Thymidine Kinase 1 Expression Correlates with Tumor Aggressiveness and Metastatic Potential in OSCC

Abstract

Background/Objectives: Oral squamous cell carcinoma (OSCC) is the most prevalent malignancy of the oral cavity and is frequently diagnosed at an advanced stage, resulting in poor prognosis and limited treatment options. Identifying reliable biomarkers that can predict tumor progression and serve as therapeutic targets remains an urgent clinical need. Methods: To identify key molecular drivers in OSCC, we performed an integrative bioinformatics analysis of five OSCC-related microarray datasets from the Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) were identified and subjected to functional enrichment, protein-protein interaction (PPI) network construction, and hub gene ranking using Cytoscape. Candidate genes were further validated using TCGA, UALCAN, and the Human Protein Atlas. In vitro functional assays were performed to evaluate the effect of TK1 knockdown on cell migration. Results: A total of 138 common DEGs were identified across datasets. GO enrichment revealed that these genes were associated with cell proliferation, extracellular matrix organization, and metastasis-related processes. Thymidine kinase 1 (TK1) was identified as a key hub gene and found to be consistently overexpressed in OSCC tissues. Kaplan-Meier analysis showed that high TK1 expression correlated with poor overall survival in head and neck cancer. TK1 knockdown in OSCC cell lines significantly impaired cell migration and wound-healing ability. Conclusions: Our findings suggest that TK1 plays an active role in promoting OSCC progression and may serve as a prognostic biomarker and potential therapeutic target for metastatic OSCC.

Keywords: biomarker; differentially expressed genes (DEGs); metastasis; oral squamous cell carcinoma (OSCC); thymidine kinase 1 (TK1).

Figure 1

Identification of common differentially expressed genes (DEGs) in OSCC datasets. (A–E) Volcano plots showing upregulated (red), downregulated (blue), and non-significant (black) genes in five GEO datasets: GSE9844, GSE23558, GSE30784, GSE37991, and GSE138206. Adjusted p-value < 0.01 and |log2 fold change| > 1 were considered significantly differentially expressed. (F) Summary of sample size for each dataset. (G) Venn diagram illustrating common DEGs consistently altered across all five datasets.

Figure 2

Functional enrichment and hub gene identification. (A) Gene Ontology (GO) analysis showing enrichment of biological processes among 138 DEGs. (B) Cellular component enrichment analysis among 138 DEGs. (C) Protein–protein interaction (PPI) network generated from STRING database and analyzed with MCODE in Cytoscape. (D) Venn diagram showing 13 common hub genes identified by five topological algorithms (Degree, EPC, MNC, DMNC, MCC) using CytoHubba. (E) List of hub genes.

Figure 3

(A–M) Expression analysis of hub genes in HNSC. TCGA analysis showing mRNA expression of 13 hub genes in HNSC compared to normal tissues. * p < 0.05 compared to normal tissues.

Figure 4

(A–M) Survival correlation of hub genes in HNSC. Kaplan–Meier plotter analysis of hub genes in stage II–III HNSC patients. Red represents higher expression, and black represents lower expression.

Figure 5

TK1 expression across cancers and stages. (A) TIMER2.0 analysis showing elevated TK1 expression across various cancer types. (B,C) IHC images from The Human Protein Atlas showing TK1 protein levels in normal and HNSC tissue. (D,E) TCGA data showing TK1 expression across clinical stages and lymph node grades. (F,G) CPTAC analysis reveals that TK1 protein levels in HNSC and cancer progression. * p < 0.05 compared to normal tissues, ** p < 0.01 compared to normal tissues, and *** p < 0.001 compared to normal tissues.

Figure 6

(A–E) Validation of TK1 expression in OSCC datasets. Dotplots of TK1 expression across OSCC samples and adjacent normal tissues from multiple GEO datasets, confirming consistent overexpression. * p < 0.05 compared to normal tissues.

Figure 7

TK1 is associated with OSCC cell motility. (A) Western blot showing TK1 expression in parent SCC4 and high-mobility SCC4 sublines. (B) Transwell migration assay shows cell migration after siRNA-mediated TK1 silencing. (C) Wound healing assay shows the closure capacity in TK1-knockdown OSCC cells. (D) Transwell migration assay shows cell migration after siRNA-mediated TK1 silencing. * p < 0.05 compared to parent cell line and control siRNA.