Activation of specific RXR heterodimers by an antagonist of RXR homodimers

RETINOID X receptor (RXR) plays a central role in the regulation of many intracellular receptor signalling pathways 1 and can mediate ligand-dependent transcription, acting as a homodimer or as a heterodimer 1-6 . Here we identify an antagonist towards RXR homodimers which also functions as an agonist when RXR is paired as a heterodimer to specific partners, including peroxisome proliferator-activated receptor and retinoic acid receptor. This dimer-selective ligand confers differential interactions on the transcription machinery : the antagonist promotes association with TAF110 (TATA-binding protein (TBP)-associated factor 110) and the co-repressor SMRT 7 , but not with TBP, and these properties are distinct from pure RXR agonists. This unique class of RXR ligands will provide a means to control distinct target genes at the level of transcription and allow the development of retinoids with a new pharmacological action.