技术资料

After DNA replication,sister chromatids must be untangled,or decatenated,before mitosis so that chromatids do not tear during anaphase. Topoisomerase IIalpha (Topo IIalpha) is the major decatenating enzyme. Topo IIalpha inhibitors prevent decatenation,causing cells to arrest during mitosis. Here we report that acute myeloid leukemia cells fail to arrest at the mitotic decatenation checkpoint,and their progression through this checkpoint is regulated by the DNA repair component Metnase (also termed SETMAR). Metnase contains a SET histone methylase and transposase nuclease domain,and is a component of the nonhomologous end-joining DNA double-strand break repair pathway. Metnase interacts with Topo IIalpha and enhances its decatenation activity. Here we show that multiple types of acute leukemia cells have an attenuated mitotic arrest when decatenation is inhibited and that in an acute myeloid leukemia (AML) cell line this is mediated by Metnase. Of further importance,Metnase permits continued proliferation of these AML cells even in the presence of the clinical Topo IIalpha inhibitor VP-16. In vitro,purified Metnase prevents VP-16 inhibition of Topo IIalpha decatenation of tangled DNA. Thus,Metnase expression levels may predict AML resistance to Topo IIalpha inhibitors,and Metnase is a potential therapeutic target for small molecule interference. View Publication

Hematopoiesis during development is a dynamic process,with many factors involved in the emergence and regulation of hematopoietic stem cells (HSCs) and progenitor cells. Whereas previous studies have focused on developmental signaling and transcription factors in embryonic hematopoiesis,the role of well-known adult hematopoietic cytokines in the embryonic hematopoietic system has been largely unexplored. The cytokine interleukin-1 (IL-1),best known for its proinflammatory properties,has radioprotective effects on adult bone marrow HSCs,induces HSC mobilization,and increases HSC proliferation and/or differentiation. Here we examine IL-1 and its possible role in regulating hematopoiesis in the midgestation mouse embryo. We show that IL-1,IL-1 receptors (IL-1Rs),and signaling mediators are expressed in the aorta-gonad-mesonephros (AGM) region during the time when HSCs emerge in this site. IL-1 signaling is functional in the AGM,and the IL-1RI is expressed ventrally in the aortic subregion by some hematopoietic,endothelial,and mesenchymal cells. In vivo analyses of IL-1RI-deficient embryos show an increased myeloid differentiation,concomitant with a slight decrease in AGM HSC activity. Our results suggest that IL-1 is an important homeostatic regulator at the earliest time of HSC development,acting to limit the differentiation of some HSCs along the myeloid lineage. View Publication

The zinc finger protein GATA-1 functions in a concentration-dependent fashion to activate the transcription of erythroid and megakaryocytic genes. Less is understood,however,regarding factors that regulate the GATA-1 gene. Presently elements within intron 1 are shown to markedly affect its erythroid-restricted transcription. Within a full-length 6. 8-kilobase GATA-1 gene construct (G6.8-Luc) the deletion of a central subdomain of intron 1 inhibited transcription textgreater/=10-fold in transiently transfected erythroid SKT6 cells,and likewise inhibited high-level transcription in erythroid FDCW2ER-GATA1 cells. In parental myeloid FDCER cells,however,low-level transcription was largely unaffected by intron 1 deletions. Within intron 1,repeated GATA and Ap1 consensus elements in a central region are described which when linked directly to reporter cassettes promote transcription in erythroid SKT6 and FDCER-GATA1 cells at high rates. Moreover,GATA-1 activated transcription from this subdomain in 293 cells,and in SKT6 cells this subdomain footprinted in vivo. For stably integrated GFP reporter constructs in erythroid SKT6 cells,corroborating results were obtained. Deletion of intronic GATA and Ap1 motifs abrogated the activity of G6.8-pEGFP; activity was decreased by 43 and 56%,respectively,by the deletion of either motif; and the above 1800-base pair region of intron 1 per se was transcribed at rates uniformly greater than G6.8-pEGFP. Also described is the differential utilization of exons 1a and 1b among primary erythromegakaryocytic and myeloid cells. View Publication

