Characterization of the human Ah receptor

Using [³H]2,3,7,8-tetrachlorodibenzo-p-dioxin ([³H]TCDD) or 7-[¹²⁵I]-iodo-2,3-dibromodibenzo-p-dioxin ([¹²⁵I]DBDD) as high affinity photoaffinity ligands, the photoaffinity-labeled nuclear Ah receptor complexes from human cell lines have been analyzed by denaturing sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results show that the apparent molecular mass for the Ah receptor from several of these cell lines was 110-kDa and no significant variations were observed. However, there were significant differences in the apparent molecular weights of the nuclear Ah receptor complexes. For example, in the estrogen receptor (ER)-positive (MCF-7) and ER-negative (MDA-MB-231) human breast cancer cell lines, the apparent molecular weights of the nuclear receptor complexes were 171,000 and 192,000, respectively. These results indicate that there are differences in the molecular weights of the human nuclear Ah receptor complexes and the intraspecies heterogeneity may be associated with the non-ligand binding protein and not the Ah receptor.