This Article Full Text Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Witt-Enderby, P. A. Articles by Dubocovich, M. L. Search for Related Content PubMed PubMed Citation Articles by Witt-Enderby, P. A. Articles by Dubocovich, M. L.

Physiological Exposure to Melatonin Supersensitizes the Cyclic Adenosine 3',5'-Monophosphate-Dependent Signal Transduction Cascade in Chinese Hamster Ovary Cells Expressing the Human mt₁ Melatonin Receptor¹

Department of Molecular Pharmacology and Biological Chemistry, Northwestern Drug Discovery Program, Northwestern University Institute for Neuroscience, Northwestern University Medical School, Chicago, Illinois 60611

Address all correspondence and requests for reprints to: Margarita L. Dubocovich, Ph.D., Department of Molecular Pharmacology and Biological Chemistry (S215), Northwestern University Medical School, 303 East Chicago Avenue, Chicago, Illinois 60611. E-mail: dubo{at}nwu.edu

Here, we report the effects of short exposure to melatonin on the human mt₁ (h mt₁) melatonin receptor-mediated signaling in Chinese hamster ovary (CHO) cells, and the consequences of an exposure that resembles the physiological pattern of melatonin release on cAMP-mediated signal transduction. Short exposure (10 min) of h mt₁ melatonin receptors to melatonin (400 pM) inhibited forskolin-stimulated cAMP formation, cAMP-dependent protein kinase activity, and phosphorylation of the cAMP response element-binding protein. However, treatment of mt₁-CHO cells with melatonin in a manner that closely mimics the in vivo activation of melatonin receptors (i.e. 400 pM melatonin for 8 h to mimic darkness) resulted in a supersensitization of the cAMP-dependent signal transduction cascade during the period of withdrawal (i.e. 16 h without melatonin to mimic the light cycle of a diurnal photoperiod). During the period of withdrawal, forskolin induced a time-dependent (1–16 h) increase in cAMP formation (200% of control cells). This effect of melatonin was dependent on the presence of the h mt₁ melatonin receptor, as no potentiation of forskolin-induced cAMP formation was observed in CHO cells transfected only with the neomycin resistance plasmid. The time-dependent increase in forskolin-stimulated cAMP levels resulted in a potentiation of cAMP-dependent protein kinase activity 1 h after withdrawal (130% of control cells; P < 0.05) and in the number of cells containing the phosphorylated form of cAMP response element-binding protein (75% of cells at 1 and 16 h compared with 30% in control cells; P < 0.05). An increase in the undissociated state (Gß) of G_i proteins may underlie this phenomenon as demonstrated by the increase in pertussis toxin-catalyzed ADP-ribosylation of G proteins (217 ± 48% of control; P < 0.05) after melatonin withdrawal. This increase in the ribosylation was not due to an up-regulation of G_i protein, as no significant change in G_i protein levels occurred at this time. We demonstrated that activation of the h mt₁ melatonin receptor in a manner that resembles the physiological pattern of melatonin exposure alters signaling, as potentiation of cAMP-mediated signal transduction events is observed after hormone withdrawal. The CHO cells expressing the human melatonin receptor may provide an in vitro cellular model in which to investigate the putative signaling mechanisms leading to gene regulation by melatonin.

This article has been cited by other articles:

				P. P. Kayampilly and K. M. J. Menon Inhibition of Extracellular Signal-Regulated Protein Kinase-2 Phosphorylation by Dihydrotestosterone Reduces Follicle-Stimulating Hormone-Mediated Cyclin D2 Messenger Ribonucleic Acid Expression in Rat Granulosa Cells Endocrinology, April 1, 2004; 145(4): 1786 - 1793. [Abstract] [Full Text] [PDF]

				F. Steffens, X.-B. Zhou, U. Sausbier, C. Sailer, K. Motejlek, P. Ruth, J. Olcese, M. Korth, and T. Wieland Melatonin Receptor Signaling in Pregnant and Nonpregnant Rat Uterine Myocytes as Probed by Large Conductance Ca2+-Activated K+ Channel Activity Mol. Endocrinol., October 1, 2003; 17(10): 2103 - 2115. [Abstract] [Full Text] [PDF]

				V. Simonneaux and C. Ribelayga Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters Pharmacol. Rev., June 1, 2003; 55(2): 325 - 395. [Abstract] [Full Text] [PDF]

				M. I. Masana and M. L. Dubocovich Melatonin Receptor Signaling: Finding the Path Through the Dark Sci. Signal., November 6, 2001; 2001(107): pe39 - pe39. [Abstract] [Full Text] [PDF]

				C. S. Nelson, M. Ikeda, H. S. Gompf, M. L. Robinson, N. K. Fuchs, T. Yoshioka, K. A. Neve, and C. N. Allen Regulation of Melatonin 1a Receptor Signaling and Trafficking by Asparagine-124 Mol. Endocrinol., August 1, 2001; 15(8): 1306 - 1317. [Abstract] [Full Text] [PDF]

				P. BARRETT, W.-S. CHOI, M. MORRIS, and P. MORGAN A role for tyrosine phosphorylation in the regulation and sensitization of adenylate cyclase by melatonin FASEB J, August 1, 2000; 14(11): 1619 - 1628. [Abstract] [Full Text]