The molecular basis of vitamin D receptor and β-catenin crossregulation

The signaling/oncogenic activity of β-catenin can be repressed by activation of the vitamin D receptor (VDR). Conversely, high levels of β-catenin can potentiate the transcriptional activity of 1,25-dihydroxyvitamin D3 (1,25D). We show here that the effects of β-catenin on VDR activity are due to interaction between the activator function-2 (AF-2) domain of the VDR and C terminus of β-catenin. Acetylation of the β-catenin C terminus differentially regulates its ability to activate TCF or VDR-regulated promoters. Mutation of a specific residue in the AF-2 domain, which renders the VDR trancriptionally inactive in the context of classical coactivators, still allows interaction with β-catenin and ligand-dependent activation of VDRE-containing promoters. VDR antagonists, which block the VDRE-directed activity of the VDR and recruitment of classical coactivators, do allow VDR to interact with β-catenin, which suggests that these and perhaps other ligands would permit those functions of the VDR that involve β-catenin interaction.