IKBKE Upregulation is Positively Associated with Squamous Cell Carcinoma of the Lung In Vivo and Malignant Transformation of Human Bronchial Epithelial Cells In Vitro

BACKGROUND: The IκB kinase inhibitor of κB kinase epsilon (IKBKE) is overexpressed in several human cancers. Although IKBKE plays an important role in smoking-induced non-small cell lung cancer carcinogenesis, its role in squamous cell carcinoma of the lung (SCCL) remains unclear. MATERIAL/METHODS: IKBKE protein expression was assessed by immunohistochemistry in 288 paraffinized SCCL specimens (with adjacent squamous dysplastic and normal tissue). IKBKE mRNA expression was assessed by reverse transcription PCR in 66 fresh SCCL specimens (with adjacent squamous dysplastic and normal tissue). Separately, immortalized human bronchial epithelial cells were cultured in 7 groups: untreated control, ethanol-treated, and cigarette smoke condensate (CSC)-exposed for 10, 20, 30, 40, and 50 generations (P10, P20, P30, P40, and P50, respectively). Malignant transformation was assessed by serum resistance and colony formation assays. IKBKE protein and mRNA expression were detected by Western blotting and reverse transcription PCR, respectively. RESULTS: IKBKE protein expression showed a significant upward trend from normal bronchial epithelium to squamous cell dysplasia to SCCL. IKBKE protein expression in SCCL was significantly associated with smoking status, smoking index, degree of differentiation, and clinical stage. Current and former smokers displayed significantly higher IKBKE protein and mRNA expression than non-smokers. IKBKE protein and mRNA expression displayed a significant upward trend with the smoking index. P30, P40, and P50 CSC-exposed cells displayed malignant transformation with increasing IKBKE mRNA and protein expression from P20 through P50. CONCLUSIONS: IKBKE upregulation is positively associated with SCCL and smoking indices as well as CSC-induced malignant transformation of human bronchial epithelial cells.