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Retinoic acid regulates ornithine decarboxylase gene expression at the transcriptional level
1Department of Dermatology, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA 19107.
Abstract:
Retinoic acid (RA) is important for normal mammalian development and growth. Ornithine decarboxylase (ODC) is the first and rate-limiting enzyme in the biosynthesis of the polyamines, and we have previously shown that ODC mRNA levels are suppressed by RA in human skin cells. Using HeLa cells, we now show that treatment with 0.5 microM RA for 24 h suppresses endogenous ODC mRNA levels and the expression of a transfected ODC/chloramphenicol acetyltransferase plasmid (Kpn-ODCCAT), containing sequences from -1450 to +810 of the human ODC gene. Co-transfection with either the alpha-RA receptor (alpha-RAR) or a chimeric alpha-RA/oestrogen receptor (alpha-RAER) followed by treatment with the cognate hormone suppresses expression of Kpn-ODCCAT and Not-ODCCAT, which contains sequences from -250 to +514. Liganded alpha-RAR suppresses the activity of Kpn-ODCCAT more markedly than does liganded alpha-RAER (98% and 80% suppression, respectively), whereas both receptors have very similar effects on Not-ODCCAT expression (73% and 67% suppression, respectively). The unliganded alpha-RAR suppresses Kpn-ODCCAT by 76%, whereas unliganded alpha-RAER has no significant effect. These data show that RA regulates ODC-gene expression at the transcriptional level, and that alpha-RAR, but not alpha-RAER, can confer full hormonal responsiveness. This suggests that the activating function present in the alpha-RAR ligand-binding domain is required for full transcriptional regulation.
Insights
Retinoic acid (RA) regulates ornithine decarboxylase (ODC) gene expression transcriptionally. The alpha-retinoic acid receptor (alpha-RAR) is crucial for full hormonal responsiveness, unlike the alpha-retinoic acid/oestrogen receptor (alpha-RAER).
Area of Science:
- Molecular Biology
- Gene Regulation
- Cellular Biology
Background:
- Retinoic acid (RA) is vital for mammalian development and growth.
- Ornithine decarboxylase (ODC) is the rate-limiting enzyme in polyamine biosynthesis.
- Previous studies indicated RA suppresses ODC mRNA in human skin cells.
Purpose of the Study:
- To investigate the transcriptional regulation of ODC gene expression by RA.
- To determine the role of alpha-retinoic acid receptor (alpha-RAR) and a chimeric alpha-RA/oestrogen receptor (alpha-RAER) in mediating RA's effects.
Main Methods:
- HeLa cells were treated with RA to assess endogenous ODC mRNA levels.
- Transfected ODC/chloramphenicol acetyltransferase (CAT) plasmids (Kpn-ODCCAT, Not-ODCCAT) were used to study transcriptional activity.
- Co-transfection with alpha-RAR or alpha-RAER followed by hormone treatment evaluated receptor-mediated effects.
Main Results:
- RA treatment suppressed endogenous ODC mRNA and expression of transfected ODC/CAT plasmids.
- Both liganded alpha-RAR and alpha-RAER suppressed Kpn-ODCCAT and Not-ODCCAT expression.
- Liganded alpha-RAR showed greater suppression of Kpn-ODCCAT than alpha-RAER.
- Unliganded alpha-RAR suppressed Kpn-ODCCAT, while unliganded alpha-RAER had no significant effect.
Conclusions:
- RA regulates ODC gene expression at the transcriptional level.
- The alpha-RAR receptor confers full hormonal responsiveness, suggesting its ligand-binding domain's activating function is essential.
- Alpha-RAER is less effective in mediating full transcriptional regulation compared to alpha-RAR.