技术资料

The core-binding factor (CBF) is a master regulator of developmental and differentiation programs,and CBF alterations are frequently associated with acute leukemia. The role of the CBF member RUNX2 in hematopoiesis is poorly understood. Genetic evidence suggests that deregulation of Runx2 may cause myeloid leukemia in mice expressing the fusion oncogene Cbfb-MYH11. In this study,we show that sustained expression of Runx2 modulates Cbfbeta-smooth muscle myosin heavy chain (SMMHC)-mediated myeloid leukemia development. Expression of Runx2 is high in the hematopoietic stem cell compartment and decreases during myeloid differentiation. Sustained Runx2 expression hinders myeloid progenitor differentiation capacity and represses expression of CBF targets Csf1R,Mpo,Cebpd,the cell cycle inhibitor Cdkn1a,and myeloid markers Cebpa and Gfi1. In addition,full-length Runx2 cooperates with Cbfbeta-SMMHC in leukemia development in transplantation assays. Furthermore,we show that the nuclear matrix-targeting signal and DNA-binding runt-homology domain of Runx2 are essential for its leukemogenic activity. Conversely,Runx2 haplo-insufficiency delays the onset and reduces the incidence of acute myeloid leukemia. Together,these results indicate that Runx2 is expressed in the stem cell compartment,interferes with differentiation and represses CBF targets in the myeloid compartment,and modulates the leukemogenic function of Cbfbeta-SMMHC in mouse leukemia. View Publication

The basic helix-loop-helix transcription factor achaete-scute complex homologue 1 (ASCL1) is essential for the development of normal lung neuroendocrine cells as well as other endocrine and neural tissues. Small cell lung cancer (SCLC) and non-SCLC with neuroendocrine features express ASCL1,where the factor may play a role in the virulence and primitive neuroendocrine phenotype of these tumors. In this study,RNA interference knockdown of ASCL1 in cultured SCLC resulted in inhibition of soft agar clonogenic capacity and induction of apoptosis. cDNA microarray analyses bolstered by expression studies,flow cytometry,and chromatin immunoprecipitation identified two candidate stem cell marker genes,CD133 and aldehyde dehydrogenase 1A1 (ALDH1A1),to be directly regulated by ASCL1 in SCLC. In SCLC direct xenograft tumors,we detected a relatively abundant CD133(high)-ASCL1(high)-ALDH1(high) subpopulation with markedly enhanced tumorigenicity compared with cells with weak CD133 expression. Tumorigenicity in the CD133(high) subpopulation depended on continued ASCL1 expression. Whereas CD133(high) cells readily reconstituted the range of CD133 expression seen in the original xenograft tumor,CD133(low) cells could not. Our findings suggest that a broad range of SCLC cells has tumorigenic capacity rather than a small discrete population. Intrinsic tumor cell heterogeneity,including variation in key regulatory factors such as ASCL1,can modulate tumorigenicity in SCLC. View Publication

There is an enormous gap between the antiproliferative and in vivo antitumor efficacy of gemcitabine in cell line-based models and its clinical efficacy. This may be due to insensitiveness of the precursor,cancer stem cell (CSC) compartment to cytotoxic agents. The hedgehog pathway is associated with CSC signaling and control. We used a direct xenograft model of pancreatic cancer and a two-stage approach was used to test the hypotheses that targeting CSC could increase the efficacy of gemcitabine. Tumors from a gemcitabine-sensitive xenograft were treated with gemcitabine first,and randomized,after tumor regression to continuing treatment with gemcitabine,a hedgehog inhibitor alone or in combination with gemcitabine. We tested markers described as associated with CSC such as CD24,CD44,ALDH,nestin,and the hedgehog pathway. After induction with gemcitabine,treated tumor showed an enrichment in CSC markers such as ALDH and CD24. Subsequently,a release from gemcitabine prompted a repopulation of proliferating cells and a decrease in such markers to equilibrate from pretreatment levels. Combined treatment with gemcitabine and cyclopamine induced tumor regression and decrease in CSC markers and hedgehog signaling. Cytoplasmic CD24 and ALDH were inversely and strongly associated with growth and were expressed in a minority of cells that we propose constitute the CSC compartment. Hedgehog inhibitors as part of a dual compartment therapeutic approach were able to further reduce tumor growth and decreased both static and dynamic markers of CSC. Direct tumor xenografts are a valid platform to test multicompartment therapeutic approaches in pancreatic cancer. View Publication

