title: Involvement of the ser-glu-pro motif in ligand species-dependent desensitisation of the rat gonadotrophin-releasing hormone receptor.
abstract: There are two forms of gonadotrophin-releasing hormone (GnRH), GnRH-I and GnRH-II, in the vertebrate brain. Both GnRH-I and GnRH-II are thought to interact with the type-I GnRH receptor (GnRHR). The present study attempted to demonstrate whether GnRH-I and GnRH-II induce differential desensitisation of GnRHR and to identify the motif involved. Time course inositol phosphate (IP) accumulation assay reveals that, in cells expressing the wild-type rat GnRHR, GnRH-I induced continuous increase in IP production, whereas GnRH-II-induced IP production rate at later time points (30-120 min after ligand treatment) became attenuated. However, in cells expressing the mutant receptor in which the Ser-Glu-Pro (SEP) motif in extracellular loop 3 was replaced by Pro-Glu-Val (PEV), IP accumulation rates at later time points were more decreased by GnRH-I than GnRH-II. Ca2+ responses to repetitive GnRH applications reveal that GnRH-II desensitised the wild-type receptor faster than GnRH-I, whereas the opposite situation was observed in the PEV mutant. In addition, cell surface loss of GFP-tagged wild-type receptor was more facilitated by GnRH-II than GnRH-I, whereas that of the GFP-tagged PEV mutant receptor was more enhanced by GnRH-I than GnRH-II. The present study indicates that the SEP motif is potentially responsible for ligand species-dependent receptor desensitisation. Together, these results suggest that GnRH-I and GnRH-II may have different effects on mammalian type-I GnRHR via modulation of desensitisation rates.
authors.affiliation: Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju, Korea.
authors.forename: J A
authors.initials: JA
authors.lastname: Song
authors.forename: D Y
authors.initials: DY
authors.lastname: Oh
authors.forename: J S
authors.initials: JS
authors.lastname: Moon
authors.forename: D
authors.initials: D
authors.lastname: Geum
authors.forename: H B
authors.initials: HB
authors.lastname: Kwon
authors.forename: J Y
authors.initials: JY
authors.lastname: Seong
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003627:Data Interpretation, Statistical; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008024:Ligands; D018613:Microscopy, Confocal; D009154:Mutation; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D011966:Receptors, LHRH / Q000235:genetics / Q000502:physiology*; D013045:Species Specificity
chemical_list: D007295:Inositol Phosphates; D008024:Ligands; D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D049452:Green Fluorescent Proteins; D002118:Calcium