Immunohistochemical demonstration of alteration of β-catenin during tumor metastasis by different mechanisms according to histology in lung cancer

The protein β-catenin exhibits a dual function in cells, by acting as a major structural component of cell-cell adherens junctions and as a central signaling molecule in the Wnt signaling pathway. However, how the regulation of β-catenin expression during tumor metastasis in non-small cell lung cancer (NSCLC) varies according to histological type remains unclear. To investigate the regulatory mechanism of β-catenin on tumor metastasis, the present study compared the expression of Wnt1, β-catenin and E-cadherin in 41 primary NSCLC tumors and their corresponding metastatic lesions by immunohistochemistry. Altered expression of β-catenin was more frequent in the metastatic tumors (34/41, 82.9%) than in the corresponding primary tumors (24/41, 58.5%; P<0.05). There were 12 cases [nine of adenocarcinoma (ADC) and three of squamous cell carcinoma (SqCC)] that revealed discordant β-catenin expression between the primary tumors and the corresponding metastatic lesions. Of these, 11 cases (11/12, 91.7%; nine ADCs and two SqCCs) demonstrated acquired β-catenin alterations in the metastatic lesions. Subgroup analysis of these nine ADCs revealed that six cases (6/9, 66.7%) were accompanied by E-cadherin loss but no Wnt1 overexpression. Subgroup analysis of the three SqCCs revealed discordant β-catenin expression. Two cases (2/3, 66.7%) demonstrated acquired β-catenin expression during metastatic progression with Wnt1 overexpression but no change in E-cadherin expression. One case of SqCC revealed normal β-catenin expression in the metastasis although the expression was aberrant in the primary tumor. The results of the present study revealed that the changes in β-catenin expression occurred during tumor metastasis by different mechanisms, depending on histological type. The alterations in β-catenin expression may be regulated by a cadherin-catenin system in ADCs with reduced membranous expression of E-cadherin, but mediated by Wnt1 overexpression in SqCCs with cytoplasmic or nuclear transition types.