O‐GlcNAcylation Regulation of SNAP29‐Dependent Autophagy Activation Dictates Chemoresistance in Gastric Cancer

ABSTRACT Chemoresistance remains a major obstacle in gastric cancer (GC) treatment, particularly to standard fluoropyrimidine and platinum regimens. O‐GlcNAc transferase (OGT) and O‐linked β‐N‐acetylglucosamine modification (O‐GlcNAcylation) are frequently elevated in cancers, yet their specific role in GC chemotherapy remains poorly defined. Contrary to its typical oncogenic function, this study demonstrates that low OGT/O‐GlcNAcylation is associated with resistance to 5‐fluorouracil (5‐FU) or oxaliplatin (OXA) in GC. Clinically, high OGT expression correlates with better prognosis in patients receiving fluoropyrimidine/platinum chemotherapy. Functionally, OGT knockdown or O‐GlcNAcylation inhibition promotes chemoresistance both in vitro and in vivo. Mechanistically, OGT interacts with and O‐GlcNAcylates synaptosomal‐associated protein 29 (SNAP29) at Ser 2 , Ser 61 , Thr 130 , and Ser 153 . This modification inhibits STX17‐SNAP29‐VAMP8 complex assembly and autophagosome maturation. Molecular dynamics simulations suggest this involves disruption of inter‐chain hydrogen bonds and increased flexibility at SNAP29 termini. Loss of SNAP29 O‐GlcNAcylation relieves this suppression, enhances protective autophagy, and drives chemoresistance. Additionally, acute 5‐FU or OXA treatment downregulates OGT and O‐GlcNAcylation, potentially initiating a feedforward resistance loop. Importantly, elevating O‐GlcNAcylation with Thiamet‐G sensitizes GC tumors to chemotherapy in vivo. These findings reveal a context‐dependent role for the OGT/SNAP29 axis in regulating chemoresistance via autophagy and nominate OGT as a promising therapeutic target in GC.