6-0-butanoylcastanospermine (MDL 28,574) inhibits glycoprotein processing and the growth of HIVs

The antiviral activity of 6-0-butanoylcastanospermine (MDL 28,574) [50% inhibitory concentration (IC50: 1.1 microM)] in JM cells infected with a recent isolate of HIV-1 (GB8), was compared with other inhibitors of glycoprotein-processing enzymes. N-butyldeoxynojirimycin (BuDNJ), deoxynojirimycin (DNJ), castanospermine (CAST) or the reverse transcriptase inhibitor 2'3'-dideoxycytidine (ddC) had activities of 56, 560, 29 and 0.1 microM, respectively. MDL 28,574 was at least 50 times more active than BuDNJ and less active but better tolerated in cell culture than ddC, two compounds currently undergoing clinical trials. The CAST derivative showed good protection in H9 cells infected with HIV-1 (RF; IIIB; U455), and HIV-2 (ROD), although the potency was less than that seen in the JM/GB8 system. HIV-1 glycoproteins, gp160 and gp120, synthesized in H9 cells chronically infected with HIV-1 (RF) and treated with MDL 28,574, were characterized by an increase in relative molecular weight of approximately 7-8000 kD. The ratio of gp120 to gp160 was markedly reduced in treated cells and provided further evidence that cleavage of the gp160 precursor molecule is a major consequence of the inhibition of glycoprotein processing. The intracellular target for MDL 28,574 was verified as alpha-glucosidase-I of the processing enzymes by the analysis of high-glucose glycopeptides recovered from treated mouse cells. This activity correlated with the antiviral effect observed against the growth of a mouse retrovirus, Moloney murine leukemia virus (MOLV), in mouse cells.

Okadaic acid blocks membrane fusion of chick embryonic myoblasts in culture

Okadaic acid was found to block membrane fusion of chick embryonic myoblasts in culture. It also induced morphological change of the cells from bipolar to spherical shape. These effects were dose-dependent, and could be reversed upon removal of the drug from the culture medium. It showed, however, no effect on the induction of muscle specific proteins including tropomyosin and creatine kinase. When okadaic acid was treated to the cell lysates, the phosphorylation state of many proteins significantly increased. These results suggest that the inhibition of myoblast fusion by okadaic acid may be mediated by the increase in the phosphorylation of certain, unknown protein(s) that regulate the fusion process.

Application of a stability statistic to international maize yield trials

Genotype x environment (GE) interaction encountered in experiments complicates genotype selection and varietal recommendation. The integration of yield and stability of genotypes into a single parameter may make selection and recommendation easier. Kang developed a rank-sum method that allows selection for both yield and the stability variance statistics (σ i (2) or s i (2) ) of Shukla. The objective of this research was to compare the rank-sum selection method to selection based on yield alone in five international maize (Zea mays L.) yield trials. Ranks were assigned for yield (the highest mean yield received a rank of 1) and for σ i (2) and s i (2) (the lowest value received a rank of 1). The yield and σ i (2) ranks and/or the yield and s i (2) ranks for each genotype were summed. Each trial contained two reference entries (REs). Yield rank or rank-sum of each genotype was compared to yield rank or rank-sum of the best RE (BRE). GE interaction was significant for all trials. Heterogeneity in the GE interaction due to the linear effect of a covariate (differences in fertility and/or cultural practices) was significant in Trials 1, 2, and 5. Overall, in all trials, 29 genotypes were selected on the basis of yield alone. On the basis of σ i (2) and yield rank-sum, 32 genotypes were identified, with 11 being lower yielding than the 29 yield-based selections. On the basis of s i (2) and yield rank-sum, 31 genotypes were selected, with 11 being lower yielding than the yield-bases selections. Obviously, yield is sacrificed when the rank-sum method is used in the selection process. However, selection based on yield alone may not be adequate when GE interaction is significant because of testing in diverse environments.

