Extrahepatic deficiency of transferrin receptor 2 is associated with increased erythropoiesis independent of iron overload.

Transferrin receptor 2 (TFR2) is a transmembrane protein expressed mainly in hepatocytes and in developing erythroid cells and is an important focal point in systemic iron regulation. Loss of TFR2 function results in a rare form of the iron-overload disease hereditary hemochromatosis. Although TFR2 in the liver has been shown to be important for regulating iron homeostasis in the body, TFR2's function in erythroid progenitors remains controversial.

LMTK3 is essential for oncogenic KIT expression in KIT-mutant GIST and melanoma.

Certain cancers, including gastrointestinal stromal tumor (GIST) and subsets of melanoma, are caused by somatic KIT mutations that result in KIT receptor tyrosine kinase constitutive activity, which drives proliferation. The treatment of KIT-mutant GIST has been revolutionized with the advent of KIT-directed cancer therapies. KIT tyrosine kinase inhibitors (TKI) are superior to conventional chemotherapy in their ability to control advanced KIT-mutant disease.

The tumor suppressor phosphatase PP2A-B56α regulates stemness and promotes the initiation of malignancies in a novel murine model.

Protein phosphatase 2A (PP2A) is a ubiquitously expressed Serine-Threonine phosphatase mediating 30-50% of protein phosphatase activity. PP2A functions as a heterotrimeric complex, with the B subunits directing target specificity to regulate the activity of many key pathways that control cellular phenotypes. PP2A-B56α has been shown to play a tumor suppressor role and to negatively control c-MYC stability and activity.

The Corepressor Rcor1 Is Essential for Normal Myeloerythroid Lineage Differentiation.

Based on its physical interactions with histone-modifying enzymes, the transcriptional corepressor Rcor1 has been implicated in the epigenetic regulation blood cell development. Previously, we have demonstrated that Rcor1 is essential for the maturation of definitive erythroid cells and fetal survival. To determine the functional role of Rcor1 in steady-state hematopoiesis in the adult, we used a conditional knockout approach.

The triterpenoid RTA 408 is a robust mitigator of hematopoietic acute radiation syndrome in mice.

Bone marrow suppression due to exposure to ionizing radiation is a significant clinical problem associated with radiation therapy as well as with nonmedical radiation exposure. Currently, there are no small molecule agents available that can enhance hematopoietic regeneration after radiation exposure. Here, we report on the effective mitigation of acute hematopoietic radiation syndrome in mice by the synthetic triterpenoid, RTA 408.

Intestinal microbiota-derived metabolomic blood plasma markers for prior radiation injury.

Purpose: Assessing whole-body radiation injury and absorbed dose is essential for remediation efforts following accidental or deliberate exposure in medical, industrial, military, or terrorist incidents. We hypothesize that variations in specific metabolite concentrations extracted from blood plasma would correlate with whole-body radiation injury and dose.

Methods And Materials: Groups of C57BL/6 mice (n=12 per group) were exposed to 0, 2, 4, 8, and 10.

Corepressor Rcor1 is essential for murine erythropoiesis.

The corepressor Rcor1 has been linked biochemically to hematopoiesis, but its function in vivo remains unknown. We show that mice deleted for Rcor1 are profoundly anemic and die in late gestation. Definitive erythroid cells from mutant mice arrest at the transition from proerythroblast to basophilic erythroblast.

HCMV infection of humanized mice after transplantation of G-CSF-mobilized peripheral blood stem cells from HCMV-seropositive donors.

Human cytomegalovirus (HCMV) infection, including primary infection resulting from transmission from a seropositive donor to a seronegative recipient (D(+)/R(-)), remains a significant problem in the setting of peripheral blood stem cell transplantation (PBSCT). The lack of a suitable animal model for studying HCMV transmission after PBSCT is a major barrier to understanding this process and, consequently, developing novel interventions to prevent HCMV infection. Our previous work demonstrated that human CD34(+) progenitor cell-engrafted NOD-scid IL2Rγc(null) (NSG) mice support latent HCMV infection after direct inoculation and reactivation after treatment with granulocyte colony-stimulating factor.

Endothelial cells mitigate DNA damage and promote the regeneration of hematopoietic stem cells after radiation injury.

Endothelial cells (ECs) are an essential component of the hematopoietic microenvironment, which maintains and regulates hematopoietic stem cells (HSCs). Although ECs can support the regeneration of otherwise lethally-irradiated HSCs, the mechanisms are not well understood. To further understand this phenomenon, we studied HSC regeneration from irradiated bone marrow using co-culture with human aortic ECs (HAECs).

Kinase pathway dependence in primary human leukemias determined by rapid inhibitor screening.

Kinases are dysregulated in most cancers, but the frequency of specific kinase mutations is low, indicating a complex etiology in kinase dysregulation. Here, we report a strategy to rapidly identify functionally important kinase targets, irrespective of the etiology of kinase pathway dysregulation, ultimately enabling a correlation of patient genetic profiles to clinically effective kinase inhibitors. Our methodology assessed the sensitivity of primary leukemia patient samples to a panel of 66 small-molecule kinase inhibitors over 3 days.

Multiplex high-throughput gene mutation analysis in acute myeloid leukemia.

Classification of acute myeloid leukemia increasingly depends on genetic analysis. However, the number of known mutations in acute myeloid leukemia is expanding rapidly. Therefore, we tested a high-throughput screening method for acute myeloid leukemia mutation analysis using a multiplex mass spectrometry-based approach.

A novel human cytomegalovirus locus modulates cell type-specific outcomes of infection.

