Human liver cholesteryl ester hydrolase: cloning, molecular characterization, and role in cellular cholesterol homeostasis

The liver regulates cholesterol homeostasis and eliminates excess cho-lesterol as bile acids or biliary cholesterol. Free cholesterol for bile acid synthesis or biliary secretion is obtained by the hydrolysis of stored cholesteryl esters or from cholesteryl esters taken up by the liver from high-density lipoproteins via a selective uptake pathway. The present study was undertaken to characterize the enzyme catalyzing this reaction, namely, cholesterol ester hydrolase (CEH) from the human liver, and demonstrate its role in regulating bile acid synthesis. Two cDNAs were isolated from the human liver that differed only in the presence of an additional alanine at position 18 in one of the clones. Transient transfec-tion of COS-7 cells with a eukaryotic expression vector containing either of these two cDNAs resulted in significant increase in the hydrolysis of cholesteryl esters, authenticating these clones as human liver CEH. CEH mRNA and protein expression in human hepatocytes were demonstrated by real-time PCR and Western blot analyses, respectively, confirming th