GULP1 Fuels Resistance to PD-1 Blockade through Lipid-Mediated Metabolic Reprogramming of Tumor-Associated Macrophages in Gastric Cancer.

Background: Immune checkpoint inhibitors targeting programmed cell death protein 1 (PD-1) have substantially improved the treatment of multiple cancers; however, only a small proportion of gastric cancer (GC) patients achieve durable clinical benefit. The underlying tumor-intrinsic mechanisms driving resistance to anti-PD-1 therapy remain poorly understood. This study aimed to identify key regulators of immunotherapy resistance in GC and to elucidate their functional and mechanistic roles. Methods: Transcriptomic data from anti-PD-1-responsive and anti-PD-1-resistant GC patients were analyzed and integrated with mouse model data and publicly available single-cell RNA sequencing datasets. Functional experiments, including in vitro assays and in vivo tumor models, were performed to validate candidate genes and explore their roles in tumor progression and immunotherapy resistance. Results: GULP PTB domain-containing engulfment adaptor 1 (GULP1) was identified as a key driver of resistance to anti-PD-1 therapy in GC. Elevated GULP1 expression was associated with poor prognosis and unfavorable clinical responses to PD-1 blockade. GULP1 promoted GC progression and attenuated the therapeutic efficacy of anti-PD-1 treatment. Functionally, GULP1 facilitated the accumulation and metabolic reprogramming of CD36+ programmed death-ligand 1 (PD-L1)+ tumor-associated macrophages (TAMs) by shaping a lipid-enriched tumor microenvironment, thereby impairing CD8+ T-cell function. Mechanistically, GULP1 promoted insulin-induced gene 2 (INSIG2) palmitoylation through the recruitment of zinc finger DHHC-type palmitoyltransferase 8 (zDHHC8), resulting in sterol regulatory element-binding protein 1 (SREBP1) nuclear translocation and enhanced de novo fatty acid biosynthesis. Importantly, pharmacological inhibition of Gulp1 with glycyrrhizic acid significantly restored sensitivity to anti-PD-1 therapy in vivo. Conclusions: Collectively, these findings uncovered a previously unrecognized GULP1-fatty acid-CD36+PD-L1+ TAM-CD8+ T-cell axis that drove resistance to PD-1 blockade in GC, highlighting GULP1 as a promising therapeutic target and predictive biomarker for immunotherapy responsiveness.