Role of the aryl hydrocarbon receptor in TCDD-induced alteration of immunoglobulin expression

Abstract

<p>Dioxin exposure is known to cause chloracne, hepatotoxicity, and immune suppression. The prototypic compound for studying dioxin toxicity 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibits immunoglobulin (lg) secretion in B cells. TCDD-induced inhibition of Ig secretion is thought to be modulated in part through transcriptional down regulation of the Ig heavy chain (lgH) locus. Although several regulatory elements control the IgH locus our research focuses on the 3'IgH regulatory region (3'lgHRR) that contains dioxin responsive elements (ORE) in two of its constituent hypersensitive regions, hsl,2 and hs4. The heterodimer of the aryl hydrocarbon receptor (AhR) and the aryl hydrocarbon nuclear translocator (ARNT) binds to OREs upon ligand (i.e. TCDD) activation. In previous luciferase reporter studies TCDD treatment in LPSactivated B cells up-regulates the hs4 region but down-regulates the 3'lgHRR. Moreover, the hs4 region contains an overlapping ORE and KB motif that have been proposed to act in concert to regulate the hs4 enhancer. The purpose of the current study is to develop an AhR-deficient model in the well-characterized CH12.LX mouse B-cell line in order to further elucidate TCDD-induced AhR regulation of the 3'IgHRR and its enhancers. Stable lentiviralmediated insertion of two shRNA constructs targeting AhR message achieved approximately 50% AhR knockdown in a heterogenous population of cells as verified by Western blot analysis. Furthermore, activity of the hs4 enhancer following LPS and TCDD co-treatment was significantly reduced in the AhR-deficient cell population. These results suggest that the AhR plays a significant role in activation of the hs4 enhancer. Furthermore, current studies are focused on utilizing this AhR-deficient model to determine the role of the AhR in TCDD-induced modulation of the 3'IgHRR which should significantly contribute to understanding the mechanisms behind altered Ig transcription and B-cell function by TCDD. (Supported by NIEHS R01ES014676 and NIEHS Supplement for Undergraduate Research Experience)</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 16, 2010</p>