Role of the 3'lgHRR in TCDD-induced suppression of the immunoglobulin heavy chain

Abstract

<p>2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibits antibody secretion and immunoglobulin heavy chain (IgH) expression. Our previous work has shown that a possible mechanism for inhibition of IgH expression could be inhibition of the 3’IgH regulatory region (3’IgHRR). The 3’IgHRR has four enhancer regions (hs3a; hs1,2; hs3b; hs4) which are purported to control IgH gene expression. Previously we demonstrated a sensitive inhibition by TCDD of LPS-induced 3’IgHRR activity which is correlated with an inhibition of LPS-induced hs1,2 enhancer activity; however, the hs4 enhancer showed TCDD-induced activation following the co-treatment of TCDD and LPS. Therefore, the objective of the current study was to determine if the hs1,2 enhancer mediates the inhibitory effect of TCDD on 3’IgHRR activation. We generated a CH12.LX cell line stably expressing a γ2b transgene under the regulation of the 3’IgHRR and containing loxp sites flanking either the hs3a/hs1,2 or the hs3b/hs4 enhancer pairs. Transient transfection with Cre recombinase results in recombination at the loxp sites and deletion of the appropriate enhancer pair. Cells expressing Cre recombinase were sorted and 96 clones from each parental (i.e., loxp flanking hs3a/hs1,2 or hs3b/hs4) were analyzed by PCR for successful recombination. We found 8 clones and 6 clones with successful deletion of the hs3a/hs1,2 and hs3b/hs4 respectively. Preliminary analysis showed inhibition of the hs3a/hs1,2 enhancer pair and no effect to inhibition of the hs3b/hs4 enhancer pair. These results suggest that the hs1,2 is the primary mediator of TCDD-induced 3’IgHRR inhibition and that the hs4 enhancer in combination with the hs3b enhancer is affected differently than when the hs4 is analyzed in isolation or by transient transfection. A polymorphism of the hs1,2 enhancer is correlated with autoimmune diseases like IgA nephropathy and Celiac disease. Hence modulation of hs1,2 enhancer activity by TCDD may influence the initiation or progression of these diseases. (Supported by NIEHS R01ES014676)</p> <p>This poster was presented at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 8, 2011</p>