Noncanonical β-catenin interactions promote leukemia-initiating activity in early T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is a T-cell malignancy, characterized by cell subsets, enriched with leukemia-initiating cells (LIC). β-Catenin modulates LIC activity in T-ALL. However, its role in maintaining established leukemia stem cells remains largely unknown. To identify functionally relevant protein interactions of -Catenin in T-ALL, we performed co-Immunoprecipitation (Co-IP) followed by liquid-chromatography mass spectrometry. Here, we report that a non-canonical functional interaction of β-Catenin with the Forkhead-Box-O3 (FOXO3) transcription factor positively regulates LIC related genes including the Cyclin-dependent-kinase-4 (CDK4), which is a crucial modulator of cell cycle and tumor maintenance. We also confirm the relevance of these findings using stably integrated fluorescent reporters of β-Catenin and FOXO3 activity in patient-derived xenografts, which identify minor subpopulations with enriched LIC activity. Additionally, gene expression data at the single-cell level of leukemic cells of primary patients at the diagnosis and minimal residual disease (MRD) up to 30 days from the standard treatments reveal that the expression of β-Catenin and FOXO3 dependent genes is present in the CD82+CD117+ cell fraction, which is substantially enriched with LICs in MRD as well as in early T-cell precursor acute lymphoblastic leukemia (ETP-ALL). These findings highlight key functional roles for β-Catenin and FOXO3 and suggest novel therapeutic strategies to eradicate aggressive cell subsets in T-ALL.