Search

The histone lysine acetyltransferase KAT6B (MYST4, MORF, QKF) is the target of recurrent chromosomal translocations causing hematological malignancies with poor prognosis. Using Kat6b germline deletion and overexpression in mice, we determined the role of KAT6B in the hematopoietic system. We found that KAT6B sustained the fetal hematopoietic stem cell pool but did not affect viability or differentiation. KAT6B was essential for normal levels of histone H3 lysine 9 (H3K9) acetylation but not for a previously proposed target, H3K23. Compound heterozygosity of Kat6b and the closely related gene, Kat6a, abolished hematopoietic reconstitution after transplantation. KAT6B and KAT6A cooperatively promoted transcription of genes regulating hematopoiesis, including the Hoxa cluster, Pbx1, Meis1, Gata family, Erg, and Flt3. In conclusion, we identified the hematopoietic processes requiring Kat6b and showed that KAT6B and KAT6A synergistically promoted HSC development, function, and transcription. Our findings are pertinent to current clinical trials testing KAT6A/B inhibitors as cancer therapeutics., Competing Interests: Declaration of interests T.T. and A.K.V. are inventors on patent WO2016198507 A1. The Thomas and Voss laboratories received research funding from the CRC for Cancer Therapeutics (CTx), Australia. T.T. and A.K.V. have received payments from a distribution of licensing income from Pfizer and have served on an advisory board for Pfizer., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

The hematopoietically expressed homeobox transcription factor (Hhex) is important for the maturation of definitive hematopoietic progenitors and B-cells during development. We have recently shown that in adult hematopoiesis, Hhex is dispensable for maintenance of hematopoietic stem cells (HSCs) and myeloid lineages but essential for the commitment of common lymphoid progenitors (CLPs) to lymphoid lineages. Here, we show that during serial bone marrow transplantation, Hhex-deleted HSCs are progressively lost, revealing an intrinsic defect in HSC self-renewal. Moreover, Hhex-deleted mice show markedly impaired hematopoietic recovery following myeloablation, due to a failure of progenitor expansion. In vitro, Hhex-null blast colonies were incapable of replating, implying a specific requirement for Hhex in immature progenitors. Transcriptome analysis of Hhex-null Lin - Sca + Kit + cells showed that Hhex deletion leads to derepression of polycomb repressive complex 2 (PRC2) and PRC1 target genes, including the Cdkn2a locus encoding the tumor suppressors p16 Ink 4 a and p19 Arf . Indeed, loss of Cdkn2a restored the capacity of Hhex-null blast colonies to generate myeloid progenitors in vitro, as well as hematopoietic reconstitution following myeloablation in vivo. Thus, HSCs require Hhex to promote PRC2-mediated Cdkn2a repression to enable continued self-renewal and response to hematopoietic stress. Stem Cells 2017;35:1948-1957., (© 2017 AlphaMed Press.)

Upon ligand binding, RIPK1 is recruited to tumor necrosis factor receptor superfamily (TNFRSF) and Toll-like receptor (TLR) complexes promoting prosurvival and inflammatory signaling. RIPK1 also directly regulates caspase-8-mediated apoptosis or, if caspase-8 activity is blocked, RIPK3-MLKL-dependent necroptosis. We show that C57BL/6 Ripk1(-/-) mice die at birth of systemic inflammation that was not transferable by the hematopoietic compartment. However, Ripk1(-/-) progenitors failed to engraft lethally irradiated hosts properly. Blocking TNF reversed this defect in emergency hematopoiesis but, surprisingly, Tnfr1 deficiency did not prevent inflammation in Ripk1(-/-) neonates. Deletion of Ripk3 or Mlkl, but not Casp8, prevented extracellular release of the necroptotic DAMP, IL-33, and reduced Myd88-dependent inflammation. Reduced inflammation in the Ripk1(-/-)Ripk3(-/-), Ripk1(-/-)Mlkl(-/-), and Ripk1(-/-)Myd88(-/-) mice prevented neonatal lethality, but only Ripk1(-/-)Ripk3(-/-)Casp8(-/-) mice survived past weaning. These results reveal a key function for RIPK1 in inhibiting necroptosis and, thereby, a role in limiting, not only promoting, inflammation., (Copyright © 2014 Elsevier Inc. All rights reserved.)

