Exosomal miR-552-5p Regulates the Role of NK Cells in EMT of Gastric Cancer via the PD-1/PD-L1 Axis.

While previous studies have established the role of exosomal miR-552-5p in promoting gastric cancer (GC) progression, the exact mechanisms through which it modulates the PD-1/PD-L1 axis to affect NK cell function and subsequently influence GC epithelial-mesenchymal transition (EMT) remain to be elucidated. Western blot, transmission electron microscopy (TEM), and nanoparticle tracking analysis were used to characterize exosomes that were isolated from GC cell supernatants. Subcutaneous AGS cell injections expressing either Lv-miR-552-5p or Lv-NC were administered to nude BALB/C mice. Mice received intraperitoneal injections of anti-PD-L1 antibody (12.5 mg/kg) or isotype control IgG weekly for two weeks. Flow cytometry assessed NK cell proportions and activation receptor (NKG2D, NKp46) and PD-L1 expression. ELISA measured cytokine levels (IFN-γ, granzyme B, perforin). Immunohistochemistry evaluated EMT marker expression in tumor tissues. An co-culture of NK cells with Exo-Lv-miR-552-5p or Exo-Lv-NC and GC cells was established. EMT protein expression in GC cells was analyzed by Western blot and immunofluorescence. Transwell assays and a tail vein-lung metastasis model in nude mice tested GC cell migration and invasion. Expression of NKG2D, NKp46, and PD-L1 was significantly reduced in Exo-Lv-miR-552-5p mice peripheral blood NK cell percentage. Increased treatment with PD-L1 inhibitors reversed the considerable reduction in IFN-γ, granzyme B, and perforin cytokine expression levels. Exosomal miR-552-5p overexpression in NK cells reduced E-cadherin expression while increasing N-cadherin and vimentin expression in GC cells, promoting migratory and invasive properties. GC-derived exosomal miR-552-5p promotes EMT in GC by inhibiting NK cell activity via the PD-1/PD-L1 axis, which provides new insights into the role of exosomal miR-552-5p in GC progression and immune escape.