技术资料

An obligatory step in retroviral growth is the integration of a DNA copy of the viral RNA into the genomic DNA of the host. Recombinant human immunodeficiency virus type I (HIV-1) integrase (IN) expressed in Escherichia coli efficiently catalyzes the overall in vitro integration reaction,namely the processing of the LTR ends and the strand transfer reaction. Using the 3' end of synthetic oligonucleotides which match the termini of the HIV-1 U5 LTR as substrate and supercoiled pSP65 DNA as target,we have investigated the effect of the polyanionic drug suramin on the catalytic activity of the IN protein. It was found that at stoichiometric suramin to protein ratios,suramin displays a strong inhibitory effect on both the processing and strand transfer reactions. This inhibitory effect is related to the decrease of IN protein binding efficiency to the LTR end DNA fragment. View Publication

Murine hematopoietic stem cells with varying proliferative capacity can be assayed by limiting dilution analysis of cobblestone area" (CA) formation on stromal layers in microlong-term bone marrow cultures. Cobblestone area forming cell (CAFC) frequency determined at early time points (day 7) correlates with mature stem cells measured as day 8 CFU-S� View Publication

To study the role of the murine heat-stable Ag (HSA) in lymphocyte maturation,we generated transgenic mice in which the HSA cDNA was under the transcriptional control of the TCR V beta promoter and Ig mu enhancer. The HSA transgene was expressed during all stages of B lymphocyte maturation. Expression was first detected in the earliest lymphoid-committed progenitors,which normally do not express HSA,and subsequently reached the highest levels in pro- and pre-B cells. In bone marrow,the number of IL-7-responsive clonogenic progenitors was textless 4% of normal,whereas the frequency of earlier B lymphocyte-restricted precursors,detectable as Whitlock-Witte culture-initiating cells,was normal. Pro- and pre-B cells detected by flow cytometry were reduced by approximately 50% relative to controls. Mature splenic B cells were also reduced but to a lesser extent than in marrow,and their response to LPS stimulation was impaired. Reconstitution of SCID and BALB/c-nu/nu mice with HSA transgenic marrow indicated that the perturbations in B lymphopoiesis were not caused by a defective marrow microenvironment or by abnormal T cells. Our previous studies showed elevated HSA expression throughout thymocyte development,which resulted in a profound depletion of CD4+CD8+ double-positive and single-positive thymocytes. Together,these results indicate that HSA levels can determine the capacity of early T and B lymphoid progenitors to proliferate and survive. Therefore,HSA could serve as an important regulator during the early stages of B and T lymphopoiesis. View Publication

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We used reverse transcription-polymerase chain reaction (RT-PCR) to clone a rat complementary DNA that encoded the PVG rat granulocyte-macrophage colony-stimulating factor (GM-CSF). PCR products were cloned into a eukaryotic expression vector and transfected into the mouse myeloma cell line Sp2/0-Ag14. Cell culture supernatants of two of these transfectants supported proliferation of the growth factor-dependent cell line,DA-3,and promoted myeloid colony formation in rat and mouse bone marrow cell (BMC) cultures. The GM-CSF activity in these supernatants was neutralized by a polyclonal antibody to mouse GM-CSF. The cloning and expression of rat GM-CSF provides a valuable reagent for the study of the biology and clinical applications of the GM-CSFs. View Publication

Elevated numbers of primitive Philadelphia chromosome-positive (Ph+) progenitors,including long-term culture-initiating cells (LTC-IC) as well as colony-forming cells (CFC),have been previously described in the blood of patients with chronic myeloid leukemia (CML) in chronic phase with high white blood cell counts. In the present study,which focused primarily on an analysis of circulating progenitors present in such patients at diagnosis,we discovered the frequent and occasionally exclusive presence of circulating normal (Ph-) LTC-IC,often at levels above those seen for LTC-IC in the blood of normal individuals. The presence of detectable numbers of circulating Ph- LTC-IC was independent of the fact that the same peripheral blood samples also contained elevated numbers of predominantly or exclusively Ph+ CFC. Interestingly,both the Ph+ and Ph- LTC-IC in these samples were CD34+CD71- and variably CD38- and Thy-1+,as previously documented for LTC-IC in normal marrow. Thus,neither CD38 nor Thy-1 expression was useful for discriminating between Ph+ and Ph- LTC-IC in mixed populations. Nevertheless,an association of these phenotypes with LTC-IC function did allow highly enriched (textgreater 5% pure) suspensions of either Ph+ or Ph- LTC-IC to be obtained from selected samples of CML blood in which the initial LTC-IC population was either predominantly Ph+ or Ph-,respectively. These findings suggest that the mechanisms causing mobilization of leukemic stem cells in untreated CML patients may affect their normal counterparts. They also indicate a possible new source of autologous cells for the support of intensive therapy of CML patients. Finally,they provide a method for obtaining the most highly purified populations of Ph+ LTC-IC described to date. This method should be useful for further analyses of the molecular activities of these very primitive neoplastic cells. View Publication

