title: Up-regulation of GABA(B) receptor signaling by constitutive assembly with the K+ channel tetramerization domain-containing protein 12 (KCTD12).
abstract: GABA(B) receptors are the G-protein coupled receptors (GPCRs) for GABA, the main inhibitory neurotransmitter in the central nervous system. Native GABA(B) receptors comprise principle and auxiliary subunits that regulate receptor properties in distinct ways. The principle subunits GABA(B1a), GABA(B1b), and GABA(B2) form fully functional heteromeric GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Principal subunits regulate forward trafficking of the receptors from the endoplasmic reticulum to the plasma membrane and control receptor distribution to axons and dendrites. The auxiliary subunits KCTD8, -12, -12b, and -16 are cytosolic proteins that influence agonist potency and G-protein signaling of GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Here, we used transfected cells to study assembly, surface trafficking, and internalization of GABA(B) receptors in the presence of the KCTD12 subunit. Using bimolecular fluorescence complementation and metabolic labeling, we show that GABA(B) receptors associate with KCTD12 while they reside in the endoplasmic reticulum. Glycosylation experiments support that association with KCTD12 does not influence maturation of the receptor complex. Immunoprecipitation and bioluminescence resonance energy transfer experiments demonstrate that KCTD12 remains associated with the receptor during receptor activity and receptor internalization from the cell surface. We further show that KCTD12 reduces constitutive receptor internalization and thereby increases the magnitude of receptor signaling at the cell surface. Accordingly, knock-out or knockdown of KCTD12 in cultured hippocampal neurons reduces the magnitude of the GABA(B) receptor-mediated K(+) current response. In summary, our experiments support that the up-regulation of functional GABA(B) receptors at the neuronal plasma membrane is an additional physiological role of the auxiliary subunit KCTD12.
authors.affiliation: Department of Biomedicine, University of Basel, CH-4056 Basel, Switzerland.
authors.forename: Klara
authors.initials: K
authors.lastname: Ivankova
authors.forename: Rostislav
authors.initials: R
authors.lastname: Turecek
authors.forename: Thorsten
authors.initials: T
authors.lastname: Fritzius
authors.forename: Riad
authors.initials: R
authors.lastname: Seddik
authors.forename: Laurent
authors.initials: L
authors.lastname: Prezeau
authors.forename: Laëtitia
authors.initials: L
authors.lastname: Comps-Agrar
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Pin
authors.forename: Bernd
authors.initials: B
authors.lastname: Fakler
authors.forename: Valerie
authors.initials: V
authors.lastname: Besseyrias
authors.forename: Martin
authors.initials: M
authors.lastname: Gassmann
authors.forename: Bernhard
authors.initials: B
authors.lastname: Bettler
mesh_terms: D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002522:Chlorocebus aethiops; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization / Q000502:physiology*; D018080:Receptors, GABA-B / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D015221:Potassium Channels; D018080:Receptors, GABA-B; D011188:Potassium
keywords: Bioluminescence Resonance Energy Transfer (BRET); G Protein-coupled Receptors (GPCR); GABA Receptors; GABA-B; Gamma-Aminobutyric Acid; Potassium Channel Tetramerization Domain; Protein Assembly; Trafficking