Nuclear Receptor Corepressor 1 Regulates Thyroid Hormone Receptor Nuclear Retention

Abstract

The thyroid hormone receptor (TR) mediates gene transcription in response to thyroid hormone (T3) and significantly affects cell growth, development and metabolism. Although TR shuttles rapidly between the nucleus and cytoplasm, it is primarily nuclear localized at steady state. A shift in the balance between export and import leading to TR mislocalization may correlate with certain cancers or endocrine disorders. Previously, we have identified multiple nuclear localization signals and nuclear export signal within TR that interact with importins and exportins, respectively, to mediate shuttling. Given that TR contains multiple, competing import and export signals, the question arises: what factors are involved in nuclear retention of TR? In addition to DNA‐binding sites, the lab's prior research indicated that nuclear coactivator MED1 facilitates TR nuclear localization. Thus, we hypothesize that certain transcriptional coregulators, including Nuclear Receptor Corepressor 1 (NCoR1), contribute to TR nuclear retention. Using transient transfection assays and fluorescence microscopy, we measured the fluorescent intensity of GFP or mCherry‐tagged TR in the nucleus (N) and cytoplasm (C) of HeLa cells, and then calculated the N/C ratio as an indicator of intracellular localization patterns. We discovered that when NCoR1 is knocked down by shRNA, the amount of TR in the nucleus decreased significantly (lower N/C ratio). Inversely, when NCoR1 is over‐expressed, the amount of TR in the nucleus significantly increased (higher N/C ratio). An even more dramatic cytosolic shift was observed for a TR mutant that cannot bind to NCoR1 (AHT‐TR). Taken together, our results suggest that NCoR1 is a key regulator of TR nuclear retention. This finding will contribute to the development of a dynamic mathematical model that aims to predict TR's N/C ratio during the interaction with different complexes and TR localization's effect on transcriptional output of T3‐dependent genes.Support or Funding InformationNIH 2R15DK058028This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.