Regulation of cholesterol metabolism and low-density lipoprotein binding in human intestinal Caco-2 cells.

In the present paper, the regulation of 3-hydroxy-3-methylglutarylcoenzyme A (HMG-CoA) reductase, acylcoenzyme A cholesterol acyltransferase (ACAT) and low-density lipoprotein (LDL) binding was studied in the human colon cancer carcinoma cell line Caco-2. LDL down-regulated HMG-CoA reductase activity in a dose-dependent fashion to a minimum of 28% of control at 200 micrograms/ml and LDL binding to 52% of control. The activity of ACAT was stimulated by LDL. High-density lipoprotein 3 (HDL3) increased HMG-CoA reductase activity, whereas cholesteryl ester formation was slightly decreased. Inhibition of the endogenous cholesterol biosynthesis by mevinolin increased both LDL binding and activity of HMG-CoA reductase. This effect was reversed by the addition of mevalonolactone but not by LDL. It is concluded that regulation of HMG-CoA reductase and LDL binding is subject to the availability of non-sterol products of mevalonic acid and of exogenous cholesterol. ACAT is regulated mainly by the level of its substrate cholesterol.