Inflammatory Signaling and Aryl Hydrocarbon Receptor Mediate Synergistic Induction of Interleukin 6 in MCF-7 Cells

Abstract

The pleiotropic cytokine interleukin 6 (IL-6) is involved in immune cell homeostasis. Additionally, IL-6 expression and signaling in tumor cells have been shown to elicit both protumor and antitumor properties. There is a plethora of mechanistic knowledge regarding how IL-6 signal transduction translates to biological responses. However, there is little understanding as to what factors control IL-6 expression within a tumor cell environment. The studies presented herein show that, in MCF-7 breast and ECC-1 endocervical cancer cells, the stimulation of aryl hydrocarbon receptor (AHR) activity, in combination with IL-1B or phorbol 12-myristate 13-acetate (PMA) treatment, results in a marked synergistic induction of IL-6 levels over what is seen without AHR activation. Chromatin immunoprecipitation experiments suggest that the regulation of IL-6 mRNA expression occurs at the chromatin level, as AHR presence on the IL-6 promoter was observed in response to treatment with AHR ligand. Synergistic induction of IL-6 expression was sustained for 72 hours, with accumulation of IL-6 protein reaching levels 4.8-fold above IL-1B treatment alone. In addition, transcriptional regulation of the prototypic AHR responsive gene Cyp1a1 was negatively regulated by PMA and IL-1B treatment. Silencing of RELA expression alleviated IL-1B-mediated repression of AHR transcriptional activity, whereas PMA-mediated repression was maintained. Additionally, small interfering RNA studies reveal that AHR and RELA are necessary for synergistic induction of IL-6. The findings presented here reveal the AHR as a potential therapeutic target for selective modulation of IL-6 expression in some tumor cell types. The data also suggest a possible previously unrecognized mechanism of AHRmediated tumor promotion. [Cancer Res 2008;68(10):3609-17]

Aryl hydrocarbon receptor-dependence of dioxin’s effects on constitutive mouse hepatic cytochromes P450 and growth hormone signaling components

“…Exogenous AHR agonists appear to have dual effects on inflammatory signaling. On the one hand, TCDD exposure can induce inflammatory responses as exemplified by: (a) the synergistic induction of IL-6 expression caused by interleukin-1β and TCDD co-treatment via an AHR-dependent and DRE-mediated mechanism (Hollingshead et al 2008); and (b) induction of Socs3 expression by TCDD via an AHR-dependent and protein kinase-dependent non-genomic pathway that does not require AHR nuclear localization (Li et al 2010). On the other hand, AHR activation by TCDD can disrupt nuclear factor-κB signaling and suppress acute phase response genes such as serum amyloid protein A3 (Saa3) via a mechanism that does not require binding of AHR to a DRE (Patel et al 2009).…”

Mechanistic Insights into the Events That Lead to Synergistic Induction of Interleukin 6 Transcription upon Activation of the Aryl Hydrocarbon Receptor and Inflammatory Signaling

“…We have previously shown that, in both the human MCF-7 breast cancer cell line and the ECC1 endocervical cancer cell line, IL6 production is synergistically increased following concomitant exposure to an AHR ligand and pro-inflammatory IL1␤ (6). The low level of AHR activation needed to mediate this response, combined with the fact that increased IL6 protein secretion continued for 72 h after the initial dose of ligand, points to a potentially low threshold that cancer cells must pass before producing and releasing extensive amounts of a known pro-growth signal.…”

DDE and PCB 153 independently induce aryl hydrocarbon receptor (AhR) expression in peripheral blood mononuclear cells

“…Thus, it is important to assess potential toxicological interactions between components of a chemical mixture in exposed populations. As we noted above, pro-inflammatory molecules can significantly amplify the effects of AhR ligands (Hollingshead et al, 2008;Umannová et al, 2007).…”

“…We hypothesize that the mechanism by which TNF amplified the effects of AhR ligands was by inducing an over-expression of the AhR. In this context, Hollingshead et al (2008) showed that TCDD treatment in combination with IL-1 or phorbol 12-myristate 13-acetate (PMA) resulted in a marked synergistic induction of IL-6 levels over that seen without AhR activation in MCF-7 cells. Since TCDD induces IL-6 expression through the AhR pathway, those authors suggested this synergistic effect could be partly explained by an inflammation-induced increase in AhR expression.…”