Molecular properties of cytosolic and nuclear TCDD receptor complexes from mouse hepatoma cell lines

Wild-type mouse Hepa 1c1c7 cells are responsive to the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds. This cell line and nonresponsive mutants (TAOc1BP^rc1 and BP^rc1) have been used to study properties of cytosolic (unactivated and activated) and nuclear Ah receptor-[³H]TCDD complexes as a model for investigating the molecular mechanism of action of halogenated aromatic hydrocarbons. Incubation of cytosolic [³H]TCDD-aryl hydrocarbon (Ah) complexes from wild-type Hepa 1c1c7 cell for 16h at 4° C in 0.4 M KCl resulted in the formation of transformed specifically-bound receptor complexes which exhibited increased binding affinity on DNA-Sepharose columns. The elution properties of the peak with the highest DNA binding affinity were similar to the elution profiles of the nuclear receptor complex isolated from wild-type cells. Comparable in vitro transformation and DNA binding properties were also observed using hepatic cytosol from C57BL/6J mice. TAOc1BP^rc1 (class I) nonresponsive mutant cells were characterized by relatively low levels of the cytosolic and nuclear Ah receptor complexes. The cytosolic TCDD-Ah receptor complex did not undergo in vitro transformation. The BP^rc1 (class II) variant cell lines contained levels of cytosolic receptor which were comparable to those observed in the wild type cells, but there were significantly reduced levels of nuclear receptor complex in the class II variant cell line. Incubation of the cytosolic receptor complex from these mutant cells at 4° C for 16 h or 20° C for 2 h did not result in transformation of the cytosolic receptor complex into forms which exhibit increased retention on DNA-Sepharose columns.