Interleukin-2 mediated NF-κB -dependent mRNA splicing induces interferon gamma protein production

Abstract

Interferon-gamma (IFNγ) is a pleiotropic cytokine produced by natural killer (NK) cells during the early response to infection. IFNγ expression is tightly regulated to mount sterilizing immunity while preventing tissue pathology. Post-transcriptional effectors resolve expression of inflammatory cytokines, and several dampen IFNγ expression through IFNG mRNA degradation. NK cells' acute induction of IFNγ defies transcription-translation kinetics, suggesting that cells may be poised for rapid IFNγ production. In this study, we identify mRNA splicing as a major regulator of IFNγ protein production. While treatment with the combination of IL-12 and IL-2 causes synergistic production of IFNG mRNA and protein, we observe that NK cells treated with IL-12 alone transcribe IFNG with its introns intact. When NK cells are treated with both IL-2 and IL-12, IFNG transcript is spliced to form mature mRNA with a concomitant increase in IFNγ protein. We found that IL-2-dependent intron splicing occurs independently of nascent transcription and translation but is NF-κB signaling dependent. We propose that while IL-12 transcriptionally induces IFNG mRNA expression, IL-2 signaling stabilizes IFNG mRNA in an NF-κB dependent manner by inducing swift splicing of detained introns, ensuring that NK cells are poised for robust IFNγ protein expression. This study uncovers a novel role for splicing in regulating IFNγ protein production through a mechanism potentially applicable to immune control of other inflammatory mediators.