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

• Published in: The journal of clinical endocrinology and metabolism Vol. 81; no. 9; pp. 3249 - 3253
• Main Authors: IMAI, A, TAKAGI, H, HORIBE, S, FUSEYA, T, TAMAYA, T
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Endocrine Society 01.09.1996
• Subjects: Adenosine Diphosphate Ribose - metabolism; Biological and medical sciences; Female; Female genital diseases; Gonadotropin-Releasing Hormone - pharmacology; GTP-Binding Proteins - analysis; GTP-Binding Proteins - metabolism; Gynecology. Andrology. Obstetrics; Humans; Immunoblotting; Leiomyoma - metabolism; Medical sciences; Ovarian Neoplasms - metabolism; Pertussis Toxin; Receptors, LHRH - analysis; Receptors, LHRH - metabolism; Tumors; Uterine Neoplasms - metabolism; Virulence Factors, Bordetella - metabolism; Virulence Factors, Bordetella - pharmacology; Human; Hormonodependence; Peptide hormone; Gonadotropin RH; Malignant tumor; Carcinogenesis; Female genital diseases; Hypothalamic hormone; Female genital duct; Female; Biological effect; Hormone releasing factor; G protein; Hormonal receptor
• ISSN: 0021-972X
• DOI: 10.1210/jc.81.9.3249

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.