Downregulation of Rap1GAP Expression Activates the TGF-β/Smad3 Pathway to Inhibit the Expression of Sodium/Iodine Transporter in Papillary Thyroid Carcinoma Cells.

Zheng Yan,Liao Haihong,Mao Jing,Wang Yangyanqiu,Han Shuwen,Zhou Qing,Gao Weili,Jin Yin,Chen Gong,Qiang Liu

doi:10.1155/2021/6840642

Abstract

Objective Rap1GAP is considered a tumor suppressor gene, but its regulatory mechanism in papillary thyroid cancer (PTC) has not been clearly elucidated. The aim of this study was to explore whether the regulation between Rap1GAP and sodium/iodine transporter (NIS) in tumorigenesis of PTC is mediated by TGF-β1. Methods Western blotting (WB) and quantitative reverse-transcription polymerase chain reaction were performed to analyze the relationships between TGF-β1 concentration and NIS expression. After transfecting BCPAP cells with siRNAs, the Rap1GAP interference model was successfully established. Then, the expression and nuclear localization of TGF-β1 and pathway-related proteins were detected. Flow cytometry was applied to analyze cell apoptosis and cycle. WB was performed to detect apoptotic-related proteins. Wound healing and transwell assays were used to measure cell migration and invasion. EDU was performed to detect cell proliferative activity. Results The results suggested that TGF-β1 could significantly inhibit the expression of NIS in both mRNA and protein levels. In BCPAP cells transfected with siRNA-Rap1GAP, the expression levels of TGF-β1, Foxp3, and p-Smad3 were significantly increased. By applying immunofluorescence assay, the nuclear localizations of TβR-1 and p-Smad3 were found to be activated. Moreover, anti-TGF-β1 can reverse the decrease in NIS expression caused by downregulation of Rap1GAP. Additionally, the knockdown of Rap1GAP could alter the cell apoptosis, cycle, migration, invasion, and proliferation of BCPAP. Conclusion The downregulation of Rap1GAP expression can activate the TGF-β/Smad3 pathway to inhibit NIS expression and alter the tumor cell functions of PTC.

Highlights

Papillary thyroid cancer (PTC) is the most common histological type of differentiated thyroid malignancies, accounting for about 85% of all pathologic types [1, 2]
The results suggested that the apoptosis rate of BCPAP in the siRNA-Rap1 GTPase-activating protein (Rap1GAP) group was significantly lower than those in the blank and NC groups (p < 0:01)
To learn whether Rap1GAP regulates NIS expression through TGF-β1, we firstly studied the expression relationship between them and confirmed that the expression of NIS was negatively associated with the TGF-β1 concentration in BCPAP cells

Summary

Introduction

Papillary thyroid cancer (PTC) is the most common histological type of differentiated thyroid malignancies, accounting for about 85% of all pathologic types [1, 2]. PTC is a low-grade malignancy with a good prognosis, there are still approximately 10-15% of cases showing tumor heterogeneity and aggressive variation along with unique clinical, pathological, and molecular characteristics [6]. These histological variations are associated with tumor recurrence, metastasis, therapeutic resistance, and radioiodine resistance and may eventually lead to lower survival rates [7]. Decoding the molecular mechanisms related to the pathogenesis of PTC may help to identify new therapeutic targets

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Conclusion