Modulation of prostaglandin H synthase-2 mRNA expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice.
Prostaglandin endoperoxide H synthases (PGHS-1 and PGHS-2) catalyze an intermediate step in the biosynthesis of prostaglandins and thromboxanes. Recently, it was observed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) modulates the expression of PGHS-2 mRNA in different cell lines. The main aim of this study was to examine whether PGHS-2 mRNA expression can be changed by acute TCDD in vivo and, second, we were also interested in whether modulation of PGHS-2 is mediated by the aryl hydrocarbon receptor (AhR) which is known to be involved in the transcriptional control of TCDD-induced phase 1 and phase 2 enzymes. Initially C57BL/6J mice were treated with a single dose of 10,000 ng TCDD/kg and the PGHS-1 and PGHS-2 mRNAs were analyzed in liver, lung, thymus, kidney, and spleen. In all tissues examined the expression of PGHS-1 mRNA was not affected by TCDD. However, TCDD treatment enhanced the PGHS-2 mRNA levels in lung and spleen. No effect of TCDD on PGHS-2 expression was found in liver and kidney. For dose-response studies C57BL/6J and DBA/2J mice were treated for 24 h with various doses of TCDD (1-50,000 ng/kg) and the PGHS-2 mRNA increases were analyzed in lungs and spleens. A significant increase of PGHS-2 mRNA in lungs of C57BL/6J mice was found at a dose of 100 ng TCDD/kg, whereas a nearly 100-fold higher TCDD dose was needed to increase PGHS-2 in DBA/2J mice. A similar dose-dependent induction of PGHS-2 was found in spleens of C57BL/6J mice; however, no significant increase of PGHS-2 was found in spleens of DBA/2 mice. These results indicate an involvement of AhR in TCDD-mediated changes of PGHS-2 expression. This suggestion is supported by studies in AhR-deficient animals which showed that TCDD had no effect on PGHS-2 mRNA. When changes of PGHS-2 mRNA expression are compared with those of CYP1A1 between 4 and 72 h after TCDD, it is noteworthy that TCDD led to a delayed and more transient increase of PGHS-2. These data suggest that the mechanism of modulation of both genes by TCDD may be different.
Vogel
C
C
Division of Toxicology, Heinrich-Heine-University of Düsseldorf, Auf'm Hennekamp 50, Düsseldorf, 40225, Germany.
Schuhmacher
U S
US
Degen
G H
GH
Bolt
H M
HM
Pineau
T
T
Abel
J
J
D000818:Animals; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics*; D007527:Isoenzymes / Q000235:genetics*; D008565:Membrane Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D018336:Receptors, Aryl Hydrocarbon / Q000502:physiology
D007527:Isoenzymes; D008565:Membrane Proteins; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D019363:Cytochrome P-450 CYP1A1; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse