Haruko Shima

Regulation of the HIF-1α Level Is Essential for Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) are sustained in a specific microenvironment known as the stem cell niche. Mammalian HSCs are kept quiescent in the endosteal niche, a hypoxic zone of the bone marrow (BM). In this study, we show that normal HSCs maintain intracellular hypoxia and stabilize hypoxia-inducible factor-1alpha (HIF-1alpha) protein. In HIF-1alpha-deficient mice, the HSCs lost their cell cycle quiescence and HSC numbers decreased during various stress settings including bone marrow transplantation, myelosuppression, or aging, in a p16(Ink4a)/p19(Arf)-dependent manner. Overstabilization of HIF-1alpha by biallelic loss of an E3 ubiquitin ligase for HIF-1alpha (VHL) induced cell cycle quiescence in HSCs and their progenitors but resulted in an impairment in transplantation capacity. In contrast, monoallelic loss of VHL induced cell cycle quiescence and improved BM engraftment during bone marrow transplantation. These data indicate that HSCs maintain cell cycle quiescence through the precise regulation of HIF-1alpha levels.

PU.1-mediated upregulation of CSF1R is crucial for leukemia stem cell potential induced by MOZ-TIF2

Leukemias and other cancers possess self-renewing stem cells that help to maintain the cancer. Cancer stem cell eradication is thought to be crucial for successful anticancer therapy. Using an acute myeloid leukemia (AML) model induced by the leukemia-associated monocytic leukemia zinc finger (MOZ)-TIF2 fusion protein, we show here that AML can be cured by the ablation of leukemia stem cells. The MOZ fusion proteins MOZ-TIF2 and MOZ-CBP interacted with the transcription factor PU.1 to stimulate the expression of macrophage colony–stimulating factor receptor (CSF1R, also known as M-CSFR, c-FMS or CD115). Studies using PU.1-deficient mice showed that PU.1 is essential for the ability of MOZ-TIF2 to establish and maintain AML stem cells. Cells expressing high amounts of CSF1R (CSF1Rhigh cells), but not those expressing low amounts of CSF1R (CSF1Rlow cells), showed potent leukemia-initiating activity. Using transgenic mice expressing a drug-inducible suicide gene controlled by the CSF1R promoter, we cured AML by ablation of CSF1Rhigh cells. Moreover, induction of AML was suppressed in CSF1R-deficient mice and CSF1R inhibitors slowed the progression of MOZ-TIF2–induced leukemia. Thus, in this subtype of AML, leukemia stem cells are contained within the CSF1Rhigh cell population, and we suggest that targeting of PU.1-mediated upregulation of CSF1R expression might be a useful therapeutic approach.

Distinct Impact of Imatinib on Growth at Prepubertal and Pubertal Ages of Children with Chronic Myeloid Leukemia

OBJECTIVE To determine the extent of growth impairment resulting from imatinib treatment in children with chronic myeloid leukemia (CML). STUDY DESIGN Clinical records of 48 chronic-phase CML children administered imatinib as the first-line therapy between 2001 and 2006 were analyzed retrospectively. Cumulative change in height was assessed using the height height-SDS and converted height data from age- and sex-adjusted Japanese norms. RESULTS A decrease in height-SDS was observed in 72.9% of children, with a median maximum reduction in height-SDS of 0.61 during imatinib treatment. Median follow-up time was 34 months (range, 10-88 months). Growth impairment was seen predominantly in children who started imatinib at a prepubertal age compared with those who started at pubertal age. Growth velocity tended to recuperate in prepubertal children with growth impairment, as they reached pubertal age, suggesting that imatinib had little impact on growth during puberty. CONCLUSIONS Growth impairment was a major adverse effect of long-term imatinib treatment in children with CML. We report the distinct inhibitory effect of imatinib on growth in prepubertal and pubertal children with CML. We should be aware of growth deceleration in children, especially in young children given imatinib before puberty and subjected to prolonged exposure.

Reconstitution activity of hypoxic cultured human cord blood CD34-positive cells in NOG mice

Hematopoietic stem cells (HSCs) reside in hypoxic areas of the bone marrow. However, the role of hypoxia in the maintenance of HSCs has not been fully characterized. We performed xenotransplantation of human cord blood cells cultured in hypoxic or normoxic conditions into adult NOD/SCID/IL-2Rgamma(null) (NOG) mice. Hypoxic culture (1% O(2)) for 6 days efficiently supported the maintenance of HSCs, although cell proliferation was suppressed compared to the normoxic culture. In contrast, hypoxia did not affect in vitro colony-forming ability. Upregulation of a cell cycle inhibitor, p21, was observed in hypoxic culture. Immunohistochemical analysis of recipient bone marrow revealed that engrafted CD34(+)CD38(-) cord blood HSCs were hypoxic. Taken together, these results demonstrate the significance of hypoxia in the maintenance of quiescent human cord blood HSCs.