Inhibition of glycoprotein processing and HIV replication by castanospermine analogues

Inhibitors of glycoprotein processing enzymes have been shown to have activity against HIV. Several analogues of the known glucosidase I inhibitor, castanospermine (CAST), were synthesized and evaluated for their inhibitory effect on glucosidases and for antiviral activity against Moloney murine leukemia virus (MOLV) and HIV-1. The most effective analogue was 6-O-butanoyl CAST (B-CAST, MDL 28,574) with an IC50 of 0.05 micrograms/mL against MOLV. A correlation between inhibition of glucosidase I and MOLV replication was observed. This analogue was further evaluated against HIV-induced syncytial formation in HeLa T4+ cells and against productive infection in JM cells infected with HIV 1 (GB8 strain). B-CAST showed an IC50 of 0.3 micrograms/mL in the HeLa T4+ assay, compared to CAST at 11 micrograms/mL. The compound also was more potent (IC50:0.15 micrograms/mL) than CAST (4-6 micrograms/mL) in JM cells. The antiretroviral activity of B-CAST was further confirmed in Friend leukemia virus (FLV) infection in mice. B-CAST showed equivalent activity to AZT and was more potent than CAST in inhibiting FLV-induced splenomegaly in mice. The data presented herein suggest the potential of these novel glucosidase inhibitors as anti-HIV agents.

Evaluation of thiol broth for the culture of Salmonella typhi and other bacteria from blood

Thiol broth is known to neutralize various antimicrobial agents. Positivity of growth of various species of bacteria from blood in thiol broth was reported as similar to that in tryptic soy broth (TSB). As blood cultures are often used for the diagnosis of typhoid fever, and as patients may receive antimicrobial therapy before blood culture, the positivity and rapidity of growth of Salmonella typhi in thiol broth were compared to those in TSB. Routine blood culture samples from Yonsei Medical Center patients were inoculated in 50-ml amounts of TSB and thiol broth. The media were prepared from dehydrated products and did not contain CO2, but TSB contained 0.025% sodium polyanethol sulfonate (SPS). Growth of S. paratyphi-A, Klebsiella pneumoniae, Enterobacter sp., Serratia marcescens and alpha-hemolytic Streptococcus were similar in both media. However, greater positivity and shorter incubation time for macroscopic detection were noted in TSB with S. typhi, Escherichia coli and Staphylococcus aureus. It is concluded that thiol broth is inferior to TSB plus SPS for the culture of S. typhi from blood.

Correlation between fibronectin and its receptor in chick myoblast differentiation

Alterations in the amount of fibronectin and in the number of its receptors during myoblast differentiation of chicken embryo were investigated. The amount of fibronectin in the cell surface pool as measured by immunoblotting decreased during myogenesis. To identify and characterize the fibronectin receptors on the myoblasts, the interactions of the 28,000 dalton (28 kDa) amino terminal fragment and 85,000 dalton (85 kDa) cell-binding fragment of fibronectin with myoblasts were examined. The binding of the 28 kDa fragment was found to be time-dependent and reached a maximum level within 60 min. The unlabeled 28 kDa fragment inhibited the binding of the radioiodinated 28 kDa fragment, whereas the unlabeled 85 kDa fragment and antibody to integrin did not inhibit it, suggesting that the 28 kDa fragment interacts with the matrix assembly receptors but not with the cell adhesion receptors. There was a single class of 3.4 x 10(5) binding sites per cell with an apparent dissociation constant of 1.4 x 10(-7) M on 30 hr old myoblasts. The specific binding of the radioiodinated 28 kDa fragment to myoblasts decreased as the fusion proceeded. This decrease of binding was consistent with the decrease in the amount of fibronectin. Furthermore, the levels of fibronectin and binding of the radioiodinated 28 kDa fragment in the fusion-blocked myoblasts by EGTA treatment appeared to remain constant. These results suggest that the decrease and/or loss of fibronectin during myoblast fusion is closely correlated with the alteration of fibronectin receptors and with the fusion of myoblasts.

A simple and rapid microplate assay for glycoprotein-processing glycosidases

A simple and convenient microplate assay for glycosidases involved in the glycoprotein-processing reactions is described. The assay is based on specific binding of high-mannose-type oligosaccharide substrates to concanavalin A-Sepharose, while monosaccharides liberated by enzymatic hydrolysis do not bind to concanavalin A-Sepharose. By the use of radiolabeled substrates [( 3H]glucose for glucosidases and [3H]mannose for mannosidases), the radioactivity in the liberated monosaccharides can be determined as a measure of the enzymatic activity. This principle was employed earlier for developing assays for glycosidases previously reported (B. Saunier et al. (1982) J. Biol. Chem. 257, 14155-14161; T. Szumilo and A. D. Elbein (1985) Anal. Biochem. 151, 32-40). These authors have reported the separation of substrate from the product by concanavalin A-Sepharose column chromatography. This procedure is handicapped by the fact that it cannot be used for a large number of samples and is time consuming. We have simplified this procedure and adapted it to the use of a microplate (96-well plate). This would help in processing a large number of samples in a short time. In this report we show that the assay is comparable to the column assay previously reported. It is linear with time and enzyme concentration and shows expected kinetics with castanospermine, a known inhibitor of alpha-glucosidase I.

