Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Studies of developmental pathways of hematopoietic stem cells (HSCs) have defined lineage relationships throughout the blood system. This is relevant to acute myeloid leukemia (AML), where aggressiveness and therapeutic responsiveness can be influenced by the initial stage of transformation. To address this, we generated a mouse model in which the mixed-lineage leukemia/eleven-nineteen-leukemia (MLL-ENL) transcription factor can be conditionally activated in any cell type. We show that AML can originate from multiple hematopoietic progenitor subsets with granulocytic and monocytic potential, and that the normal developmental position of leukemia-initiating cells influences leukemic development. However, disease failed to arise from HSCs. Although it maintained or upregulated the expression of target genes associated with leukemic development, MLL-ENL dysregulated the proliferative and repopulating capacity of HSCs. Therefore, the permissiveness for development of AML may be associated with a narrower window of differentiation than was previously appreciated, and hijacking the self-renewal capacity of HSCs by a potent oncogene is insufficient for leukemic development.
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PMID:Hematopoietic stem cells are intrinsically protected against MLL-ENL-mediated transformation. 2545 27

Misregulation of transcription elongation is proposed to underlie the pathobiology of MLL leukemia. AF4, AF9, and ENL, common MLL fusion partners, are found in complex with positive transcription elongation factor b (P-TEFb). AF9 and its homolog ENL directly interact with AF4 within these complexes. Previously, we designed a peptide that mimics the AF9 binding domain of AF4 and reported that MLL leukemia cell lines are inhibited by it. Extending these studies, we have modified the peptide design in order to avoid recognition by proteases. The peptide is as effective as its predecessor in vitro and enhances survival in mice bearing MLL leukemia cell lines.
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PMID:An AF9/ENL-targted peptide with therapeutic potential in mixed lineage leukemias. 2550 85

MLL aberrations are detected in around 5-10% of acute myeloid and lymphatic leukemias and an additional 5% of acute myeloid leukemias show a partial internal MLL duplication (PTD). MLL rearrangements are important for therapy stratification, assessment of minimal residual disease and for targeted therapies. However, no truly evidence-based RT-PCR methods for the detection of most of these aberrations have been published yet. Based on the large data collection of MLL genomic breakpoints in acute leukemias comprising more than 1.600 cases at the Diagnostic Center for Acute Leukemias (DCAL) in Frankfurt, Germany that provide an overview over the experimentally observed fusion transcript variants, we developed RT-PCR methods for the reliable detection of the 8 most common MLL aberrations (MLL-AF4, MLL-AF6, MLL-AF9, MLL-AF10, MLL-ENL, MLL-ELL, MLL-EPS15, MLL PTD), together accounting for around 90% of MLL-r cases. The easily implementable RT-PCRs should enable a reliable detection of these MLL fusion transcripts by RT-PCR.
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PMID:Evidence-based RT-PCR methods for the detection of the 8 most common MLL aberrations in acute leukemias. 2551 Apr 85

Translocation of the mixed-lineage leukemia (MLL) gene with AF4, AF9, or ENL results in acute leukemia with both lymphoid and myeloid involvement. We characterized leukemia-initiating cells (LICs) in primary infant MLL-rearranged leukemia using a xenotransplantation model. In MLL-AF4 patients, CD34(+)CD38(+)CD19(+) and CD34(-)CD19(+) cells initiated leukemia, and in MLL-AF9 patients, CD34(-)CD19(+) cells were LICs. In MLL-ENL patients, either CD34(+) or CD34(-) cells were LICs, depending on the pattern of CD34 expression. In contrast, in patients with these MLL translocations, CD34(+)CD38(-)CD19(-)CD33(-) cells were enriched for normal hematopoietic stem cells (HSCs) with in vivo long-term multilineage hematopoietic repopulation capacity. Although LICs developed leukemic cells with clonal immunoglobulin heavy-chain (IGH) rearrangement in vivo, CD34(+)CD38(-)CD19(-)CD33(-) cells repopulated recipient bone marrow and spleen with B cells, showing broad polyclonal IGH rearrangement and recipient thymus with CD4(+) single positive (SP), CD8(+) SP, and CD4(+)CD8(+) double-positive (DP) T cells. Global gene expression profiling revealed that CD9, CD32, and CD24 were over-represented in MLL-AF4, MLL-AF9, and MLL-ENL LICs compared with normal HSCs. In patient samples, these molecules were expressed in CD34(+)CD38(+) and CD34(-) LICs but not in CD34(+)CD38(-)CD19(-)CD33(-) HSCs. Identification of LICs and LIC-specific molecules in primary human MLL-rearranged acute lymphoblastic leukemia may lead to improved therapeutic strategies for MLL-rearranged leukemia.
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PMID:Identification of CD34+ and CD34- leukemia-initiating cells in MLL-rearranged human acute lymphoblastic leukemia. 2553 41

