Direct interaction between estrogen receptor α and NF-κB in the nucleus of living cells

Inhibition of NF-kappa B transcriptional activity by steroid receptors is the basis for the antiinflammatory actions of steroid hormones and the molecular mechanism underlying this cross-talk is thought to involve direct protein-protein interactions. In this study, we show that estrogen receptor (ER)alpha and NF-kappa B interact in vivo by using fluorescence resonance energy transfer (FRET) and co-immunoprecipitation. U2-OS cells were used to study direct interactions between fluorescent fusion proteins of ER alpha and the NF-kappa B subunits p50 and p65. Interactions were observed only in the nucleus and maximal FRET signal was detected when ER alpha is co-expressed with both NF-kappa B subunits and cells were stimulated with estrogen. This is in agreement with the induction of nuclear co-localization of the proteins under this condition. Moreover, in a U2-OS clone stably expressing ERa, interaction with NF-kappa B was confirmed. A p65 deletion mutant lacking the Rel homology domain was strongly impaired in its interaction with ER alpha showing the importance of this domain. Taken together, these findings provide a strong basis for the direct protein-protein interaction model for cross-talk between ERa and NF-kappa B. (c) 2007 Elsevier Ireland Ltd. All rights reserved.