Clinical strains of HCMV encode 20 putative ORFs within a region of the genome termed ULb' that are postulated to encode functions related to persistence or immune evasion. We have previously identified ULb'-encoded pUL138 as necessary, but not sufficient, for HCMV latency in CD34+ hematopoietic progenitor cells (HPCs) infected in vitro. pUL138 is encoded on polycistronic transcripts that also encode 3 additional proteins, pUL133, pUL135, and pUL136, collectively comprising the UL133-UL138 locus.

Granulocyte-colony stimulating factor reactivates human cytomegalovirus in a latently infected humanized mouse model.

Human cytomegalovirus (HCMV) is a significant cause of morbidity and mortality in organ transplant recipients. The use of granulocyte-colony stimulating factor (G-CSF)-mobilized stem cells from HCMV seropositive donors is suggested to double the risk of late-onset HCMV disease and chronic graft-versus-host disease in recipients when compared to conventional bone marrow transplantation with HCMV seropositive donors, although the etiology of the increased risk is unknown. To understand mechanisms of HCMV transmission in patients receiving G-CSF-mobilized blood products, we generated a NOD-scid IL2Rγ(c)(null)-humanized mouse model in which HCMV establishes latent infection in human hematopoietic cells.

Fancd2-/- mice have hematopoietic defects that can be partially corrected by resveratrol.

Progressive bone marrow failure is a major cause of morbidity and mortality in human Fanconi Anemia patients. In an effort to develop a Fanconi Anemia murine model to study bone marrow failure, we found that Fancd2(-/-) mice have readily measurable hematopoietic defects. Fancd2 deficiency was associated with a significant decline in the size of the c-Kit(+)Sca-1(+)Lineage(-) (KSL) pool and reduced stem cell repopulation and spleen colony-forming capacity.

BMP4 regulates the hematopoietic stem cell niche.

Bone morphogenetic protein 4 (BMP4) is required for mesoderm commitment to the hematopoietic lineage during early embryogenesis. However, deletion of BMP4 is early embryonically lethal and its functional role in definitive hematopoiesis is unknown. Consequently, we used a BMP4 hypomorph to investigate the role of BMP4 in regulating hematopoietic stem cell (HSC) function and maintaining steady-state hematopoiesis in the adult.

Endothelial cells mediate the regeneration of hematopoietic stem cells.

Recent studies suggest that endothelial cells are a critical component of the normal hematopoietic microenvironment. Therefore, we sought to determine whether primary endothelial cells have the capacity to repair damaged hematopoietic stem cells. Highly purified populations of primary CD31(+) microvascular endothelial cells isolated from the brain or lung did not express the pan hematopoietic marker CD45, most hematopoietic lineage markers, or the progenitor marker c-kit and did not give rise to hematopoietic cells in vitro or in vivo.

Apoptosis-stimulating protein of p53 (ASPP2) heterozygous mice are tumor-prone and have attenuated cellular damage-response thresholds.

The expression of ASPP2 (53BP2L), a proapoptotic member of a family of p53-binding proteins, is frequently suppressed in many human cancers. Accumulating evidence suggests that ASPP2 inhibits tumor growth; however, the mechanisms by which ASPP2 suppresses tumor formation remain to be clarified. To study this, we targeted the ASPP2 allele in a mouse by replacing exons 10-17 with a neoR gene.

Hematopoietic stem cells contribute to lymphatic endothelium.

Background: Although the lymphatic system arises as an extension of venous vessels in the embryo, little is known about the role of circulating progenitors in the maintenance or development of lymphatic endothelium. Here, we investigated whether hematopoietic stem cells (HSCs) have the potential to give rise to lymphatic endothelial cells (LEC).

Methodology/principal Findings: Following the transfer of marked HSCs into irradiated recipients, donor-derived LEC that co-express the lymphatic endothelial markers Lyve-1 and VEGFR-3 were identified in several tissues.

Transvection mediated by the translocated cyclin D1 locus in mantle cell lymphoma.

In mantle cell lymphoma (MCL) and some cases of multiple myeloma (MM), cyclin D1 expression is deregulated by chromosome translocations involving the immunoglobulin heavy chain (IgH) locus. To evaluate the mechanisms responsible, gene targeting was used to study long-distance gene regulation. Remarkably, these targeted cell lines lost the translocated chromosome (t(11;14)).

Myeloid lineage progenitors give rise to vascular endothelium.

Despite an important role in vascular development and repair, the origin of endothelial progenitors remains unknown. Accumulating evidence indicates that cells derived from the hematopoietic system participate in angiogenesis. However, the identity and functional role of these cells remain controversial.

Mouse models of hematopoietic engraftment: limitations of transgenic green fluorescent protein strains and a high-performance liquid chromatography approach to analysis of erythroid chimerism.

Transgenic mouse strains ubiquitously expressing green fluorescent protein (GFP) have enabled investigators to develop in vivo transplant models that can detect donor contributions to many different tissues. However, most GFP transgenics lack expression of the reporter in the erythroid lineage. We evaluated expression of GFP in the bone marrow of the OsbY01 transgenic mouse (B6-GFP) in the context of CD71 and TER-119 expression and found that GFP fluorescence is lost prior to the basophilic erythroblast stage of development.

Bone marrow-derived cells fuse with normal and transformed intestinal stem cells.

Transplanted adult bone marrow-derived cells (BMDCs) have been shown to adopt the phenotype and function of several nonhematopoietic cell lineages and promote tumorigenesis. Beyond its cancer enhancing potential, cell fusion has recently emerged as an explanation of how BMDCs regenerate diseased heptocytes, contribute to Purkinje neurons and skeletal and cardiac muscle cells, and participate in skin and heart regeneration. Although bone marrow-derived epithelial cells also have been observed in the intestine, fusion as a mechanism has not been investigated.