Circular RNA hsa_circ_0001598 promotes programmed death-ligand-1-mediated immune escape and trastuzumab resistance via sponging miR-1184 in breast cancer cells.

Approximately 25% of breast cancer (BC) patients are HER2-positive. Trastuzumab is used as a targeted therapy drug to treat HER2-positive BC patients; however, the drug resistance remains a big challenge. Circular RNAs (circRNAs) are reported to be involved in drug resistance, but the role of circ_0001598 has never been studied in BC. First, we identified the expression of circ_0001598 by RT-qPCR in BC. The gain-of-function and loss-of-function studies were applied to study the functional roles of circ_0001598 and its target gene. We observed upregulation of circ_0001598 in BC tissues, especially in trastuzumab-resistant BC samples. We further identified that miR-1184 is a functional target of circ_0001598. Moreover, it was found that programmed death-ligand 1 (PD-L1) was a direct target of miR-1184. The oncogenic effects of circ_0001598 in promoting BC cell growth, trastuzumab-resistance, PD-L1 expression, and escaping of CD8 T cell killing were abolished after the restoration of miR-1184. In conclusion, we demonstrate that circ_0001598/miR-1184/PD-L1 signaling plays a crucial role in the regulation of BC progression and trastuzumab-resistance phonotypes, which suggests that circ_0001598 may be a molecular target to treat HER2-positive BC patients.