Structure and function of the N-cadherin/catenin complex in retinoblastoma

PURPOSE. To identify in human retinoblastoma and normal retinal tissue the type of cadherin, its relationship with cytoplasmic catenins, and its participation in invasion. METHODS. The cadherin/catenin complex was characterized in surgical retinoblastoma. specimens from five patients and human retinas from four donor eyes by immunocytochemistry, flow cytometry, and coimmunoprecipitation with antibodies against N-cadherin, alpha-catenin, and beta-catenin, followed by Western blot analysis or autoradiography. Y79 and WERI-Rb-1 retinoblastoma cell lines serve the evaluation of the cadherin/ catenin complex in aggregation and Collagen type I invasion in vitro. The association of the cadherin/catenin complex with the cytoskeleton was examined by an antibody-capping assay. RESULTS. In retinoblastoma and normal retina N-cadherin associated with a-catenin and beta-catenin but not E- or P-cadhcrin. The N-cadherin/catenin complex formed a regular, linear, and continuous honeycomb pattern in normal retina that was irregular, clustered, and interrupted in retinoblastoma. The Ncadherin/catenin complex was found also in the retinoblastoma cell lines WERI-Rb and Y79, in which it also showed an irregular pattern. Both cell lines were invasive in Collagen type I, and invasion was inhibited by the GC-4 antibody, which functionally neutralizes N-cadherin. Less GC-4 antibody was needed to inhibit invasion of Y79 cells, which expressed N-cadherin at a lower level, than to inhibit invasion of WERI-Rb-1 cells. In both cell lines, antibody capping of the N-cadherin/ catenin complex indicated that its linkage with the cytoskeleton were weak or absent. CONCLUSIONS. Retinoblastoma cells, in contrast with normal retina, express an N-cadherin/catenin complex that is irregularly distributed and weakly linked to the cytoskeleton. In retinoblastoma, this complex acts as an invasion promoter.