The Mechanism by which Cycloheximide and Related Glutarimide Antibiotics Inhibit Peptide Synthesis on Reticulocyte Ribosomes

Incadronate amplifies prostaglandin F2 alpha-induced vascular endothelial growth factor synthesis in osteoblasts. Enhancement of MAPK activity

We have previously reported that prostaglandin F2 alpha (PGF2 alpha) activates p44/p42 mitogen-activated protein kinase (MAPK) through protein kinase C (PKC) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the mechanism of vascular endothelial growth factor (VEGF) synthesis induced by PGF2 alpha and the effect of incadronate on the VEGF synthesis in these cells. PGF2 alpha significantly stimulated the VEGF synthesis in a dose-dependent manner between 1 pm and 10 microm. Cycloheximide reduced the PGF2 alpha effect. PGF2 alpha increased the levels of mRNA for VEGF. Cloprostenol, a PGF2 alpha-sensitive receptor agonist, potently induced the VEGF synthesis. Indomethacin, an inhibitor of cyclooxygenase, significantly reduced the PGF2 alpha-induced VEGF synthesis. Bisindolylmaleimide, an inhibitor of PKC, reduced the PGF2 alpha-induced VEGF synthesis. The VEGF synthesis induced by PGF2 alpha was significantly attenuated in the PKC down-regulated cells. PGF2 alpha elicited the translocation of PKC beta I from cytosol to membrane fraction. PD98059 or U0126, inhibitors of MEK, suppressed the VEGF synthesis induced by PGF2 alpha. Farnesyltransferase inhibitor failed to affect the PGF2 alpha-induced VEGF synthesis. Incadronate enhanced the synthesis of VEGF induced by PGF2 alpha. NaF-induced VEGF synthesis was also amplified by incadronate. PD98059 suppressed the enhancement by incadronate of PGF2 alpha-induced VEGF synthesis. Incadronate markedly enhanced the phosphorylation of Raf-1, MEK1/2, and p44/p42 MAPK induced by PGF2 alpha or 12-O-tetradecanoylphorbol-13-acetate, a PKC activator. Incadronate significantly enhanced the cloprostenol-increased level of VEGF concentration in mouse plasma in vivo. These results strongly suggest that PGF2 alpha stimulates VEGF synthesis through the PKC-dependent activation of p44/p42 MAPK in osteoblasts and that the incadronate enhances the VEGF synthesis at the point between PKC and Raf-1.

Induction of 5alpha-reductase type II mRNA transcription in primary cultured prostate epithelial cells by a soluble factor produced by primary cultured prostate fibroblast cells

The role of DHT in the development of BPH has resulted in the formulation of several drugs, which have been designed to inhibit the formation of DHT by the 5alpha-reductase enzymes (5alpha-reductase type I (5alpha-RI) & 5alpha-reductase type II (5alpha-RII)). Although the function of these enzymes is well understood, the biochemical stimulus for initiation of 5alpha-RI and II gene expression has not been described. Study of a co-culture model indicated the presence of a diffusible factor secreted by prostatic fibroblast cells, which is responsible for the transcription of 5alpha-II mRNA in primary prostatic epithelial cells. In this study, we describe the partial characterisation of a fibroblast-secreted, soluble factor which we believe induces the transcription of 5alpha-RII mRNA in long-term primary cultures of prostate epithelial cells which can no longer transcribe 5alpha-RII mRNA.

Apoptotic pathway and MAPKs differentially regulate chemotropic responses of retinal growth cones

Previous work has shown that guidance cues trigger rapid changes in protein dynamics in retinal growth cones: netrin-1 stimulates both protein synthesis and degradation, while Sema3A elicits synthesis, and LPA induces degradation. What signaling pathways are involved? Our studies confirm that p42/44 MAPK mediates netrin-1 responses and further show that inhibiting its activity blocks cue-induced protein synthesis. Unexpectedly, p38 MAPK is also activated by netrin-1 in retinal growth cones and is required for chemotropic responses and translation. Sema3A- and LPA-induced responses, by contrast, require a single MAPK, p42/p44 and p38, respectively. In addition, we report that caspase-3, an apoptotic protease, is rapidly activated by netrin-1 and LPA in a proteasome- and p38-dependent manner and is required for chemotropic responses. These findings suggest that the apoptotic pathway may be used locally to control protein levels in growth cones and that the differential activation of MAPK pathways may underlie cue-directed migration.

Electrochemical desorption of self-assembled monolayers noninvasively releases patterned cells from geometrical confinements

This report describes a method to pattern mammalian cells using self-assembled monolayers (SAMs), and then to use electrochemical desorption of these monolayers to release cells from their patterns. This method uses an oligo(ethyleneglycol)-terminated SAM to prevent,-and a methyl-terminated SAM to allow-adsorption of proteins and attachment of bovine capillary endothelial cells. Electrochemical removal of the oligo(ethyleneglycol)-terminated SAM allowed proteins to adsorb onto areas that had been previously inert and enabled cells to migrate into these areas. This straightforward technique is useful in bioassays for drug screening and for fundamental studies in cell biology.

Pharmacological interference with dimerization of human neuronal nitric-oxide synthase expressed in adenovirus-infected DLD-1 cells

A recombinant adenovirus containing the cDNA of human neuronal nitric-oxide synthase (nNOS) was constructed to characterize the interaction of nNOS with N-[(1,3-benzodioxol-5-yl)methyl]-1-[2-(1H-imidazole-1-yl)pyrimidin-4-yl]-4-(methoxycarbonyl)-piperazine-2-acetamide (BBS-1), a potent inhibitor of inducible NOS dimerization [Proc Natl Acad Sci USA 97:1506-1511, 2000]. BBS-1 inhibited de novo expression of nNOS activity in virus-infected cells at a half-maximal concentration (IC(50)) of 40 +/- 10 nM in a reversible manner. Low-temperature gel electrophoresis showed that BBS-1 attenuated the formation of SDS-resistant nNOS dimers with an IC(50) of 22 +/- 5.2 nM. Enzyme inhibition progressively decreased with increasing time of addition after infection. BBS-1 did not significantly inhibit dimeric nNOS activity (IC(50) > 1 mM). Long-term incubation with BBS-1 of human embryonic kidney cells stably transfected with nNOS or endothelial NOS revealed a slow time- and concentration-dependent decrease of NOS activity with half-lives of 30 and 43 h and IC(50) values of 210 +/- 30 nM and 12 +/- 0.5 microM, respectively. These results establish that BBS-1 interferes with the assembly of active nNOS dimers during protein expression. Slow inactivation of constitutively expressed NOS in intact cells may reflect protein degradation and interference of BBS-1 with the de novo synthesis of functionally active NOS dimers. As time-dependent inhibitors of NOS dimerization, BBS-1 and related compounds provide a promising strategy to develop a new class of selective and clinically useful NOS inhibitors.

Translation elongation after assembly of ribosomes on the Cricket paralysis virus internal ribosomal entry site without initiation factors or initiator tRNA

Reconstitution of translation elongation from purified components confirmed that ribosomes that assembled on the Cricket paralysis virus intercistronic internal ribosomal entry site (IRES) without the involvement of initiation factors or initiator tRNA were active in elongation and are, therefore, true initiation complexes. The first elongation cycle occurred without peptide bond formation on 80S ribosomes that did not contain tRNA in the P site. It required elongation factors 1A and 2 and A site-cognate aminoacylated tRNA. Cycloheximide arrested ribosomes on the IRES only after two cycles of elongation, when the first deacylated tRNA reached the E-site after translocation from the A-site.