PURPOSE: Preclinical in vivo studies can help guide the selection of agents and regimens for clinical testing. However,one of the challenges in screening anticancer therapies is the assessment of off-target human toxicity. There is a need for in vivo models that can simulate efficacy and toxicities of promising therapeutic regimens. For example,hematopoietic cells of human origin are particularly sensitive to a variety of chemotherapeutic regimens,but in vivo models to assess potential toxicities have not been developed. In this study,a xenograft model containing humanized bone marrow is utilized as an in vivo assay to monitor hematotoxicity. EXPERIMENTAL DESIGN: A proof-of-concept,temozolomide-based regimen was developed that inhibits tumor xenograft growth. This regimen was selected for testing because it has been previously shown to cause myelosuppression in mice and humans. The dose-intensive regimen was administered to NOD.Cg-Prkdc(scid)IL2rg(tm1Wjl)/Sz (NOD/SCID/γchain(null)),reconstituted with human hematopoietic cells,and the impact of treatment on human hematopoiesis was evaluated. RESULTS: The dose-intensive regimen resulted in significant decreases in growth of human glioblastoma xenografts. When this regimen was administered to mice containing humanized bone marrow,flow cytometric analyses indicated that the human bone marrow cells were significantly more sensitive to treatment than the murine bone marrow cells and that the regimen was highly toxic to human-derived hematopoietic cells of all lineages (progenitor,lymphoid,and myeloid). CONCLUSIONS: The humanized bone marrow xenograft model described has the potential to be used as a platform for monitoring the impact of anticancer therapies on human hematopoiesis and could lead to subsequent refinement of therapies prior to clinical evaluation. View Publication

Stem cell leukemia/T cell acute leukemia 1 (SCL/TAL1) plays a key role in the development of murine primitive hematopoiesis but its functions in adult definitive hematopoiesis are still unclear. Using lentiviral delivery of TAL1-directed shRNA in human hematopoietic cells,we show that decreased expression of TAL1 induced major disorders at different levels of adult hematopoietic cell development. Erythroid and myeloid cell production in cultures was dramatically decreased in TAL1-directed shRNA-expressing cells,whereas lymphoid B-cell development was normal. These results confirm the role of TAL1 in the erythroid compartment and show TLA1's implication in the function of myeloid committed progenitors. Moreover,long-term cultures and transplantation of TAL1-directed shRNA-expressing CD34+ cells into irradiated nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice led to dramatically low levels of human cells of all lineages including the B-lymphoid lineage,strongly suggesting that TAL1 has a role in the early commitment of hematopoietic stem cells (HSCs) in humans. Cultures and transplantation experiments performed with mouse Sca1+ cells gave identical results. Altogether,these observations definitively show that TAL1 participates in the regulation of hematopoiesis from HSCs to myeloid progenitors,and pinpoint TAL1 as a master protein of human and murine adult hematopoiesis. View Publication

Although a large proportion of patients with polycythemia vera (PV) harbor a valine-to-phenylalanine mutation at amino acid 617 (V617F) in the JAK2 signaling molecule,the stage of hematopoiesis at which the mutation arises is unknown. Here we isolated and characterized hematopoietic stem cells (HSC) and myeloid progenitors from 16 PV patient samples and 14 normal individuals,testing whether the JAK2 mutation could be found at the level of stem or progenitor cells and whether the JAK2 V617F-positive cells had altered differentiation potential. In all PV samples analyzed,there were increased numbers of cells with a HSC phenotype (CD34+CD38-CD90+Lin-) compared with normal samples. Hematopoietic progenitor assays demonstrated that the differentiation potential of PV was already skewed toward the erythroid lineage at the HSC level. The JAK2 V617F mutation was detectable within HSC and their progeny in PV. Moreover,the aberrant erythroid potential of PV HSC was potently inhibited with a JAK2 inhibitor,AG490. View Publication

