R. Zolfaghari et al., THE EFFECTS OF VARYING THE EXPRESSION OF A NEUTRAL CHOLESTERYL ESTER HYDROLASE ON THE TURNOVER OF CHOLESTERYL ESTER IN RAT HEPATOMA-CELLS, The Journal of biological chemistry, 268(18), 1993, pp. 3532-3538
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.