Okadaic acid decreases the leptin content in isolated mouse fat pads

Okadaic acid (OA) decreased the leptin content in isolated mouse fat pads in a time and dose-dependent manner. MG-132, a membrane-permeable proteasome inhibitor, prevented the decrease by OA, suggesting the involvement of proteasome in the OA action. No significant decrease in the incorporation of [(3)H]leucine into leptin was observed with a 4-h incubation, although the amino acid incorporation was stimulated by insulin and decreased by cycloheximide. These results suggest that the OA action is independent of the decrease in protein synthesis. The proteasome fraction, which had been separated from the fat pads pretreated with OA, enhanced the proteolytic degradation of exogenous [(125)I]leptin in the presence of an ATP-regenerating system together with an ubiquitination system. No enhancement of hydrolytic activity against Suc-Leu-Leu-Val-Tyr-AMC was detected in the OA-treated proteasome fraction, suggesting that the activation of proteasome is not involved in the OA action. The OA-treated proteasome fraction had decreased phosphatase activity against p-nitrophenyl phosphate, suggesting that OA entering the cells may exert its action by preventing dephosphorylation of key molecules. OA may reduce the intracellular leptin content through the increased ubiquitination and proteolytic turnover of leptin by the proteasome, based on the decreased phosphatase activity.

Deletion of individual mRNA capping genes is unexpectedly not lethal to Candida albicans and results in modified mRNA cap structures

Eukaryotic mRNAs are modified at the 5' end with a cap structure. In fungal cells, the formation of the mRNA cap structure is catalyzed by three enzymes: triphosphatase, guanylyltransferase, and methyltransferase. Fungal capping enzymes have been proposed to be good antifungal targets because they differ significantly from their human counterparts and the genes encoding these enzymes are essential in Saccharomyces cerevisiae. In the present study, Candida albicans null mutants were constructed for both the mRNA triphosphatase-encoding gene (CET1) and the mRNA methyltransferase encoding gene (CCM1), proving that these genes are not essential in C. albicans. Heterozygous deletions were generated, but no null mutants were isolated for the guanylyltransferase-encoding gene (CGT1), indicating that this gene probably is essential in C. albicans. Whereas these results indicate that Cet1p and Ccm1p are not ideal molecular targets for development of anticandidal drugs, they do raise questions about the capping of mRNA and translation initiation in this fungus. Southern blot analysis of genomic DNA indicates that there are not redundant genes for CET1 and CCM1 and analysis of mRNA cap structures indicate there are not alternative pathways compensating for the function of CET1 or CCM1 in the null mutants. Instead, it appears that C. albicans can survive with modified mRNA cap structures.

Brain inducible nitric oxide synthase is involved in interleukin-1beta-induced activation of the central sympathetic outflow in rats

Nitric oxide (NO) has been recognized as a neurotransmitter or a neuromodulator in the central nervous system. Brain NO is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. Previously we reported that central NO is involved in the elevation of plasma noradrenaline levels induced by intracerebroventricularly (i.c.v.) administered interleukin-1beta in rats [Eur. J. Phamacol. 317 (1996) 61]. In the present study, therefore, we tried to characterize which type of NOS isoforms is involved in the cytokine-induced responses using selective inhibitors of each NOS isoform in urethane-anesthetized rats. I.c.v. administered interleukin-1beta (100 ng/animal) elevated plasma levels of noradrenaline but not adrenaline. The cytokine-induced elevation of plasma noradrenaline levels was attenuated by cycloheximide, an inhibitor of protein synthesis, in a dose-dependent manner (10 and 20 microg/animal, i.c.v.). S-ethylisothiourea (0.1 and 0.5 microg/animal, i.c.v.), an inhibitor of inducible NOS, dose-dependently reduced the cytokine-induced elevation of plasma noradrenaline levels, while 7-nitroindazole (5 and 10 microg/animal, i.c.v.), an inhibitor of neuronal NOS, had no effect. These results suggest the involvement of brain inducible NOS in the interleukin-1beta-induced activation of the central sympathetic outflow in rats.

Orthovanadate decreases the leptin content in isolated mouse fat pads via proteasome activation

When isolated mouse fat pads were incubated with insulin or sodium orthovanadate (vanadate) for up to 4h, the intracellular leptin content was increased by insulin, while it was decreased by vanadate. Bupranolol, a beta3-adrenergic receptor antagonist, prevented both effects of vanadate, i.e., the decrease in intracellular leptin and increase in cellular cAMP content, while BRL 37344, a beta3-adrenergic receptor antagonist mimicked the action of vanadate. H-89 prevented the vanadate-induced decrease in intracellular leptin, suggesting the involvement of a cAMP-dependent protein kinase (PKA). No detectable difference in the incorporation of [3H]leucine into leptin was observed between incubations of the fat pads with and without vanadate, suggesting that the action of vanadate is independent of decreasing synthesis. Similar concentrations of MG-132, a membrane-permeable proteasome inhibitor, prevented the vanadate-induced decrease in both intracellular leptin content and leptin secretion, suggesting the involvement of the proteasome in the vanadate action. The proteasome fraction separated from the vanadate-treated fat pads increased the degradation of exogenous [125I]leptin in the presence of an ATP-regenerating system together with an ubiqutination system. The endopeptidase activity against Cbz-Leu-Leu-Glu-beta-naphthylamine also was increased by the proteasome fraction. MG-132 prevented both increased effects. The 8-Br-cAMP-treated proteasome fraction increased the degradation of the exogenous leptin. H-89 prevented the effect of 8-Br-cAMP. These results indicate that vanadate decreases the intracellular leptin content by increased degradation via a cAMP/PKA-dependent process involving proteasome activation.

Different action of IBMX, isoproterenol and rutin on orthovanadate-induced nitric oxide release in mouse macrophage cells

The effects of cAMP-elevating compounds IBMX (3-isobutyl-1-methylxanthine) and isoproterenol, and that of rutin (an effective superoxide scavenger) were studied on orthovanadate--(a putative protein-phosphotyrosine phosphatase inhibitor) induced nitric oxide (NO) production in J774A.1 mouse macrophage cells. As we previously reported (Koncz and Horváth, 2000), rutin and sodium orthovanadate act synergistically to induce production of high amount of NO in J774A.1 cells. IBMX, an agent that can elevate cAMP level in the cells, can reduce the production of both the LPS- and rutin + orthovanadate-induced NO in macrophages. In contrast, isoproterenol, a non-selective beta-adrenergic receptor agonist, that reduced the LPS-induced NO production in macrophage cells, was unable to reduce the rutin + orthovanadate-induced NO production without negatively affecting cell viability. Moreover, isoproterenol dramatically enhanced the orthovanadate-induced NO synthesis in J774A.1 cells. Our previous study clarified that rutin and orthovanadate, in a specific concentration ratio of both, were able to produce hydrogen peroxide (H2O2). Using 2',7'-dichlorofluorescein-diacetate as a marker for H2O2, isoproterenol alone induced its oxidation but the rutin plus orthovanadate-induced H2O2 production was reduced by isoproterenol. These observations have revealed that, in some cases, H2O2 and superoxide (O2-) scavengers can act in a reverse mode on macrophage cells depending on the presence or absence of orthovanadate.

The role of cyclo-oxygenase 1 and 2 activity in prostaglandin E2 secretion by cultured human adult microglia: Implications for Alzheimer’s disease

Microglial cyclo-oxygenase (COX) expression is considered to be important in the pathogenesis of Alzheimer's disease (AD) and, therefore, constitutes a key target for therapeutic intervention. We investigated the influence of AD plaque associated factors on COX-1 and COX-2 expression and activity in adult human microglial cells in vitro. COX-2 immunoreactivity and mRNA were induced by lipopolysaccharide (LPS), not by AD plaque associated cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, tumor necrosis factor (TNF)-alpha, or amyloid (A)beta(1-42). To assess functional COX activity, the release of PGE(2) into the culture medium was determined. LPS and also arachidonic acid (AA) dose-dependently stimulated PGE(2) release. The effects of AA are independent from induction of COX mRNA expression, or of de novo protein synthesis. No effects of either plaque-associated cytokines or Abeta(1-42) on PGE(2) secretion were seen, even when cells were co-stimulated with AA, to provide enough substrate. COX isotype selective inhibitors were used to discern relative contributions of COX-1 and COX-2 activities to microglial PGE(2) secretion. COX-2 and in part COX-1-selective inhibitors inhibited LPS-induced PGE(2) secretion, whereas the AA-induced PGE(2) secretion was reduced by COX-1-selective inhibitors only. Apparently, adult human microglia in vitro (1) constitutively express COX-1, and (2) do not express COX-2 upon exposure to either Abeta or plaque associated cytokines. In the light of microglial COX activity as a potential therapeutical target in AD, the data presented in this study suggest that classical NSAIDs, rather than selective COX-2 inhibitors, are more potent in reducing microglial prostaglandin secretion.