Potentiation of human lymphokine-activated killer cell activity by swainsonine, an inhibitor of glycoprotein processing

Interleukin 2 (IL-2) is a secreted glycoprotein which acts as an activation and proliferative signal for lymphocytes expressing membrane-bound glycoprotein IL-2 receptors. We have recently established that swainsonine (SW), an inhibitor of mannosidase II during N-linked glycoprotein processing, augmented mitogen-induced mononuclear leukocyte IL-2 receptor expression and IL-2-induced proliferation. The objective of the present investigation was to examine the effect of SW on lymphokine-activated killer (LAK) cell induction. Human mononuclear leukocytes were treated with various concentrations of SW (0.1-10 micrograms/ml) and IL-2 (1-100 units/ml) for up to 72 h. SW augmented IL-2-induced LAK activity directed against human lung carcinoma, melanoma, and leukemia cells 2-3-fold. LAK activity generated in the presence of SW at suboptimal doses of IL-2 (10 units/ml) was similar to that observed with higher concentrations of IL-2 (100 units/ml) alone. SW treatment alone or in combination with IL-2 increased the percentage of IL-2 receptor-positive cells. Furthermore, pretreatment with SW subsequently enhanced IL-2-induced lymphocyte proliferation. SW-treated mononuclear leukocytes exhibited an increase in high-mannose type glycoproteins based upon [3H]mannose labeling, susceptibility to alpha-mannosidase, and binding to concanavalin A-Sepharose. These results indicate that modulators of glycoprotein processing may be useful in lowering the concentrations of IL-2 required for LAK induction and maintenance.

Evaluation of dialyzers used in shortened dialysis

The clearance of urea and beta 2-microglobulin are important considerations along with biocompatibility in selecting membranes for use in shortened dialysis. During 3 hr of dialysis we have measured the in vivo urea clearances, pre- and post-beta 2-M levels, plasma clearance and simultaneous dialysance of beta 2-M. Leucopenia was compared after 15 min of dialysis on a cellulose acetate (CA) dialyzer and a polyacrylonitrile dialyzer (PAN). Clearance of urea was similar in both dialyzers. In contrast to CA, PAN removed beta 2-M and exhibited minimal leucopenia. The dialysance of beta 2-M was significantly less than the simultaneous blood side clearance. The disparity between blood clearance and dialysance by PAN membranes suggests removal of beta 2-M by adsorption and diffusion. We conclude that in comparison with CA dialyzers, PAN membranes remove beta 2-M, have equivalent urea clearances, and are more biocompatible.

Site-directed mutagenesis of the cell-binding domain of human fibronectin: separable, synergistic sites mediate adhesive function

Polypeptide sequences required for function of the cell-binding domain of human fibronectin were analyzed by site-directed mutagenesis. Site-specific deletion of the putative recognition sequence Arg-Gly-Asp-Ser or an Asp-to-Glu mutation decreased the adhesive activity of fibronectin fusion proteins expressed in E. coli by greater than or equal to 97%. A second functional site over 0.5 kb away was identified by deletion mutagenesis. These mutants also showed a greater than or equal to 96% loss of activity, indicating cooperativity between sites. The two classes of mutant protein displayed synergism of activity in a trans complementation assay. Effective actin microfilament bundle organization was also dependent on the combined function of both sites. Thus, fibroblast adhesion and intracellular response to the fibronectin cell-binding domain involve two synergistic sites, each of major quantitative importance.

