ABSTRACT: Enforcement of stem-cell dormancy by nucleophosmin mutation is a critical determinant of unrestricted self-renewal during myeloid leukemogenesis
Project description:Mutation in nucleophosmin (NPM1) causes relocalization of this normally nucleolar protein to the cytoplasm (NPM1c+). Despite NPM1 mutation being the most common driver mutation in cytogenetically normal adult acute myeloid leukemia (AML), the mechanisms of NPM1c+-induced leukemogenesis remain unclear. Caspase-2 is a pro-apoptotic protein activated by NPM1 in the nucleolus. Here, we show that caspase-2 is also activated by NPM1c+ in the cytoplasm and DNA damage-induced apoptosis is caspase-2-dependent in NPM1c+ but not in NPM1wt AML cells. Strikingly, in NPM1c+ cells, caspase-2 loss results in profound cell cycle arrest, differentiation, and down-regulation of stem cell pathways that regulate pluripotency including impairment in the AKT/mTORC1 and Wnt signaling pathways, and inhibition of Rictor cleavage. In contrast, there were minimal differences in proliferation, differentiation, or the transcriptional profile of NPM1wt cells lacking caspase-2. Our results show that caspase-2 is essential for proliferation and self-renewal of AML cells expressing mutated NPM1. This study demonstrates that caspase-2 is a major effector of NPM1c+ function.
Project description:Down syndrome (DS) confers a 20-fold increased risk of B cell acute lymphoblastic leukemia (ALL), yet the mechanisms underlying this association are undefined. We show that triplication of only 31 genes orthologous to the putative DS Critical Region (DSCR) on chr.21q22 is sufficient to promote B cell-autonomous self-renewal, in vivo maturation defects and leukemogenesis in concert with BCR-ABL. DSCR triplication results in histone H3 lysine 27 (H3K27) hypomethylation at gene promoters and a transcriptional signature characterized by de-repression of genes targeted by polycomb repressor complex 2 (PRC2), which methylates H3K27. The same signature is highly enriched among human DS-associated ALLs. Pharmacologic inhibition of PRC2 function is sufficient to confer self-renewal in wild-type B cells while inhibition of H3K27me3 demethylases completely blocks self-renewal induced by DSCR triplication. Finally, overexpression of the DSCR factor HMGN1, a nucleosome remodeling protein that suppresses H3K27me3, is necessary for self-renewal in B cells with DSCR triplication. Gene expression analysis of 6 samples, 3 wild-type and 3 Ts1Rhr proB cells at passage 1
Project description:NUDT15 encodes nucleotide triphosphate diphosphatase that is responsible for metabolizing purine analog drugs, and its genetic mutation results in severe side effects from thiopurine therapy. However, the functions of Nudt15 in leukemic stem cells (LSCs) and hematopoietic stem cells (HSCs) remain unknown. Here we reveal the Nudt15-regulating self-renewal of both mouse LSCs and HSCs. Our data show that Nudt15 negatively regulates murine leukemogenesis and its deficiency prolongs the survival of murine AML recipients by impairing LSC self-renewal, while Nudt15 ablation markedly enhances mouse HSC regenerative potential and self-renewal. Mechanistically, Nudt15 modulates inflammatory signaling in mouse LSCs and HSCs, leading to divergent self-renewal outcomes. Nudt15 depletion inhibits mouse LSC self-renewal by downregulating Ifi30, resulting in elevating intracellular ROS levels. Gata2, a key regulator, is required for Nudt15-mediating inflammatory signaling in mouse HSCs. Collectively, our results present new crucial roles of Nudt15 in maintaining the functions of mouse LSC and HSC through inflammatory signaling and have a new insight into clinical implications.
Project description:Loss of GADD45A expression is implicated in poor patient outcomes in acute myeloid leukemia (AML) but its role in leukemia stem cells (LSCs) and disease pathogenesis remains largely unknown. Here we report that GADD45A loss is a critical determinant of high self-renewal potential and knockout of GADD45A supports long-term self-renewal and promotes LSC quiescence, accompanied by the acquisition of an increasingly aggressive phenotype upon serial transplantation in mice. The enhanced LSC characteristics are associated with GADD45A deletion-induced increase in key WNT/self-renewal-related genes. GADD45A knockout promotes engraftment of patient-derived xenograft (PDX) of relapsed AML in mice. Single cell RNA-seq on primary LSCs of AML PDXs and subsequent functional studies show that low expression of GADD45A, an important sensor of oxidative stress, confers ferroptosis resistance through upregulation of genes involved in detoxification of excess iron and reactive oxygen species (ROS), revealing a mechanism of drug resistance in primary AML with unfavorable cytogenetics.
Project description:Down syndrome (DS) confers a 20-fold increased risk of B cell acute lymphoblastic leukemia (ALL), yet the mechanisms underlying this association are undefined. We show that triplication of only 31 genes orthologous to the putative DS Critical Region (DSCR) on chr.21q22 is sufficient to promote B cell-autonomous self-renewal, in vivo maturation defects and leukemogenesis in concert with BCR-ABL. DSCR triplication results in histone H3 lysine 27 (H3K27) hypomethylation at gene promoters and a transcriptional signature characterized by de-repression of genes targeted by polycomb repressor complex 2 (PRC2), which methylates H3K27. The same signature is highly enriched among human DS-associated ALLs. Pharmacologic inhibition of PRC2 function is sufficient to confer self-renewal in wild-type B cells while inhibition of H3K27me3 demethylases completely blocks self-renewal induced by DSCR triplication. Finally, overexpression of the DSCR factor HMGN1, a nucleosome remodeling protein that suppresses H3K27me3, is necessary for self-renewal in B cells with DSCR triplication.
Project description:Leukemogenesis requires enhanced self-renewal activity, which is induced by specific oncogenes. The underlying molecular mechanisms remain incompletely understood. We transduced mouse lineage negative bone marrow cells (enriched for hematopoietic stem and progenitor cells) with retrovirus expressing leukemic oncogene AML1-ETO9a, MYC and MLL-AF9 as well as empty vector (MIG). We found that all three oncogenes enhanced snoRNA formation. High abundance of snoRNAs was observed in primary human AML specimens with the notable exception of NPM1 mutant AML. Leukemogenesis by AML1-ETO required expression of the groucho related Amino Enhancer of Split (AES). AES functioned by inducing snoRNA/RNP formation via interaction with the RNA helicase DDX21. Similarly, loss of C/D box snoRNAs with concomitant loss of rRNA 2’-O-methylation resulted in decreased leukemia self-renewal potential.In summary, we identified C/D box snoRNAs and rRNA 2’-O-methylation as critical determinants of leukemic stem cell activity.