There are only three known stimuli for eosinophil formation-GM-CSF, interleukin-5 (IL-5), and IL-3. Because mice with inactivation of the gene encoding the common beta receptor chain for GM-CSF, IL-5, and IL-3 (betac(-/-) mice) cannot respond to GM-CSF or IL-5 and do not produce IL-3, they should lack eosinophils. However, they produce reduced numbers of eosinophils, indicating the existence of at least one additional stimulatory factor. Use of betac(-/-) mouse marrow cells failed to detect a novel eosinophil-stimulating factor in cell line- or organ-conditioned media, but stem cell factor (SCF) was found to have a previously unrecognized ability to stimulate the formation of eosinophil colonies or mixed neutrophil-eosinophil colonies. This action of SCF was also observable with marrow cells from other mouse strains and was enhanced by the addition of G-CSF but no other factor tested. Recloning of SCF-stimulated blast colonies showed that progenitors forming pure eosinophil or mixed neutrophil-eosinophil colonies can have a common ancestor but many appear to arise independently from different preprogenitor cells. The observed activity of SCF in marrow cultures was relatively weak, but its action may be stronger in vivo, and SCF needs to be added to GM-CSF, IL-5, and IL-3 in the list of cytokines able to stimulate eosinophil formation.

Mice with homozygous inactivation of the gene encoding the suppressor of cytokine signaling-1 (SOCS-1) protein die within 21 days of birth with low body weight, fatty degeneration and necrosis of the liver, infiltration of the lung, pancreas, heart and skin by macrophages and granulocytes and a profound depletion of T- and B-lymphocytes. In the present study, SOCS-1 -/- mice were found to have a moderate neutrophilia, and reduced platelet and hematocrit levels. Replacement of the SOCS-1 gene by a lac-Z reporter gene allowed documentation by FACS sorting that at least a proportion of granulocyte-macrophage progenitor cells transcribe SOCS-1. Most hematopoietic progenitor cell frequencies were normal in -/- marrow as were the size and cellular content of colonies formed by -/- progenitor cells in response to various stimulating factors. However, there was an increased frequency of macrophage progenitor cells in -/- mice and, abnormally, one quarter of all progenitor cells were located in the liver. Progenitor cells from -/- mice were hyper-responsive to stimulation by GM-CSF but not by M-CSF or Multi-CSF (IL-3). Progenitor cells from -/- mice were also hypersensitive to inhibition by interferon-gamma (IFN-gamma), the degree of inhibition varying markedly with the stimulating factor used. The suppressive effects of IFN-gamma therefore appear to involve interactions with particular growth factor-initiated signals in -/- cells--interactions that are strongly modulated by the action of the SOCS-1 protein.

Double transgenic mice were produced by mating granulocyte-macrophage colony-stimulation factor (GM-CSF) transgenic mice with max 41 transgenic mice that exhibit excess granulopoiesis and a predisposition to thymic lymphoma development. Although only two-thirds of the double transgenic mice had elevated circulating GM-CSF levels, double transgenic mice maintained significantly higher blood granulocytes and monocytes and more extreme granulopoietic hypercellularity in the marrow and spleen than max 41 transgenic mice. In double transgenic mice, early death occurred from the GM-CSF transgenic syndrome. Because of these early deaths, the incidence of thymic and generalized lymphomas was artificially lower than in max 41 mice but those lymphomas that did develop occurred earlier than in max 41 mice. While the excess GM-CSF levels in double transgenic mice stimulated increased granulocyte and monocyte formation and peritoneal dendritic cells were excessive, this failed to prevent the spontaneous development of T lymphomas, suggesting that dendritic cell-initiated suppression of tumor development may not be effective with this type of tumor.

Two types of blast colonies can be stimulated to develop in semisolid agar cultures of murine bone marrow cells. Typically. these are either multicentric colonies stimulated by stem cell factor (SCF) plus interleukin-6 (IL-6) or dispersed colonies stimulated by Flt3 ligand (FL) plus IL-6. Both types of blast colony-forming cells (BL-CFC5) can generate large numbers of lineage-committed granulocyte-macrophage progenitor cells and exhibit some capacity for self-generation and the formation of eosinophil and megakaryocyte progenitor cells. However, the two populations of BL-CFCs are largely distinct and partially separable by fluorescence-activated cell sorting and are distinguished by differing capacity to form granulocyte-committed progeny. Both types of BL-CFC5 can generate dendritic cells and small numbers of lymphocytes but the FL-responsive BL-CFCs have a greater capacity to form both B and I lymphocytes. Both types of blast colonies offer remarkable opportunities to analyze multilineage commitment at a clonal level in vitro [ABSTRACT FROM AUTHOR]