Hormonal-regulation Of Cholesterol-7-alpha-hydroxylase Messenger-rna Levels And Transcriptional Activity In Primary Rat Hepatocyte Cultures

Hormonal-regulation Of Cholesterol-7-alpha-hydroxylase Messenger-rna Levels And Transcriptional Activity In Primary Rat Hepatocyte Cultures

Hylemon P B; Gurley E C; Stravitz R T; Litz J S; Pandak W M; Chiang J Y L; Vlahcevic Z R

Journal of Biological Chemistry

1992

1992-08

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-mu-M, 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 (<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-mu-M), or dibutyryl cAMP (50-mu-M) decreased (90%) cholesterol 7-alpha-hydroxylase mRNA within 6 h. Transcriptional activity decreased (62%) in 6 h following the addition of glucagon (0.2-mu-M) 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.

bile-acid synthesis; Biochemistry & Molecular Biology; chick-embryo hepatocytes; cholesterol 7-alpha-hydroxylase activity; circadian-rhythm; cyclic-amp; enzyme; gene; liver; malic; metabolism; monolayer-cultures

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Journal Article or Conference Abstract Publication

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16866-16871

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