title: Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a.
abstract: Ghrelin synergizes with growth hormone-releasing hormone (GHRH) to potentiate growth hormone (GH) response through a mechanism not yet fully characterized. This study was conducted to analyze the role of GHRH as a potential ligand of the ghrelin receptor, GHS-R1a. The results show that hGHRH(1-29)NH(2) (GHRH) induces a dose-dependent calcium mobilization in HEK 293 cells stably transfected with GHS-R1a an effect not observed in wild-type HEK 293 cells. This calcium rise is also observed using the GHRH receptor agonists JI-34 and JI-36. Radioligand binding and cross-linking studies revealed that calcium response to GHRH is mediated by the ghrelin receptor GHS-R1a. GHRH activates the signaling route of inositol phosphate and potentiates the maximal response to ghrelin measured in inositol phosphate turnover. The presence of GHRH increases the binding capacity of (125)I-ghrelin in a dose dependent-fashion showing a positive binding cooperativity. In addition, confocal microscopy in CHO cells transfected with GHS-R1a tagged with enhanced green fluorescent protein shows that GHRH activates the GHS-R1a endocytosis. Furthermore, the selective GHRH-R antagonists, JV-1-42 and JMR-132, act also as antagonists of the ghrelin receptor GHS-R1a. Our findings suggest that GHRH interacts with ghrelin receptor GHS-R1a, and, in consequence, modifies the ghrelin-associated intracellular signaling pathway. This interaction may represent a form of regulation, which could play a putative role in the physiology of GH regulation and appetite control.
authors.affiliation: Laboratory of Molecular and Cellular Endocrinology, Research Area, Complejo Hospitalario Universitario de Santiago, Santiago de Compostela, Spain. felipe.casanueva@usc.es
authors.forename: Felipe F
authors.initials: FF
authors.lastname: Casanueva
authors.forename: Jesus P
authors.initials: JP
authors.lastname: Camiña
authors.forename: Marcos C
authors.initials: MC
authors.lastname: Carreira
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Pazos
authors.forename: Jozsef L
authors.initials: JL
authors.lastname: Varga
authors.forename: Andrew V
authors.initials: AV
authors.lastname: Schally
mesh_terms: D020013:Calcium Signaling; D002460:Cell Line; D004705:Endocytosis; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D011485:Protein Binding; D054440:Receptors, Ghrelin / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
chemical_list: D007295:Inositol Phosphates; D054440:Receptors, Ghrelin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone