Repression of cholesterol 7 alpha-hydroxylase transcription by bile acids is mediated through protein kinase C in primary cultures of rat hepatocytes.
Inhibitors of protein kinases were screened for the ability to prevent the repression of cholesterol 7 alpha-hydroxylase mRNA by taurocholate in primary cultures of adult rat hepatocytes. The addition of taurocholate (25 microM) for 6 h decreased cholesterol 7 alpha-hydroxylase mRNA by 64 +/- 3%. However, after a preincubation with the protein kinase C inhibitors calphostin C or chelerythrine, taurocholate had no significant effect on cholesterol 7 alpha-hydroxylase mRNA, or decreased levels by only 23 +/- 8%, respectively. Protein kinase C activation with phorbol 12-myristate, 13-acetate (100 nM) decreased cholesterol 7 alpha-hydroxylase mRNA and transcriptional activity by 71 +/- 5% and 60 +/- 16%, respectively, within 3 h. mRNA levels recovered to control levels by 18-24 h, however, consistent with downregulation of protein kinase C. Furthermore, after depletion of protein kinase C with a 24-h preincubation with phorbol diesters, taurocholate (25 microM) repressed cholesterol 7 alpha-hydroxylase mRNA by only 14 +/- 17%. The addition of taurocholate (50 microM) to the culture medium transiently increased membrane-associated protein kinase C activity by approximately twofold, while causing a concomitant decrease in cytosolic activity. Other bile acids increased membrane-associated protein kinase C activity in approximate proportion to their relative hydrophobicity. Finally, immunoblotting experiments revealed translocation of the alpha isoform of protein kinase C to hepatocyte membranes in response to taurocholate. These data suggest that hydrophobic bile acids repress cholesterol 7 alpha-hydroxylase transcription through a protein kinase C-dependent mechanism.
Stravitz
R T
RT
Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
Vlahcevic
Z R
ZR
Gurley
E C
EC
Hylemon
P B
PB
D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics*; D003470:Culture Media; D004789:Enzyme Activation / Q000187:drug effects; D015151:Immunoblotting; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013656:Taurocholic Acid / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects*
D001647:Bile Acids and Salts; D003470:Culture Media; D012333:RNA, Messenger; D013656:Taurocholic Acid; D002790:Cholesterol 7-alpha-Hydroxylase; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate