Abstract

Protein monoaminylation represents a new layer of neural–cancer regulation, but its role in gastric tumorigenesis is not understood. Using untargeted plasma metabolomics, we revealed that the level of serotonin (5-HT) is significantly elevated in gastric cancer (GC) patients. Functionally, 5-HT treatment dramatically promoted GC cell proliferation and tumor growth in a dose-dependent manner. Importantly, this oncogenic effect was abrogated by the inhibition of transglutaminase 2 (TGM2), indicating a crucial role for protein serotonylation via a receptor-independent mechanism. Using a 5-HT-based chemoproteomic probe, we identified a broad spectrum of serotonylation targets, including key ferroptosis-related proteins such as glutathione peroxidase 4 (GPX4). Specifically, we found that GPX4 is serotonylated by TGM2 at residues Gln55 and Gln77, which increases GPX4 protein stability by attenuating its ubiquitin-mediated degradation, thereby conferring resistance to ferroptosis and facilitating tumor growth. Clinically, TGM2 levels were positively correlated with tumoral GPX4 expression in GC patient specimens. Collectively, our results establish TGM2-mediated GPX4 serotonylation as a key mechanism driving GC progression through ferroptosis resistance, highlighting its potential as both a diagnostic biomarker and a therapeutic target within the neural–tumor axis.