The dioxin receptor: A comparison with the glucocorticoid receptor

The physico-chemical properties of the dioxin and glucocorticoid receptors from rat liver and wild-type and mutant cell lines were investigated and compared. In rat liver, the receptors are virtually indistinguishable. Both are highly asymmetrical proteins with axial ratios of 12-15, have Stokes radii of 6 nm and sedimentation coefficients of ~4 S. This results in a calculated apparent mol. wt of ~ 100,000. The dioxin receptor from the mouse hepatoma cell line Hepa lclc7 represents an atypical form of the dioxin receptor with a pronounced tendency to aggregate to form M_r ≈ 300,000 complexes in high ionic strength and in the absence of sodium molybdate. In the presence of sulphydryl reducing agents, however, the Hepa lclc7 dioxin receptor dissociates to an M_r ≈ 100,000 species. In analogy to the nt^- mutant glucocorticoid receptor in mouse lymphoma cells, there is no gross change in the structure of the nt^- dioxin mutant in mouse hepatoma cells compared with the wild-type receptor. The nt~ dioxin receptor does, however, have a reduced affinity for DNA.