Poorly Differentiated Colon Carcinoma Cell Lines Deficient in α-Catenin Expression Express High Levels of Surface E-cadherin but Lack Ca2+-Dependent Cell-Cell Adhesion

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Abstract
Studies on several different types of carcinomas, with the notable exception of colon carcinoma, have shown that poorly differentiated tumors are frequently deficient in E-cadherin dependent cell-cell adhesion. In this study, we examined Ca2+-dependent cell-cell adhesion in colon carcinoma cell lines. Five poorly differentiated (Clone A, MIP 101, RKO, CCL 222, CCL 228) and four moderately-well differentiated (CX-1, CCL 235, DLD-2, CCL 187) colon carcinoma cell lines were assayed for their ability to form cell-cell aggregates and for their levels of E-cadherin expression. All of the poorly differentiated cell lines exhibited low levels of Ca2+-dependent cell-cell aggregation, in contrast to the moderately-well differentiated cell lines. Contrary to most previous studies, however, we observed that three of the five poorly differentiated cell lines examined expressed E-cadherin by FACS analysis and immunoprecipitation using an E-cadherin mAb. In fact, two of these cell lines expressed a 3- to 4-fold higher level of E-cadherin than that found in the moderately-well differentiated cell lines. mRNA levels for E-cadherin, as evaluated by both RT-PCR and Northern hybridization, corresponded to the levels of protein expression in each of the cell lines. Immunoprecipitation with an E-cadherin mAb, which is known to co-precipitate the catenins, demonstrated that the three poorly differentiated cell lines expressing E-cadherin did not co-precipitate α-catenin, although all of the moderately-well differentiated cell lines expressed both α- and β-catenin. RT-PCR confirmed the absence of the α-catenin mRNA from two of these cell lines. Stable expression of an α-catenin cDNA in one of the poorly differentiated cell lines lacking α-catenin expression resulted in a 5-fold increase in its level of Ca2+-dependent cell-cell aggregation, providing evidence that α-catenin is directly responsible for the loss of cell-cell adhesion in some cell lines. The α-catenin transfectants also exhibited a marked reduction in migration on collagen I. These data indicate that loss of α-catenin expression, as well as E-cadherin expression, can lead to a phenotype associated with poorly differentiated colon carcinomas.