Initiation of MLL-rearranged AML is orchestrated by C/EBPa
Ontology highlight
ABSTRACT: Acute Myeloid Leukemia (AML) is associated with a number of genetic and epigenetic events that result in malignant transformation of hematopoietic cells. In particular, transcription factors essential for normal hematopoiesis and stem cell function are often found mutated leading to the formation of leukemic stem cells and the accumulation of immature blasts. Among them, translocations involving the mixed lineage leukemia (MLL) gene at chromosome band 11q23 are one of the most commonly events (~10 %) and is associated with poor prognosis in human leukemias. Whereas the downstream effects of MLL-fusion proteins are well established, the modes on which these effects are mediated are still unclear and whether MLL-fusion proteins are dependent on other transcriptional regulators or act alone remains elusive. To investigate this we searched gene expression profiles from patients with MLL-rearranged AML compared with normal hematopoietic progenitor cells for transcriptional regulators and found targets of C/EBPα to be up-regulated in the AML samples, suggesting that C/EBPα might collaborate with MLL-fusion proteins in the initial transformation process. We could show that transformation by MLL-fusion proteins is dependent on C/EBPα activity both in early progenitors as well as in GMPs. In contrast, C/EBPα was found to be indispensable in an already established leukemia. These finding led us to study the early transcriptional changes induced by MLL-ENL expression and we identified a combined C/EBPα / MLL-ENL transcriptional signature. Collectivly, our data shows that C/EBPα configure a proper chromatin state required for MLL-fusions to induce malignant transformation. Histone modification profiles (H3K4me3 and H3K27me3) in haematopoietic progenitor cells (preGM, wild type and Cebpa knock out), and C/EBPα binding in GMP cells
Project description:Translocations involving the MLL genes are frequently found in Acute Myeloid Leukemia (AML) and are associated with poor prognosis. The MLL fusion proteins act as aberrant transcription factor activating a transcriptional program that transforms the cells, potentially through collaboration with other transcription factors. To investigate this we searched gene expression profiles from patients with MLL-rearranged AML compared with normal hematopoietic progenitor cells for transcriptional regulators and found targets of C/EBPα to be up-regulated in the AML samples, suggesting that C/EBPα might collaborate with MLL fusion proteins in the initial transformation process. We could show that transformation by MLL fusion proteins is dependent on C/EBPα activity both in early progenitors as well as in GMPs. In contrast, C/EBPα was found to be indispensable in an already established leukemia. These results suggest that C/EBPα play an important role in the early transforming event of leukemogenesis. We used microarray to study the early transcriptional changes induced by MLL-ENL expression and we identified a combined C/EBPα / MLL-ENL transcriptional signature. 3 Cebpaflox/flox;Mx1Cre and 3 Cebpaflox/flox;Mx1Cre- mice were sacrificed 14 days after pIpC injection and bone marrow cells were harvested, enriched for cKit-expression and transduced with a pMIG retroviral vector expressing the MLL-ENL fusion protein and GFP. 72 h post first transduction, GFP-positive or negative PreGM cells were sorted.
Project description:Acute Myeloid Leukemia (AML) is associated with a number of genetic and epigenetic events that result in malignant transformation of hematopoietic cells. In particular, transcription factors essential for normal hematopoiesis and stem cell function are often found mutated leading to the formation of leukemic stem cells and the accumulation of immature blasts. Among them, translocations involving the mixed lineage leukemia (MLL) gene at chromosome band 11q23 are one of the most commonly events (~10 %) and is associated with poor prognosis in human leukemias. Whereas the downstream effects of MLL-fusion proteins are well established, the modes on which these effects are mediated are still unclear and whether MLL-fusion proteins are dependent on other transcriptional regulators or act alone remains elusive. To investigate this we searched gene expression profiles from patients with MLL-rearranged AML compared with normal hematopoietic progenitor cells for transcriptional regulators and found targets of C/EBPα to be up-regulated in the AML samples, suggesting that C/EBPα might collaborate with MLL-fusion proteins in the initial transformation process. We could show that transformation by MLL-fusion proteins is dependent on C/EBPα activity both in early progenitors as well as in GMPs. In contrast, C/EBPα was found to be indispensable in an already established leukemia. These finding led us to study the early transcriptional changes induced by MLL-ENL expression and we identified a combined C/EBPα / MLL-ENL transcriptional signature. Collectivly, our data shows that C/EBPα configure a proper chromatin state required for MLL-fusions to induce malignant transformation.
