B Tizazu

Ludwig-Maximilians-University of Munich, München, Bavaria, Germany

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Publications (7)47.9 Total impact

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    ABSTRACT: The CALM/AF10 fusion gene is found in various hematological malignancies including AML, T-cell ALL, and malignant lymphoma. We have previously identified the leukemia stem cell (LSC) in a CALM/AF10-driven murine bone marrow transplant acute myeloid leukemia model as B220-positive lymphoid cells with B cell characteristics. To identify the target cell for leukemic transformation or 'cell of origin of leukemia' (COL) in non-disturbed steady-state hematopoiesis we inserted the CALM/AF10 fusions gene preceded by a loxP-flanked transcriptional stop cassette into the Rosa26 locus. Vav-Cre induced pan-hematopoietic expression of the CALM/AF10 fusion gene led to acute leukemia with a median latency of 12 months. Mice expressing CALM/AF10 in the B lymphoid compartment using Mb1-Cre or CD19-Cre inducer lines did not develop leukemia. Leukemias had a predominantly myeloid phenotype but showed co-expression of the B cell marker B220, and had clonal B-cell receptor rearrangements. Using whole-exome sequencing, we identified an average of 2 to 3 additional mutations per leukemia, including activating mutations in known oncogenes like FLT3 and PTPN11. Our results show that the COL for CALM/AF10 is a stem or early progenitor cell and not a cell of B-cell lineage with a phenotype similar to that of the LSC in CALM/AF10-positive leukemia.Leukemia accepted article preview online, 21 December 2015. doi:10.1038/leu.2015.349.
    No preview · Article · Dec 2015 · Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K
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    ABSTRACT: Cytogenetically normal acute myeloid leukemia (CN-AML) with biallelic CEBPA gene mutations (biCEPBA) represents a distinct disease entity with a favorable clinical outcome. So far, it is not known whether other genetic alterations cooperate with biCEBPA mutations during leukemogenesis. To identify additional mutations, we performed whole exome sequencing of 5 biCEBPA patients and detected somatic GATA2 zinc finger 1 (ZF1) mutations in 2 of 5 cases. Both GATA2 and CEBPA are transcription factors crucial for hematopoietic development. Inherited or acquired mutations in both genes have been associated with leukemogenesis. Further mutational screening detected novel GATA2 ZF1 mutations in 13 of 33 biCEBPA-positive CN-AML patients (13/33, 39.4%). No GATA2 mutations were found in 38 CN-AML patients with a monoallelic CEBPA mutation and in 89 CN-AML patients with wild-type CEBPA status. The presence of additional GATA2 mutations (n=10) did not significantly influence the clinical outcome of 26 biCEBPA-positive patients. In reporter gene assays, all tested GATA2 ZF1 mutants showed reduced capacity to enhance CEBPA-mediated activation of transcription, suggesting that the GATA2 ZF1 mutations may collaborate with biCEPBA mutations to deregulate target genes during malignant transformation. We thus provide evidence for a genetically distinct subgroup of CN-AML. The German AML cooperative group trials 1999 and 2008 are registered with the identifiers NCT00266136 and NCT01382147 at www.clinicaltrials.gov.
    Full-text · Article · May 2012 · Blood
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    ABSTRACT: The t(10;11)(p13;q14) translocation results in the fusion of the CALM (clathrin assembly lymphoid myeloid leukemia protein) and AF10 genes. This translocation is observed in acute myeloblastic leukemia (AML M6), acute lymphoblastic leukemia (ALL) and malignant lymphoma. Using a yeast two-hybrid screen, the four and a half LIM domain protein 2 (FHL2) was identified as a CALM interacting protein. Recently, high expression of FHL2 in breast, gastric, colon, lung as well as in prostate cancer was shown to be associated with an adverse prognosis. The interaction between CALM and FHL2 was confirmed by glutathione S-transferase-pulldown assay and co-immunoprecipitation experiments. The FHL2 interaction domain of CALM was mapped to amino acids 294-335 of CALM. The transcriptional activation capacity of FHL2 was reduced by CALM, but not by CALM/AF10, which suggests that regulation of FHL2 by CALM might be disturbed in CALM/AF10-positive leukemia. Extremely high expression of FHL2 was seen in acute erythroid leukemia (AML M6). FHL2 was also highly expressed in chronic myeloid leukemia and in AML with complex aberrant karyotype. These results suggest that FHL2 may play an important role in leukemogenesis, especially in the case of AML M6.
    Full-text · Article · Nov 2011 · Blood Cancer Journal

  • No preview · Article · May 2011 · Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K

  • No preview · Conference Paper · Dec 2008
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    PA Greif · B Tizazu · A Krause · E Kremmer · S K Bohlander
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    ABSTRACT: The t(10;11)(p13;q14) translocation leads to the fusion of the CALM and AF10 genes. This translocation can be found as the sole cytogenetic abnormality in acute lymphoblastic leukemia, acute myeloid leukemia and in malignant lymphomas. The expression of CALM/AF10 in primary murine bone marrow cells results in the development of an aggressive leukemia in a murine bone marrow transplantation model. Using a yeast two-hybrid screen, we identified the lymphoid regulator Ikaros as an AF10 interacting protein. Interestingly, Ikaros is required for normal development of lymphocytes, and aberrant expression of Ikaros has been found in leukemia. In a murine model, the expression of a dominant negative isoform of Ikaros causes leukemias and lymphomas. The Ikaros interaction domain of AF10 was mapped to the leucine zipper domain of AF10, which is required for malignant transformation both by the CALM/AF10 and the MLL/AF10 fusion proteins. The interaction between AF10 and Ikaros was confirmed by GST pull down and co-immunoprecipitation. Coexpression of CALM/AF10 but not of AF10 alters the subcellular localization of Ikaros in murine fibroblasts. The transcriptional repressor activity of Ikaros is reduced by AF10. These results suggest that CALM/AF10 might interfere with normal Ikaros function, and thereby block lymphoid differentiation in CALM/AF10 positive leukemias.
    Full-text · Article · Jun 2008 · Oncogene
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    ABSTRACT: The ets-family transcription factor ETV6 (TEL) has been shown to be the target of a large number of balanced chromosomal translocations in various hematological malignancies and in some soft tissue tumors. Furthermore, ETV6 is essential for hematopoietic stem cell function. We identified ETV6 interacting proteins using the yeast two hybrid system. One of these proteins is the HIV Tat interacting protein (TIP60), a histone acetyltransferase (HAT) containing the highly conserved MYST domain. TIP60 functions as a corepressor of ETV6 in reporter gene assays. Fluorescently tagged ETV6 and TIP60 colocalize in the nucleus and an increase in nuclear localization of ETV6 was seen when TIP60 was cotransfected. ETV6 interacts with TIP60 through a 63 amino acids region located in the central domain of ETV6 between the pointed and the ets domain. The ETV6 interacting region of TIP60 mapped to the C2HC zinc finger of the TIP60 MYST domain. The interaction of TIP60 with full length ETV6 required an intact acetyltransferase domain of TIP60. Interestingly, the MYST domains of MOZ and MORF were also able to interact with portions of ETV6. These observations suggest that MYST domain HATs regulate ETV6 transcriptional activity and may therefore play critical roles in leukemogenesis and possibly in normal hematopoietic development.
    Full-text · Article · Jan 2008 · Biochimica et Biophysica Acta