ABSTRACT
The t(8;21) rearrangement, which creates the AML1-ETO fusion protein, represents the most common chromosomal translocation in acute myeloid leukemia (AML). Clinical data suggest that CBL mutations are a frequent event in t(8;21) AML, but the role of CBL in AML1-ETO-induced leukemia has not been investigated. In this study, we demonstrate that CBL mutations collaborate with AML1-ETO to expand human CD34+ cells both in vitro and in a xenograft model. CBL depletion by shRNA also promotes the growth of AML1-ETO cells, demonstrating the inhibitory function of endogenous CBL in t(8;21) AML. Mechanistically, loss of CBL function confers hyper-responsiveness to thrombopoietin and enhances STAT5/AKT/ERK/Src signaling in AML1-ETO cells. Interestingly, we found the protein tyrosine phosphatase UBASH3B/Sts-1, which is known to inhibit CBL function, is upregulated by AML1-ETO through transcriptional and miR-9-mediated regulation. UBASH3B/Sts-1 depletion induces an aberrant pattern of CBL phosphorylation and impairs proliferation in AML1-ETO cells. The growth inhibition caused by UBASH3B/Sts-1 depletion can be rescued by ectopic expression of CBL mutants, suggesting that UBASH3B/Sts-1 supports the growth of AML1-ETO cells partly through modulation of CBL function. Our study reveals a role of CBL in restricting myeloid proliferation of human AML1-ETO-induced leukemia, and identifies UBASH3B/Sts-1 as a potential target for pharmaceutical intervention.
Subject(s)
Core Binding Factor Alpha 2 Subunit/genetics , Gene Expression Regulation, Leukemic , Leukemia, Myeloid, Acute/genetics , Oncogene Proteins, Fusion/genetics , Preleukemia/genetics , Protein Tyrosine Phosphatases/genetics , Proto-Oncogene Proteins c-cbl/genetics , Animals , Cell Proliferation , Chromosomes, Human, Pair 21 , Chromosomes, Human, Pair 8 , Core Binding Factor Alpha 2 Subunit/metabolism , Extracellular Signal-Regulated MAP Kinases/genetics , Extracellular Signal-Regulated MAP Kinases/metabolism , Fetal Blood/cytology , Fetal Blood/drug effects , Fetal Blood/metabolism , Heterografts , Humans , Leukemia, Myeloid, Acute/metabolism , Leukemia, Myeloid, Acute/pathology , Mice , Mice, SCID , MicroRNAs/genetics , MicroRNAs/metabolism , Myeloid Cells/cytology , Myeloid Cells/drug effects , Myeloid Cells/metabolism , Oncogene Proteins, Fusion/metabolism , Preleukemia/metabolism , Preleukemia/pathology , Protein Tyrosine Phosphatases/metabolism , Proto-Oncogene Proteins c-akt/genetics , Proto-Oncogene Proteins c-akt/metabolism , Proto-Oncogene Proteins c-cbl/antagonists & inhibitors , Proto-Oncogene Proteins c-cbl/metabolism , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , RUNX1 Translocation Partner 1 Protein , STAT5 Transcription Factor/genetics , STAT5 Transcription Factor/metabolism , Thrombopoietin/pharmacology , Transgenes , Translocation, Genetic , src-Family Kinases/genetics , src-Family Kinases/metabolismABSTRACT
Suppression of apoptosis by TP53 mutation contributes to resistance of acute myeloid leukemia (AML) to conventional cytotoxic treatment. Using differentiation to induce irreversible cell cycle exit in AML cells could be a p53-independent treatment alternative, however, this possibility requires evaluation. In vitro and in vivo regimens of the deoxycytidine analogue decitabine that deplete the chromatin-modifying enzyme DNA methyl-transferase 1 without phosphorylating p53 or inducing early apoptosis were determined. These decitabine regimens but not equimolar DNA-damaging cytarabine upregulated the key late differentiation factors CCAAT enhancer-binding protein É and p27/cyclin dependent kinase inhibitor 1B (CDKN1B), induced cellular differentiation and terminated AML cell cycle, even in cytarabine-resistant p53- and p16/CDKN2A-null AML cells. Leukemia initiation by xenotransplanted AML cells was abrogated but normal hematopoietic stem cell engraftment was preserved. In vivo, the low toxicity allowed frequent drug administration to increase exposure, an important consideration for S phase specific decitabine therapy. In xenotransplant models of p53-null and relapsed/refractory AML, the non-cytotoxic regimen significantly extended survival compared with conventional cytotoxic cytarabine. Modifying in vivo dose and schedule to emphasize this pathway of decitabine action can bypass a mechanism of resistance to standard therapy.
