title: A tetratricopeptide repeat half-site in the aryl hydrocarbon receptor is important for DNA binding and trans-activation potential.
abstract: Similar to certain unliganded steroid hormone receptor complexes, the unliganded aryl hydrocarbon receptor has been shown to consist of a multimeric core complex that includes the 90-kDa heat shock protein (hsp90) and the immunophilin-like hepatitis B X-associated protein 2 (XAP2). Immunophilins and XAP2 associated with these complexes bind to the carboxyl-terminal end of hsp90 through an interaction with their tetratricopeptide repeat (TPR) domains. The consensus TPR binding motif contains two domains, A and B. Recently, the carboxyl terminus of XAP2 has been shown to contain a highly conserved TPR domain that is required for the assembly of XAP2 with both hsp90 and AhR. A search of the murine AhR sequence identified domain B (A-F-A-P) of the consensus TPR sequence directly adjacent to the carboxyl-terminal side of the helix-loop-helix region of the murine and human AhR. We hypothesized that this conserved domain B region may be involved with mediating interactions between either AhR-hsp90, AhR-XAP2, and/or AhR-AhR nuclear translocator protein. Site-directed mutagenesis of the amino-terminal alanine residue of this region to an aspartic acid (A78D) completely inhibited 2,3,7, 8-tetrachloro-p-dioxin (TCDD) -dependent activation of a xenobiotic response element (XRE) driven gene expression construct in transfected COS-1 and BP8 cells. The A82F mutation caused a 40 to 50% decrease in TCDD-dependent activation. The inability of A78D and the reduction of A82F to trans-activate XRE-driven reporter activity did not result from impaired AhR-XAP2-hsp90 interactions, TCDD-dependent AhR translocation to the nucleus, or AhR-AhR nuclear translocator protein interactions. In vitro DNA binding analysis demonstrated that loss of trans-activation potential by the A78D mutation resulted from impaired XRE binding. This study underscores the potential importance of AhR mutations that occur naturally outside of known functional domains.
authors.affiliation: Center for Molecular Toxicology and Carcinogenesis, Department of Veterinary Science, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Levine
authors.forename: J R
authors.initials: JR
authors.lastname: Petrulis
authors.forename: A
authors.initials: A
authors.lastname: Dubil
authors.forename: G H
authors.initials: GH
authors.lastname: Perdew
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D019281:Dimerization; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020449:Repetitive Sequences, Amino Acid; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation
chemical_list: D018076:DNA, Complementary; D018841:HSP90 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D018336:Receptors, Aryl Hydrocarbon; C103265:aryl hydrocarbon receptor-interacting protein; D004247:DNA