Date Thesis Awarded
5-2024
Access Type
Honors Thesis -- Access Restricted On-Campus Only
Degree Name
Bachelors of Science (BS)
Department
Biology
Advisor
Lizabeth Allison
Committee Members
Shanta D. Hinton
Beverly Sher
Abstract
The thyroid hormone receptors, TRα1, TRβ1, and TRβ2, are nuclear receptors that regulate many genes involved in development, growth, and homeostasis in response to thyroid hormone (T3). TRs undergo nucleocytoplasmic shuttling and mutations in TR can lead to altered intracellular localization and diseases such as Resistance to Thyroid Hormone (RTH). RTH is caused by mutations in TR leading to a decreased response to T3. Previous studies in our lab have established, using acetylation and non-acetylation mimics, that the acetylation of TR at specific sites leads to a more cytosolic localization and non-acetylation leads to a more nuclear localization, indicating that the deacetylation of TR plays an important role in modulating nucleocytoplasmic shuttling. To determine if histone deacetylases (HDAC) 1 and 3 play a role in altering TR localization by the deacetylation of TR, HeLa cells were transfected with GFP-tagged TRα1, TRβ1, or TRβ2 and an HDAC 1/3 inhibitor was added at 1μM and 10μM concentrations. Analysis of average relative nucleocytoplasmic (N/C) ratios revealed no significant change in localization of any TR variant when compared to the solvent control. These data suggest that the deacetylase activity of HDAC 1 and HDAC 3 is not directly responsible for the localization patterns of TR; as a result, other members of the deacetylase family are now under investigation. While in the nucleus, TR binds to nuclear receptor corepressor 1 (NCoR1), silencing gene expression in the absence of T3. In our investigation of RTHα mutations and NCoR1 binding, it was hypothesized that nuclear retention of RTHα mutants would be increased in the presence of overexpressed NCoR1, since some RTHα mutants have been reported to have increased affinity for NCoR1. RTHα mutants with substitution of arginine for either a cysteine or histidine at position 384 (R384C or R384H) were selected for analysis, because it had previously been shown that these TR variants have a more cytosolic population than wild-type TRα1. HeLa cells were transfected with mCherry-tagged wild type TRα1, R384C, or R384H, as well as GFP-tagged wild type NCoR1 or an NCoR1 mutant that does not bind TR, as a control. N/C ratios for wild-type TRα1 and the RTHα mutants were not significantly different in the presence of overexpressed NCoR1 compared with the non-binding NCoR1. To further investigate the role of NCoR1, HeLa cells were designed with NCoR1 knocked out and transfected with mCherry-tagged wild type TRα1, R384C, or R384H. The N/C ratios for wild-type TRα1 and the RTHα mutants were calculated and compared to those calculated from wild-type HeLa cells. It was determined that the N/C ratios were not significantly different. These experiments suggest that interaction with NCoR1 is not a key factor affecting localization patterns of these RTHα mutants. Overall, these findings provide further insight into TR’s interactions with other proteins and the resulting impacts on nuclear retention. The implications of these findings can be applied to learning more about multiple diseases in the endocrine system including Resistance to Thyroid Hormone syndrome and cancer.
Recommended Citation
Beasley, Katelyn, "Examining Factors Affecting Nuclear Retention of the Thyroid Hormone Receptor" (2024). Undergraduate Honors Theses. William & Mary. Paper 2189.
https://scholarworks.wm.edu/honorstheses/2189