Interrelationships among stabilities of important agronomic traits in sugarcane

The stability-variance statistic, ĝs i (2) , measures the contribution of the i(th) genotype to genotype x environment interaction. In addition to the knowledge of cultivar stability for an agronomic trait, information on whether stability of one trait can be used to predict stability of another should be useful to breeders. Three separate groups of data, respectively involving CP 79 series, CP 80 series, and CP 81 series experimental clones of sugarcane (Saccharum spp.) were used in this study. Rank-correlation coefficients (rs) between ranks of genotypes for ĝs i (2) 's for paired traits indicated in both plant-cane and ratoon crops that stability of tons per hectare of sugar can be predicted from the stability of tons per hectare of cane (THC) and also, to a lesser extent, from the stability of stalk number. The stability of THC also can be reasonably well predicted from the stability of stalk number. Brix stability may give some indication of the stabilities for percentage sucrose and sugar concentration (SC). The ĝs i (2) 's for percentage sucrose and SC were almost identical in the CP 79 and CP 81 series (rs varied from 0.93, P<0.01, in plant-cane crop for CP 79 series to 0.98, P<0.01, in plant-cane crop for CP 81 series). Whether correlations were based on ĝs i (2) 's estimated across locations within crops or across crops, the magnitude of rs was about the same. Means of various traits were not correlated with their respective ĝs i (2) 's (for CP 81 series), indicating that identification and selection of high-yielding sugarcane genotypes with a relatively high degree of stability of performance across test environments should be possible.

Expression of the cell-binding domain of human fibronectin in E. coli. Identification of sequences promoting full to minimal adhesive function

Two cDNA subfragments containing the cell-attachment site of human fibronectin (FN) were expressed as beta-galactosidase fusion proteins in E. coli. The products were purified to homogeneity by monoclonal antibody affinity chromatography and assayed for activity in a standard cell-adhesion assay. A fusion protein containing an 80 kDa fragment of human FN appeared functionally equivalent to intact FN purified from human plasma, whereas a truncated fusion protein of 33 kDa still containing a previously postulated cell-attachment site was approx. 50-fold less active. Our study establishes a system for analyzing adhesive protein function by DNA manipulation, rules out any major role for eukaryotic post-translational modifications in FN adhesive function, and localizes additional functional activity to a 1.3 kb region.

Regulation of fungal cell wall growth: a guanine nucleotide-binding, proteinaceous component required for activity of (1----3)-beta-D-glucan synthase

By treatment with detergent and NaCl, particulate (1----3)-beta-D-glucan synthase (EC 2.4.1.34) from Hansenula anomala or Neurospora crassa was dissociated into a "soluble fraction" and a "membrane fraction." Each fraction alone was almost inactive, but enzymatic activity could be reconstituted by mixing the two fractions and adding GTP or one of its analogs. Based on their lability to heat and to incubation with trypsin, the activity in both fractions is proteinaceous. The active component in the soluble fraction appears to bind guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S]), since it was specifically protected by this nucleotide against heat inactivation and against inactivation in the presence of EDTA. Furthermore, precipitation of the soluble component with ammonium sulfate in the presence of GTP[gamma S] gave rise to a fraction that was highly active in the absence of added nucleotide, indicating either tight binding or covalent interaction between GTP[gamma S] and the soluble component. The membrane fraction probably contains the catalytic moiety, because it was partially protected against heat inactivation by the substrate, UDP-glucose. Soluble fractions that stimulated membrane fractions from H. anomala and N. crassa were obtained from several other fungi, including Saccharomyces cerevisiae. We propose that the soluble fraction contains a GTP-binding protein that modulates the biosynthesis of (1----3)-beta-D-glucan of fungal cell walls and probably has a major role in the regulation of cell wall morphogenesis.

The effect of papulacandin B on (1----3)-beta-D-glucan synthetases. A possible relationship between inhibition and enzyme conformation

The antibiotic, papulacandin B, inhibited growth or (1----3)-beta-D-glucan synthetase (or both) in the fungi Saccharomyces cerevisiae, Hansenula anomala, Neurospora crassa, Cryptococcus laurentii, Schizophyllum commune and Wangiella dermatitidis. No effect was observed on Achlya ambisexualis. There was no apparent correlation between the inhibition of growth and that of the synthetase. With most of the fungal extracts, the inhibition of glucan synthetase by papulacandin B became less pronounced as the substrate (UDP-glucose) concentration was decreased. At very low levels of UDP-glucose, with the enzymes from S. cerevisiae and W. dermatitidis, the antibiotic stimulated the activity of glucan synthetase. As further studied with the W. dermatitidis enzyme, those low concentrations of UDP-glucose corresponded to a sigmoidal portion of the rate vs. substrate curve. The sigmoid segment of the curve extended to higher concentrations of UDP-glucose as the temperature was increased. Concomitantly, the range of substrate concentrations at which papulacandin B stimulated the reaction or was noninhibitory was broadened. It is tentatively concluded that glucan synthetase may exist in more than one interconvertible form. The stimulatory effect of papulacandin B is possibly due to preferential binding to the active form of the enzyme. The equilibrium between these forms could be shifted by structural changes in the membrane in which the enzyme is embedded. The lack of correlation between the effects of papulacandin B in whole cells and in extracts is discussed in terms of the variations in membrane structure in the two situations.

