Conditional MLL-CBP targets GMP and models therapy-related myeloproliferative disease

Abstract

Chromosomal translocations that fuse the mixed lineage leukemia (MLL) gene with multiple partners typify acute leukemias of infancy as well as therapy-related leukemias. We utilized a conditional knockin strategy to bypass the embryonic lethality caused by MLL-CBP expression and to assess the immediate effects of induced MLL-CBP expression on hematopoiesis. Within days of activating MLL-CBP, the fusion protein selectively expanded granulocyte/ macrophage progenitors (GMP) and enhanced their selfrenewal/proliferation. MLL-CBP altered the gene expression program of GMP, upregulating a subset of genes including Hox a9. Inhibition of Hox a9 expression by RNA interference demonstrated that MLL-CBP required Hox a9 for its enhanced cell expansion. Following exposure to sublethal c-irradiation or N-ethyl-N-nitrosourea (ENU), MLL-CBP mice developed myelomonocytic hyperplasia and progressed to fatal myeloproliferative disorders. These represented the spectrum of therapy-induced acute myelomonocytic leukemia/chronic myelomonocytic leukemia/myelodysplastic/myeloproliferative disorder similar to that seen in humans possessing the t(11;16). This model of MLL-CBP therapy-related myeloproliferative disease demonstrates the selectivity of this MLL fusion for GMP cells and its ability to initiate leukemogenesis in conjunction with cooperating mutations.

Identification of Zfp521/ZNF521 as a cooperative gene for E2A-HLF to develop acute B-lineage leukemia

“…However, no disease was developed in EHKI DNeo mice during the long-term observation period (Figure 2a, thin lines), indicating that the acquired expression of E2A-HLF per se is insufficient for the development of leukemia. This finding is in line with previous reports showing that iKI mice of other leukemogenic transcription factor chimeras, such as AML1-ETO and MLL-CBP, did not show hematopoietic disorders, and secondary mutations induced by N-methyl-N-nitrosourea or irradiation were required to induce a fully malignant phenotype (Higuchi et al, 2002;Wang et al, 2005). In this study, to introduce additional gene alterations, we used RIM, as it not only …”

Bid protects the mouse hematopoietic system following hydroxyurea-induced replicative stress

“…This 'wave effect' is highly reproducible and is commonly observed in serial replating studies. 30,31 Cytospin analysis of bone marrow cells after the third methylcellulose plating demonstrated increased progenitor cells in Bid À / À cultures ( Figure 4a). The black arrow denotes a neutrophil, the terminally differentiated myeloid cell type.…”

MLL-AF9 and FLT3 cooperation in acute myelogenous leukemia: development of a model for rapid therapeutic assessment

“…17 Thus, histologic and immunophenotypic analysis show that MLL-AF9 and MLL-AF9 combined with FLT3-ITD induce a similar leukemia in this system. Recent experiments have shown that leukemias derived from MLL fusion proteins 14,18 demonstrate expansion of a GMP-like population at the expense of other myeloid progenitors. In order to verify that this phenomenon occurs when a second oncogene is introduced along with MLL-AF9, we performed flow cytometry on bone marrow from normal and leukemic mice.…”

“…Similarly, a conditional MLL-CBP knock-in mouse that recapitulates t-AML induced by the t(11;16) requires chemical or irradiation-induced mutagenesis for generation of a fatal myeloproliferative disease or leukemia. 18 Furthermore, bone marrow transplant models progress to oligoclonal leukemias pointing to the need for cooperating mutations in MLL-induced leukemogenesis. 19 Recent hypotheses as to the multistep nature of leukemogenesis suggest mutant signaling molecules are good candidates for cooperation with DNA-binding fusion oncogenes during leukemogenesis.…”