Abstract C012: Exploring thrombospondin-1 variant and splicing factors as potential diagnostic biomarkers and therapeutic targets in thyroid cancer
Authors: Hong Yukyung , Kim Ilju , Moon Hyunjin , Lee Jaehak , Lertpatipanpong Pattawika , Ryu Chang Hwan , Ryu Junsun , Baek Seung Joon 
Published: December 2023

Abstract
Thyroid cancer is the most common type of cancer affecting the thyroid gland, accounting for 11.8% of all cancer cases in Korea as of 2020. The majority of thyroid cancer cases belong to the papillary thyroid cancer (PTC) subtype. Diagnostic methods for thyroid cancer include blood tests, ultrasound examinations, fine needle aspiration cytology (FNAC), PET/CT scans, and others. However, distinguishing between different subtypes of thyroid cancer, such as follicular variant of papillary thyroid carcinoma (FVPTC), follicular adenoma (FA), and follicular thyroid carcinoma (FTC), remains challenging, often leading to unnecessary surgeries for patients. In this study, antibody arrays were used to analyze tumor and adjacent normal tissues from thyroid cancer patients. Thrombospondin 1 (TSP1), was found to be more highly expressed in tumor tissue compared to normal tissue. TSP1 is a glycoprotein with diverse biological functions that can either inhibit or promote tumorigenesis depending on the context. The researchers discovered a transcriptional variant of TSP1 (TSP1V) generated by intron retention (IR), which was more highly expressed in normal tissue compared to tumor tissue. Overexpression of TSP1V in thyroid cancer cells resulted in the secretion of the protein into the medium or its deposition in the extracellular matrix (ECM). TSP1V exhibited anti-cancer properties, inhibiting proliferation, migration, invasion, colony formation, and spheroid formation of thyroid cancer cells in vitro. It also suppressed tumor growth in a mouse experiment. The researchers explored the TGF-β pathway, a well-known signaling pathway associated with TSP1, and found that TSP1V inhibited the phosphorylation of Smad2 and FAK, unlike TSP1 wild-type (TSP1W). To investigate the mechanism behind TSP1V's generation through IR, we examined splicing factors. RBM5 overexpression inhibited IR induced by anti-cancer compounds, while RBM5 knockdown increased IR. Sulindac sulfide, one of the compounds tested, increased IR by inhibiting the phosphorylation of RBM5. Additionally, trans-chalcone was found to increase IR by demethylating DNA. Trans-chalcone also reduced the expression of TSP1W, DNMT3b, and MeCP2 in a time-dependent manner. The study concluded by analyzing tumor and adjacent normal tissues from patients with follicular neoplasm (FN), including benign thyroid nodule (BTN) and differentiated thyroid carcinoma (DTC). We also observed significant differences in the ratio of TSP1V to TSP1W. These findings provide evidence that secreted proteins like TSP1 have the potential to serve as diagnostic biomarkers and therapeutic targets for thyroid cancer. Moreover, the study enhances our understanding of the molecular mechanisms underlying the anti-cancer activities of these proteins.
Citation Format: Yukyung Hong, Ilju Kim, Hyunjin Moon, Jaehak Lee, Pattawika Lertpatipanpong, Chang Hwan Ryu, Junsun Ryu, Seung Joon Baek. Exploring thrombospondin-1 variant and splicing factors as potential diagnostic biomarkers and therapeutic targets in thyroid cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C012.