Scientific Resources

Mutations in the RUNX1 gene are found at high frequencies in minimally differentiated acute myelogenous leukemia. In addition to null mutations,many of the mutations generate Runx1 DNA-binding (RDB) mutants. To determine if these mutants antagonize wild-type protein activity,cDNAs were transduced into murine bone marrow or human cord blood cells using retroviral vectors. Significantly,the RDB mutants did not act in a transdominant fashion in vivo to disrupt Runx1 activity in either T-cell or platelet development,which are highly sensitive to Runx1 dosage. However,RDB mutant expression impaired expansion and differentiation of the erythroid compartment in which Runx1 expression is normally down-regulated,showing that a RDB-independent function is incompatible with erythroid differentiation. Significantly,both bone marrow progenitors expressing RDB mutants or deficient for Runx1 showed increased replating efficiencies in vitro,accompanied by the accumulation of myeloblasts and dysplastic progenitors,but the effect was more pronounced in RDB cultures. Disruption of the interface that binds CBFbeta,an important cofactor of Runx1,did not impair RDB mutant replating activity,arguing against inactivation of Runx1 function by CBFbeta sequestration. We propose that RDB mutants antagonize Runx1 function in early progenitors by disrupting a critical balance between DNA-binding-independent and DNA-binding-dependent signaling. View Publication

The transcription factor PAX5 is a critical regulator of B-cell commitment and development. Although normally not expressed in myeloid progenitors,PAX5 has recently been shown to be frequently expressed in myeloid malignancies and to suppress expression of myeloid differentiation genes,compatible with an effect on the differentiation or maintenance of myeloid progenitors. However,previous studies in which PAX5 was ectopically expressed in normal myeloid progenitors in vivo and in vitro provided conflicting results as to the effect of PAX5 on myeloid development. Herein,we demonstrate that on ectopic expression of PAX5 in bone marrow multipotent stem/progenitor cells,cells with a biphenotypic B220(+)GR-1/MAC-1(+) phenotype are produced. These remain cytokine-dependent,but unlike control-transduced cells they sustain long-term generation of myeloid progenitors in vitro and remain capable of myeloid differentiation. Notably,PAX5(+)B220(+)GR-1/MAC-1(+) myeloid progenitors coexpress,at the single-cell level,myeloid genes and otherwise B-cell-specific PAX5 target genes. These findings establish that ectopic expression of PAX5 introduces extensive self-renewal properties in otherwise short-lived myeloid progenitors. Along with the established ectopic expression of PAX5 in acute myeloid leukemia,this motivates a careful investigation of the potential involvement of ectopic PAX5 expression in myeloid and biphenotypic leukemias. View Publication

Multiple myeloma is characterized by increased osteoclast activity that results in bone destruction and lytic lesions. With the prolonged overall patient survival achieved by new treatment modalities,additional drugs are required to inhibit bone destruction. We focused on a novel and more potent structural analog of the nonsteroidal anti-inflammatory drug etodolac,known as SDX-308,and its effects on osteoclastogenesis and multiple myeloma cells. SDX-101 is another structural analog of etodolac that is already used in clinical trials for the treatment of B-cell chronic lymphocytic leukemia (B-CLL). Compared with SDX-101,a 10-fold lower concentration of SDX-308 induced potent (60%-80%) inhibition of osteoclast formation,and a 10- to 100-fold lower concentration inhibited multiple myeloma cell proliferation. Bone resorption was completely inhibited by SDX-308,as determined in dentin-based bone resorption assays. SDX-308 decreased constitutive and RANKL-stimulated NF-kappaB activation and osteoclast formation in an osteoclast cellular model,RAW 264.7. SDX-308 effectively suppressed TNF-alpha-induced IKK-gamma and IkappaB-alpha phosphorylation and degradation and subsequent NF-kappaB activation in human multiple myeloma cells. These results indicate that SDX-308 effectively inhibits multiple myeloma cell proliferation and osteoclast activity,potentially by controlling NF-kappaB activation signaling. We propose that SDX-308 is a promising therapeutic candidate to inhibit multiple myeloma growth and osteoclast activity and that it should receive attention for further study. View Publication

