Evidence that signalling pathways by which thyrotropin-releasing hormone and gonadotropin-releasing hormone act are both common and distinct

• Published in: Molecular endocrinology (Baltimore, Md.) Vol. 8; no. 8; p. 1038
• Main Authors: Kaiser, U B, Katzenellenbogen, R A, Conn, P M, Chin, W W
• Format: Journal Article
• Language: English
• Published: United States 01-08-1994
• Subjects: Adenoma - pathology; Animals; Buserelin - pharmacology; Calcium - physiology; DNA, Complementary - genetics; Gene Expression Regulation - drug effects; Glycoprotein Hormones, alpha Subunit - biosynthesis; Glycoprotein Hormones, alpha Subunit - genetics; Gonadotropin-Releasing Hormone - analogs & derivatives; Gonadotropin-Releasing Hormone - pharmacology; GTP-Binding Proteins - physiology; Luciferases - biosynthesis; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoric Diester Hydrolases - physiology; Pituitary Neoplasms - pathology; Prolactin - genetics; Prolactin - secretion; Protein Kinase C - physiology; Rats; Receptors, LHRH - drug effects; Receptors, LHRH - physiology; Receptors, Thyrotropin-Releasing Hormone - drug effects; Receptors, Thyrotropin-Releasing Hormone - physiology; Recombinant Fusion Proteins - biosynthesis; Signal Transduction; Thyrotropin-Releasing Hormone - pharmacology; Transfection; Tumor Cells, Cultured
• ISSN: 0888-8809
• DOI: 10.1210/me.8.8.1038

TRH and GnRH receptors are each coupled to G proteins of the Gq/11 family. Activation of each of these receptors by their respective ligands results in the stimulation of phospholipase C activity, leading to calcium mobilization and protein kinase C activation. Thus, the effects of TRH and GnRH may be mediated through the same intracellular signal transduction pathway. To compare responses to TRH and GnRH directly within one cell type, we have stably transfected the rat pituitary GH3 lactotrope cell line, which expresses the endogenous TRH receptor, with an expression vector containing rat GnRH receptor cDNA. Transfected cells specifically bound GnRH with high affinity and responded to GnRH stimulation with an increase in PRL mRNA levels, analogous to their response to TRH stimulation. Stably transfected GH3 cells, which were then transiently transfected with luciferase reporter constructs containing either the PRL or the glycoprotein hormone alpha-subunit promoter, responded to either GnRH or TRH stimulation with an increase in luciferase activity in a time- and dose-dependent fashion. The stimulatory effects of maximally effective concentrations of TRH and GnRH were additive on PRL, but not alpha-subunit, gene expression. These data, coupled with evidence of cross-desensitization of alpha-subunit, but not PRL, promoter activity stimulation by TRH and GnRH, suggest that there may be differences in the signal transduction pathways activated by TRH and GnRH receptors in the regulation of PRL and alpha-subunit gene expression.