In vitro stimulation of protein kinase C by melatonin.
It has been shown that melatonin through binding to calmodulin acts both in vitro and in vivo as a potent calmodulin antagonist. It is known that calmodulin antagonists both bind to the hydrophobic domain of Ca2+ activated calmodulin, and inhibit protein kinase C activity. In this work we explored the effects of melatonin on Ca2+ dependent protein kinase C activity in vitro using both a pure commercial rat brain protein kinase C, and a partially purified enzyme from MDCK and N1E-115 cell homogenates. The results showed that melatonin directly activated protein kinase C with a half stimulatory concentration of 1 nM. In addition the hormone augmented by 30% the phorbol ester stimulated protein kinase C activity and increased [3H] PDBu binding to the kinase. In contrast, calmodulin antagonists (500 microM) and protein kinase C inhibitors (100 microM) abolished the enzyme activity. Melatonin analogs tested were ineffective in increasing either protein kinase C activity or [3H] PDBu binding. Moreover, the hormone stimulated protein kinase C autophosphorylation directly and in the presence of phorbol ester and phosphatidylserine. The results show that besides the melatonin binding to calmodulin, the hormone also interacts with protein kinase C only in the presence of Ca2+. They also suggest that the melatonin mechanism of action may involve interactions with other intracellular hydrophobic and Ca2+ dependent proteins.
Antón-Tay
F
F
Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Biología de la Reproducción, CBS, Mexico DF, Mexico. fat@xanum.uam.mx
Ramírez
G
G
Martínez
I
I
Benítez-King
G
G
D000818:Animals; D001921:Brain / Q000201:enzymology*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D008550:Melatonin / Q000494:pharmacology*; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats
D002147:Calmodulin; D004791:Enzyme Inhibitors; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D008550:Melatonin