Targeting of Aryl Hydrocarbon Receptor-Mediated Activation of Cyclooxygenase-2 Expression by the Indole-3-Carbinol Metabolite 3,3′-Diindolylmethane in Breast Cancer Cells

Abstract

Ligands of the aryl hydrocarbon receptor (AhR) include the environmental xenobiotic 2,3,7,8 tetrachlorodibenzo(p)dioxin (TCDD), polycyclic aryl hydrocarbons, and the dietary compounds 3, 3'-diindolylmethane (DIM), a condensation product of indol-3-carbinol found in Brassica vegetables, and the phytoalexin resveratrol (RES). The AhR and its cofactors regulate the expression of target genes at pentameric (GCGTG) xenobiotic responsive elements (XRE). Because the activation of cyclooxygenase-2 (COX-2) expression by AhR ligands may contribute to inflammation and tumorigenesis, we investigated the epigenetic regulation of the COX-2 gene by TCDD and the reversal effects of DIM in MCF-7 breast cancer cells. Results of DNA binding and chromatin immunoprecipitation (ChIP) studies documented that the treatment with TCDD induced the association of the AhR to XRE harbored in the COX-2 promoter and control CYP1A1 promoter oligonucleotides. The TCDD-induced binding of the AhR was reduced by small-interfering RNA for the AhR or the cotreatment with synthetic (3-methoxy-4-naphthoflavone) or dietary AhR antagonists (DIM, RES). In time course ChIP studies, TCDD induced the rapid (15 min) occupancy by the AhR, the histone acetyl transferase p300, and acetylated histone H4 (AcH4) at the COX-2 promoter. Conversely, the cotreatment of MCF-7 cells with DIM (10 micromol/L) abrogated the TCDD-induced recruitment of the AhR and AcH4 to the COX-2 promoter and the induction of COX-2 mRNA and protein levels. Taken together, these data suggest that naturally occurring modulators of the AhR such as DIM may be effective agents for dietary strategies against epigenetic activation of COX-2 expression by AhR agonists.

Epigenetic Modifications of Nrf2 by 3,3′-diindolylmethane In Vitro in TRAMP C1 Cell Line and In Vivo TRAMP Prostate Tumors

“…DIM appears to elicit multiple targets anticancer effects through many potential mechanisms including antiinflammation, antioxidative stress effect, cell-cycle regulation, and apoptosis depending on the context of tissues and cell types (10,(34)(35)(36)(37)(38). Several naturally occurring anticancer phytochemicals have been shown to possess the ability to prevent cancer via epigenetic modifications (14,15,(39)(40)(41). A previous study showed that DIM possesses the ability to inhibit HDAC activity which correlated with increased expression of p21in both human PC-3 and LNCaP cells (19).…”

Chemopreventive properties of 3,3′-diindolylmethane in breast cancer: evidence from experimental and human studies

“…35 Evidence from mammary cell lines has demonstrated the role of DIM in reducing oxidative stress by stimulating the phosphorylation of BRCA1. 36 Further, DIM has a demonstrated role in reducing cyclooxygenase-2-induced inflammation in mammary cell lines.…”

“…36 Further, DIM has a demonstrated role in reducing cyclooxygenase-2-induced inflammation in mammary cell lines. 35 In advanced stages of tumor development, DIM has been shown in tumor cell line models to inhibit the expression of genes involved in angiogenesis and energy metabolism, including those involved in the induction of survivin 37 and hypoxiainducible factor-1. 38 The interferon-c signaling pathway also is activated by DIM through the interferon-c receptor and the interferon-c-responsive proteins p56-and p69-oligoadenylate synthase, which inhibit growth of human breast cancer cells, resulting in inhibition of cell proliferation.…”

Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism

“…Such compounds include low-molecular-weight aliphatic isothiocyanates, 13 phenethyl isothiocyanate, 14,15 and two products of indole glucosinolate degradation, indole-3-carbinol and diindolylmethane. 16,17 In contrast to these beneficial effects of glucosinolates, there is evidence (primarily from animal studies) of adverse effects on the thyroid caused by the glucosinolate progoitrin, from which the product of myrosinase-induced degradation is goitrin (Figure 1). [18][19][20][21] Iodine is a dietary micronutrient required for the production of thyroid hormone, and the potential adverse effects of goitrin and thiocyanates are based on their ability to inhibit iodine utilization by the thyroid.…”