Circ_0006174 Drives Triple Negative Breast Cancer Progression and Immune Escape Through Regulating miR-3139/PD-L1 Axis.

Triple-negative breast cancer (TNBC) is characterized as an aggressive malignancy with limited therapeutic options. The circular RNA circ_0006174 has been implicated in oncogenic processes across various cancers; however, its specific role in the pathogenesis of TNBC remains unclear. This study employed a range of in vitro assays, including cell counting kit-8, transwell invasion, ELISA, flow cytometry, RNA pull-down, dual-luciferase reporter, RNA immunoprecipitation, and western blotting, to investigate the function of circ_0006174 in TNBC. In vivo validation was conducted using xenograft models, with HE staining and immunohistochemistry. The results showed that overexpression of circ_0006174 was associated with poor prognosis in TNBC patients. Silencing circ_0006174 genetically resulted in reduced proliferation, invasion, and PD-L1-mediated immune-moderation in TNBC cells. At the molecular level, circ_0006174 was found to sequester miR-3139, leading to the upregulation of PD-L1. Furthermore, the regulation of circ_0006174 by METTL3 was shown to be dependent on m6A methylation, with the primary m6A methylation site identified at position 315. In vivo interference led to a reduction in tumor burden and the decreased expression of ki-67 and PD-L1, while increasing the levels of miR-3139 and IFN-γ. Therefore, circ_0006174, regulated by METTL3-mediated m6A methylation, promoted the progression of TNBC through the miR-3139/PD-L1 axis. This study was the first to validate the circ_0006174 as a novel m6A-modified circRNA as well as the circ_0006174/miR-3139/PD-L1 axis as a potential target for TNBC.