LAUSR

5‐Fluorouracil (5‐FU) is widely used in gastric cancer treatment, yet 5‐FU resistance remains an important clinical challenge. We established a model based on five long noncoding RNAs (lncRNA) to effectively assess the prognosis of gastric cancer patients; among them, lncRNA OVAAL was markedly upregulated in gastric cancer and associated with poor prognosis and 5‐FU resistance. In vitro and in vivo assays confirmed that OVAAL promoted proliferation and 5‐FU resistance of gastric cancer cells. Mechanistically, OVAAL bound with pyruvate carboxylase (PC) and stabilized PC from HSC70/CHIP‐mediated ubiquitination and degradation. OVAAL knockdown reduced intracellular levels of oxaloacetate and aspartate, and the subsequent pyrimidine synthesis, which could be rescued by PC overexpression. Moreover, OVAAL knockdown increased sensitivity to 5‐FU treatment, which could be reversed by PC overexpression or repletion of oxaloacetate, aspartate, or uridine. OVAAL overexpression enhanced pyrimidine synthesis to promote proliferation and 5‐FU resistance of gastric cancer cells, which could be abolished by PC knockdown. Thus, OVAAL promoted gastric cancer cell proliferation and induced 5‐FU resistance by enhancing pyrimidine biosynthesis to antagonize 5‐FU induced thymidylate synthase dysfunction. Targeting OVAAL‐mediated nucleotide metabolic reprograming would be a promising strategy to overcome chemoresistance in gastric cancer.