Inhibition of p38 mitogen-activated protein kinase enhances adrenergic-stimulated arylalkylamine N-acetyltransferase activity in rat pinealocytes.
We have previously shown that inhibition of p38(MAPK) increases adrenergic-stimulated p42/44(MAPK) activation in rat pinealocytes. In this study we investigated whether p38(MAPK) played a role in the adrenergic regulation of arylalkylamine-N-acetyltransferase (AA-NAT) induction and melatonin (MT) synthesis. Treatment of pinealocytes with norepinephrine (NE) caused a time-dependent increase in the levels of AA-NAT mRNA, AA-NAT protein, and enzymatic activity as well as MT production. Cotreatment with SB202190, a selective p38(MAPK) inhibitor, although having no effect on AA-NAT activity or protein level 3 h after NE treatment, caused a sustained increase in AA-NAT activity and protein level after 6 h of NE treatment. The increases in NE-stimulated AA-NAT activity and protein level by SB202190 occurred in the absence of an increase in AA-NAT mRNA. Similar results were obtained when AA-NAT was induced by (Bu)(2)cAMP or when SB203580 was used to inhibit p38(MAPK). In comparison, SB202474, the inactive analog, had no effect on NE or (Bu)(2)cAMP-stimulated AA-NAT activity or protein level. SB202190 also increased cumulative NE-stimulated MT production, provided that the medium was supplemented with 5-methoxytryptamine. p38(MAPK) inhibitors had no effect on hydroxyindole-O-methyltransferase activity. These results show that inhibition of p38(MAPK), although having no effect on cAMP-mediated AA-NAT transcription, appears to increase AA-NAT activity either by increasing translation or by reducing degradation of the AA-NAT protein. The lack of effect on NE-stimulated MT accumulation by p38(MAPK) inhibitors in the absence of 5-methoxytryptamine could be secondary to a lack of substrate, or alternatively, hydroxyindole-O-methyltransferase may become limiting.
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Department of Physiology, Faculty of Medicine, University of Alberta, Edmonton, Canada T6G 2H7.
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D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000096:biosynthesis / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D010870:Pineal Gland / Q000166:cytology / Q000201:enzymology*; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013566:Sympathomimetics / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D007093:Imidazoles; D011725:Pyridines; D012333:RNA, Messenger; D013566:Sympathomimetics; D003994:Bucladesine; D000121:Acetylserotonin O-Methyltransferase; D001191:Arylamine N-Acetyltransferase; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D008550:Melatonin; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole; D009638:Norepinephrine