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: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.
Project description:Oncogenic NRAS mutations are frequently identified in human myeloid leukemias. In mice, expression of endogenous oncogenic Nras (NrasG12D/+) in hematopoietic cells leads to expansion of myeloid progenitors, increased long-term reconstitution of bone marrow cells, and a chronic myeloproliferative neoplasm (MPN). However, acute expression of NrasG12D/+ in a pure C57BL/6 background does not induce hyperactivated GM-CSF signaling or increased proliferation in myeloid progenitors. It is thus unclear how NrasG12D/+ signaling promotes leukemogenesis. Here we show that hematopoietic stem cells (HSCs) expressing NrasG12D/+ serve as MPN initiating cells. They undergo moderate hyperproliferation with increased self-renewal. The aberrant NrasG12D/+ HSC function is associated with hyperactivation of ERK1/2 in HSCs. Conversely, downregulation of MEK/ERK by pharmacological and genetic approaches attenuates the cycling of NrasG12D/+ HSCs and prevents the expansion of NrasG12D/+ HSCs and myeloid progenitors. Our data delineate critical mechanisms of oncogenic Nras signaling in HSC function and leukemogenesis. three NrasG12D/G12D HSCs samples, three NrasG12D/+ HSCs samples, two Nras+/+ HSCs control samples.
Project description:Our study disclosed previously unrecognized heterogeneity in fetal liver (FL) hematopoietic stem cells (HSC), highlighting biosynthetic dormancy as a key to symmetric self-renewal of engraftable HSC and supports recent studies demonstrating distinct developmental origins for multipotent progenitors and HSC in definitive hematopoiesis.
