Abstract
BACKGROUND: Perforin-1 (Prf1) is the predominant cytolytic protein secreted by natural killer (NK) cells. For a rapid immune response, resting NK cells contain high Prf1 mRNA concentrations while exhibiting minimal cytotoxicity caused by a blockage of Prf1 protein synthesis, implying that an unknown posttranscriptional regulatory mechanism exists. OBJECTIVE: We sought to determine whether microRNA-150 (miR-150) posttranscriptionally regulates Prf1 translation in both mouse and human NK cells at rest and at various time points after activation. METHODS: Mouse NK cells with a targeted deletion of miR-150 (miR-150(-/-) NK cells), primary human NK cells, and NK92 MI cells were used to investigate the role of miR-150 in NK cells. NK cell cytotoxicity assays and Western blotting proved that activated miR-150(-/-) NK cells expressed upregulated Prf1, augmenting NK cell cytotoxicity. When immunodeficient mice were injected with miR-150(-/-) NK cells, there was a significant reduction in tumor growth and metastasis of B16F10 melanoma. RESULTS: We report that miR-150 binds to 3' untranslated regions of mouse and human Prf1, posttranscriptionally downregulating its expression. Mouse wild-type NK cells displayed downregulated miR-150 expression in response to IL-15, which led to corresponding repression and induction of Prf1 during rest and after IL-15 activation, respectively. CONCLUSION: Our results indicate that miR-150 is a common posttranscriptional regulator for Prf1 in mouse and human NK cells that represses NK cell lytic activity. Thus the therapeutic control of miR-150 in NK cells could enhance NK cell-based immunotherapy against cancer, providing a better clinical outcome.