Bcr-abl fusion protein is essential for maintaining the VE-cadherin/β-catenin axis in Ph⁺ ALL. (A top) Western blot analysis of Bcr-abl expression by Sup-B15 in LTMC (Med) or LTCC (S10 or PatX). (Bottom) DLR assays of LTMC (Med) and LTCC (S10 and PatX) Sup-B15 cells transiently cotransfected with the Bcr-abl promoter reporters phRL-pp210L or phRL-pp210S with an internal control pGL4.13-CMV-Luc2 firefly luciferase reporter. Data were shown as mean plus or minus SD (n = 3). The * denotes statistically significant differences compared with values from cells in media alone (P < .01) based on the Student t test. (B) Western blot analysis of Bcr-abl expression by Sup-B15 cells transduced with retroviruses containing p185-eGFP or p210-eGFP forms of Bcr-abl, or the empty vector control (MSCV-IRES-eGFP, MiG) alone (top Western blot). Dual-color flow cytometric analysis of VE-cadherin expression in Sup-B15 cells overexpressing the exogenous Bcr-abl fusion proteins or empty retroviral control vector (bottom flow cytometry). Baseline VE-cadherin was set to zero for comparison of the net increases after retroviral transduction. (C) DLR assay of Sup-B15 cells infected with p185-eGFP, p210-eGFP or MiG vector control retroviruses. Data are shown as mean plus or minus SD (n = 3). The * denotes significant differences compared with MSCV empty vector controls (P < .01) based on the Student t test. (D) Western blot analysis of cell lysates from Sup-B15 cells treated with the Bcr-abl kinase inhibitors Imatinib Mesylate or AG957 at various concentrations. (E) Western blot of Sup-B15 or Nalm27 leukemic cells treated with 20 μM imatinib mesylate, 10 μM proteosome inhibitor MG132, or a combination of both inhibitors for 16 hours.