Part of “CHAPTER 31 – THYROID PHYSIOLOGY: HORMONE ACTION, RECEPTORS, AND POSTRECEPTOR EVENTS“

TRs bind to TREs as monomers, dimers, and heterodimers in vitro.8,9,18 However, the functional roles of these putative complexes in transcriptional regulation are not well understood. Although TRs can form heterodimers with several other family members on TREs, their major heterodimer partner appears to be the retinoid X receptor (RXR), which bears some amino-acid homology with the retinoic acid receptor and binds 9-cis retinoic acid.8,9,18 At least three major isoforms of RXR exist, so possibly different TR/RXR-isoform complexes may have differential affinities for TREs and/or abilities to transactivate target genes.