Preferential ligand selectivity of the monkey type-II gonadotropin-releasing hormone (GnRH) receptor for GnRH-2 and its analogs

Gonadotropin-releasing hormone (GnRH) regulates the reproductive system through the cognate GnRH receptor (GnRHR) in vertebrates. In this study, we cloned a cDNA encoding the full-length open reading frame sequence for green monkey type-II GnRHR (gmGnRHR-2) from the genomic DNA of CV-1 cells. Transient transfection study showed that gmGnRHR-2 was able to induce both c-fos promoter and cAMP responsive element-driven transcriptional activities, indicating that gmGnRHR-2 couples to both G(s)- and G(q/11)-linked signaling pathways. gmGnRHR-2 responded better to GnRH-2 ([His(5), Trp(7), Tyr(8)]GnRH) than GnRH-1 ([Tyr(5), Leu(7), Arg(8)]GnRH). Substitutions of His(5), Trp(7), and/or Tyr(8) in GnRH-1 increased the potency to activate gmGnRHR-2, suggesting that individual His(5), Trp(7), and Tyr(8) in GnRH-2 contributed to differential ligand sensitivity of gmGnRHR-2. Substitution Of D-Ala for Gly(6) in GnRH-2 increased the potency to activate the receptor, suggesting that GnRH-2 has a constrained conformation when it binds to the receptor. GnRH-induced gmGnRHR-2 activation was specifically inhibited by GnRH-2 antagonists, Trptorelix-1 and -2, but not by a GnRH-1 antagonist, Cetrorelix. In conclusion, gmGnRHR-2 revealed preferential ligand selectivity for GnRH-2 and its analogs, suggesting that gmGnRHR-2 has a functional activity that is different from mammalian type-I GnRHRs but similar to non-mammalian GnRHRs. (C) 2003 Elsevier Ireland Ltd. All rights reserved.