Double-stranded RNA and TGF-alpha promote MUC5AC induction in respiratory cells

Viral infection is a major trigger for exacerbation of asthma and induces overproduction of mucins. We investigated whether dsRNA could amplify the induction of mucin by TGF-alpha in human bronchial epithelial cells, as well as the molecular mechanisms regulating MUC5AC expression. Human pulmonary mucoepidermoid carcinoma (NCI-H292) cells and normal human bronchial epithelial cells were exposed to polyinosinic-cytidyric acid (poly(I:C)) and TGF-alpha. Then, MUC5AC protein production, mRNA expression, and promoter activity were evaluated. Cells were pretreated with a selective inhibitor of ERK, and phosphorylation of ERK was examined by Western blotting. Furthermore, the expression of MAPK phosphatase 3 (MKP3) mRNA was evaluated and the effect of MKP3 overexpression was assessed. Poly(I:C) synergistically increased MUC5AC induction by TGF-alpha in both NCI-H292 and normal human bronchial epithelial cells. This increase was dependent on MUC5AC gene transcription. A MEK1/2 inhibitor (U0126) significantly inhibited MUC5AC production. Phosphorylation of ERK was enhanced by poly(I:C). TGF-alpha stimulation up-regulated MKP3 mRNA expression, while costimulation with poly(I:C) inhibited this up-regulation dose-dependently. Enhanced expression of MUC5AC mRNA by poly(I:C) in wild-type cells was completely suppressed in cells transfected with the MKP3 expression vector. dsRNA can synergistically amplify the induction of MUC5AC mucin by TGF-alpha. This synergistic effect on MUC5AC production may be due to enhanced activation of ERK through inhibition of MKP3 by poly(I:C).