The TAK1→IKKβ→TPL2→MKK1/MKK2 Signaling Cascade Regulates IL-33 Expression in Cystic Fibrosis Airway Epithelial Cells Following Infection by Pseudomonas aeruginosa

In cystic fibrosis (CF), chronic respiratory infections result in an exaggerated and uncontrolled inflammatory response that ultimately lead to a decrease in pulmonary function. We have previously described the presence of the alarmin IL-33 in lung explants from CF patients. The signals regulating IL-33 expression in the airway epithelium following a gram-negative bacterial infection are currently unknown. Our objective was to characterize the pathways in CF airway epithelial cells (AECs) leading to an increase in IL-33 expression. We found that, in CF AECs expressing a deletion of a phenylalanine at position 508 of the gene coding for Cystic Fibrosis Transmembrane Conductance Regulator (CFTRdelF508), exposure to live Pseudomonas aeruginosa upregulates IL-33 via the TLR2 and TLR5 signaling pathways. This up-regulation can be partially or fully reverted by pre-incubating CFTRdelF508 AECs with a CFTR corrector (VX-809) and/or a CFTR potentiator (VX-770). Similarly, incubation with the CFTR corrector and/or the CFTR potentiator also decreased IL-8 expression in response to infection. Moreover, using different protein kinase inhibitors that target elements downstream of TLR signaling, we show that the TAK1→IKKβ→TPL2→MKK1/MKK2 pathway regulates IL-33 expression following an infection with P. aeruginosa. Our findings represent the first characterization of the signals regulating IL-33 expression in CF airway epithelial cells in response to a bacterial infection.