[Upstream signaling pathway of neutrophil elastase-induced mucous hypersecretion].

OBJECTIVE: To investigate the upstream signal transduction pathway of neutrophil elastase (NE)-induced mucous hypersecretion via epidermal growth factor receptor (EGFR). METHODS: The airway epithelial cells of the line BEAS-2B were cultured and divided into 6 groups: control group, cultured in serum-free DMEM/Ham's F12 mixture; NE group, incubated with NE alone, transforming growth factor (TGF)-alpha protease inhibitor (TAPI)-1 + NE group, incubated with NE and TAP I-1; 1, 3-dimethyl-2-thiourea (DMTU) + NE group, preincubated with DMTU, a reactive oxygen species (ROS) scavenger, and then incubated with NE; TGF-alpha group, incubated with TGF-alpha; and DMTU + TGF-alpha group, incubated with DMTU and TGF-alpha. The mucin (MUC) 5AC mRNA level was analyzed by RT-PCR, MUC5AC protein and soluble TGF-alpha were detected by enzyme-linked immunosorbent assay, and the phosphorylated EGFR (p-EGFR) protein production was assayed by Western blotting. RESULTS: The MUC5AC mRNA expression and protein expression of the NE group were 0.81 +/- 0.13 and 0.78 +/- 0.06 respectively, both significantly higher than those of the control group (0.32 +/- 0.07 and 0.24 +/- 0.08 both P < 0.01. The protein expression of soluble TGF-alpha and the protein expression of p-EGFR protein of the NE group were 0.83 +/- 0.14 and 0.88 +/- 0.07 respectively, both significantly higher than those of the control group (0.25 +/- 0.13 and 0.28 +/- 0.11 respectively, both P < 0.01). The expression rates of MUC5AC mRNA, MUC5AC protein, soluble TGF-alpha, and p-EGFR of the TAPI-1 group were 0.37 +/- 0.04, 0.30 +/- 0.11, 0.32 +/- 0.07, and 0.43 +/- 0.09 respectively, all significantly lower than those of the NE group (all P < 0.01). The level of MUC5AC mRNA, MUC5AC mucin protein, and soluble TGF-alpha of the DMTU + NE group were 0.36 +/- 0.03, 0.39 +/- 0.12, and 0.43 +/- 0.05 respectively, all significantly lower than those of the NE group (all P < 0.01), however, the MUC5AC mRNA expression and MUC5AC protein expression of the DMTU + TGF-alpha group were 0.58 +/- 0.13 and 0.55 +/- 0.11 respectively, both not significantly different from those of the TGF-alpha group (0.56 +/- 0.08 and 0.57 +/- 0.13 respectively, both P > 0.05). CONCLUSION: NE induces MUC5AC expression via ROS/TACE/pro-TGF-alpha/EGFR in the airway epithelial cells.