Differential impact of Ink4a and Arf on hematopoietic stem cells and their bone marrow microenvironment in Bmi1-deficient mice

The polycomb group (PcG) protein Bmi1 plays an essential role in the self-renewal of hematopoietic and neural stem cells. Derepression of the Ink4a/Arf gene locus has been largely attributed to Bmi1-deficient phenotypes in the nervous system. However, its role in hematopoietic stem cell (HSC) self-renewal remained undetermined. In this study, we show that derepressed p16Ink4a and p19Arf in Bmi1-deficient mice were tightly associated with a loss of self-renewing HSCs. The deletion of both Ink4a and Arf genes substantially restored the self-renewal capacity of Bmi1−/− HSCs. Thus, Bmi1 regulates HSCs by acting as a critical failsafe against the p16Ink4a- and p19Arf-dependent premature loss of HSCs. We further identified a novel role for Bmi1 in the organization of a functional bone marrow (BM) microenvironment. The BM microenvironment in Bmi1−/− mice appeared severely defective in supporting hematopoiesis. The deletion of both Ink4a and Arf genes did not considerably restore the impaired BM microenvironment, leading to a sustained postnatal HSC depletion in Bmi1−/−Ink4a-Arf−/− mice. Our findings unveil a differential role of derepressed Ink4a and Arf on HSCs and their BM microenvironment in Bmi1-deficient mice. Collectively, Bmi1 regulates self-renewing HSCs in both cell-autonomous and nonautonomous manners

Low toxicity of a conditioning with 8-Gy total body irradiation, fludarabine and cyclophosphamide as preparative regimen for allogeneic hematopoietic stem cell transplantation in pediatric hematological malignancies

The definitive version is available at www.blackwell-synergy.comWe here report the efficacy and toxicity of a conditioning regimen with fractionated 8-Gy TBI, fludarabine, and cyclophosphamide in allogeneic HSCT for pediatric hematological malignancies. Among 22 children who received related or unrelated HSCT, nine were transplanted with refractory disease and/or from HLA two or more loci-mismatched family donors. None of the patients developed graft failure. The Seattle grading system revealed that 18 patients had no RRT, and the remaining patients had grade I gastrointestinal toxicity alone. The estimated overall survival and leukemia-free survival at two yr were 57.1% and 48.0%, respectively, in 10 patients with acute lymphoblastic leukemia; 91.7% and 71.3%, respectively, in 12 patients with myeloid leukemia. The incidence of TRM was 4.8% at two yr. The rates of RRT above grade II and TRM in an 8-Gy TBI-containing regimen were significantly lower than the data of historical control patients who underwent 12-Gy TBI and cyclophosphamide with or without etoposide. The intermediate-dose TBI-based conditioning regimen may confer successful engraftment combined with minimized RRT, although its efficacy should be further evaluated.ArticlePEDIATRIC TRANSPLANTATION. 13(6):737-745 (2009)journal articl

Expression of nephronectin is inhibited by oncostatin M via both JAK/STAT and MAPK pathways

AbstractNephronectin (Npnt), also called POEM, is an extracellular matrix protein considered to play critical roles as an adhesion molecule in the development and functions of various tissues, such as the kidneys, liver, and bones. In the present study, we examined the molecular mechanism of Npnt gene expression and found that oncostatin M (OSM) strongly inhibited Npnt mRNA expression in MC3T3-E1 cells from a mouse osteoblastic cell line. OSM also induced a decrease in Npnt expression in both time- and dose-dependent manners via both the JAK/STAT and MAPK pathways. In addition, OSM-induced inhibition of osteoblast differentiation was recovered by over-expression of Npnt. These results suggest that OSM inhibits Npnt expression via the JAK/STAT and MAPK pathways, while down-regulation of Npnt by OSM influences inhibition of osteoblast differentiation

Regulation of the MDM2-P53 pathway and tumor growth by PICT1 via nucleolar RPL11

PICT1 (also known as GLTSCR2) is considered a tumor suppressor because it stabilizes phosphatase and tensin homolog (PTEN), but individuals with oligodendrogliomas lacking chromosome 19q13, where PICT1 is located, have better prognoses than other oligodendroglioma patients. To clarify the function of PICT1, we generated Pict1-deficient mice and embryonic stem (ES) cells. Pict1 is a nucleolar protein essential for embryogenesis and ES cell survival. Even without DNA damage, Pict1 loss led to p53-dependent arrest of cell cycle phase G1 and apoptosis. Pict1-deficient cells accumulated p53, owing to impaired Mdm2 function. Pict1 binds Rpl11, and Rpl11 is released from nucleoli in the absence of Pict1. In Pict1-deficient cells, increased binding of Rpl11 to Mdm2 blocks Mdm2-mediated ubiquitination of p53. In human cancer, individuals whose tumors express less PICT1 have better prognoses. When PICT1 is depleted in tumor cells with intact P53 signaling, the cells grow more slowly and accumulate P53. Thus, PICT1 is a potent regulator of the MDM2-P53 pathway and promotes tumor progression by retaining RPL11 in the nucleolu

How Do Telomere Abnormalities Regulate the Biology of Neuroblastoma?

