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HDAC7 is a major contributor in the pathogenesis of t(4;11)/MLL-AF4+ infant B-cell acute lymphoblastic leukemia

ABSTRACT: Infants diagnosed of precursor B-cell acute lymphoblastic leukemia (iB-ALL) presenting MLL-AF4 chromosomal rearrangement are at high risk of disease progression into fatal outcome. This specific subtype of pediatric leukemia constitutes a tough challenge in leukemia research, given the difficulties found when trying in vivo modelling. However, the understanding of mechanisms leading to proper lymphocyte generation may become of high utility in gaining deep insight on this malignancy. As we report here, the lack of HDAC7, a key transcriptional regulator in B lymphocyte differentiation, worsens the prognosis of iB-ALL patients. In fact, MLL-AF4+ iB-ALL patients with high expression of HDAC7 display an improved survival, partially mediated by the repression of oncogenes, such as c-MYC, and chemoresistance markers, like the ASNS enzyme. Accordingly, HDAC7 drastically reduces leukemic cells proliferation in MLL-AF4+ iB-ALL through the induction of apoptosis. Moreover, RNA sequencing of HDAC7-overexpressing cells has revealed that HDAC7 alters the genomic profiling of MLL-AF4+ iB-ALL cells towards that of healthy B-cell progenitors. In summary, the findings here reported highlight the role of HDAC7 in predicting prognosis of a lethal subtype of iB-ALL and open new clinical perspectives, since MLL-AF4+ iB-ALL infants would highly benefit from therapeutic options eventually restoring HDAC7 expression.

ORGANISM(S): Homo sapiens

PROVIDER: GSE151793 | GEO | 2021/06/04

REPOSITORIES: GEO

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Project description:The MLL-AF4 fusion gene is a hallmark genomic aberration in high-risk acute lymphoblastic leukemia in infants. Although it is well-established that MLL-AF4 arises pre-natally during human development, its effects on hematopoietic development in utero remains unexplored. We have created a human-specific in vitro system to study early hemato-endothelial development in MLL-AF4-expressing human embryonic stem cells (hESCs). Differentiation and functional studies as well as clonal analyses and gene expression profiling reveal that expression of MLL-AF4 in hESCs has a phenotypic, functional and gene expression impact. It enhances the specification of hemogenic precursors from hESCs and impairs further hematopoietic commitment of these precursors in favour of the endothelial cell fate. Similar to that reported in cord blood CD34+ hematopoietic stem/progenitor cells (HSPCs), MLL-AF4 expression is not sufficient to transform hESC-derived hematopoietic cells in vitro or in vivo, indicating that additional events may be required to initiate leukemogenesis or that embryonic hematopoiesis is not the appropriate human cellular target for MLL-AF4-mediated leukemogenesis. This work illustrates how hESCs can provide unique insights into human development and further our understanding of how leukemic fusion genes known to arise pre-natally regulate human embryonic hematopoietic specification. MLL is involved in transcriptional regulation and most MLL translocations appear to result in increased expression of Hox genes and hematopoietic genes. We therefore assessed the impact of MLL-AF4 expression on the transcriptome of hESCs. Gene expression profiling performed in MLL-AF4 hESCs revealed that MLL-AF4 preferentially activates transcription. 1826 out of the 3001 genes (61%) expressed were up-regulated in MLL-AF4 hESCs. Human ESC samples were collected during the exponential cell growth phase and stabilized in RNA later. 500 ng of each total RNA sample was labelled with Cy3 using the Quick-Amp Labelling kit and hybridized with the Gene Expression Hybridization kit to a Whole Human Genome Oligo Microarray (Agilent Technologies) following the Manufacturer’s instructions. Each cell line was analyzed as independent duplicates. NEO-expressing (empty lentivector) hESC line was used as the baseline.

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HDAC7 is a major contributor in the pathogenesis of t(4;11)/MLL-AF4+ infant B-cell acute lymphoblastic leukemia

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