title: Melatonin receptor activation regulates GnRH gene expression and secretion in GT1-7 GnRH neurons. Signal transduction mechanisms.
abstract: Melatonin plays a significant role in the control of the hypothalamic-pituitary-gonadal axis. Using the GT1-7 cell line, an in vitro model of GnRH-secreting neurons of the hypothalamus, we examined the potential signal transduction pathways activated by melatonin directly at the level of the GT1-7 neuron. We found that melatonin inhibits forskolin-stimulated adenosine 3'-, 5'-cyclic monophosphate accumulation in GT1-7 cells through an inhibitory G protein. Melatonin induced protein kinase C activity by 1.65-fold over basal levels, increased the phosphorylation of extracellular signal-regulated kinase 1 and 2 proteins, and activated c-fos and junB mRNA expression in GT1-7 cells. Using the protein kinase A inhibitor H-89, the protein kinase C inhibitor bisindolylmaleimide, and the mitogen-activated protein kinase kinase inhibitor PD98059, we found that the melatonin-mediated cyclical regulation of GnRH mRNA expression may involve the protein kinase C and the extracellular signal-regulated kinase 1 and 2 pathways, but not the protein kinase A pathway. We found that melatonin suppresses GnRH secretion by approximately 45% in the GT1-7 neurons. However, in the presence of the inhibitors H-89, bisindolylmaleimide, and PD98059 melatonin was unable to suppress GnRH secretion. These results provide insights into the potential signal transduction mechanisms involved in the control of GnRH gene expression and secretion by melatonin.
authors.affiliation: Institute for Medical Sciences, University of Toronto, University Health Network, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Deboleena
authors.initials: D
authors.lastname: Roy
authors.forename: Denise D
authors.initials: DD
authors.lastname: Belsham
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000096:biosynthesis; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D005786:Gene Expression Regulation; D017781:Genes, Immediate-Early; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics*; D020962:Heterotrimeric GTP-Binding Proteins / Q000502:physiology; D020935:MAP Kinase Signaling System; D008550:Melatonin / Q000494:pharmacology; D051379:Mice; D011493:Protein Kinase C / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D044094:Receptors, Melatonin; D015398:Signal Transduction
chemical_list: D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins; D008550:Melatonin