Role of Wnt–β-catenin signaling in MSC-mediated protection of CML stem/progenitor cells from TKI treatment. (A) Apoptosis of CML CD34⁺ cells treated with IM (5 µM), ICG001 (5 µM), or IM plus ICG001 in the absence and presence of MSCs. Cell cycle of CML CD34⁺ cells treated with IM, ICG001, or IM plus ICG001 in the absence (B) and presence (C) of MSCs. (D) CML CD34⁺ cells were exposed to CM from Wnt1-transfected cells and Wnt reporter activity measured after 2 days. (E) Flow cytometry plots and (F) graph showing apoptosis of CML CD34⁺ cells cocultured with Wnt1-CM with or without IM treatment. (G) β-catenin protein expression and (H) nuclear localization of β-catenin in IM-treated CML CD34+ cells after addition of Wnt receptor antagonist DKK1(1 µg/mL). Results shown are representative of 100 cells analyzed per slide. (I) Apoptosis of IM-treated CML CD34⁺ cells cocultured with MSCs in the presence and absence of DKK1. (J) Proposed Wnt–β-catenin and N-cadherin interactions in CML CD34⁺ cells treated with TKI in the presence of MSCs. TKI treatment stabilizes β-catenin by reducing β-catenin phosphorylation, increasing N-cadherin–mediated adhesion to MSCs, and enhancing N-cadherin–β-catenin interaction. Wnt proteins secreted by MSCs activate β-catenin signaling in MSC-adherent CML stem/progenitor cells, leading to enhanced nuclear translocation of β-catenin and transcription of target genes. Complex formation with N-cadherin in MSC-adherent CML stem/progenitor cells may protect β-catenin from degradation and provide a β-catenin pool that can be activated by exogenous Wnt ligands. MSC-induced N-cadherin and Wnt–β-catenin signaling protects and preserves CML stem/progenitor cells from TKI treatment. ns, not significant. n = 3. *P < .05.