Aryl Hydrocarbon Receptor Activation Suppresses EBF1 and PAX5 and Impairs Human B Lymphopoiesis.

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates biological responses to endogenous and environmental chemical cues. Increasing evidence shows that the AHR plays physiological roles in regulating development, homeostasis, and function of a variety of cell lineages in the immune system. However, the role of AHR in human B cell development has not been investigated. Toward this end, an in vitro feeder-free human B cell developmental model system was employed using human cord blood CD34+ hematopoietic stem/progenitor cells. Using this model, we found that AHR activation by the high-affinity ligand 2,3,7,8-tetrachlorodibenzo- p -dioxin significantly suppressed the generation of early B cells and pro-B cells from hematopoietic stem/progenitor cells, indicating the impairment of B cell lineage specification and commitment. Addition of an AHR antagonist reversed 2,3,7,8-tetrachlorodibenzo- p -dioxin-elicited suppression of early B and pro-B cells, suggesting a role of AHR in regulating B lymphopoiesis. Gene expression analysis revealed a significant decrease in the messenger RNA level of early B cell factor 1 (EBF1) and paired box 5, two critical transcription factors directing B cell lineage specification and commitment. Additionally, binding of the ligand-activated AHR to the putative dioxin response elements in the EBF1 promoter was demonstrated by EMSAs and chromatin immunoprecipitation analysis, suggesting transcriptional regulation of EBF1 by AHR. Taken together, this study demonstrates a role for the AHR in regulating human B cell development, and it suggests that transcriptional alterations of EBF1 by the AHR are involved in the underlying mechanism.