Differential regulation of hepatic triglyceride lipase and 3-hydroxy-3-methylglutaryl-CoA reductase gene expression in a human hepatoma cell line, HepG2.
The level of hepatic triglyceride lipase (H-TGL) synthesis and secretion was examined in response to changes in cholesterol biosynthesis in the human hepatoma cell line HepG2. Cells were first fed a lipoprotein-deficient serum-supplemented medium to eliminate exogenous cholesterol. Mevinolin, a 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitor, was then added at a concentration (37 microM) which inhibited cholesterol biosynthesis by greater than 85% and decreased total cell cholesterol from 36.1 to 27.4 micrograms/ml of cell protein. Mevinolin treatment caused a 4.9 +/- 0.8-fold increase in the amount of H-TGL activity secreted into the medium, a 1.8 +/- 0.4-fold rise in H-TGL-specific mRNA, and a concurrent 14-fold increase in HMG-CoA reductase mRNA. Addition of 1 mM mevalonic acid to normal or mevinolin-treated cells raised the cellular cholesterol content and decreased the amount of secreted H-TGL activity to levels below control values. Mevalonic acid also prevented mevinolin-induction of H-TGL and HMG-CoA reductase mRNA, suggesting a common regulatory step for H-TGL and HMG-CoA reductase. Exposure of cells to mevinolin and 25-hydroxycholesterol together resulted in a marked repression of HMG-CoA reductase mRNA levels, whereas these conditions further enhanced the secretion of H-TGL activity and the expression of H-TGL mRNA. These results demonstrate a differential role for 25-hydroxycholesterol in the regulation of H-TGL and HMG-CoA reductase expression.
Busch
S J
SJ
Merrell Dow Research Institute, Cincinnati, Ohio 45215.
Barnhart
R L
RL
Martin
G A
GA
Flanagan
M A
MA
Jackson
R L
RL
D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics*; D007700:Kinetics; D008049:Lipase / Q000235:genetics* / Q000378:metabolism; D008113:Liver Neoplasms; D008148:Lovastatin / Q000494:pharmacology; D008798:Mevalonic Acid / Q000494:pharmacology; D015347:RNA Probes; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D014158:Transcription, Genetic
D015347:RNA Probes; D012333:RNA, Messenger; D002784:Cholesterol; D008148:Lovastatin; D006903:Hydroxymethylglutaryl CoA Reductases; D008049:Lipase; D008798:Mevalonic Acid