Proposed working model of the FXR-mediated regulation of HER2 expression in Tam-resistant breast cancer cells. In the absence of CDCA, HER2 expression is regulated by several serum factors, including NF-κB, acting through a regulatory region in HER2 promoter and enabling gene transcription. Upon CDCA treatment, FXR binds NF-κB inhibiting its recruitment on the response element located in the proximal HER2 promoter, causing displacement of RNA polymerase II with consequent repression of HER2 expression.