Cigarette smoke extract inhibits the proliferation of alveolar epithelial cells and augments the expression of P21^WAF1

Cigarette smoking is intimately related with the development of chronic obstructive pulmonary diseases, and alveolar epithelium is a major target for the exposure of cigarette smoke extract. In order to investigate the effect of cigarette smoke extract on the proliferation of alveolar epithelial cell type II and its relationship with P21^WAF1, the alveolar epithelial type II cell line (A549) cells were chosen as surrogate cells to represent alveolar epithelial type II cells. MTT assay was used to detect cell viability after interfered with different concentrations of cigarette smoke extract. It was observed cigarette smoke extract inhibited the growth of A549 cells in a dose-and time-dependent manner. The morphological changes, involving the condensation and margination of nuclear chromatin, even karyorrhexis, were observed by both Hoechst staining and electronic microscopy. Flow cytometry analysis demonstrated the increased cell percentages in G₁ and subG₁ phases after the cells were incubated with cigarette smoke extract. The expression of p21^WAF1 protein and mRNA was also significantly increased as detected by the methods of Western blot or reverse transcription-polymerase chain reaction respectively. In conclusion, cigarette smoke extract inhibits the proliferation of alveolar epithelial cell type II and blocks them in G₁/S phase. The intracellular accumulation of P21^WAF1 may be one of the mechanisms which contribute to cigarette smoke extract-induced inhibition of cell proliferation.