The homeobox gene Hoxa-9 is normally expressed in primitive bone marrow cells,and overexpression of Hoxa-9 markedly expands hematopoietic stem cells,suggesting a function in early hematopoiesis. We present evidence for major functional defects in Hoxa-9-/- hematopoietic stem cells. Hoxa-9-/- marrow cells have normal numbers of immunophenotypic stem cells (Lin(-)c-kit(+)flk-2(-)Sca-1+ [KLFS] cells). However,sublethally irradiated Hoxa-9-/- mice develop persistent pancytopenia,indicating unusual sensitivity to ionizing irradiation. In competitive transplantation assays,Hoxa-9-/- cells showed an 8-fold reduction in multilineage long-term repopulating ability,a defect not seen in marrow cells deficient for the adjacent Hoxa-10 gene. Single-cell cultures of KLFS cells showed a 4-fold reduction in large high-proliferation potential colonies. In liquid cultures,Hoxa-9-deficient Lin(-)Sca-1(+) cells showed slowed proliferation (a 5-fold reduction in cell numbers at day 8) and delayed emergence of committed progenitors (a 5-fold decrease in colony-forming cells). Slowing of proliferation was accompanied by a delay in myeloid maturation,with a decrease in Gr-1hiMac-1hi cells at the end of the culture. Retroviral transduction with a Hoxa-9 expression vector dramatically enhanced the cytokine-driven proliferation and in vivo engraftment of Hoxa-9-/- marrow cells. Hoxa-9 appears to be specifically required for normal hematopoietic stem cell function both in vitro and in vivo. View Publication

Internal tandem duplications (ITDs) of the FMS-like tyrosine kinase 3 (FLT3) receptor tyrosine kinase are found in approximately 30% of patients with acute myelogenous leukemia (AML) and are associated with a poor prognosis. FLT3 ITD mutations result in constitutive kinase activation and are thought to be pathogenetically relevant,implicating FLT3 as a plausible therapeutic target. MLN518 (formerly CT53518) is a small molecule inhibitor of the FLT3,KIT,and platelet-derived growth-factor receptor (PDGFR) tyrosine kinases with significant activity in murine models of FLT3 ITD-positive leukemia. Given the importance of FLT3 and KIT for normal hematopoietic progenitor cells,we analyzed the effect of MLN518 on murine hematopoiesis under steady-state conditions,after chemotherapy-induced myelosuppression,and during bone marrow transplantation. In these assays,we show that MLN518 has mild toxicity toward normal hematopoiesis at concentrations that are effective in treating FLT3 ITD-positive leukemia in mice. We also demonstrate that MLN518 preferentially inhibits the growth of blast colonies from FLT3 ITD-positive compared with ITD-negative patients with AML,at concentrations that do not significantly affect colony formation by normal human progenitor cells. In analogy to imatinib mesylate in BCR-ABL-positive acute leukemia,MLN518-induced remissions may not be durable. Our studies provide the basis for integrating this compound into chemotherapy and transplantation protocols. View Publication

Singlet oxygen ((1)O(2)) is widely believed to be the major cytotoxic agent involved in photodynamic therapy (PDT). We showed recently that measurement of the weak near infrared luminescence of (1)O(2) is possible in cells in vitro and tissues in vivo. Here,we investigated the relationship between the integrated luminescence signal and the in vitro PDT response of AML5 leukemia cells sensitized with aminolevulinic acid-induced protoporphyrin IX (PpIX). Sensitized cell suspensions were irradiated with pulsed 523 nm laser light at average fluence rates of 10,25,or 50 mWcm(-2) and,(1)O(2) luminescence measurements were made throughout the treatment. Cell survival was measured with either propidium iodide-labeled flow cytometry or colony-forming assay. The PpIX concentration in the cells,the photobleaching,and the pO(2) in the cell suspensions were also monitored. There were large variations in cell survival and (1)O(2) generation in different experiments due to different controlled treatment parameters (fluence and fluence rate) and other uncontrolled factors (PpIX synthesis and oxygenation). However,in all of the cases,cell kill correlated strongly with the cumulative (1)O(2) luminescence and allowed direct estimation of the (1)O(2) per cell required to achieve a specific level of cell kill. This study supports the validity and potential utility of (1)O(2) luminescence measurement as a dosimetric tool for PDT,as well as confirming the likely role of (1)O(2) in porphyrin-based PDT. View Publication

