技术资料

The AMP-activated protein kinase (AMPK) is believed to protect cells against environmental stress (e.g. heat shock) by switching off biosynthetic pathways,the key signal being elevation of AMP. Identification of novel targets for the kinase cascade would be facilitated by development of a specific agent for activating the kinase in intact cells. Incubation of rat hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) results in accumulation of the monophosphorylated derivative (5-aminoimidazole-4-carboxamide ribonucleoside; ZMP) within the cell. ZMP mimics both activating effects of AMP on AMPK,i.e. direct allosteric activation and promotion of phosphorylation by AMPK kinase. Unlike existing methods for activating AMPK in intact cells (e.g. fructose,heat shock),AICAR does not perturb the cellular contents of ATP,ADP or AMP. Incubation of hepatocytes with AICAR activates AMPK due to increased phosphorylation,causes phosphorylation and inactivation of a known target for AMPK (3-hydroxy-3-methylglutaryl-CoA reductase),and almost total cessation of two of the known target pathways,i.e. fatty acid and sterol synthesis. Incubation of isolated adipocytes with AICAR antagonizes isoprenaline-induced lipolysis. This provides direct evidence that the inhibition by AMPK of activation of hormone-sensitive lipase by cyclic-AMP-dependent protein kinase,previously demonstrated in cell-free assays,also operates in intact cells. AICAR should be a useful tool for identifying new target pathways and processes regulated by the protein kinase cascade. View Publication

Sphingolipids,particularly gangliosides,are enriched in neuronal membranes where they have been implicated as mediators of various regulatory events. We recently provided evidence that sphingolipid synthesis is necessary to maintain neuronal growth by demonstrating that in hippocampal neurons,inhibition of ceramide synthesis by Fumonisin B1 (FB1) disrupted axonal outgrowth (Harel,R. and Futerman,A. H. (1993) J. Biol. Chem. 268,14476-14481). We now analyze further the relationship between neuronal growth and sphingolipid metabolism by examining the effect of an inhibitor of glucosylceramide synthesis,D-threo-1-phenyl-2-decanoylamino-3-morpholino-1- propanol (PDMP) and by examining the effects of both FB1 and PDMP at various stages of neuronal development. No effects of FB1 or PDMP were observed during the first 2 days in culture,but by day 3 axonal morphology was significantly altered,irrespective of the time of addition of the inhibitors to the cultures. Cells incubated with FB1 or PDMP had a shorter axon plexus and less axonal branches. FB1 appeared to cause a retraction of axonal branches between days 2 and 3,although long term incubation had no apparent effect on neuronal morphology or on the segregation of axonal or dendritic proteins. In contrast,incubation of neurons with conduritol B-epoxide,an inhibitor of glucosylceramide degradation,caused an increase in the number of axonal branches and a corresponding increase in the length of the axon plexus. A direct correlation was observed between the number of axonal branch points per cell and the extent of inhibition of either sphingolipid synthesis or degradation. These results suggest that sphingolipids play an important role in the formation or stabilization of axonal branches. View Publication

We have recently shown that conservation and differentiation of primitive human hematopoietic progenitors in in vitro long-term bone marrow cultures (LTBMC) occurs to a greater extent when hematopoietic cells are grown separated from the stromal layer than when grown in direct contact with the stroma. This finding suggests that hematopoiesis may depend mainly on soluble factors produced by the stroma. To define these soluble factors,we examine here whether a combination of defined early-acting cytokines can replace soluble stroma-derived biologic activities that induce conservation and differentiation of primitive progenitors. Normal human Lineage-/CD34+/HLA-DR- cells (DR-) were cultured either in the absence of a stromal layer (stroma-free") or in a culture system in which DR- cells were separated from the stromal layer by a microporous membrane ("stroma-noncontact"). Both culture systems were supplemented three times per week with or without cytokines. These studies show that culture of DR- cells for 5 weeks in a "stroma-free" culture supplemented with a combination of four early acting cytokines (Interleukin-3 [IL-3]� View Publication

