2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated membrane translocation of c-Src protein kinase in liver WB-F344 cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a widespread environmental contaminant and the most potent agonist of the aryl hydrocarbon receptor (AhR). Persistent activation of the AhR has been shown to be responsible for most TCDD-mediated toxic responses, including liver tumour promotion. However, the mechanisms responsible for these complex toxic reactions are still unknown. TCDD (1 nM) has previously been shown to reduce DNA synthesis of primary hepatocyte cultures and cell contact inhibition of confluent WB-F344 cells. The latter model was used to study early effects of TCDD on protein tyrosine kinase c-Src in confluent WB-F344 cells. It was found that TCDD decreased cytosolic c-Src (protein and tyrosine kinase activity) after 20-60 min, and increased c-Src in the membrane fraction. Membrane translocation of c-Src occurred in the presence of 100 mu M cycloheximide and was observed after treatment with 1 nM TCDD or 50 nM 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin. Under these conditions epidermal growth factor (EGF) receptor tyrosine phosphorylation was also studied. As expected, its phosphorylation was low in confluent cells but was significantly enhanced by TCDD treatment. Pretreatment of WB-F344 cells for 1 h with 1 mu M geldanamycin, which disrupts cytosolic heat shock protein Hsp90 complexes with AhR and Src, abolished TCDD-mediated Src translocation and TCDD-mediated reduction of cell contact inhibition. The WB-F344 cell model appears to be very useful to study TCDD effects on protein tyrosine kinases and of signaling pathways responsible for modulation of the cell cycle by TCDD.