Effect of hyperthermia on the lactic acid and beta-hydroxybutyric acid content in tumour

The effects of hyperthermia on the content of lactic acid and beta-hydroxybutyric acid in the SCK mammary carcinoma and the leg muscle of A/J mice were studied. The contents of lactic acid in the SCK tumour before heating was 9.32 mumol/g, and the content of beta-hydroxybutyric acid was only 0.013 mumol/g. The lactic acid content in the tumour increased to 17.5 mumol/g at 0 h after heating at 41.5 degrees C for 30 min and then decreased to the control level 3 h later. When heated at 43.5 degrees C for 30 min, the lactic acid content in the tumour increased to 24 mumol/g at the end of heating and remained elevated for 24 h. The content of beta-hydroxybutyric acid increased continuously reaching 0.45 mumol/g at 5 h after heating at 43.5 degrees C for 30 min, and then declined thereafter. The contents of lactic acid and beta-hydroxybutyric acid in the muscle also increased after heating, but these increases were far less than those observed in the tumours. The absolute amount of lactic acid in the heated tumours was far greater than that of beta-hydroxybutyric acid, and thus appeared to play the major role for the increased acidity in the heated tumours.

Evaluation of cultivar-testing locations in sugarcane

Selection of test locations, representative of conditions and practices of an area can be a challenging process in a breeding program. Data from two groups of sugarcane (trispecies hybrids of Saccharum sp.) cultivar experiments in Florida were analyzed to determine if relative cultivar response at any two of six current locations was sufficiently similar so that at least one location could be replaced by a location with a different environment. The parameter analyzed was metric tons per ha of sugar (THS). To determine similarity between location pairs for all cultivars within each group of cultivars, an unbiased stability-variance parameter ([Formula: see text]) developed by Shukla was used. After [Formula: see text]identified similar location pairs, single degree of freedom interactions were calculated for important cultivars to determine which of the location pairs identified by [Formula: see text]contained the two most similar locations. Use of the above procedure can assist in making optimum location assignments in a breeding program.

Modification of yeast plasma membrane density by concanavalin A attachment. Application to study of chitin synthetase distribution

Yeast protoplasts were coated with different amounts of concanavalin A. Upon subsequent lysis and centrifugation in isopycnic density gradients, it was found that the buoyant density of plasma membranes was progressively increased from 1.125 to 1.21, according to the amount of bound concanavalin A. Enzymes that are attached to the plasma membrane showed the same density modifications and could thus be distinguished from constituents of intracellular membranes and organelles. With this methodology, it was confirmed that about two-thirds of yeast chitin synthetase is associated with the plasma membrane. The remainder of the enzyme was found in a peak at a lower density. Vanadate-sensitive ATPase showed a similar pattern, whereas GDP-mannose dolichyl-phosphate mannosyltransferase, an enzyme attached to the endoplasmic reticulum, remained in the same position in the gradients, irrespective of the amount of concanavalin A associated with the plasma membrane. Potential applications of this technique to the determination of plasma membrane markers and to the separation of subcellular organelles are discussed.

Stimulation of beta(1----3)glucan synthetase of various fungi by nucleoside triphosphates: generalized regulatory mechanism for cell wall biosynthesis

Particulate fractions from the taxonomically diverse fungi Achlya ambisexualis, Hansenula anomala, Neurospora crassa, Cryptococcus laurentii, Schizophyllum commune, and Wangiella dermatitidis were found to catalyze the time-dependent incorporation of glucose from UDP-[14C]glucose into a water-insoluble material. The reaction was stimulated by bovine serum albumin. The product was characterized as beta(1----3)glucan on the basis of its resistance to alpha- and beta-amylase and susceptibility to beta(1----3)glucanase. With the exception of the preparation from A. ambisexualis, all others were stimulated by nucleoside triphosphates and their analogs. The best activators were GTP and guanosine 5'-(gamma-thio)triphosphate. It is concluded that the stimulation by nucleotides, previously found with the glucan synthetase of Saccharomyces cerevisiae, is a regulatory mechanism that was well conserved during fungal evolution, presumably because of its importance in controlling cell wall biosynthesis and cell growth.

