Promoter Methylation-Mediated Silencing of b-Catenin Enhances Invasiveness of Non-Small Cell Lung Cancer and Predicts Adverse Prognosis

b-Catenin plays dual role in adhesion complex formation and the Wnt signaling pathway. Although b-catenin expression appears to be upregulated and Wnt signaling pathway is activated in the majority of cancers, its expression level seems to be lost in non-small cell lung cancer (NSCLC). We previously reported that the promoter of b-catenin was hypermethylated in two NSCLC cell lines. In the current study, we expanded our analysis for the methylation status of b-catenin promoter region and its protein expression in seven NSCLC cell lines and a series of 143 cases of primary human lung cancer with adjacent non-neoplastic tissues. Quantitative methylation specific PCR (qMSP) analysis showed methylation of b-catenin promoter region in five NSCLC cell lines, with increased b-catenin protein levels upon 59-Aza-29-deoxycytidine (5-aza-dC) treatment. The methylation status in SPC (methylated) and A549 (unmethylated) was confirmed by bisulfite sequencing PCR. 5-Aza-dC treatment inhibited invasiveness of SPC but not A549. Immunofluorescence analysis showed membranous b-catenin expression was lost in SPC and could be re-established by 5-aza-dC, while Wnt3a treatment led to nuclear translocation of b-catenin in both SPC and A549. Dual-luciferase assays indicated that 5-aza-dC treatment caused no significant increase in Wnt signaling activity compared with Wnt3a treatment. The effect of demethylation agent in SPC can be reversed by b-catenin depletion but not E-cadherin depletion which indicated that the methylation mediated b-catenin silencing might enhance NSCLC invasion and metastasis in an E-cadherin independent manner. Subsequen