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Background: Orphan class A G protein-coupled receptors (GPCRs) are a large and diverse family with broad tissue expression, and their roles in tumors are increasingly recognized. However, their involvement in gastric cancer (GC) remains unclear. Methods: We performed survival and differential expression analyses to characterize orphan class A GPCR expression patterns in stomach adenocarcinoma (STAD). A prognostic risk model was developed using univariate Cox and LASSO regression analysis and validated in the GEO database. Drug sensitivity and immune infiltration were evaluated across different risk groups. The role of GPR176 in GC and its relationship with tumor immunity were further explored using cellular assays. Results: A model incorporating nine orphan class A GPCRs (GPR15, GPR150, GPR176, GPR4, GPR26, GPR78, GPR101, GPR34, and GPR87) was constructed, showing a positive correlation with M2 macrophages and naive B cells. Low-risk patients showed higher sensitivity to AZD6482, BX.795, GDC0941, and pazopanib. GPR176 was found to be upregulated in GC, and functional assays demonstrated that its knockdown suppressed proliferation and migration in the GC cell lines SGC-7901 and HGC-27. GPR176 also modulated the Wnt/β-catenin pathway and M2 macrophage polarization. Conclusion: These findings may provide new insights into the role of orphan class A GPR genes in STAD and identify GPR176 as a new therapeutic target for GC.