Thrombin stimulates dissociation and induction of HSP27 via p38 MAPK in vascular smooth muscle cells

We investigated the effects of thrombin on the induction of heat shock proteins (HSP) 70 and 27, and the mechanism behind the induction in aortic smooth muscle A10 cells. Thrombin increased the level of HSP27 but had little effect on the level of HSP70. Thrombin stimulated the accumulation of HSP27 dose dependently between 0.01 and 1 U/ml and cycloheximide reduced the accumulation. Thrombin stimulated an increase in the level of HSP27 mRNA and actinomycin D suppressed the thrombin-increased mRNA level. Thrombin induced the phosphorylation of p38 mitogen-activated protein kinase (MAPK). The HSP27 accumulation by thrombin was reduced by SB-203580 and PD-169316 but not by SB-202474. SB-203580 and PD-169316 suppressed the thrombin-induced phosphorylation of p38 MAPK. SB-203580 reduced the thrombin-increased level of HSP27 mRNA. Dissociation of the aggregated HSP27 to the dissociated HSP27 was induced by thrombin. Dissociation was inhibited by SB-203580. Thrombin induced the phosphorylation of HSP27 and the phosphorylation was suppressed by SB-203580. These results indicate that thrombin stimulates not only the dissociation of HSP27 but also the induction of HSP27 via p38 MAPK activation in aortic smooth muscle cells.

1alpha,25-dihydroxyvitamin D(3) and 24R,25-dihydroxyvitamin D(3) modulate growth plate chondrocyte physiology via protein kinase C-dependent phosphorylation of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase

Membrane-mediated increases in protein kinase C (PKC) activity and PKC-dependent physiological responses of growth plate chondrocytes to vitamin D metabolites depend on the state of endochondral maturation; 1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)] regulates growth zone (GC) cells, whereas 24R,25-(OH)(2)D(3) regulates resting zone (RC) cells. Different mechanisms, including protein kinase A signaling, mediate the effects of 1alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) on PKC, suggesting that different mechanisms may also regulate any MAPK involvement in the physiological responses. This study used confluent cultures of rat costochondral chondrocytes as a model. 1alpha,25-(OH)(2)D(3) stimulated MAPK specific activity in GC in a time- and dose-dependent manner, evident within 9 min. 24R,25-(OH)(2)D(3) stimulated MAPK in RC; increases were dose dependent, occurred after 9 min, and were greatest at 90 min. In both cells the effect was due to ERK1/2 activation (p42 > p44 in GC; p42 = p44 in RC). MAPK activation was dependent on PKC, but not protein kinase A. The effect of 1alpha,25-(OH)(2)D(3) required phospholipase C, and the effect of 24R,25-(OH)(2)D(3) required phospholipase D. Inhibition of cyclooxygenase activity reduced the effect of 1alpha,25-(OH)(2)D(3) on MAPK in GC and enhanced the effect of 24R,25-(OH)(2)D(3) in RC. Based on MAPK inhibition with PD98059, ERK1/2 MAPK mediated the effect of 24R,25-(OH)(2)D(3) on [(3)H]thymidine incorporation and [(35)S]sulfate incorporation by RC, but only partially mediated the effect of 1alpha,25-(OH)(2)D(3) on GC. ERK1/2 was not involved in the regulation of alkaline phosphatase specific activity by either metabolite. This paper supports the hypothesis that 1alpha,25-(OH)(2)D(3) regulates the physiology of GC via rapid membrane-mediated signaling pathways, and some, but not all, of the response to 1alpha,25-(OH)(2)D(3) is via the ERK family of MAPKs. In contrast, 24R,25-(OH)(2)D(3) exerts its effects on RC via PKC-dependent MAPK. Whereas 1alpha,25-(OH)(2)D(3) increases MAPK activity via phospholipase C and increased prostaglandin production, 24R,25-(OH)(2)D(3) increases MAPK via phospholipase D and decreased prostaglandin production. The cell specificity, metabolite stereospecificity, and the dependence on PKC argue for the participation of membrane receptors for 1alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) in the regulation of ERK1/2 in the growth plate.

Consequences of mevalonate depletion. Differential transcriptional, translational, and post-translational up-regulation of Ras, Rap1a, RhoA, AND RhoB

Ras-related proteins are small GTPases that are post-translationally modified with mevalonate-derived isoprenoids. Although the effects of inhibition of isoprenylation on protein function have been examined, the consequences of depletion of isoprenoid pools on regulation of expression of isoprenylated proteins have yet to be investigated. In these studies we have shown that depletion of mevalonate results in increased total levels of Ras, Rap1a, RhoA, and RhoB in K562 cells. Cycloheximide and [(35)S]methionine pulse/pulse-chase experiments reveal that mevalonate depletion increases the de novo synthesis of Ras and RhoA and decreases the degradation of existing Ras and RhoA protein. Pretreatment with actinomycin D completely prevents the induced up-regulation of RhoB and only partially prevents the up-regulation of Ras, Rap1a, and RhoA. Although depletion of mevalonate does not alter steady state levels of Ras mRNA, there is an increase in RhoB mRNA. Our results are the first to demonstrate that mevalonate depletion induces up-regulation of Ras and Ras-related proteins by discrete mechanisms that include modulation of transcriptional, translational, and post-translational processes.

Chemotropic responses of retinal growth cones mediated by rapid local protein synthesis and degradation

Growth cones contain mRNAs, translation machinery, and, as we report here, protein degradation machinery. We show that isolated retinal growth cones immediately lose their ability to turn in a chemotropic gradient of netrin-1 or Sema3A when translation is inhibited. Translation inhibition also prevents Sema3A-induced collapse, while LPA-induced collapse is not affected. Inhibition of proteasome function blocks responses to netrin-1 and LPA but does not affect Sema3A responses. We further demonstrate in isolated growth cones that netrin-1 and Sema3A activate translation initiation factors and stimulate a marked rise in protein synthesis within minutes, while netrin-1 and LPA elicit similar rises in ubiquitin-protein conjugates. These results suggest that guidance molecules steer axon growth by triggering rapid local changes in protein levels in growth cones.

Golgi retention of human protein NEFA is mediated by its N-terminal Leu/Ile-rich region

The subcellular localization of the human Ca(2+)-binding EF-hand/leucine zipper protein NEFA was studied in HeLa cells by immunofluorescence microscopy. Double immunostaining using mouse anti-NEFA monoclonal antibody 1H8D12 and rabbit anti-ERD2 polyclonal antibody proved that NEFA is localized in the Golgi apparatus. The result was confirmed by the expression of NEFA-green fluorescent protein (GFP) fusion protein in the Golgi in the same cell line. Cycloheximide treatment proved NEFA to be a Golgi-resident protein. Seven NEFA deletion mutants were constructed to ascertain the peptide region relevant for Golgi retention. The expression of each NEFA-GFP variant was detected by fluorescence microscopy and immunoblotting. Only the DeltaN mutant, lacking the N-terminal Leu/Ile-rich region, failed to be retained in the Golgi after cycloheximide treatment. The other six deletion mutants in which either the basic region, the complete EF-hand pair domain, the two EF-hand motifs separately, the leucine zipper and the leucine zipper plus the C-terminal region is deleted, were localized to the Golgi. The peptide sequence within the Leu/Ile-rich region is discussed as a novel Golgi retention motif.