Resveratrol,a phytoalexin found in grapes and other food products,was purified and shown to have cancer chemopreventive activity in assays representing three major stages of carcinogenesis. Resveratrol was found to act as an antioxidant and antimutagen and to induce phase II drug-metabolizing enzymes (anti-initiation activity); it mediated anti-inflammatory effects and inhibited cyclooxygenase and hydroperoxidase functions (antipromotion activity); and it induced human promyelocytic leukemia cell differentiation (antiprogression activity). In addition,it inhibited the development of preneoplastic lesions in carcinogen-treated mouse mammary glands in culture and inhibited tumorigenesis in a mouse skin cancer model. These data suggest that resveratrol,a common constituent of the human diet,merits investigation as a potential cancer chemopreventive agent in humans. View Publication

Previous studies demonstrated that inhibition of sphingolipid synthesis by the mycotoxin fumonisin B1 (FB1) disrupts axonal growth in cultured hippocampal neurons (Harel,R.,and Futerman,A. H. (1993) J. Biol. Chem. 268,14476-14481) by affecting the formation or stabilization of axonal branches (Schwarz,A.,Rapaport,E.,Hirschberg,K.,and Futerman,A.H. (1995) J. Biol. Chem. 270,10990-10998). We now demonstrate that long term incubation with FB1 affects fibroblast morphology and proliferation. Incubation of Swiss 3T3 cells with FB1 resulted in a decrease in synthesis of ganglioside GM3,the major glycosphingolipid in 3T3 fibroblasts and of sphingomyelin. The projected cell area of FB1-treated cells was approximately 45% less than control cells. FB1 had no affect on the organization of microtubules or intermediate filaments,but fewer actin-rich stress fibers were observed,and there was a loss of actin-rich lamellipodia at the leading edge. Three other processes involving the actin cytoskeleton,cytokinesis,microvilli formation,and the formation of long processes induced by protein kinase inhibitors,were all disrupted by FB1. All the effects of FB1 on cell morphology could be reversed by addition of ganglioside GM3 even in the presence of FB1,whereas the bioactive intermediates,sphinganine,sphingosine,and ceramide,were without effect. Finally,FB1 blocked cell proliferation and DNA synthesis in a reversible manner,although ganglioside GM3 could not reverse the effects of FB1 on cell proliferation. Together,these data suggest that ongoing sphingolipid synthesis is required for the assembly of both new membrane and of the underlying cytoskeleton. View Publication

Phosphatidylinositol (PtdIns) 4-kinases catalyze the synthesis of PtdIns-4-P,the immediate precursor of PtdIns-4,5-P2. Here we report the cloning of a novel,ubiquitously expressed PtdIns 4-kinase (PI4Kbeta). The 2.4-kilobase pair cDNA encodes a putative translation product of 801 amino acids which shows greatest homology to the yeast PIK1 gene. The recombinant protein exhibits lipid kinase activity when expressed in Escherichia coli,and specific antibodies recognize a 110-kDa PtdIns 4-kinase in cell lysates. The biochemical properties of PI4Kbeta are characteristic of a type III enzyme. Interestingly,both recombinant PI4Kbeta and the endogenous protein are inhibited by 150 nM wortmannin,suggesting that we have cloned the previously described PtdIns 4-kinase that is responsible for regulating the synthesis of agonist-sensitive pools of polyphosphoinositides (Nakanishi,S.,Catt,J. K.,and Balla,T. (1995) Proc. Natl. Acad. Sci. U. S. A. 92,5317-5321). View Publication

