GPX4 knockdown suppresses M2 macrophage polarization in gastric cancer by modulating kynurenine metabolism

<b>Background:</b> Glutathione peroxidase 4 (GPX4), an important factor regulating redox homeostasis, plays an important role in tumor microenvironment and progression. However, the role of GPX4 in gastric cancer (GC) is unclear. <b>Methods:</b> Spectral flow cytometry and multiplex immunohistochemistry were employed to assess the correlation between GPX4 expression and immune cell infiltration. Metabolomics analysis of conditioned media from GPX4 knockdown NUGC3 cells identified metabolic alterations. Additionally, both in vitro and in vivo functional studies were conducted to elucidate the mechanistic role of GPX4 in regulating the tumor microenvironment and progression. <b>Results:</b> Knockdown of GPX4 in GC cells inhibited tumor growth, enhanced CD8⁺ T cell infiltration, and suppressed the polarization of tumor-associated macrophages (TAMs) toward the pro-tumor M2 phenotype. Multiplex immunohistochemistry revealed a positive correlation between GPX4 expression and M2 macrophage infiltration in clinical samples from patients with GC. Metabolomics revealed that GPX4 knockdown regulate kynurenine metabolism pathway. Furthermore, mechanistic studies reveal that GPX4 silencing elevates lipid peroxidation, triggering the conversion of KYNU ubiquitin chain modifications from K48 to K63. Such ubiquitination remodeling stabilizes KYNU expression (a key kynurenine-metabolizing enzyme), reduces kynurenine accumulation, and ultimately reprograms TAM polarization to enhance antitumor immunity. We also identified that the K96 and K163 sites are important for KYNU's modification by K48 and K63 ubiquitin chains. <b>Conclusion:</b> Our study not only affirm the role of GPx4 in GC progression but also highlight it as a promising target for reshaping the immune microenvironment.