MazF Cleaves Cellular mRNAs Specifically at ACA to Block Protein Synthesis in Escherichia coli

Escherichia coli contains operons called "addiction modules," encoding toxin and antitoxin, which are responsible for growth arrest and cell death. Here, we demonstrate that MazF toxin encoded by "mazEF addiction module" is a sequence-specific (ACA) endoribonuclease functional only for single-stranded RNA. MazF works as a ribonuclease independent of ribosomes, and is, therefore, functionally distinct from RelE, another E. coli toxin, which assists mRNA cleavage at the A site on ribosomes. Upon induction, MazF cleaves whole cellular mRNAs to efficiently block protein synthesis. Purified MazF inhibited protein synthesis in both prokaryotic and eukaryotic cell-free systems. This inhibition was released by MazE, the labile antitoxin against MazF. Thus, MazF functions as a toxic endoribonuclease to interfere with the function of cellular mRNAs by cleaving them at specific sequences leading to rapid cell growth arrest and cell death. The role of such endoribonucleases may have broad implication in cell physiology under various growth conditions.

The checkpoint protein MAD2 and the mitotic regulator CDC20 form a ternary complex with the anaphase-promoting complex to control anaphase initiation

The spindle assembly checkpoint mechanism delays anaphase initiation until all chromosomes are aligned at the metaphase plate. Activation of the anaphase-promoting complex (APC) by binding of CDC20 and CDH1 is required for exit from mitosis, and APC has been implicated as a target for the checkpoint intervention. We show that the human checkpoint protein hMAD2 prevents activation of APC by forming a hMAD2-CDC20-APC complex. When injected into Xenopus embryos, hMAD2 arrests cells at mitosis with an inactive APC. The recombinant hMAD2 protein exists in two-folded states: a tetramer and a monomer. Both the tetramer and the monomer bind to CDC20, but only the tetramer inhibits activation of APC and blocks cell cycle progression. Thus, hMAD2 binding is not sufficient for inhibition, and a change in hMAD2 structure may play a role in transducing the checkpoint signal. There are at least three different forms of mitotic APC that can be detected in vivo: an inactive hMAD2-CDC20-APC ternary complex present at metaphase, a CDC20-APC binary complex active in degrading specific substrates at anaphase, and a CDH1-APC complex active later in mitosis and in G1. We conclude that the checkpoint-mediated cell cycle arrest involves hMAD2 receiving an upstream signal to inhibit activation of APC.

Induction of nuclear envelope breakdown, chromosome condensation, and spindle formation in cell-free extracts

Incubation of demembranated sperm chromatin in cytoplasmic extracts of unfertilized Xenopus laevis eggs resulted in nuclear envelope assembly, chromosome decondensation, and sperm pronuclear formation. In contrast, egg extracts made with EGTA-containing buffers induced the sperm chromatin to form chromosomes or irregularly shaped clumps of chromatin that were incorporated into bipolar or multipolar spindles. The 150,000 g supernatants of the EGTA extracts could not alone support these changes in incubated nuclei. However, these supernatants induced not only chromosome condensation and spindle formation, but also nuclear envelope breakdown when added to sperm pronuclei or isolated Xenopus liver or brain nuclei that were incubated in extracts made without EGTA. Similar changes were induced by partially purified preparations of maturation-promoting factor. The addition of calcium chloride to extracts containing condensed chromosomes and spindles caused dissolution of the spindles, decondensation of the chromosomes, and re-formation of interphase nuclei. These results indicate that nuclear envelope breakdown, chromosome condensation, and spindle assembly, as well as the regulation of these processes by Ca2+-sensitive cytoplasmic components, can be studied in vitro using extracts of amphibian eggs.

