title: Ischemia-like oxygen and glucose deprivation mediates down-regulation of cell surface γ-aminobutyric acidB receptors via the endoplasmic reticulum (ER) stress-induced transcription factor CCAAT/enhancer-binding protein (C/EBP)-homologous protein (CHOP).
abstract: Cerebral ischemia frequently leads to long-term disability and death. Excitotoxicity is believed to be the main cause for ischemia-induced neuronal death. Although a role of glutamate receptors in this process has been firmly established, the contribution of metabotropic GABAB receptors, which control excitatory neurotransmission, is less clear. A prominent characteristic of ischemic insults is endoplasmic reticulum (ER) stress associated with the up-regulation of the transcription factor CCAAT/enhancer-binding protein-homologous protein (CHOP). After inducing ER stress in cultured cortical neurons by sustained Ca(2+) release from intracellular stores or by a brief episode of oxygen and glucose deprivation (in vitro model of cerebral ischemia), we observed an increased expression of CHOP accompanied by a strong reduction of cell surface GABAB receptors. Our results indicate that down-regulation of cell surface GABAB receptors is caused by the interaction of the receptors with CHOP in the ER. Binding of CHOP prevented heterodimerization of the receptor subunits GABAB1 and GABAB2 and subsequent forward trafficking of the receptors to the cell surface. The reduced level of cell surface receptors diminished GABAB receptor signaling and, thus, neuronal inhibition. These findings indicate that ischemia-mediated up-regulation of CHOP down-regulates cell surface GABAB receptors by preventing their trafficking from the ER to the plasma membrane. This mechanism leads to diminished neuronal inhibition and may contribute to excitotoxicity in cerebral ischemia.
authors.affiliation: From the Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Maier
authors.forename: Khaled
authors.initials: K
authors.lastname: Zemoura
authors.forename: Mario A
authors.initials: MA
authors.lastname: Acuña
authors.forename: Gonzalo E
authors.initials: GE
authors.lastname: Yévenes
authors.forename: Hanns Ulrich
authors.initials: HU
authors.lastname: Zeilhofer
authors.forename: Dietmar
authors.initials: D
authors.lastname: Benke
mesh_terms: D000818:Animals; D002545:Brain Ischemia / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D059865:Endoplasmic Reticulum Stress; D005260:Female; D015870:Gene Expression; D005947:Glucose / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D018613:Microscopy, Confocal; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D018080:Receptors, GABA-B / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism*
chemical_list: D018080:Receptors, GABA-B; D051742:Transcription Factor CHOP; D005947:Glucose; D010100:Oxygen
keywords: CHOP; Cell Surface; Cerebral Ischemia; Endoplasmic Reticulum (ER); Endoplasmic Reticulum Stress; G Protein-coupled Receptors (GPCR); GABA Receptors; Neurons; Trafficking