min
authors.initials: XM
authors.lastname: Yu
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D005998:Glycine / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D016202:N-Methylaspartate / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*
chemical_list: D016194:Receptors, N-Methyl-D-Aspartate; D010768:Phosphoserine; D008734:Methoxyhydroxyphenylglycol; D016202:N-Methylaspartate; C089212:protein kinase D; D011493:Protein Kinase C; D005998:Glycine; C010117:3,4-dihydroxyphenylglycol