Oxidative stress causes mucin synthesis via transactivation of epidermal growth factor receptor: role of neutrophils

Oxidative stress has been implicated in the pathogenesis of inflammatory diseases of airways. Here we show that oxidative stress causes ligand-independent activation of epidermal growth factor receptors (EGFR) and subsequent activation of mitogen-activated protein kinase kinase (MEK)-p44/42 mitogen-activated protein kinase (p44/42mapk), resulting in mucin synthesis in NCI-H292 cells. Exogenous hydrogen peroxide and neutrophils activated by IL-8, FMLP, or TNF-alpha increased EGFR tyrosine phosphorylation and subsequent activation of p44/42mapk and up-regulated the expression of MUC5AC at both mRNA and protein levels in NCI-H292 cells. These effects were blocked by selective EGFR tyrosine kinase inhibitors (AG1478, BIBX1522) and by a selective MEK inhibitor (PD98059), whereas a selective platelet-derived growth factor receptor tyrosine kinase inhibitor (AG1295), a selective p38 MAPK inhibitor (SB203580), and a negative compound of tyrosine kinase inhibitors (A1) were without effect. Neutrophil supernatant-induced EGFR tyrosine phosphorylation, activation of p44/42mapk, and MUC5AC synthesis were inhibited by antioxidants (N-acetyl-cysteine, DMSO, dimethyl thiourea, or superoxide dismutase); neutralizing Abs to EGFR ligands (EGF and TGF-alpha) were without effect, and no TGF-alpha protein was found in the neutrophil supernatant. In contrast, the EGFR ligand, TGF-alpha, increased EGFR tyrosine phosphorylation, activation of p44/42mapk, and subsequent MUC5AC synthesis, but these effects were not inhibited by antioxidants. These results implicate oxidative stress in stimulating mucin synthesis in airways and provide new therapeutic approaches in airway hypersecretory diseases.

Amyloid beta-peptide induces apoptosis-related events in synapses and dendrites

Synapse loss in cerebral cortex and hippocampus is a prominent feature of Alzheimer's disease (AD) that is correlated with cognitive impairment. Postsynaptic regions of dendrites are subjected to particularly high levels of calcium influx and oxidative stress as a result of local activation of glutamate receptors, and are therefore likely to be sites at which neurodegenerative processes are initiated in AD. Data suggest that neurons may die in AD by a process called apoptosis which involves a stereotyped series of biochemical changes that culminate in nuclear fragmentation, and that amyloid beta-peptide (Abeta) may play a role in such apoptosis. We now report that Abeta induces apoptosis-related biochemical changes in cortical synaptosomes, and in dendrites of cultured hippocampal neurons. Exposure of synaptosomes to Abeta resulted in loss of membrane phospholipid asymmetry, caspase activation, and mitochondrial membrane depolarization. Cytosolic extracts from synaptosomes exposed to Abeta induced chromatin condensation and fragmentation in isolated nuclei indicating that signals capable of inducing nuclear apoptosis can be generated locally in synapses. Exposure of cultured hippocampal neurons to Abeta resulted in caspase activation and mitochondrial membrane depolarization in dendrites and cell bodies. A caspase inhibitor prevented Abeta-induced mitochondrial membrane depolarization in synaptosomes, and mitochondrial membrane depolarization and nuclear apoptosis in cultured hippocampal neurons. Collectively, the data demonstrate that apoptotic biochemical cascades can be activated in synapses and dendrites by Abeta, and suggest that such 'synaptic apoptosis' may contribute to synaptic dysfunction and degeneration in AD.

A highly efficient cell-free protein synthesis system from Escherichia coli

We modified a cell-free coupled transcription/translation system from Escherichia coli with the T7 phage RNA polymerase, and achieved a productivity as high as 0.4 mg protein/ml reaction mixture. First, we found that the optimal concentrations of phosphoenolpyruvate and poly(ethylene glycol) are interdependent; higher concentrations of the former should be used at higher concentrations of the latter. Second, the use of a condensed 30000 x g cell extract, in place of the conventional one, significantly increased the initial rate of protein synthesis. This phenomenon was demonstrated to be due to a reason other than elimination of inhibitory molecule(s) from the extract. For this system with the condensed extract, the phosphoenolpyruvate and poly(ethylene glycol) concentrations were again co-optimized, resulting in production of chloramphenicol acetyltransferase at a productivity of 0.3 mg/ml. Finally, the productivity was further increased up to 0.4 mg/ml, by supplementation of the pool of amino acids. This improved cell-free protein synthesis system is superior in productivity to any other cell-free systems reported so far, including the continuous-flow cell-free system.

