Abstract
CYP3A4, the predominant cytochrome P450 (P450) expressed in human liver and intestine, contributes to the metabolism of approximately half the drugs in clinical use today. CYP3A4 catalyzes the 6β-hydroxylation of a number of steroid hormones and is involved in the bioactivation of environmental procarcinogens. The expression of CYP3A4 is affected by several stimuli, including environmental factors such as insecticides and pesticides. The o,p′-1,1,1,-trichloro-2,2-bis (p-chlorophenyl)ethane (DDT) isomer of DDT comprises approximately 20% of technical grade DDT, which is an organochloride pesticide. We have recently shown that o,p′-DDT exposure increases CYP3A4 mRNA levels in HepG2 cells. To determine the mechanism by which o,p′-DDT induces CYP3A4 expression, transactivation and electrophoretic mobility shift assays were carried out, revealing that o,p′-DDT activates the CYP3A4 gene promoter through the pregnane X receptor (PXR). CYP3A4 gene promoter activation resulted in both an increase in CYP3A4 mRNA levels and an increase in the total CYP3A4 activity in HepG2 cells. We also observed induction of CYP3A4 and mouse Cyp3a11 mRNA in the intestine of CYP3A4-transgenic mice after exposure to 1 mg/kg o,p′-DDT. At higher doses, a decrease of CYP3A4 inducibility was observed together with an increase in levels of interleukin 6 mRNA, a proinflammatory cytokine that strongly represses CYP3A4 transcription. The present study indicates that regulation of other genes under PXR control may be altered by o,p′-DDT exposure.
Footnotes
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This work was supported by Consejo Nacional de Ciencia y Tecnologia Grant 36173M.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.106.011759.
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ABBREVIATIONS: P450, cytochrome P450; ER, estrogen receptor; PXR, pregnane X receptor; DDT, 1,1,1,-trichloro-2,2-bis (p-chlorophenyl)ethane; PCN, pregnenolone 16α-carbonitrile; DMEM, Dulbecco's modified Eagle's medium; PCR, polymerase chain reaction; rtPCR, quantitative real-time polymerase chain reaction; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; RT-PCR, reverse transcription-polymerase chain reaction; IL-6, interleukin 6; PBS, phosphate-buffered saline; ERE, estrogen response element; PXRE, pregnane X receptor response element; XREM, xenobiotic responsive enhancer module; EMSA, electrophoretic mobility shift assay; LBD, ligand binding domain; DDE, 1,1,-dichloro-2,2-bis (p-chlorophenyl)ethylene.
- Received June 29, 2006.
- Accepted October 6, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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