FLT3 regulates b-catenin tyrosine phosphorylation, nuclear localization, and transcriptional activity in acute myeloid leukemia cells

Deregulated accumulation of nuclear b-catenin enhances transcription of b-catenin target genes and promotes malignant transformation. Recently, acute myeloid leukemia (AML) cells with activating mutations of FMS-like tyrosine kinase-3 (FLT3) were reported to display elevated b-catenin-dependent nuclear signaling. Tyrosine phosphorylation of b-catenin has been shown to promote its nuclear localization. Here, we examined the causal relationship between FLT3 activity and b-catenin nuclear localization. Compared to cells with wild-type FLT3 (FLT3-WT), cells with the FLT3 internal tandem duplication (FLT3-ITD) and tyrosine kinase domain mutation (FLT3-TKD) had elevated levels of tyrosine-phosphorylated b-catenin. Although b-catenin was localized mainly in the cytoplasm in FLT3-WT cells, it was primarily nuclear in FLT3-ITD cells. Treatment with FLT3 kinase inhibitors or FLT3 silencing with RNAi decreased b-catenin tyrosine phosphorylation and nuclear localization. Conversely, treatment of FLT3-WT cells with FLT3 ligand increased tyrosine phosphorylation and nuclear accumulation of b-catenin. Endogenous b-catenin co-immunoprecipitated with endogenous activated FLT3, and recombinant activated FLT3 directly phosphorylated recombinant b-catenin. Finally, FLT3 inhibitor decreased tyrosine phosphorylation of b-catenin in leukemia cells obtained from FLT3-ITD-positive AML patients. These data demonstrate that FLT3 activation induces b-catenin tyrosine phosphorylation and nuclear localization, and thus suggest a mechanism for the association of FLT3 activation and b-catenin oncogeneic signaling in AML.Leukemia (2007) 21, 2476-2484; doi:10.1038/sj.leu.2404923; published online 13 September 2007