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 choles...
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Published in | The Journal of biological chemistry Vol. 267; no. 24; pp. 16866 - 16871 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Biochemistry and Molecular Biology
25.08.1992
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Subjects | |
Online Access | Get full text |
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Summary: | 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. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/s0021-9258(18)41864-9 |