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Objectives. The emergence of electronic cigarettes (e-cigarettes) has created new perceptions of the tobacco market. Unlike traditional tobacco, the greatest advantage of e-cigarettes is that they have less smell and are convenient and inexpensive. Most e-cigarette smokers believe that e-cigarette smoking is less harmful than traditional smoking. Information on the effects of e-cigarettes on human health is limited, and the issue remains controversial.Methods. We studied the effects of e-cigarette vapor on mucin (MUC5AC and MUC5B) and the change of MUC5AC and MUC5B from e-cigarette liquid with or without nicotine in respiratory epithelial cells. The effects of e-cigarette vapor with or without nicotine on mucin, along with the involved signaling pathways, were investigated using reverse transcriptase-polymerase chain reaction (PCR), real-time PCR, enzyme immunoassays, and immunoblot analysis with several specific inhibitors and small interfering RNA.Results. E-cigarette vapor with or without nicotine stimulated MUC5AC, but not MUC5B, expression in respiratory epithelial cells. In addition, we showed that e-cigarette vapor with and without nicotine induced MUC5AC expression via activation of the mitogen-activated protein kinase (MAPK; extracellular signal-regulated kinase [ERK] 1/2 and p38) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathways in human airway epithelial cells.Conclusion. E-cigarette vapor with and with nicotine significantly increased MUC5AC expression in human airway epithelial cells.

Objectives Clusterin (CLU) is known as apolipoprotein J, and has three isoforms with different biological functions. CLU is associated with various diseases such as Alzheimer disease, atherosclerosis, and some malignancies. Recent studies report an association of CLU with inflammation and immune response in inflammatory airway diseases. However, the effect of CLU on mucin secretion of airway epithelial cells has not yet been understood. Therefore, the effect and brief signaling pathway of CLU on MUC5AC (as a major secreted mucin) expression were investigated in human airway epithelial cells. Methods In the tissues of nasal polyp and normal inferior turbinate, the presence of MUC5AC and CLU was investigated using immunohistochemical stain and Western blot analysis. In mucin-producing human NCI-H292 airway epithelial cells and primary cultures of normal nasal epithelial cells, the effect and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway of CLU on MUC5AC expression were investigated using immunohistochemical stain, reverse transcription-polymerase chain reaction, real-time polymerase chain reaction, enzyme immunoassay, and Western blot analysis. Results In the nasal polyps, MUC5AC and CLU were abundantly present in the epithelium on immunohistochemical stain, and nuclear CLU (nCLU) was strongly detected on Western blot analysis. In human NCI-H292 airway epithelial cells or the primary cultures of normal nasal epithelial cells, recombinant nCLU increased MUC5AC expression, and significantly activated phosphorylation of NF-κB. And BAY 11-7085 (a specific NF-κB inhibitor) and knockdown of NF-κB by NF-κB siRNA (small interfering RNA) significantly attenuated recombinant nCLU-induced MUC5AC expression. Conclusion These results suggest that nCLU induces MUC5AC expression via the activation of NF-κB signaling pathway in human airway epithelial cells.

Objectives Endoplasmic reticulum (ER) stress is known to be associated with inflammatory airway diseases, and three major transmembrane receptors: double-stranded RNA-activated protein kinase-like ER kinase, inositol requiring enzyme 1, and activating transcription factor 6 (ATF6) play important roles in ER stress-related proinflammatory signaling. However, the effects of ER stress and these three major signaling pathways on the regulation of the production of airway mucins in human nasal airway epithelial cells have not been elucidated. Methods In primary human nasal epithelial cells, the effect of tunicamycin (an ER stress inducer) and 4-phenylbutyric acid (4-PBA, ER stress inhibitor) on the expression of MUC5AC and MUC5B was investigated by reverse transcriptase-polymerase chain reaction, real-time polymerase chain reaction, enzyme immunoassay, and immunoblot analysis. Small interfering RNA (siRNA) transfection was used to identify the mechanisms involved. Results Tunicamycin increased the expressions of MUC5AC and MUC5B and the mRNA expressions of ER stress-related signaling molecules, including spliced X-box binding protein 1 (XBP-1), transcription factor CCAAT-enhancer-binding protein homologous protein (CHOP), and ATF6. In addition, 4-PBA attenuated the tunicamycin-induced expressions of MUC5AC and MUC5B and the mRNA expressions of ER stress-related signaling molecules. Furthermore, siRNA knockdowns of XBP-1, CHOP, and ATF6 blocked the tunicamycin-induced mRNA expressions and glycoprotein productions of MUC5AC and MUC5B. Conclusion These results demonstrate that ER stress plays an important role in the regulation of MUC5AC and MUC5B via the activations of XBP-1, CHOP, and ATF6 in human nasal airway epithelial cells.

Objectives Doxycycline is commonly used in medicine for its bacteriostatic antimicrobial properties. Recent studies have reported that doxycycline also has anti-inflammatory effects. Matrix metalloproteinase (MMP)-9 has been found to be involved in the physiological and pathological process of inflammatory airway disease. Phorbol 12-myristate 13-acetate (PMA), a protein kinase C activator, is known to stimulate the expression of MMP and mucin genes in the airway and intestinal epithelial cells. Therefore, the effects and signal pathways of doxycycline on PMA-induced MUC5B expression dependent MMP-9 in human airway epithelial cells were investigated. Methods In human NCI-H292 airway epithelial cells, MUC5B and MMP-9 mRNA expression, MUC5B protein expression, and MMP-9 protein activity after the treatment with PMA, MMP-9 or doxycycline were determined by reverse transcriptase-polymerase chain reaction, enzyme immunoassay, gelatin zymography, and Western blot analysis. Results PMA increased MMP-9 and MUC5B expression. MMP-9 increased MUC5B expression. Doxycycline inhibited PMA-induced MUC5B expression, and PMA-induced MMP-9 mRNA expression and protein activity. Doxycycline inhibited phosphorylation of p38 induced by PMA and MMP-9. Conclusion The results of this study suggest that doxycycline inhibited PMA-induced MUC5B mRNA expression and protein production through the MMP-9 and p38 pathways in human NCI-H292 airway epithelial cells.

