Modulation of E-cadherin localization in cells expressing wild-type E1A 12S or hypertransforming mutants.

The adenovirus E1A 12S gene can immortalize primary epithelial cells such that they retain expression of epithelial cell characteristics. E1A 12S can also cooperate with an activated ras oncogene to cause tumorigenic transformation of primary cells. Specific substitution and deletion mutants of E1A 12S cooperate more efficiently with ras to produce foci with a hypertransformed phenotype, wherein the cells are less differentiated and exhibit invasive properties. Loss of epithelial differentiation in carcinomas is often a consequence of reduced intercellular adhesion involving loss of a functional cell-cell adhesion molecule, E-cadherin. Therefore, expression of E-cadherin was analyzed in mock-infected primary epithelial cells, cells expressing E1A 12S protein, and in hypertransformed cells. Primary epithelial cells express E-cadherin and correctly localize it to the cell-cell junctions, as detected by immunofluorescence. The level of E-cadherin expression decreases with time in culture. Primary cells expressing the E1A 12S protein maintain the expression and correct localization of E-cadherin. This effect of E1A 12S on E-cadherin expression is not at the transcriptional level. Immortalized cells expressing the 12S protein and primary epithelial cells transformed with the E1A 12S gene and ras continue to express E-cadherin at the cell-cell junctions. In contrast to the 12S-immortalized and wild-type transformed cells, hypertransformed cells are defective for localization of E-cadherin and exhibit altered subcellular distribution of E-cadherin, as detected by immunoprecipitation with an anti-E-cadherin antibody. Furthermore, the aberrant localization exhibited by the hypertransformed cells can be overcome by superinfection of the hypertransformed cells with a virus expressing the E1A 12S cDNA or treatment with retinoic acid. Thus, the E1A 12S protein appears to act as a differentiation factor to maintain the differentiated characteristics of epithelial cells.