Received for publication January 2, 2008.
Revised April 2, 2008.
Accepted for publication April 3, 2008.

Roles of Cytosolic Phospholipase A2 and Src Kinase in the Early Action of TCDD through a Nongenomic Pathway in MCF10A Cells

Abstract

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, or dioxin) is known to induce rapid inflammatory cellular responses through the mechanism which has not been fully elucidated yet. 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 attested 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 MAFP, a specific inhibitor of cPLA2, siRNA 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 (AhR), but not on aryl hydrocarbon receptor nuclear translocator (ARNT). 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 classical model of action of TCDD through the "genomic" pathway.

Key words: Phospholipase A2's, Src and other nonreceptor tyrosine kinases, Ah receptor, Cyclooxygenases