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Regulation of prostaglandin endoperoxide H synthase-2 expression by 2,3,7,8,-tetrachlorodibenzo-p-dioxin
S A Kraemer1, K A Arthur, M S Denison
1Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Abstract:
We have examined the molecular mechanisms for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-stimulated prostaglandin synthesis in Mardin Darvey canine kidney cells (MDCK). TCDD stimulates prostaglandin synthesis in these cells, at least in part, by elevating prostaglandin endoperoxide H2 synthase-2 (PGHS-2) levels. TCDD-stimulated transcription of the PGHS-2 gene was maximal (6-fold) within 2 h and resulted in a 100-fold increase in PGHS-2 mRNA and a 25-fold increase in PGHS-2 protein levels by 4 h. Transient transfection experiments using luciferase-reporter plasmids demonstrated that control element(s) responsible for TCDD activation of the murine PGHS-2 promoter in MDCK cells are located in the first 965 nucleotides upstream from the PGHS-2 transcriptional initiation site. A canonical xenobiotic response element, similar to those that control transcription of other well-known TCDD-sensitive genes, is present at position -157, but does not appear to be sufficient for halogenated aromatic hydrocarbon (HAH) activation of the PGHS-2 promoter. TCDD failed to stimulate transcription from the PGHS-2 promoter when reporter plasmids were transfected into Hepa 1c1c7 cells, a line which contains the functional aryl hydrocarbon receptor. It seems likely that inappropriate expression of PGHS-2 may contribute to the toxic effects of TCDD and other HAHs. In particular, PGHS-2 expression may affect those toxic reactions that involve inappropriate cellular growth, such as dermal hyperplasia and tumor formation. It is also likely that elevated synthesis of prostaglandins, which are potent regulators of immune function, could play a role in the immunotoxicity associated with HAH exposure.
Insights
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increases prostaglandin synthesis by elevating prostaglandin endoperoxide H2 synthase-2 (PGHS-2) in kidney cells. This TCDD-induced PGHS-2 expression may contribute to toxic effects like cellular growth abnormalities and immune dysfunction.
Area of Science:
- Toxicology
- Molecular Biology
- Biochemistry
Background:
- 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent environmental toxicant.
- Prostaglandins play crucial roles in cellular functions, including growth and immune response.
Purpose of the Study:
- To elucidate the molecular mechanisms by which TCDD stimulates prostaglandin synthesis in canine kidney cells (MDCK).
- To identify the regulatory elements responsible for TCDD-induced gene transcription of prostaglandin endoperoxide H2 synthase-2 (PGHS-2).
Main Methods:
- Utilized Mardin Darvey canine kidney (MDCK) cells and Hepa 1c1c7 cells.
- Employed transient transfection assays with luciferase-reporter plasmids containing the murine PGHS-2 promoter.
- Quantified PGHS-2 mRNA and protein levels following TCDD exposure.
Main Results:
- TCDD significantly increased PGHS-2 gene transcription, mRNA, and protein levels in MDCK cells.
- The TCDD-responsive elements in the PGHS-2 promoter are located within the first 965 nucleotides upstream of the transcriptional start site.
- A canonical xenobiotic response element was insufficient for TCDD activation, and TCDD failed to activate the promoter in Hepa 1c1c7 cells expressing the aryl hydrocarbon receptor.
Conclusions:
- Inappropriate PGHS-2 expression induced by TCDD may contribute to toxic effects, including abnormal cellular growth and tumor formation.
- Elevated prostaglandin synthesis resulting from TCDD exposure could be implicated in the immunotoxicity associated with halogenated aromatic hydrocarbon (HAH) exposure.