Effect of 25-hydroxycholesterol and bile acids on the regulation of cholesterol metabolism in Hep G2 cells.
The effect of 25-hydroxycholesterol (25-OH-cholesterol) and chenodeoxycholic (CDC) acid on apoprotein secretion, low-density lipoprotein receptor activity, and [3H]triacylglycerol secretion in Hep G2 cells was studied. Both 25-OH-cholesterol and CDC acid increased the secretion of apolipoprotein (apo) E by Hep G2 cells. The secretion of apo A-I was slightly lowered (less than 10% disease). The maximal increase in apo E secretion was observed in culture medium containing 2 micrograms of 25-OH-cholesterol/ml or 10 micrograms of CDC acid/ml plus 10% fetal calf serum. Cholesterol, 7-OH-cholesterol and other bile acids were ineffective in inducing increases in apo E secretion. Another cholesterol synthesis inhibitor, mevinolin, was also ineffective in generating an increase in apoprotein secretion. The data indicated a specific interaction between 25-OH-cholesterol or CDC acid and apo E secretion in Hep G2 cells. Cholesterol synthesis, as measured by the incorporation of [14C]acetic acid into sterols, was repressed in Hep G2 cells in the presence of 25-OH-cholesterol (17% of control value). CDC acid, on the other hand, increased [14C]acetic acid incorporation (156% of control value). The number of LDL receptors in Hep G2 cells was decreased after incubation with 25-OH-cholesterol (62% of control value), but increased significantly after incubation with CDC acid (149% of control value). The secretion of [3H]triacylglycerol by Hep G2 cells incubated with 25-OH-cholesterol was greatly increased (248% of control value). On the contrary, CDC acid did not cause any increase in [3H]triacylglycerol secretion. The above results suggest that 25-OH-cholesterol and CDC acid have different effects on lipid metabolism in Hep G2 cells. The mRNA levels of apo E increased in cells preincubated with 25-OH-cholesterol and CDC acid, which suggested that the increase in apo E secretion is at least partly due to an increase in synthesis.
Carlson
T L
TL
Atherosclerosis Research Unit, Mayo Clinic and Foundation, Rochester, MN 55905.
Kottke
B A
BA
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000378:metabolism; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism*; D002635:Chenodeoxycholic Acid / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism*; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology*; D066298:In Vitro Techniques; D008077:Lipoproteins, LDL / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008148:Lovastatin / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011973:Receptors, LDL / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D001057:Apolipoproteins E; D006888:Hydroxycholesterols; D008077:Lipoproteins, LDL; D012333:RNA, Messenger; D011973:Receptors, LDL; D014280:Triglycerides; D002635:Chenodeoxycholic Acid; C007997:25-hydroxycholesterol; D002784:Cholesterol; D008148:Lovastatin