Characterization of mechanisms of interleukin-6 gene repression by estrogen receptor

Estrogens are the most effective agents available for preventing osteoporosis, and their principal role in bone metabolism is the inhibition of interleukin-6 (IL-6) production in osteoblasts and bone marrow stromal cells. We examined the mechanism of inhibitory effect of estrogens on the 190 bp proximal promoter of the IL-6 gene. Promoter activity induced by transfection of both NF-kappa B p65 subunit and NF-IL6 was decreased by 45% by estradiol (E-2)-estrogen receptor (ER) complexes. The inhibitory effect of E-2 was also observed on a mutant IL-6 promoter in which the NF-IL6 binding site was disrupted. E-2 repressed the wild-type promoter activity induced by NF-kappa B p65 subunit alone, but had no effect on that induced by NF-IL6 alone. These findings suggested that estrogens inhibit IL-6 production by interfering with the function of NF-kappa B rather than that of NF-IL6. The ER mutant, HE19, which does not contain the A/B domain, repressed the induction by NF-kappa B to the same extent as wild-type ER HE0, whereas the effect of C-terminal deletion mutant, HE21, was only marginal. The antiestrogen, 4-hydroxytamoxifen (OHT), had no effect on IL-6 promoter activity, suggesting that E-2-induced conformational change of the hormone binding domain plays an important role in protein-protein interaction between ER and NF-kappa B. E-2 had no effect on the nuclear translocation of NF-kappa B, and electrophoretic mobility shift assay showed that the presence of E-2-ER complexes did not affect the ability of NF-kappa B to bind to specific DNA sequences. Copyright (C) 1997 Elsevier Science Ltd.