title: Assembly and cell surface expression of KA-2 subunit-containing kainate receptors.
abstract: Kainate receptors (KARs) modulate synaptic transmission at both pre-synaptic and post-synaptic sites. The overlap in the distribution of KA-2 and GluR6/7 subunits in several brain regions suggests the co-assembly of these subunits in native KARs. The molecular mechanisms that control the assembly and surface expression of KARs are unknown. Unlike GluR5-7, the KA-2 subunit is unable to form functional homomeric KAR channels. We expressed the KA-2 subunit alone or in combination with other KAR subunits in HEK-293 cells. The cell surface expression of the KAR subunit homo- and heteromers were analysed using biotinylation and agonist-stimulated cobalt uptake. While GluR6 or GluR7 homomers were expressed on the cell surface, KA-2 alone was retained within the endoplasmic reticulum. We found that the cell surface expression of KA-2 was dramatically increased by co-expression with either of the low-affinity KAR subunits GluR5-7. However, co-expression with other related ionotropic glutamate receptor subunits (GluR1 and NR1) does not facilitate the cell surface expression of KA-2. The analysis of subcellular fractions of neocortex revealed that synaptic KARs have a relatively high KA-2 content compared to microsomal ones. Thus, KA-2 is likely to contain an endoplasmic reticulum retention signal that is shielded on assembly with other KAR subunits.
authors.affiliation: MRC Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, Bristol, UK.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Gallyas
authors.forename: Simon M
authors.initials: SM
authors.lastname: Ball
authors.forename: Elek
authors.initials: E
authors.lastname: Molnar
mesh_terms: D000818:Animals; D019921:Biotinylation; D001921:Brain / Q000378:metabolism; D001923:Brain Chemistry; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D003035:Cobalt / Q000493:pharmacokinetics; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000378:metabolism; D021122:Protein Subunits / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000032:analysis / Q000096:biosynthesis; D018092:Kainic Acid Receptors / Q000032:analysis / Q000096:biosynthesis*; D013569:Synapses / Q000378:metabolism; D000097806:GluK2 Kainate Receptor; D000097808:GluK3 Kainate Receptor
chemical_list: D003035:Cobalt; D021122:Protein Subunits; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D000097806:GluK2 Kainate Receptor; D000097808:GluK3 Kainate Receptor