Core fucosylation of IL-15 receptor delineates homeostatic proliferation and apoptosis signalling required for natural killer cell development

Natural Killer (NK) cell development and effector function requires context-dependent signalling via numerous receptors including the IL-15 receptor. The modulation of receptor signalling can be regulated by the post-translational modifications affecting receptor turnover and trafficking. Core fucosylation is one such modification known to impact receptor expression and is uniquely mediated by fucosyltransferase 8 (FUT8). To investigate core fucosylation in NK cell biology, we generated mice lacking FUT8 in NK cells (Fut8fl/flNcr1cre/+). Loss of core fucose resulted in pronounced NK lymphopenia in Fut8fl/flNcr1cre/+ mice associated with a reduction in IL-15 receptor expression and loss of in vivo proliferation. Inhibition of intrinsic apoptosis pathways could not overcome compromised IL-15 receptor signalling to rescue FUT8-null NK cell development delineating the contribution of proliferation to NK cell homeostasis. Surprisingly, loss of core fucose enhanced NK cell expansion following viral infection and this was associated with upregulation of IL-2Rα following pro-inflammatory cytokine exposure and enhanced IL-2-mediated proliferation. Lastly, loss of FUT8 activity impaired TGFBR2 expression and immunosuppressive effects of TGF-β on NK cells. Taken together, we have identified fucosyltransferase 8 as a key modulator of NK cell development and function by regulating IL-15 receptor responsiveness. RNA-seq of enriched splenic NK cells after culturing for 5 days in the presence of 50 ng/ml IL-15; Three replicates each for WT (Ncr1-Cre- Fut8 fl/fl) and Fut8 knockout (Fut8.Ncr1; Ncr1-Cre+ Fut8 fl/fl).