Pax5 may mediate TCDD-induced differences in transcriptional regulation of the mouse and human hs1,2 enhancer

Abstract

<p>Immunoglobulin heavy chain (lgH) expression and Ig secretion is inhibited by the environmental contaminant 2,3,7,8tetrachlorodibenzo-para-dioxin (TCDD). Within the IgH gene, the 3' IgH regulatory region (3'lgHRR) has been identified as a transcriptional target of TCDD. The 3'IgHRR, which in part regulates transcription of the IgH gene, is composed of four enhancers in the mouse: hs3a; hsl,2; h3b; hs4 and three enhancers in the human: hs3a; hsl,2; hs4. Interestingly, a repeating polymorphism, approximately 53 bp in length, within the human hsl,2 enhancer, has been correlated with several autoimmune disorders. TCDD induces a decrease in transcriptional activity of the mouse hsl,2 enhancer, while the human polymorphic hsl,2 enhancer is increased. The purpose of the current study is to determine if this opposing result may be partially due to Pax5, a regulator of B-cell maturation that is down-regulated at the plasma cell stage to allow IgH transcription and Ig secretion. Two Pax5 binding sites are present in the mouse hsl,2 whereas none are present in the human hsl,2 and TCDD has been shown to interfere with the down-regulation of Pax5. Utilizing site-directed mutagenesis, a Pax5 binding site identical to the mouse was inserted into a human hsl,2 enhancer reporter plasmid. Transient transfection studies using a mouse (CH12.LX) and human (IM-9) B cell line expressing functional AhR signaling demonstrated a decrease in overall TCDDinduced transcriptional activity with the insertion of a Pax5 site within the human hsl,2 enhancer. These results suggest Pax5 may be in part responsible for the differing transcriptional regulation between the mouse and human hsl,2 enhancer following TCDD treatment. Additionally, species specific sequence differences may complicate the translation of mouse studies to humans. (Supported by NIEHS R01ES014676)</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 8, 2011</p>