A kinase-independent Bcr-Abl function mediating an Hsp70-Bim protein-protein interaction in chronic myeloid leukemia.

Despite the transformative impact of tyrosine kinase inhibitors (TKIs) on chronic myeloid leukemia (CML), a subset of TKIs-resistant CML cells survives independent of Bcr-Abl kinase activity, forming a persistent therapeutic challenge. In this study, we present the first direct evidence that Bcr-Abl, through its DNA-binding domain (DBD), interacts with the nucleotide-binding domain (NBD) of Hsp70 to mediate the formation of a Bcr-Abl/Hsp70/Bim tri-complex, independent of its kinase function. Using a combination of in vitro biophysical assays-including fluorescent polarization assays (FPAs), isothermal titration calorimetry (ITC), circular dichroism spectroscopy, ATPase activity measurement, and rhodanese aggregation suppression-and cell-based co-immunoprecipitation (Co-IP), we demonstrate that this interaction induces a conformational change in Hsp70 that enhances its affinity for Bim and significantly elevates its ATPase activity. The resulting complex stabilizes oncogenic survival proteins such as AKT and eIF4E, thereby protecting TKIs-resistant CML cells from apoptosis in a Bcr-Abl kinase-independent manner. Importantly, pharmacologic disruption of this complex using the Hsp70/Bim inhibitor S1g-10 or Bcr-Abl PROTAC molecule effectively suppresses TKIs-resistant CML cell proliferation. These findings reveal a novel non-canonical function of Bcr-Abl and provide a new therapeutic strategy for overcoming TKIs-resistance in CML.