Purification and characterization of novel ribosome inactivating proteins, alpha- and beta-pisavins, from seeds of the garden pea Pisum sativum

Two ribosome inactivating proteins designated alpha- and beta-pisavins were isolated from seeds of the garden pea Pisum sativum var. arvense Poir with a procedure involving affinity chromatography on Affi-gel Blue gel, immobilized metal ion affinity chromatography on Iminodiacetic acid-agarose, cation exchange chromatography on Resource-S, and gel filtration on Superose 12. alpha- and beta-pisavins are nonglycoproteins with a molecular weight of 20.5 kDa and 18.7 kDa respectively. The sequences of the first sixty N-terminal amino acids of alpha- and beta-pisavins were identical. In isoelectric focusing these two proteins merged into one band with a pI greater than 9.3. Inhibition of protein synthesis by a rabbit reticulocyte lysate system was achieved at an IC50 of approximately 0.5 nM. Activity of the proteins toward tRNA was observed. The proteins acted on ribosomal RNA through its RNA N-glycosidase activity to release an Endo's fragment, and converted the conformation of DNA from supercoiled and circular forms into a linear form.

Polyethylene glycol immediately repairs neuronal membranes and inhibits free radical production after acute spinal cord injury

Membrane disruption and the production of reactive oxygen species (ROS) are important factors causing immediate functional loss, progressive degeneration, and death in neurons and their processes after traumatic spinal cord injury. Using an in vitro guinea pig spinal cord injury model, we have shown that polyethylene glycol (PEG), a hydrophilic polymer, can significantly accelerate and enhance the membrane resealing process to restore membrane integrity following controlled compression. As a result of PEG treatment, injury-induced ROS elevation and lipid peroxidation (LPO) levels were significantly suppressed. We further show that PEG is not an effective free radical scavenger nor does it have the ability to suppress xanthine oxidase, a key enzyme in generating superoxide. These observations suggest that it is the PEG-mediated membrane repair that leads to ROS and LPO inhibition. Furthermore, our data also imply an important causal effect of membrane disruption in generating ROS in spinal cord injury, suggesting membrane repair to be an effective target in reducing ROS genesis.

Coupling between clathrin-dependent endocytic budding and F-BAR-dependent tubulation in a cell-free system

Cell-free reconstitution of membrane traffic reactions and the morphological characterization of membrane intermediates that accumulate under these conditions have helped to elucidate the physical and molecular mechanisms involved in membrane transport. To gain a better understanding of endocytosis, we have reconstituted vesicle budding and fission from isolated plasma membrane sheets and imaged these events. Electron and fluorescence microscopy, including subdiffraction-limit imaging by stochastic optical reconstruction microscopy (STORM), revealed F-BAR (FBP17) domain coated tubules nucleated by clathrin-coated buds when fission was blocked by GTPgammaS. Triggering fission by replacing GTPgammaS with GTP led not only to separation of clathrin-coated buds, but also to vesicle formation by fragmentation of the tubules. These results suggest a functional link between FBP17-dependent membrane tubulation and clathrin-dependent budding. They also show that clathrin spatially directs plasma membrane invaginations that lead to the generation of endocytic vesicles larger than those enclosed by the coat.

