Open AccessThe Modulation of Apolipoprotein E Gene Expression by 3,3′‐5‐triiodothyronine in HepG 2 Cells Occurs at Transcriptional and Post‐transcriptional Levels
Author(s) -
Vandenbrouck Yves,
Janvier Brigitte,
Loriette Claude,
Bereziat Gilbert,
MangeneyAndreani Marise
Publication year - 1994
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1994.00463.x
Subject(s) - cycloheximide , triiodothyronine , thyroid , medicine , endocrinology , hormone , apolipoprotein e , biology , thyroid hormone receptor , thyroid hormone receptor beta , gene expression , messenger rna , microbiology and biotechnology , gene , protein biosynthesis , hormone receptor , biochemistry , disease , cancer , breast cancer
The regulation of the synthesis and secretion of apolipoprotein E (apoE) is incompletely understood. This study examines the mechanisms responsible for regulating apoE gene expression in HepG 2 cells by thyroid hormone (3,3′‐5‐triiodothyronine). The secretion rate of apoE was by thyroid hormone increased (1.5–1.8‐fold) in pulse/chase experiments. Thyroid hormone doubled apoE mRNA concentration as determined by Northern‐blot analysis. Inhibition of protein synthesis by cycloheximide increased the thyroid‐hormone‐induced stimulation of apoE mRNA. This suggests that the synthesis of new protein is not required for thyroid hormone to stimulate apoE mRNA. Actinomycin D was used to inhibit new transcription; there was a more rapid degradation of mature apoE mRNA in thyroid hormone‐treated HepG 2 cells than in control cells, suggesting that thyroid hormone acts post‐transcriptionally to regulate apoE gene expression. Cycloheximide blocked the action of thyroid hormone, suggesting that thyroid hormone regulates the turnover of apoE mRNA via the synthesis of de novo protein. Nuclear run‐on transcription assays demonstrated that thyroid hormone stimulated apoE gene transcription threefold in 24 h. These findings indicate that the expression of the apoE gene is controlled at both transcriptional and post‐transcriptional loci by the thyroid hormone.