MicroRNA-206 enhances antitumor immunity by disrupting the communication between malignant hepatocytes and regulatory T cells in c-Myc mice.

ABSTRACT

BACKGROUND AND AIMS: Intertumoral accumulation of regulatory T cells (Tregs) has been implicated in the pathogenesis of HCC. Because of poor understanding of the immunosuppression mechanism(s) in HCC, immunotherapy is largely unsuccessful for the treatment of HCC. APPROACH AND RESULTS: Hydrodynamic injection (HDI) of c-Myc into mice resulted in enlarged spleens and lethal HCC associated with an increase in hepatic Tregs and depletion of CTLs (cytotoxic T lymphocytes). Malignant hepatocytes in c-Myc mice overproduced TGFß1, which enhanced the suppressor function of Tregs and impaired the proliferation and cytotoxicity of CTLs. In addition to activating TGFß signaling, c-Myc synergized with Yin Yang 1 to impair microRNA-206 (miR-206) biogenesis. HDI of miR-206 fully prevented HCC and the associated enlargement of the spleen, whereas 100% of control mice died from HCC within 5-9 weeks postinjection. Mechanistically, by directly targeting errant kirsten ras oncogene (KRAS) signaling, miR-206 impeded the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) axis that drives expression of Tgfb1. By blocking the KRAS/MEK/ERK axis, miR-206 prevented TGFß1 overproduction, thereby impairing the suppressor function and expansion of Tregs, but enhancing the expansion and cytotoxic program of CTLs. Disrupting the interaction between miR-206 and Kras offset the roles of miR-206 in inhibiting immunosuppression and HCC. Depletion of CD8+ T cells impaired the ability of miR-206 to inhibit HCC. CONCLUSIONS: c-Myc-educated hepatocytes promoted immunosuppression by overproducing TGFß1, which promoted HCC development. miR-206, by attenuating TGFß1 overproduction, disrupted the communication of malignant hepatocytes with CTLs and Tregs, which prevented HCC. miR-206 represents a potential immunotherapeutic agent against HCC.