IKAROS and AIOLOS activate AP-1 transcriptional complexes and are essential for natural killer cell development

Abstract

Ikaros family transcription factors regulate lymphocyte biology and are targets of the immunomodulatory imide drugs (IMiDs) for hematological maligancies. Ikaros (Ikzf1/IKZF1) is the most broadly expressed family member in lymphocytes, yet its role in innate lymphopoiesis was unknown. Here we used conditional gene inactivation to reveal that Ikaros is required for normal NK cell development. Ikzf1-null NK cells had impaired IL-15 signaling, manifesting in reduced proliferation and enhanced apoptosis. Cish and Socs2, known negative regulators of IL-15 signaling are increased in Ikzf1-null NK cells and are direct targets of Ikaros-mediated repression. Ikzf1-null NK cells have extensive transcriptional alterations with a striking reduction in expression of genes encoding AP-1 transcriptional complexes as well as a compensatory increase in Ikaros-family members, Ikzf2 and Ikzf3. Deletion of both Ikzf1 and Ikzf3 in NK cells further reduced AP-1 gene expression culminating in a complete loss of peripheral NK cells in mice. Inactivation of Ikaros-family members in human NK cells also impaired their fitness and function, while genetic screens revealed a co-dependency on IKZF1 and individual AP-1 genes in hematopoietic cell survival, suggesting that IMiDs induce apoptosis of malignant IKZF1/3-dependent cells by ablating AP-1 transcriptional activity. Collectively we show the Ikaros-family are novel regulators of cytokine responsiveness and essential for promoting AP-1 transcriptional activity required for NK cell development.