Cell-free protein synthesis inside giant unilamellar vesicles analyzed by flow cytometry

Lipid vesicles have been used as model cell systems, in which an in-vitro transcription-translation system (IVTT) is encapsulated to carry out intravesicular protein synthesis. Despite a large number of previous studies, a quantitative understanding of how protein synthesis inside the vesicles is affected by the lipid membrane remains elusive. This is mainly because of the heterogeneity in structural properties of the lipid vesicles used in the experiments. We investigated the effects of the phospholipid membrane on green fluorescent protein (GFP) synthesis occurring inside cell-sized giant unilamellar vesicles (GUV), which have a defined quantity of lipids relative to the reaction volume. We first developed a method to distinguish GUV from multilamellar vesicles using flow cytometry (FCM). Using this method, we investigated the time course of GFP synthesis using one of the IVTT, the PURE system, and found that phospholipid in the form of GUV has little effect on GFP synthesis based on three lines of investigation. (1) GFP synthesis inside the GUV was not dependent on the size of GUV (2) or on the fraction of cholesterol or anionic phospholipid constituting the GUV, and (3) GFP synthesis proceeded similarly in GUV and in the test tube. The present results suggest that GUV provides an ideal reaction environment that does not affect the internal biochemical reaction. On the other hand, we also found that internal GFP synthesis is strongly dependent on the chemical composition of the outer solution.

Effect of sulphasalazine and its metabolites on the generation of reactive oxygen species

The relative in vitro anti-oxidant efficacy of sulphasalazine (salicylazosulphapyridine, SASP) and its metabolites (5-aminosalicylic acid, 5-ASA; sulphapyridine, SP) was examined by studying their effects on the generation of reactive oxygen species (ROS) using zymosan-stimulated polymorphonuclear leucocytes (PMNs) and a cell free, xanthine-xanthine oxidase system. Salicylazosulphapyridine, 5-ASA, and SP showed anti-oxidant effects to the various degrees. In particular, production of OH, which is one of the most potent reactive oxygen species, was remarkably suppressed by 5-ASA dose relatedly. These findings suggest that SASP and its metabolites play an important role in the inhibition of respiratory bursts. As the potent products of the respiratory burst by polymorphonuclear leucocytes are thought to be important inflammatory mediators, suppression of toxic reactive oxygen species generation by these agents may partly explain the therapeutic efficacy of SASP in ulcerative colitis, which is characterised by an acute mucosal inflammation dominated by polymorphonuclear leucocytes accumulation.

Chondroitinase treatment increases the effective length of acellular nerve grafts

Acellular nerve allografts have been explored as an alternative to nerve autografting. It has long been recognized that there is a distinct limit to the effective length of conventional acellular nerve grafts, which must be overcome for many grafting applications. In rodent models nerve regeneration fails in acellular nerve grafts greater than 2 cm in length. In previous studies we found that nerve regeneration is markedly enhanced with acellular nerve grafts in which growth-inhibiting chondroitin sulfate proteoglycan was degraded by pretreatment with chondroitinase ABC (ChABC). Here, we tested if nerve regeneration can be achieved through 4-cm acellular nerve grafts pretreated with ChABC. Adult rats received bilateral sciatic nerve segmental resection and repair with a 4 cm, thermally acellularized, nerve graft treated with ChABC (ChABC graft) or vehicle-treated acellularized graft (Control graft). Nerve regeneration was examined 12 weeks after implantation. Our findings confirm that functional axonal regeneration fails in conventional long acellular grafts. In this condition we found very few axons in the distal host nerve, and there were marginal signs of sciatic nerve reinnervation in few (2/9) rats. This was accompanied by extensive structural disintegration of the distal graft and abundant retrograde axonal regeneration in the proximal nerve. In contrast, most (8/9) animals receiving nerve repair with ChABC grafts showed sciatic nerve reinnervation by direct nerve pinch testing. Histological examination revealed much better structural preservation and axonal growth throughout the ChABC grafts. Numerous axons were found in all but one (8/9) of the host distal nerves and many of these regenerated axons were myelinated. In addition, the amount of aberrant retrograde axonal growth (originating near the proximal suture line) was markedly reduced by repair with ChABC grafts. Based on these results we conclude that ChABC treatment substantially increases the effective length of acellular nerve grafts.

