title: In vitro inhibition of Ca2+/calmodulin-dependent kinase II activity by melatonin.
abstract: Recent evidence suggests that a melatonin (MEL) mechanism of action may be through modulation of Ca2+-activated calmodulin (CaM). MEL binds to CaM with a high affinity, and has been shown to act as a CaM antagonist. Among the CaM-dependent enzymes, Ca2+/Calmodulin-dependent protein kinase II (CaM-kinase II) is a particularly abundant enzyme in the nervous system. In the brain it phosphorylates a broad spectrum of substrates, thus modulating important neuronal functions. We describe the MEL effect on CaM-kinase II activity in vitro. CaM-kinase II was purified from rat brain by column chromatography, and identified by Western immunoblotting. CaM-kinase II activity was assessed in the presence of Ca2+/CaM by the kinase's ability to phosphorylate the synthetic substrate syntide-2 and by enzyme autophosphorylation. MEL inhibited CaM-kinase II activity, and enzyme autophosphorylation. Inhibition of the enzyme by 10(-9) M MEL was nearly of 30%. Trifluoperazine (10 microM), W7 (10 microM), and compound 48/80 (30 micrograms/ml), inhibited CaM-kinase II activity by 40%, 42%, and 93%, respectively. Both EGTA (5 mM) and MEL (10(-5) M) abolished autophosphorylation. The effect of MEL on CaM-kinase II activity was specific, since neither serotonin, N-acetylserotonin, nor 6-hydroxymelatonin inhibited its activity. Our results support the hypothesis that MEL acts as a CaM antagonist and cellular functions may be rhythmically regulated by MEL modulation of CaM-dependent protein phosphorylation.
authors.affiliation: Instituto Mexicano de Psiquiatría, Departamento de Neurofarmacología, Mexico City, Mexico.
authors.forename: G
authors.initials: G
authors.lastname: Benítez-King
authors.forename: A
authors.initials: A
authors.lastname: Ríos
authors.forename: A
authors.initials: A
authors.lastname: Martínez
authors.forename: F
authors.initials: F
authors.lastname: Antón-Tay
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats
chemical_list: D002147:Calmodulin; D004791:Enzyme Inhibitors; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D008550:Melatonin; D002118:Calcium