Isolation of chitin synthetase from Saccharomyces cerevisiae. Purification of an enzyme by entrapment in the reaction product

Chitin synthetase, in the zymogen form, was extracted with digitonin from a particulate fraction from Saccharomyces cerevisiae and converted into active form by treatment with immobilized trypsin. When the activated enzyme was incubated with UDP-GlcNAc and other components of an assay mixture, a chitin precipitate formed, trapping a large portion of the synthetase. The enzyme was easily extracted frm the chitin gel with a recovery of approximately 50% and an enrichment of approximately 100-fold. Further purification was obtained by repeating the chitin step. After polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the purified synthetase showed a major band corresponding to Mr 63,000, a weaker band at Mr 74,000, and some other minor bands. Under nondenaturing conditions, an Mr of 570,000 was calculated for the enzyme from Stokes radius and sedimentation coefficient determinations. After electrophoresis in a nondenaturing gel and incubation with the components of the standard assay, chitin was formed and precipitated in the gel, yielding an opaque band. Soluble oligosaccharides were not precursors for insoluble chitin, suggesting that synthesis of chitin chains takes place by a processive mechanism. N-Acetylglucosamine stimulated the purified synthetase only slightly and did not participate as a primer in the reaction. The same chain length, somewhat more than 100 units of GlcNAc, was determined in samples of chitin that had been synthesized either in vivo, or with a membrane preparation or with purified synthetase. These results suggest that chitin synthetase itself is capable both of initiating chitin chains without a primer and of determining their length.

Solubilization of mannosyltransferase activities for the biosynthesis of mammary glycoproteins. Elongation of tetrasaccharide-lipid to heptasaccharide-lipid by a solubilized enzyme preparation

The microsomal preparation from the lactating bovine mammary tissue was solubilized by treatment with nonionic detergent, NP-40, at a protein/detergent ratio of 1.5:1 and a detergent concentration of 0.5%. Following centrifugation at 147000 X g for 120 min, the supernatant fraction was incubated with labeled sugar nucleotides, GDP-Man and UDP-GlcNAc. It was found to synthesize a series of lipid-linked saccharides up to (Man)5-(GlcNAc)2. The solubilized glycosyltransferases retained up to about 60% of the activity after two weeks of storage at 4 degrees C. The biosynthesis of glycolipids was stimulated by a mixture of lipids obtained by extracting the mammary microsomes with CHCl3/CH3OH (2:1). A labeled lipid-linked tetrasaccharide of the structure Man alpha 1----3 Man beta----GlcNAc beta----GlcNAc was isolated by labeling baby hamster kidney cells with [2-3H]mannose under conditions of glucose starvation followed by extraction of the cells with CHCl3/CH3OH (2:1) and separation of the lipids by high-performance liquid chromatography. When this lipid-linked tetrasaccharide was incubated with the solubilized bovine mammary microsomes and GDP-Man, it was elongated to a lipid-linked heptasaccharide having the structure Man alpha 1----2Man alpha 1----2Man alpha 1----3(Man alpha 1----6)Man beta----GlcNAc beta----GlcNAc. The kinetics of the elongation reaction also revealed the intermediary formation of smaller amounts of lipid-linked pentasaccharide and hexasaccharide. The elongation reaction did not require any divalent metal ion and had a broad pH optimum between 6.8 and 7.6. The lack of inhibition of the elongation reaction by EDTA or amphomycin support earlier studies that GDP-Man rather than mannosylphosphoryldolichol, is the direct donor of mannosyl residues for the biosynthesis of glycolipids up to (Man)5(GlcNAc)2. Mannosylphosphorylretinol was ineffective as mannosyl donor for the elongation reaction.

