The Mixed Lineage Leukemia (MLL) gene codes for a histone methyltransferase that is frequently mutated by chromosomal translocations in human leukemias associated with a poor clinical outcome. The studies proposed in this competitive renewal application address the hypothesis that the leukemogenic actions of MLL oncoproteins are critically dependent on proteins recently discovered to associate with MLL or its fusion partners, and that the activities or interactions of these associated factors constitute potential targets for molecular therapies. This hypothesis is based on major discoveries during the current award period that have substantially advanced our understanding of the molecular mechanisms of MLL leukemias. We have shown that menin, a tumor suppressor protein and MLL- associated factor, is paradoxically required for MLL-mediated leukemogenesis. Menin functions as a transcriptional co-factor for MLL oncoproteins, and in this capacity we demonstrated that its only role is to promote interactions with a newly discovered MLL- associated protein known as LEDGF/p75. The latter is a chromatin-associated protein with co-activator activity but unknown molecular function, previously implicated in leukemia and HIV pathogenesis. Studies in the first specific aim will characterize the molecular functions of LEDGF/p75 required for MLL-mediated leukemogenesis using biochemical and genetic approaches in pre-clinical and cell line transformation model systems. These studies will identify a potential ligand for the putative methyl-lysine recognition motif of LEDGF/p75 and also establish the feasibility of antagonizing their interactions as a molecular therapeutic strategy. Studies in the second aim will employ genetic and biochemical techniques to determine the molecular mechanisms that underlie oncogenic activation of LEDGF/p75 itself by chromosomal translocations in leukemias, and establish its specific roles in leukemogenesis mediated through the MLL and/or Myc transcriptional pathways. Studies in the third specific aim are based on our discovery of a multi-protein complex (AEP) that contains several MLL fusion partners and the P-TEFb transcription elongation factor. This novel complex is tethered by a subset of MLL oncoproteins to critical target genes in MLL leukemia cells, however its molecular contributions required for leukemogenesis have not been fully defined. Our studies will further characterize the AEP complex, its critical enzymatic activities, its implications for MLL transcriptional regulation in general, and its role in MLL-mediated leukemogenesis. The therapeutic value of targeting the activities or interactions of AEP components with pathogenic roles in MLL leukemia will be interrogated using preclinical transformation models.

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This application proposes to investigate the critical molecular processes that cause cancers of blood-forming cells. Highly refined genetic and biochemical model systems will be employed to study cancer-associated pathways in normal stem cells as well as their cancerous counterparts and progeny. A greater understanding of the similarities and differences among normal and cancer stem cells will facilitate efforts to selectively target the latter while sparing the former to achieve more efficacious therapies.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Hematopoiesis Study Section (HP)
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Mufson, R Allan
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Stanford University
Schools of Medicine
United States
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Schneidawind, Corina; Jeong, Johan; Schneidawind, Dominik et al. (2018) MLL leukemia induction by t(9;11) chromosomal translocation in human hematopoietic stem cells using genome editing. Blood Adv 2:832-845
Zhu, Li; Li, Qin; Wong, Stephen H K et al. (2016) ASH1L Links Histone H3 Lysine 36 Dimethylation to MLL Leukemia. Cancer Discov 6:770-83
Wong, Stephen H K; Goode, David L; Iwasaki, Masayuki et al. (2015) The H3K4-Methyl Epigenome Regulates Leukemia Stem Cell Oncogenic Potential. Cancer Cell 28:198-209
Iwasaki, Masayuki; Liedtke, Michaela; Gentles, Andrew J et al. (2015) CD93 Marks a Non-Quiescent Human Leukemia Stem Cell Population and Is Required for Development of MLL-Rearranged Acute Myeloid Leukemia. Cell Stem Cell 17:412-21
Buechele, Corina; Breese, Erin H; Schneidawind, Dominik et al. (2015) MLL leukemia induction by genome editing of human CD34+ hematopoietic cells. Blood 126:1683-94
Duque-Afonso, Jesús; Cleary, Michael L (2014) The AML salad bowl. Cancer Cell 25:265-7
Yokoyama, Akihiko; Ficara, Francesca; Murphy, Mark J et al. (2013) MLL becomes functional through intra-molecular interaction not by proteolytic processing. PLoS One 8:e73649
Kuo, Hsu-Ping; Wang, Zhong; Lee, Dung-Fang et al. (2013) Epigenetic roles of MLL oncoproteins are dependent on NF-?B. Cancer Cell 24:423-37
Yokoyama, Akihiko; Ficara, Francesca; Murphy, Mark J et al. (2011) Proteolytically cleaved MLL subunits are susceptible to distinct degradation pathways. J Cell Sci 124:2208-19
Chang, Pei-Yun; Hom, Robert A; Musselman, Catherine A et al. (2010) Binding of the MLL PHD3 finger to histone H3K4me3 is required for MLL-dependent gene transcription. J Mol Biol 400:137-44

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