Developmental neurotoxicity of chlorpyrifos in vivo and in vitro: effects on nuclear transcription factors involved in cell replication and differentiation

Chlorpyrifos is a widely used organophosphate insecticide that is a suspected developmental neurotoxin. Although chlorpyrifos exerts some effects through cholinesterase inhibition, recent studies suggest additional, direct actions on developing cells. We assessed the effects of chlorpyrifos on nuclear transcription factors involved in cell replication and differentiation using in vitro and in vivo models. HeLa nuclear protein extracts were incubated with the labeled consensus oligonucleotides for AP-1 and Sp1 transcription factors in the presence and absence of chlorpyrifos. In concentrations previously shown to affect cell development, chlorpyrifos reduced AP-1, but not Sp1 DNA-binding activity. Next, chlorpyrifos was incubated with PC12 cells either during cell replication or after initiation of differentiation with NGF. Chlorpyrifos evoked stage-specific interference with the expression of the transcription factors: Sp1 was reduced in replicating and differentiating cells, whereas AP-1 was affected only during differentiation. Finally, neonatal rats were given apparently subtoxic doses of chlorpyrifos either on postnatal days 1-4 or 11-14 and the effects were evaluated in the forebrain (an early-developing, cholinergic target region) and cerebellum (late-developing region, poor in cholinergic innervation). Again, chlorpyrifos evoked stage-specific changes in transcription factor expression and binding activity, with greater effects on Sp1 during active neurogenesis, and effects on AP-1 during differentiation. The changes were present in both forebrain and cerebellum and were gender-specific. These results indicate that chlorpyrifos interferes with brain development, in part by multiple alterations in the activity of transcription factors involved in the basic machinery of cell replication and differentiation. Noncholinergic actions of chlorpyrifos that are unique to brain development reinforce the need to examine endpoints other than cholinesterase inhibition.

BRCA1-independent ubiquitination of FANCD2

Monoubiquitination of the FANCD2 protein is a key step in the Fanconi anemia (FA) tumor suppressor pathway, coinciding with this molecule's accumulation at sites of genome damage. Strong circumstantial evidence points to a requirement for the BRCA1 gene product in this step. Here, we show that the purified BRCA1/BARD1 complex, together with E1 and UbcH5a, is sufficient to reconstitute the monoubiquitination of FANCD2 in vitro. Although siRNA-mediated knockdown of BRCA1 in human cells results in defective targeting of FANCD2 to sites of DNA damage, it does not lead to a defect in FANCD2 ubiquitination. Furthermore, ablation of the RING finger domains of either BRCA1 or BARD1 in the chicken B cell line DT40 also leaves FANCD2 modification intact. Consequently, while BRCA1 affects the accumulation of FANCD2 at sites of DNA damage, BRCA1/BARD1 E3 ligase activity is not essential for the monoubiquitination of FANCD2.

Mechanism of action of DuP 721: inhibition of an early event during initiation of protein synthesis

The mode of action of DuP 721 was investigated. This compound was active primarily against gram-positive bacteria, including multiply resistant strains of staphylococci. Although inactive against wild-type Escherichia coli, DuP 721 did inhibit E. coli when the outer membrane was perturbed by genetic or chemical means. Pulse-labeling studies with E. coli PLB-3252, a membrane-defective strain, showed that DuP 721 inhibited amino acid incorporation into proteins. The 50% inhibitory concentration of DuP 721 for protein synthesis was 3.8 micrograms/ml, but it was greater than 64 micrograms/ml for RNA and DNA syntheses. The direct addition of DuP 721 to cell-free systems did not inhibit any of the reactions of protein synthesis from chain initiation through chain elongation with either synthetic or natural mRNA as template. However, cell extracts prepared from DuP 721 growth-arrested cells were defective in initiation-dependent polypeptide synthesis directed by MS2 bacteriophage RNA. These cell-free extracts were not defective in polypeptide elongation or in fMet-tRNA(fMet)-dependent polypeptide synthesis stimulated by poly(G.U). We conclude, therefore, that DuP 721 exerts its primary action at a step preceding the interaction of fMet-tRNA(fMet) and 30S ribosomal subunits with the initiator codon.

