Different Activation of WNT Signaling Pathway in B-Cell and T-Cell Acute Leukemias.

WNT signaling pathway proteins function as hematopoietic growth factors and regulate proliferation in normal T-cell and B-cell development. Recent experimental evidence demonstrated that oncogenic transformation in leukemias of both lymphoid and myeloid lineages is dependent on WNT signaling. Not much is known about activation of WNT signaling pathway, its ligands and receptors in hematopoiesis and leukemia pathogenesis. To define its role in leukemia, we aimed to determine mRNA levels of the critical members of WNT pathway (WNT5A, WNT10B, FZ5, β catenin, APC, TCF-1 and LEF-1) by using quantitative real time PCR in acute lymphoblastic leukemia (ALL) patients (T-cell n=42, B-cell n=46 and pre B-cell n=30) and normal hematopoietic cells (bone marrow n=6, peripheral blood n=10, and CD19+ cells from peripheral blood). These genes expressed varying levels in B-cells, preB-cells and T-cells. In the B-cell leukemia patients, WNT5A was expressed notably (OR=58.05 CI 95% 1.63–1219.55, p>0,001). WNT5A directs Ca⁺⁺ dependent signaling by PKC and a G protein dependent manner which is an alternative pathway for beta-catenin mediated signaling. Also LEF-1 levels were higher in B-ALL patients and APC expression was down regulated when compared to normal tissue (OR=18.81 CI 95% 0.34–5703, p>0.001 and OR=0.212 CI 95% 0.006–8.816, p=0.001, respectively). It is known that LEF-1 blocks APC mediated β catenin nuclear export and activates transcription of various transforming genes, including cyclin, D1, c-myc, MMP7, and LEF-1 itself. WNT5A or WNT10B proteins were not found to be up regulated in preB-ALL whereas APC and LEF-1 gene expressions were increased compared to normal hematopoietic cells (OR=32.97 CI 95% 0.27–1281, 38 p>0.001 and OR=5.57 CI 95% 0.28–89.51, p=0.01, respectively). We found increased TCF-1 expression (7.4 fold) without any β catenin accumulation in T-ALL patients. It is known that TCF-1 in absence of β catenin functions as a tumor suppressor gene. WNT5A, APC and LEF-1 gene expression levels were also different between T-cell, B-cell and preB cell ALL cases. WNT5A expression had the highest levels in B-ALL compared to T-ALL cases, whereas the highest APC expression levels were observed in preB and T-ALL patients. Also LEF-1 expression levels were significantly different between preB and T-cell ALL patients. Taken together these results indicate that WNT signaling genes have abnormal expression and are active in acute lymphoblastic leukemia. This data suggests different WNT activation mechanisms exist in the leukemic transformation in different hematopoietic cells.