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The role of reciprocal fusions in MLL-r acute leukemia: studying the chromosomal translocation t(4;11).

ABSTRACT: Leukemia patients bearing the t(4;11)(q21;q23) translocations can be divided into two subgroups: those expressing both reciprocal fusion genes, and those that have only the MLL-AF4 fusion gene. Moreover, a recent study has demonstrated that patients expressing both fusion genes have a better outcome than patients that are expressing the MLL-AF4 fusion protein alone. All this may point to a clonal process where the reciprocal fusion gene AF4-MLL could be lost during disease progression, as this loss may select for a more aggressive type of leukemia. Therefore, we were interested in unraveling the decisive role of the AF4-MLL fusion protein at an early timepoint of disease development. We designed an experimental model system where the MLL-AF4 fusion protein was constitutively expressed, while an inducible AF4-MLL fusion gene was induced for only 48 h. Subsequently, we investigated genome-wide changes by RNA- and ATAC-Seq experiments at distinct timepoints. These analyses revealed that the expression of AF4-MLL for only 48 h was sufficient to significantly change the genomic landscape (transcription and chromatin) even on a longer time scale. Thus, we have to conclude that the AF4-MLL fusion protein works through a hit-and-run mechanism, probably necessary to set up pre-leukemic conditions, but being dispensable for later disease progression.

SUBMITTER: Wilhelm A

PROVIDER: S-EPMC8530991 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Rearrangement of the mixed lineage leukemia (MLL; also known as lysine methyltransferase 2A) gene is a recurrent genomic aberration in acute myeloid leukemia (AML). MLLT3, super elongation complex subunit (AF9) is one of the most common MLL fusion partners in AML. The present study aimed to explore the aberrant expression of genes associated with the MLL‑AF9 translocation and identified potential new targets for the therapy of AML with MLL‑AF9 translocation. The transcriptomic and epigenetic datasets were downloaded from National Center of Biotechnology Information Gene Expression Omnibus (GEO) database. Differentially expressed genes were obtained from two independent datasets (GSE68643 and GSE73457). Gene Ontology biological process and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis was performed using the Database for Annotation, Visualization and Integrated Discovery. MLL‑AF9‑associated chromatin immunoprecipitation sequencing (ChIP‑Seq) data was analyzed and identified binding sites for MLL‑AF9 and wild type MLL (MLL WT). The ChIP‑Seq of histone modification data was downloaded from the GEO database, including histone 3 lysine 4 trimethylation (H3K4me3), histone 3 lysine 79 dimethylation (H3K79me2) and histone 3 lysine 27 acetylation (H3K27ac), was used for comparing histone modification marks between the MLL‑AF9 leukemia cells and normal hematopoietic cells at MLL‑AF9 and MLL WT binding sites. The differentially expressed genes with the same trend in H3K79me2, H3K27ac and H3K4me3 alteration were identified as potential MLL‑AF9 direct target genes. Upon validation using RNA‑Seq data from the Therapeutically Applicable Research to Generate Effective Treatments AML project, eight potential direct target genes of MLL‑AF9 were identified and further confirmed in MLL‑AF9 mouse model using reverse transcription‑quantitative polymerase chain reaction. These genes may have a critical role in AML with MLL‑AF9 translocation.

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The role of reciprocal fusions in MLL-r acute leukemia: studying the chromosomal translocation t(4;11).

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