Putative link between transcriptional regulation of IgM expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin and the aryl hydrocarbon receptor/dioxin-responsive enhancer signaling pathway.

Oct 25, 2000The Journal of pharmacology and experimental therapeutics

Possible connection between gene control of IgM production and the dioxin receptor signaling pathway

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Circadian Biology on OpenScience ↗PubMed ↗

Abstract

Inhibition of mu gene expression and IgM protein secretion in B-cells is associated with a structure-activity relationship for AhR binding.

TCDD affects B-cells, which are critical for immune response.
The effects on gene expression and protein secretion may be mediated by the aryl hydrocarbon receptor (AhR).
Two dioxin-responsive enhancer-like sites were identified within the Ig heavy chain 3'alpha-enhancer.
TCDD induced binding of the AhR nuclear complex to both DRE-like sites.
TCDD also triggered binding of nuclear factor-kappa B/Rel proteins to a kappa B site overlapping one DRE-like site.
An AhR-independent effect of TCDD on kappa B binding was observed in AhR-deficient B-cells.

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The B-cell, a major cellular component of humoral immunity, has been identified as a sensitive target of 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD). The actual molecular mechanism responsible for the immunotoxic effects produced by TCDD is unclear; however, many of the biological effects produced by TCDD are thought to be mediated by the aryl hydrocarbon receptor (AhR). Using the CH12.LX B-cell line, the present studies show that inhibition of mu gene expression and IgM protein secretion by polychlorinated dibenzo-p-dioxin congeners follow a structure-activity relationship for AhR binding. Furthermore, these effects may be mediated by the two dioxin-responsive enhancer (DRE)-like sites that were identified within the Ig heavy chain 3'alpha-enhancer. Electrophoretic mobility shift assay-Western analysis demonstrated TCDD-induced binding of the AhR nuclear complex to both DRE-like sites as well as TCDD-induced binding of several nuclear factor-kappa B/Rel proteins to a kappa B site, which overlaps one of the DRE-like sites. Interestingly, kappa B binding in the AhR-deficient BCL-1 B-cells was also induced by TCDD, demonstrating an AhR-independent effect of TCDD on kappa B binding. Taken together, these results support an AhR/DRE-mediated mechanism for TCDD-induced inhibition of IgM expression.

Putative link between transcriptional regulation of IgM expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin and the aryl hydrocarbon receptor/dioxin-responsive enhancer signaling pathway.

Abstract

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