Distribution and properties of major ribosome-inactivating proteins (28 S rRNA N-glycosidases) of the plant Saponaria officinalis L. (Caryophyllaceae)

We have studied the distribution of the protein synthesis inhibitory activity in the tissues of Saponaria officinalis L. (Caryophyllaceae). Seven major saporins, ribosome-inactivating proteins, were purified to apparent homogeneity from leaves, roots and seeds using a new procedure of RIPs isolation including ion-exchange and hydrophobic chromatography. They all catalysed the depurination of rat liver ribosomes, which generate the Endo's diagnostic rRNA fragment upon treatment with acid aniline, thus indicating that A4324 from the 28S rRNA has been released (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912). The molecular mass of saporins by SDS-PAGE ranged between 30.2 and 31.6 kDa and by gel-filtration between 27.5 and 30.1 kDa. Amino acid composition and amino-terminal amino acid sequence indicate that all saporins may be considered isoforms. Only two saporins present in roots were glycosylated (SO-R1 and SO-R3). All saporins are very active on cell-free translation systems derived from rabbit reticulocyte lysates, rat liver, Triticum aestivum L., Cucumis sativus L. and Vicia sativa L. However, they are poor inhibitors of an Escherichia coli translation system. They inhibit protein synthesis in HeLa, BeWo and NB 100 cells, HeLa cells being the most resistant. The enzymatic activity of at least one saporin isoform was dependent on magnesium concentration in the standard rat liver cell-free system.

Mitochondrial regulation of caspase activation by cytochrome oxidase and tetramethylphenylenediamine via cytosolic cytochrome c redox state

Cytochrome c release from mitochondria induces caspase activation in cytosols; however, it is unclear whether the redox state of cytosolic cytochrome c can regulate caspase activation. By using cytosol isolated from mammalian cells, we find that oxidation of cytochrome c by added cytochrome oxidase stimulates caspase activation, whereas reduction of cytochrome c by added tetramethylphenylenediamine (TMPD) or yeast lactate dehydrogenase/cytochrome c reductase blocks caspase activation. Scrape-loading of cells with this reductase inhibited caspase activation induced by staurosporine. Similarly, incubating intact cells with ascorbate plus TMPD to reduce intracellular cytochrome c strongly inhibited staurosporine-induced cell death, apoptosis, and caspase activation but not cytochrome c release, indicating that cytochrome c redox state can regulate caspase activation. In homogenates from healthy cells cytochrome c was rapidly reduced, whereas in homogenates from apoptotic cells added cytochrome c was rapidly oxidized by some endogenous process. This oxidation was prevented if mitochondria were removed from the homogenate or if cytochrome oxidase was inhibited by azide. This suggests that permeabilization of the outer mitochondrial membrane during apoptosis functions not just to release cytochrome c but also to maintain it oxidized via cytochrome oxidase, thus maximizing caspase activation. However, this activation can be blocked by adding TMPD, which may have some therapeutic potential.

Effect of topical corticosteroids on ulceration in alkali-burned corneas

Dexamethasone sodium phosphate was administered topically to one eye of rabbits with bilateral alkali corneal burns, and saline solution was administered to the contralateral eye. Topical steroids were also administered in animals with moderate corneal ulcers and were found to enhance the severity of ulceration when given during the second and third weeks following the burn. If the corticosteroids were given daily in the first six days or in the fourth and fifth weeks following the burn, they did not have an adverse effect on the cornea. Corticosteroids can be used intensively during the first week following an alkali burn, without increasing the risk of corneal melting. The mechanism for the enhancement of corneal ulceration is not a direct augmentation of collagenase activity, but probably involves the inhibition of repair processes.

