MicroRNA-497-5p down-regulation increases PD-L1 expression in clear cell renal cell carcinoma

Recent advances in immunotherapy are raising hope to treat clear cell renal cell carcinoma (ccRCC) with PD-L1 inhibitors, but only a small portion of patients are PD-L1 positive. The heterogeneous expression pattern of PD-L1 in patient population suggests that PD-L1 expression is under the control of diverse regulatory mechanisms. Although recent studies have identified numerous novel PD-L1 regulators, reports on microRNAs which modulate PD-L1 expression are much scarce. In this study, we confirmed that PD-L1 expression was up-regulated in ccRCC compared to paired normal tissues. Using miRDB and miRTarBase, 11 microRNAs were predicted to target PD-L1. After measuring the microRNA panel with TaqMan assays, we found that microRNA-497-5p down-regulation was associated with PD-L1 up-regulation. In TCGA-KIRC dataset, microRNA-497-5p down-regulation was also associated with PD-L1 up-regulation as well as shorter survival. We further validated that PD-L1 was a direct target of microRNA-497-5p in two RCC cell lines. In addition, microRNA-497-5p inhibited cell proliferation, clone formation and migration, while promoted apoptosis in in-vitro assays. Our study reveals a novel regulatory mechanism of PD-L1 expression and the potential of miR-497-5p as therapeutic target and biomarker deserves further investigation.