Cigarette smoke condensate inhibits ENaC alpha-subunit expression in lung epithelial cells

Cigarette smoke has been associated with lung fluid accumulation and increased risk of acute respiratory distress syndrome. It was postulated that ENaC alpha-subunit, which plays a critical role in lung fluid absorption, is affected by cigarette smoke. Cigarette smoke condensate (CSC) was used to treat a human lung epithelial cell line. ENaC alpha-subunit expression was measured using immunoblotting, quantitative PCR and promoter-reporter assays. The current authors found that CSC, without affecting cell survival, suppressed alpha-subunit expression at the transcriptional level in a dose- and time-dependent fashion. This suppression is neither related to nicotine nor due to an increase of hydrogen peroxide levels in CSC-treated cells. CSC also suppressed alpha-subunit core promoter activity. Dexamethasone, which activates the core promoter, was able to attenuate the inhibitory effect of CSC. However, in the presence of CSC, dexamethasone was unable to elicit a full-scale activation of alpha-subunit expression. This inhibition of dexamethasone was partially reversed by withdrawal of CSC. The present results demonstrate that cigarette smoke condensate inhibits ENaC alpha-subunit expression at the transcriptional level through its promoter. This inhibition could be reversed by dexamethasone. The results also suggest that higher doses of dexamethasone may be needed to activate alpha-subunit expression in smokers' lungs compared with nonsmokers' lungs, and that quitting smoking might improve the effectiveness of dexamethasone.