miR-301a promotes lung tumorigenesis by suppressing Runx3.

Background: Our previous report demonstrated that genetic ablation of miR-301a reduces Kras-driven lung tumorigenesis in mice. However, the impact of miR-301a on host anti-tumor immunity remains unexplored. Here we assessed the underlying molecular mechanisms of miR-301a in the tumor microenvironment.

Methods: The differentially expressed genes were identified by using deep sequencing. The immune cell counts, and cytokines expression were analyzed by realtime PCR, immunohistochemistry and flow cytometry. The role of miR-301a/Runx3 in lung tumor was evaluated on cell growth, migration and invasion. The function of miR-301a/Runx3 in regulating tumor microenvironment and tumor metastasis were evaluated in Kras transgenic mice and B16/LLC1 syngeneic xenografts tumor models.

Results: In this work, we identified 1166 up-regulated and 475 down-regulated differentially expressed genes in lung tumor tissues between Kras and miR-301a; Kras mice. Immune response and cell cycle were major pathways involved in the protective role of miR-301a deletion in lung tumorigenesis. Overexpression of the miR-301a target, Runx3, was an early event identified in miR-301a; Kras mice compared to WT-Kras mice. We found that miR-301a deletion enhanced CD8 T cell accumulation and IFN-γ production in the tumor microenvironment and mediated antitumor immunity. Further studies revealed that miR-301a deficiency in the tumor microenvironment effectively reduced tumor metastasis by elevating Runx3 and recruiting CD8 T cells, whereas miR-301a knockdown in tumor cells themselves restrained cell migration by elevating Runx3 expression.

Conclusions: Our findings further underscore that miR-301a facilitates tumor microenvironment antitumor immunity by Runx3 suppression in lung tumorigenesis.