PS-1145

Periostin is an extracellular matrix protein that is highly expressed in nasal polyp (NP) tissues in patients with chronic rhinosinusitis (CRS). This study investigated the cellular source of periostin in sinonasal tissues and the mechanism of IL‐13‐induced periostin production in nasal epithelial cells.

The amount and localization of the periostin protein and mRNA were examined via immunohistochemistry and in situ hybridization analysis in control subjects and subjects with eosinophilic chronic rhinosinusitis (ECRS) and non‐ECRS. The expression levels of periostin and type 2 inflammatory cytokines in the tissue were measured by protein and mRNA levels. Normal human nasal epithelial cells were cultured in the presence of IL‐13, and the effect of the specific inhibitors, leflunomide, PD98059, or PS1145, on periostin production was evaluated.

Periostin was mainly deposited in the subepithelial region of NP tissues in ECRS and was more highly expressed than in non‐ECRS ( p < 0.01) and control subjects ( p < 0.001). The number of periostin mRNA‐positive basal epithelial cells was significantly increased in NP tissues in ECRS. The IL‐13 concentration was strongly correlated with periostin expression in the tissues ( p < 0.0001, r = 0.8802). Periostin production was much greater in differentiated cells under long‐term stimulation with IL‐13 than in ciliated cells, and this effect was attenuated by leflunomide and PD98059, but not by PS1145.

NP tissues from ECRS patients exhibit increased type 2 inflammatory cytokines and periostin. Nasal epithelial cells, particularly basal cells, are an important source of periostin. Exposure to IL‐13 is important for periostin production from nasal epithelial cells.

While IκB-kinase-ε (IKKε) induces immunomodulatory genes following viral stimuli, its up-regulation by inflammatory cytokines remains under-explored. Since airway epithelial cells respond to airborne insults and potentiate inflammation, IKKε expression was characterized in pulmonary epithelial cell lines (A549, BEAS-2B) and primary human bronchial epithelial cells grown as submersion or differentiated air-liquid interface cultures. IKKε expression was up-regulated by the pro-inflammatory cytokines, interleukin-1β (IL-1β) and tumour necrosis factor-α (TNFα). Thus, mechanistic interrogations in A549 cells were used to demonstrate the NF-κB dependence of cytokine-induced IKKε. Furthermore, chromatin immunoprecipitation in A549 and BEAS-2B cells revealed robust recruitment of the NF-κB subunit, p65, to one 5′ and two intronic regions within the IKKε locus (IKBKE). In addition, IL-1β and TNFα induced strong RNA polymerase 2 recruitment to the 5′ region, the first intron, and the transcription start site. Stable transfection of the p65-binding regions into A549 cells revealed IL-1β- and TNFα-inducible reporter activity that required NF-κB, but was not repressed by glucocorticoid. While critical NF-κB motifs were identified in the 5′ and downstream intronic regions, the first intronic region did not contain functional NF-κB motifs. Thus, IL-1β- and TNFα-induced IKKε expression involves three NF-κB-binding regions, containing multiple functional NF-κB motifs, and potentially other mechanisms of p65 binding through non-classical NF-κB binding motifs. By enhancing IKKε expression, IL-1β may prime, or potentiate, responses to alternative stimuli, as modelled by IKKε phosphorylation induced by phorbol 12-myristate 13-acetate. However, since IKKε expression was only partially repressed by glucocorticoid, IKKε-dependent responses could contribute to glucocorticoid-resistant disease.