Type III secretion system of Pseudomonas aeruginosa affects mucin gene expression via NF-κB and AKT signaling in human carcinoma epithelial cells and a pneumonia mouse model

The type III secretion system (T3SS) in Pseudomonas aeruginosa has been linked to severe disease and poor clinical outcomes in animal and human studies. Of the various T3SS effector genes, ExoS and ExoT showed mutually exclusive distributions, and these two genes showed varied virulence. We aimed to investigate whether the ExoS and ExoT effector proteins of P. aeruginosa affect the expression of the proinflammatory mediators Muc7, Muc13, Muc15, and Muc19 via the NF-{kappa}B and AKT signaling pathways. To understand the role of the T3SS, we used AExoS, AExoT, and T3SS transcriptional activator ExsA mutants (ExsA::{Omega}), as well as A549 cells stimulated with P. aeruginosa strain K (PAK). We investigated the effects of {Delta}ExoS, {Delta}ExoT, and ExsA::{Omega} on the development of pneumonia in a mouse model and on Muc7, Muc13, Muc15, and Muc19 production in A549 cells. {Delta}ExoS and {Delta}ExoT markedly decreased the neutrophil count in the bronchoalveolar lavage fluid, with a reduction in Muc7, Muc13, Muc15, and Muc19 expression {Delta}ExoS and{Delta}ExoT reduced NF-{kappa}B and AKT phosphorylation, together with Muc7, Muc13, Muc15, and Muc19 expression in PAK-infected mice and A549 cells. In conclusion, P. aeruginosa infection induced the expression of Mucus, and the P. aeruginosa T3SS appeared to be a key player in Muc7, Muc13, Muc15, and Muc19 expression, which is further controlled by NF-{kappa}B and AKT signaling. These findings might be useful to devise a novel therapeutic approach for the treatment of chronic pulmonary infections by targeting ExoS and ExoT.\n\nAuthor SummaryPseudomonas aeruginosa is a ubiquitous gram-negative bacterium causing serious infections. Many clinical isolates of P. aeruginosa have a specialized apparatus for injecting toxins into eukaryotic cells, namely, the type III secretion system (T3SS). The T3SS is a syringe-like apparatus on the bacterial surface, with 4 effector toxins: ExoS, ExoT, ExoY, and ExoU. We investigated the effect of ExoS and ExoT of the T3SS of P. aeruginosa K strain (PAK). Mucus plays a vital role in protecting the lungs from environmental factors, but conversely, in muco-obstructive airway disease, mucus becomes pathologic. We showed that infection with ExoS and ExoT induced Muc7, Muc13, Muc15, and Muc19 expression in host cells. PAK clinical strains induce proinflammatory cytokine production through the T3SS, and this involves NF-{kappa}B and SP1/AKT activation in pneumonia mouse models. Mucus induction in response to ExoS and ExoT infection relied on NF-{kappa}B and SP1/AKT activation. Our findings highlight the roles of Muc7, Muc13, Muc15, and Muc19 in inducing proinflammatory cytokine expression during ExoS and ExoT exposure in PAK infections, paving the way for a novel therapeutic approach for the treatment of pulmonary infections.