The growth of human megakaryocyte progenitors from human bone marrow (BM) cells was compared using a methylcellulose semisolid assay supplemented either by normal human plasma or by a serum-free medium. Far better growth of megakaryocyte colonies from CD34+ BM cells stimulated by interleukin 3 (IL-3) and interleukin 6 (IL-6) was observed in serum-free medium compared with human plasma supplemented cultures. These results were confirmed in liquid cultures using the same serum-free medium composition. The megakaryocytes were identified by using an immunocytochemical procedure after labeling with an anti-GPIIb-IIIa monoclonal antibody. High percentages (15 to 20%) of megakaryocytes were present in serum-free cultures stimulated by IL-3 alone or combined with IL-6. The absolute number of megakaryocytes in serum-free medium exceeds by 3.3 (IL-3 plus IL-6) to 4.4 (IL-3 alone) times the corresponding number of megakaryocytes observed in human plasma supplemented cultures. The optimal concentration of IL-3 alone was 5 ng/ml,and an optimal synergistic effect of IL-6 (5 ng/ml) was obtained when combined with a suboptimal dose of IL-3 (1 ng/ml). The poor growth of megakaryocyte colonies from CD34+ BM cells in human plasma suggested the presence of an inhibitory factor. When a neutralizing monoclonal antibody against transforming growth factor beta (TGF beta) is present in human plasma supplemented cultures of CD34+ BM cells,the number of megakaryocyte colonies is increased to the level observed in corresponding serum-free cultures. The high efficiency of this serum-free medium to promote the growth of human megakaryocytes will be useful to study the effects of regulators and platelet agonists acting on human megakaryocytes,without interference from factors in the serum. View Publication

DNA-dependent protein kinase (DNA-PK),which is involved in DNA double-stranded break repair and V(D)J recombination,comprises a DNA-targeting component called Ku and an approximately 460 kDa catalytic subunit,DNA-PKcs. Here,we describe the cloning of the DNA-PKcs cDNA and show that DNA-PKcs falls into the phosphatidylinositol (PI) 3-kinase family. Biochemical assays,however,indicate that DNA-PK phosphorylates proteins but has no detectable activity toward lipids. Strikingly,DNA-PKcs is most similar to PI kinase family members involved in cell cycle control,DNA repair,and DNA damage responses. These include the FKBP12-rapamycin-binding proteins Tor1p,Tor2p,and FRAP,S. pombe rad3,and the product of the ataxia telangiectasia gene,mutations in which lead to genomic instability and predisposition to cancer. The relationship of these proteins to DNA-PKcs provides important clues to their mechanisms of action. View Publication

The microbial product wortmannin has previously been shown to be a potent inhibitor of phosphatidylinositol-3-kinase. In view of the potential role of this enzyme in transduction of mitogenic signals,we determined the cytotoxic activity of wortmannin against several human tumor cell lines in vitro. The most sensitive lines included GC3 colon carcinoma,IGROV1 ovarian carcinoma,and CCRF-CEM leukemia (IC-50s ranging from 0.7-2.1 microM). The cytotoxicity of wortmannin was decreased approximately 10-fold by serum-free conditions. Wortmannin was generally less active in low passage human breast cancer cell lines that overexpress either epidermal growth factor receptor or Her2/neu. Wortmannin was also tested for in vivo antitumor activity against seven murine tumor and ten human tumor xenograft models. Activity (textgreater 60% inhibition of tumor growth) was observed in only the C3H mammary carcinoma and the human BxPC-3 pancreatic carcinoma xenograft. In vivo antitumor activity did not correlate with in vitro sensitivity to wortmannin cytotoxicity. View Publication

