title: The human gonadotropin releasing hormone type I receptor is a functional intracellular GPCR expressed on the nuclear membrane.
abstract: The mammalian type I gonadotropin releasing hormone receptor (GnRH-R) is a structurally unique G protein-coupled receptor (GPCR) that lacks cytoplasmic tail sequences and displays inefficient plasma membrane expression (PME). Compared to its murine counterparts, the primate type I receptor is inefficiently folded and retained in the endoplasmic reticulum (ER) leading to a further reduction in PME. The decrease in PME and concomitant increase in intracellular localization of the mammalian GnRH-RI led us to characterize the spatial distribution of the human and mouse GnRH receptors in two human cell lines, HEK 293 and HTR-8/SVneo. In both human cell lines we found the receptors were expressed in the cytoplasm and were associated with the ER and nuclear membrane. A molecular analysis of the receptor protein sequence led us to identify a putative monopartite nuclear localization sequence (NLS) in the first intracellular loop of GnRH-RI. Surprisingly, however, neither the deletion of the NLS nor the addition of the Xenopus GnRH-R cytoplasmic tail sequences to the human receptor altered its spatial distribution. Finally, we demonstrate that GnRH treatment of nuclei isolated from HEK 293 cells expressing exogenous GnRH-RI triggers a significant increase in the acetylation and phosphorylation of histone H3, thereby revealing that the nuclear-localized receptor is functional. Based on our findings, we conclude that the mammalian GnRH-RI is an intracellular GPCR that is expressed on the nuclear membrane. This major and novel discovery causes us to reassess the signaling potential of this physiologically and clinically important receptor.
authors.affiliation: The Children's Health Research Institute, London, Canada.
authors.forename: Michelle
authors.initials: M
authors.lastname: Re
authors.forename: Macarena
authors.initials: M
authors.lastname: Pampillo
authors.forename: Martin
authors.initials: M
authors.lastname: Savard
authors.forename: Céléna
authors.initials: C
authors.lastname: Dubuc
authors.forename: Craig A
authors.initials: CA
authors.lastname: McArdle
authors.forename: Robert P
authors.initials: RP
authors.lastname: Millar
authors.forename: P Michael
authors.initials: PM
authors.lastname: Conn
authors.forename: Fernand
authors.initials: F
authors.lastname: Gobeil
authors.forename: Moshmi
authors.initials: M
authors.lastname: Bhattacharya
authors.forename: Andy V
authors.initials: AV
authors.lastname: Babwah
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D004252:DNA Mutational Analysis; D005455:Fluorescent Antibody Technique; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D009154:Mutation; D009685:Nuclear Envelope / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism*
chemical_list: C484844:GNRHR protein, human; D007295:Inositol Phosphates; D043562:Receptors, G-Protein-Coupled; D011966:Receptors, LHRH