Hsa_circ_0136666 stimulates gastric cancer progression and tumor immune escape by regulating the miR-375/PRKDC Axis and PD-L1 phosphorylation

Abstract Background Targeted drugs are not quite effective for prolonging the survival of patients with gastric cancer due to off-target effects as well as tumor immune escape mechanisms. Circular RNAs widely exist in tumor regions as biomarkers and can be developed as effective drug targets. Methods Western blot, QRT-PCR, fluorescence in situ hybridization, and flow cytometry were used to investigate the function of hsa_circ_0136666 in promoting the proliferation of gastric cancer cells. Tissue immunofluorescence, enzyme-linked immunosorbent assay (ELISA), as well as flow cytometric analysis, was conducted to explore the process of tumor immune evasion in tumor-bearing mice. The differences of circRNA expression in clinical samples were analyzed through tissue microarray FISH. The effect of siRNA on improving the efficacy of anti-PDL1 drugs and suppressing the immune microenvironment was evaluated by the coadministration model. Results We demonstrated that hsa_circ_0136666 was widely and highly expressed in gastric cancer tissues and cells. Functionally, hsa_circ_0136666 promoted gastric cancer tumor proliferation and tumor microenvironment formation, leading to tumorigenesis immune escape, and this effect was dependent on CD8 + T cells. Mechanistically, we confirmed that hsa_circ_0136666 competitively upregulated PRKDC expression by sponging miR-375-3p, regulating immune checkpoint proteins, prompting phosphorylation of PD-L1 to preventing its degradation, driving PD-L1 aggregation and suppressing immune function, thereby impairing cancer immune responses. In terms of application, we found that LNP-siRNA effectively improved anti-PDL1 drug efficacy and inhibited immune escape. Conclusion Our results reveal an oncogenic role played by hsa_circ_0136666 in gastric cancer, driving PD-L1 phosphorylation via the miR-375/PRKDC signaling axis, prompting immune escape. This work proposes a completely new pathogenic mechanism of gastric cancer, uncovers a novel role for hsa_circ_0136666 as an immune target, and provides a rationale for enhancing the efficacy of anti-PD-L1 therapy for gastric cancer.