β-catenin is involved in N-cadherin-dependent adhesion, but not in canonical Wnt signaling in E2A-PBX1-positive B acute lymphoblastic leukemia cells

Objective. The t(1;19)(q23;13) translocation, resulting in the production of the E2A-PBX1 chimeric protein, is a common nonrandom translocation in pediatric B-lineage acute lymphoblastic leukemia (B-ALL). The E2A-PBX1 chimeric protein activates expression of several genes, including Wnt16. In the present study, we explored the role of Wnt16 and P-catenin in t(1;19) B-ALL cells. Materials and Methods. Canonical Wnt signaling was measured by TOPflash activity. Localization of P-catenin in the cell membrane and its involvement in leukemia-stroma interaction were studied by confocal microscopy. Adhesion to N-cadherin was analyzed by adding H-3-thymidin-labeled cells to N-cadherin-coated wells. Results. In contrast to previous reports, we detected no effects on cell viability or proliferation upon modulation of the Wnt16 levels. Moreover, despite high levels of Wnt16 and beta-catenin, the cells had very low levels of canonical Writ signaling. Instead, beta-catenin was located in the cell membrane along with N-cadherin. E2A-PBX1-positive leukemia cells adhered strongly to bone marrow stroma cells, and we showed that adherence junctions stained strongly for both proteins. Moreover, knockdown of beta-catenin reduced the adhesion of E2A-PBX1-positive leukemia cells to N-cadherin, suggesting that beta-catenin and N-cadherin play a central role in homotypic cell-to-cell adhesion and in leukemia-stroma adhesion. Interestingly, knockdown of Wnt16 by small interfering RNA reduced the level of N-cadherin. Conclusion. Wnt16 does not activate canonical Writ signaling in E2A-PBX1-positive cells. Instead, beta-catenin is involved in N-cadherin-dependent adherence junctions, suggesting for the first time that leukemia-stroma interactions may be mediated via an N-cadherin-dependent mechanism. (C) 2009 ISEH - Society for Hematology and Stein Cells. Published by Elsevier Inc.