Background: Tobacco smoke (TS) critically contributes to the development of lung cancer; however, the underlying molecular mechanisms remain unclear. The induction of cancer stem cells (CSCs) by TS represents an early event in tumor initiation. The lung cancer-related gene ΔNp63α is highly expressed in epithelial tissues and drives tumor formation and cancer stem cell properties. This study investigated the role of ΔNp63α in the long-term acquisition of TS-induced lung CSC-like properties. Methods: The expression levels of ΔNp63α, lung CSC markers, and interleukin (IL)-6 in lung carcinoma specimens were determined by western blotting and enzyme linked immunosorbent assays. Human bronchial epithelial (HBE) cells were chronically exposed to 2 % cigarette smoke extract for 55 passages, following which colony formation capacity, expression of proteins associated with malignant transformation, lung CSC markers, and tumor incidence were investigated. The effects of ΔNp63α on long-term TS exposure-induced lung CSC-like properties and Notch activation were analyzed using tumorsphere formation ability, immunofluorescence assays, luciferase reporter assays, and western blotting. The roles of IL-6 on chronic TS exposure-induced lung CSC-like properties and ΔNp63α expression were also examined. Moreover, the effects of sulforaphane (SFN) on TS-transformed lung CSC-like properties, IL-6 and ΔNp63α expression, and Notch signaling were investigated in vitro and in vivo. Results: Higher levels of ΔNp63α were observed in the lung cancer tissues of smokers than in those of non-smokers, whereas ΔNp63α was positively correlated with CD133 and Oct4 expression in lung cancer tissues. Data from the in vivo and in vitro experiments demonstrated that long-term TS exposure-transformed HBE (THBE) cells acquired lung CSC-like properties. Furthermore, ΔNp63α transcriptionally activated the Notch signaling pathway to promote the acquisition of CSC-like properties by the THBE cells. TS upregulated IL-6, which increased ΔNp63α expression in THBE sphere-forming cells. Finally, SFN inhibited the TS-induced CSC-like properties of THBE cells via the IL-6/ΔNp63α/Notch axis. Conclusion: Our data suggest that the IL-6/ΔNp63α/Notch axis plays an important role in the long-term TS exposure-induced acquisition of lung CSC-like properties and SFN intervention.
Keywords: IL-6; Notch pathway; lung cancer stem cells; sulforaphane; tobacco smoke; ΔNp63α.