Project description:Pre-leukemic mutations are thought to promote clonal expansion of hematopoietic stem cells (HSCs) by increasing self-renewal and competitiveness. However, mutations that increase HSC proliferation tend to reduce competitiveness and self-renewal potential, raising the question of how a mutant HSC can sustainably outcompete wild-type HSCs. Activating mutations in NRAS are prevalent in human myeloproliferative disease and leukemia. Here we show that a single allele of oncogenic NrasG12D increases HSC proliferation but also increases reconstituting and self-renewal potential upon serial transplantation in irradiated mice, all without immortalizing HSCs or causing leukemia in our experiments. NrasG12D also confers long-term self-renewal potential upon multipotent progenitors. To explore the mechanism by which NrasG12D promotes HSC proliferation and self-renewal we assessed HSC cell cycle kinetics using H2B-GFP label retention. We found that NrasG12D had a bimodal effect on HSCs, increasing the proliferation of some HSCs while increasing the quiescence and competitiveness of other HSCs. One signal can therefore increase HSC proliferation, competitiveness, and self-renewal through a bimodal effect that promotes proliferation in some HSCs and quiescence in others. 12 RNA samples from mouse bone marrows were analyzed. There are three biological replicates for each subtype.
Project description:Pre-leukemic mutations are thought to promote clonal expansion of hematopoietic stem cells (HSCs) by increasing self-renewal and competitiveness. However, mutations that increase HSC proliferation tend to reduce competitiveness and self-renewal potential, raising the question of how a mutant HSC can sustainably outcompete wild-type HSCs. Activating mutations in NRAS are prevalent in human myeloproliferative disease and leukemia. Here we show that a single allele of oncogenic NrasG12D increases HSC proliferation but also increases reconstituting and self-renewal potential upon serial transplantation in irradiated mice, all without immortalizing HSCs or causing leukemia in our experiments. NrasG12D also confers long-term self-renewal potential upon multipotent progenitors. To explore the mechanism by which NrasG12D promotes HSC proliferation and self-renewal we assessed HSC cell cycle kinetics using H2B-GFP label retention. We found that NrasG12D had a bimodal effect on HSCs, increasing the proliferation of some HSCs while increasing the quiescence and competitiveness of other HSCs. One signal can therefore increase HSC proliferation, competitiveness, and self-renewal through a bimodal effect that promotes proliferation in some HSCs and quiescence in others.
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: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.
Project description:Ionizing radiation (IR) has long been associated with reduced hematopoietic function and increased malignancies, although the mechanisms behind this relationship remain poorly understood. The carcinogenic effect of IR has been commonly attributed to the direct induction of DNA damage. We demonstrate that IR exposure results in long-term, somatically heritable, cell-intrinsic reductions in HSC self-renewal that is mediated by C/EBP? and reversed by Notch, both of which are associated with human leukemias. Remarkably, restoration of HSC self-renewal prevents selection for C/EBP? loss of function in previously irradiated HSC pools. We propose that environmental insults prompt HSC to initiate a program limiting their self-renewal to prevent damaged HSC from contributing to hematopoiesis. This "programmed mediocrity" is advantageous for the localized insults animals have evolved to deal with, but becomes tumor promoting when the entire HSC compartment is damaged, such as during total body irradiation, by increasing selective pressure for adaptive oncogenic mutations Examination of mRNA levels in in vitro and in vivo Hematopoietic Stem Cell that exposed to IR Ionizing radiation (IR) or control. Each group has three replicates.
Project description:Polycomb group (PcG) proteins play important roles in hematopoietic stem cell (HSC) self-renewal. Mel18 and Bmi1 are homologs of the PCGF subunit within the Polycomb repressive complex 1 (PRC1). Bmi1 (PCGF4) enhances HSC self-renewal and promotes terminal differentiation. However, the role of Mel18 (PCGF2) in hematopoiesis is not fully understood and how Mel18 regulates gene transcription in HSCs remains elusive. We found that acute deletion of Mel18 in the hematopoietic compartment significantly increased the frequency of functional HSCs in the bone marrow. Furthermore, we demonstrate that Mel18 inhibits HSC self-renewal and proliferation. RNA-seq studies revealed that HSC self-renewal and proliferation gene signatures are enriched in Mel18-/- hematopoietic stem and progenitors (HSPCs) compared to Mel18+/+ HSPCs. Notably, ATAC-seq revealed increased chromatin accessibility at genes important for HSC self-renewal, whereas CUT&RUN showed decreased enrichment of H2AK119ub1 at genes important for proliferation, leading to increased expression of both Hoxb4 and Cdk4 in Mel18-/- HSPCs. Furthermore, leukemia stem cells and several types of acute leukemia gene signatures are enriched in Mel18-/- HSCs compared to WT HSCs. Thus, we demonstrate that Mel18 inhibits hematopoietic stem cell self-renewal through repressing the transcription of genes important for HSC self-renewal and proliferation.