Telomere maintenance plays important roles in genome stability and cell proliferation. Tumor cells acquire replicative immortality by activating a telomere-maintenance mechanism (TMM), either telomerase, a reverse transcriptase, or the alternative lengthening of telomeres (ALT) mechanism. Recent advances in the genetic and molecular characterization of TMM revealed that telomerase activation and ALT define distinct neuroblastoma (NB) subgroups with adverse outcomes, and represent promising therapeutic targets in high-risk neuroblastoma (HRNB), an aggressive childhood solid tumor that accounts for 15% of all pediatric-cancer deaths. Patients with HRNB frequently present with widely metastatic disease, with tumors harboring recurrent genetic aberrations (MYCN amplification, TERT rearrangements, and ATRX mutations), which are mutually exclusive and capable of promoting TMM. This review provides recent insights into our understanding of TMM in NB tumors, and highlights emerging therapeutic strategies as potential treatments for telomerase- and ALT-positive tumors

Enhancer of zeste homolog 2 regulates cell differentiation and proliferation in neuroblastoma

BACKGROUND Neuroblastoma  (NB)  is  one  of  the  most  common  extracranial  solid  tumors occurring in infancy and childhood with highly variable outcomes. Polycomb group (PcG) proteins are epigenetic gene silencers. Enhancer of zeste homolog 2 (EZH2) is a member of the polycomb repressor complex 2 (PRC2) group, with  the  main  function  to  catalyze  the  polycomb  repressor  complex  by methylating lysine 9 and 27 of histone H3. This study aimed to investigate the biological functionality of EZH2 in NB.   METHODS This was an experimental study with an analysis of correlation initially of the known prognostic factors of NB patients’ outcomes, by comparing the expression of v-myc avian myelocytomatosis viral oncogene neuroblastoma (MYCN) with that of EZH2, on the basis of the patients’ overall and relapse free survival rates. This was followed with a biological functional study to assess the role of EZH2 expression in NB.   RESULTS EZH2 knockdown induces neurite extension and differentiation marker growth associated  protein  43  (GAP43)  in  NB  cells,  although  it  does  not  affect  cell cycle. By ectopic expression of EZH2, all-trans retinoic acid (ATRA) inducedneurite extension was suppressed and GAP43 was decreased. Overall, EZH2 seems to have an important role in NB cell differentiation. Although EZH2 did not alter cell proliferation, in the soft agar colony formation assay there was a significant increase in total colony number and number of large colonies.   CONCLUSION Our  result  clarified  the  potential  role  of  EZH2  in  the  regulation  of  cell differentiation and proliferation, which subsequently may play an important role in the poor prognosis of NB patients

The Role of XRCC4 in Sensitizing Human Colon Cancer Stem-Like Cells to X-ray or Carbon Ion Beam

Inactivation of XRCC4 is associated with various human carcinogenesis. Here we report expression changes of cancer stem-like cell markers in XRCC4 deficient human colon cancer cells after X-ray or carbon ion beam. FACS analysis showed that the percentage of CD133+, CD44+ and ESA+ cells in HCT116-WT cells were 3.2%, 6.8%, and 7.2%, whereas 1.6%, 19.2% and 20% in HCT116-XRCC4 KO cells. The proportion of CD133+ and CD44+ cells was increased 3 to 4-fold after 2 Gy X-ray irradiation in HCT116-WT cells, in comparison, 4 to 6- fold increment of CD133+ and CD44+ cells was induced in HCT116-XRCC4 KO cells. There was no change in proportion of ESA+ cells in HCT116-WT cells, but 10-fold enhancement of ESA+ cells was induced in HCT116-XRCC4 KO cells after 2 Gy X-ray irradiation. Colony and spheroid formation from CD133+, CD44+/ESA+ cells were higher compared to CD133-, CD44-/ESA- cells in HCT116-XRCC4 KO cells, but extremely decreased compared to HCT116-WT cells. In conclusion, expression of cancer stem-like cell markers significantly increased after X-ray irradiation in XRCC4 deficient cells, suggesting that XRCC4 may be involved in cancer cell stemness.54th Annual Meeting of ASTR