Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, or dioxin) is known to induce rapid inflammatory cellular responses through the mechanism that has not yet been fully elucidated. In this report, we show that in MCF10A cells, an immortalized, normal mammary epithelial cell line, TCDD rapidly activates the enzymatic activity of cytosolic phospholipase A2 (cPLA2) as at-tested to by arachidonic acid release within 15 min, followed by activation of Src kinase and induction of several inflammation markers. Such an action of TCDD is clearly blocked by methylarachidonyl fluorophosphonate, a specific inhibitor of cPLA2, short interfering RNA against cPLA2, and several calcium signaling blockers, indicating that this action of TCDD is mediated by calcium-triggered activation of cPLA2. This action of TCDD is quite different from the classic action of TCDD to induce cytochrome P450 1A1 (CYP1A1) because blocking this newly identified pathway did not affect the induction of CYP1A1. Moreover, this newly identified pathway was found to depend only on aryl hydrocarbon receptor but not on aryl hydrocarbon receptor nuclear translocator. Together, these findings support the model that the early action of TCDD to induce rapid inflammatory responses is carried out through a characteristic “nongenomic” pathway, which is clearly different from the conventional model of action of TCDD through the “genomic” pathway.
Footnotes
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This work was supported by research grants R01-ES05233 and R01-ES07284 and a center grant P30-ES05707 from the National Institute of Environmental Health Sciences.
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ABBREVIATIONS: TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; AhR, aryl hydrocarbon receptor; ARNT, aryl hydrocarbon receptor nuclear translocator; Cox-2, cyclooxygenase-2; cPLA2, cytosolic phospholipase A2; IκB-α, Inhibitor κ B-α; IL, interleukin; NFκB, nuclear factor κB; PAI-2, plasminogen activator inhibitor-2; TNF-α, tumor necrosis factor-α; VEGF, vascular endothelial growth factor; PVDF, polyvinylidene diflouride; MNF, 3′-methoxy-4′-nitroflavone; PCR, polymerase chain reaction; MAFP, methylarachidonyl fluorophosphonate; siRNA, short interfering RNA; PP2, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine; AM, acetoxymethyl ester; 2-APB, 2-aminoethoxydiphenyl borate; A23187, calcimycin; si-AhR, short interfering RNA against the aryl hydrocarbon receptor; si-ARNT, short interfering RNA against the aryl hydrocarbon receptor nuclear translocator.
- Received December 26, 2007.
- Accepted April 3, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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