Valproic acid suppresses interleukin-1ß-induced microsomal prostaglandin E2 synthase-1 expression in chondrocytes through upregulation of NAB1.
OBJECTIVE
Microsomal prostaglandin E(2) synthase-1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE(2). Early growth response factor-1 (Egr-1) is a key transcription factor in the regulation of mPGES-1, and its activity is negatively regulated by the corepressor NGF1-A-binding protein-1 (NAB1). We examined the effects of valproic acid (VA), a histone deacetylase inhibitor, on interleukin 1ß (IL-1ß)-induced mPGES-1 expression in human chondrocytes, and evaluated the roles of Egr-1 and NAB1 in these effects.


METHODS
Chondrocytes were stimulated with IL-1 in the absence or presence of VA, and the level of mPGES-1 protein and mRNA expression were evaluated using Western blotting and real-time reverse-transcription polymerase chain reaction (PCR), respectively. mPGES-1 promoter activity was analyzed in transient transfection experiments. Egr-1 and NAB1 recruitment to the mPGES-1 promoter was evaluated using chromatin immunoprecipitation assays. Small interfering RNA (siRNA) approaches were used to silence NAB1 expression.


RESULTS
VA dose-dependently suppressed IL-1-induced mPGES-1 protein and mRNA expression as well as its promoter activation. Treatment with VA did not alter IL-1-induced Egr-1 expression, or its recruitment to the mPGES-1 promoter, but prevented its transcriptional activity. The suppressive effect of VA requires de novo protein synthesis. VA induced the expression of NAB1, and its recruitment to the mPGES-1 promoter, suggesting that NAB1 may mediate the suppressive effect of VA. Indeed, NAB1 silencing with siRNA blocked VA-mediated suppression of IL-1-induced mPGES-1 expression.


CONCLUSIONS
VA inhibited IL-1-induced mPGES-1 expression in chondrocytes. The suppressive effect of VA was not due to reduced expression or recruitment of Egr-1 to the mPGES-1 promoter and involved upregulation of NAB1.
Osteoarthritis Research Unit, Centre hospitalier de l'Université de Montréal, Hôpital Notre-Dame, Montréal, Québec, Canada.
Nadia
N
Zayed
Fatima Ezzahra
FE
El Mansouri
Nadir
N
Chabane
Mohit
M
Kapoor
Johanne
J
Martel-Pelletier
Mohamed
M
Benderdour
Jean-Pierre
JP
Pelletier
Nicolas
N
Duval
Hassan
H
Fahmi
D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D051766:Early Growth Response Protein 1 / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism; D053583:Interleukin-1beta / Q000494:pharmacology*; D019746:Intramolecular Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D000071876:Prostaglandin-E Synthases; D034741:RNA, Small Interfering / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014635:Valproic Acid / Q000494:pharmacology*
C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D004791:Enzyme Inhibitors; D007375:Interleukin-1; D053583:Interleukin-1beta; C094815:NAB1 protein, human; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014635:Valproic Acid; D019746:Intramolecular Oxidoreductases; C000605862:PTGES protein, human; D000071876:Prostaglandin-E Synthases