title: Inhibition of human type i gonadotropin-releasing hormone receptor (GnRHR) function by expression of a human type II GnRHR gene fragment.
abstract: Humans possess only one functional GnRH receptor, the type I GnRH receptor (GnRHR-I). A type II GnRH receptor (GnRHR-II) gene homolog exists, but it is disrupted by a frame shift and premature stop codon, suggesting that a conventional receptor is not translated from this gene. However, the gene remains transcriptionally active and displays alternative splicing. We identified a putative translational start site 117 bp downstream of the premature stop codon. Use of this start codon encodes a protein (designated as the GnRHR-II-reliquum) corresponding to the domains from the cytoplasmic end of transmembrane domain-5 to the carboxyl terminus of the putative full-length receptor. Immunocytochemistry revealed that GnRHR-II-reliquum expression appeared to be localized throughout the cytoplasm. Transient cotransfection of GnRHR-I and GnRHR-II-reliquum constructs into COS-7 cells resulted in reduced expression of the GnRHR-I at the cell surface and impaired signaling via the GnRHR-I as revealed by reduction of GnRH-induced inositol phosphate accumulation. This inhibitory effect was specific and dependent on the degree of GnRHR-II-reliquum coexpressed. Immunoblot analysis revealed that the total cell GnRHR-I complement, i.e. both cell-surface and nascent intracellular receptors, was markedly reduced by coexpression of the GnRHR-II-reliquum. Treatments with cell-permeable agents that blocked either de novo protein synthesis (cycloheximide) or proteinase-mediated degradation (leupeptin and phenylmethylsulfonyl fluoride) failed to alter the inhibitory effect of GnRHR-II-reliquum coexpression, suggesting that the inhibitory effect is exerted at the nucleus/endoplasmic reticulum or Golgi apparatus level, possibly by perturbing normal processing of GnRHR-I from these sites. We suggest that the GnRHR-II-reliquum plays a modulatory role in GnRHR-I expression.
authors.affiliation: Human Reproductive Sciences Unit, Medical Research Council, The University of Edinburgh Chancellor's Building, 49 Little France Crescent, Edinburgh EH16 4SB, Scotland, United Kingdom. a.pawson@hrsu.mrc.ac.uk
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Pawson
authors.forename: Stuart
authors.initials: S
authors.lastname: Maudsley
authors.forename: Kevin
authors.initials: K
authors.lastname: Morgan
authors.forename: Lindsay
authors.initials: L
authors.lastname: Davidson
authors.forename: Zvi
authors.initials: Z
authors.lastname: Naor
authors.forename: Robert P
authors.initials: RP
authors.lastname: Millar
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002522:Chlorocebus aethiops; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011966:Receptors, LHRH / Q000737:chemistry / Q000235:genetics*; D015398:Signal Transduction / Q000502:physiology
chemical_list: C484844:GNRHR protein, human; C427484:GNRHR2 protein, human; D011966:Receptors, LHRH