Coupling of gonadotropin-releasing hormone receptor to Gi protein in human reproductive tract tumors.

Abstract

The signaling pathway by which GnRH acts in peripheral tumors is distinct from that in the anterior pituitary. We attempted to identify the guanosine triphosphate (GTP)-binding protein (G protein) subtypes linked to GnRH receptor in the genital tract tumor membranes. Surgically removed ovarian carcinomas and uterine leiomyosarcomas were screened for GnRH receptor expression before plasma membrane isolation. The G alpha i was detected by immunoblotting of membrane extracts with specific antibody and pertussis toxincatalyzed ADP-ribosylation from nicotinamide adenine dinucleotide. Membrane phosphotyrosine phosphatase activity was determined as a GnRH-sensitive membrane event using synthetic substrate p-nitrophenyl in a spectrophotometric assay. Pertussis toxin, but not cholera toxin, brought about ADP-ribosylation of an immunodetected G alpha i of 41 kDa in the GnRH receptor-positive tumor membrane. Incubation with a GnRH analog and GTP decreased the ADP-ribosylation activity in a dose-dependent manner; a half-maximal effect occurred with 30 nmol/L buserelin (P < 0.01). The apparent inhibition by GnRH of the ADP-ribosylation demonstrated that GnRH resolved the alpha-subunit of the Gi to GTP-bound form in the membranes. The action of GnRH was neutralized by a competitive antagonist, antide. Pretreatment of the membrane with the pertussis toxin completely inhibited GnRH-sensitive phosphotyrosine phosphatase activity (P < 0.01). These data demonstrate the coupling of GnRH receptor to Gi protein subfamily. The Gi which couples GnRH receptor to the effector may define the difference of responses by peripheral tumor and the anterior pituitary.

Expression and Function of Gonadotropin-releasing Hormone (GnRH) Receptor in Human Olfactory GnRH-secreting Neurons

“…This G protein activates adenylate cyclase, cAMP production, and protein kinase A activation (41,42). Antiproliferative signaling of GnRH in human reproductive tract tumors is mediated through the PTX-sensitive G i protein (43,44). Moreover, recent research has demonstrated that, in GT1 cells, GnRH-modulated neuronal Ca 2ϩ signaling occurs also via G i inhibitory mechanisms (45).…”

“…A specific GnRH receptor antagonist blocked the migratory promoting activity of GnRH. Moreover, the fact that PTX pretreatment was able to reduce GnRH-dependent migration in a dose-dependent manner suggests that these effects were coupled to PTX-sensitive G i/o proteins (43)(44)(45). Several factors, including anosmin-1 (48), NELF (3), the receptor tyrosine kinase Ark (11), and FGFR1 (20), have been described as playing a role in some aspects of GnRH cell migration.…”

Involvement of Both Gq/11 and Gs Proteins in Gonadotropin-releasing Hormone Receptor-mediated Signaling in LβT2 Cells

“…In human reproductive tract tumors, the GnRH receptor also couples to G i (16). However, in G-GH3 cells, which are GH3 somatomammotropes transfected with the rat GnRH-receptor, GnRH evoked IP turnover is insensitive to PTX (17), indicating that a different G protein may be involved in signal transduction in these cells.…”

The role of peripheral gonadotropin-releasing hormone receptors in female reproduction

“…This intracellular cascade of events mediates the biologic activity of GnRH, which stimulates the synthesis and secretion of gonadotropins. On the other hand, the peripheral GnRH receptor is coupled to the Gi protein in uterine leiomyosarcoma, ovarian carcinoma, and endometrial carcinoma (17,18). Activation of the peripheral GnRH receptor leads to a decrease of intracellular cyclic adenosine monophosphate (cAMP) level, which causes activation of protein tyrosine phosphatase.…”