Hormonal regulation of cholesterol 7 alpha-hydroxylase mRNA levels and transcriptional activity in primary rat hepatocyte cultures.
In primary cultures of adult rat hepatocytes the level of cholesterol 7 alpha-hydroxylase steady-state mRNA markedly decreased by 72 h. However, the addition of L-thyroxine (T4) and dexamethasone synergistically returned cholesterol 7 alpha-hydroxylase steady-state mRNA levels near to that of cholestyramine-fed animals. The maximal responses to T4 and dexamethasone in serum-free medium were at 1.0 and 0.1 microM, respectively. The addition of T4 in combination with dexamethasone resulted in an 11-fold increase in transcriptional activity of the cholesterol 7 alpha-hydroxylase gene as compared to no addition controls. The specific activities of cholesterol 7 alpha-hydroxylase in microsomes prepared from cultures treated with dexamethasone and T4 were 1.56 +/- 1.17 nmol/h/mg protein which is similar to that of intact liver (1.70 +/- 0.062 nmol/h/mg protein), but lower than cholestyramine-fed animals. Cholesterol 7 alpha-hydroxylase activity was not detectable (less than 0.020 nmol/h/mg protein) at 72 h in cultures without the addition of both dexamethasone and T4. In the presence of optimal concentrations of dexamethasone and T4, glucagon (0.2 microM), or dibutyryl cAMP (50 microM) decreased (90%) cholesterol 7 alpha-hydroxylase mRNA within 6 h. Transcriptional activity decreased (62%) in 6 h following the addition of glucagon (0.2 microM) to the culture medium. The results reported in this paper suggest an important role for multiple hormones in the regulation of cholesterol 7 alpha-hydroxylase in the liver.
Hylemon
P B
PB
Department of Microbiology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
Gurley
E C
EC
Stravitz
R T
RT
Litz
J S
JS
Pandak
W M
WM
Chiang
J Y
JY
Vlahcevic
Z R
ZR
D000591:Amino Acid Isomerases / Q000235:genetics; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics; D002467:Cell Nucleus / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D002790:Cholesterol 7-alpha-Hydroxylase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D002792:Cholestyramine Resin / Q000494:pharmacology*; D003524:Cyclosporins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology*; D019696:Peptidylprolyl Isomerase; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D013974:Thyroxine / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*
D001647:Bile Acids and Salts; D002352:Carrier Proteins; D003524:Cyclosporins; D012333:RNA, Messenger; D002792:Cholestyramine Resin; D003907:Dexamethasone; D005934:Glucagon; D002784:Cholesterol; D002790:Cholesterol 7-alpha-Hydroxylase; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase; D013974:Thyroxine