Abstract
The regulation of cytochrome P450 (CYP) 2E1, the ethanol-inducible isoform, is particularly complex. The level is affected by a variety of other foreign compounds, by insulin (as studied in several laboratories), and by triiodothyronine (T3), which has not been previously examined at the molecular level. In the present investigation, a stably transfected HepG2 cell line harboring a rabbitCYP2E1 minigene containing the coding sequence together with 1.6 kilobases of the 5′ flanking region and the untranslated region (UTR), as well as 0.5 kilobases of the 3′ UTR, was established. Western blot analysis showed that 1 μm insulin decreased the CYP2E1 protein level in a dose- and time-dependent manner, whereas 1 μm T3 increased the level 2-fold in 1 day and 8-fold in 5 days. Similarly, steady state CYP2E1 mRNA levels were decreased by insulin but were increased by T3. Neither hormone affected the transcription rate of the CYP2E1 5′ flanking region with an UTR/luciferase fusion gene, indicating that the regulation is post-transcriptional in this system under our experimental conditions. When the CYP2E1 3′ UTR was removed from the minigene, CYP2E1 mRNA and protein were up-regulated by insulin but were not affected by T3. These findings, including mRNA half-life determinations, indicate that the effects of insulin and T3 are a result of altered mRNA stability and that the 3′ UTR of CYP2E1 contains regulatory information for these hormone-mediated effects.
Footnotes
-
Send reprint requests to: Hwei-Ming Peng, Ph.D., Department of Biological Chemistry, Medical Science I, Box 0606, The University of Michigan, Ann Arbor, MI 48109-0606. E-mail: hwpeng{at}umich.edu
-
This research was supported by National Institutes of Health Grant AA06221 (to M.J.C.).
- Abbreviations:
- IRS
- insulin response sequence
- UTR
- untranslated region
- T3
- triiodothyronine
- T4
- thyroxine
- TRE
- thyroid response element
- MEM
- minimal essential medium
- FBS
- fetal bovine serum
- ECL
- enhanced chemiluminescence
- kb
- kilobase(s)
- bp
- base pair(s)
- RT
- reverse transcription
- PCR
- polymerase chain reaction
- DRB
- 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole
- Received May 8, 1998.
- Accepted July 14, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|