Proteomic identification and functional characterisation of nucleolar protein POP1 in anaplastic thyroid cancer

Purpose: Anaplastic thyroid cancer (ATC) is a rare and highly aggressive endocrine malignancy with limited therapeutic options. This study aimed to identify novel therapeutic targets in thyroid cancer, particularly ATC, through comprehensive omics analyses and functional characterization of the selected target protein POP1. Methods: Cell lines derived from normal thyroid tissue, anaplastic thyroid cancer, and papillary thyroid cancer were analysed using nanoHPLC-MS-based proteomics. POP1 expression was silenced by siRNA transfection. Cell proliferation, viability, cell-cycle distribution, apoptosis, gene and protein expression were assessed using standard molecular and cellular biology methods. Publicly available transcriptomic and proteomic datasets were used to evaluate POP1 expression in ATC tissues. Results: Proteomic analysis and Western blot validation demonstrated consistent POP1 overexpression in all thyroid cancer cell lines compared with normal thyroid cells. POP1 silencing reduced proliferation in most cell lines and decreased viability in ATC and BcPAP cells. POP1 knockdown also reduced the proportion of cells in S phase across all cancer cell lines and increased apoptosis in most models. These effects were associated with altered expression of cell-cycle-related genes, including CDKN1B, CDKN2B, TGFB2, BRIP1, CDC6, CDC25A, CDT1, RBBP4, MCM10, and SFN . The effect of POP1 silencing on CDKN1A expression was cell-type dependent. POP1 expression was also statistically significantly elevated in ATC patient tissues. Conclusions: POP1 is overexpressed in thyroid cancer cell lines and ATC tissues and promotes tumour cell proliferation, cell-cycle progression, and resistance to apoptosis. These findings identify POP1 as a novel oncogenic factor and a promising therapeutic target in anaplastic thyroid cancer.