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Breast cancer resistance protein (BCRP) is a novel member of the adenosine triphosphate-binding cassette superfamily of transport proteins. Transfection and enforced expression of BCRP in drug-sensitive cells confer resistance to mitoxantrone,doxorubicin,daunorubicin,and topotecan. We studied blast cells from 21 acute leukemia patients (20 acute myeloid leukemia,1 acute lymphocytic leukemia) for the expression of BCRP mRNA using a quantitative reverse-transcription polymerase chain reaction assay. BCRP mRNA expression varied more than 1000-fold among the samples tested,with low or barely detectable expression in half of the samples. Seven samples (33%) had relatively high expression of BCRP mRNA. High expression of BCRP did not correlate strongly with high expression of P-glycoprotein,suggesting that BCRP may cause resistance to certain antileukemic drugs in P-glycoprotein-negative cases. High expression of BCRP mRNA is sufficiently frequent in AML to warrant more extensive investigations to determine the relation of disease subtype and treatment outcome to BCRP expression and function. View Publication

Infusion of transduced hematopoietic stem cells into nonmyeloablated hosts results in ineffective in vivo levels of transduced cells. To increase the proportion of transduced cells in vivo,selection based on P140K O6-methylguanine-DNA-methyltransferase (MGMT[P140K]) gene transduction and O6-benzylguanine/1,3-bis(2-chloroethyl)-1-nitrosourea (BG/BCNU) treatment has been devised. In this study,we transduced human NOD/SCID repopulating cells (SRCs) with MGMT(P140K) using a lentiviral vector and infused them into BG/BCNU-conditioned NOD/SCID mice before rounds of BG/BCNU treatment as a model for in vivo selection. Engraftment was not observed until the second round of BG/BCNU treatment,at which time human cells emerged to compose up to 20% of the bone marrow. Furthermore,99% of human CFCs derived from NOD/SCID mice were positive for provirus as measured by PCR,compared with 35% before transplant and 11% in untreated irradiation-preconditioned mice,demonstrating selection. Bone marrow showed BG-resistant O6-alkylguanine-DNA-alkyltransferase (AGT) activity,and CFUs were stained intensely for AGT protein,indicating high transgene expression. Real-time PCR estimates of the number of proviral insertions in individual CFUs ranged from 3 to 22. Selection resulted in expansion of one or more SRC clones containing similar numbers of proviral copies per mouse. To our knowledge,these results provide the first evidence of potent in vivo selection of MGMT(P140K) lentivirus-transduced human SRCs following BG/BCNU treatment. View Publication

Like their human counterparts,mouse plasmacytoid dendritic cells (pDCs) play a central role in innate immunity against viral infections,but their capacity to prime T cells in vivo remains unknown. We show here that virus-activated pDCs differentiate into antigen-presenting cells able to induce effector/memory CD8(+) T-cell responses in vivo against both epitopic peptides and endogenous antigen,whereas pDCs activated by synthetic oligodeoxynucleotides containing unmethylated cytosine-guanine motifs (CpG) acquire only the ability to recall antigen-experienced T-cell responses. We also show that immature pDCs are unable to induce effector or regulatory CD8(+) T-cell responses. Thus,murine pDCs take part in both innate and adaptive immune responses by directly priming naive CD8(+) T cells during viral infection. View Publication

