beta-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 beta-catenin in t(1;19) B-ALL cells.


METHODS
Canonical Wnt signaling was measured by TOPflash activity. Localization of beta-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 (3)H-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 Wnt 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.


CONCLUSIONS
Wnt16 does not activate canonical Wnt 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.
Nygren
Marit Kveine
MK
Department of Immunology, Institute for Cancer Research, Norwegian Radium Hospital, Rikshospitalet University Hospital, Montebello, Oslo, Norway.
Døsen-Dahl
Guri
G
Stubberud
Heidi
H
Wälchli
Sébastien
S
Munthe
Else
E
Rian
Edith
E
D022005:Adherens Junctions / Q000235:genetics / Q000378:metabolism; D015820:Cadherins / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion / Q000235:genetics; D045744:Cell Line, Tumor; D002648:Child; D002675:Child, Preschool; D002877:Chromosomes, Human / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015448:Leukemia, B-Cell / Q000378:metabolism*; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D014178:Translocation, Genetic / Q000235:genetics; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
D015820:Cadherins; D018398:Homeodomain Proteins; D015514:Oncogene Proteins, Fusion; C417262:WNT16 protein, human; D051153:Wnt Proteins; D051176:beta Catenin; C089847:E2A-Pbx1 fusion protein