Estrogen receptors (ER) and nuclear factor-κB (NF-κB) are known to play important roles in breast cancer, but these factors are generally thought to repress each other's activity. However, we have recently found that ER and NF-κB can also act together in a positive manner to synergistically increase gene transcription. To examine the extent of cross-talk between ER and NF-κB, a microarray study was conducted in which MCF-7 breast cancer cells were treated with 17β-estradiol (E 2 ), tumor necrosis factor α (TNFα), or both. Followup studies with an ER antagonist and NF-κB inhibitors show that cross-talk between E 2 and TNFα is mediated by these two factors. We find that although transrepression between ER and NF-κB does occur, positive cross-talk is more prominent with three gene-specific patterns of regulation: (a) TNFα enhances E 2 action on ∼30% of E 2 -upregulated genes; (b) E 2 enhances TNFα activity on ∼15% of TNFα-upregulated genes; and (c) E 2 + TNFα causes a more than additive upregulation of ∼60 genes. Consistent with their prosurvival roles, ER and NF-κB and their target gene, BIRC3, are involved in protecting breast cancer cells against apoptosis. Furthermore, genes positively regulated by E 2 + TNFα are clinically relevant because they are enriched in luminal B breast tumors and their expression profiles can distinguish a cohort of patients with poor outcome following endocrine treatment. Taken together, our findings suggest that positive cross-talk between ER and NF-κB is more extensive than anticipated and that these factors may act together to promote survival of breast cancer cells and progression to a more aggressive phenotype. [Cancer Res 2009;69(23):8918-25]

Inflammatory mediators, such as cytokines and prostaglandins, play a fundamental role in estrogen-dependent breast cancer through their ability to up-regulate aromatase expression and subsequent local production of estrogens in the breast. To study the link between estrogens and inflammation further, we examined the regulation of prostaglandin E synthase (PTGES), a key enzyme in the production of prostaglandin E2. We found that 17beta-estradiol (E2) rapidly and robustly up-regulates PTGES mRNA and protein levels in estrogen receptor (ER)-positive breast cancer cells through ER recruitment to an essential estrogen response element located in the 5' flanking region of the PTGES gene. PTGES is also up-regulated by the proinflammatory cytokines TNFalpha or IL-1beta. Surprisingly, the combination of E2 and cytokines leads to a synergistic up-regulation of PTGES in an ER and nuclear factor-kappaB (NFkappaB)-dependent manner. This is in contrast to the mutual transrepression between ER and NFkappaB that has been well characterized in other cell types. Furthermore, we found enhanced recruitment of ERalpha as well as the NFkappaB family member, p65, to the PTGES estrogen response element by the combination of E2 and TNFalpha compared with either E2 or TNFalpha alone. The synergistic up-regulation of PTGES may result in enhanced prostaglandin E2 production, which in turn may further enhance aromatase expression and production of local estrogens. Our findings suggest that a finely tuned positive feedback mechanism between estrogens and inflammatory factors may exist in the breast and contribute to hormone-dependent breast cancer growth and progression.

Supplementary Table 1 from Positive Cross-Talk between Estrogen Receptor and NF-κB in Breast Cancer

Supplementary Table 1 from Positive Cross-Talk between Estrogen Receptor and NF-κB in Breast Cancer

<div>Abstract<p>Estrogen receptors (ER) and nuclear factor-κB (NF-κB) are known to play important roles in breast cancer, but these factors are generally thought to repress each other's activity. However, we have recently found that ER and NF-κB can also act together in a positive manner to synergistically increase gene transcription. To examine the extent of cross-talk between ER and NF-κB, a microarray study was conducted in which MCF-7 breast cancer cells were treated with 17β-estradiol (E₂), tumor necrosis factor α (TNFα), or both. Follow-up studies with an ER antagonist and NF-κB inhibitors show that cross-talk between E₂ and TNFα is mediated by these two factors. We find that although transrepression between ER and NF-κB does occur, positive cross-talk is more prominent with three gene-specific patterns of regulation: (<i>a</i>) TNFα enhances E₂ action on ∼30% of E₂-upregulated genes; (<i>b</i>) E₂ enhances TNFα activity on ∼15% of TNFα-upregulated genes; and (<i>c</i>) E₂ + TNFα causes a more than additive upregulation of ∼60 genes. Consistent with their prosurvival roles, ER and NF-κB and their target gene, <i>BIRC3</i>, are involved in protecting breast cancer cells against apoptosis. Furthermore, genes positively regulated by E₂ + TNFα are clinically relevant because they are enriched in luminal B breast tumors and their expression profiles can distinguish a cohort of patients with poor outcome following endocrine treatment. Taken together, our findings suggest that positive cross-talk between ER and NF-κB is more extensive than anticipated and that these factors may act together to promote survival of breast cancer cells and progression to a more aggressive phenotype. [Cancer Res 2009;69(23):8918–25]</p></div>