Exosomal miR-196b secreted from bronchial epithelial cells chronically exposed to low-dose PM 2.5 promotes invasiveness of adjacent and lung cancer cells.

Fine particulate matter (PM 2.5 ) is a risk factor for pulmonary diseases and lung cancer, and inhaled PM 2.5 is mainly deposited in the bronchial epithelium. In this study, we investigated the effect of long-term exposure to low-dose PM 2.5 on BEAS-2B cells derived from the normal bronchial epithelium. BEAS-2B cells chronically exposed to a concentration of 5 µg/ml PM 2.5 for 30 passages displayed the phenotype promoting epithelial-mesenchymal transition (EMT) and cell invasion. Cellular internalization of exosomes (designated PM 2.5 Exo) extracted from BEAS-2B cells chronically exposed to low-dose PM 2.5 promoted cell invasion in vitro and metastatic potential in vivo. Hence, to identify the key players driving phenotypic alterations, we analyzed microRNA (miRNA) expression profiles in PM 2.5 Exo. Five miRNAs with altered expression were selected: miRNA-196b-5p, miR-135a-2-5p, miR-3117-3p, miR-218-5p, and miR-497-5p. miR-196b-5p was the most upregulated in both BEAS-2B cells and isolated exosomes after PM 2.5 exposure. In a functional validation study, genetically modified exosomes overexpressing a miR-196b-5p mimic induced an enhanced invasive phenotype in BEAS-2B cells. Conversely, miR-196b-5p inhibition diminished the PM 2.5 -enhanced EMT and cell invasion. These findings indicate that exosomal miR-196b-5p may be a candidate biomarker for predicting the malignant behavior of the bronchial epithelium and a therapeutic target for inhibiting PM 2.5 -triggered pathogenesis.