Project description:Polycomb group (PcG) proteins play important roles in hematopoietic stem cell (HSC) self-renewal. Mel18 and Bmi1 are homologs of the PCGF subunit within the Polycomb repressive complex 1 (PRC1). Bmi1 (PCGF4) enhances HSC self-renewal and promotes terminal differentiation. However, the role of Mel18 (PCGF2) in hematopoiesis is not fully understood and how Mel18 regulates gene transcription in HSCs remains elusive. We found that acute deletion of Mel18 in the hematopoietic compartment significantly increased the frequency of functional HSCs in the bone marrow. Furthermore, we demonstrate that Mel18 inhibits HSC self-renewal and proliferation. RNA-seq studies revealed that HSC self-renewal and proliferation gene signatures are enriched in Mel18-/- hematopoietic stem and progenitors (HSPCs) compared to Mel18+/+ HSPCs. Notably, ATAC-seq revealed increased chromatin accessibility at genes important for HSC self-renewal, whereas CUT&RUN showed decreased enrichment of H2AK119ub1 at genes important for proliferation, leading to increased expression of both Hoxb4 and Cdk4 in Mel18-/- HSPCs. Furthermore, leukemia stem cells and several types of acute leukemia gene signatures are enriched in Mel18-/- HSCs compared to WT HSCs. Thus, we demonstrate that Mel18 inhibits hematopoietic stem cell self-renewal through repressing the transcription of genes important for HSC self-renewal and proliferation.
Project description:Polycomb group (PcG) proteins play important roles in hematopoietic stem cell (HSC) self-renewal. Mel18 and Bmi1 are homologs of the PCGF subunit within the Polycomb repressive complex 1 (PRC1). Bmi1 (PCGF4) enhances HSC self-renewal and promotes terminal differentiation. However, the role of Mel18 (PCGF2) in hematopoiesis is not fully understood and how Mel18 regulates gene transcription in HSCs remains elusive. We found that acute deletion of Mel18 in the hematopoietic compartment significantly increased the frequency of functional HSCs in the bone marrow. Furthermore, we demonstrate that Mel18 inhibits HSC self-renewal and proliferation. RNA-seq studies revealed that HSC self-renewal and proliferation gene signatures are enriched in Mel18-/- hematopoietic stem and progenitors (HSPCs) compared to Mel18+/+ HSPCs. Notably, ATAC-seq revealed increased chromatin accessibility at genes important for HSC self-renewal, whereas CUT&RUN showed decreased enrichment of H2AK119ub1 at genes important for proliferation, leading to increased expression of both Hoxb4 and Cdk4 in Mel18-/- HSPCs. Furthermore, leukemia stem cells and several types of acute leukemia gene signatures are enriched in Mel18-/- HSCs compared to WT HSCs. Thus, we demonstrate that Mel18 inhibits hematopoietic stem cell self-renewal through repressing the transcription of genes important for HSC self-renewal and proliferation.
Project description:Polycomb group (PcG) proteins play important roles in hematopoietic stem cell (HSC) self-renewal. Mel18 and Bmi1 are homologs of the PCGF subunit within the Polycomb repressive complex 1 (PRC1). Bmi1 (PCGF4) enhances HSC self-renewal and promotes terminal differentiation. However, the role of Mel18 (PCGF2) in hematopoiesis is not fully understood and how Mel18 regulates gene transcription in HSCs remains elusive. We found that acute deletion of Mel18 in the hematopoietic compartment significantly increased the frequency of functional HSCs in the bone marrow. Furthermore, we demonstrate that Mel18 inhibits HSC self-renewal and proliferation. RNA-seq studies revealed that HSC self-renewal and proliferation gene signatures are enriched in Mel18-/- hematopoietic stem and progenitors (HSPCs) compared to Mel18+/+ HSPCs. Notably, ATAC-seq revealed increased chromatin accessibility at genes important for HSC self-renewal, whereas CUT&RUN showed decreased enrichment of H2AK119ub1 at genes important for proliferation, leading to increased expression of both Hoxb4 and Cdk4 in Mel18-/- HSPCs. Furthermore, leukemia stem cells and several types of acute leukemia gene signatures are enriched in Mel18-/- HSCs compared to WT HSCs. Thus, we demonstrate that Mel18 inhibits hematopoietic stem cell self-renewal through repressing the transcription of genes important for HSC self-renewal and proliferation.