Abstract

Western blot analysis and indirect immunofluorescence microscopy were used to evaluate the fate of the aryl-hydrocarbon receptor (AhR) and aryl-hydrocarbon receptor nuclear translocator (Arnt) protein in culture cell models exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In wild-type (WT) murine Hepa-1c1c7 cells, AhR protein was depleted by 85% after 4 hr of TCDD treatment as measured in total cell lysates. In contrast, the concentration of Arnt protein was unaffected by TCDD treatment in WT cells. Analysis of the AhR with immunofluorescence microscopy revealed that nuclear translocation of the liganded AhR preceded its depletion from cells. AhR protein was depleted from Hepa-1 type I variants (that contain a concentration of AhR that is 10% of WT) with a similar time course and to the same maximal level observed in WT cells (85%). The EC50 for AhR depletion in Hepa-1 cells was 39 pm TCDD and correspond to the EC50 for induction of P4501A1 protein. Murine embryonic fibroblasts (NIH-3T3), rat aortic smooth muscle cells (A7), and murine skeletal muscle cells (C2C12) all exhibited >90% depletion of the AhR after 2-4 hr of TCDD treatment. Arnt concentration was not affected by TCDD in these cell lines. These results indicate that the liganded AhR is rapidly depleted within the nuclear compartment of hepatic and nonhepatic cells in a manner independent of the Arnt protein.