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Event: 1253

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

MLL chromosomal translocation

Short name

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MLL translocation

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Biological Context

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Level of Biological Organization
Cellular

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place. For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable. For individual/population events, the organ context is not applicable. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Cell term
embryonic cell

Organ term

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor). Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Process	Object	Action
Translocation, Genetic		occurrence

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help

AOP Name	Role of event in AOP	Point of Contact	Author Status	OECD Status
topoisomerase II binding, infant leukaemia	KeyEvent	Andrea Terron (send email)	Open for comment. Do not cite	WPHA/WNT Endorsed

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Term	Scientific Term	Evidence	Link
mammals	mammals	High	NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Sex Applicability

An indication of the the relevant sex for this KE. More help

Term	Evidence
Mixed	High

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

Chromosomal rearrangements of the mixed-lineage leukaemia (MLL) gene, located on the q23 band of chromosome 11 (11q23), are the genetic hallmark of most infant leukaemias (Meyer et al 2013; Sanjuan-Pla et al 2015). MLL is located within the fragile site FRA11G; chromosomal fragile sites are regions of the genome susceptible to breakage under conditions of replication stress; interference with TopoII may promote fragile site instability. MLL encodes a protein homologous to the Drosophila trithorax gene, which has relevant functions in embryogenesis and hematopoiesis (Ernest et al 2004, Hess et al 1997).

MLL, a human homologue of the epigenetic transcriptional regulator Trithorax of Drosophila, is an upstream transcriptional effector of HOX genes. The importance of normal MLL protein for normal axial-skeletal developmental process and HOX gene regulation has been demonstrated in the embryos of heterozygous and homozygous MLL knockout and MLL truncation mutant mice. Furthermore, expression of MLL protein is not necessary for turning on transcription of certain HOX genes, but for the maintenance of their transcription. Experiments in vitro using hematopoietic progenitors from embryos of homozygous MLL knockout mice or mice with MLL mutant showed that MLL was also critical for hematopoietic development. Recent findings suggested that MLL is required during embryogenesis for the specification or expansion of hematopoietic stem cells. As HOX genes also play a key role in the regulation of hematopoietic development, the hematopoietic dysfunction of MLL null cells is likely to be attributed to deregulated patterns of HOX gene expression in hematopoietic stem cells or progenitors. This link between MLL, HOX gene regulation, and hematopoiesis is of particular importance (Li et al. 2005).

There are many translocation and fusion partners for MLL; DNA breakage within MLL can lead to rearrangement with over 120 partner genes (Meyer et al 2013).

MLL protein (complexed with a large number of other protein factors) serves as a transcriptional activator or repressor via the binding to promoter regions of active genes, marking these regions by covalent histone modifications (Sanjuan-Pla et al 2015). Translocation and creation of fusion genes and products destroys the intrinsic control mechanisms of the MLL protein. The resulting ‘ectopic’ functions involve promoter hyper-activation and re-acquiring stem cell features (Sanjuan-Pla et al 2015). A schematic presentation of the drastic changes of the MLL product is depicted in the figure below.

Proposed model for the oncogenic conversion of MLL fusion: A. Physiological situation and B: . A chromosomal translocation, which leads to the intrinsic regulatory mechanism of MLL being destroyed. (Sanjuan-Pla et al. 2015).

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

MLL rearrangements can be identified following different methods. It is worthnoting that different methods will give a different information detail.

Split-signal FISH: The split-signal FISH approach uses two differentially labeled probes, located in one gene at opposite sites of the breakpoint region. Probe sets were developed for the genes TCF3 (E2A) at 19p13, MLL at 11q23, ETV6 at 12p13, BCR at 22q11, SIL-TAL1 at 1q32 and TLX3 (HOX11L2) at 5q35. In normal karyotypes, two colocalized green/red signals are visible, but a translocation results in a split of one of the colocalized signals. Split-signal FISH has three main advantages over the classical fusion-signal FISH approach, which uses two labeled probes located in two genes. First, the detection of a chromosome aberration is independent of the involved partner gene. Second, split-signal FISH allows the identification of the partner gene or chromosome region if metaphase spreads are present, and finally it reduces false-positivity (Van der Burg et al, 2004).
RT-PCR in combination with long-distance inverse PCR (LDI-PCR) performed on isolated genomic DNA. This method allows the identification of any kind of MLL rearrangement if located within the breakpoint cluster region. The method uses LDI-PCR to identify MLL translocations independent of the involved partner gene or other MLL aberrations that occurred within the MLL breakpoint cluster region. This method allows high-throughput analyses because genomic MLL fusion sequences can be obtained with a minimum of only four PCR reactions. Moreover, this method requires only small quantities of genomic patient DNA (1 μg) and provides relevant genetic information that can be used directly for quantitative minimal residual disease (MRD) analyses (Meyer et al. 2005).

Assays measuring chromosomal aberrations, micronuclei or DNA and chromosome damage (Comet assay) may indirectly identify the KE through its consequences in experimental systems in vitro and in vivo. FISH staining is however necessary for identification of MLL translocations.

