The acyl-CoA thioesterase I is regulated by PPARα and HNF4α via a distal response element in the promoter

Bikesh Dongol,Yatrik Shah,Insook Kim,Frank J Gonzalez,Mary C Hunt

doi:10.1194/jlr.m700119-jlr200

Abstract

The cytosolic acyl-coenzyme A thioesterase I (Acot1) is an enzyme that hydrolyzes long-chain acyl-CoAs of C(12)-C(20)-CoA in chain length to the free fatty acid and CoA. Acot1 was shown previously to be strongly upregulated at the mRNA and protein level in rodents by fibrates. In this study, we show that Acot1 mRNA levels were increased by 90-fold in liver by treatment with Wy-14,643 and that Acot1 mRNA was also increased by 15-fold in the liver of hepatocyte nuclear factor 4alpha (HNF4alpha) knockout animals. Our study identified a direct repeat 1 (DR1) located in the Acot1 gene promoter in mouse, which binds the peroxisome proliferator-activated receptor alpha (PPARalpha) and HNF4alpha. Chromatin immunoprecipitation (ChIP) assay showed that the identified DR1 bound PPARalpha/retinoid X receptor alpha (RXRalpha) and HNF4alpha, whereas the binding in ChIP was abrogated in the PPARalpha and HNF4alpha knockout mouse models. Reporter gene assays showed activation of the Acot1 promoter in cells by the PPARalpha agonist Wy-14,643 after cotransfection with PPARalpha/RXRalpha. However, transfection with a plasmid containing HNF4alpha also resulted in an increase in promoter activity. Together, these data show that Acot1 is under regulation by an interplay between HNF4alpha and PPARalpha.

Highlights

The cytosolic acyl-coenzyme A thioesterase I (Acot1) is an enzyme that hydrolyzes long-chain acyl-CoAs of C12-C20-CoA in chain length to the free fatty acid and CoA
Acot1 is regulated by fibrate treatment via peroxisome proliferator-activated receptor a (PPARa) in vivo It has been shown that Acot1 is upregulated at mRNA
Protein levels in rodents by treatment with clofibrate [17,18,19] and di(2-ethylhexyl) phthalate [21]. This upregulation at the mRNA level was shown only by Northern blot analysis; to quantitatively examine the level of induction of Acot1 mRNA in mouse liver by Wy-14,643, real-time PCR was carried out using specific primers toward Acot1

Summary

Introduction

The cytosolic acyl-coenzyme A thioesterase I (Acot1) is an enzyme that hydrolyzes long-chain acyl-CoAs of C12-C20-CoA in chain length to the free fatty acid and CoA. There is a family of enzymes that hydrolyze acyl-CoAs to the free fatty acid and CoA, and acyl-CoAs/ free fatty acids act as either agonists or antagonists for PPARa and HNF4a These enzymes are called acyl-CoA thioesterases (Acots) (for review, see Ref. 15), and a new Abbreviations: Acot, acyl-coenzyme A thioesterase I; ChIP, chromatin immunoprecipitation; DR1, direct repeat 1; EMSA, electromobility shift assay; HNF4a, hepatic nuclear factor 4a; MCAD, medium-chain acyl-coenzyme A dehydrogenase; OTC, ornithine transcarbamylase; PPARa, peroxisome proliferator-activated receptor a; PPRE, peroxisome proliferator response element; RXR, retinoid X receptor. Nomenclature was recently introduced [16] One member of this gene family, the cytosolic acyl-coenzyme A thioesterase I (Acot, but previously known as CTE-I), was identified as a peroxisome proliferator-induced enzyme in rodent liver [17,18,19,20]. Our data show that Acot is regulated by a delicate interplay between PPARa/RXRa and HNF4a

Methods

Results

Conclusion