Treatment of cells with a variety of growth factors triggers a phosphorylation cascade that leads to activation of mitogen-activated protein kinases (MAPKs,also called extracellular signal-regulated kinases,or ERKs). We have identified a synthetic inhibitor of the MAPK pathway. PD 098059 [2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one] selectively inhibited the MAPK-activating enzyme,MAPK/ERK kinase (MEK),without significant inhibitory activity of MAPK itself. Inhibition of MEK by PD 098059 prevented activation of MAPK and subsequent phosphorylation of MAPK substrates both in vitro and in intact cells. Moreover,PD 098059 inhibited stimulation of cell growth and reversed the phenotype of ras-transformed BALB 3T3 mouse fibroblasts and rat kidney cells. These results indicate that the MAPK pathway is essential for growth and maintenance of the ras-transformed phenotype. Further,PD 098059 is an invaluable tool that will help elucidate the role of the MAPK cascade in a variety of biological settings. View Publication

Retinoids elicit biological responses by activating a series of nuclear receptors. Six retinoid receptors belonging to two families are currently known: retinoic acid receptors (RAR alpha,beta,and gamma) and retinoid X receptors (RXR alpha,beta,and gamma). Stilbene retinoid analogs of retinoic acid (RA),such as (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)prope n-1- yl]benzoic acid (TTNPB,1) and (E)-4-[2-(5,6,7,8-tetrahydro-3,5,5,8,8-pentamethyl-2-naphthalenyl)pro pen-1- yl]benzoic acid (3-methyl-TTNPB,2),display differential RAR and RXR activities,depending on the substituent at C3 of the naphthalene ring. We report here structural modifications of the benzoate moiety of 2 that result in analogs with greater RXR selectivity as well as those with pan-agonist (activate both RAR and RXR receptors) activities,analyze the structural features that impart receptor selectivity,and describe a stereoselective method for the synthesis of these analogs. The biological activities associated with the RAR and RXR receptors were examined by testing representative examples with different receptor activation profiles for their ability to induce tissue transglutaminase (Tgase) activity in a human promyelocytic leukemia cell line (HL-60 cdm-1) and to inhibit tumor-promoter-induced ornithine decarboxylase (ODC) activity in hairless mouse skin. These results suggest that RAR agonists and RXR agonists may have different therapeutic applications. Finally,we show that RXR agonists are significantly reduced in teratogenic potency relative to RAR agonists and may therefore have significant advantages in clinical practice. View Publication

In this report,we describe a modification of the assay for long-term culture-initiating cells (LTC-IC) that allows a subset of murine LTC-IC (designated as LTC-ICML) to express both their myeloid (M) and lymphoid (L) differentiative potentials in vitro. The modified assay involves culturing test cells at limiting dilutions on irradiated mouse marrow feeder layers for an initial 4 weeks under conditions that support myelopoiesis and then for an additional week under conditions permissive for B-lymphopoiesis. All of the clonogenic pre-B progenitors (colony-forming unit [CFU] pre-B) detected in such postswitch LTC appear to be the progeny of uncommitted cells present in the original cell suspension because exposure of lymphoid-restricted progenitors to myeloid LTC conditions for textgreater or = 7 days was found to irreversibly terminate CFU-pre-B production and,in cultures initiated with limiting numbers of input cells (no progenitors of any type detected in textgreater 70% of cultures 1 week after the switch),the presence of CFU-pre-B was tightly associated with the presence of myeloid clonogenic cells,regardless of the purity of the input population. Limiting dilution analysis of the proportion of negative cultures measured for different numbers of input cells showed the frequency of LTC-ICML in normal adult mouse marrow to be 1 per 5 x 10(5) cells with an enrichment of approximately 500-fold in the Sca-1+ Lin-WGA+ fraction,as was also found for competitive in vivo repopulating units (CRU) and conventionally defined LTC-IC. LTC-ICML also exhibited the same resistance to treatment in vivo with 5-fluorouracil (5-FU) as CRU and LTC-IC,thereby distinguishing these three populations from the great majority of both in vitro clonogenic cells and day 12 CFU-S. The ability to quantitate cells with dual lymphoid and myeloid differentiation potentials in vitro,without the need for their prior purification,should facilitate studies of totipotent hematopoietic stem cell regulation. View Publication

