BAALC potentiates oncogenic ERK pathway through interactions with MEKK1 and KLF4

Although high brain and acute leukemia, cytoplasmic (BAALC) expression is a well-characterized poor prognostic factor in acute myeloid leukemia (AML), neither the exact mechanisms by which BAALC drives leukemogenesis and drug resistance nor therapeutic approaches against BAALC-high AML have been properly elucidated. In this study, we found that BAALC induced cell-cycle progression of leukemia cells by sustaining extracellular signal-regulated kinase (ERK) activity through an interaction with a scaffold protein MEK kinase-1 (MEKK1), which inhibits the interaction between ERK and MAP kinase phosphatase 3 (MKP3/DUSP6). BAALC conferred chemoresistance in AML cells by upregulating ATP-binding cassette proteins in an ERK-dependent manner, which can be therapeutically targeted by MEK inhibitor. We also demonstrated that BAALC blocks ERK-mediated monocytic differentiation of AML cells by trapping Krüppel-like factor 4 (KLF4) in the cytoplasm and inhibiting its function in the nucleus. Consequently, MEK inhibition therapy synergizes with KLF4 induction and is highly effective against BAALC-high AML cells both in vitro and in vivo. Our data provide a molecular basis for the role of BAALC in regulating proliferation and differentiation of AML cells and highlight the unique dual function of BAALC as an attractive therapeutic target against BAALC-high AML.