Fig 2: Thymidine kinase 1 (TK1) knockdown suppressed thyroid carcinoma cell invasion, migration, and EMT. (A,B) Transwell invasion assay was used to investigate the invasion ability of TPC-1 and BC-PAP cells transfected with scrambled siRNA (si-NC) or TK1 siRNAs (TK1 siRNA#1 or #2), respectively. (C,D) The migration ability of TPC-1 and BC-PAP cells transfected with scrambled siRNA (si-NC) or TK1 siRNAs (TK1 siRNA#1 or #2) was assessed by wound healing assay, respectively. (E,F) Protein expression levels of epithelial–mesenchymal transition (EMT)-related markers vimentin, N-cadherin, and E-cadherin in TPC-1 and BC-PAP cells transfected with scrambled siRNA (si-NC) or TK1 siRNAs (TK1 siRNA#1 or #2) were detected by Western blot. N = 3; *P < 0.05 and **P < 0.01.

Fig 3: Thymidine kinase 1 (TK1) knockdown suppressed thyroid carcinoma cell proliferation and induced cell apoptosis. (A) Quantitative real-time PCR (qRT-PCR) analysis of TK1 messenger RNA (mRNA) expression level in normal thyroid follicular epithelial cells and thyroid carcinoma cells (TPC-1 and BC-PAP). (B–E) qRT-PCR and Western blot analysis of TK1 mRNA and protein expression levels in TPC-1 and BC-PAP cells after scrambled siRNA (si-NC) or TK1 siRNAs (TK1 siRNA#1 or #2) transfections. (F,G) Cells proliferation by CCK-8 assay was determined in TPC-1 and BC-PAP cells, respectively. (H,I) Colony formation ability was assessed in TPC-1 and BC-PAP cells, respectively. (J,K) Flow cytometry analysis was used to detect the cell apoptotic rates in TPC-1 and BC-PAP cells, respectively. (L,M) Caspase-3 activity assay was used to determine the capsase-3 activity of TPC-1 and BC-PAP cells, respectively. (N,O) Protein expression levels of active caspase-3 and caspase-9 in TPC-1 and BC-PAP cells were detected by Western blot, respectively. N = 3; *P < 0.05, **P < 0.01, and ***P < 0.001.

Fig 4: Thymidine kinase 1 (TK1) was upregulated in patients with thyroid nodules and thyroid carcinoma. (A) The serum TK1 levels of normal subjects and subjects with thyroid nodules were detected by ELISA assay. (B) Online database [The Cancer Genome Atlas (TCGA)] analysis of the TK1 expression levels in the thyroid tissues from normal subjects and thyroid carcinoma patients. (C) The disease-free survival of the thyroid carcinoma patients as stratified by TK1 expression levels. *P < 0.05 and **P < 0.01.

Fig 5: Thymidine kinase 1 (TK1) knockdown suppressed in vivo tumor growth of thyroid carcinoma cells. (A) In vivo tumor growth of TPC-1 cells from sh_NC group and sh_TK1 group. (B) Weight of the tumor tissues from sh_NC and sh_TK1 group. (C) qRT-PCR analysis of TK1 mRNA expression levels in tumor tissues from sh_NC and sh_TK1 groups. (D) Western blot analysis of active caspase-3, caspase-9, vimentin, N-cadherin, and E-cadherin protein expression levels of the tumor tissues from sh_NC and sh_TK1. N = 6; *P < 0.05 and ***P < 0.001.