Basal and inducible CYP1 mRNA quantitation and protein localization throughout the mouse gastrointestinal tract.
The CYP1A1, CYP1A2, and CYP1B1 enzymes are inducible by benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD); metabolism of BaP by these enzymes leads to electrophilic intermediates and genotoxicity. Throughout the gastrointestinal (GI) tract, we systematically compared basal and inducible levels of the CYP1 mRNAs by Q-PCR, and localized the CYP1 proteins by immunohistochemistry. Cyp1(+/+) wild-type were compared with the Cyp1a1(-/-), Cyp1a2(-/-), and Cyp1b1(-/-) single-knockout and Cyp1a1/1b1(-/-) and Cyp1a2/1b1(-/-) double-knockout mice. Oral BaP was compared with intraperitoneal TCDD. In general, maximal CYP1A1 mRNA levels were 3-10 times greater than CYP1B1, which were 3-10 times greater than CYP1A2 mRNA levels. Highest inducible concentrations of CYP1A1 and CYP1A2 occurred in proximal small intestine, whereas the highest basal and inducible levels of CYP1B1 mRNA occurred in esophagus, forestomach, and glandular stomach. Ablation of either Cyp1a2 or Cyp1b1 gene resulted in a compensatory increase in CYP1A1 mRNA - but only in small intestine. Also in small intestine, although BaP- and TCDD-mediated CYP1A1 inductions were roughly equivalent, oral BaP-mediated CYP1A2 mRNA induction was approximately 40-fold greater than TCDD-mediated CYP1A2 induction. CYP1B1 induction by TCDD in Cyp1(+/+) and Cyp1a2(-/-) mice was 4-5 times higher than that by BaP; however, in Cyp1a1(-/-) animals CYP1B1 induction by TCDD or BaP was approximately equivalent. CYP1A1 and CYP1A2 proteins were generally localized nearer to the lumen than CYP1B1 proteins, in both squamous and glandular epithelial cells. These GI tract data suggest that the inducible CYP1A1 enzyme, both in concentration and in location, might act as a "shield" in detoxifying oral BaP and, hence, protecting the animal.
Uno
Shigeyuki
S
Department of Environmental Health, and The Center for Environmental Genetics (CEG), University of Cincinnati Medical Center, Cincinnati, OH 45267-0056, USA.
Dragin
Nadine
N
Miller
Marian L
ML
Dalton
Timothy P
TP
Gonzalez
Frank J
FJ
Nebert
Daniel W
DW
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000032:analysis* / Q000235:genetics*; D001564:Benzo(a)pyrene / Q000494:pharmacology; D015153:Blotting, Western; D019363:Cytochrome P-450 CYP1A1 / Q000032:analysis* / Q000235:genetics*; D019388:Cytochrome P-450 CYP1A2 / Q000032:analysis* / Q000235:genetics*; D065633:Cytochrome P-450 CYP1B1; D004790:Enzyme Induction / Q000187:drug effects; D041981:Gastrointestinal Tract / Q000201:enzymology*; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology
D000072317:Polychlorinated Dibenzodioxins; D001564:Benzo(a)pyrene; D001189:Aryl Hydrocarbon Hydroxylases; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D065633:Cytochrome P-450 CYP1B1