Objectives Delphinidin is one of the anthocyanidins. It is believed to have anti-inflammatory property including antioxidant, antiangiogenic, and anti-cancer properties. However, the anti-inflammatory effect of delphinidin in mucin-producing human airway epithelial cells has not been determined. Therefore, this study was conducted in order to investigate the effect and the brief signaling pathway of delphinidin in lipopolysaccharide (LPS)-induced MUC8 and MUC5B expression in human airway epithelial cells. Methods In mucin-producing human NCI-H292 airway epithelial cells and primary cultures of normal nasal epithelial cells, the reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, enzyme immunoassay were used for investigating the expressions of MUC8, MUC5, and Toll-like receptor 4 (TLR4), after LPS treatment and delphinidin treatment. And the signaling pathway of delphinidin on LPS-induced MUC8 and MUC5B expression was investigated using the RT-PCR, and immunoblot analysis. To confirm the involvement of TLR4 in LPS-induced MUC8 and MU5B expression, the cells were transfected with TLR4 siRNA. Results In NCI-H292 airway epithelial cells, LPS (100 ng/mL) significantly induced TLR4, MUC8, and MUC5B expression. TLR4 siRNA significantly blocked LPS-induced MUC8 and MUC5B mRNA expression. LPS (100 ng/mL) significantly activated the phosphorylation of extracellular signal related kinase (ERK) 1/2 and p38 mitogen-activated protein kinase (MAPK). Delphinidin (50 and 100 µM) inhibited LPS-induced TLR4, MUC8, and MUC5B expression and LPS-induced phosphorylation of ERK1/2 and p38 MAPK. In the primary cultures of normal nasal epithelial cells, delphinidin (50 and 100 µM) significantly inhibited LPS-induced TLR4, MUC8, and MUC5B gene expression. Conclusion These results suggest that delphinidin attenuates LPS-induced MUC8 and MUC5B expression through the TLR4-mediated ERK1/2 and p38 MAPK signaling pathway in human airway epithelial cells. These findings indicated that delphinidin may be a therapeutic agent for control of inflammatory airway diseases.

Objectives Among the inflammatory mediators, phorbol 12-myristate 13-acetate (PMA) is associated with the regulation of MUC5B expression in the airway epithelial cells. Epigallocatechin-3-gallate (EGCG) is the major component of green tea extract. The biological activity of EGCG includes reduction of cholesterol and antioxidant activity, as well as anti-inflammatory effect. However, the precise action mechanism of anti-inflammatory effect of EGCG in the airway epithelial cells has not been fully defined. This study investigates the effect and the brief signaling pathway of EGCG on PMA-induced MUC5B expression in the airway epithelial cells. Methods In NCI-H292 airway epithelial cells, the effect and signaling pathway of EGCG on MUC5B expression were investigated using real-time polymerase chain reaction analysis, enzyme immunoassay, immunohistochemical analysis, gelatin zymography assay, and immunoblot analysis. Results In NCI-H292 airway epithelial cells, PMA induced MUC5B expression, phosphorylation of p38 mitogen-activated protein kinase (MAPK), and matrix metalloproteinase-9 (MMP-9) expression and protein activity. EGCG significantly decreased PMA-induced MUC5B expression, phosphorylation of p38 MAPK, and MMP-9 expression and protein activity. SB203580 (p38 MAPK inhibitor) significantly decreased PMA-induced MMP-9 expression. In addition, SB203580 and MMP-9 I (MMP-9 inhibitor) significantly decreased PMA-induced MUC5B expression. Conclusion These results suggest that EGCG down-regulates PMA-induced MUC5B expression through the p38 MAPK dependent MMP-9 signaling pathway in human airway epithelial cells.

OBJECTIVES: Phorbol 12-myristate 13-acetate (PMA) is widely used as a protein kinase C (PKC) activator, PKC is involved in the secretion of mucins. MUC16, one of the membrane-bound mucins, is produced in human airway epithelial cells. However, the effect and signaling pathway of PMA on MUC16 expression in human airway epithelial cells has not been reported. Therefore, the effect and brief signaling pathway of PMA on MUC16 expression were investigated in human airway epithelial cells in this study. METHODS: In the mucin-producing human NCI-H292 airway epithelial cells and the primary cultures of normal nasal epithelial cells, the effect and signaling pathway of PMA on MUC16 expression were investigated using reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, enzyme immunoassay, and immunoblot analysis with several specific inhibitors and small interfering RNA (siRNA) for p38 mitogen-activated protein kinase (MAPK). RESULTS: PMA increased MUC16 expression, and activated phosphorylation of p38 MAPK. However, it did not activate phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). SB203580 (p38 MAPK inhibitor) inhibited PMA-induced MUC16 expression, while U0126 (ERK1/2 inhibitor) did not. In addition, the knockdown of p38 MAPK by p38 MAPK siRNA significantly blocked PMA-induced MUC16 mRNA expression. Rottlerin (PKCδ inhibitor) inhibited PMA-induced MUC16 expression, and also inhibited the phosphorylation of activated p38 MAPK by PMA. CONCLUSION: These results show for the first time that PMA-induced MUC16 expression is regulated by activation of the PKCδ and p38 MAPK signaling pathway in human airway epithelial cells.