Analysis of the Role of Wnt Signaling for the Interaction between Leukemia Cells and Stroma.

Wnt signaling plays an important role in hematopoietic stem cell self-renewal and proliferation. Recent results also revealed that an aberrant activation of Wnt signaling has been related with hematological malignancies. We have previously reported a stroma-dependent human leukemia cell line, TRL-01, which could not be maintained by any cytokines without stroma or on fibronectin-coated plate although they periodically stimulated the proliferation. We here analyzed the role of Wnt signaling on the cell-adhesion, proliferation and survival of this cell line. TRL-01 was maintained on human bone marrow stroma cell line, hTERT. The apoptosis of TRL-01 on hTERT was suppressed by Wnt-receptor competitor, secreted Frizzled related protein (sFRP)-1, or Rho kinase inhibitor, Y29632 but not by specific inhibitor of canonical pathway, DKK-1. However, the apoptosis of TRL-01 without hTERT was not affected by sFRP-1, Y29632 or DKK-1. These results suggest that survival of TRL-01 on stroma was regulated by non-canonical pathway of Wnt signaling. Next, the effects of Wnt3A, 5A and 10B on TRL-01 were analyzed by establishing hTERT transduced with Wnt3A, 5A or 10B genes. Wnt3A is known as an important factor for the stimulation of self-renewal and proliferation of hematopoietic stem cells, and Wnt5A and 10B were reported to be expressed in B-ALL. When TRL-01 was cocultured with hTERT/Wnt3A or 10B, adhesion was reduced and β-catenin was significantly increased. The condition medium from hTERT/Wnt3A or 10B also stimulates the accumulation of β-catenin but inhibited the survival and proliferation of TRL-01. Wnt5A did not have any significant effects. These results suggest that Wnt3A and 10B stimulate canonical pathway with accumulation of β-catenin but negatively regulate the survival and proliferation of TRL-01. Comparing the expression pattern of Wnt transcripts of TRL-01 and hTERT by RT-PCR, Wnt5A, 5B and 14 were found to be dominantly expressed in hTERT. The role of Wnt5B and 14 for the interaction between TRL-01 and hTERT remains to be elucidated.