Proteasomal proteolysis in the adrenergic induction of arylalkylamine-N-acetyltransferase in rat pinealocytes.
In this study, we investigated the effect of proteasomal inhibition on the induction of arylalkylamine-N-acetyltransferase (AA-NAT) enzyme in cultured rat pinealocytes, using two proteasome inhibitors, MG132 and clastolactacystin beta-lactone (c-lact). Addition of c-lact or MG132 3 h after norepinephrine (NE) stimulation produced a significant increase in AA-NAT protein level and enzyme activity. However, when the proteasome inhibitors were added before or together with NE, significant reductions of the NE-induced aa-nat mRNA, protein, and enzyme activity were observed. A similar inhibitory effect of MG132 on aa-nat transcription was observed when cells were stimulated by dibutyryl cAMP, indicating an effect distal to a post-cAMP step. The inhibitory effect of MG132 on adrenergic-induced aa-nat transcription was long lasting because it remained effective after 14 h of washout and appeared specific for aa-nat because the induction of another adrenergic-regulated gene, MAPK phosphatase-1, by NE was not affected. Time-profile studies revealed that the inhibitory effect of MG132 on NE-stimulated aa-nat induction was detected after 1 h, suggesting accumulation of a protein repressor as a possible mechanism of action. This possibility was also supported by the finding that the inhibitory effect of c-lact on NE-induced aa-nat induction was markedly reduced by cycloheximide, a protein synthesis inhibitor. Together, these results support an important role of proteasomal proteolysis in the adrenergic-mediated induction of aa-nat transcription through its effect on a protein repressor.
Terriff
David L
DL
Department of Physiology, University of Alberta, 7-33 Medical Sciences Building, Edmonton, Alberta, Canada T6G 2H7.
Chik
Constance L
CL
Price
Donald M
DM
Ho
Anthony K
AK
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D007976:Leupeptins / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D009638:Norepinephrine / Q000494:pharmacology*; D010447:Peptide Hydrolases / Q000378:metabolism*; D010870:Pineal Gland / Q000166:cytology / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D047068:Arylalkylamine N-Acetyltransferase; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; D008550:Melatonin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D009638:Norepinephrine