The Wnt/β-Catenin Pathway Promotes Growth and Survival of Acute Lymphoblastic Leukaemia (ALL) Cells In Vitro.

Wnt signalling is known to play an important regulatory role in self-renewal of haematopoietic stem cells as well as development of normal lymphocyte progenitors. Recently this pathway was implicated in a number of haematological malignancies including AML, CML, MM and CLL. However its role in acute lymphoblastic leukaemia is not clear. We have previously shown that primary pre-B ALL cells and cell lines express various Wnt family members, receptors and downstream transcription factors. We extended these studies further to elucidate a functional role of Wnt signalling in leukemic cells. Exposure to Wnt3a, a ligand inducing the canonical Wnt signal cascade, resulted in stabilisation of beta-catenin and its nuclear translocation in all growth factor independent pre-B cell lines (n=3), stromal-dependent cell line (n=1) and primary cases (n=3) examined. Wnt3a treated pre-B ALL cell lines and a patient sample were more resistant to apoptosis induced by serum deprivation (viability on day 4, 51.3±18.4% Wnt3a treated vs 29.5±19.9% control treated, p-value <0.05). 3H-thymidine incorporation studies revealed 4.0±1.7 fold increase in proliferation which was associated with increased cell cycle entry as determined by Ki-67 staining. Cell cycle analysis confirmed an increase in the proportion of cells in S and G2M phases of cell cycle. These effects were associated with increased transcriptional activity of toposiomerase II-alpha as assessed by semi-quantitative PCR and protein expression. Taken together our results indicate that Wnt-dependant β-catenin signalling pathway is active in pre-B ALL cells and promotes their growth and survival in vitro.