Biology subjects

Azazi, D.

Publications and source records attributed to Azazi, D..

4 recordsLinked to original sources

bioRxiv2025

Delayed Trp53 activation protects Dnmt3a-mutant hematopoietic stem cells from inflammatory attrition.

Hematopoietic stem cells (HSCs) accumulate somatic mutations over time, some conferring a fitness advantage that can lead to clonal hematopoiesis (CH). Mutations in DNMT3A, particularly at hotspot R882, are the most prevalent in CH and carry an increased risk of acute myeloid leukemia (AML). Although DNMT3A R882 mutations are linked to global DNA hypomethylation, the mechanisms underlying their selective advantage remain unclear. Here, we show that Dnmt3a-R882H mutant HSCs exhibit resilience under inflammatory and genotoxic stress. During IL-1{beta}-induced emergency granulopoiesis, Dnmt3a R882H/+ HSCs uncouple increased proliferation from stem cell exhaustion. In contrast, wild-type HSCs rapidly progress to terminal differentiation. We link this phenotype to a delayed activation of the p53-p21-DREAM axis, that allows mutant HSCs to avoid attrition, despite increased replication stress. Similarly, mutant HSCs exhibit delayed Trp53 activation following irradiation, but eventually recover a physiological Trp53 response. Analysis of patient data reveals shared phenotypic features between DNMT3A and monoallelic TP53 mutations in CH and myeloid neoplasms, highlighting potential functional similarities. Collectively, these findings suggest that the expansion of DNMT3A-mutant clones is affected by impaired TP53 signaling, which confers resilience against stressors. Therapeutic strategies targeting inflammatory pathways or the p53-p21-DREAM axis may reduce DNMT3A-CH expansion and/or progression and its associated risks.

molecular biology↗

bioRxiv2024

Mutational synergy with CREBBP loss in lymphomagenesis identified through forward insertional mutagenesis in a new DLBCL mouse model

Loss-of-function mutations in the gene encoding the acetyltransferase CREBBP have been reported in numerous cancers but are particularly frequent in lymphoid malignancies. However, the functional significance of CREBBP loss in transformation and disease progression, most likely through cooperation with secondary genetic hits, has not yet been fully unravelled. Similarly, the contribution of the initial cell population sustaining CREBBP loss in the course of disease remains elusive. Here, we developed a new lymphoma mouse model integrating Crebbp loss at various stages of B cell development with a transposon-based insertional mutagenesis system. We demonstrated that Crebbp loss from the HSPC compartment resulted in an aggressive DLBCL-like disease, recapitulating well-characterised histological and molecular features of the human disease, as well as the recently described enhanced CD24 expression. More importantly, we identified candidate genes functionally equivalent to patient mutated genes. Those genes, mainly related to B cell development and cellular signalling, may represent novel therapeutic targets. Overall, this new model provides a powerful resource in which to conduct future mechanistic and therapeutic studies.

cancer biology↗

bioRxiv2022

HOXA9 forms a repressive complex with nuclear matrix-associated protein SAFB to maintain acute myeloid leukemia

HOXA9 is commonly upregulated in acute myeloid leukemia (AML), where it confers poor prognosis. Characterising the protein interactome of endogenous HOXA9 in human AML, we identified a chromatin complex of HOXA9 with the nuclear matrix attachment protein-SAFB. SAFB perturbation phenocopied HOXA9 knockout to decrease AML proliferation, increase differentiation and apoptosis in vitro and prolonged survival in vivo. Integrated genomic, transcriptomic and proteomic analyses further demonstrated that the HOXA9-SAFB-chromatin complex associates with NuRD and HP1{gamma} to repress the expression of factors associated with differentiation and apoptosis, including NOTCH, CEBP{delta}, S100A8, and CDKN1A. Chemical or genetic perturbation of NuRD and HP1{gamma} catalytic activity also triggered differentiation, apoptosis and the induction of these tumor-suppressive genes. Importantly, this mechanism is operative in other HOXA9-dependent AML genotypes. This mechanistic insight demonstrates active HOXA9-dependent differentiation block as a potent mechanism of disease maintenance in AML, that may be amenable to therapeutic intervention via therapies targeting the HOXA9/SAFB interface and/or NuRD and HP1{gamma} activity. Key Points- Identification of the endogenous human HOXA9 protein interactome in AML - HOXA9 forms a repressive complex with S/MAR binding protein (SAFB) that is critical for the maintenance of AML by facilitating proliferation and preventing differentiation and cell death. - The HOXA9/SAFB (H9SB) complex represses gene expression via recruitment of NuRD and HP1{gamma}.

cancer biology↗

bioRxiv2020

Functional signatures of evolutionarily young CTCF binding sites

The introduction of novel CTCF binding sites in gene regulatory regions in the rodent lineage is partly the effect of transposable element expansion. The exact mechanism and functional impact of evolutionarily novel CTCF binding sites are not yet fully understood. We investigated the impact of novel species-specific CTCF binding sites in two Mus genus subspecies, Mus musculus domesticus and Mus musculus castaneus, that diverged 0.5 million years ago. The activity of the B2-B4 family of transposable elements independently in both lineages leads to the proliferation of novel CTCF binding sites. A subset of evolutionarily young sites may harbour transcriptional functionality, as evidenced by the stability of their binding across multiple tissues in M. musculus domesticus (BL6), while overall the distance of species-specific CTCF binding to the nearest transcription start sites and/or topologically-associated domains (TADs) is largely similar to musculus-common CTCF sites. Remarkably, we discovered a recurrent regulatory architecture consisting of a CTCF binding site and an interferon gene that appears to have been tandemly duplicated to create a 15-gene cluster on chromosome 4, thus forming a novel BL6 specific immune locus, in which CTCF may play a regulatory role. Our results demonstrate that thousands of CTCF binding sites show multiple functional signatures rapidly after incorporation into the genome.

genomics↗