It is well established that mitogens inhibit differentiation of skeletal muscle cells,but the insulin-like growth factors (IGFs),acting through a single receptor,stimulate both proliferation and differentiation of myoblasts. Although the IGF-I mitogenic signaling pathway has been extensively studied in other cell types,little is known about the signaling pathway leading to differentiation in skeletal muscle. By using specific inhibitors of the IGF signal transduction pathway,we have begun to define the signaling intermediates mediating the two responses to IGFs. We found that PD098059,an inhibitor of mitogen-activated protein (MAP) kinase kinase activation,inhibited IGF-stimulated proliferation of L6A1 myoblasts and the events associated with it,such as phosphorylation of the MAP kinases and elevation of c-fos mRNA and cyclin D protein. Surprisingly,PD098059 caused a dramatic enhancement of differentiation,evident both at a morphological (fusion of myoblasts into myotubes) and biochemical level (elevation of myogenin and p21 cyclin-dependent kinase inhibitor expression,as well as creatine kinase activity). In sharp contrast,LY294002,an inhibitor of phosphatidylinositol 3-kinase,and rapamycin,an inhibitor of the activation of p70 S6 kinase (p70(S6k)),completely abolished IGF stimulation of L6A1 differentiation. We found that p70(S6k) activity increased substantially during differentiation,and this increase was further enhanced by PD098059. Our results demonstrate that the MAP kinase pathway plays a primary role in the mitogenic response and is inhibitory to the myogenic response in L6A1 myoblasts,while activation of the phosphatidylinositol 3-kinase/p70(S6k) pathway is essential for IGF-stimulated differentiation. Thus,it appears that signaling from the IGF-I receptor utilizes two distinct pathways leading either to proliferation or differentiation. View Publication

The immunosuppressive effects of microcolin A,a lipopeptide extracted from the marine blue green alga Lyngbya majuscula were investigated. Microcolin A suppressed concanavalin A (IC50 = 5.8 nM),phytohemagglutinin (IC50 = 12.5 nM) and lipopolysaccharide (IC50 = 8.0 nM) induced proliferation of murine splenocytes. Mixed lymphocyte reaction (IC50 = 5.0 nM),anti-IgM (mu-chain specific) (IC50 = 10.0 nM),and phorbol 12-myristate 13-acetate plus ionomycin (IC50 = 5.8 nM) stimulation of murine splenocytes were all similarly suppressed by microcolin A. The inhibitory activity of microcolin A was time-dependent and reversible and was not associated with a reduction in cell viability. Moreover,microcolin A not only inhibited IL-2 production and IL-2 receptor expression by concanavalin A activated splenocytes,but also suppressed in vitro antibody responsiveness to keyhole limpet hemocyanin. These results indicate that microcolin A is a potent immunosuppressive and antiproliferative agent. View Publication

Human progenitors of the megakaryocyte (Mk) lineage were detected by their ability to generate colonies-containing from 3 to textgreater 100 Mk,detectable as glycoprotein IIb/IIIa+ cells in APAAP-stained whole mount agarose cultures. Optimal growth conditions were achieved through the use of a defined serum substitute and a suitable cocktail of recombinant cytokines. Under these culture conditions,the smallest Mk-containing colonies (CFC-Mk) were detectable within a week followed by colonies containing larger numbers of Mk over the ensuing 2 weeks. The total number of CFC-Mk at 18-21 d was linearly related to the number of cells plated. Variation in the cytokines added showed that thrombopoietin (TPO) or IL-3 alone would support the formation of large numbers of CFC-Mk. However,optimal yields of colonies containing cells of both Mk and non-Mk lineages required the addition of other growth factors,of which a combination of IL-3,IL-6,GM-CSF and Steel factor (SF) +/- TPO was the best of those tested. The further addition of erythropoietin to this combination reduced the number of large pure' Mk colonies seen and in their place a corresponding number of mixed erythroid-Mk colonies became detectable. Flt3-ligand alone was unable to support the growth of CFC-Mk nor did it enhance their growth when combined with other factors. Plating of FACS-sorted sub-populations of CD34+ marrow cells in both serum-free agarose and methylcellulose assays demonstrated that most CFC-Mk are generated from CD34+ cells that are CD45RA- and CD71+� View Publication