Upregulation of MTHFD2 is associated with PD-L1 activation in bladder cancer via the PI3K/AKT pathway

Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) has been implicated in the etiology of various human malignant tumors; however, its exact role in bladder cancer (BC) remains to be explored. Through reverse transcription-quantitative PCR, western blotting and immunohistochemistry detection of BC tissue, combined with The Cancer Genome Atlas (TCGA) database analysis, the present study demonstrated that MTHFD2 was upregulated in BC tissues. MTHFD2 expression in patients with BC was frequently associated with worse prognosis, tumor immune cell infiltration and programmed death-ligand 1 (PD-L1) expression. Subsequently, using short hairpin RNA, the expression levels of MTHFD2 were knocked down in BC cell lines, and the results revealed that the tumor cell proliferation and colony formation abilities of cells were greatly reduced, as determined by Cell Counting Kit 8 and colony formation assays, as was the expression of PD-L1, as determined by western blotting. These findings were also confirmed in a xenograft nude mouse model. Simultaneously, it was revealed that abnormal expression of MTHFD2 was closely associated with the PI3K/AKT signaling pathway in both RNA-sequencing and TCGA datasets. This observation was verified in vitro by detecting the protein expression levels of PI3K and AKT by western blotting. The activation of PI3K and AKT was enhanced in BC cells (T24) following stimulation with 740Y-P, a PI3K activator, and cellular activities and PD-L1 expression levels were restored. Finally, it was demonstrated that the MTHFD2 levels were correlated with chemosensitivity to traditional BC chemotherapeutic agents and various PI3K/AKT-targeted drugs, as determined by analyzing the Genomics of Drug Sensitivity in Cancer database. Overall, the present findings revealed that upregulation of MTHFD2 was associated with PD-L1 activation in BC via the PI3K/AKT signaling pathway, suggesting that it could be a promising marker of chemotherapy and immunotherapy for BC.