Hormonal regulation of cholesterol 7 alpha-hydroxylase mRNA levels and transcriptional activity in primary rat hepatocyte cultures

• Published in: The Journal of biological chemistry Vol. 267; no. 24; pp. 16866 - 16871
• Main Authors: HYLEMON, P. B, GURLEY, E. C, TODD STRAVITZ, R, LITZ, J. S, PANDAK, W. M, CHIANG, J. Y. L, RENO VLAHCEVIC, Z
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25.08.1992
• Subjects: Amino Acid Isomerases - genetics; Analytical, structural and metabolic biochemistry; Animals; Bile Acids and Salts - metabolism; Biological and medical sciences; Blotting, Northern; Carrier Proteins - genetics; Cell Nucleus - drug effects; Cell Nucleus - physiology; Cells, Cultured; Cholesterol - metabolism; Cholesterol 7-alpha-Hydroxylase - biosynthesis; Cholesterol 7-alpha-Hydroxylase - genetics; Cholesterol 7-alpha-Hydroxylase - metabolism; Cholestyramine Resin - pharmacology; Cyclosporins - metabolism; Dexamethasone - pharmacology; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Glucagon - pharmacology; Kinetics; Liver - drug effects; Liver - enzymology; Microsomes, Liver - enzymology; Oxidoreductases; Peptidylprolyl Isomerase; Rats; RNA, Messenger - genetics; RNA, Messenger - metabolism; Thyroxine - pharmacology; Transcription, Genetic - drug effects; Vertebrata; Mammalia; Dexamethasone; Hepatocyte; Rat; Transcription; Enzyme; Rodentia; Hormonal regulation; Thyroxine; Cholesterol 7α-monooxygenase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)41864-9

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.