The signaling axis atypical protein kinase C l/i-Satb2 mediates leukemic transformation of B-cell progenitors

Oncogene driven transformation of leukemic progenitors results in B-acute lymphoblastic leukemia. Genetic deletions at specific hotspots are driven by recombination of epigenetically repressed loci and cause B cell transformation, and epigenetically regulated transcriptional plasticity has been proposed as a mechanism of differentiation arrest and resistance to therapy. The upstream signals driving epigenetic silencing have not been elucidated. BCR-ABL leukemias are initiated by leukemic stem cells/progenitors, and their modeling in vivo represents an opportunity for the identification of the epigenetic progress contributing to lineage leukemogenesis. We have found that primary human and murine BCR-ABL+ leukemic progenitors have increased activation of Cdc42 and the downstream atypical protein kinase C (aPKC). While the isoform aPKCz behaves as a leukemic suppressor, aPKCl/i is critically required for oncogenic progenitor proliferation, survival, and B cell differentiation arrest, but not for normal B cell lineage differentiation. We found that in vitro and in vivo B cell transformation by BCR-ABL requires the downregulation of key genes in the B-cell differentiation program through an aPKCl/i-dependent Etv5/Satb2 chromatin repressive signaling complex. Thus genetic or pharmacological targeting of aPKC impairs human oncogenic addicted leukemias in vitro and in vivo. Therefore, the aPKCl/i-SATB2 signaling cascade is required for leukemic BCR-ABL+ B-cell progenitor transformation and is amenable to non-BCR-ABL kinase inhibition. RNA seq analyse to identify the gene expression changes associated with the deficiency of atypical protein kinase C (aPKC) in p210-BCR-ABL+ leukemic B- cell progenitors. In 3 independent experiments, 50,000 leukemic B cell precursors were isolated from WT and aPKC deficient chimeric secondary recipient mice at 2 months post transplantation. Total RNA was isolated using QIAGEN RNAeasy minikit.