INHIBITION OF ACYL-COENZYME-A-CHOLESTEROL ACYLTRANSFERASE BLOCKS ESTERIFICATION BUT NOT UPTAKE OF CHOLESTEROL IN CACO-2 CELLS

The effects of cholesterol esterase (CEase) and acyl coenzyme A:choles terol acyltransferase (ACAT) inhibitors on the uptake and esterificati on of cholesterol in Caco-2 cells were examined. CEase increased the u ptake of [H-3]cholesterol from bile salt mixed-micelles by 2.5- to 3.0 -fold and its esterification by greater than 25-fold. Inhibition of ce llular ACAT activity with CL277082 or CP113818 had little or no effect on cholesterol uptake measured in the presence or absence of CEase. T he subsequent esterification of [H-3]cholesterol was reduced greater t han 90% by each ACAT inhibitor. Similar results were obtained in cells in which ACAT activity was induced by preincubation either with 25-hy droxycholesterol and mevalonic acid or with CEase and bile salt mixed- micelles containing 100 mu mol/L cholesterol. Neither ACAT inhibitor h ad an effect on CEase-mediated synthesis or hydrolysis of cholesteryl oleate in vitro. Thus, the uptake of cholesterol from bile salt mixed- micelles in the presence or absence of CEase was not regulated by the level of cellular ACAT expression. The subsequent esterification of ex ogenous sterol was not due to CEase, but was completely dependent on A CAT activity. The dissociation of cholesterol uptake from ACAT activit y suggests that the factors controlling the transfer of sterol from ex tracellular media to the cell are different from the factors regulatin g the cellular level of cholesterol esterification. Copyright (C) 1998 by W.B. Saunders Company.