The requirement of complex sphingolipid biosynthesis for growth of neurons was examined in developing rat cerebellar Purkinje neurons using a dissociated culture system. Purkinje cells developed well-differentiated dendrites and axons after 2 weeks in a serum-free nutrient condition. Addition of 2 microM fumonisin B1,a fungal inhibitor of mammalian ceramide synthase,inhibited incorporation of [3H]galactose/glucosamine and [14C]-serine into complex sphingolipids of cultured cerebellar neurons. Under this condition,the expression of Purkinje cell-enriched sphingolipids,including GD1 alpha,9-O-acetylated LD1 and GD3,and sphingomyelin,was significantly decreased. After 2 weeks' exposure to fumonisin B1,dose-dependent measurable decreases in the survival and visually discernible differences in the morphology were seen in fumonisin-treated Purkinje cells. The Purkinje cell dendrites exhibited two types of anomalies; one population of cells developed elongated but less-branched dendrites after a slight time lag,but their branches began to degenerate. In some cells,formation of elongated dendrite trees was severely impaired. However,treatment with fumonisin B1 also led to the formation of spinelike protrusions on the dendrites of Purkinje cells as in control cultures. In contrast to the alterations observed in Purkinje cells,morphology of other cell types including granule neurons appeared to be almost normal after treatment with fumonisin B1. These observations indicated strongly that membrane sphingolipids participate in growth and maintenance of dendrites and in the survival of cerebellar Purkinje cells. Indeed,these effects of fumonisin B1 were reversed,but not completely,by the addition of 6-[[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-amino dcaproyl]sphingosine (C6-NBD-ceramide),a synthetic derivative of ceramide. Thus,we conclude that deprivation of membrane sphingolipids in a culture environment is responsible for aberrant growth of Purkinje cells. View Publication

Hypoxia-inducible factor 1 (HIF-1) is found in mammalian cells cultured under reduced O2 tension and is necessary for transcriptional activation mediated by the erythropoietin gene enhancer in hypoxic cells. We show that both HIF-1 subunits are basic-helix-loop-helix proteins containing a PAS domain,defined by its presence in the Drosophila Per and Sim proteins and in the mammalian ARNT and AHR proteins. HIF-1 alpha is most closely related to Sim. HIF-1 beta is a series of ARNT gene products,which can thus heterodimerize with either HIF-1 alpha or AHR. HIF-1 alpha and HIF-1 beta (ARNT) RNA and protein levels were induced in cells exposed to 1% O2 and decayed rapidly upon return of the cells to 20% O2,consistent with the role of HIF-1 as a mediator of transcriptional responses to hypoxia. View Publication

We have investigated the potential of stirred suspension cultures to support hematopoiesis from starting innocula of normal human bone marrow cells. Initial studies showed that the short-term maintenance of both colony-forming cell (CFC) numbers and their precursors,detected as long-term culture-initiating cells (LTC-IC),could be achieved as well in stirred suspension cultures as in static cultures. Neither of these progenitor cell populations was affected in either type of culture when porous microcarriers were added to provide an increased surface for adherent cell attachment. Supplementation of the medium with 10 ng/ml of Steel factor (SF) and 2 ng/ml of interleukin-3 (IL-3) resulted in a significant expansion of LTC-IC,CFC and total cell numbers in stirred cultures. Both the duration and ultimate magnitude of these expansions were correlated with the initial cell density and after 4 weeks the number of LTC-IC and CFC present in stirred cultures initiated with the highest starting cell concentration tested reflected average increases of 7- and 22-fold,respectively,above input values. Stirred suspension cultures offer the combined advantages of homogeneity and lack of dependence on the formation and maintenance of an adherent cell layer. Our results suggest their applicability to the development of scaled-up bioreactor systems for clinical procedures requiring the production of primitive hematopoietic cell populations. In addition,stirred suspension cultures may offer a new tool for the analysis of hematopoietic regulatory mechanisms. View Publication