Effect of cell cycle on the regulation of the cell surface and secreted forms of type I and type II human tumor necrosis factor receptors

The cell cycle has been shown to regulate the biological effects of human tumor necrosis factor (TNF), but to what extent that regulation is due to the modulation of TNF receptors is not clear. In the present report we investigated the effect of the cell cycle on the expression of surface and soluble TNF receptors in human histiocytic lymphoma U-937. Exposure to hydroxyurea, thymidine, etoposide, bisbensimide, and democolcine lead to accumulation of cells primarily in G₁/S, S, S/G₂/M, G₂/M, and M stages of the cell cycle, respectively. Whilie no significant change in TNF receptors occurred in cells arrested in G₁/S or S/G₂ stages, about a 50% decrease was observed in cells at M phase of the cycle. Scatchard analysis showed a reduction in receptor number rather than affinity. In contrast, cells arrested at S phase (thymidine) showed an 80% increase in receptor number. The decrease in the TNF receptors was not due to changes in cell size or protein synthesis. The increase in receptors, however, correlated with an increase in total protein synthesis (to 3.8-fold of the control levels). A proportional change was observed in the p60 and p80 forms of the TNF receptors. A decrease in the surface receptors in cells arrested in M phase correlated with an increase in the amount of soluble receptors. The cellular response to TNF increased to 8- and 2-fold in cells arrested in G₁ and S phase, respectively; but cells at G2/M phase showed about 6-fold decrease in response. In conclusion, our results demonstrate that the cell cycle plays an important role in regulation of cell-surface and soluble TNF receptors and also in the modulation of cellular response. © 1995 Wiley-Liss, Inc.     

Identification of somaclonal variants of sugarcane (Saccharum spp.) resistant to sugarcane mosaic virus via RAPD markers

Somaclonal variants resistant to sugarcane mosaic virus (SCMV) were obtained from susceptible sugarcane cv PR62258 through somatic embryogenesis by increasing the number of subcultures of the embryogenic callus tissue in MS medium with 3 mg/L 2,4-dichlorophenoxyacetic acid. Transfers were made at 30-day intervals for 1, 2 or 3 subcultures. Two somaclones, namely AT626 and BT627, were selected by their resistance to SCMV. These subclones have maintained the resistance trait over seven years of testing in the field. In this report we identified the somaclonal SCMV resistant variants from the maternal line and the nonresistant somaclones, using the RAPD technique.     

Plant transformation by particle bombardment of embryogenic pollen

Summary Direct delivery of DNA into embryogenic pollen was used to produce transgenic plants in tobacco. A plasmid bearing the ß-glucuronidase (GUS) marker gene in fusion with the 35S-promoter was introduced by microprojectile bombardment into mid-binucleate pollen of Nicotiana tabacum that had been induced to form embryos by a starvation treatment. In cytochemical expression assays, 5 out of 10⁴ pollen grains were GUS⁺. Visual selection by staining with a non-lethal substrate for GUS was used to manually isolate transformed embryos. From the initial population of embryogenic GUS⁺ pollen, 1–5% developed into multicellular structures and 0.02% formed regenerable embryos. Two haploid transformants were regenerated. GUS expression was detected in different parts of the plants, and Southern analysis confirmed stable integration of the foreign DNA. Diploidisation was induced by injection of colchicine into the stem near adventitious buds. Offspring from selfings and backcrosses of one transformant were tested for GUS expression and by Southern blots. All F1-plants were transgenic, in accordance with Mendelian inheritance.Abbreviations GUS ß-glucuronidase - CaMV Cauliflower Mosaic Virus - MCS multicellular structure - NPTII neomycin phosphotransferase - PEG polyethylene glycol - X-gluc 5-bromo-4-chloro-3-indolyl glucuronide - DAPI 4,6-diamidino-2-phenylindole - Tris Tris(hydroxymethyl)aminomethane hydrochloride - EDTA ethylenedinitrilo tetraacetic acid, disodium salt dihydrate     

Diastereoselective hydrogenations of unsymmetrically substituted aromatics

Attempts to induce enantioselectivity in the catalytic hydrogenation of unsymmetrically substituted aromatics using covalently bound, well known chiral auxiliaries are described. Marked differences in stereoselectivity and rate of hydrogenolysis are noted as a function of the auxiliary used. Enantioselectivities obtained in the resulting cyclohexyl derivatives are rather poor. © 1995 Wiley-Liss, Inc.     