Project description:Translocations involving the MLL genes are frequently found in Acute Myeloid Leukemia (AML) and are associated with poor prognosis. The MLL fusion proteins act as aberrant transcription factor activating a transcriptional program that transforms the cells, potentially through collaboration with other transcription factors. To investigate this we searched gene expression profiles from patients with MLL-rearranged AML compared with normal hematopoietic progenitor cells for transcriptional regulators and found targets of C/EBPα to be up-regulated in the AML samples, suggesting that C/EBPα might collaborate with MLL fusion proteins in the initial transformation process. We could show that transformation by MLL fusion proteins is dependent on C/EBPα activity both in early progenitors as well as in GMPs. In contrast, C/EBPα was found to be indispensable in an already established leukemia. These results suggest that C/EBPα play an important role in the early transforming event of leukemogenesis. We used microarray to study the early transcriptional changes induced by MLL-ENL expression and we identified a combined C/EBPα / MLL-ENL transcriptional signature.
Project description:Infant and adult MLL-rearranged (MLLr) leukemia represents a disease with few treatment options and a dismal prognosis. Here, we present an in-depth proteomic characterization of in utero-initiated and adult-onset MLLr leukemia in a mouse model of MLL-ENL-mediated leukemogenesis. We characterize early proteomic events of MLL-ENL-mediated transformation in fetal and adult progenitors.
Project description:The purpose of this study is to investigate the transcriptional programs as it relates to disease latency initiated by different MLL fusion proteins, including: MLL-AF1p, MLL-AF6, MLL-Gas7, MLL-AF9 and MLL-ENL. Leukemia cell lines were established by transforming kit+ mouse bone marrow cells with retroviruses coding MLL-AF1p, MLL-AF6, MLL-Gas7, MLL-AF9 or MLL-ENL. At early phase after the cell lines were established, cells growing at exponential phase (cell density at 0.5~1x106/ml) were harvested for RNA extraction and sequencing purpose. Sequencing is performed on total RNA isolated from mouse leukemia cell lines generated from kit+ mouse bone marrow cells transduced with various MLL fusion proteins and is compared to control total RNA isolated from kit+ mouse bone marrow cells.
Project description:ZNF521 is a multiple zinc finger transcription factor previously identified because abundantly and selectively expressed in normal CD34+ hematopoietic stem and progenitor cells. From microarray datasets, aberrant expression of ZNF521 has been reported in both pediatric and adult acute myeloid leukemia (AML) patients with MLL gene rearrangements. However, a proper validation of microarray data is lacking, likewise ZNF521 contribution in MLL-rearranged AML is still uncertain. In this study, we show that ZNF521 is significantly upregulated in MLL translocated AML patients from a large pediatric cohort, regardless of the type of MLL translocations such as MLL-AF9, MLL-ENL, MLL-AF10 and MLL-AF6 fusion genes. Our in vitro functional studies demonstrate that ZNF521 play a critical role in the maintenance of the undifferentiated state of MLL-rearranged cells. Furthermore, analysis of the ZNF521 gene promoter region shows that ZNF521 is a direct downstream target of both MLL-AF9 and MLL-ENL fusion proteins. Gene expression profiling of MLL-AF9-rearranged THP-1 cells after depletion of ZNF521 reveals correlation with several expression signatures including stem cell-like and MLL fusion dependent programs. These data suggest that MLL fusion proteins activate ZNF521 expression to maintain the undifferentiated state and contribute to leukemogenesis. ZNF521 is required to block differentiation in MLL-rearranged AML cells
Project description:MLL-fusions represent a large group of leukemia drivers, whose diversity originates from the vast molecular heterogeneity of C-terminal fusion partners of MLL protein. While studies of selected MLL-fusions have revealed critical molecular pathways, unifying mechanisms across all MLL-fusions remain poorly understood. We present the first comprehensive survey of protein-protein interactions of seven distantly related MLL-fusion proteins: MLL-AF1p, MLL-AF4, MLL-AF9, MLL-CBP, MLL-EEN, MLL-ENL and MLL-GAS7.
