Regulation of prostaglandin endoperoxide H synthase-2 induction by dioxin in rat hepatocytes: possible c-Src-mediated pathway.
The tumor promoter 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known to increase the expression of prostaglandin endoperoxide H synthase (PGHS)-2. This study focused on the regulatory mechanism of TCDD-mediated transcriptional activation of PGHS-2. Treatment of rat hepatocytes with TCDD led to a dose-dependent induction of PGHS-2 mRNA levels associated with an increased synthesis of prostaglandin E(2), whereas expression of PGHS-1 was not affected. In vitro experiments with c-Src inhibitors, such as herbimycin A and geldanamycin, and in vivo studies with c-Src-deficient mice indicated that up-regulation of PGHS-2 but not the cytochrome P450 gene CYP1A1 by TCDD is mediated via a c-Src-dependent pathway. Transient transfection studies with different reporter constructs of the murine PGHS-2 promoter mutated in the xenobiotic-responsive element (XRE) or CCAAT/enhancer binding protein (C/EBP) element revealed that a C/EBP-binding site is an important regulatory cis-acting factor for trans-activation of the PGHS-2 gene by TCDD. Consistent with transfection studies, gel mobility shift assays showed that TCDD led to an enhanced DNA-binding activity of C/EBP beta transcription factor. The experimental data presented in this article reveal a XRE-independent and c-Src-mediated activation of the PGHS-2 gene by TCDD through the C/EBP response element located in its promoter region.
Vogel
C
C
Department of Experimental Toxicology, Medical Institute of Environmental Hygiene at the Heinrich-Heine-University, 40225 Duesseldorf, Germany.
Boerboom
A M
AM
Baechle
C
C
El-Bahay
C
C
Kahl
R
R
Degen
G H
GH
Abel
J
J
D000818:Animals; D002273:Carcinogens / Q000494:pharmacology; D002478:Cells, Cultured; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D022781:Hepatocytes / Q000201:enzymology*; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D008565:Membrane Proteins; D051379:Mice; D016297:Mutagenesis, Site-Directed; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects
D002273:Carcinogens; D007527:Isoenzymes; D008565:Membrane Proteins; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D019363:Cytochrome P-450 CYP1A1; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse; C496513:Ptgs1 protein, rat