MicroRNA-155 tunes both the threshold and extent of NK cell activation via targeting of multiple signaling pathways

Area of Science:

• Immunology
• Molecular Biology
• Cellular Signaling

Background:

• Natural killer (NK) cells are crucial innate immune cells for antiviral and antitumor responses.
• The precise molecular mechanisms governing NK cell activation remain incompletely understood.
• MicroRNA-155 (miR-155) expression is induced upon NK cell activation by cytokines.

Purpose of the Study:

• To elucidate the role of miR-155 in regulating NK cell activation and function.
• To investigate how miR-155 influences the production of interferon-gamma (IFN-γ) by NK cells.

Main Methods:

• Analysis of NK cells with miR-155 overexpression or deficiency (miR-155(-/-)) in vitro and in vivo.
• Quantification of IFN-γ production and assessment of NK cell activation phenotypes.
• RNA-induced silencing complex (RISC) sequencing to identify miR-155 targets.
• Pharmacological inhibition of key signaling pathways (PI3K, NF-κB, calcineurin).

Main Results:

• Both miR-155 overexpression and deficiency led to increased IFN-γ secretion by NK cells, but through different mechanisms.
• miR-155(-/-) NK cells exhibited a higher percentage of IFN-γ-producing cells, indicating a lower activation threshold.
• miR-155-overexpressing NK cells showed increased per-cell IFN-γ production.
• RISC sequencing revealed miR-155 targets within NK cell activation signaling pathways, including PI3K, NF-κB, and calcineurin.
• In vivo studies using murine cytomegalovirus (MCMV) infection confirmed these findings.

Conclusions:

• miR-155 acts as a complex regulator, or 'dynamic tuner,' of NK cell activation.
• It influences both the threshold for activation and the magnitude of the response.
• Understanding miR-155's role provides insights into optimizing NK cell-mediated immunity against viral infections and cancer.