Rat hepatoma L35 cells, a liver-differentiated cell line, display resistance to bile acid repression of cholesterol 7 alpha-hydroxylase.
A stable hepatoma cell line (L35 cells) showing an activation of the cholesterol 7 alpha-hydroxylase gene (CYP7) that had been silent in the parental hepatoma cell line (H35 cells) was used to examine the influence of bile acids on its gene expression and activity. L35 cells were found to concentrate taurocholate from the culture medium, without any significant effect on the expression of 7 alpha-hydroxylase. At physiologic levels (up to 100 microM), CYP7 mRNA expression was not repressed by any bile acid. At supra-physiologic levels (1 mM), the more hydrophobic dihydroxy bile acids, taurodeoxycholate and taurochenodeoxycholate, decreased CYP7 mRNA without decreasing the relative abundance of beta-actin mRNA. Similar results were obtained by culturing cells with sodium dodecylsulfate (50 microM). The medium of L35 cells treated with either taurochenodeoxycholate (1 mM), taurodeoxycholate (1 mM), or sodium dodecylsulfate (50 microM) contained significantly greater activities of two cytosolic enzymes, lactate dehydrogenase and phosphoglucose isomerase, indicating a cytotoxic response. Activation of protein kinase C by phorbol esters decreased the expression of 7 alpha-hydroxylase mRNA without evidence of cytotoxicity; therefore, the inability of L35 cells to show bile acid repression cannot be ascribed to a lack of an effect by this secondary messenger system. In addition, insulin decreased and dexamethasone increased 7 alpha-hydroxylase mRNA without increasing the release of the cytoplasmic enzyme markers. The combined data suggest that L35 cells are resistant to repression of CYP7 gene expression by bile acids, but display physiologic expression to hormones and protein kinase C activation.
Trawick
J D
JD
Department of Biology, San Diego State University, CA 92182-0057, USA.
Lewis
K D
KD
Dueland
S
S
Moore
G L
GL
Simon
F R
FR
Davis
R A
RA
D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology*; D048429:Cell Size / Q000187:drug effects; D002790:Cholesterol 7-alpha-Hydroxylase / Q000096:biosynthesis* / Q000235:genetics; D019826:Cholic Acid; D002793:Cholic Acids / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects; D000072474:Cytochrome P450 Family 7; D003902:Detergents / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004794:Enzyme Repression / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology; D008099:Liver / Q000201:enzymology*; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013250:Steroid Hydroxylases; D013655:Taurochenodeoxycholic Acid / Q000494:pharmacology; D013656:Taurocholic Acid / Q000378:metabolism; D013657:Taurodeoxycholic Acid / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D001647:Bile Acids and Salts; D002793:Cholic Acids; D003902:Detergents; D007328:Insulin; D012333:RNA, Messenger; D012967:Sodium Dodecyl Sulfate; D013655:Taurochenodeoxycholic Acid; D013657:Taurodeoxycholic Acid; D013656:Taurocholic Acid; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D002790:Cholesterol 7-alpha-Hydroxylase; D000072474:Cytochrome P450 Family 7; C490784:Cyp7b1 protein, rat; D011493:Protein Kinase C; D019826:Cholic Acid; D013755:Tetradecanoylphorbol Acetate