Potential role for a carbohydrate moiety in anti-Candida activity of human oral epithelial cells

Candida albicans is both a commensal and a pathogen at the oral mucosa. Although an intricate network of host defense mechanisms are expected for protection against oropharyngeal candidiasis, anti-Candida host defense mechanisms at the oral mucosa are poorly understood. Our laboratory recently showed that primary epithelial cells from human oral mucosa, as well as an oral epithelial cell line, inhibit the growth of blastoconidia and/or hyphal phases of several Candida species in vitro with a requirement for cell contact and with no demonstrable role for soluble factors. In the present study, we show that oral epithelial cell-mediated anti-Candida activity is resistant to gamma-irradiation and is not mediated by phagocytosis, nitric oxide, hydrogen peroxide, and superoxide oxidative inhibitory pathways or by nonoxidative components such as soluble defensin and calprotectin peptides. In contrast, epithelial cell-mediated anti-Candida activity was sensitive to heat, paraformaldehyde fixation, and detergents, but these treatments were accompanied by a significant loss in epithelial cell viability. Treatments that removed existing membrane protein or lipid moieties in the presence or absence of protein synthesis inhibitors had no effect on epithelial cell inhibitory activity. In contrast, the epithelial cell-mediated anti-Candida activity was abrogated after treatment of the epithelial cells with periodic acid, suggesting a role for carbohydrates. Adherence of C. albicans to oral epithelial cells was unaffected, indicating that the carbohydrate moiety is exclusively associated with the growth inhibition activity. Subsequent studies that evaluated specific membrane carbohydrate moieties, however, showed no role for sulfated polysaccharides, sialic acid residues, or glucose- and mannose-containing carbohydrates. These results suggest that oral epithelial cell-mediated anti-Candida activity occurs exclusively with viable epithelial cells through contact with C. albicans by an as-yet-undefined carbohydrate moiety.

Integrative cartilage repair: adhesive strength is correlated with collagen deposition

Procedures to repair focal articular cartilage defects often result in poor integration between the host cartilage and the graft tissue, and this may be related to the lack of matrix deposition and the death of chondrocytes near a cut cartilage surface. The objective of this study was to determine if cartilage repair was related to deposition of newly synthesized collagen. The mechanical integration that occurred between two live adult bovine cartilage blocks cultured in partial apposition for two weeks was correlated with [3H]proline incorporation, a measure of protein synthesis, of which more than 66% was accounted for by collagen. A similar level of mechanical integration occurred in sample pairs consisting of a live and killed cartilage block, and this adhesive strength was also correlated with [3H]proline deposition into both the live and the killed blocks. In these samples, the [3H]proline deposited into the killed cartilage appeared to originate from chondrocytes in the live cartilage, since live cells were not detected in the killed cartilage block by either viability staining or [35S]sulfate incorporation. These results suggest a mechanism of integrative cartilage repair in which live chondrocytes within cartilage secrete matrix molecules that are components of a collagen network, and subsequent deposition of these molecules near the repair interface contributes to functional integration.

Synthesis of several light-harvesting complex I polypeptides is blocked by cycloheximide in symbiotic chloroplasts in the sea slug, Elysia chlorotica (Gould): a case for horizontal gene transfer between alga and animal?

The chloroplast symbiosis between the ascoglossan (=Sacoglossa) sea slug Elysia chlorotica and plastids from the chromophytic alga Vaucheria litorea is the longest-lived relationship of its kind known, lasting up to 9 months. During this time, the plastids continue to photosynthesize in the absence of the algal nucleus at rates sufficient to meet the nutritional needs of the slugs. We have previously demonstrated that the synthesis of photosynthetic proteins occurs while the plastids reside within the diverticular cells of the slug. Here, we have identified several of these synthesized proteins as belonging to the nuclear-encoded family of polypeptides known as light-harvesting complex I (LHCI). The synthesis of LHCI is blocked by the cytosolic ribosomal inhibitor cycloheximide and proceeds in the presence of chloramphenicol, a plastid ribosome inhibitor, indicating that the gene encoding LHCI resides in the nuclear DNA of the slug. These results suggest that a horizontal transfer of the LHCI gene from the alga to the slug has taken place.

Cell death in spinal cord injury (SCI) requires de novo protein synthesis. Calpain inhibitor E-64-d provides neuroprotection in SCI lesion and penumbra

Degradation of cytoskeletal proteins by calpain, a Ca(2+)-dependent cysteine protease, may promote neuronal apoptosis in the lesion and surrounding areas following spinal cord injury (SCI). Clinically relevant moderate (40 g-cm force) SCI in rats was induced at T12 by a standardized weight-drop method. Internucleosomal DNA fragmentation or apoptosis in the lesion was inhibited by 24-h treatment of SCI rats with cycloheximide (1 mg/kg), indicating a requirement for de novo protein synthesis in this process. To prove an involvement of calpain activity in mediation of apoptosis in SCI, we treated SCI rats with a cell-permeable calpain inhibitor E-64-d (1 mg/kg). Following 24-h treatment, a 5-cm-long spinal cord section centered at the lesion was collected, and divided equally into five segments (1 cm each) to determine calpain activity, as shown by degradation of the 68-kD neurofilament protein (NFP), and apoptosis as indicated by internucleosomal DNA fragmentation. Neurodegeneration propagated from the site of injury to neighboring rostral and caudal regions. Both calpain activity and apoptosis were readily detectable in the lesion, and moderately so in neighboring areas of untreated SCI rats, whereas these were almost undetectable in E-64-d-treated SCI rats, and absent in sham animals. Results indicate that apoptosis in the SCI lesion and penumbra is prominently associated with calpain activity and is inhibited by the calpain inhibitor E-64-d providing neuroprotective benefit.

Long-term regulation of catecholamine formation by ouabain in cultured bovine adrenal chromaffin cells

The long-term effects of ouabain, an inhibitor of Na+/K+ -ATPase, on catecholamine formation in cultured bovine adrenal chromaffin cells were examined. The increase in [14C]catecholamine formation from [14C]tyrosine induced by ouabain was dependent on incubation time, and its maximal effect was observed after incubation for 8 h. The stimulatory effect of ouabain was concentration dependent (10-300 nM), causing maximal stimulation at 300 nM. The formation of [14C]catecholamines induced by ouabain was not increased by incubation with [14C]DOPA instead of [14C]tyrosine. Ouabain-induced [14C]catecholamine formation was influenced by decreases in extracellular Ca2+ concentration, but not by the presence of cycloheximide or actinomycin D. These results suggested that ouabain stimulates continuous activation of hydroxylation of tyrosine through a Ca2+ -dependent mechanism in cultured bovine adrenal chromaffin cells.

Synergistic action of rutin and orthovanadate on nitric oxide release from mouse macrophage cells

The cooperative action of sodium orthovanadate (a putative protein-phosphotyrosine phosphatase inhibitor) and rutin (an effective superoxide scavenger) on the nitric oxide (NO) production of J774A.1 mouse macrophage cells has been investigated. Orthovanadate alone caused a mild but significant increase in NO production of the cells at its highest concentration used (500 microM). Orthovanadate and rutin together caused a significant increase in the nitrite level of the supematants of the J774A.1 cells after a 24-hour incubation period, in a concentration dependent manner. The optimal doses for orthovanadate and rutin were 50 microM and 100 microM, respectively. This cooperative action of rutin and orthovanadate was totally inhibitable by catalase, reduced glutathion, N-acetylcystein, cycloheximide, pyrrolidine dithiocarbamate (a putative NF-kappaB inhibitor), genistein and tyrphostin-AG126 (two protein tyrosine-kinase inhibitors). Superoxide dismutase had no inhibitory effect. Orthovanadate and rutin (only together) could induce the oxidation of 2',7'-dichlorofluorescein-diacetate, a marker of hydrogen peroxide. This effect was inhibitable by reduced glutathion, a hydrogen peroxide specific scavenger. These findings suggest, that orthovanadate can induce the production of NO by J774A.1 macrophages not only by inhibition of protein tyrosine-phosphatases, but, using it with rutin, by increasing the level of hydrogen peroxide in the cells.