Cell-to-cell virus transmission is one of the most efficient mechanisms of human immunodeficiency virus (HIV) spread,requires CD4 and coreceptor expression in target cells,and may also lead to syncytium formation and cell death. Here,we show that in addition to this classical coreceptor-mediated transmission,the contact between HIV-producing cells and primary CD4 T cells lacking the appropriate coreceptor induced the uptake of HIV particles by target cells in the absence of membrane fusion or productive HIV replication. HIV uptake by CD4 T cells required cellular contacts mediated by the binding of gp120 to CD4 and intact actin cytoskeleton. HIV antigens taken up by CD4 T cells were rapidly endocytosed to trypsin-resistant compartments inducing a partial disappearance of CD4 molecules from the cell surface. Once the cellular contact was stopped,captured HIV were released as infectious particles. Electron microscopy revealed that HIV particles attached to the surface of target cells and accumulated in large (0.5-1.0 microm) intracellular vesicles containing 1-14 virions,without any evidence for massive clathrin-mediated HIV endocytosis. The capture of HIV particles into trypsin-resistant compartments required the availability of the gp120 binding site of CD4 but was independent of the intracytoplasmic tail of CD4. In conclusion,we describe a novel mechanism of HIV transmission,activated by the contact of infected and uninfected primary CD4 T cells,by which HIV could exploit CD4 T cells lacking the appropriate coreceptor as an itinerant virus reservoir. View Publication

Zebularine (2(1H)-pyrimidinone riboside,Zeb),a synthetic analogue of cytidine that is a potent inhibitor of cytidine deaminase,has been recently identified as a general inhibitor of DNA methylation. This inhibition of DNA methyltransferase (DNMT) is hypothesized to be mechanism-based and result from formation of a covalent complex between the enzyme and zebularine-substituted DNA. Metabolic activation of Zeb thus requires that it be phosphorylated and incorporated into DNA. We have quantitatively assessed the phosphorylation and DNA incorporation of Zeb in T24 cells using 2-[(14)C]-Zeb in conjunction with gradient anion-exchange HPLC and selected enzymatic and spectroscopic analyses. The corresponding 5'-mono-,di- and triphosphates of Zeb were readily formed in a dose- and time-dependent manner. Two additional Zeb-containing metabolites were tentatively identified as diphosphocholine (Zeb-DP-Chol) and diphosphoethanolamine adducts. Intracellular concentrations of Zeb-TP and Zeb-DP-Chol were similar and greatly exceeded those of other metabolites. DNA incorporation occurred but was surpassed by that of RNA by at least seven-fold. Equivalent levels and similar intracellular metabolic patterns were also observed in the Molt-4 (human T-lymphoblasts) and MC38 (murine colon carcinoma) cell lines. For male BALB/c nu/nu mice implanted s.c. with the EJ6 variant of T24 bladder carcinoma and treated i.p. with 500mg/kg 2-[(14)C]-Zeb,the in vivo phosphorylation pattern of Zeb in tumor tissue examined 24h after drug administration was similar to that observed in vitro. The complex metabolism of Zeb and its limited DNA incorporation suggest that these are the reasons why it is less potent than either 5-azacytidine or 5-aza-2'-deoxycytidine and requires higher doses for equivalent inhibition of DNMT. View Publication

The present study examined whether nestin+ neural-like stem cells detected in the scar tissue of rats 1 week after myocardial infarction (MI) were derived from bone marrow and/or were resident cells of the normal myocardium. Irradiated male Wistar rats transplanted with beta-actin promoter-driven,green fluorescent protein (GFP)-labeled,unfractionated bone marrow cells were subjected to coronary artery ligation. Three weeks after MI,GFP-labeled bone marrow cells were detected in the infarct region,and a modest number were associated with nestin immunoreactivity. The paucity of GFP+/nestin+ cells in the scar tissue provided the impetus to explore whether neural-like stem cells were derived from cardiac tissue. Nestin mRNA and immunoreactivity were detected in normal rat myocardium,and transcript levels were increased in the damaged heart after MI. In primary-passage,cardiac tissue-derived neural cells,filamentous nestin staining was associated with a diffuse,cytoplasmic glial fibrillary acidic protein signal. Unexpectedly,in viable myocardium,numerous nestin+/glial fibrillary acidic protein+ fiberlike structures of varying length were detected and observed in close proximity to neurofilament-M+ fibers. The infarct region was likewise innervated,and the preponderance of neurofilament-M+ fibers appeared to be physically associated with nestin+ fiberlike structures. These data highlight the novel observation that the normal rat heart contained resident nestin+/glial fibrillary acidic protein+ neural-like stem cells,fiberlike structures,and nestin mRNA levels that were increased in response to myocardial ischemia. Cardiac tissue-derived neural stem cell migration to the infarct region and concomitant nestin+ fiberlike innervation represent obligatory events of reparative fibrosis in the damaged rat myocardium. View Publication

