DUOX1-dependent IL-33 secretion from the airway epithelium involves positive feedback signaling through activation of IL-33R/ST2

The airway epithelium forms a first line of defense against environmental triggers, and through secretion of epithelial cytokines, such as IL-33, presents a critical innate response mechanism to injurious insults by initiating type 2 cytokine responses. We recently demonstrated that airway epithelial IL-33 secretion depends on activation of the NADPH oxidase dual oxidase 1 (DUOX1) and redox-dependent activation of the epidermal growth factor receptor (EGFR) and Src kinases. Curiously, activation of type 2 responses by direct airway administration of IL-33 was markedly diminished in DUOX1-deficient mice, suggesting DUOX1 is activated by IL-33 and participates in its downstream signaling. Furthermore, activation of epithelial IL-33 secretion in response to injury or allergens was dramatically attenuated by blockade or siRNA-mediated deletion of the IL-33 receptor (IL-33R/ST2), suggesting that epithelial IL-33 evokes a positive autocrine or paracrine feedback mechanism in which it regulates its own secretion through IL-33R/ST2-mediated signaling. Studies with human bronchial epithelial cells (H292) and primary mouse tracheal epithelial cells (MTEC) showed that IL-33 can directly trigger EGFR and Src activation and type 2 cytokine secretion, via intermediate activation of DUOX1. The activation of these kinases was shown to be associated with increased levels of DUOX1-dependent sulfenylation. Additionally, IL-33 stimulation resulted in ST2-mediated calcium-dependent extracellular secretion of ATP, a known damage signal capable of activating DUOX1. Consistent with its activation by IL-33, inhibition of Src with AZD0530 or siRNA-mediated deletion of Src led to decreased secretion of type 2 cytokines, confirming that Src plays a role in these downstream processes. Overall, our findings suggest that the role of DUOX1 in allergen-induced IL-33 secretion, and activation of type 2 responses, is largely mediated by its involvement in IL-33-dependent signaling and subsequent oxidation and activation of Src and EGFR.