Differences in voriconazole trough plasma concentrations per oral dosages between children younger and older than 3 years of age

The relationship between trough plasma concentrations and daily doses of voriconazole was retrospectively analyzed in ≤18‐year‐old children because optimal oral voriconazole dosages for children, especially <2 years of age, is unknown. We demonstrated that the relationship changed around the age of 3 years, and that children <3 years of age required higher optimal daily doses with greater variations compared with those for older children, resulting in complicated optimal dose adjustments. Therefore, plasma concentration monitoring and individual dose adjustments are recommended for optimal and less toxic voriconazole treatments, especially for <3‐year‐old children, although additional studies are needed to validate this approach. Pediatr Blood Cancer 2010;54:1050–1052

Acquisition of G0 state by CD34-positive cord blood cells after bone marrow transplantation

OBJECTIVE Hematopoietic stem cells are kept in a quiescent state in the hypoxic area of the bone marrow, which is essential for hematopoietic stem cell maintenance. However, when and how hematopoietic stem cells acquire their hypoxic state and maintain quiescence has not been fully elucidated. The aim of this study was to understand this process in human hematopoietic stem cells after bone marrow transplantation. MATERIALS AND METHODS Human CD34-positive cord blood cells were transplanted into nonobese diabetic/severe combined immunodeficient interleukin-2 receptor γ chain knockout mice. Cell cycle and hypoxia assay analyses were performed, to identify changes in the characteristics of human hematopoietic stem cells following transplantation. Quantitative real-time reverse transcription polymerase chain reaction analysis was used to analyze the transcriptional changes accompanying this transition. RESULTS Engrafted primitive lineage-negative CD34-positive CD38-negative cells acquired hypoxic state and quiescence in the recipient bone marrow between 4 and 8 weeks, and between 8 and 12 weeks after transplantation, respectively. During 4 and 8 weeks after transplantation, changes in the transcription levels of G₀ regulatory factors, such as CCNC and RBL1, and stem cell regulators, such as Flt3, were also seen, which may be related to the characteristic changes in the cell cycle or oxygenation state. CONCLUSIONS Behavioral changes of hematopoietic stem cells in their cell cycle and oxygenation state during and after bone marrow engraftment may provide insights into hematopoietic stem cell regulation, mediating the improvement of clinical hematopoietic stem cell transplantation protocols and the eradication of leukemia stem cells.

Protein-Losing Enteropathy Caused by Gastrointestinal Tract–Involved Langerhans Cell Histiocytosis

Protein-losing enteropathy (PLE) is frequently complicated in patients with gastrointestinal tract–involved Langerhans cell histiocytosis (LCH); however, LCH per se is not generally included in the list of diseases that cause PLE. We report here a case of infantile PLE that presented with continuous diarrhea at the onset of LCH. She was initially diagnosed as having allergic gastroenteropathy and, thus, received intravenous prednisolone, which was thought to have induced immunodeficiency and consequently resulted in life-threatening cytomegalovirus-associated hemophagocytic syndrome and disseminated intravascular coagulation. Because chemotherapy for hemophagocytic syndrome was transiently effective for underlying LCH as well, the diagnosis of LCH was delayed until its recurrence. Gastrointestinal tract–involved LCH, a rare but highly fatal disease, should be considered for infants with refractory gastrointestinal symptoms, especially for those with PLE; endoscopic biopsy is strongly recommended for immediate diagnosis.

Bromodomain-PHD finger protein 1 is critical for leukemogenesis associated with MOZ-TIF2 fusion

Chromosomal translocations that involve the monocytic leukemia zinc finger (MOZ) gene are typically associated with human acute myeloid leukemia (AML) and often predict a poor prognosis. Overexpression of HOXA9, HOXA10, and MEIS1 was observed in AML patients with MOZ fusions. To assess the functional role of HOX upregulation in leukemogenesis by MOZ–TIF2, we focused on bromodomain-PHD finger protein 1 (BRPF1), a component of the MOZ complex that carries out histone acetylation for generating and maintaining proper epigenetic programs in hematopoietic cells. Immunoprecipitation analysis showed that MOZ–TIF2 forms a stable complex with BRPF1, and chromatin immunoprecipitation analysis showed that MOZ–TIF2 and BRPF1 interact with HOX genes in MOZ–TIF2-induced AML cells. Depletion of BRPF1 decreased the MOZ localization on HOX genes, resulting in loss of transformation ability induced by MOZ–TIF2. Furthermore, mutant MOZ–TIF2 engineered to lack histone acetyltransferase activity was incapable of deregulating HOX genes as well as initiating leukemia. These data indicate that MOZ–TIF2/BRPF1 complex upregulates HOX genes mediated by MOZ-dependent histone acetylation, leading to the development of leukemia. We suggest that activation of BRPF1/HOX pathway through MOZ HAT activity is critical for MOZ–TIF2 to induce AML.

A case of multisystem Langerhans cell histiocytosis with primary hypothyroidism followed by type 1 diabetes mellitus

We report a case of a 13‐year‐old female with Langerhans cell histiocytosis (LCH) and primary hypothyroidism followed by type 1 diabetes mellitus (DM), both of which are rare complications. In LCH diagnosis, imaging studies showed an enlargement of the thyroid gland, suggesting the involvement of LCH cells. While the pancreas appeared normal, insulin secretion markedly deteriorated 11 months after cessation of chemotherapy. Even without direct pancreatic involvement, there is a possibility that LCH could induce DM as a part of its long‐term complications. In particular, thyroid involvement may be related to the onset of DM. Pediatr Blood Cancer 2009;53:232–234.

Leukostasis in Children and Adolescents with Chronic Myeloid Leukemia: Japanese Pediatric Leukemia/Lymphoma Study Group

The details of leukostasis in children and adolescents with chronic myeloid leukemia (CML) are unknown. This study determined the characteristics of leukostasis in children and adolescents with CML.