Translation is not required To generate virion precursor RNA in human immunodeficiency virus type 1-infected T cells

The retroviral primary transcription product is a multifunctional RNA that is utilized as pre-mRNA, mRNA, and genomic RNA. The relationship between human immunodeficiency virus type 1 (HIV-1) unspliced transcripts used as mRNA for viral protein synthesis and as virion precursor RNA (vpRNA) for encapsidation remains an important question. We developed a biochemical assay to evaluate the hypothesis that prior utilization as mRNA template for protein synthesis is necessary to generate vpRNA. HIV-1-infected T cells were treated with translation inhibitors under conditions that maintain virus production. Immunoprecipitation of newly synthesized HIV-1 Gag protein revealed that de novo translation is not necessary to sustain assembly, release, or processing of Gag structural protein. Both newly synthesized protein and steady-state Gag are competent for assembly, and the extracellular accumulation of Gag is proportional to the intracellular abundance of Gag. As early as 2 h after transcription, newly synthesized RNA is detectable in cell-free virions and encapsidation is sustained upon inhibition of host cell translation. Results of both [(3)H]uridine incorporation assays and HIV-1-specific RNase protection assays (RPAs) indicate that translation inhibition reduces the absolute amounts of both cytoplasmic and virion-associated RNA. Evaluation of encapsidation efficiency by RPA revealed that the cytoplasmic availability of vpRNA is increased, indicating that HIV-1 unspliced mRNA can be rerouted to function as vpRNA. Our data contrast with results from the HIV-2 and murine leukemia virus systems and indicate that HIV-1 unspliced RNA constitutes a single functional pool that can function interchangeably as mRNA and as vpRNA.

Parathyroid hormone-related protein down-regulates bone sialoprotein gene expression in cementoblasts: role of the protein kinase A pathway

PTH-related protein (PTHrP) acts as a paracrine and/or autocrine regulator of cell proliferation, apoptosis, and differentiation and is implicated in tooth development. The current studies employed cementoblasts to determine the role(s) and mechanisms of PTHrP in regulating cementum formation. Results demonstrated that PTHrP repressed gene expression and protein synthesis of bone sialoprotein (BSP) and abolished cementoblast-mediated biomineralization in vitro. The BSP gene inhibition required protein synthesis. The PTHrP analog (1-31) and other activators of the PKA pathway (3-isobutyl-1-methylxathine (IBMX), forskolin (FSK) and Sp-Adenosine-3', 5'-cyclic monophosphorothioate (Sp-cAMPss) also down-regulated BSP gene expression and blocked cementoblast-mediated biomineralization. In contrast, the PTHrP analog (7-34), a PTHrP antagonist, and the activators of the PKC pathway [phorbol 12-myristate 13-acetate (PMA) and phorbol 12, 13-dibutyrate (PDBu)] promoted BSP gene expression. In addition, the PKA pathway inhibitor (9-(2-tetrahydrofuryl) adenine (THFA) partially, but significantly reversed the PTHrP-mediated down-regulation of BSP gene expression. Furthermore, THFA alone significantly increased BSP messenger RNA (mRNA) expression in cementoblasts. In contrast, the inhibitor of the PKC pathway (GF109203X) did not reverse the PTHrP inhibitory effect on BSP gene expression. Furthermore, GF109203X alone dramatically reduced the BSP transcript levels. These data indicate that the cAMP/PKA pathway mediates the PTHrP-mediated down-regulation of BSP mRNA expression in cementoblasts; and furthermore, this pathway may, through an intrinsic inhibition mechanism, regulate the basal level of BSP mRNA expression. In contrast, the activation of PKC promotes BSP gene expression. These data provide new insights into the molecular mechanisms involved in PTHrP regulation of cementogenesis.

Inhibition of protein synthesis by didemnins: cell potency and SAR

Synthetic and naturally occurring didemnins are potent and specific inhibitors of protein synthesis in vitro. Structure-activity analysis indicates a requirement for the intact macrocycle; however, the smaller ring size represented by the didemnin analogue, tamandarin A, is equipotent to didemnin B. Replacement of the N,O-dimethyltyrosine by a N-methylphenylalanine or N-methylleucine residue is also well-tolerated. The rank order for inhibition of protein synthesis in vitro appears to be retained in MCF-7 cells, albeit at much higher potency. This increase in potency is explained for the first time by data indicating that MCF-7 cells can accumulate didemnin B up to 2-3 orders of magnitude compared to the growth medium.

Fibronectin-mediated hepatocyte shape change reprograms cytochrome P450 2C11 gene expression via an integrin-signaled induction of ribonuclease activity

A major limitation to the use of rat hepatocytes in the study of drug metabolism and toxicity is the rapid loss of CYPs. We demonstrate that the culture of rat hepatocytes results in a rapid loss of liver-specific CYP2C11 mRNA and transcripts encoding the general housekeeping gene copper-zinc superoxide dismutase (CuZnSOD) as well as poly(A(+)) mRNA. These losses are accelerated by fibronectin, which has no effect on the transcription of CYP2C11 and CuZnSOD. However, fibronectin, an extracellular matrix protein involved in cell adhesion and spreading, induces ribonuclease (RNase) activity. Fibronectin also increases hepatocyte diameter and data are presented that cell spreading is involved in the loss of both CYP2C11 and CuZnSOD mRNAs. The use of functional blocking antibodies demonstrates that fibronectin is operating through its alpha(5)beta(1) integrin receptor and genistein, a tyrosine kinase inhibitor, prevents hepatocyte spreading, RNase induction, and CYP2C11 mRNA loss. Collectively, the data indicate that hepatocytes in vitro actively promote the extinction of their phenotype via the autocrine effects of fibronectin rather than the current consensus that they simply lose differentiated function, such as CYP2C11 expression, through the absence of extracellular matrix proteins. The substrate specificity of the ribonuclease induced is also considered.

Interaction of GRASP, a protein encoded by a novel retinoic acid-induced gene, with members of the cytohesin family of guanine nucleotide exchange factors

A novel, retinoic acid-induced gene, GRP1-associated scaffold protein (GRASP), was isolated from P19 embryonal carcinoma cells using a subtractive screening strategy. GRASP was found to be highly expressed in brain and exhibited lower levels of expression in lung, heart, embryo, kidney, and ovary. The predicted amino acid sequence of GRASP is characterized by several putative protein-protein interaction motifs, suggesting that GRASP may be a component of a larger protein complex in the cell. Although GRASP does not harbor a predicted membrane spanning domain(s), the protein was observed to be associated with the plasma membrane of transiently transfected mammalian cells. Yeast two-hybrid screening revealed that GRASP interacted strongly with the General Receptor for Phosphoinositides 1 (GRP1), a brefeldin A-insensitive guanine nucleotide exchange factor for the ADP-ribosylation factor family of proteins. GRASP. GRP1 interactions were also demonstrated in vitro and in mammalian cells in which GRASP was shown to enhance GRP1 association with the plasma membrane. Furthermore, GRASP colocalized with endogenous ADP-ribosylation factors at the plasma membrane in transfected cells, suggesting that GRASP may modulate signaling by this family of small GTPases.

Routing, processing and export of rat pituitary prolactin: identification of a 36 kDa disulphide-bridged oligomeric preprolactin

To gain an insight in the routing, processing and export of rat prolactin, rat pituitary cells were cultured in serum-free medium in the presence of cycloheximide, carbonyl cyanide m-chlorophenylhydrazone, Brefeldin A and monensin. The potential influence of these perturbants, whose well documented effects are the altering of protein synthesis and transport, was studied on rat prolactin molecular size isoforms appearing in cellular extracts and in culture medium. The outcome of the culture experiments as recorded in vertical SDS-PAGE, thiol gradient electrophoresis and sequential SDS-PAGE followed by prolactin specific immunoblotting and densitometry, was as follows: (1) at the cellular level we were able to characterize a novel 36 kDa protein as a disulphide-bridged oligomeric precursor prolactin, which is presumably rapidly transformed in the cis/medial Golgi; to designate monomeric rat prolactin as an early Golgi protein and t o advance evidence that the main processing of the glycosylated rat prolactin is a cis/medial Golgi event; (2) in release none of the perturbants disturbed the relative distribution of monomeric and glycosylated rat prolactin, the main molecular size isoforms currently secreted by untreated pituitary cells, or induced the appearance of transformed molecular size isoforms; (3) the secretion mode indicates that rat prolactin is released via the regulated pathway in the presence of the perturbants used.

