Molecular cloning and characterization of the murine acyl-CoA thioesterase CTE-I

Abstract

Mouse cytosolic type I acyl-CoA thioesterase (CTE-I) is a member of the type I family of acylCoA thioesterases. These enzymes hydrolyze acyl-CoAs to non-esterified fatty acids (NEFAs) and Coenzyme A (CoA-SH) and are strongly induced in rodent liver by a diverse group of compounds called peroxisome proliferators. These peroxisome proliferators have been characterized as ligands for the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha). PPARalpha is the key nuclear receptor involved in control of fatty acid metabolism, and regulation of acyl-CoA thioesterases by this receptor functionally links them to fatty acid metabolism. We have cloned and characterized the mouse CTE-I both structurally and functionally. CTE-I is a serine esterase and its activity is dependent on a catalytic triad including amino acid residues serine 232, aspartic acid 324 and histidine 358. We have investigated the role of the PPARalpha in regulating CTE-I expression and conclude that the strong induction of the CTE-I mRNA via peroxisome proliferators is dependent on this receptor. We have demonstrated a partially PPARalpha-dependent mRNA induction by fasting. We have analyzed the CTE-I promoter region and identified a putative peroxisome proliferator response element (PPRE) at -9680 bp upstream of the start methionine (ATG). We initially purified CTE-I from rat and mouse liver cytosol, but later re-investigated the subcellular localization of CTE-I and conclude that it is a nucleo-cytoplasmic protein. We suggest a function for CTE-I in regulating fatty acid metabolism and propose that in the cytosol, CTE-I shuttles fatty acids towards oxidation, thereby limiting esterification and triglyceride synthesis. In the nucleus, CTE-I mediates crosstalk between the nuclear receptors PPARalpha and hepatocyte nuclear factor 4 alpha (HNF-4alpha) by controlling the amount of available agonists/antagonists for these receptors.