title: Multiple trafficking signals regulate kainate receptor KA2 subunit surface expression.
abstract: The kainate receptor subunit KA2 does not form functional homomeric channels despite its structural similarity to the functional glutamate receptor 5-7subunits and high agonist binding affinity in in vitro assays. In this study, we first demonstrate that homomeric KA2 receptors fail to reach the plasma membrane and then identify the molecular mechanisms preventing surface expression. Specifically, we show that KA2 subunits form homooligomeric receptors that are confined to the endoplasmic reticulum (ER). We then demonstrate that, in both heterologous expression systems and primary neurons, the intracellular retention of KA2 is not caused by subunit misfolding but, rather, is mediated through discrete protein trafficking signals, including an arginine-rich ER retention/retrieval motif and a di-leucine endocytic sequence in the C terminus of the KA2 subunit. Disruption of these motifs results in ER exit and surface expression of KA2 homomeric receptors that remain nonfunctional. Furthermore, our data suggest that the ER retention/retrieval signal in KA2 is sterically shielded during heteromeric assembly, allowing delivery of functional heteromeric receptors to the plasma membrane. Taken together, our results illustrate novel regulatory mechanisms that control the intracellular trafficking and surface expression of kainate receptors.
authors.affiliation: Department of Molecular Pharmacology, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Ren
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Riley
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Garcia
authors.forename: James M
authors.initials: JM
authors.lastname: Sanders
authors.forename: Geoffrey T
authors.initials: GT
authors.lastname: Swanson
authors.forename: John
authors.initials: J
authors.lastname: Marshall
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D019921:Biotinylation; D002451:Cell Compartmentation / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018092:Kainic Acid Receptors / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection
chemical_list: D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D021122:Protein Subunits; D018092:Kainic Acid Receptors; D011993:Recombinant Fusion Proteins