The effect of 25-hydroxycholesterol on the regulation of apolipoprotein E mRNA levels and secretion in the human hepatoma HepG2
| Autor: | Shui-Pang Tam, Randy Ramharack |
|---|---|
| Rok vydání: | 1992 |
| Předmět: |
Apolipoprotein E
medicine.medical_specialty Carcinoma Hepatocellular Oxysterol Lipoproteins Phospholipid Centrifugation Biology Reductase chemistry.chemical_compound Apolipoproteins E Internal medicine Tumor Cells Cultured medicine Humans Secretion RNA Messenger Cholesterol Liver Neoplasms Hydroxycholesterols Kinetics Endocrinology chemistry Cell culture Hydroxymethylglutaryl CoA Reductases lipids (amino acids peptides and proteins) Cardiology and Cardiovascular Medicine Intracellular Sterol O-Acyltransferase |
| Zdroj: | Atherosclerosis. 95:137-146 |
| ISSN: | 0021-9150 |
| DOI: | 10.1016/0021-9150(92)90017-b |
| Popis: | The human hepatoma cell line, HepG2, was cultured with 25 OH cholesterol, a potent inhibitor of HMG-CoA reductase, in order to examine the effect of the oxysterol on apo E synthesis and secretion. Treatment of cells with oxysterol (2.5 microM) resulted in a greater than 90% inhibition of HMG-CoA reductase activity and a 3-fold reduction in its cognate mRNA level. However, apo E mRNA level and secretion were not affected after 24 h of drug treatment. This drug treatment was associated with a reduction in both cellular free and esterified cholesterol levels by 50% and 40%, respectively. Exposure of HepG2 cells to an ACAT inhibitor, the Sandoz compound (58-035) for 24 h, at a concentration of 5 micrograms/ml, resulted in a 30% increase and 70% decrease in the intracellular levels of free and esterified cholesterol, respectively. Under this regimen of drug treatment, the level of apo E mRNA was increased by approximately 70%, while HMG-CoA reductase mRNA level was decreased by 35%. When the cells were exposed to the combination of the ACAT inhibitor and 25 OH cholesterol, the cellular levels of free and esterified cholesterol were reduced by 30% and 80%, respectively. This combination of drugs had no effect on apo E mRNA; however, the level of HMG-CoA reductase mRNA was decreased by 3.5-fold. Taken together, the data suggested that reduction in the intracellular levels of either free or esterified cholesterol had no effect on apo E mRNA level. By contrast, a small increment in cellular free cholesterol content was associated with a significant induction in apo E mRNA level. Furthermore, 25 OH cholesterol caused a significant redistribution (50%) of apo E from the HDL fraction to the d greater than 1.21 g/ml infranatant. By using high performance liquid chromatography and molecular sieve columns, it was found that the appearance of a lipid-poor apo E particle was not an artifact of ultracentrifugation. This particle contained 85 wt% protein and 15 wt% of free cholesterol and phospholipid. The results suggested that a lipid-poor apo E particle was secreted by the HepG2 cells under certain circumstances. |
| Databáze: | OpenAIRE |
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