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 C-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.