CircSPARC mediates an immunosuppressive tumor microenvironment by regulating the miR-199a-5p/LASP1 axis in non-small cell lung cancer

Abstract Non-small cell lung cancer (NSCLC) is a major cause of cancer-related mortality globally, linked to an immunosuppressive microenvironment. Circular RNA circSPARC is crucial in cancer, but its function in NSCLC remains unclear. 66 NSCLC tissue samples and 4 cell lines were analyzed for circSPARC and PD-L1 expression via qRT-PCR. A549 and H1299 cells were transfected with shRNA targeting circSPARC. THP-1 cells were differentiated into macrophages with phorbol 12-myristate-13-acetate (PMA). A549 and H1299 cells were co-cultured separately with CD8+T cells. Cell viability, invasion, expression of M2 macrophage markers (CD206, CD163), immune checkpoint (PD-L1), cytokines (IL-10, TGF-β, IFN-γ, TNF-α), and the proportion of CD8+ TNF-α+ T cells were analyzed by CCK-8 assay, Transwell, Western blot, ELISA, and flow cytometry. Dual-luciferase reporter and RNA pull-down assays were employed to confirm interactions between circSPARC, miR-199a-5p, and LASP1. Rescue experiments involved inhibiting miR-199a-5p or by overexpressing/silencing LASP1. Finally, the role of circSPARC was investigated in vivo using a subcutaneous tumor model. CircSPARC was highly expressed in NSCLC tissues and cells. circSPARC knockdown inhibited NSCLC cell viability, invasion, and reduced CD206 and CD163 expressions. Moreover, circSPARC knockdown reduced the excretion of immunosuppressive cytokines (IL-10 and TGF-β) as well as PD-L1 expression but promoting release of effector cytokines (IFN-γ and TNF-α) and increasing the proportion of CD8+ TNF-α+ T cells. Mechanistically, circSPARC sponged miR-199a-5p to upregulate LASP1. These findings were validated in a mouse xenograft model. The circSPARC/miR-199a-5p/LASP1 axis mediated the immunosuppressive microenvironment of NSCLC, highlighting circSPARC as a potential therapeutic target.