Hematologic stem cell rescue after high-dose cytotoxic therapy is extensively used for the treatment of many hematopoietic and solid cancers. Gene marking studies suggest that occult tumor cells within the autograft may contribute to clinical relapse. To date purging of autografts contaminated with cancer cells has been unsuccessful. The selective oncolytic property of reovirus against myriad malignant histologies in in vitro,in vivo,and ex vivo systems has been previously demonstrated. In the present study we have shown that reovirus can successfully purge cancer cells within autografts. Human monocytic and myeloma cell lines as well as enriched ex vivo lymphoma,myeloma,and Waldenström macroglobulinemia patient tumor specimens were used in an experimental purging model. Viability of the cell lines or purified ex vivo tumor cells of diffuse large B-cell lymphoma,chronic lymphocytic leukemia,Waldenström macroglobulinemia,and small lymphocytic lymphoma was significantly reduced after reovirus treatment. Further,[35S]-methionine labeling and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of cellular proteins demonstrated reovirus protein synthesis and disruption of host cell protein synthesis as early as 24 hours. Admixtures of apheresis product with the abovementioned tumor cells and cell lines treated with reovirus showed complete purging of disease. In contrast,reovirus purging of enriched ex vivo multiple myeloma,Burkitt lymphoma,and follicular lymphoma was incomplete. The oncolytic action of reovirus did not affect CD34+ stem cells or their long-term colony-forming assays even after granulocyte colony-stimulating factor (G-CSF) stimulation. Our results indicate the ex vivo use of an unattenuated oncolytic virus as an attractive purging strategy for autologous stem cell transplantations. View Publication

OBJECTIVE: The aim of this study was the preclinical evaluation of imatinib mesylate (Gleevec,formerly STI571) in conjunction with arsenic trioxide (As2O3,Trisenox) for the treatment of chronic myelogenous leukemia (CML). MATERIALS AND METHODS: Tetrazolium-based cell line proliferation assays (MTT assays) were performed to determine the cytotoxicity of As2O3 alone and in combination with imatinib. Cell lines tested in this study were Bcr-Abl-expressing cells (K562,MO7p210,32Dp210) and parental cells (MO7e,32D). Isobologram analysis was performed manually and using the median effect method. In vitro cytotoxicity also was determined in colony-forming assays using CML patient cells. Western blot analysis was performed to detect Bcr-Abl protein levels in K562 cells exposed to As2O3 at graded concentrations. Bcr-Abl protein level kinetics were correlated with cell viability (trypan blue count) and activated caspase-3 detected by flow cytometry. RESULTS: We show additive to synergistic cytotoxicity in Bcr-Abl+ cell lines depending on inhibitory concentrations and cell type. Results obtained by colony-forming assays confirmed the findings in cell line proliferation assays. Flow cytometric detection of activated caspase-3 revealed synergistic activity in K562 cells. Treatment of K562 cells with As2O3 alone led to down-regulation of Bcr-Abl protein within 24 hours,even at low doses. The decline of Bcr-Abl preceded activation of caspase-3 and the loss of viable cells. CONCLUSIONS: Favorable cytotoxicity and proapoptotic activity of imatinib in conjunction with As2O3 and specific down-regulation of Bcr-Abl protein levels by As2O3 in K562 cells indicate that As2O3 in combination with imatinib might be useful for circumventing resistance to imatinib monotherapy. View Publication

The classical model of hematopoiesis predicts a dichotomous lineage restriction of multipotent hematopoietic progenitors (MPPs) into common lymphoid progenitors (CLPs) and common myeloid progenitors (CMPs). However,this idea has been challenged by the identification of lymphoid progenitors retaining partial myeloid potential (e.g.,LMPPs),implying that granulocytes can arise within both the classical lymphoid and the myeloid branches. Here,we resolve this issue by using cell-surface CD133 expression to discriminate functional progenitor populations. We show that eosinophilic and basophilic granulocytes as well as erythrocytes and megakaryocytes derive from a common erythro-myeloid progenitor (EMP),whereas neutrophilic granulocytes arise independently within a lympho-myeloid branch with long-term progenitor function. These findings challenge the concept of a CMP and restore dichotomy to the classical hematopoietic model. View Publication