MTHFD2 is a potential oncogene for its strong association with poor prognosis and high level of immune infiltrates in urothelial carcinomas of bladder.

BACKGROUND: The bifunctional methylenetetrahydrofolate dehydrogenase (NADP+ dependent) 2, methenyltetrahydrofolate cyclohydrolase (MTHFD2) has been reported to play an oncogenic role in various types of cancers. However, the function of MTHFD2 in urothelial carcinomas of bladder (UCB) and its association with tumor immune infiltration remains unknown. We aim to examine the suitability of MTHFD2 to be a novel biomarker of bladder cancer and whether MTHFD2 is linked to immune infiltration. METHODS: RNA sequencing data and clinical information (bladder cancer samples: normal samples = 414: 19) were downloaded from The Cancer Genome Atlas official website. Western blot analysis was performed to detect MTHFD2 expression in human bladder cancer (BLCA) cells and normal urothelial cell line SV-HUC-1. Associations between MTHFD2 expression and clinicopathological features were analyzed using Mann Whitney U test or Kruskal-Wallis H test. The "survival" and "survminer" packages were utilized to plot Kaplan-Meier survival curves. Moreover, the gene set enrichment analysis (GSEA) was conducted using a clusterProfiler package. The correlation of MTHFD2 expression with immune infiltration level was estimated using the single sample GSEA (ssGSEA) algorithm. Furthermore, associations between MTHFD2 and immune checkpoint genes were evaluated using the correlation analysis. RESULTS: Transcriptome analysis manifested that MTHFD2 was highly expressed in UCB tissues than normal bladder tissues, which was further confirmed by western blot analysis in human BLCA cells and SV-HUC-1 cells. Moreover, MTHFD2 high expression was significantly associated with the advanced disease progression. Also, the high expression of MTHFD2 was correlated with poor prognosis, and MTHFD2 was considered as an independent prognostic factor for disease specific survival. Furthermore, a number of cancer-related pathways were enriched in MTHFD2 high group, including NF-κB activation, JAK/STAT, and cancer immunotherapy by PD1 blockade. Several immune checkpoint molecules were also strongly associated with MTHFD2 expression, including PDCD1, CD274, CTLA4, CD276, LAG3, HAVCR2, and TIGIT. CONCLUSIONS: MTHFD2 expression was remarkably elevated in UCB, suggesting that MTHFD2 could be a promising biomarker for BLCA as well as novel target for anti-cancer immunotherapy since its close association with immune infiltration.