Peptidoglycan from Staphylococcus aureus Increases MUC5AC Gene Expression via RSK1-CREB Pathway in Human Airway Epithelial Cells

Respiratory tract exposure to viruses, air pollutants, or bacterial pathogens can lead to pulmonary diseases. The molecular mechanism of mucous overproduction increased by these pathogens provides the knowledge for developing new therapeutic strategies. There is established in vitro data demonstrating that the overexpression of MUC5AC is induced by peptidoglycan (PGN) derived from Staphylococcus aureus. However, the mechanisms by which PGN activates MUC5AC gene expression in the airway remain unclear. The aim of this study was to identify the mechanism of PGN-induced MUC5AC gene expression. We found that PGN could induce MUC5AC gene expressions in a time- and dose-dependent manner. Moreover, activations of ERK1/2 and JNK increased after treatment of cells with PGN, whereas phosporylation of p38 was undetected. Of these MAPKs, pharmacologic inhibition of ERK1/2 decreased PGN-induced MUC5AC gene expression. In addition, we checked the activation of p90 ribosomal S6 kinase 1 (RSK1) as a downstream signaling target of ERK1/2 in PGN signaling. The activation of RSK1 was prevented by pretreatment with PD98059. We also found that RSK1 mediated the PGN-induced phosphorylation of cAMP response element-binding protein (CREB) and the transcription of MUC5AC. Furthermore, the cAMP-response element (CRE) in the MUC5AC promoter appears to be important for PGN-induced MUC5AC gene expression in NCI-H292 cells.