Membrane-Proximal Region of the Carboxyl Terminus of the Gonadotropin-Releasing Hormone Receptor (GnRHR) Confers Differential Signal Transduction between Mammalian and Nonmammalian GnRHRs

Abstract

Recently, we demonstrated that the mammalian type-I GnRH receptor (GnRHR) has a high preference for the phospholipase C/protein kinase C (PLC/PKC)-linked signaling pathway, whereas non-mammalian bullfrog (bf) GnRHRs couple to both adenylate cyclase/protein kinase A (AC/PKA)- and PLC/PKC-linked signaling pathways. In the pre-sent study, using AC/PKA-specific reporter (cAMP-responsive element-luciferase) and PLC/PKC-specific reporter (serum-responsive element-luciferase) systems, we attempted to identify the motif responsible for this difference. A deletion of the intracellular carboxyl-terminal tail (C tail) of bfGnRHR-1 remarkably decreased its ability to induce the AC/PKA-linked signaling pathway. Further dissection of the C tail indicated that an HFRK motif in the membrane-proximal sequence of bfGnRHR-1 C tail is a minimal requirement for the AC/PKA-linked signaling pathway as the addition of this motif to rat GnRHR or deletion of it from bfGnRHR-1 significantly affected the ability to induce the AC/PKA-linked signaling pathway. Deletion or addition of the HFRK motif, however, did not critically influence the PLC/PKC-linked signaling pathway. These results indicate that the HFRK motif in the membrane-proximal region confers the differential signal transduction pathways between mammalian and nonmammalian GnRHRs.

Insulin Contributes to Fine-Tuning of the Pancreatic Beta-Cell Response to Glucagon-Like Peptide-1

“…The reactions were terminated by replacing medium with ice-cold 5% trichloroacetic acid containing 1 mM ATP and 1 mM cAMP. [ 3 H]cAMP and [ 3 H]ATP were separated on an AG50W-X4 resin (Bio-Rad, USA) and alumina columns as previously described (Oh et al, 2005). The cAMP accumulation was expressed as…”

Functional characterization and kinetic studies of an ancestral lamprey GnRH-III selective type II GnRH receptor from the sea lamprey, Petromyzon marinus

“…Pituitary GnRH receptors are thought to primarily signal through G q/11 , resulting in the stimulation of the IP 3 second messenger system; however, G s activation and cAMP signaling has been reported as well , Grosse et al 2000, Liu et al 2002, Oh et al 2005. G-protein coupling to type I GnRH receptors clearly occurs within the intracellular loops (ILs), where several motifs have been identified that may be involved in G-protein coupling (see Table 3).…”

“…GnRH receptor signaling has been characterized in several systems, and is primarily thought to function through the Inositol 1,4,5-triphospate (IP 3 ) second messenger pathway; however, type II GnRH receptors and in some cases type I GnRH receptors have been shown to also activate cAMP signaling , Grosse et al 2000, Liu et al 2002, Oh et al 2005. The presence or absence of the C-terminal tail in type II and type I GnRH receptors respectively could possibly explain the signaling disparity between the two groups, where, for example, histidinephenylalanine-arginine-lysine (an HFRK) motif in the membrane proximal region of bullfrog type II GnRH receptors was recently shown to be required for cAMP signaling (Oh et al 2005).…”

“…The presence or absence of the C-terminal tail in type II and type I GnRH receptors respectively could possibly explain the signaling disparity between the two groups, where, for example, histidinephenylalanine-arginine-lysine (an HFRK) motif in the membrane proximal region of bullfrog type II GnRH receptors was recently shown to be required for cAMP signaling (Oh et al 2005). Rapid, ligand-dependant internalization resulting in desensitization and/or signal switching is another key functional difference between type I and type II GnRH receptors; this has been described and attributed to the presence or absence of specific Ser/Thr residues located throughout the C-terminal tail (Blomenrohr et al 1999, Willars et al 1999, Pawson et al 2003, Ronacher et al 2004.…”

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“…GnRH-R2 GnRH-R3 2 3 5 GnRH-R GnRH-R1 GnRH-R 53,54 GnRH-R2 GnRH-R3 C 47,55 IP3 cAMP 55,56 GnRH-R2 GnRH-R3 …”