Histone acetyltransferases (HATs) regulate transcription,chromatin structure and DNA repair. Here,we utilized a novel HAT inhibitor,anacardic acid,to examine the role of HATs in the DNA damage response. Anacardic acid inhibits the Tip60 HAT in vitro,and blocks the Tip60-dependent activation of the ATM and DNA-PKcs protein kinases by DNA damage in vivo. Further,anacardic acid sensitizes human tumor cells to the cytotoxic effects of ionizing radiation. These results demonstrate a central role for HATs such as Tip60 in regulating the DNA damage response. HAT inhibitors provide a novel therapeutic approach for increasing the sensitivity of tumors to radiation therapy. View Publication

Expansion of hematopoietic stem cells could be used clinically to shorten the prolonged aplastic phase after umbilical cord blood (UCB) transplantation. In this report,we investigated rapid severe combined immunodeficient (SCID) repopulating activity (rSRA) 2 weeks after transplantation of CD34(+) UCB cells cultured with serum on MS5 stromal cells and in serum- and stroma-free cultures. Various subpopulations obtained after culture were studied for rSRA. CD34(+) expansion cultures resulted in vast expansion of CD45(+) and CD34(+) cells. Independent of the culture method,only the CD34(+)33(+)38(-) fraction of the cultured cells contained rSRA. Subsequently,we subfractionated the CD34(+)38(-) fraction using stem cell markers CD45RA and CD90. In vitro differentiation cultures showed CD34(+) expansion in both CD45RA(-) and CD90(+) cultures,whereas little increase in CD34(+) cells was observed in both CD45RA(+) and CD90(-) cultures. By four-color flow cytometry,we could demonstrate that CD34(+)38(-)45RA(-) and CD34(+)38(-)90(+) cell populations were largely overlapping. Both populations were able to reconstitute SCID/nonobese diabetic mice at 2 weeks,indicating that these cells contained rSRA activity. In contrast,CD34(+)38(-)45RA(+) or CD34(+)38(-)90(-) cells contributed only marginally to rSRA. Similar results were obtained when cells were injected intrafemorally,suggesting that the lack of reconstitution was not due to homing defects. In conclusion,we show that after in vitro expansion,rSRA is mediated by CD34(+)38(-)90(+)45RA(-) cells. All other cell fractions have limited reconstitutive potential,mainly because the cells have lost stem cell activity rather than because of homing defects. These findings can be used clinically to assess the rSRA of cultured stem cells. View Publication

Although hepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) are considered a promising model for predicting hepatotoxicity,their application has been restricted because of the low activity of drug metabolizing enzymes (DMEs). Here we found that the low expression of xenobiotic receptors (constitutive androstane receptor,CAR; and pregnane X receptor,PXR) contributes to the low activity of DMEs in hPSC-HLCs. Most CAR- and PXR-regulated DMEs and transporters were transcriptionally down-regulated in hPSC-HLC. Transcriptional expression of CAR and PXR was highly repressed in hPSC-HLCs,whereas mRNA levels of aryl hydrocarbon receptor (AHR) were comparable to those of adult liver. Furthermore,ligand-induced transcriptional activation was observed only at AHR in hPSC-HLCs. Bisulfite sequencing analysis demonstrated that promoter hypermethylation of CAR and PXR was associated with diminished transcriptional activity in hPSC-HLCs. Treatment with AHR-selective ligands increased the transcription of AHR-dependent target genes by direct AHR-DNA binding at the xenobiotic response element. In addition,an antagonist of AHR significantly inhibited AHR-dependent target gene expression. Thus,AHR may function intrinsically as a xenosensor as well as a ligand-dependent transcription factor in hPSC-HLCs. Our results indicate that hPSC-HLCs can be used to screen toxic substances related to AHR signaling and to identify potential AHR-targeted therapeutics. View Publication

