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

J Biol Chem. 1992 Aug 25;267(24):16866-71.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Isomerases / genetics
  • Animals
  • Bile Acids and Salts / metabolism
  • 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*
  • Glucagon / pharmacology*
  • Kinetics
  • Liver / drug effects
  • Liver / enzymology*
  • Microsomes, Liver / enzymology*
  • Peptidylprolyl Isomerase
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism*
  • Rats
  • Thyroxine / pharmacology*
  • Transcription, Genetic / drug effects*

Substances

  • Bile Acids and Salts
  • Carrier Proteins
  • Cyclosporins
  • RNA, Messenger
  • Cholestyramine Resin
  • Dexamethasone
  • Glucagon
  • Cholesterol
  • Cholesterol 7-alpha-Hydroxylase
  • Amino Acid Isomerases
  • Peptidylprolyl Isomerase
  • Thyroxine