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided). More help

Although the KE deals with the general process of DNA integrity, the available evidence do not allow for evaluating whether any significant difference occurs among cell types or species. It has been shown that the mouse has an analogous fusion gene mll-af4. A recent study has shown that in utero exposure to etoposide induces mll translocations in Atm-knockout mice, which are defective in the DNA damage response, albeit not in wild-type mice; moreover, fetal liver hematopoietic stem cells were more susceptible to etoposide than maternal bone marrow mononuclear cells, pointing out the life stage-related susceptibility in regards to TopoII “poison” also in the mouse (Nanya et al., 2015).

MLL-AF4 fusion gene is present and expressed in bone marrow mesenchymal stem cells in infant patients with t(4;11) B cell-ALL (Menendez et al. 2009). However, other paediatric B cell-ALL-specific translocations/gene fusions were never found in this cell population. This suggests that the origin of the fusion gene in infant B cell-ALL is likely prehaematopoietic. Consequently, the target cell for transformation may be an early prehaematopoietic mesodermal precursor, a haematopoietic stem cell or a haematopoietic progenitor cell residing mainly in the liver (Greaves et al. 2015; sanjuan-Pla et al. 2015).

References

List of the literature that was cited for this KE description. More help

Ernest P, Fisher JK, Avery W, Sade S, Foy D, Korsmeyer SJ. Definitive hematopoiesis requires the mixed-lineage leukemia gene. Dev Cell 2004; 6: 437-443.

Ford AM, Ridge SA, Cabrera ME, Mahmoud H, Steel CM, Chan LC, et al. In utero rearrangements in the trithorax-related oncogene in infant leukaemias. Nature. 1993; 363(6427):358–60. doi: 10.1038/363358a0

Gale KB, Ford AM, Repp R, Borkhardt A, Keller C, Eden OB, et al. Backtracking leukemia to birth: identification of clonotypic gene fusion sequences in neonatal blood spots. Proc Natl Acad Sci USA. 1997; 94(25):13950–4.

Greaves M. When one mutation is all it takes. Cancer Cell. 2015; 27(4): 433-434.

Hess JL, Yu BD, Li B, Hanson RD, Korsmeyer SJ, Defect in yolk sac hematopoiesis in mll-null embryos. Blood 1997; 90: 1799-1806.

Jansen MW, Corral L, van der Velden VH, Panzer-Grumayer R, Schrappe M, Schrauder A et al. Immunobiological diversity in infant acute lymphoblastic leukemiais related to the occurence and type of MLL rearrangment. Leukemia 2007; 21(4): 633-641.

Z-Y Li, D-P Liu and C-C Liang. 2005. New insight into the molecular mechanisms of MLL-associated leukemia. Leukemia (2005) 19, 183–190. doi:10.1038/sj.leu.2403602 Published online 16 December 2004.

Menendez P, Catalina P, Rodriguez R, Melen GJ, Bueno C, Arriero M, Garcia-Sanchez F, Lassaletta A, Garcia-Sanz R, Garcia-Castro J. Bone marrow mesenchymal stem cells from infants with MLL-AF4+ acute leukemia harbor and express the MLL-AF4 fusion gene. J Exp Med. 2009 Dec 21;206(13):3131-41. doi: 10.1084/jem.20091050.

Meyer C, Hofmann J, Burmeister T, et al. The MLL recombinome of acute leukemias in 2013. Leukemia 2013;27(11):2165-2176.

Meyer Claus, Bjoern Schneider, Martin Reichel, Sieglinde Angermueller, Sabine Strehl, Susanne Schnittger,Claudia Schoch, Mieke W. J. C. Jansen, Jacques J. van Dongen, Rob Pieters, Oskar A. Haas, Theo Dingermann,Thomas Klingebiel,and Rolf Marschalek. 2005. Diagnostic tool for the identification of MLL rearrangements including unknown partner genes. Proc Natl Acad Sci U S A. 2005 Jan 11; 102(2): 449–454.Published online 2004 Dec 30. doi: 10.1073/pnas.0406994102 PMCID: PMC544299 Medical Sciences

Nanya M, Sato M, Tanimoto K, Tozuka M, Mizutani S, Takagi M (2015) Dysregulation of the DNA Damage Response and KMT2A Rearrangement in Fetal Liver Hematopoietic Cells.PLoS ONE 10(12): e0144540. doi:10.1371/journal. pone.0144540

Sam TN, Kersey JH, Linabery AM, Johnson KJ, Heerema NA, Hilden JM, et al. MLL gene rearrangements in infant leukaemia vary with age at diagnosis and selected demographic factors: a Children’s Oncology Group (COG) study. Pediatr Blood cancer. 2012; 58 (6): 836-839.

Sanjuan-Pla A, Bueno C, Prieto C, Acha P, Stam RW, Marschalek R, Menendez P. Revisiting the biology of infant t(4;11)/MLL-AF4+ B-cell acute lymphoblastic leukemia. Blood. 2015; 126(25): 2676-2685 DOI 10.1182/blood-2015-09-667378.

M van der Burg, T S Poulsen, S P Hunger, H B Beverloo, E M E Smit, K Vang-Nielsen, A W Langerak and J J M van Dongen. 2004. Split-signal FISH for detection of chromosome aberrations in acute lymphoblastic leukemia. Leukemia (2004) 18, 895–908. doi:10.1038/sj.leu.2403340 Published online 25 March 2004.