MicroRNA-34a enhances immune response and suppresses PI3K/AKT signaling through targeting PD-L1 in triple-negative breast cancer

Triple-negative breast cancer (TNBC) remains a significant clinical challenge due to its aggressive nature and limited therapeutic options. PD-L1 and the PI3K/AKT signaling pathway have previously been shown to form a feed-forward loop that promotes tumor progression and immune evasion. This study investigates miR-34a as a key regulator of this interaction, integrating comprehensive bioinformatics analysis with experimental validation. Weighted gene co-expression network analysis (WGCNA) of 255 TNBC samples revealed regulatory links between PD-L1 and PI3K signaling, while the analysis of 50 paired clinical samples confirmed an inverse correlation between miR-34a and PD-L1 expression. Luciferase reporter assays validated miR-34a as a direct regulator of PD-L1, leading to its downregulation and suppression of the PI3K/AKT signaling pathway in MDA-MB-231 cells transduced with a miR-34a-expressing lentivirus, as confirmed by Western blot analysis. Functional assays showed that miR-34a reduces cell viability, induces apoptosis, and causes G1 cell cycle arrest while also downregulating the stemness-associated transcription factors Nanog and Oct-4, suggesting a loss of tumor plasticity. Furthermore, co-culture experiments with PBMCs demonstrated that miR-34a enhances anti-tumor immune responses, as indicated by increased IL-2, IFN-γ, and TNF-α expression and IL-10 downregulation. Our results characterize miR-34a as a potential tumor-suppressor miRNA in TNBC that regulates both immune responses and key cancer hallmarks by targeting PD-L1 and suppressing the PI3K/AKT signaling pathway. These findings underscore miR-34a as a promising candidate for developing a multifaceted, miRNA-based immunotherapeutic approach for TNBC.