Abstract

In most cell types, nuclear {beta}-catenin functions as prominent oncogenic driver and pairs with TCF7-family factors for transcriptional activation of MYC. Surprisingly, B-lymphoid malignancies not only lacked expression and activating lesions of {beta}-catenin but critically depended on GSK3{beta} for effective {beta}-catenin degradation. Our interactome studies in B-lymphoid tumors revealed that {beta}-catenin formed repressive complexes with lymphoid-specific Ikaros factors at the expense of TCF7. Instead of MYC-activation, {beta}-catenin was essential to enable Ikaros-mediated recruitment of nucleosome remodeling and deacetylation (NuRD) complexes for transcriptional repression of MYC. To leverage this previously unrecognized vulnerability of B-cell-specific repressive {beta}-catenin-Ikaros-complexes in refractory B-cell malignancies, we examined GSK3{beta} small molecule inhibitors to subvert {beta}-catenin degradation. Clinically approved GSK3{beta}-inhibitors that achieved favorable safety prof les at micromolar concentrations in clinical trials for neurological disorders and solid tumors were effective at low nanomolar concentrations in B-cell malignancies, induced massive accumulation of {beta}-catenin, repression of MYC and acute cell death. Preclinical in vivo treatment experiments in patient-derived xenografts validated small molecule GSK3{beta}-inhibitors for targeted engagement of lymphoid-specific {beta}-catenin-Ikaros complexes as a novel strategy to overcome conventional mechanisms of drug-resistance in refractory malignancies. HIGHLIGHTSO_LIUnlike other cell lineages, B-cells express nuclear {beta}-catenin protein at low baseline levels and depend on GSK3{beta} for its degradation. C_LIO_LIIn B-cells, {beta}-catenin forms unique complexes with lymphoid-specific Ikaros factors and is required for Ikaros-mediated tumor suppression and assembly of repressive NuRD complexes. C_LIO_LICRISPR-based knockin mutation of a single Ikaros-binding motif in a lymphoid MYC superenhancer region reversed {beta}-catenin-dependent Myc repression and induction of cell death. C_LIO_LIThe discovery of GSK3{beta}-dependent degradation of {beta}-catenin as unique B-lymphoid vulnerability provides a rationale to repurpose clinically approved GSK3{beta}-inhibitors for the treatment of refractory B-cell malignancies. C_LI GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/532152v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1b70e4dorg.highwire.dtl.DTLVardef@10bfcc8org.highwire.dtl.DTLVardef@b10eorg.highwire.dtl.DTLVardef@1683a3e_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIAbundant nuclear {beta}-catenin C_LIO_LI{beta}-catenin pairs with TCF7 factors for transcriptional activation of MYC C_LIO_LIB-cells rely on efficient degradation of {beta}-catenin by GSK3{beta} C_LIO_LIB-cell-specific expression of Ikaros factors C_LI Unique vulnerability in B-cell tumors: O_LIGSK3{beta}-inhibitors induce nuclear accumulation of {beta}-catenin. C_LIO_LI{beta}-catenin pairs with B-cell-specific Ikaros factors for transcriptional repression of MYC C_LI