Deubiquitinase USP48 Promotes Gastric Cancer Peritoneal Metastasis by Stabilizing S100A9 to Drive Neutrophil Extracellular Traps Formation

Peritoneal metastasis (PM) represents the primary cause of death in patients with advanced gastric cancer (GC), yet its underlying mechanisms remain poorly understood. Neutrophil extracellular traps (NETs) have emerged as key mediators of tumor progression, but how cancer cells regulate NETs formation to facilitate PM is unknown. This study investigates the role of the deubiquitinating enzyme USP48 in this process. USP48 expression was analyzed in GC tissues from patients with or without PM. To evaluate the functional role of USP48 in NETs formation and metastasis, we employed a range of in vitro and in vivo models, including co-culture systems, subcutaneous xenografts, and peritoneal dissemination models. Molecular interactions were examined through co-immunoprecipitation, ubiquitination assays, and protein stability analysis. USP48 was significantly overexpressed in GC tissues, with the highest levels observed in PM samples, correlating with poor prognosis. The proliferation, migration, invasion, and adhesion to peritoneal mesothelial cells of gastric cancer (GC) cells were all inhibited upon USP48 knockdown, the effects rescued by NETs-conditioned medium. Mechanistically, USP48 directly interacted with and deubiquitinated the alarmin S100A9, enhancing its stability and secretion. The receptor for advanced glycation end-products (RAGE) and toll-like receptor 4 (TLR4) in neutrophils were subsequently activated and induced NETs formation by S100A9 in neutrophils. In vivo, knockdown of USP48 suppressed tumor growth, NETs formation, and PM, while S100A9 overexpression reversed these effects. Our findings unveil a novel USP48/S100A9 axis through which GC cells drive NETs formation to promote PM. This pathway may serve as a promising therapeutic strategy for the prevention and treatment of PM in GC.