Cytoplasmic redistribution of E-cadherin-catenin adhesion complex is associated with down-regulated tyrosine phosphorylation of E-cadherin in human bronchopulmonary carcinomas

Abstract

The E-cadherin-catenin complex, by mediating intercellular adhesion, regulates the architectural integrity of epithelia. Down-regulation of its expression is thought to contribute to invasion of carcinoma cells. To investigate the involvement of the E-cadherin-catenin adhesion system in the progression of human bronchopulmonary carcinomas, we compared the immunohistochemical distribution of E-cadherin, alpha-catenin, and beta-catenin in four human bronchial cancer cell lines with different invasive abilities and in 44 primary bronchopulmonary tumors. Although invasive bronchial cell lines did not express E-cadherin and alpha-catenin, complete down-regulation of cadherin-catenin complex expression was a rare event in vivo in bronchopulmonary carcinomas. Nevertheless, a spotty and cytoplasmic pattern of E-cadherin and catenins was observed in 32 primary tumors, only in invasive tumor clusters. Immunoprecipitation experiments showed that this redistribution was not related to a disruption of cadherin-catenin interaction but to down-regulated tyrosine phosphorylation of E-cadherin. We conclude that loss of E-cadherin and/or catenins is not a prominent early event in the invasive progression of human bronchopulmonary carcinomas in vivo. The decreased tyrosine phosphorylation of E-cadherin may reflect a loss of functionality of the complex and implicates a major role in tumor invasion.

Figure 1.

Spatial distribution of E-cadherin and catenins in human bronchial cell lines by confocal microscopy. Ephithelioid noninvasive 16HBE cells displayed a strong membranous E-cadherin (A), α-catenin (B), and β-catenin (C) expression pattern. However, only β-catenin was expressed in highly invasive BZR cells, where it was distributed in a spotty cytoplasmic pattern (D). Scale bar = 11 μm.

Figure 2.

Detection of E-cadherin and catenins expression in human bronchial cell lines by Western blot analysis. 16HBE cells expressed E-cadherin, α-catenin and β-catenin (lane 1), whereas Beas2B (lane 2), BZR (lane 3), and BZR-T33 (lane 4) cells expressed only β-catenin.

Figure 3.

Localization by immunofluorescence of E-cadherin-catenin complex molecules on cryosections of bronchopulmonary carcinomas. E-cadherin was strongly expressed in tumor cells of a squamous cell carcinoma (A); hematoxylin counterstaining (B). Magnification, ×160. Some infiltrating isolated tumor cells (arrowheads) that were detached from the primary tumor were E-cadherin-negative (C); heamatoxylin counterstaining (D). Magnification, ×160. Isolated invasive tumor cells (arrowhead) preserved a cytoplasmic β-catenin expression (E); hematoxylin counterstaining (F). Magnification, ×320.

Figure 4.

Spatial distribution of E-cadherin and catenins in bronchopulmonary carcinomas by confocal microscopy. E-cadherin (A), α-catenin (C), and β-catenin (E) were expressed in a thin pericellular pattern in an adenocarcinoma. A focal area of invasive tumor cluster of a squamous cell carcinoma displayed a clear intracytoplasmic distribution of E-cadherin (B), α-catenin (D), and β-catenin (F). Scale bar = 6 μm.

Figure 5.

E-cadherin immunoprecipitation in nontumoral and tumoral samples. A: E-cadherin was complexed to α- and β-catenins in nontumoral lung parenchyma (N) and in a tumoral sample displaying a cytoplasmic pattern (T). B: E-cadherin was tyrosine-phosphorylated in the same nontumoral sample (N), whereas no tyrosine phosphorylation was detected in the carcinoma sample (T). C: Immunoprecipitation by PY20 antibody confirmed that tyrosine-phosphorylated band was E-cadherin in normal samples (N).