Abstract

Wnt proteins are important bone marrow-derived growth factors known to support normal hematopoietic progenitor and stem cell development. Here we report that B cell progenitor acute lymphoblastic leukemia (pre-B ALL) cells express Wnt proteins, including Wnt-2b in 33%, Wnt-5a in 42%, Wnt-10b in 58% and Wnt-16b in 25% of cases. The Wnt receptors, Frizzled (Fz)-7 and -8 were also expressed in most cases while Fz-3, -4 and -9 were occasionally detected. Stimulation of pre-B ALL cells with Wnt-3a activated canonical Wnt signaling with increased expression and nuclear translocation of β-catenin. This resulted in a 1.7 to 5.3-fold increase in cell proliferation, which was associated with enhanced cell cycle entry. Wnt-3a also significantly increased the survival of pre-B ALL cells under conditions of serum deprivation. To determine the mechanisms involved we examined the effects of Wnt-3a on gene expression using the leukemic pre-B ALL cell line NALM6 and a cancer specific microarray (GEArray® OHS-802), which contains 440 known cancer genes. Expression of 83 genes (19%) could be detected on the array. Exposure to Wnt-3a for 24 hours resulted in increased (>1.5 fold) expression of 29 genes and reduced (<50% of control) expression of 3 genes. The most highly regulated genes in response to Wnt-3a were MYBL2, E2F1, CD10, VDAC1, CDC25B (upregulated) and TRAIL-R2 (downregulated). Using qRT-PCR, we confirmed regulation of these genes in NALM6 cells and/or in another leukemic cell line LK63. These genes play important roles in the control of cell cycle (MYBL2, E2F1 and CDC25B), apoptosis (VDAC1 and TRAIL-R2) and motility (CD10) in cancer cells. Our results suggest that Wnt signalling regulates cell growth and proliferation in leukemic cells by modulating the expression of a number of genes. To our knowledge this is the first study examining the gene expression profile following Wnt stimulation in leukemic cells and potentially identifies new therapeutic targets for treatment.

Disclosure: No relevant conflicts of interest to declare.

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