Regulation of NRF2, AP‐1 and NF‐κB by cigarette smoke exposure in three‐dimensional human bronchial epithelial cells

Cigarette smoke (CS) is a complex mixture of chemicals and interacts with various physiological processes. We previously reported that nuclear factor erythroid 2‐related factor 2 (NRF2) was the most sensitive transcription factor to aqueous CS extract (AqCSE) exposure in monolayer cultured human bronchial epithelial cell lines. Recently, in vitro three‐dimensional (3D) culture models have been used to supplement pharmacological and toxicological assessments. Bronchial epithelium models in particular are useful for the evaluation of substances that directly contact the respiratory tract, such as CS. In the present study, we used 3D‐cultured human bronchial epithelial cells (HBECs) to assess activation of transcription factors and relevant gene expression in response to AqCSE, primarily focusing on NRF2 and nuclear factor‐kappa B (NF‐κB) pathways. The 3D‐cultured HBECs exposed to AqCSE showed expression of NRF2 and its nuclear translocation in addition to upregulation of genes related to oxidative stress. Our results suggest that the NRF2 pathway was the dominant pathway when 3D‐cultured HBECs were exposed to AqCSE at a low dose, supporting our previous findings that NRF2 was the most sensitive transcription factor in response to AqCSE. Expression and nuclear translocation of NF‐κB were not increased, although proinflammatory genes were upregulated. However, another inflammation‐related transcription factor, activation protein 1, was induced by AqCSE. Gene classification analysis suggested that induction of the inflammatory response by AqCSE was dependent on NRF2 and activation protein 1 rather than NF‐κB. We assessed activation of transcription factors and relevant signaling pathways when human bronchial epithelial cells in three‐dimensional culture were exposed to aqueous cigarette smoke extract (AqCSE). Our results suggest that the nuclear factor erythroid 2‐related factor 2 (NRF2) pathway is the dominant pathway at low‐dose exposure, supporting our previous findings that NRF2 is the most sensitive transcription factor to AqCSE. Moreover, the AqCSE‐induced inflammatory response is dependent on NRF2 and activation protein 1 rather than nuclear factor‐kappa B.