SUSTAINED INCREASE IN INTRACELLULAR FREE CALCIUM AND ACTIVATION OF CYCLOOXYGENASE-2 EXPRESSION IN MOUSE HEPATOMA-CELLS TREATED WITH DIOXIN

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a non-genotoxic environm ental pollutant that causes multiple adverse effects in experimental a nimals and in humans. We show here that TCDD treatment of mouse hepato ma cells causes a rapid mobilization of intracellular calcium both in wild type Hepa-1 cells and in its c2 variant, a cell line that has hig hly reduced levels of functional aromatic hydrocarbon (Ah) receptor (A HR). In wild tripe cells, but not in the c2 variant, TCDD treatment le ads to a sustained elevation of cytosolic free calcium. TCDD also indu ces elevated levels of cyclooxygenase-2 (COX-2) mRNA in wild type and in c37, a CYP1A1-deficient cell line, but not in c2 cells. Induction o f Cox 2 is in fact dependent on the presence of a functional Ah recept or, since it can be blocked by antisense oligonucleotides to Ah recept or mRNA. Most likely as a consequence of Cox-2 induction, we find a si gnificant increase in the level of 12-hydroxyheptadecatrienoic acid (1 2-HHT) secreted from TCDD-treated Hepa-1 cells. In addition, we observ e elevated levels of 6-keto prostaglandin F-1 alpha in c2 cells and hi gh levels of secreted prostaglandin F-2 alpha, in c2, c37 and c4, the variant cell line lacking aromatic hydrocarbon nuclear translocator pr otein. These data suggest that Cox-2 activation by TCDD leads to the r elease of prostaglandins, eicosanoids and other mediators which may ha ve an important role in the biological and toxic effects of TCDD. (C) 1997 Elsevier Science Inc.