Abstract
Short palate, lung, and nasal epithelium clone 1 (SPLUNC1) protein is expressed in human nasopharyngeal and respiratory epithelium and has demonstrated antimicrobial activity. SPLUNC1 is now referred to as bactericidal/permeability-increasing fold containing family A, member 1 (BPIFA1). Reduced BPIFA1 expression is associated with bacterial colonization in patients with chronic rhinosinusitis with nasal polyps (CRSwNP). Interleukin 13 (IL-13), predominately secreted by T helper 2 (TH2) cells, has been found to contribute to airway allergies and suppress BPIFA1 expression in nasal epithelial cells. However, the molecular mechanism of IL-13 perturbation of bacterial infection and BPIFA1 expression in host airways remains unclear. In this study, we found that lipopolysaccharide (LPS)-induced BPIFA1 expression in nasal epithelial cells was mediated through the JNK/c-Jun signaling pathway and AP-1 activation. We further demonstrated that IL-13 downregulated the LPS-induced activation of phosphorylated JNK and c-Jun, followed by attenuation of BPIFA1 expression. Moreover, the immunohistochemical analysis showed that IL-13 prominently suppressed BPIFA1 expression in eosinophilic CRSwNP patients with bacterial infection. Taken together, these results suggest that IL-13 plays a critical role in attenuation of bacteria-induced BPIFA1 expression that may result in eosinophilic CRSwNP.
Highlights
Short palate, lung, and nasal epithelium clone 1 (SPLUNC1) protein, a member of the bactericidal/permeability-increasing protein (BPI) family, is expressed in human nasopharyngeal and PLOS ONE | DOI:10.1371/journal.pone.0143484 December 8, 2015Interleukin 13 (IL-13) Suppresses LPS-Induced BPIFA1 Expression and analysis, decision to publish, or preparation of the manuscript
Pretreatment of cells with inhibitors (SP600125, curcumin, and tanshinone) resulted in a marked inhibition of c-Jun phosphorylation in the nucleus (Fig 5A) and of BPIFA1 expression (Fig 5B) in the cytoplasm. These results indicate that AP-1 activation is involved in LPSinduced BPIFA1 expression in nasal epithelial cells and that this activation is mediated through the JNK/c-Jun signaling pathway
There were 3, 2, 1, and 0 patients showing IL-13 staining of grades 0, 1, 2, and 3, respectively, in the chronic rhinosinusitis with nasal polyps (CRSwNP) group with bacterial infection. These results collectively demonstrate that the T helper 2 (TH2)-skewed cytokine IL-13 prominently suppressed BPIFA1 expression in eosinophilic CRSwNP patients with bacterial infection
Summary
Antibodies against β-actin, BPIFA1 (SPLUNC1), and phospho-JNK were purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Monoclonal antibody specific to BPIFA1 (MAB1897) was purchased from R&D Systems (Minneapolis, MN, USA). Antibodies specific for phospho-c-Jun (Ser63) and phospho-p38 MAPK (Thr180/Tyr182) were purchased from Cell Signaling (Danvers, MA, USA). Anti-phospho-Erk1/2 (Thr180/Tyr182) antibody was purchased from Millipore (Billerica, MA, USA). SB203580 (p38 inhibitor), PD98059 (ERK inhibitor), and SP600125 (JNK inhibitor) were purchased from Calbiochem (San Diego, CA, USA). 4',6-Diamidino-2-phenylindole (DAPI) was purchased from Molecular Probes (Invitrogen, Carlsbad, CA, USA). Human recombinant interleukin 13 (IL-13) was purchased from SigmaAldrich (St. Louis, MO, USA). JNK-dominant negative mutant and AP-1 luciferase reporter were kindly provided by Dr Chih-Hsin Tang (China Medical University) [16]. All other reagents and chemicals were purchased from Sigma-Aldrich
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