title: Endoplasmic reticulum degradation impedes olfactory G-protein coupled receptor functional expression.
abstract: BACKGROUND
  Research on olfactory G-protein coupled receptors (GPCRs) has been severely impeded by poor functional expression in heterologous systems. Previously, we demonstrated that inefficient olfactory receptor (OR) expression at the plasma membrane is attributable, in part, to degradation of endoplasmic reticulum (ER)-retained ORs by the ubiquitin-proteasome system and sequestration of ORs in ER aggregates that are degraded by autophagy. Thus, experiments were performed to test the hypothesis that attenuation of ER degradation improves OR functional expression in heterologous cells.
  
  
  RESULTS
  To develop means to increase the functional expression of ORs, we devised an approach to measure activation of the mOREG OR (Unigene # Mm.196680; Olfr73) through coupling to an olfactory cyclic nucleotide-gated cation channel (CNG). This system, which utilizes signal transduction machinery coupled to OR activation in native olfactory sensory neurons, was used to demonstrate that degradation, both by the ubiquitin-proteasome system and autophagy, limits mOREG functional expression. The stimulatory effects of proteasome and autophagy inhibitors on mOREG function required export from the ER and trafficking through the biosynthetic pathway.
  
  
  CONCLUSIONS
  These findings demonstrate that poor functional expression of mOREG in heterologous cells is improved by blocking proteolysis. Inhibition of ER degradation may improve the function of other ORs and assist future efforts to elucidate the molecular basis of odor discrimination.
authors.affiliation: Senomyx, Inc, 11099 North Torrey Pines Road, La Jolla, CA 92037, USA. senomyx.com
authors.forename: Min
authors.initials: M
authors.lastname: Lu
authors.forename: Lena
authors.initials: L
authors.lastname: Staszewski
authors.forename: Fernando
authors.initials: F
authors.lastname: Echeverri
authors.forename: Hong
authors.initials: H
authors.lastname: Xu
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Moyer
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005054:Eugenol / Q000378:metabolism; D015870:Gene Expression; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating; D051379:Mice; D009812:Odorants; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D021381:Protein Transport; D018035:Receptors, Odorant / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012243:Rhodopsin; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D061988:Proteasome Inhibitors; D018035:Receptors, Odorant; D011993:Recombinant Fusion Proteins; D025801:Ubiquitin; D005054:Eugenol; D012243:Rhodopsin; D046988:Proteasome Endopeptidase Complex