Inhibition of MiR-20a by Pterostilbene Facilitates Prostate Cancer Cells Killed by NK Cells Via up-Regulation of NKG2D Ligands and Down-Regulation of TGF-β1

Purpose: - Natural killer (NK) cells play a potent role in antitumor immunity via spontaneously eliminating tumor directly. However, some tumors such as prostate cancer constantly escape this immune response by down-regulating cell surface molecule recognition and/or secreting immune impressive cytokines. Pterostilbene, a dietary compound primarily found in blueberries, exhibits a potential anti-tumor activities and immunoregulation function. However, whether it could affect NK cells immune response against prostate cancer is not clear. Methods: - NK cell cytotoxicity against prostate cancer cells was analyzed using the CytoTox 96 cytotoxicity assay kit. Flow cytometry was used to detected NK cell degranulation, NK cell-surface and intracellular protein expression. The effects of pterostilbene on TGF-β1 secretion were determined by Enzyme-linked immunosorbent assay. The candidate target gene of miR-20a was determined by luciferase reporter assay and the expression of major histocompatibility complex class I chain-related proteins A and B (MICA/B) was detected by quantitative real-time polymerase chain reaction. Results: - We found pterostilbene could enhance expression of MICA/B on prostate cancer cells surface, which are ligands of the natural killer group 2 member D (NKG2D) expressed by NK cells, and inhibit TGF-β1 secretion by prostate cancer cells. Further, we discovered that these effects were caused by inhibition of miR-20a in prostate cancer cells by pterostilbene. MiR-20a could target the 3’ untranslated region (UTR) of MICA/B, resulting in their expression down-regulation. Inhibition of TGF-β1 function by its specific antibody attenuated its impairment to NKG2D on NK cells. Finally, we observed that pterostilbene-treated prostate cancer cells were more easily to be killed by NK cells. Conclusions: - Our findings demonstrated inhibition of miR-20a by pterostilbene in prostate cancer cells could increase MICA/B expression and decrease TGF-β1 secretion, which enhanced NK cell-mediated cytotoxicity againt prostate cancer cells, suggesting a potential approach for increasing anti-prostate cancer immune.