Synthesis and cytotoxic evaluation of cycloheximide derivatives as potential inhibitors of FKBP12 with neuroregenerative properties

On the basis of the new finding that the protein synthesis inhibitor cycloheximide (1, 4-[2-(3, 5-dimethyl-2-oxocyclohexyl)-2-hydroxyethyl]-2,6-piperidinedione) is able to competitively inhibit hFKBP12 (K(i) = 3.4 microM) and homologous enzymes, a series of derivatives has been synthesized. The effect of the compounds on the activity of hFKBP12 and their cytotoxicity against eukaryotic cell lines (mouse L-929 fibroblasts, K-562 leukemic cells) were determined. As a result, several less toxic or nontoxic cycloheximide derivatives were identified by N-substitution of the glutarimide moiety and exhibit IC(50) values in the range of 22.0-4.4 microM for inhibition of hFKBP12. Among these compounds cycloheximide-N-(ethyl ethanoate) (10, K(i) = 4.1 microM), which exerted FKBP12 inhibition to an extent comparable to that of cycloheximide (1), was found to cause an approximately 1000-fold weaker inhibitory effect on eukaryotic protein synthesis (IC(50) = 115 microM). Cycloheximide-N-(ethyl ethanoate) (10) was able to significantly speed nerve regeneration in a rat sciatic nerve neurotomy model at dosages of 30 mg/kg.

Isolation, antifungal activity, and structure elucidation of the glutarimide antibiotic, streptimidone, produced by Micromonospora coerulea

The antibiotic Ao58A,which showed strong antifungal activity against some plant pathogenic fungi, was purified from the culture broth and mycelial mats of Micromonospora coerulea strain Ao58 using various chromatographic procedures. The molecular formula of the antibiotic Ao58A was deduced to be C(16)H(23)NO(4) (M + H, m/z 294.1707) by high-resolution FAB mass spectroscopy. Analyses of (1)H NMR, (13)C NMR, and 2D NMR spectral data revealed that the antibiotic Ao58A is the glutarimide antibiotic streptimidone, 4-(2-hydroxy-5, 7-dimethyl-4-oxo-6,8-nonadienyl)-2,6-piperidinedione. The antibiotic Ao58A was very effective in inhibiting growth of Phytophthora capsici,Didymella bryoniae, Magnaporthe grisea, and Botrytis cinerea in the range approximately 3-10 microg mL(-)(1) of MICs. In vivo evaluation of the antibiotic Ao58A under greenhouse condition showed strong control efficacies against the development of P. capsici, B. cinerea, and M. grisea on pepper, cucumber, and rice plants, respectively. The antibiotic Ao58A was equally as effective as metalaxyl, vinclozolin, and tricyclazole in the control of these plant diseases. However, it did not show any phytotoxicity on the plants even when treated with 500 microg mL(-)(1).

Evidence for and consequences of chronic heme deficiency in Belgrade rat reticulocytes

The Belgrade rat has a microcytic, hypochromic anemia inherited as an autosomal recessive trait (gene symbol b). Transferrin-dependent iron uptake is defective because of a mutation in Nramp2 (now DMT1, also called DCT1), the protein responsible for endosomal iron efflux. Hence, Belgrade reticulocytes are iron deficient. We show that a chromatographic method is able to measure the amount of 'free' heme in reticulocytes. Most of the 'free' heme is the result of biosynthesis. Succinylacetone, an inhibitor of heme synthesis, decreases the level of 'free' heme and cycloheximide, an inhibitor of globin synthesis, increases the 'free' heme level. In a pulse-chase experiment with 59Fe-transferrin, the 'free' heme pool behaves as an intermediate, with a half-life of just over 2 h. Belgrade reticulocytes contain about 40% as much 'free' heme as do heterozygous or homozygous reticulocytes. This deficiency of 'free' heme slows initiation of translation in Belgrade reticulocytes by increasing the level of an inhibitor of initiation. Thus the Belgrade rat makes a whole animal model available with chronic heme deficiency.

Superoxide-induced changes in endothelin (ET) receptors in hepatic stellate cells

BACKGROUND/AIMS

Reactive oxygen species are mediators of various pathophysiologic events, including postischemic reperfusion injury and inflammation. Generation of reactive oxygen species and consequent organ injury are associated with increased levels of a powerful vasoconstrictor peptide endothelin-1. Current evidence suggests that actions of endothelin-1 on the contractile and fibrogenic transdifferentiated stellate cells may play a critical role in hepatic pathophysiology. The aim of this investigation was to determine whether reactive oxygen species modulate the synthesis of endothelin-1 and its receptors in stellate cells.

METHODS

Primary cultures of transdifferentiated stellate cells were exposed to reactive oxygen species-generating system, hypoxanthine/xanthine oxidase, before determination of endothelin-1 and its receptors.

RESULTS

The treatment caused an initial decrease in ET-1 receptor density (about 30% at 30 min), followed by a significant increase over the basal level at 6 h. The increase in the receptors, which occurred specifically in the ET(B) subtype, progressed thereafter up to 24 h and was accompanied by an augmented functional response, as indicated by an enhanced endothelin-1-induced release of [3H]arachidonic acid from the prelabeled cells. Furthermore, treatment of cells for 24 h but not 30 min caused increased expression of ET(B) mRNA as determined by semi-quantitative polymerase chain reaction. The release of endothelin-1 in the culture medium was also enhanced by hypoxanthine/xanthine oxidase treatment. These effects of hypoxanthine/xanthine oxidase were inhibited by superoxide dismutase and dimethyl sulfoxide. ET-1-induced [3H]arachidonic acid release was also inhibited by the ET(B) receptor antagonist BQ788, but not by the ET(A) receptor antagonist BQ123.

CONCLUSIONS

These findings indicate that interactions between ET-1 and stellate cells during episodes of the generation of reactive oxygen species can be an important mechanism in the pathophysiology of hepatic disorders.

IRP-1 binding to ferritin mRNA prevents the recruitment of the small ribosomal subunit by the cap-binding complex eIF4F

Binding of iron regulatory proteins (IRPs) to IREs located in proximity to the cap structure of ferritin H- and L-chain mRNAs blocks ferritin synthesis by preventing the recruitment of the small ribosomal subunit to the mRNA. We have devised a novel procedure to examine the assembly of translation initiation factors (eIFs) on regulated mRNAs. Unexpectedly, we find that the cap binding complex eIF4F (comprising eIF4E, eIF4G, and eIF4A) assembles even when IRP-1 is bound to the cap-proximal IRE. This assembly is futile, because bridging interactions between eIF4F and the small ribosomal subunit cannot be established in the presence of IRP-1. Our findings provide insight into translational control by an mRNA binding protein at the level of translation initiation factors and uncover a key regulatory step in iron homeostasis.

Effect of actinomycin D and cycloheximide on human sperm function

The effects of actinomycin D and cycloheximide on human spermatozoal function were examined to investigate the potential transcriptional and translational activities of human sperm cell during capacitation/acrosome reaction. Treatment with actinomycin D significantly increased and treatment with cycloheximide decreased the acrosome reaction, and the penetration rates in the human sperm penetration of zona-free hamster oocytes assay (SPA). [35(S)]Methionine got incorporated into 3-9 de novo synthesized proteins present in the head and midpiece regions of the swim-up population of human sperm. Treatment with actinomycin D completely blocked and treatment with cycloheximide slightly reduced the synthesis of proteins. There seem to be some transcriptional and translational activities in the head and midpiece regions of human sperm during capacitation/acrosome reaction.

Sulfation of intrinsic glycoproteins of the rabbit vitreous

The experiments reported here were designed to characterize the intrinsic vitreous glycoproteins and to understand the process of their sulfation. Rabbits were injected intravitreally with 35S-sodium sulfate and killed at several time intervals after injection. In another series of experiments, rabbits were injected either with 35S-sodium sulfate, 3H-fucose or 3H-tyrosine, associated or not associated with tunicamycin administration. Vitreous from the control eyes was also digested with N-glycosidase. Furthermore, ciliary bodies, the putative source of the intrinsic vitreous glycoproteins, were incubated with 35S-sodium sulfate in the presence or absence of the protein synthesis inhibitor cycloheximide, and the culture media recovered for analysis. These and the vitreous samples of the other experiments were processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. Except for serum albumin, practically all polypeptide bands of the vitreous and culture media were labeled with radioactive sulfate and were shown to undergo renewal. The experiments using tunicamycin or enzyme treatment suggest that radioactive sulfate was incorporated not only into the carbohydrate side chains of the glycoproteins but also into the amino acid tyrosine of the polypeptide backbone of these glycoproteins.

