title: Suppression of ligand-dependent estrogen receptor activity by bone-resorbing cytokines in human osteoblasts.
abstract: Estrogens are important for bone homeostasis and are classified as antiresorptive agents. One of the mechanisms for this effect is the inhibition of cytokine-induced bone resorption, which is mediated in part through an interaction between the estrogen receptor (ER) and nuclear factor (NF)-kappaB in osteoblasts. We present evidence that bone-resorbing cytokines that activate NF-kappaB conversely inhibit ligand-dependent ER activity in the conditionally immortalized human osteoblast cell line, HOB-03-CE6. Treatment of HOB-03-CE6 cells with 17beta-estradiol (17beta-E2) up-regulated reporter gene activity [ERE-thymidine kinase (tk)-luciferase] 3- to 5-fold in a dose-dependent manner (EC50 = 1.0 pM). However, cotreatment of the cells with 17beta-E2 and increasing concentrations of either tumor necrosis factor-alpha (TNF alpha), interleukin-1alpha (IL-1alpha), or IL-1beta completely suppressed ERE-tk-luciferase activity in a dose-dependent manner (IC50 = 0.05-5.0 pM). On the other hand, treatment of the cells with growth factors either up-regulated or had no effect on ERE-tk-luciferase expression. Neither TNF alpha, IL-1alpha, nor IL-1beta treatment affected basal reporter gene activity in the cells, and the TNF alpha effect was reversed by a neutralizing antibody to the cytokine. TNF alpha treatment also suppressed ligand-dependent ER activity in MCF-7 human breast cancer cells, but not in Chinese hamster ovary cells that overexpressed human ER alpha, even though both cell lines responded to the cytokine as measured by the up-regulation of NFkappaB-tk-luciferase activity. TNF alpha treatment did not affect the steady state levels of either ER alpha or ER beta messenger RNA expression by the HOB-03-CE6 cells, nor did it reduce [125I]17beta-E2 binding. Moreover, TNF alpha treatment only weakly inhibited ligand-dependent glucocorticoid receptor activity in the HOB-03-CE6 cells. Bone-resorbing cytokines, which do not signal through the NF-kappaB pathway, did not suppress ERE-tk-luciferase activity in HOB-03-CE6 cells. Treatment of the cells with 17beta-E2 partially suppressed the activation of NF-kappaB by TNF alpha, but did not block cytokine-induced IL-6 secretion. Finally, cotreatment of HOB-03-CE6 cells with an antisense oligonucleotide to NF-kappaB p50 partially reversed the suppression of ERE-tk-luciferase activity by TNF alpha. In summary, these data provide evidence for a potent feedback inhibition of estrogen action in human osteoblasts that is at least partly mediated by the activation of NF-kappaB.
authors.affiliation: Women's Health Research Institute, Wyeth-Ayerst Research, Inc., Radnor, Pennsylvania 19087, USA. bodinep@war.wyeth.com
authors.forename: P V
authors.initials: PV
authors.lastname: Bodine
authors.forename: H A
authors.initials: HA
authors.lastname: Harris
authors.forename: B S
authors.initials: BS
authors.lastname: Komm
mesh_terms: D000818:Animals; D001862:Bone Resorption / Q000209:etiology*; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D016207:Cytokines / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology*; D006801:Humans; D016328:NF-kappa B / Q000502:physiology; D052002:NF-kappa B p50 Subunit; D010006:Osteoblasts / Q000187:drug effects*; D012333:RNA, Messenger / Q000032:analysis; D011960:Receptors, Estrogen / Q000032:analysis / Q000187:drug effects* / Q000235:genetics; D011965:Receptors, Glucocorticoid / Q000032:analysis; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D016207:Cytokines; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011965:Receptors, Glucocorticoid; D014409:Tumor Necrosis Factor-alpha; D004958:Estradiol