Ambient particulate matter induces alveolar epithelial cell cycle arrest: role of G1 cyclins.

We hypothesized that the ambient air pollution particles (particulate matter; PM) induce cell cycle arrest in alveolar epithelial cells (AEC). Exposure of PM (25 μg/cm2) to AEC induced cells cycle arrest in G1 phase, inhibited DNA synthesis, blocked cell proliferation and caused decrease in cyclin E, A, D1 and Cyclin E- cyclin-dependent kinase (CDK)-2 kinase activity after 4 h. PM induced upregulation of CDK inhibitor, p21 protein and p21 activity in AEC. SiRNAp21 blocked PM-induced downregulation of cyclins and AEC G1 arrest. Accordingly, we provide the evidence that PM induces AEC G1 arrest by altered regulation of G1 cyclins and CDKs.