MECHANISM OF ACTION OF PROBUCOL ON CHOLESTERYL ESTER TRANSFER PROTEIN(CETP) MESSENGER-RNA IN A CHINESE-HAMSTER OVARY CELL-LINE THAT HAD BEEN STABLY TRANSFECTED WITH A HUMAN CETP GENE

Probucol, a widely used lipid-lowering agent, is associated with a sig nificant reduction of plasma high density lipoprotein (HDL)-cholestero l levels. To examine the mechanism of probucol HDL-lowering and probuc ol's effects on cholesteryl ester transfer protein (CETP) and choleste rol metabolism in cells, we used a Chinese hamster ovary (CHO) cell li ne that had been stably transfected with a human CETP gene (hCETP-CHO) . After this cell line was incubated with various concentrations of pr obucol (5, 10 and 50 mu M) for 24 h, mean intracellular probucol conce ntrations reached 0.47, 0.67, and 1.52 mu g/mg cell protein, respectiv ely. Northern blot analysis showed that cellular CETP mRNA was increas ed by probucol in a dose-dependent manner (137%, 162%, and 221% of the control, respectively). The specific CET activity in the culture medi um, measured as the percentage of [H-3]cholesterol oleate transferred from discoidal bilayer particles (which mimic HDL) to LDL, also increa sed in a dose-dependent manner. Intracellular total cholesterol levels were decreased to 87.5%, 74.9%, and 52.5% of the control, respectivel y. Probucol had no effects on HMG-CoA reductase activity or cholestero l synthesis from [1-C-14]acetate in hCETP-CHO. However, C-14-incorpora ted cholesterol secretion into the culture medium from hCETP-CHO was i ncreased to 181%, 256% and 354% of the control by 5, 10 and 50 mu M pr obucol, respectively. We concluded that (1) treatment with probucol in creased the CETP mRNA level and specific CET activity in the hCETP-CHO cell line, and (2) probucol promoted cholesterol efflux from hCETP-CH O, which resulted in a decrease in intracellular cholesterol levels. ( C) 1998 Elsevier Science B.V. All rights reserved.