Activation of transcription factors in human bronchial epithelial cells exposed to aqueous extracts of mainstream cigarette smoke in vitro
Transcription factors are recognised as important components of signalling cascades controlling all types of normal cellular processes as well as response to external stimulus. Activation of transcription factors can alter the expression of specific genes.
The present study aimed to identify transcription factors activated by aqueous extracts of mainstream cigarette smoke (MCS) in vitro and assess cigarette smoke from different experimentally-designed cigarettes on transcription factor activation.
Ten transcription factors were selected by pathway analysis from comprehensive gene expression profile in NCI-H292 cells exposed to MCS. Luciferase reporter assays for each transcription factor were developed with two human bronchial epithelial cells, NCI-H292 and BEAS-2B, to assess the activation of these transcription factors. Activation of each transcription factor by aqueous extracts of MCS from Kentucky Reference 3R4F cigarettes (3R4F) showed the same tendency in both cells. However, BEAS-2B showed higher reactivity than NCI-H292. Nuclear factor erythroid 2-related factor 2 (Nrf2) was the most activated transcription factor by MCS from 3R4F under the same condition.
The luciferase reporter assay for Nrf2 was utilised to assess cigarette smoke from different experimentally-designed cigarettes. Charcoal-filtered cigarette reduced Nrf2 activation in comparison with non-charcoal filtered cigarette. Furthermore, aqueous extracts of MCS from the flue-cured cigarette (FC) activated Nrf2 more strongly than those from the Burley cigarette (BLY).
In summary, the results suggest that Nrf2 is activated by both particulate and gas/vapor phase in MCS, and more so in FC than in BLY.