Synthetic biology has advanced the design of standardized transcription control devices that programme cellular behaviour. By coupling synthetic signalling cascade- and transcription factor-based gene switches with reverse and differential sensitivity to the licensed food additive vanillic acid,we designed a synthetic lineage-control network combining vanillic acid-triggered mutually exclusive expression switches for the transcription factors Ngn3 (neurogenin 3; OFF-ON-OFF) and Pdx1 (pancreatic and duodenal homeobox 1; ON-OFF-ON) with the concomitant induction of MafA (V-maf musculoaponeurotic fibrosarcoma oncogene homologue A; OFF-ON). This designer network consisting of different network topologies orchestrating the timely control of transgenic and genomic Ngn3,Pdx1 and MafA variants is able to programme human induced pluripotent stem cells (hIPSCs)-derived pancreatic progenitor cells into glucose-sensitive insulin-secreting beta-like cells,whose glucose-stimulated insulin-release dynamics are comparable to human pancreatic islets. Synthetic lineage-control networks may provide the missing link to genetically programme somatic cells into autologous cell phenotypes for regenerative medicine. View Publication

Predictive toxicology using stem cells or their derived tissues has gained increasing importance in biomedical and pharmaceutical research. Here,we show that toxicity category prediction by support vector machines (SVMs),which uses qRT-PCR data from 20 categorized chemicals based on a human embryonic stem cell (hESC) system,is improved by the adoption of gene networks,in which network edge weights are added as feature vectors when noisy qRT-PCR data fail to make accurate predictions. The accuracies of our system were 97.5-100% for three toxicity categories: neurotoxins (NTs),genotoxic carcinogens (GCs) and non-genotoxic carcinogens (NGCs). For two uncategorized chemicals,bisphenol-A and permethrin,our system yielded reasonable results: bisphenol-A was categorized as an NGC,and permethrin was categorized as an NT; both predictions were supported by recently published papers. Our study has two important features: (i) as the first study to employ gene networks without using conventional quantitative structure-activity relationships (QSARs) as input data for SVMs to analyze toxicogenomics data in an hESC validation system,it uses additional information of gene-to-gene interactions to significantly increase prediction accuracies for noisy gene expression data; and (ii) using only undifferentiated hESCs,our study has considerable potential to predict late-onset chemical toxicities,including abnormalities that occur during embryonic development. View Publication

Human induced pluripotent stem cells (iPSCs) can be derived from various types of somatic cells by transient overexpression of 4 Yamanaka factors (OCT4,SOX2,C-MYC,and KLF4). Patient-specific iPSC derivatives (e.g.,neuronal,cardiac,hepatic,muscular,and endothelial cells [ECs]) hold great promise in drug discovery and regenerative medicine. In this study,we aimed to evaluate whether the cellular origin can affect the differentiation,in vivo behavior,and single-cell gene expression signatures of human iPSC-derived ECs. We derived human iPSCs from 3 types of somatic cells of the same individuals: fibroblasts (FB-iPSCs),ECs (EC-iPSCs),and cardiac progenitor cells (CPC-iPSCs). We then differentiated them into ECs by sequential administration of Activin,BMP4,bFGF,and VEGF. EC-iPSCs at early passage (10 textless P textless 20) showed higher EC differentiation propensity and gene expression of EC-specific markers (PECAM1 and NOS3) than FB-iPSCs and CPC-iPSCs. In vivo transplanted EC-iPSC-ECs were recovered with a higher percentage of CD31(+) population and expressed higher EC-specific gene expression markers (PECAM1,KDR,and ICAM) as revealed by microfluidic single-cell quantitative PCR (qPCR). In vitro EC-iPSC-ECs maintained a higher CD31(+) population than FB-iPSC-ECs and CPC-iPSC-ECs with long-term culturing and passaging. These results indicate that cellular origin may influence lineage differentiation propensity of human iPSCs; hence,the somatic memory carried by early passage iPSCs should be carefully considered before clinical translation. View Publication