Tumor suppressive activity of miR-424-5p in breast cancer cells through targeting PD-L1 and modulating PTEN/PI3K/AKT/mTOR signaling pathway

MicroRNAs (miRs) are key modulators of cellular processes such as proliferation, apoptosis, as well as anti-cancer immune responses. Here, we evaluated the role of miR-424-5p in breast cancer (BC) and investigated its effects on T cell-related immune response. BC tissues and cell lines were prepared and the expression of miR-424-5p and PD-L1, as well as the underlying molecular pathways, were assessed via qRT-PCR and western blotting. The MTT assay and flow cytometry were used to assess the effect of miR-424-5p on proliferation, apoptosis, autophagy, and cell cycle progression. The co-culture of T cells with MDA-MB-231 was performed for evaluating the role of miR-424-5p in rescuing T cell exhaustion. The results indicated the down-regulation of miR-424-5p and up-regulation of PD-L1 expression in BC tissue specimens. MiR-424-5p transfection into PD-L1 overexpressing MDA-MB-231 cells decreased the expression of PD-L1. Also, miR-424-5p could reduce MDA-MB-231 cell viability through modulating apoptosis and autophagy pathways. Furthermore, miR-424-5p transfection leads to decreased colony formation and increased cell number at the G2/M phase. Western blot analysis illustrated that miR-424-5p could exert its anti-proliferative effect via modulating PTEN/PI3K/AKT/mTOR pathway. Moreover, it was demonstrated that suppression of PD-L1 by miR-424-5p could participate in regulating the expression of effector cytokines in T cells. MiR-424-5p could be considered as a potential tumor-suppressor miR in regulating BC cellular growth, apoptosis, and T cell-related immune response through targeting PD-L1, and its downstream mediators. Therefore, we recognized miR-424-5p as a promising candidate for miR restoration therapy in BC patients.