CHARACTERIZATION OF THE ARYL-HYDROCARBON RECEPTOR COMPLEX IN HUMAN B-LYMPHOCYTES - EVIDENCE FOR A DISTINCT NUCLEAR DNA-BINDING FORM

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) suppresses B lymphocyte pro liferation and immunoglobulin production, We previously reported that the aryl hydrocarbon receptor (AhR) complex, composed of the AhR ligan d binding subunit and the Ah receptor nuclear translocator (ARNT), was constitutively present in nuclear extracts from two human B lymphocyt e cell lines (Biochem, Biophys, Res, Commun, 212, 27-34, 1995), The pr esent study compared the AhR complex in the IM-9 and PJS-91 human B ly mphocyte and HepG2 human hepatoma cell lines, AhR mRNA levels in the t wo lymphocyte cell lines were substantially lower than those in HepG2 cells, as was immunoreactive AhR protein, In contrast, ARNT mRNA and p rotein were expressed at a high level in all three cell lines. TCDD in duction of cytochrome P450 1A1 mRNA and protein was detected in only t he PJS-91 lymphocyte cell line, and at a markedly lower level than tha t in HepG2 cells, In gel shift assays, the cytosolic DNA-binding AhR c omplex in IM-9 and PJS-91 cells was indistinguishable from that in Hep G2 cells, In contrast, the nuclear DNA-binding AhR complex in IM-9 and PJS-91 cells consisted of several closely migrating species, one bein g recognized by an AhR antibody, while an ARNT antibody reacted with a ll species, Protein:DNA crosslinking analysis revealed the presence of a novel M(r) 100,000 DNA-binding protein in nuclear extracts from IM- 9 and PJS-91, but not HepG2, cells that was not recognized by either A hR Or ARNT antibodies, These results show that IM-9 and PJS-91 human B cells constitutively express a distinct nuclear DNA-binding form of t he AhR complex that may result from the presence of an additional prot ein or a structural variant Of the AhR. (C) 1996 Academic Press, Inc.