THE EFFECTS OF VARYING THE EXPRESSION OF A NEUTRAL CHOLESTERYL ESTER HYDROLASE ON THE TURNOVER OF CHOLESTERYL ESTER IN RAT HEPATOMA-CELLS

A neutral bile salt-dependent cholesteryl ester hydrolase (CEH) in rat liver has been shown to be indistinguishable from the pancreatic CEH by a number of criteria (Harrison, E. H. (1988) Biochim. Biophys. Acta 963,28-34; Zolfaghari, R., Harrison, E. H., Ross, A. C., and Fisher, E. A. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 6913-6919; Camulli, E . D., Linke, M. J., Brockman, H. L., and Hui, D. Y. (1989) Biochim. Bi ophys. Acta 1005, 177-182). The rat hepatoma cell line Fu5AH, which la cks this particular CEH activity, was stably transfected with the cDNA of rat pancreatic CEH, and the effects on cholesterol and cholesteryl ester metabolism in clones with varying levels of CEH expression dete rmined. In spite of significant amounts of intracellular enzyme protei n demonstrated by Western blotting, in cell lysates there was a consis tently low level of catalytic activity, and in cultured cells there wa s no evidence that CEH served as an effective intracellular cholestery l ester hydrolase or synthase. In contrast, the catalytic activity of the secreted enzyme was relatively higher and there was a small, but s ignificant, increase in the ability of high density lipoprotein (added to the medium) to promote the clearance of cholesteryl ester from cel ls secreting high levels of CEH. Overall, these results suggest that i n the liver, intracellular CEH does not significantly affect the turno ver of cholesteryl esters and warrant future studies focusing on the f unction of the secreted enzyme. For example, secreted CEH may modify l ipoproteins and affect their interactions with cells.