Chromosomal rearrangements of the MLL gene are associated with high-risk infant, pediatric, adult, and therapy-induced acute leukemias. So far, about 80 different direct MLL fusions and about 120 reciprocal MLL fusions have been characterized at the molecular level. The common theme in these leukemia-associated genetic rearrangements is the genetic disruption of the MLL gene. This leads to MLL-X fusion proteins that still bind to nuclear factors (e.g., MEN1, LEDGF), which in turn allow them to target promoters and cause ectopic gene transcription. In addition, the most frequent MLL fusions (MLL-AF4, MLL-AF9, MLL-AF10, and MLL-ENL) are all recruiting the wild-type AF4 multiprotein complex that contains the target proteins P-TEFb, BRD4, and DOT1L. Vice versa, reciprocal X-MLL fusions exhibit a PHD domain (H3K4me3 reader domain), sequester the histone acetyltransferases CREBBP and MOF1 and bear a histone methyltransferase domain at their very C-terminus (SET domain). Except for AF4-MLL, the functional consequences deriving from reciprocal fusion proteins are not very well understood. However, based on our knowledge about the above-mentioned MLL fusions, it is reasonable to inhibit their oncogenic activity in a targeted fashion. Recent efforts in developing such inhibitors and their mode of action will be critically discussed.
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PMID:MLL leukemia and future treatment strategies. 2574 Mar 45

Chromosomal rearrangements involving the mixed-lineage leukemia (MLL) gene occur in primary and treatment-related leukemias and confer a poor prognosis. Studies based primarily on mouse models have substantially advanced our understanding of MLL leukemia pathogenesis, but often use supraphysiological oncogene expression with uncertain implications for human leukemia. Genome editing using site-specific nucleases provides a powerful new technology for gene modification to potentially model human disease, however, this approach has not been used to re-create acute leukemia in human cells of origin comparable to disease observed in patients. We applied transcription activator-like effector nuclease-mediated genome editing to generate endogenous MLL-AF9 and MLL-ENL oncogenes through insertional mutagenesis in primary human hematopoietic stem and progenitor cells (HSPCs) derived from human umbilical cord blood. Engineered HSPCs displayed altered in vitro growth potentials and induced acute leukemias following transplantation in immunocompromised mice at a mean latency of 16 weeks. The leukemias displayed phenotypic and morphologic similarities with patient leukemia blasts including a subset with mixed phenotype, a distinctive feature seen in clinical disease. The leukemic blasts expressed an MLL-associated transcriptional program with elevated levels of crucial MLL target genes, displayed heightened sensitivity to DOT1L inhibition, and demonstrated increased oncogenic potential ex vivo and in secondary transplant assays. Thus, genome editing to create endogenous MLL oncogenes in primary human HSPCs faithfully models acute MLL-rearranged leukemia and provides an experimental platform for prospective studies of leukemia initiation and stem cell biology in a genetic subtype of poor prognosis leukemia.
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PMID:MLL leukemia induction by genome editing of human CD34+ hematopoietic cells. 2631 62

Gene rearrangements generate MLL fusion genes, which can lead to aggressive leukemia. In most cases, MLL fuses with a gene encoding a component of the AEP (AF4 family/ENL family/P-TEFb) coactivator complex. MLL-AEP fusion proteins constitutively activate their target genes to immortalize haematopoietic progenitors. Here we show that AEP and MLL-AEP fusion proteins activate transcription through selectivity factor 1 (SL1), a core component of the pre-initiation complex (PIC) of RNA polymerase I (RNAP1). The pSER domain of AF4 family proteins associates with SL1 on chromatin and loads TATA-binding protein (TBP) onto the promoter to initiate RNA polymerase II (RNAP2)-dependent transcription. These results reveal a previously unknown transcription initiation mechanism involving AEP and a role for SL1 as a TBP-loading factor in RNAP2-dependent gene activation.
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PMID:AF4 uses the SL1 components of RNAP1 machinery to initiate MLL fusion- and AEP-dependent transcription. 2659 43

