Estrogen receptor impairs interleukin-6 expression by preventing protein binding on the NF- B site

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Abstract
Interleukin-6 (IL-6) is a multifunctional cytokine thought to be a key factor in post-menopausal osteoporosis, given its ability to induce osteoclast maturation and its down regulation by estrogens. We have previously shown that the effects of TNFα and estradiol on the human IL-6 promoter were dependent on a region of the promoter containing a C/EBP site and a NF-κB site. To define the molecular mode of action of estrogens, we performed gel shift assays with this DNA fragment as a probe, and nuclear extracts from TNFα-induced HeLa, MCF7 and Saos2 cells. Several induced complexes specifically bound the probe. The use of various competitor DNA suggested that most of the complexes detected contained NF-κB factors, and that C/EBP site binding factors were important for the overall binding to the probe. Addition of in vitro translated human estrogen receptor (hER) impaired the binding of three complexes in HeLa cells and two complexes in MCF7 and Saos2 cells. Competition experiments suggested that the NF-κB site was necessary for the effect of hER. The use of antisera against NF-κB and C/EBP proteins showed that the target complexes of hER contained the c-rel proto-oncogene product and to a lesser extent, the RelA protein. Taken together, these data show that hER impairs TNFα induction of IL-6 by preventing c-rel and, to a lesser extent, RelA proteins binding to the NF-κB site of the IL-6 promoter.