Nasopharyngeal carcinoma (NPC), a type of head and neck squamous cell carcinoma (HNSCC), is a malignant tumor that originates in the nasopharynx. In 2022, the global NPC incidence reached 120,416 cases, resulting in 73,476 deaths. The incidence of NPC is predominantly concentrated in Asia, which accounts for 83.3 % of the global cases and 83.6 % of the global deaths (Su et al., 2024). The pathogenesis of NPC is complex and closely associated with various factors, including environmental influences, genetic predispositions, and Epstein-Barr virus infection (Chen et al., 2019). At present, radiotherapy and chemotherapy are the primary treatment modalities for NPC. For early-stage NPC, radiotherapy and chemotherapy can yield a favorable prognosis (Guan et al., 2020). However, the clinical outcomes of these treatments for recurrent and metastatic NPC are often unsatisfactory. The combination of chemotherapy agents is the first-line treatment for recurrent and metastatic NPC; however, the response rate is only approximately 60 % and may lead to hematotoxicity (Prawira et al., 2017). In contrast, the combination of molecular targeted therapies has demonstrated promising efficacy (Guan et al., 2020). At present, the effects of targeted therapeutic drugs, such as anti-EGFR monoclonal antibodies and Vascular Endothelial Growth Factor Receptor (VEGFR) inhibitors, have been validated in various studies (You et al., 2022, Zuo et al., 2010). Therefore, it is crucial to explore the regulatory mechanisms of key molecules involved in the metastasis of NPC to enhance patient survival rates.

Thymidylate synthetase (TYMS) is an essential enzyme in the de novo synthesis pathway of thymine deoxythymidine monophosphate, playing a critical role in DNA synthesis and replication. This indicates a possible role in the development and progression of cancer. TYMS was highly expressed in various cancers, including hepatocellular carcinoma, colorectal cancer (CRC), and glioma (Wang et al., 2022, Zhang et al., 2022, Zhao et al., 2019). Studies have demonstrated that TYMS facilitates the metastasis of CRC by regulating proteins associated with EMT (Zhang, F. et al., 2022). TYMS has been shown to promote the EMT phenotype in non-small cell lung cancer cells, and the depletion of TYMS inhibited the expression of EMT markers and lung metastasis (Siddiqui et al., 2021). The EMT process consistently promoted the NPC, and inhibiting the expression of EMT-related proteins effectively prevented NPC cell migration and invasion (Wu, A. et al., 2022). However, the role of TYMS in nasopharyngeal carcinoma EMT has not been revealed. Therefore, we hypothesize that TYMS may play a role in the EMT process during the development of NPC.

Cytoplasmic activation/proliferation-associated protein-1 (CAPRIN1) is a widely expressed cytoplasmic phosphoprotein that is essential for cell proliferation and is important for maintaining the normal progression of the cell cycle (Solomon et al., 2007), which gives it the potential to promote the proliferation of tumor cells. Studies have demonstrated that the upregulation of CAPRIN1 expression promotes the occurrence and development of prostate cancer, breast cancer, gastric cancer, and other malignancies (Gong et al., 2013, Lu et al., 2018, Shi et al., 2019). More importantly, CAPRIN1 is an RNA-binding protein, indicating its regulatory effect on downstream target genes (Solomon et al., 2007). It has been reported that CAPRIN1 enhances the stability of ZIC family member 5 (ZIC5) by binding to the 3’UTR of ZIC5 mRNA, thereby promoting the malignant behavior of laryngeal squamous cell carcinoma (Zhang et al., 2022). CAPRIN1 was highly expressed in NPC, and the knockdown of CAPRIN1 inhibited tumor cell proliferation and migration by regulating EMT-related proteins (Yang et al., 2022). Based on an analysis of the ENCORI database, we found that CAPRIN1 may bind to the 3’UTR of TYMS mRNA, suggesting a potential regulatory effect of CAPRIN1 on TYMS. However, the interaction between CAPRIN1 and TYMS remains unclear.

Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) was upregulated in various cancers, including stomach, breast, and ovarian cancers (Huang et al., 2021, Li et al., 2021, Mo et al., 2024), and often played a role in promoting tumor malignant behavior and cancer development. Studies have shown that MTHFD2 is highly expressed in NPC and promotes the proliferation and migration of NPC cells (Wu, S. et al., 2022). In this study, we observed that the expression of MTHFD2 was downregulated (Log2FC=-1.29, adj. p value<0.05) in the human NPC cell line HK-1 following TYMS silencing, as determined by RNA sequencing (RNA-seq) analysis. This finding suggests that MTHFD2 may play a role in mediating the regulation of NPC as a target gene of TYMS, a relationship that has not yet been elucidated.

This study aims to investigate the roles of CAPRIN1, TYMS, and MTHFD2 in the EMT process during the development of NPC. Additionally, it seeks to elucidate the significance of the CAPRIN1/TYMS/MTHFD2 axis in NPC development, thereby providing preclinical evidence for targeted therapies for NPC.