Relationship Between PTBP1 and Pancreatic Cancer Based on microRNA and Behavior During TYMS-Mediated Carcinogenesis.

Polypyrimidine tract-binding protein 1, an alternative splicing factor, drives cancer-associated metabolic reprogramming by modulating pyruvate kinase M splicing. Although organ-abundant microRNAs (miRs) regulate this protein, its role in tumor progression remains unclear. Therefore, we investigated the functional relationship between polypyrimidine tract-binding protein 1-associated microRNAs and this protein in pancreatic cancer to identify pancreas-enriched microRNAs and explore polypyrimidine tract-binding protein 1 function beyond metabolic regulation. The expression of miR-216b-5p, which is typically pancreas-enriched, was significantly downregulated in clinical pancreatic cancer samples, whereas polypyrimidine tract-binding protein 1 expression was markedly upregulated. Mechanistically, miR-216b-5p directly binds to the 3' UTR of polypyrimidine tract-binding protein 1 mRNA, thereby suppressing its expression and inhibiting cancer cell proliferation. Proteomic analysis, integrated with publicly available individual-nucleotide resolution UV crosslinking and immunoprecipitation data, identified thymidylate synthase as a novel downstream target of polypyrimidine tract-binding protein 1, likely regulated via splicing-related RNA-level mechanisms. Thymidylate synthase expression was also elevated in pancreatic cancer tissues and correlated with poor prognosis. Functional assays revealed that polypyrimidine tract-binding protein 1 and thymidylate synthase silencing induced cell cycle arrest. Our findings uncover a previously unrecognized miR-216b-5p/polypyrimidine tract-binding protein 1/thymidylate synthase regulatory axis that promotes pancreatic cancer progression and establish polypyrimidine tract-binding protein 1 as a central molecular regulator of tumor biology beyond its metabolic role.