Evidence suggests the transcription factor GATA-2 is a critical regulator of murine hematopoietic stem cells. Here,we explore the relation between GATA-2 and cell proliferation and show that inducing GATA-2 increases quiescence (G(0) residency) of murine and human hematopoietic cells. In human cord blood,quiescent fractions (CD34(+)CD38(-)Hoechst(lo)Pyronin Y(lo)) express more GATA-2 than cycling counterparts. Enforcing GATA-2 expression increased quiescence of cord blood cells,reducing proliferation and performance in long-term culture-initiating cell and colony-forming cell (CFC) assays. Gene expression analysis places GATA-2 upstream of the quiescence regulator MEF,but enforcing MEF expression does not prevent GATA-2-conferred quiescence,suggesting additional regulators are involved. Although known quiescence regulators p21(CIP1) and p27(KIP1) do not appear to be responsible,enforcing GATA-2 reduced expression of regulators of cell cycle such as CCND3,CDK4,and CDK6. Enforcing GATA-2 inhibited human hematopoiesis in vivo: cells with highest exogenous expression (GATA-2(hi)) failed to contribute to hematopoiesis in nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice,whereas GATA-2(lo) cells contributed with delayed kinetics and low efficiency,with reduced expression of Ki-67. Thus,GATA-2 activity inhibits cell cycle in vitro and in vivo,highlighting GATA-2 as a molecular entry point into the transcriptional program regulating quiescence in human hematopoietic stem and progenitor cells. View Publication

ETS2 and ERG are transcription factors,encoded on human chromosome 21 (Hsa21),that have been implicated in human cancer. People with Down syndrome (DS),who are trisomic for Hsa21,are predisposed to acute megakaryoblastic leukemia (AMKL). DS-AMKL blasts harbor a mutation in GATA1,which leads to loss of full-length protein but expression of the GATA-1s isoform. To assess the consequences of ETS protein misexpression on megakaryopoiesis,we expressed ETS2,ERG,and the related protein FLI-1 in wild-type and Gata1 mutant murine fetal liver progenitors. These studies revealed that ETS2,ERG,and FLI-1 facilitated the expansion of megakaryocytes from wild-type,Gata1-knockdown,and Gata1s knockin progenitors,but none of the genes could overcome the differentiation block characteristic of the Gata1-knockdown megakaryocytes. Although overexpression of ETS proteins increased the proportion of CD41(+) cells generated from Gata1s-knockin progenitors,their expression led to a significant reduction in the more mature CD42 fraction. Serial replating assays revealed that overexpression of ERG or FLI-1 immortalized Gata1-knockdown and Gata1s knockin,but not wild-type,fetal liver progenitors. Immortalization was accompanied by activation of the JAK/STAT pathway,commonly seen in megakaryocytic malignancies. These findings provide evidence for synergy between alterations in GATA-1 and overexpression of ETS proteins in aberrant megakaryopoiesis. View Publication

The Rho subgroup of the Rho GTPases consisting of RhoA,RhoB and RhoC induces a specific type of actin cytoskeleton and carry out a variety of functions in the cell. mDia and ROCK are downstream effectors of Rho mediating Rho action on the actin cytoskeleton; mDia produces actin filaments by nucleation and polymerization and ROCK activate myosin to cross-link them for induction of actomyosin bundles and contractility. mDia is potentially linked to Rac activation and membrane ruffle formation through c-Src-induced phosphorylation of focal adhesion proteins,and ROCK antagonizes this mDia action. Thus,cell morphogenesis,adhesion,and motility can be determined by the balance between mDia and ROCK activities. Though they are not oncogenes by themselves,overexpression of RhoA and RhoC are often found in clinical cancers,and RhoC has been repeatedly identified as a gene associated with metastasis. The Rho-ROCK pathway is implicated in Ras-mediated transformation,the amoeboid movement of tumor cells in the three-dimensional matrix,and transmigration of tumor cells through the mesothelial monolayer. On the other hand,the Rho-mDia1 pathway is implicated in Src-mediated remodeling of focal adhesions and migration of tumor cells. There is also an indication that the Rho pathway other than ROCK is involved in Src-mediated induction of podosome and regulation of matrix metalloproteases. Thus,Rho mediates various phenotypes of malignant transformation by Ras and Src through its effectors,ROCK and mDia. View Publication