Alterations in the structure of the oligosaccharide of vesicular stomatitis virus G protein by swainsonine

Swainsonine, an inhibitor of glycoprotein processing, inhibits the formation of the normal oligosaccharide chain of the G protein of vesicular stomatitis virus. Thus, when vesicular stomatitis virus was grown in baby hamster kidney cells in the presence of swainsonine (15 to 500 ng/ml) and labeled with [2-(3)H]mannose, the oligosaccharide portion of the G protein was completely susceptible to the action of endoglucosaminidase H. However, the normal viral glycoprotein is not susceptible to this enzyme. Various enzymatic treatments and methylation studies of the mannose-labeled oligosaccharides suggest that swainsonine causes the formation of a hybrid-type oligosaccharide having an oligomannosyl core (Man(5)GlcNAc(2)-Asn) characteristic of neutral oligosaccharides plus the branch structure (NeuNAc-Gal-GlcNAc) characteristic of the complex oligosaccharides. A structure for this hybrid oligosaccharide is proposed. Swainsonine had no effect on the incorporation of [(14)C]leucine into viral proteins, nor did it change the number of PFU produced in these cultures. It did, however, slightly decrease the incorporation of [(3)H]glucosamine and increase the incorporation of [(3)H]mannose. Vesicular stomatitis virus raised in the presence of swainsonine bound much more tightly to columns of concanavalin A-Sepharose than did control virus. Swainsonine had to be added within the first 4 or 5 h of virus infection to be effective. Thus, when 100 ng of the alkaloid per ml was added at any time within the first 3 h of infection, essentially all of the glycoprotein was susceptible to digestion by endoglucosaminidase H. However, when swainsonine was added 4 h after the start of infection, 30% of the glycopeptides became resistant to endoglucosaminidase H; at 5 h, 70% were resistant. The effect of swainsonine was reversible since removal of the alkaloid allowed the cells to form the normal complex glycoproteins. However, the time of removal was critical in terms of oligosaccharide structure.

Mechanism of Inhibition of Jack Bean alpha-Mannosidase by Swainsonine

The indolizidine alkaloid, swainsonine, was previously shown to be a potent inhibitor of lysosomal and jack bean alpha-mannosidase (Dorling, Huxtable, Colegate 1980 Biochem J 191: 649-651). We examined the effects of various concentrations of this alkaloid on a number of commercially available glycosidases and found swainsonine to be quite specific for alpha-mannosidase (50% inhibition at 1-5 x 10(-7) molar). Optimum inhibition was observed after a 2-minute preincubation of enzyme and inhibitor. Lineweaver-Burk plots of substrate concentration versus velocity in the presence of various amounts of swainsonine showed considerable curvature at high substrate concentrations, suggesting that swainsonine may be a competitive inhibitor that binds tightly to the enzyme and is only slowly removed. Periodate oxidation of swainsonine completely destroyed its inhibitory activity.

The effect of hyperthermia on vascular function, pH, and cell survival

Blood flow in rat skin and muscle increased three- to fourfold during heating at 43 degrees C for one hour, while that in Walker tumors did not change significantly; however, blood flow in the tumors decreased a few hours after heating at 45 degrees C. The temperature of Walker tumors was significantly higher than in the muscle during heating, probably due to inefficient heat dissipation caused by the sluggish blood flow. Severe vascular occlusion occurred in SCK tumors in mice after heating at 41.5-45.0 degrees C. Upon heating, the pH in the tumors significantly decreased, while that in the muscle increased. The clonogenic cell number continuously decreased when SCK tumors were left in situ after hyperthermia. The vascular occlusion and increase in acidity may account for the progressive death of tumor cells after heating.

Role of vascular function in response of tumors in vivo to hyperthermia

The response of SCK tumor cells in vivo and in vitro to heat was compared, and the relationship between the kinetics of cell death and vascular function in tumors in vivo after hyperthermia was studied. The number of clonogenic cells in tumors excised immediately after heating was significantly less than that in the in vitro culture treated with the same heat doses. This suggested that the tumor cells in vivo are far more sensitive to direct damage by heat than are the cells in vitro. When the tumors were left in situ after hyperthermia at 43.5 degrees for 30 min, there was a progressive decrease in cell survival until 6 to 12 hr after the heating. The study of intravascular volume using the 51Cr-labeled red blood cell method indicated that severe vascular occlusion occurs in the tumor after hyperthermia. It therefore appeared that delayed cell death in tumors in vivo after hyperthermia resulted from an insufficient supply of oxygen and nutrients and an increase in acidity due to the vascular occlusion. Both the direct damage to tumor cells and the indirect damage to tumor cells as a consequence of vascular occlusion may play important roles in the eradication of tumors by hyperthermia.