Project description:MLL-rearrangements (MLL-r) are recurrent genetic events in acute myeloid leukemia (AML) and frequently associate with poor prognosis. In infants, MLL-r have been suggested to be sufficient to drive transformation. However, despite the prenatal origin of MLL-r, the incidence of congenital leukemia is very low with transformation usually occurring postnatally. The influence of prenatal signals on leukemogenesis, such as those mediated by the fetal-specific RNA binding protein LIN28B, remains controversial. Here, using a dual-transgenic mouse model that co-express MLL-ENL and LIN28B, we investigated the impact of LIN28B on AML. We show that LIN28B impedes the progression of MLL-r AML through a compromised leukemia initiating cell activity and a suppression of MYB signaling. Mechanistically, rather than involving the well-studied Lin28B-let7 miR axis, we found that LIN28B directly bound MYBBP1A mRNA, a co-repressor of MYB, and that positively correlated with MYBBP1A protein levels. Overexpression of MYBBP1A in MLL-ENL driven leukemogenesis largely phenocopied the tumor suppressor effects of LIN28B. Thereby, our work proposes that the developmentally-restricted expression of LIN28B during fetal development provides a protection against MYB-dependent AML.
Project description:MLL encodes a histone methyltransferase that is critical in maintaining gene expression during embryonic development and hematopoiesis. 11q23 translocations encode chimeric MLL fusions that act as potent drivers of acute leukemia. However, it remains unclear what portion of the leukemic genome is under the direct control of the MLL fusion protein. By comparing patient-derived leukemic cell lines, we find that MLL fusion-bound genes are a small subset of that recognized by wild-type MLL. In an inducible MLL-ENL cellular model, binding of the MLL fusion protein and changes in H3K79 methylation are limited to a specific portion of the genome, whereas wild-type MLL distributes to a much larger set of gene loci. Surprisingly, among 223 MLL fusion-bound genes, only 12 demonstrate a significant increase in mRNA expression upon induction of the fusion protein. In addition to Hoxa9 and Meis1, this includes Eya1 and Six1 which comprise a heterodimeric transcription factor important in several developmental pathways. We show that Eya1 has the capacity to immortalize hematopoietic progenitor cells in vitro and collaborates with Six1 in hematopoietic transformation assays. Altogether, our data suggest that MLL fusions contribute to the development of acute leukemia through direct activation of a small set of target genes. We explored an inducible MLL-ENL cellular model, which was obtained from Dr. Robert Slany (University Erlangen, Germany). We wished to examine the differential expressed genes that are bound by MLL wild type (No 4-OHT) and fusion (4-OHT) proteins, combinding the ChIP-chip data to explore the potential MLL fusion-regulated genes.
Project description:The purpose of this study is to investigate the transcriptional programs as it relates to disease latency initiated by different MLL fusion proteins, including: MLL-AF1p, MLL-AF6, MLL-Gas7, MLL-AF9 and MLL-ENL. Leukemia cell lines were established by transforming kit+ mouse bone marrow cells with retroviruses coding MLL-AF1p, MLL-AF6, MLL-Gas7, MLL-AF9 or MLL-ENL. At early phase after the cell lines were established, cells growing at exponential phase (cell density at 0.5~1x106/ml) were harvested for RNA extraction and sequencing purpose.