A novel interaction between inhibitory melatonin receptors and protein kinase C-dependent signal transduction in ovine pars tuberalis cells.
This study revealed an important and unexpected finding: namely, that inhibitory melatonin receptors can inhibit a phorbol 12,13 myristate acetate (PMA)-induced, protein kinase C (PKC)-dependent increase in c-fos messenger RNA expression in ovine pars tuberalis (PT) cells. PMA induces dose-dependent stimulation of c-fos expression that is attenuated by melatonin in a dose-dependent and pertussis toxin-sensitive manner. The effect of 100 nM PMA is blocked by Ro31-8220 (1 microM), yet is not mimicked by 4alpha-PMA (100 nM). PMA (100 nM) induces PKC activity in PT cells (P < 0.05) within 5 min, but melatonin has no effect on this response. PMA (100 nM) stimulates both phospholipase D and mitogen-activated protein kinase (MAPK) (p42/44) activities in PT cells, but melatonin has no effect on these responses. The results indicate that neither of these second-messenger activities contribute to the melatonin-sensitive pathway of c-fos activation. The MEK (MAPK kinase) inhibitor, PD98059 (50 microM), does not block the induction of c-fos by PMA, although at the same dose it inhibits PMA-mediated activation of p42/44 MAPK by 50-70%, and activation by forskolin or insulin-like growth factor-I by 100%. These data suggest that p42/44 MAPK may not be the primary mediator of PKC-dependent c-fos induction. In contrast to the effect of melatonin on PMA-mediated c-fos induction in PT cells, in L cells stably transfected with the sheep Mel1 alphabeta receptor, melatonin potentiates the c-fos response in a pertussis toxin-sensitive manner. These data indicate the tissue-specific nature of melatonin receptor signaling, and reveal that a pertussis toxin-sensitive pathway can block PKC-mediated c-fos induction in PT cells.
Ross
A W
AW
Molecular Neuroendocrinology Unit, Rowett Research Institute, Aberdeen, Scotland, United Kingdom.
Webster
C A
CA
Thompson
M
M
Barrett
P
P
Morgan
P J
PJ
D000818:Animals; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression; D016762:Genes, fos / Q000235:genetics*; D007739:L Cells; D008550:Melatonin / Q000494:pharmacology; D051379:Mice; D010902:Pituitary Gland / Q000378:metabolism*; D011493:Protein Kinase C / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D044094:Receptors, Melatonin; D012756:Sheep; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005419:Flavonoids; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D008550:Melatonin; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one