This study was designed to investigate one component of the Wnt/beta-catenin signaling pathway that has been implicated in stem cell self-renewal. Retroviral-mediated introduction of stable beta-catenin to primitive murine bone marrow cells allowed the expansion of multipotential c-Kit(low)Sca-1(low/-)CD19(-) CD11b/Mac-1(-)Flk-2(-)CD43(+)AA4.1(+)NK1.1(-)CD3(-)CD11c(-)Gr-1(-)CD45R/B220(+) cells in the presence of stromal cells and cytokines. They generated myeloid,T,and B lineage lymphoid cells in culture,but had no T lymphopoietic potential when transplanted. Stem cell factor and IL-6 were found to be minimal requirements for long-term,stromal-free propagation,and a beta-catenin-transduced cell line was maintained for 5 mo with these defined conditions. Although multipotential and responsive to many normal stimuli in culture,it was unable to engraft several types of irradiated recipients. These findings support previous studies that have implicated the canonical Wnt pathway signaling in regulation of multipotent progenitors. In addition,we demonstrate how it may be experimentally manipulated to generate valuable cell lines. View Publication

Progranulin (pgrn; granulin-epithelin precursor,PC-cell-derived growth factor,or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis,development,inflammation,and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34(+) progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO,and,in U-937 only,phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation,suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937,ATRA and chemical differentiation agents greatly increased pgrn mRNA stability,whereas,in HL-60,ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-kappaB (NF-kappaB) activation impaired ATRA-stimulated pgrn expression in HL-60 but not U-937,whereas in U-937 it blocked PMA-induced pgrn mRNA expression,suggestive of cell-specific roles for NF-kappaB in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-kappaB signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation. 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

BACKGROUND: Resistance to imatinib monotherapy frequently emerges in advanced stages of chronic myelogenous leukemia (CML),supporting the rationale for combination drug therapy. In the present study,the activities of the farnesyltransferase inhibitors (FTIs) L744,832 and LB42918,as single agents and in combination with imatinib,were investigated in different imatinib-sensitive and -resistant BCR-ABL-positive CML cells. MATERIALS AND METHODS: Growth inhibition of the cell lines and primary patient cells was assessed by MTT assays and colony-forming cell assays,respectively. Drug interactions were analyzed according to the median-effect method of Chou and Talalay. The determination of apoptotic cell death was performed by annexin V/propidium iodide staining. RESULTS: Combinations of both FTIs with imatinib displayed synergism or sensitization (potentiation) in all the cell lines tested. In primary chronic phase CML cells,additive and synergistic effects were discernible for the combination of imatinib plus L744,832 and imatinib plus LB42918,respectively. Annexin V/propidium iodide staining showed enhancement of imatinib-induced apoptosis with either drug combination,both in imatinib-sensitive and -resistant cells. CONCLUSION: The results indicated the potential of L744,832 and LB42918 as combination agents for CML patients on imatinib treatment. View Publication