Wheat germ cell-free translation, purification, and assembly of a functional human stearoyl-CoA desaturase complex

A wheat germ cell-free extract was used to perform in vitro translation of human stearoyl-CoA desaturase in the presence of unilamelar liposomes, and near complete transfer of the expressed integral membrane protein into the liposome was observed. Moreover, co-translation of the desaturase along with human cytochrome b(5) led to transfer of both membrane proteins into the liposomes. A simple, single step purification via centrifugation in a density gradient yielded proteoliposomes with the desaturase in high purity as judged by capillary electrophoresis. After in vitro reconstitution of the non-heme iron and heme active sites, the function of the reconstituted enzyme complex was demonstrated by conversion of stearoyl-CoA to oleoyl-CoA. This simple translation approach obviates the use of detergents or other lipids to stabilize and isolate a catalytically active integral membrane enzyme. The applicability of cell-free translation to the assembly and purification of other integral membrane protein complexes is discussed.

Mitochondria-targeting drugs arsenic trioxide and lonidamine bypass the resistance of TPA-differentiated leukemic cells to apoptosis

Exposure of U937 human leukemic cells to the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) induces their differentiation into monocyte/macrophage-like cells. This terminal differentiation is associated with a resistant phenotype to apoptosis induced by the topoisomerase II inhibitor etoposide. The inhibition occurs upstream of the mitochondrial release of cytochrome c and the activation of procaspase-2, -3, -6, -7, -8, and -9. By using cell-free systems, it was demonstrated that the mitochondrial pathway to cell death that involves mitochondrial membrane depolarization, cytochrome c release and cytosolic activation of procaspases by cytochrome c/dATP remains functional in TPA-differentiated U937 cells. Accordingly, 2 drugs recently shown to target the mitochondria, namely lonidamine and arsenic trioxide, bypass the resistance of TPA-differentiated U937 cells to classical anticancer drugs. Cell death induced by the 2 compounds is associated with mitochondrial membrane depolarization, release of cytochrome c and Smac/Diablo from the mitochondria, activation of caspases, poly(ADP-ribose) polymerase cleavage and internucleosomal DNA fragmentation. Moreover, the decreased glutathione content associated with the differentiation process amplifies the ability of arsenic trioxide to activate the mitochondrial pathway to cell death. Similar results were obtained by comparing undifferentiated and TPA-differentiated human HL60 leukemic cells. These data demonstrate that mitochondria-targeting agents bypass the resistance to classical anticancer drugs induced by TPA-mediated leukemic cell differentiation. (Blood. 2001;97:3931-3940)

Structural aspects of Congo red as an inhibitor of protease-resistant prion protein formation

Congo red (CR) has been shown to inhibit the accumulation in scrapie-infected cells of prion protein (PrP) in the abnormal protease-resistant form (PrP-res). However, it was not clear if this effect was due to a direct interaction of CR with either PrP-res or its protease-sensitive precursor (PrP-sen) or to a less direct effect on living cells. Here we show that CR inhibits PrP-res formation in a simple cell-free reaction composed predominantly of purified PrP-res and PrP-sen. Structurally modified CR analogues were also compared in both the cell-free conversion reaction and scrapie-infected neuroblastoma cells. Methylation of the central phenyl groups at the 2,2' positions diminished the inhibitory potency by > or = 10-fold. In contrast, there was little effect of 3,3' methylation of the phenyls, deletion of one phenyl, or addition of an amido group between the phenyls. The relative activities of these compounds were well correlated in both cellular and acellular systems. Molecular modeling indicated that CR and 3,3'-methyl-CR have little rotational restriction about the biphenyl bond and can readily adopt a planar conformation, as can phenyl-CR and amido-CR. In contrast, 2,2'-methyl-CR is restricted to a nonplanar conformation of the biphenyl group. Thus, planarity and/or torsional mobility of the central phenyl rings of CR and its analogues is probably important for inhibition of PrP-res formation. On the other hand, variations in the intersulfonate distance in these molecules had little effect on PrP-res inhibition. These results indicated a high degree of structural specificity in the inhibition of PrP-res formation by CR and related compounds.

