CircRUNX1 Drives Immune Evasion and anti-PD1 Immunotherapy Resistance in Lung Adenocarcinoma by the miR-4739/PCSK9/MHC I Axis

Abstract

Background: Lung adenocarcinoma (LUAD) is the commonest pathological subtype of lung-derived malignant tumor. Blocking the immune checkpoints interaction between programmed death-1 (PD-1) and programmed death ligand 1 (PD-L1) via naturalizing PD-1 or PD-L1 monoclonal antibody is proved to be a effective therapeutic method for drive gene negative LUAD. Dysregulation of circular RNA (circRNA) is a hallmark of cancer and has a critical role in the progression of cancers, including LUAD. However, the exact role of circular RUNX family transcription factor 1 (circRUNX1, hsa_circ_0002360) in LUAD remains unknown. Methods: The expression levels of circRUNX1, miR-4739, and proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA were examined by quantitative real-time polymerase chain reaction (qRT-PCR). PCSK9, histocompatibility complex I (MHC I), CD8, and Foxp3 protein expression was examined by immunohistochemistry (IHC) or western blot analysis. In vivo assay was carried out to determine the biological function of circRUNX1 on LUAD immune evasion in vivo. The binding relationship between miR-4739 and circRUNX1 or PCSK9 was predicted and verified by Starbase V3.0 online databases, dual-luciferase reporter assay, and RNA-pull down assay. Results: CircRUNX1 expression was frequently increased in LUAD tissues, and forced circRUNX1 expression was associated with poor prognosis, big tumor size, advanced stage, and resistance to anti-PD1 immunotherapy in LUAD patients. Functionally, circRUNX1 overexpression promoted LUAD immune evasion in vivo. In addition, our results demonstrated that circRUNX1 could sponge miR-4739, subsequently, upregulating the PCSK9 expression and promoting to LUAD immune evasion. Conclusion: circRUNX1 promoted cancer immune evasion and resistance to anti-PD1 immunotherapy by regulate miR-4739/PCSK9/MHC I axis in LUAD. Taken together, our findings indicate that circRUNX1 may be a promising therapeutic target for improve the anti-PD1 therapy effect in LUAD patients.