miR‐186‐5p Down‐Regulates PD‐L1 Level in Acute Myeloid Leukemia Cells and Inhibits Tumorigenesis and Immune Escape

Acute myeloid leukemia (AML) is a malignant tumor of blood cells, which seriously interferes with the generation of normal cells. Although miR-186-5p is diminished in AML, its exact mechanism is not well understood. miR-186-5p and PD-L1 levels in AML cells (HL-60, KG-1, TF-1a, MOLT-3) and subcutaneous tumor tissue were discovered through qRT-PCR and Western blot. miR-186-5 p and PD-L1 combining sites were foreseen by the database and verified by dual luciferase and immunoprecipitation experiments. AML cells with miR-186-5p overexpression or knockdown and PD-L1 overexpression were cocultured with CD4⁺ and CD8⁺ T cells. The proliferation, migration, invasion and apoptosis of AML cells, CD8⁺ and CD4⁺ T cell growth and apoptosis, and activated markers (Perforin and Granzyme B) and secreted cytokines (IFN-γ, IL-4 and TNF-α) levels were detected by CCK8, Transwell, flow cytometry, CFSE, Western blot and ELISA, respectively. Subcutaneous xenograft magnitude and mass in nude mice were measured. Ki67 level was identified through immunohistochemistry. CD4⁺ and CD8⁺ T cell level and infiltration were detected by immunofluorescence and flow cytometry. miR-186-5p was downregulated, and PD-L1 was boosted in AML cells and subcutaneous tumor tissues (p < 0.05), while miR-186-5p targeted down-regulate PD-L1. miR-186-5p upregulation hindered AML cell multiplication, migration, invasion and facilitate cell death, and enhanced the proliferation activity, activation markers (Perforin and Granzyme B) and secreted cytokines (IFN-γ, IL-4, TNF-α) of CD8⁺ and CD4⁺ T cells, inhibited apoptosis, and inhibited immune escape (p < 0.05). Knockdown of miR-186-5p can promote AML progression, but PD-L1 upregulation weakens the antitumor impact of miR-186-5p overexpression (p < 0.05). Transplanted tumor mice experiments also found that miR-186-5p hindered PD-L1 and tumor growth (p < 0.05). In conclusion, miR-186-5p can target inhibit PD-L1, suppress AML cells multiplication, movement, invasion and immune escape, and then reduce AML, aiming to provide support and basis for the pathological mechanism and prevention and treatment strategy of AML.