BRD4-S reprograms glutathione metabolism to reduce ferroptosis sensitivity and limits oxaliplatin response in gastric cancer

Abstract Background Bromodomain-containing protein 4 (BRD4) exists as distinct isoforms with potentially different biological functions, but their roles in ferroptosis and chemotherapy response in gastric cancer (GC) remain poorly understood. Here, we investigated the isoform-specific functions of BRD4 and the mechanisms linking BRD4-S to ferroptosis and oxaliplatin response. Methods BRD4 isoform expression was evaluated in GC tissues and cell lines. The biological functions of BRD4-S and BRD4-L were examined using isoform-specific genetic manipulation. Protein interactions and chromatin occupancy were assessed by co-immunoprecipitation and chromatin immunoprecipitation. Glutamine metabolism was investigated using 13 C, 15 N-labeled glutamine tracing. The contribution of PCK2 and SLC7A11 to BRD4-S-mediated ferroptosis and oxaliplatin response was evaluated in vitro and in vivo. The clinical relevance of BRD4-S was further examined in GC patients. Results BRD4-S, but not BRD4-L, promoted GC cell proliferation and invasion and was associated with unfavorable clinical outcomes. BRD4-S depletion increased ferroptotic sensitivity, accompanied by reduced SLC7A11 and PCK2 expression, decreased intracellular glutathione (GSH), and increased lipid peroxidation. Mechanistically, BRD4-S interacted with YY1 and facilitated YY1 occupancy at the PCK2 and SLC7A11 promoters. PCK2 modulated glutamine metabolic flux toward GSH production, while SLC7A11 supported cystine uptake required for GSH synthesis. Restoration of PCK2 and SLC7A11 partially reversed the ferroptotic phenotype and the increased oxaliplatin sensitivity caused by BRD4-S depletion in vitro and in vivo. Clinically, lower BRD4-S expression was associated with a higher rate of major pathological response and a more favorable post-treatment pathological stage following oxaliplatin-based neoadjuvant chemotherapy. Conclusion BRD4-S promotes ferroptosis resistance through a YY1-dependent transcriptional program involving PCK2 and SLC7A11, thereby supporting GSH homeostasis and limiting lipid peroxidation. BRD4-S expression is associated with oxaliplatin response in GC, providing a rationale for further investigating BRD4-S as a potential therapeutic vulnerability.