TRDMT1-mediated mRNA m5C methylation decreases chemotherapy sensitivity by activating homologous recombination-mediated DNA damage repair and IRS2 expression in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by high malignancy and poor prognosis. However, chemotherapy remains the cornerstone of its treatment. Through transcriptomic analysis of gemcitabine-treated PDAC cells, we identified TRDMT1, rather than other known 5-methylcytosine (m5C) methyltransferases, as a principal regulator of mRNA m5C methylation. TRDMT1 deficiency attenuated the malignant phenotype of PDAC cells and increased their sensitivity to gemcitabine, 5-fluorouracil, oxaliplatin, and irinotecan. Furthermore, deletion of TRDMT1 impaired the recruitment of homologous recombination-related proteins, including BRCA1, RAD51, and RAD52. Analysis of mRNA m5C modification sequencing in TRDMT1-deficient PDAC cells demonstrated that IRS2 exhibited significantly reduced m5C methylation levels and decreased expression. The IRS2/PI3K/AKT axis was identified as the potential downstream signaling pathway through which TRDMT1 mediated the chemotherapeutic response. Survival data from patients with PDAC, and findings from TRDMT1-deficient mouse models, further supported the role of TRDMT1 in reducing chemosensitivity. Collectively, these findings indicate that TRDMT1-mediated mRNA m5C methylation is essential for homologous recombination repair in PDAC and suggest that TRDMT1 may represent a potential therapeutic target for overcoming chemoresistance.