Publication Date

2014

Document Type

Dissertation

Committee Members

Don Cipollini (Other), David Cool (Committee Member), Rodney Dekoter (Committee Member), Michael Leffak (Committee Member), Mill Miller (Committee Member), Courtney Sulentic (Advisor)

Degree Name

Doctor of Philosophy (PhD)

Abstract

Transcriptional regulation of the murine immunoglobulin heavy chain gene involves several regulatory elements including the 3'Igh regulatory region (3'IghRR) composed of at least four enhancers (hs3A; hs1,2; hs3B; hs4). Enhancers hs1,2 and hs4 contain binding sites for several transcription factors including NF-κB/Rel proteins and the AhR. Interestingly, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) profoundly inhibits 3'IghRR and hs1,2 activation induced by the B-cell activator lipopolysaccharide (LPS), but enhances the activation of the hs4. Within the hs4, the AhR binding site overlaps an NF-κB/Rel binding site suggesting that both the AhR and the NF-κB together may modulate of the 3'IghRR. The objective of the current study was to evaluate the role of NF-κB/Rel and the AhR following LPS stimulation and TCDD treatment on 3'IghRR, hs1,2, and hs4. In our studies we utilized the CH12.LX B cell line; the CH12.IκBαAA cell line, which expresses an inducible IκBα super repressor (IκBαAA); the CH12.γ2b-3'IghRR cell line that stably expresses a γ2b-3'IghRR-regulated γ2b transgene reporter; and splenocytes derived from B6C3F1 mice. The stimulation of the CH12.γ2b-3'IghRR cell line with Toll-like receptor (TLR) agonists LPS, Resiquimod (R848), or Cytosine-phosphate-Guanine (CpG)-oligodeoxynucleotides combined with a co-treatment of TCDD significantly inhibited the TLR-induced activation of the 3'IghRR. Utilizing transiently expressed luciferase reporters, we found induction of IκBαAA expression partially attenuated LPS-induced activation of the 3'IghRR and hs4, partially reversed the effects of a TCDD and LPS co-treatment on the activity of the 3'IghRR and hs4, and the addition of an AhR antagonist, CH223191, markedly reversed the LPS and TCDD induced inhibition of the 3'IghRR and inhibited the synergistic activation of the hs4. Chromatin immunoprecipitation analysis of CH12.LX and murine splenocytes demonstrated a LPS and a LPS co-treatment with TCDD-dependent increase in RelA and AhR binding, and a significant decrease in RelB binding to the hs4 and hs1,2. These results suggest that a shift in binding of the NF-κB/Rel proteins, perhaps through an interaction with the AhR are partially responsible for 3'IghRR modulation by LPS and TCDD. These results suggest that interactions between the AhR and NF-κB within the 3'IghRR mediate the inhibitory effects of TCDD on immunoglobulin (Ig) expression and therefore antibody levels.

Page Count

114

Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded

2014

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