Estrogen decreases TNF gene expression by blocking JNK activity and the resulting production of c-Jun and JunD

Abstract

Central to the bone-sparing effect of estrogen (E 2 ) is its ability to block the monocytic production of the osteoclastogenic cytokine TNF-α (TNF).However, the mechanism by which E 2 downregulates TNF production is presently unknown.Transient transfection studies in HeLa cells, an E 2 receptor-negative line, suggest that E 2 inhibits TNF gene expression through an effect mediated by estrogen receptor β (ERβ).We also report that in RAW 264.7 cells, an E 2 receptor-positive murine monocytic line, E 2 downregulates cytokine-induced TNF gene expression by decreasing the activity of the Jun NH 2 -terminal kinase (JNK).The resulting diminished phosphorylation of c-Jun and JunD at their NH 2 -termini decreases the ability of these nuclear proteins to autostimulate the expression of the c-Jun and JunD genes, thus leading to lower production of c-Jun and JunD.The consequent decrease in the nuclear levels of c-Jun and JunD leads to diminished binding of c-Jun/c-Fos and JunD/c-Fos heterodimers to the AP-1 consensus sequence in the TNF promoter and, thus, to decreased transactivation of the TNF gene.J. Clin.Invest.104:503-513 (1999).Jun, Fos, and ATF (CREB) families of nuclear proteins (26).The Jun family consists of c-Jun, JunB, and JunD (26), and the Fos family includes c-Fos, Fra-1, Fra-2, FosB, and FosB2 (26).The presence of TRE sites in the TNF promoter, and the fact that AP-1 is known to be a critical inducer of human and murine TNF gene expression (27), suggests that E 2 could downregulate the production of TNF by decreasing the ability of AP-1 to transactivate the TNF promoter.In this study, we have investigated the effects of E 2 on cytokine-induced monocytic production of TNF.We report that E 2 downregulates cytokine-induced TNF gene expression by decreasing the activity of the Jun NH 2 -terminal kinase (JNK) through an effect that is likely mediated by ERβ.Decreased JNK activity results in blunted production of c-Jun and JunD, thus leading to decreased binding of c-Jun/Fos and JunD/Fos heterodimers to the AP-1 binding site in the TNF promoter.