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MiR-155 is a well-documented small RNA regulator of a variety of immune cells, including adaptive T and B lymphocytes. However, its role in regulating the innate NK cell response is unclear. We evaluated the expression of miR-155 using real-time qPCR and found that miR-155 is expressed at modest levels in resting mouse and human NK cells, but is upregulated upon stimulation, especially with IL-12+15+18 (30-fold). Therefore, we hypothesized that miR-155 regulates NK cell function following activation. We utilized miR-155-/- mice (155KO), NK-specific miR-155 overexpression mice (155OE), and miR-155 lentiviral transduction to examine the role of miR-155 in NK cell functional responses. miR-155KO, miR-155OE, and miR-155-transduced NK cells were all found to secrete more IFN-γ (by ELISA) upon ligation-mediated or cytokine stimulation, with no apparent defects in maturation or development. When further dissected by flow cytometry, we found that 155OE and transduced NK cells had increased IFN-γ MFI, indicating more “per-cell” production. In contrast, the 155KO NK cells had a higher percentage of IFN-γ+ NK cells, with similar MFI, indicating a potential activation threshold defect. Though both 155KO and 155OE NK cells produce more IFN-γ, the cellular basis for each, i.e. miR-155 target, likely differs. Therefore, we used unbiased RISC-IP to identify relevant miR-155 targets, which included previously validated miR-155 targets (e.g., SHIP-1) as well as novel miR-155 NK cell targets.

No abstract