Effects of testosterone on messenger ribonucleic acid and protein synthesis in rat seminal vesicle

In a previous report [Higgins et al. (1976) Biochem. J.158, 271-282] we described the effects of alterations in androgen status on the synthesis of two basic secretory proteins of the rat seminal vesicle. In the present paper we examine the effects of testosterone on the activity of mRNA in the seminal vesicle. Total cellular poly(A)-rich RNA was isolated and translated in a cell-free system prepared from wheat germ. Translation products were separated on denaturing polyacrylamide gels and the protein bands corresponding to the two basic secretory proteins were identified immunologically. Incorporation of radioactive methionine into these bands was taken as a measure of the individual mRNA activities. Total mRNA activity was estimated by radioactivity in total acid-precipitable material. The results show that 1 to 2 weeks after castration the activities of mRNA molecules for the basic secretory proteins were decreased 10-20-fold on a tissue basis. Testosterone given in vivo rapidly and substantially restores mRNA activity to normal. Since these changes correlate closely with variations in the rates of synthesis of the secretory proteins in whole cells it suggests that androgenic steroids control protein synthesis chiefly via mRNA availability. In this respect their action resembles those of other steroid hormones acting in other systems. However, these effects of testosterone on the mRNA molecules for the major secretory proteins could not be distinguished from those on total mRNA. Thus the proportion of the total mRNA population accounted for by the two specific mRNA molecules showed less than a 2-fold variation with androgen status. Similarly the two secretory proteins always accounted for 25-33% of general protein synthesis. This is in sharp contrast with the markedly differential effects of other steroid hormones controlling synthesis of major proteins in other well-studied systems. We interpret our results as indicating that testosterone regulates the mRNA population of the seminal vesicle as a whole.

Mode of action of the new selective leukotriene synthesis inhibitor BAY X 1005 ((R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) and structurally related compounds

BAY X 1005 ((R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) has been demonstrated to be a potent inhibitor of leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE) synthesis in various in vitro systems. Using mainly human polymorphonuclear leukocytes (PMNL) this study elucidates the mechanism of inhibition of 5-lipoxygenase (5-LOX, EC 1.13.11.34)-derived arachidonic acid metabolites by BAY X 1005. At concentrations of BAY X 1005 which almost totally inhibited the formation of 5-LOX-derived metabolites, both arachidonic acid release and platelet-activating factor synthesis were only modestly affected. This suggests that the inhibitory effect of BAY X 1005 is not due to a limitation of substrate availability for 5-LOX. Compared to the inhibition of leukotriene synthesis in intact human PMNL about 800-fold higher concentrations of BAY X 1005 were required to inhibit leukotriene formation in a cell-free system suggesting that the inhibitory effect of BAY X 1005 cannot be explained by a direct effect on 5-LOX. In an attempt to identify possible target proteins of BAY X 1005, [14C]BAY X 1005 was used in binding studies under equilibrium conditions. The quantitative analysis of specific binding in intact human PMNL revealed two binding sites for BAY X 1005. Upon subcellular fractionation of these cells the BAY X 1005 high affinity binding site was localized in the microsomal fraction whereas the low affinity binding site was localized in the granule fraction. The Kd for BAY X 1005 binding to the high affinity binding site (0.165 mumol/L) was almost identical to the IC50 value for inhibition of LTB4 synthesis (0.22 mumol/L). Furthermore, the IC50 values for competition of BAY X 1005 binding at the high affinity binding site were almost identical to the IC50 values for inhibition of LTB4 synthesis in the case of BAY X 1005, 12 other structurally related quinoline derivatives and the reference compounds REV-5901, WY-50,295 and MK-886, but not in the case of the direct 5-LOX inhibitors A-64077 and AA-861. The analysis of BAY X 1005 binding in rat PMNL also revealed two binding sites. Whereas the low affinity binding site in rat PMNL exhibited a Kd similar to the human, the rat high affinity binding site showed a 5.5-fold higher affinity for BAY X 1005 compared to the human. This correlates well with the 8.5-fold higher sensitivity of rat versus human PMNL concerning inhibition of LTB4 synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)