Innate and adaptive immunity plays a critical role in defense against cancer but can be undermined by the tumor microenvironment. To understand the underlying mechanism, we set out to analyze the molecular and cellular basis for natural killer (NK) and CD8 T cell suppression by human lung tumor cells. We found that transforming growth factor-beta (TGFb), abundantly produced by tumor cells, effectively reduced tumoricidal function in activated NK cells and CD8 T cells by specifically targeting a key adaptor protein, DAP12, which is required for surface anchoring of multiple NK receptors, including NKp44. For proof of the TGFb-miR-183-DAP12 circuit, flow cytometric analysis demonstrated that TGFb reduced surface levels of NKp44 on activated primary human NK and CD8 T cells, but western blot analysis demonstrated their intact presence in the cytoplasm. This was due to loss of DAP12, which is critical for surface expression of NKp44 and for downstream signaling to mobilize lytic granules to kill tumor cells. Mechanistically, TGFb readily induced miR-183 expression in both primary human NK cells and T cells which could bind specifically to the 3′UTR of human DAP12 to inhibit transcription and translation. Only miR-183 but not miR-185 or control (CT) transfection repressed luciferase activity of DAP12 3′UTR luciferase reporter constructs transferred into HELA cells. Moreover, we overexpressed lentiviral miR-183 in either primary NK and T cells and found that such expression effectively reduced DAP12 levels in both cell types. Flow cytometric analysis of these same cells indicated that loss of DAP12 was accompanied by loss of NKp44 surface expression and by loss of cytotoxic function against tumor cells. As further proof, we showed that lentiviral anti-sense miR-183 transfection into NK cells and T cells prevented TGFb from suppressing DAP12 expression. Thus, we have uncovered a seminal TGFb-miR-183-DAP12 pathway utilized by tumor cells to silence infiltrating NK and T cells, constituting the first report of miR control of an adaptor protein to control both NK and T cell immune function.

Citation Format: Melba Marie Tejera, Melba Marie Tejera, Sarah S. Donatelli, Jun-Min Zhou, Danielle L. Gilvary, Xianghong Chen, Erika A.. Suppression of innate and adaptive immune responses in the human lung tumor microenvironment via microRNA-183. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 450. doi:10.1158/1538-7445.AM2015-450