Expression and estrogen regulation of the HEM45 MRNA in human tumor lines and in the rat uterus

A human estrogen regulated transcript, HEM45, was characterized that encodes a novel protein of 181 amino-acid residues (Mr 20300). It was identified using differential-display-PCR and mRNA from a human cervical cancer cell line (UP1) stably transfected with an estrogen receptor (ER) expression construct. The HEM45 protein has similarity to the bracket fungus protein FRT1 that can cause fruiting-body production and to a Xenopus product, XPMC2, that affects cell-cycle control. These similarities suggest that HEM45 will have a role in mediating estrogen control of cellular proliferation and differentiation. HEM45 mRNA was widely expressed at low levels in cell lines and was up regulated by E2 in ER-positive breast cancer lines. The in vivo regulation of HEM45 was confirmed by demonstrating estrogen stimulation of the rat HEM45 homolog in the rat uterus. The levels of the rat uterine HEM45 sequence were elevated by estrogen 3 to 15 h after treatment. The maximal response, at six hours, was greater than eight-fold. The uterine HEM45 response was distinct from that reported for 'early-response' genes as the increase in HEM45 mRNA levels occurred later but could be induced by lower levels of hormone. HEM45 mRNA expression in cultured cells was increased by estrogen in the presence of cycloheximide, indicating direct ER-regulation of HEM45.

Thrombin regulates interleukin-6 synthesis through phosphatidylcholine hydrolysis by phospholipase D in osteoblasts

We previously reported that thrombin stimulates Ca2+ influx and activates phosphatidylcholine-hydrolyzing phospholipase D in osteoblast-like MC3T3-E1 cells. In this study, we investigated the effect of thrombin on interleukin-6 (IL-6) synthesis in these cells. Thrombin stimulated IL-6 synthesis dose-dependently in the range between 0.01 and 1 U/ml. The depletion of extracellular Ca2+ by EGTA suppressed the thrombin-induced IL-6 synthesis. TMB-8, an inhibitor of intracellular Ca2+ mobilization, also inhibited the IL-6 synthesis by thrombin. Propranolol, a phosphatidic acid phosphohydrolase inhibitor, enhanced the IL-6 synthesis by thrombin. Calphostin C, a highly potent and specific inhibitor for protein kinase C, significantly amplified the IL-6 synthesis by thrombin. The thrombin-induced IL-6 synthesis was enhanced in PKC down-regulated MC3T3-E1 cells. These results strongly suggest that thrombin stimulates IL-6 synthesis, which depends on intracellular Ca2+ mobilization mainly from extracellular space in osteoblasts, and that the IL-6 synthesis by thrombin is regulated due to thrombin-activated protein kinase C through phosphatidylcholine-hydrolyzing phospholipase D.

Calumenin, a Ca2+-binding protein retained in the endoplasmic reticulum with a novel carboxyl-terminal sequence, HDEF

We have identified and characterized a cDNA encoding a novel Ca2+-binding protein named calumenin from mouse heart by the signal sequence trap method. The deduced amino acid sequence (315 residues) of calumenin contains an amino-terminal signal sequence and six Ca2+-binding (EF-hand) motifs and shows homology with reticulocalbin, Erc-55, and Cab45. These proteins seem to form a new subset of the EF-hand protein family expressed in the lumen of the endoplasmic reticulum (ER) and Golgi apparatus. Purified calumenin had Ca2+-binding ability. The carboxyl-terminal tetrapeptide His-Asp-Glu-Phe was shown to be responsible for retention of calumenin in ER by the retention assay, immunostaining with a confocal laser microscope, and the deglycosylation assay. This is the first report indicating that the Phe residue is included in the ER retention signal. Calumenin is expressed most strongly in heart of adult and 18.5-day embryos. The calumenin gene (Calu) was mapped at the proximal portion of mouse chromosome 7.

Biochemical studies on the secretion of glycoproteins by isolated ciliary body of rabbits

The contribution of the ciliary body to the origin of vitreous proteins was investigated in rabbits by incubating explants of this eye component under novel conditions. At the end of incubations for up to 21 h, the tissues were processed histologically and were shown to be in an excellent state of morphological preservation. When radioactive amino acids and fucose were added to the culture medium, protein and glycoprotein synthesis and secretion were detected using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) plus fluorography. The origin of these secretory products was traced by autoradiography to the ciliary epithelium. When samples of vitreous bodies - injected intravitreally with the same radioactive precursors - were run beside samples of the tissue culture media, comigration of at least 8 radioactively labelled bands including the one previously identified as transferrin was detected. This indicates that some vitreous proteins may be secreted by the ciliary body and that cultures of explants of ciliary body-iris are useful tools for studies on vitreous protein secretion.

Selective inhibition of interleukin-1 beta gene expression in activated RAW 264.7 macrophages by interferon-gamma

The ability of interleukin-1 (IL-1) to activate epidermal cell populations supports its role as a key cytokine in the pathogenesis of a number of inflammatory skin diseases. In the present study, we have examined the effect of interferon (IFN)-gamma on the expression of the IL-1 beta gene in mouse RAW 264.7 macrophages activated by lipopolysaccharide (LPS) plus tumor necrosis factor (TNF)-alpha. Incubation of macrophages with both LPS and TNF-alpha resulted in the expression of both IL-1 beta and inducible nitric oxide synthase (iNOS) mRNA transcripts and increased the release of IL-1 beta protein and nitrite production in culture supernatants. Addition of IFN-gamma up-regulated the expression of the iNOS gene in cells activated by LPS + TNF-alpha, but significantly suppressed the induction of IL-1 beta gene expression in a dose-dependent manner. The suppression required neither de novo protein synthesis nor involved destabilization of the mRNA transcripts. Together, these findings suggest that IFN-gamma can be an important regulatory cytokine in a chronic inflammatory site and may explain its purported anti-inflammatory effects in certain dermatological diseases.

Interleukin 10 (IL-10) regulation of tumour necrosis factor alpha (TNF-alpha) from human alveolar macrophages and peripheral blood monocytes

BACKGROUND

Regulation of the inflammatory response within the human lung is essential to prevent this important part of the normal host defence response becoming a pathological process. Tumour necrosis factor alpha (TNF-alpha) is a cytokine involved in the pathogenesis of shock and in granuloma formation, tissue necrosis, and fibrosis in many organ systems including the lung. Interleukin 10 (IL-10) has been proposed as having an inhibitory effect on the production of several inflammatory cytokines including TNF-alpha.

METHODS

The effect of IL-10 administration on TNF-alpha production was explored in human alveolar macrophages and peripheral blood monocytes from matched individuals. The effects of IL-10 on TNF-alpha protein production were determined by sandwich enzyme linked immunosorbant assay (ELISA), whereas the TNF-alpha mRNA response was established by Northeren blotting using a TNF-alpha specific oligonucleotide probe. The protein synthesis inhibitors actinomycin D and cyclohexamide were utilised to monitor IL-10 effects on mRNA degradation and de novo protein synthesis, respectively.

RESULTS

The lipopolysaccharide-mediated TNF-alpha production in alveolar macrophages was reduced from 3.508 (0.629) to 2.035 (0.385) ng/ml by 100 U/ml IL-10. Lipopolysaccharide-induced TNF-alpha production in peripheral blood monocytes was reduced from 2.035 (0.284) to 0.698 (0.167) ng/ml. TNF-alpha gene expression was also inhibited in both alveolar macrophages and peripheral blood monocytes; lipopolysaccharide-induced TNF-alpha mRNA was reduced by 47.8 (15.2)% and 83.1 (4.2)%, respectively, by IL-10. The IL-10 mediated suppression of TNF-alpha mRNA was unaffected by addition of cyclohexamide, suggesting that de novo protein synthesis was not required for TNF-alpha inhibition. mRNA stability experiments indicated no acceleration in lipopolysaccharide-induced TNF-alpha mRNA degradation in response to IL-10.

CONCLUSIONS

These findings suggest that IL-10 is a potent inhibitor of TNF-alpha expression and release from alveolar macrophages and peripheral blood monocytes, and thus it may have an important role in the cytokine network of the pulmonary immune response.