Alcohol abuse predisposes the host to bacterial infections. In response to bacterial infection,the bone marrow hematopoietic activity shifts toward granulocyte production,which is critical for enhancing host defense. This study investigated the hematopoietic precursor cell response to bacteremia and how alcohol affects this response. Acute alcohol intoxication was induced in BALB/c mice 30 min before initiation of Escherichia coli bacteremia. Bacteremia caused a significant increase in the number of bone marrow lineage (lin(-))-c-kit(+)Sca-1(+) cells. Marrow lin(-)c-kit(+)Sca-1(+) cells isolated from bacteremic mice showed an increase in CFU-granulocyte/macrophage activity compared with controls. In addition to enhanced proliferation of lin(-)c-kit(+)Sca-1(+) cells as reflected by BrdU incorporation,phenotypic inversion of lin(-)c-kit(+)Sca-1(+)Sca-1(-) cells primarily accounted for the rapid increase in marrow lin(-)c-kit(+)Sca-1(+) cells following bacteremia. Bacteremia increased plasma concentration of TNF-alpha. Culture of marrow lin(-)c-kit(+)Sca-1(+)Sca-1(-) cells with murine rTNF-alpha for 24 h caused a dose-dependent increase in conversion of these cells to lin(-)c-kit(+)Sca-1(+) cells. Sca-1 mRNA expression by the cultured cells was also up-regulated following TNF-alpha stimulation. Acute alcohol intoxication inhibited the increase in the number of lin(-)c-kit(+)Sca-1(+) cells in the bone marrow after E. coli infection. Alcohol impeded the increase in BrdU incorporation into marrow lin(-)c-kit(+)Sca-1(+) cells in response to bacteremia. Alcohol also suppressed the plasma TNF-alpha response to bacteremia and inhibited TNF-alpha-induced phenotypic inversion of lin(-)c-kit(+)Sca-1(+)Sca-1(-) cells in vitro. These data show that alcohol inhibits the hematopoietic precursor cell response to bacteremia,which may serve as one mechanism underlying the impaired host defense in alcohol abusers with severe bacterial infections. View Publication

Protein phosphatase 2A (PP2A) is a major serine/threonine protein phosphatase in eukaryotic cells and is involved in many essential aspects of cell function. The catalytic subunit of the enzyme (PP2Ac),a part of the core enzyme,has two isoforms,alpha (PP2Ac alpha) and beta (PP2Ac beta),of which PP2Ac alpha is the major form expressed in vivo. Deregulation of PP2A expression has been linked to several diseases,but the mechanisms that control the expression of this enzyme are still unclear. We conducted experiments to decipher molecular mechanisms involved in the regulation of the PP2Ac alpha promoter in human primary T cells. After preparing serially truncated PP2Ac alpha promoter luciferase constructs,we found that the region stretching around 240 bases upstream from the translation initiation site was of functional significance and included a cAMP response element motif flanked by three GC boxes. Shift assays revealed that CREB/phosphorylated CREB and stable protein 1 could bind to the region. Furthermore,we demonstrated that methylation of deoxycytosine in the CpG islands limited binding of phosphorylated CREB and the activity of the PP2Ac alpha promoter. In contrast,the binding of stable protein 1 to a GC box within the core promoter region was not affected by DNA methylation. Primary T cells treated with 5-azacitidine,a DNA methyltransferase inhibitor,showed increased expression of PP2Ac alpha mRNA. We propose that conditions associated with hypomethylation of CpG islands,such as drug-induced lupus,permit increased PP2Ac expression. View Publication

Proviruses carrying drug-inducible Oct4,Sox2,Klf4 and c-Myc used to derive 'primary' induced pluripotent stem (iPS) cells were segregated through germline transmission,generating mice and cells carrying subsets of the reprogramming factors. Drug treatment produced 'secondary' iPS cells only when the missing factor was introduced. This approach creates a defined system for studying reprogramming mechanisms and allows screening of genetically homogeneous cells for compounds that can replace any transcription factor required for iPS cell derivation. View Publication

