Direct interdomain interactions can mediate allosterism in the thyroid receptor.

Area of Science:

• Molecular biology
• Endocrinology
• Biochemistry

Background:

• Thyroid (TR) and retinoid X receptors (RXR) are nuclear receptors regulating gene transcription.
• TR activity is modulated by ligands (T3), RXR, DNA, and coactivators like SRC1.
• Previous studies suggested indirect regulation between DNA/coactivator binding sites and receptor activity.

Purpose of the Study:

• To investigate direct, DNA-dependent communication between the DNA-binding domain (DBD) and ligand-binding domain (LBD) of TR.
• To explore how RXR influences this interdomain communication within RXR:TR complexes.
• To elucidate the molecular basis for differential transactivation by TR on various TREs.

Main Methods:

• Isothermal titration calorimetry (ITC) to measure binding interactions.
• Cell-based assays to assess receptor activity and interactions.
• Electrophoretic mobility shift assays (EMSA) were referenced from prior studies.

Main Results:

• Direct, DNA-dependent allosteric communication exists between TR's DBD and LBD.
• This communication regulates interactions with SRC1 and DNA binding.
• RXR influences interdomain communication in RXR:TR complexes, showing DNA-dependent cross-talk between RXR and TR.
• Differences in TRE binding affinity correlate with observed transactivation variations.

Conclusions:

• Evidence supports direct, allosteric regulation of TR and RXR:TR complex activity via DNA-dependent interdomain communication.
• RXR plays a crucial role in modulating this communication.
• Differential TRE affinities likely underlie variations in TR-mediated transactivation, providing mechanistic insight into nuclear receptor function.