PHGDH phosphorylation mediated by WNK1 serves as a dual marker of metabolic vulnerability and responsiveness to oxaliplatin treatment.

Metabolic reprogramming is a fundamental hallmark of cancer progression. However, the oncogenic mechanisms underlying serine metabolism and its impact on chemotherapeutic sensitivity in gastric cancer (GC) remain poorly defined. Here, through integrated metabolomics and 13C-labeled metabolic flux analysis, we identify marked dysregulation of serine metabolism in GC, primarily driven by increased expression of phosphoglycerate dehydrogenase (PHGDH). Mechanistically, we show that with no lysine kinase 1 (WNK1) phosphorylates PHGDH at Ser349 and Ser371, enhancing its enzymatic activity and protein stability by preventing ubiquitin-mediated degradation. In vivo, WNK1 knockout mice exhibit significantly reduced gastric tumor burden, accompanied by decreased serine levels and disrupted redox balance, supporting the protumorigenic role of the WNK1-PHGDH axis. Clinically, enhanced PHGDH activity, elevated serine levels, and increased glutathione abundance are strongly associated with poor oxaliplatin response in GC patient cohorts, suggesting PHGDH as a potential predictive biomarker for chemotherapy resistance. Together, these findings delineate a WNK1-PHGDH-driven serine metabolic reprogramming axis that promotes redox adaptation and chemoresistance in GC, highlighting its dual value as a mechanistic driver and a therapeutic vulnerability in cancer treatment.