p53 downregulates PD-L1 expression via miR-34a to inhibit the growth of triple-negative breast cancer cells: a potential clinical immunotherapeutic target

Background Compared with other breast cancer subtypes, triple-negative breast cancer (TNBC) has poorer responses to therapy and lower overall survival rates. The use of an inhibitor of immune checkpoint programmed cell death ligand 1 (PD-L1) is a promising treatment strategy and is approved for malignant tumors, especially for TNBC. p53 regulates various biological processes, but the association between p53 and immune evasion remains unknown. miR-34a is a known tumor suppressor and p53-regulated miRNA that is downregulated in several cancers; however, it has not been reported in TNBC. Herein, we aimed to explore the regulatory signaling axis among p53, miR-34a and PD-L1 in TNBC cells in vivo and in tissue and to improve our understanding of immunotherapy for TNBC. Methods and results p53-EGFP, p53-siRNA and miR-34a mimics were transfected into TNBC cell lines, and the interaction between miR-34a and PD-L1 was analyzed via dual-luciferase reporter assays. We found that p53 could inhibit the expression of PD-L1 via miR-34a and that miR-34a could inhibit both cell activity and migration and promoted apoptosis and cytotoxicity in TNBC. Furthermore, miR-34a agomir was injected into MDA-MB-231 tumors of nude mice. The results showed that miR-34a could inhibit tumor growth and downregulate the expression of PD-L1 in vivo. A total of 133 TNBC tissue samples were analyzed by immunochemistry; the proportion of positive expression of PD-L1 was 57.14% (76/133), and the proportion of samples with negative expression of PD-L1 was 42.86% (57/133). Conclusion Our research may provide a novel potential target for TNBC.