IL-1ra Secreted by ATP-Induced P2Y2 Negatively Regulates MUC5AC Overproduction via PLCβ3 during Airway Inflammation

Mucus secretion is often uncontrolled in many airway inflammatory diseases of humans. Identifying the regulatory pathway(s) of mucus gene expression, mucus overproduction, and hypersecretion is important to alleviate airway inflammation in these diseases. However, the regulatory signaling pathway controlling mucus overproduction has not been fully identified yet. In this study, we report that the ATP/P2Y(2) complex secretes many cytokines and chemokines to regulate airway inflammation, among which IL-1 receptor antagonist (IL-1ra) downregulates MUC5AC gene expression via the inhibition of G alpha q-induced Ca2+ signaling. IL-1ra inhibited IL-1 alpha protein expression and secretion, and vice versa. Interestingly, ATP/P2Y(2)-induced IL-1ra and IL-1 alpha secretion were both mediated by PLC beta 3. A dominant-negative mutation in the PDZ-binding domain of PLC beta 3 inhibited ATP/P2Y(2)-induced IL-1ra and IL-1 alpha secretion. IL-1 alpha in the presence of the ATP/P2Y(2) complex activated the ERK1/2 pathway in a greater degree and for a longer duration than the ATP/P2Y(2) complex itself, which was dramatically inhibited by IL-1ra. These findings suggest that secreted IL-1ra exhibits a regulatory effect on ATP/P2Y(2)-induced MUC5AC gene expression, through inhibition of IL-1 alpha secretion, to maintain the mucus homeostasis in the airway. Therefore, IL-1ra could be an excellent modality for regulating inflamed airway microenvironments in respiratory diseases.