The mammalian target of rapamycin (mTOR) kinase is the catalytic subunit of two functionally distinct complexes,mTORC1 and mTORC2,that coordinately promote cell growth,proliferation,and survival. Rapamycin is a potent allosteric mTORC1 inhibitor with clinical applications as an immunosuppressant and anti-cancer agent. Here we find that Torin1,a highly potent and selective ATP-competitive mTOR inhibitor that directly inhibits both complexes,impairs cell growth and proliferation to a far greater degree than rapamycin. Surprisingly,these effects are independent of mTORC2 inhibition and are instead because of suppression of rapamycin-resistant functions of mTORC1 that are necessary for cap-dependent translation and suppression of autophagy. These effects are at least partly mediated by mTORC1-dependent and rapamycin-resistant phosphorylation of 4E-BP1. Our findings challenge the assumption that rapamycin completely inhibits mTORC1 and indicate that direct inhibitors of mTORC1 kinase activity may be more successful than rapamycin at inhibiting tumors that depend on mTORC1. View Publication

Beta glucans are cell wall constituents of yeast,fungi and bacteria,as well as mushrooms and barley. Glucans are not expressed on mammalian cells and are recognized as pathogen-associated molecular patterns (PAMPS) by pattern recognition receptors (PRR). Beta glucans have potential activity as biological response modifiers for hematopoiesis and enhancement of bone marrow recovery after injury. We have reported that Maitake beta glucan (MBG) enhanced mouse bone marrow (BMC) and human umbilical cord blood (CB) cell granulocyte-monocyte colony forming unit (GM-CFU) activity in vitro and protected GM-CFU forming stem cells from doxorubicin (DOX) toxicity. The objective of this study was to determine the effects of MBG on expansion of phenotypically distinct subpopulations of progenitor and stem cells in CB from full-term infants cultured ex vivo and on homing and engraftment in vivo in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse. MBG promoted a greater expansion of CD34+CD33+CD38- human committed hematopoietic progenitor (HPC) cells compared to the conventional stem cell culture medium (P = 0.002 by ANOVA). CD34+CXCR4+CD38- early,uncommitted human hematopoietic stem cell (HSC) numbers showed a trend towards increase in response to MBG. The fate of CD34+ enriched CB cells after injection into the sublethally irradiated NOS/SCID mouse was evaluated after retrieval of xenografted human CB from marrow and spleen by flow cytometric analysis. Oral administration of MBG to recipient NOS/SCID mice led to enhanced homing at 3 days and engraftment at 6 days in mouse bone marrow (P = 0.002 and P = 0.0005,respectively) compared to control mice. More CD34+ human CB cells were also retrieved from mouse spleen in MBG treated mice at 6 days after transplantation. The studies suggest that MBG promotes hematopoiesis through effects on CD34+ progenitor cell expansion ex vivo and when given to the transplant recipient could enhance CD34+ precursor cell homing and support engraftment. View Publication

The fate of neural stem cells (NSCs),including their proliferation,differentiation,survival,and death,is regulated by multiple intrinsic signals and the extrinsic environment. We had previously reported that 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) directly induces astroglial differentiation of NSCs by activation of the Janus kinase (JAK)/Signal transducer and activator of transcription 3 (STAT3) pathway independently of AMP-activated protein kinase (AMPK). Here,we reported the observation that AICAR inhibited NSC proliferation and its underlying mechanism. Analysis of caspase activity and cell cycle showed that AICAR induced G1/G0 cell cycle arrest in NSCs,associated with decreased levels of poly(ADP-ribose) polymerase,phospho-retinoblastoma protein (Rb),and cyclin D but did not cause apoptosis. Iodotubericidin and Compound C,inhibitors of adenosine kinase and AMPK,respectively,or overexpression of a dominant-negative mutant of AMPK,but not JAK inhibitor,were able to reverse the anti-proliferative effect of AICAR. Glucose deprivation also activated the AMPK pathway,induced G0/G1 arrest,and suppressed the proliferation of NSCs,an effect associated with decreased levels of phospho-Rb and cyclin D protein. Furthermore,Compound C and overexpression of dominant-negative AMPK in C17.2 NSCs could block the glucose deprivation-mediated down-regulation of cyclin D and partially reverse the suppression of proliferation. These results suggest that AICAR and glucose deprivation might induce G1/G0 cell cycle arrest and suppress proliferation of NSCs via phospho-Rb and cyclin D down-regulation. AMPK,but not JAK/STAT3,activation is key for this inhibitory effect and may play an important role in the responses of NSCs to metabolic stresses such as glucose deprivation. View Publication