The Role of CBP in Estrogen Receptor Cross-Talk with Nuclear Factor-κB in HepG2 Cells

Abstract

Functional interactions or cross-talk between ligand-activated nuclear receptors and the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) may play a major role in ligand-mediated modification of diseases processes. In particular, the cardioprotective effects of estrogen replacement therapy are thought to be due in part to the ability of ligand-bound estrogen receptor (ER) to inhibit NF-kappaB function. In the current study 17beta-estradiol-bound ERalpha interfered with cytokine-induced activation of a NF-kappaB reporter in HepG2 cells. The estrogen metabolite, 17alpha-ethinyl estradiol, and the phytoestrogen, genistein, were also effective inhibitors of NF-kappaB activation, whereas tamoxifen, 4-hydroxytamoxifen, and raloxifene were inactive. This inhibition was reciprocal, as NF-kappaB interfered with the trans-activation properties of ERalpha. Ligand-bound ERalpha did not inhibit NF-kappaB binding to DNA, but it did decrease the histone acetyltransferase activity required for NF-kappaB transcriptional activity. Coexpression of the transcription coactivator CREB binding protein (CBP), but not steroid receptor coactivator 1a, reversed the ERalpha-mediated inhibition of NF-kappaB activity. Mammalian two-hybrid experiments also revealed that ligand-bound ERalpha can interact functionally with CBP-NF-kappaB complexes. We suggest that CBP targeting by ERalpha results in the inhibition of NF-kappaB and may occur through formation of transcriptionally inert multimeric complexes that are dependent upon the nature of the ERalpha ligand.

Identification of pathway-selective estrogen receptor ligands that inhibit NF-κB transcriptional activity

“…A variety of selective ER ligands have been described, and each of them displays an unique biological profile (32,39,40). Whereas both WAY-169916 and E2 can inhibit NF-B functional activity, neither the tissue-selective estrogen receptor modulator, raloxifene, nor the pure ER antagonist, ICI, can promote this activity, which is consistent with previous observations (20). Therefore, the nature of the ER ligand imparts the NF-B-suppressive activity, likely through the conformation the ER adopts upon ligand binding.…”

“…1B). The tissue-selective estrogen receptor modulator, raloxifene, was unable to inhibit NF-B activity, which is consistent with previous observations (20). This inhibition of NF-B luciferase activity by WAY-169916 correlated with the reduction of IL-6 expressed in the media from these cells (Fig.…”

“…Differences are considered significant if P Ͻ 0.05. luciferase reporter were used to demonstrate the in vitro selectivity of WAY-169916. NF-B luciferase reporter activity was induced by treatment with IL-1␤, and its activity can be repressed upon cotreatment with nonselective estrogens such as E2 as observed previously (15,16,20). Estrogen treatment of HAECT-1 cells also induces the expression of CK (34).…”

“…The resulting adenorecombinant plasmid was then linearized and used for recombinant virus isolation as described above. The Ad5-3x(NF B).Luc and Ad5-wt-ER␤ virus were described (20,28).…”

“…This nonclassical antiinflammatory activity of estrogen has been attributed to interference of NF-B activity (15,16), and one that has been reported to occur through multiple mechanisms, including direct protein-protein interactions (15,16), inhibition of NF-B DNA binding (17,18), induction of I B expression (19), or by means of coactivator sharing, as we and others have demonstrated (20,21).…”