GLUCOCORTICOIDS STIMULATE CHOLESTERYL ESTER FORMATION IN HUMAN SMOOTH-MUSCLE CELLS

The aim of the present study was to investigate the effect of syntheti c glucocorticoid dexamethasone (Dex) on cholesterol esterification in cultured human smooth muscle cells (SMC). In labeled SMC, Dex stimulat ed the esterification of [H-3]cholesterol in a dose-dependent manner. This effect was specific for glucocorticoid hormones and could be inhi bited by cycloheximide (3 ng/mL), actinomycin D (10(-5) mol/L), and th e specific glucocorticoid antagonist RU 486 (10(-8) mol/L). When plasm a membrane was selectively labeled with trace quantities of [H-3]chole sterol (0.25 mu Ci/mL, 1 hour, 10 degrees C), Dex (10(-8) mol/L caused a net flux of free [H-3]cholesterol into the cells. Moreover, Dex (10 (-8) mol/L, 24 hours) stimulated the esterification of sterols, newly synthesized from [C-14]mevalonate (10 mu Ci/mL, 4 hours) and lowered t he amount of [C-14]sterols susceptible for cholesterol oxidase. The in corporation of [C-14]oleic acid into cholesteryl esters was markedly h igher in Dex-pretreated SMC than in the control cells (2.1 +/- 0.07 an d 1.4 +/- 0.1 pmol/h/mu g protein, respectively, P<.01). At the time, cholesteryl ester hydrolysis in Dex-treated cells was reduced (72 +/- 8 pmol cholesteryl esters/h per milligram versus 130 +/- 10 in the con trol cells). HDL3-mediated [H-3]cholesterol efflux was also inhibited in Dex-treated cells; moreover, HDL3 (40 mu g/mL, 24 hours) had practi cally no effect on [3H]cholesteryl ester content in Dex-treated SMC bu t caused a 50% reduction of [H-3]cholesteryl esters in the control cel ls. Thus, in human SMC glucocorticoids alter the redistribution of cho lesterol between the pools of free and esterified cholesterol, paralle led by the change in acyl coenzyme A:cholesteryl acyltransferase and n eutral cholesteryl eater hydrolase activities, leading to the impaired HDL3-mediated cholesterol efflux.