Induction of the blood/brain-barrier-associated enzyme alkaline phosphatase in endothelial cells from cerebral capillaries is mediated via cAMP

The mammalian blood/brain barrier is located at the endothelial cells of the cerebral capillaries. Alkaline phosphatase is associated to a very large extent with these cells and has been established as a marker enzyme for a differentiated blood/brain barrier phenotype in vivo and in vitro. Nevertheless cultured brain capillary endothelial cells (BCEC) lose this marker enzyme because of a cessation of de novo synthesis. Since astrocytes have been shown to possess the capability to re-induce the enzymic activity of alkaline phosphatase in BCEC in vitro we were interested in the second messengers involved in the signal-transduction mechanism of this induction in BCEC. For this reason we treated cultured porcine BCEC with a water-soluble and membrane-permeable analogue of cAMP, 8-(4-chlorophenylthio)-cAMP (C1PhS-cAMP) in the absence of astrocytes. By means of enzymic activity assays we were able to show that within three days the activity of alkaline phosphatase increased up to sixfold compared with the controls. The total activity of alkaline phosphatase in C1PhS-cAMP-treated BCEC was comparable to that of freshly isolated cells. Addition of cycloheximide inhibited the alkaline phosphatase activity increase. We conclude that cAMP is one of the second messengers involved in the induction of alkaline phosphatase activity in BCEC in vitro.

Regulation of protein kinase C by transforming growth factor beta 1 in rat costochondral chondrocyte cultures

Transforming growth factor beta (TGF-beta) regulates the proliferation and differentiation of chondrocytes; however, the mechanism of TGF-beta signal transduction remains unclear. We examined whether the response to TGF-beta is mediated by protein kinase C activity in chondrocytes at different stages of maturation. The aims were to examine the effect of recombinant human TGF-beta 1 (rhTGF-beta 1) on protein kinase C in rat costochondral chondrocyte cultures; determine the major isoform present; assess the involvement of phospholipase C or tyrosine kinases; determine whether genomic or nongenomic pathways are involved; and test whether these mechanisms differ as a function of the stage of cell maturation. Dose-dependent increases in protein kinase C activity were observed in confluent, fourth-passage cultures of rat costochondral growth zone and resting zone chondrocytes treated with rhTGF-beta 1. In growth zone cells, elevated activity was observed at 12 h and decreased markedly by 24 h. In resting zone cells, elevated activity was observed at 9 h, maximum stimulation occurred at 12 h, and activity returned to baseline levels after 48 h. Immunoprecipitation studies showed protein kinase C alpha is the major isoform present in both untreated and treated cells. Neither the phospholipase C inhibitor, U73122, nor the tyrosine kinase inhibitor, genistein, significantly reduced the protein kinase C response to rhTGF-beta 1. Actinomycin D and cycloheximide, inhibitors of transcription and translation, produced dose-dependent inhibition of rhTGF-beta 1 stimulated protein kinase C activity in both resting zone and growth zone chondrocytes. The time course of activation and insensitivity to U73122 suggest that phospholipase C-mediated events are not involved in rhTGF-beta 1 stimulation of protein kinase C in costochondral chondrocytes. Similarly, because genistein had no effect, tyrosine kinases are not implicated. Rather, the reduction in protein kinase C activity observed when rhTGF-beta 1 is administered along with actinomycin D or cycloheximide indicates that new gene expression and protein synthesis are required for the response. These results indicate that the effect of rhTGF-beta 1 is mediated by protein kinase C; however, it is very slow and may require new protein kinase C production, perhaps via a cytokine cascade. Moreover, the classic mechanism of activation of protein kinase C by phospholipase C was not found, suggesting a novel mechanism of activation. Finally, the effects of rhTGF-beta 1 on protein kinase C are dependent on the state of cell maturation with respect to onset and duration of response.

Initial expression of glucokinase gene in cultured hepatocytes from suckling rats is linked to the synthesis of an insulin-dependent protein

The initial accumulation of glucokinase mRNA in response to insulin in cultured hepatocytes from 10-day-old suckling rats was characterized by a delay of 18-24 h with a maximal level reached after 48 h. This delay is not observed in cultured adult rat hepatocytes. When hepatocytes from 10-day-old suckling rats were cultured for 48 h in the presence of insulin (to obtain a maximal accumulation of glucokinase mRNA) and then deprived of insulin for 18 h, glucokinase mRNA returned to very low levels. Reexposure of these cultured hepatocytes to insulin allowed a rapid accumulation of glucokinase mRNA, with a maximal level reached after 8 h, as in adult rat hepatocytes. The aim of the present study was to investigate the factors responsible for the delay in insulin action during first exposure to insulin. The difference in the kinetics of glucokinase mRNA accumulation after the first and secondary exposure to insulin was due to differences in the rate of transcriptional activity of the glucokinase gene, as shown by a run-on assay on isolated nuclei. The half-life of glucokinase mRNA was similar after the first and second exposure to insulin. The delay in the initial accumulation of glucokinase mRNA in response to the first exposure to insulin was not due to elevated levels of cAMP (a potent inhibitor of glucokinase gene expression) or to a defect in insulin signalling (insulin inhibited without delay phosphoenolpyruvate carboxykinase gene expression). In contrast, it was markedly dependent upon whether glucokinase has been already expressed in vivo. Hepatocytes from rats that had already expressed glucokinase in vivo (suckling rats force-fed with glucose or rats weaned to a high-carbohydrate diet) showed no delay in their response to insulin in culture, whereas hepatocytes from rats that have never expressed glucokinase in vivo (suckling rats or rats weaned to a high-fat diet) showed a delay of 24 h. Two different inhibitors of protein synthesis (cycloheximide and puromycin) prevented the initial accumulation of glucokinase mRNA in response to the first exposure to insulin but not to the secondary accumulation of glucokinase mRNA in response to reexposure to insulin. This suggests that the synthesis of one or several insulin-dependent proteins is necessary for the first activation of glucokinase gene transcription in response to the first exposure to insulin.

Toxins that inhibit host protein synthesis

Methods have been described that are sufficient to determine if a bacterial protein toxin is a selective inhibitor of eukaryotic protein synthesis, and, if so, which part of the overall process is affected. More defined assays are presented for studying the steps of peptide elongation as this is where such toxins have been shown to act.

Differential involvement of phospholipase A2 in phorbol ester-induced luteinizing hormone and growth hormone release from rat anterior pituitary tissue

The protein kinase C (PKC) activator, phorbol 12,13-dibutyrate (PDBu) induced the release of both luteinizing hormone (LH) and growth hormone (GH) from proestrous rat anterior pituitary pieces in vitro. Phorbol 12,13-dibutyrate-induced LH, but not GH release was readily inhibited by the phospholipase A2 (PLA2) inhibitors, quinacrine, aristolochic acid, ONO-RS-082 and chloracysine. Furthermore, PDBu induced release of [3H]arachidonic acid ([3H]AA) from pre-labelled anterior pituitary tissue that was prevented in the presence of quinacrine, aristolochic acid and ONO-RS-082 but not the diglyceride lipase inhibitor RHC 80267. The effect of PDBu was completely inhibited by staurosporine and the selective PKC inhibitor Ro 31-8220 but only partially by low concentrations of H7; consistent with the involvement of both H7-sensitive and H7-resistant forms of PKC in the activation of PLA2 by PDBu. The protein synthesis inhibitor cycloheximide inhibited the release of both [3H]AA and LH that had been induced by PDBu, whereas LH release induced by the PLA2 activator mellitin was cycloheximide-insensitive. These results suggest that PKC activators may induce LH but not GH release from anterior pituitary tissue by a mechanism involving activation of a PLA2, brought about by a process which is reliant on protein synthesis.

Transient transfection and expression in the obligate intracellular parasite Toxoplasma gondii

Toxoplasma gondii is a protozoan pathogen that produces severe disease in humans and animals. This obligate intracellular parasite provides an excellent model for the study of how such pathogens are able to invade, survive, and replicate intracellularly. DNA encoding chloramphenicol acetyltransferase was introduced into T. gondii and transiently expressed with the use of three vectors based on different Toxoplasma genes. The ability to introduce genes and have them efficiently and faithfully expressed is an essential tool for understanding the structure-function relation of genes and their products.