Project description:Tyrosine kinase inhibitors (TKIs) directed against BCR-ABL1, the product of the Philadelphia (Ph) chromosome, have revolutionized treatment of patients with chronic myeloid leukemia (CML). However, acquired resistance to TKIs is a significant clinical problem in CML, and TKI therapy is much less effective against Ph+ B-cell acute lymphoblastic leukemia (B-ALL). BCR-ABL1, via phosphorylated Tyr177, recruits the adapter GAB2 as part of a GRB2/GAB2 complex. We showed previously that GAB2 is essential for BCR-ABL1-evoked myeloid transformation in vitro. Using a genetic strategy and mouse models of CML and B-ALL, we show here that GAB2 is essential for myeloid and lymphoid leukemogenesis by BCR-ABL1. In the mouse model, recipients of BCR-ABL1-transduced Gab2-/- bone marrow failed to develop CML-like myeloproliferative neoplasia. Leukemogenesis was restored by expression of GAB2 but not by GAB2 mutants lacking binding sites for its effectors PI3K or SHP2. GAB2 deficiency also attenuated BCR-ABL1-induced B-ALL, but only the SHP2 binding site was required. The SHP2 and PI3K binding sites were differentially required for signaling downstream of GAB2. Hence, GAB2 transmits critical transforming signals from Tyr177 to PI3K and SHP2 for CML pathogenesis, whereas only the GAB2-SHP2 pathway is essential for lymphoid leukemogenesis. Given that GAB2 is dispensable for normal hematopoiesis, GAB2 and its effectors PI3K and SHP2 represent promising targets for therapy in Ph+ hematologic neoplasms. RNA-Seq expression profiling of 6 mouse bone marrow samples: 3 GAB2 WT (+/+) and 3 GAB2 NULL (-/-)
Project description:Unlike clustered HOX genes, the role of non-clustered homeobox gene family members in hematopoiesis and leukemogenesis has not been extensively studied. Here we find that the Hematopoietically-expressed Homeobox gene, Hhex, is overexpressed in acute myeloid leukemia (AML) and is essential for the initiation and propagation of MLL-ENL induced AML, but dispensable for normal myelopoiesis, indicating a specific requirement for Hhex for leukemic growth. Loss of Hhex leads to upregulated expression of the tumor suppressors p16INK4a and p19ARF, which are required for growth arrest and myeloid differentiation following Hhex deletion. Mechanistically, we show that Hhex binds to the Cdkn2a locus and is required for H3K27Me3-mediated repression of this locus. Thus, Hhex is a novel therapeutic target that is specifically required for AML stem cells to repress tumor suppressor pathways and enable continued self-renewal.
Project description:Primary leukemia stem cells (LSCs) reside in an in vivo microenvironment that supports the growth and survival of malignant cells. We used an in vivo short hairpin RNA (shRNA) screening approach to identify novel genes that are essential for primary murine MLL-AF9 acute myeloid leukemia (AML). We found that Integrin Beta 3 (Itgb3) is selectively essential for murine leukemia cells in vivo, and for human leukemia cells in xenotransplantation studies. In leukemia cells, Itgb3 knockdown impaired homing, downregulated LSC transcriptional programs, and induced differentiation. In contrast, loss of Itgb3 in normal HSPCs did not affect engraftment, reconstitution, or differentiation in long term transplantation assays. We explored the signaling pathways downstream of Itgb3 using an additional in vivo shRNA screen and identified Syk as a critical mediator of Itgb3 activity in leukemia. Finally, we confirmed that Itgb3 is dispensable for normal hematopoiesis and required for leukemogenesis using the Itgb3 knockout mouse model. Our results establish the significance of the Itgb3 signaling pathway as a potential therapeutic target in AML, and demonstrate the utility of in vivo RNA interference screens. We examined the effect of Itgb3 knockdown by gene expression profiling in primary leukemia cells.
Project description:This SuperSeries is composed of the following subset Series: GSE16432: MSI2 regulates hematopoiesis and accelerates leukemogenesis GSE22773: Musashi 2 regulates normal hematopoiesis and accelerates leukemogenesis (LK and MS12-inducible) GSE22774: Musashi 2 regulates normal hematopoiesis and accelerates leukemogenesis (LSK and LK) GSE22775: Musashi 2 regulates normal hematopoiesis and accelerates leukemogenesis (Leukemia cell lines) Refer to individual Series
Project description:Tyrosine kinase inhibitors (TKIs) directed against BCR-ABL1, the product of the Philadelphia (Ph) chromosome, have revolutionized treatment of patients with chronic myeloid leukemia (CML). However, acquired resistance to TKIs is a significant clinical problem in CML, and TKI therapy is much less effective against Ph+ B-cell acute lymphoblastic leukemia (B-ALL). BCR-ABL1, via phosphorylated Tyr177, recruits the adapter GAB2 as part of a GRB2/GAB2 complex. We showed previously that GAB2 is essential for BCR-ABL1-evoked myeloid transformation in vitro. Using a genetic strategy and mouse models of CML and B-ALL, we show here that GAB2 is essential for myeloid and lymphoid leukemogenesis by BCR-ABL1. In the mouse model, recipients of BCR-ABL1-transduced Gab2-/- bone marrow failed to develop CML-like myeloproliferative neoplasia. Leukemogenesis was restored by expression of GAB2 but not by GAB2 mutants lacking binding sites for its effectors PI3K or SHP2. GAB2 deficiency also attenuated BCR-ABL1-induced B-ALL, but only the SHP2 binding site was required. The SHP2 and PI3K binding sites were differentially required for signaling downstream of GAB2. Hence, GAB2 transmits critical transforming signals from Tyr177 to PI3K and SHP2 for CML pathogenesis, whereas only the GAB2-SHP2 pathway is essential for lymphoid leukemogenesis. Given that GAB2 is dispensable for normal hematopoiesis, GAB2 and its effectors PI3K and SHP2 represent promising targets for therapy in Ph+ hematologic neoplasms.
Project description:Unlike clustered HOX genes, the role of non-clustered homeobox gene family members in hematopoiesis and leukemogenesis has not been extensively studied. Here we find that the Hematopoietically-expressed Homeobox gene, Hhex, is overexpressed in acute myeloid leukemia (AML) and is essential for the initiation and propagation of MLL-ENL induced AML, but dispensable for normal myelopoiesis, indicating a specific requirement for Hhex for leukemic growth. Loss of Hhex leads to upregulated expression of the tumor suppressors p16INK4a and p19ARF, which are required for growth arrest and myeloid differentiation following Hhex deletion. Mechanistically, we show that Hhex binds to the Cdkn2a locus and is required for H3K27Me3-mediated repression of this locus. Thus, Hhex is a novel therapeutic target that is specifically required for AML stem cells to repress tumor suppressor pathways and enable continued self-renewal.
Project description:CARM1 is essential for the development and maintenance of myeloid neoplasms. We found that non-phosphorylatable CARM1 mutation impairs cell cycle progression, induces apoptosis, and downregulates stemness in JAK2-mutant cell lines, suggesting that CARM1 phosphorylation is required for maximal proliferation of myeloid neoplasms.