The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor that mediates the toxic responses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The identification and functional analysis of AHR single nucleotide polymorphisms is important in understanding the functional diversity of this receptor as it might give rise to individuals with differing sensitivities to TCDD. In this study, the functional properties of six (I277V, P517S, R554K, V570I, Q666K, and R554K/V570I) human AHR variants were examined in human breast cancer cells (MCF-7 AHR100) and mouse hepatoma cells (Hepa c12) deficient in AHR. CYP1A1- or CYP1B1-regulated reporter gene assays in AHR100 or Hepa c12 cells exposed to TCDD revealed no significant differences in reporter gene activity among the different AHR variants. In contrast to previous findings describing the AHR-R554K/V570I variant to be transcriptionally deficient, no differences in TCDD-dependent increases in CYP1A1 and CYP1B1 mRNA levels were observed between AHR and AHR-R554K/V570I after 24h or 48h of exposure. Chromatin immunoprecipitation assays also revealed similar recruitment patterns of AHR and AHR-R554K/V570I to the 5'-regulatory regions of CYP1A1 and CYP1B1. Collectively, our findings show that none of the AHR variants examined exhibited an altered ability to regulate CYP1A1- or CYP1B1-driven transcription in AHR100 or Hepa c12 cell lines, and that AHR and AHR-R554K/V570I are functionally equivalent in the two cell lines examined.
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