STAT3 Operates As a Rheostat Regulating Sensitivity of NK Cells to Inflammatory Cytokines

NK cells are innate lymphocytes that respond to a variety of cytokines during viral infection. Several homeostatic and inflammatory cytokines bind to receptors that signal via STAT3. STAT3 can form homodimers or heterodimers. To understand the role of STAT3 homodimers and heterodimers, we made use of knockout models in which NK cells lack STAT3 or specific cytokine receptors. We found that NK cells deficient in STAT3 expand less than wildtype NK cells during mouse cytomegalovirus (MCMV) infection. IL-21R and IL-10R are the only receptors expressed on NK cells that signal through STAT3 homodimers. However, IL-21R or IL-10R-deficient NK cells showed no or little expansion differences, suggesting additional cytokine receptors may be signaling through STAT3. To evaluate whether STAT3 regulates the sensitivity of NK cells to cytokines that signal through heterodimerization partners STAT1 and STAT5, we performed cytokine titrations. We found that sensitivity towards IFN-a and IL-15 was reduced in STAT3-deficient NK cells. NK cells require inflammatory cytokines for antiviral expansion but proliferate poorly in hyper-inflammatory environments. Because STAT3 appears to regulate the sensitivity of NK cells to inflammatory cytokines, we hypothesized that STAT3-deficient NK cells would be shielded in settings of hyper-inflammation. Indeed, using high-dose MCMV infection, we observed that STAT3-deficient NK cells expanded better than WT NK cells. RNA-seq analysis further corroborated that in high-dose infection STAT3-deficient NK cells are nearly indistinguishable from WT NK cells during regular-dose infection. Thus, we believe STAT3 operates as a rheostat, modulating the sensitivity of NK cells to their inflammatory environment. Supported by the Cancer Research Institute, Donald J. Gogel Postdoctoral Fellowship, CRI393