Date Thesis Awarded

5-2020

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Lizabeth Allison

Committee Members

Laurie Sanderson

Diane Shakes

Douglas Young

Abstract

The thyroid hormone receptor (TR) is a nuclear receptor that plays a critical role in human development and metabolism, regulating thyroid hormone interactions. TR rapidly shuttles between the nucleus and cytoplasm but is primarily localized to the nucleus at steady state, where it acts as a hormone-dependent transcription factor. This process of nuclear import and export is mediated by two nuclear localization signals (NLSs) and multiple nuclear export signals (NESs). Previous studies have shown that TR may act as a tumor suppressor by regulating key genes in cell growth and proliferation in response to thyroid hormone. However, if TR shuttling is misregulated, it will not be able to perform its transcriptional regulatory functions. In this project, we analyzed the impact of NLS and NES amino acid substitutions on the intracellular localization patterns of TRα1 mutants previously associated with resistance to thyroid hormone syndrome, termed RTH (P398R and C392X); hepatocellular carcinoma (G24E, M256V, E343A, P269L); and thyroid cancer (K29T, C97A). We transfected mammalian cells with expression plasmids for green fluorescent protein (GFP)-tagged and mCherry-tagged wild-type and mutant TRα1 and examined localization patterns through quantitative fluorescence microscopy. Here, we show that both RTH-associated mutations exhibited similar intracellular localization as wild-type TRα1. On the other hand, TRα1 (G24E, M256V, E343A, P269L) and TRα1 (K29T, C97A) exhibited increased cytosolic distributions, while point mutations from each variant, TRα1(M256V) and TRα1 (K29T), had wild-type localization. Further, mutant TRα1 (K29T, C97A) had an increased tendency to form nuclear and cytosolic protein aggregates. In co-transfection experiments, TRα1 (K29T, C97A) failed to co-localize with LC3, a well-characterized autophagy marker, but showed significant co-localization with GFP-170, a marker for aggresome formation. These data suggest that aggregates formed by TRα1 (K29T, C97A) are actively recruited to cellular aggresomes as a cellular stress response. Overall, our study provides evidence that even minor alterations to TR’s primary structure can have a significant impact on its intracellular localization and interactions.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Available for download on Sunday, May 08, 2022

Share

COinS