MLL fusions are leukemogenic transcription factors that enhance transcriptional elongation through modification of chromatin and RNA Pol II. Global transcription rates and chromatin changes accompanying the transformation process induced by MLL-ENL were monitored by nascent RNA-seq and ChIP-seq, revealing 165 direct target genes separated into two distinct clades. ME5 genes bound MLL-ENL at the promoter, relied on DOT1L-mediated histone methylation, and coded preferentially for transcription factors, including many homeobox genes. A distinct ME3 group accumulated MLL-ENL beyond the termination site, was dependent on P-TEFb-mediated phosphorylation of RNA Pol II for transcription, and translated mainly into proteins involved in RNA biology and ribosome assembly. This dichotomy was reflected by a differential sensitivity toward small molecule inhibitors, suggesting the possibility of a combinatorial strategy for treatment of MLL-induced leukemia.
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PMID:Leukemogenic MLL-ENL Fusions Induce Alternative Chromatin States to Drive a Functionally Dichotomous Group of Target Genes. 2705 May 21

Polycomb group (PcG) repress, whereas Trithorax group (TrxG) activate transcription for tissue development and cellular proliferation, and misregulation of these factors is often associated with cancer. ENL (MLLT1) and AF9 (MLLT3) are fusion partners of Mixed Lineage Leukemia (MLL), TrxG proteins, and are factors in Super Elongation Complex (SEC). SEC controls transcriptional elongation to release RNA polymerase II, paused around transcription start site. In MLL rearranged leukemia, several components of SEC have been found as MLL-fusion partners and the control of transcriptional elongation is misregulated leading to tumorigenesis in MLL-SEC fused Leukemia. It has been suggested that unexpected collaboration of ENL/AF9-MLL and PcG are involved in tumorigenesis in leukemia. Recently, we found that the collaboration of ENL/AF9 and PcG led to a novel mechanism of transcriptional switch from elongation to repression under ATM-signaling for genome integrity. Activated ATM phosphorylates ENL/AF9 in SEC, and the phosphorylated ENL/AF9 binds BMI1 and RING1B, a heterodimeric E3-ubiquitin-ligase complex in Polycomb Repressive complex 1 (PRC1), and recruits PRC1 at transcriptional elongation sites to rapidly repress transcription. The ENL/AF9 in SEC- and PcG-mediated transcriptional repression promotes DSB repair near transcription sites. The implication of this is that the collaboration of ENL/AF9 in SEC and PcG ensures a rapid response of transcriptional switching from elongation to repression to neighboring genotoxic stresses for DSB repair. Therefore, these results suggested that the collaboration of ENL/AF9 and PcG in transcriptional control is required to maintain genome integrity and may be link to the MLL-ENL/AF9 leukemia.
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PMID:Collaboration of MLLT1/ENL, Polycomb and ATM for transcription and genome integrity. 2731 Mar 6

Gene rearrangement of the mixed lineage leukemia (MLL) gene causes leukemia by inducing the constitutive expression of a gene subset normally expressed only in the immature haematopoietic progenitor cells. MLL gene rearrangements often generate fusion products of MLL and a component of the AF4 family/ENL family/P-TEFb (AEP) complex. MLL-AEP fusion proteins have the potential of constitutively recruiting the P-TEFb elongation complex. Thus, it is hypothesized that relieving the promoter proximal pausing of RNA polymerase II is the rate-limiting step of MLL fusion-dependent transcription. AEP also has the potential to recruit the mediator complex via MED26. We recently showed that AEP activates transcription initiation by facilitating TBP loading to the TATA element through the SL1 complex. In the present study, we show that the key activity responsible for the oncogenic property of MLL-AEP fusion proteins is the TBP loading activity, and not the mediator recruitment or transcriptional elongation activities. Thus, we propose that TBP loading by AF4 through SL1 is the major rate-limiting step in MLL fusion-dependent transcription.
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PMID:TBP loading by AF4 through SL1 is the major rate-limiting step in MLL fusion-dependent transcription. 2756 29


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