Growth hormone-releasing hormone as an agonist of the ghrelin receptor GHS-R1a.
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.
Casanueva
Felipe F
FF
Laboratory of Molecular and Cellular Endocrinology, Research Area, Complejo Hospitalario Universitario de Santiago, Santiago de Compostela, Spain. felipe.casanueva@usc.es
Camiña
Jesus P
JP
Carreira
Marcos C
MC
Pazos
Yolanda
Y
Varga
Jozsef L
JL
Schally
Andrew V
AV
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
D007295:Inositol Phosphates; D054440:Receptors, Ghrelin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone