Ala/Thr(201) in extracellular loop 2 and Leu/Phe(290) in transmembrane domain 6 of type 1 frog gonadotropin-releasing hormone receptor confer differential ligand sensitivity and signal transduction.

Abstract

Recently, we have identified three distinct types of bullfrog GnRH receptor (designated bfGnRHR-1, bfGnRHR-2, and bfGnRHR-3). In the present study, we have isolated three GnRHR clones in Rana dybowskii (dyGnRHR-1, dyGnRHR-2, and dyGnRHR-3). Despite high homology of dyGnRHRs with the corresponding bfGnRHRs, dyGnRHRs revealed different signaling pathways and ligand sensitivity compared with the bfGnRHR counterparts. Activation of dyGnRHRs with GnRH stimulated cAMP-mediated gene expression. However, dyGnRHR-3 but not dyGnRHR-1 and -2 induced c-fos promoter-driven gene expression. Consistently, dyGnRHR-1 and dyGnRHR-2 were not able to increase GnRH-induced inositol phosphate accumulation, whereas all bfGnRHRs and dyGnRHR-3 were, indicating that dyGnRHR-1 and dyGnRHR-2 are coupled to solely G(s), whereas all bfGnRHRs and dyGnRHR-3 are coupled to both G(s) and G(q/11). Moreover, dyGnRHR-1 and dyGnRHR-2 showed about 10-fold less sensitivity to each ligand than that of the bfGnRHR counterparts. Using type 1 chimeric and point-mutated receptors, we further elucidated that specific amino acids, Ala/Thr(201) in extracellular loop 2 and Leu/Phe(290) in transmembrane domain 6 of the type 1 receptor, are responsible for ligand sensitivity and signal transduction pathway. Particularly, substitution of Leu(290) to Phe in dyGnRHR-1 increased GnRH-induced inositol phosphate production as well as c-fos promoter-driven gene expression whereas substitution of Phe(290) to Leu in bfGnRHR-1 decreased those activities. Collectively, these results demonstrate the presence of three types of GnRHR in amphibians, and suggest species- and type-specific ligand recognition and different signaling pathways in frog GnRHRs.

Cite this paper

@article{Seong2003AlaThr201IE, title={Ala/Thr(201) in extracellular loop 2 and Leu/Phe(290) in transmembrane domain 6 of type 1 frog gonadotropin-releasing hormone receptor confer differential ligand sensitivity and signal transduction.}, author={Jae Young Seong and Li Wang and Da Young Oh and Oim Yun and Kaushik Maiti and Jian Li and Jae Mok Soh and Hueng Sik Choi and Kyungjin Kim and Hubert Vaudry and Hyuk Bang Kwon}, journal={Endocrinology}, year={2003}, volume={144 2}, pages={454-66} }