Current therapies for delayed- or nonunion bone fractures are still largely ineffective. Previous studies indicated that the VEGF homolog placental growth factor (PlGF) has a more significant role in disease than in health. Therefore we investigated the role of PlGF in a model of semi-stabilized bone fracture healing. Fracture repair in mice lacking PlGF was impaired and characterized by a massive accumulation of cartilage in the callus,reminiscent of delayed- or nonunion fractures. PlGF was required for the early recruitment of inflammatory cells and the vascularization of the fracture wound. Interestingly,however,PlGF also played a role in the subsequent stages of the repair process. Indeed in vivo and in vitro findings indicated that PlGF induced the proliferation and osteogenic differentiation of mesenchymal progenitors and stimulated cartilage turnover by particular MMPs. Later in the process,PlGF was required for the remodeling of the newly formed bone by stimulating osteoclast differentiation. As PlGF expression was increased throughout the process of bone repair and all the important cell types involved expressed its receptor VEGFR-1,the present data suggest that PlGF is required for mediating and coordinating the key aspects of fracture repair. Therefore PlGF may potentially offer therapeutic advantages for fracture repair. 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 2 most frequent human MLL hematopoietic malignancies involve either AF4 or AF9 as fusion partners; each has distinct biology but the role of the fusion partner is not clear. We produced Mll-AF4 knock-in (KI) mice by homologous recombination in embryonic stem cells and compared them with Mll-AF9 KI mice. Young Mll-AF4 mice had lymphoid and myeloid deregulation manifest by increased lymphoid and myeloid cells in hematopoietic organs. In vitro,bone marrow cells from young mice formed unique mixed pro-B lymphoid (B220(+)CD19(+)CD43(+)sIgM(-),PAX5(+),TdT(+),IgH rearranged)/myeloid (CD11b/Mac1(+),c-fms(+),lysozyme(+)) colonies when grown in IL-7- and Flt3 ligand-containing media. Mixed lymphoid/myeloid hyperplasia and hematologic malignancies (most frequently B-cell lymphomas) developed in Mll-AF4 mice after prolonged latency; long latency to malignancy indicates that Mll-AF4-induced lymphoid/myeloid deregulation alone is insufficient to produce malignancy. In contrast,young Mll-AF9 mice had predominately myeloid deregulation in vivo and in vitro and developed myeloid malignancies. The early onset of distinct mixed lymphoid/myeloid lineage deregulation in Mll-AF4 mice shows evidence for both instructive" and "noninstructive" roles for AF4 and AF9 as partners in MLL fusion genes. The molecular basis for "instruction" and secondary cooperating mutations can now be studied in our Mll-AF4 model." View Publication

Ikaros is expressed in early hematopoietic progenitors and is required for lymphoid differentiation. In the absence of Ikaros,there is a lack of markers defining fate restriction along lympho-myeloid pathways,but it is unclear whether formation of specific progenitors or expression of their markers is affected. Here we use a reporter based on Ikaros regulatory elements to separate early progenitors in wild-type and Ikaros-null mice. We found previously undetected Ikaros-null lympho-myeloid progenitors lacking the receptor tyrosine kinase Flt3 that were capable of myeloid but not lymphoid differentiation. In contrast,lack of Ikaros in the common myeloid progenitor resulted in increased formation of erythro-megakaryocytes at the expense of myeloid progenitors. Using this approach,we identify previously unknown pivotal functions for Ikaros in distinct fate 'decisions' in the early hematopoietic hierarchy. View Publication

We have established a system for directed differentiation of human embryonic stem (hES) cells into myeloid dendritic cells (DCs). As a first step,we induced hemopoietic differentiation by coculture of hES cells with OP9 stromal cells,and then,expanded myeloid cells with GM-CSF using a feeder-free culture system. Myeloid cells had a CD4+CD11b+CD11c+CD16+CD123(low)HLA-DR- phenotype,expressed myeloperoxidase,and included a population of M-CSFR+ monocyte-lineage committed cells. Further culture of myeloid cells in serum-free medium with GM-CSF and IL-4 generated cells that had typical dendritic morphology; expressed high levels of MHC class I and II molecules,CD1a,CD11c,CD80,CD86,DC-SIGN,and CD40; and were capable of Ag processing,triggering naive T cells in MLR,and presenting Ags to specific T cell clones through the MHC class I pathway. Incubation of DCs with A23187 calcium ionophore for 48 h induced an expression of mature DC markers CD83 and fascin. The combination of GM-CSF with IL-4 provided the best conditions for DC differentiation. DCs obtained with GM-CSF and TNF-alpha coexpressed a high level of CD14,and had low stimulatory capacity in MLR. These data clearly demonstrate that hES cells can be used as a novel and unique source of hemopoietic and DC precursors as well as DCs at different stages of maturation to address essential questions of DC development and biology. In addition,because ES cells can be expanded without limit,they can be seen as a potential scalable source of cells for DC vaccines or DC-mediated induction of immune tolerance. View Publication