title: A novel spliced variant of the type 1 corticotropin-releasing hormone receptor with a deletion in the seventh transmembrane domain present in the human pregnant term myometrium and fetal membranes.
abstract: CRH exerts its actions via activation of specific G protein-coupled receptors, which exist in two types, CRH-R1 and CRH-R2, and arise from different genes with multiple spliced variants. RT-PCR amplification of CRH receptor sequences from human myometrium and fetal membranes yielded cDNAs that encode a novel CRH-R type 1 spliced variant. This variant (CRH-R1d) is present in the human pregnant myometrium at term only, which suggests a physiologically important role at the end of human pregnancy and labor. The amino acid sequence of CRH-R1d is identical to the CRH-R1alpha receptor except that it contains an exon deletion resulting in the absence of 14 amino acids in the predicted seventh transmembrane domain. Binding studies in HEK-293 cells stably expressing the CRH-R1d or CRH-R1alpha receptors revealed that the deletion does not change the binding characteristics of the variant receptor. In contrast, studies on the G protein activation demonstrated that CRH-R1d is not well coupled to the four subtypes of G proteins (G(s), G(i), G(o), G(q)) that CRH-R1alpha can activate. These data suggest that although the deleted segment is not important for CRH binding, it plays a crucial role in CRH receptor signal transduction. Second messenger studies of the variant receptor showed that CRH and CRH-like peptides can stimulate the adenylate cyclase system, with reduced sensitivity and potency by 10-fold compared with the CRH-R1alpha. Furthermore, CRH failed to stimulate inositol trisphosphate production. Coexpression studies between the CRH-R1d or CRH-R1alpha showed that this receptor does not play a role as a dominant negative receptor for CRH.
authors.affiliation: Sir Quinton Hazell Molecular Medicine Research Centre, Department of Biological Sciences, University of Warwick, Coventry, United Kingdom. chdg@dna.bio.warwick.ac.uk
authors.forename: D K
authors.initials: DK
authors.lastname: Grammatopoulos
authors.forename: Y
authors.initials: Y
authors.lastname: Dai
authors.forename: H S
authors.initials: HS
authors.lastname: Randeva
authors.forename: M A
authors.initials: MA
authors.lastname: Levine
authors.forename: E
authors.initials: E
authors.lastname: Karteris
authors.forename: A J
authors.initials: AJ
authors.lastname: Easton
authors.forename: E W
authors.initials: EW
authors.lastname: Hillhouse
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D005321:Extraembryonic Membranes / Q000737:chemistry*; D005260:Female; D017353:Gene Deletion; D006801:Humans; D007163:Immunosorbent Techniques; D007668:Kidney; D008969:Molecular Sequence Data; D009215:Myometrium / Q000737:chemistry*; D011247:Pregnancy; D012333:RNA, Messenger / Q000378:metabolism; D018019:Receptors, Corticotropin-Releasing Hormone / Q000032:analysis / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: D012333:RNA, Messenger; D018019:Receptors, Corticotropin-Releasing Hormone; D003346:Corticotropin-Releasing Hormone