Protein exporter function and in vitro ATPase activity are correlated in ABC-domain mutants of HlyB

The Escherichia coli toxin exporter HlyB comprises an integral membrane domain fused to a cytoplasmic domain of the ATP-binding casette (ABC) super-family, and it directs translocation of the 110kDa haemolysin protein out of the bacterial cell without using an N-terminal secretion signal peptide. We have exploited the ability to purify the soluble HlyB ABC domain as a fusion with glutathione S-transferase to obtain a direct correlation of the in vivo export of protein by HlyB with the degree of ATP binding and hydrolysis measured in vitro. Mutations in residues that are invariant or highly conserved in the ATP-binding fold and glycine-rich linker peptide of prokaryotic and eukaryotic ABC transporters caused a complete less of both HlyB exporter function and ATPase activity in proteins still able to bind ATP effectively and undergo ATP-induced conformational change. Mutation of less-conserved residues caused reduced export and ATP hydrolysis, but not ATP binding, whereas substitutions of poorly conserved residues did not impair activity either in vivo or in vitro. The data show that protein export by HlyB has an absolute requirement for the hydrolysis of ATP bound by its cytoplasmic domain and indicate that comparable mutations that disable other prokaryotic and eukaryotic ABC transporters also cause a specific loss of enzymatic activity.     

Energy metabolism in the cyanobacterium Plectonema boryanum. Participation of the thylakoid photosynthetic electron transfer chain in the dark respiration of NADPH and NADH

The oxidation of NADPH and NADH was studied in the light and in the dark using sonically derived membrane vesicles and osmotically shocked spheroplasts. These two types of cell-free membrane preparations mostly differ in that the cell and thylakoid membranes are scrambled in the former type and that they are more or less separated in the latter type of preparations. In the light, using both kinds of preparations, each of NADPH and NADH donates electrons via the plastoquinone-cytochrome $\text{b}\text{c}$ redox complex (Qbc redox complex) to the thylakoid membrane-bound cytochrome c-553 preoxidized by a light flash and to methylviologen via Photosystem I. NADPH donates electrons to the thylakoid membrane via a weakly rotenone-sensitive dehydrogenase to a site that is situated beyond the 3(3′,4′-dichlorophenyl)-1,1-dimethylurea sensitive site and before plastoquinone. Ferredoxin and easily soluble cytoplasmic proteins are presumably not involved in light-mediated NADPH oxidation. Inhibitors of electron transfer at the Qbc redox complex as the dinitrophenylether of 2-iodo-4-nitrothymol, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 2-n-heptyl-4-hydroxy-quinone-N-oxide are effective, but antimycin A and KCN are not. The oxidation of NADH showed comparable sensitivity to these inhibitors. However, the oxidation of NADH is antimycin-A-sensitive regardless of the kind of membrane preparation used, indicating that in this case electrons are donated to a different site on the thylakoid membrane. In the dark, NADPH and NADH donate electrons at sites that behave similar to those of light-mediated oxidation, indicating that the initial steps of electron transfer are situated at the thylakoid membranes. However, NADPH oxidation is in some cases not sensitive to inhibitors active at the Qbc redox complex. It is concluded that O₂ reduction takes place at two different sites, one partly developed in vitro, situated near the rotenone-sensitive NADPH dehydrogenase, and another, highly KCN-sensitive one, situated beyond the Qbc redox complex and used in vivo. The terminal oxygen-reducing step of NADPH and NADH oxidation in the dark showed a preparation-dependent sensitivity for KCN, more than 80% inhibition in sonically derived membrane vesicles and less than 30% inhibition in osmotically shocked spheroplasts. From this result we tentatively conclude that the highly KCN-sensitive oxidase is not necessarily located at the thylakoid membrane and could be located at the cytoplasmic membrane.     

Processing of McCoy cell cultures infected with Chlamydia trachomatis: sequential isolation of chlamydial elementary bodies and lipopolysaccharide

Abstract Triton X-100 (TX100) enhances the liberation of chlamydial elementary bodies (EB) from host cells and dissolves the host cell membrane. In the presence of TX100 only differential centrifugation is needed to isolate reasonably pure EBs. The remaining high-speed supernatant still contains a large part of the chlamydial lipopolysaccharide (LPS), which can be isolated with the standard phenol-chloroform-petroleum ether extraction.     

Population and formal genetics of the human C81(α-γ) polymorphism

Summary One hundred and ninety-six unrelated healthy individuals and 30 families with 75 offspring have been studied for the C81(-) polymorphism. The following allele frequencies were calculated: C81^*A=0.5536; C81^*B=0.4286; C81^*A1=0.0178. Observed and expected phenotype frequencies were in a good agreement according to the Hardy Weinberg law. No exceptions from the mode of inheritance were found. In family W the segregation of the rare allele C81^*A1 could be followed. Comparing the results of this study with previous data from Boston and Oslo, a combined technology including C8-dependent lysis and C8 structural variation is suggested for future investigations.     

Natural killer cells in mice and man and their possible biological significance

Conclusions Despite active and extensive research on human and murine NK cells in the last few years a number of basic questions remain to be answered. These include the nature of the antigen(s) on target cells to which NK cells react, the nature of the receptors on NK cells allowing the recognition, the mechanism of NK cell cytotoxicity, the exact relationship between NK cell activities in vivo and in vitro, genetic control of NK cells, involvement of NK cells in the field of bone marrow transplantation, and finally their involvement in immunosurveillance of malignancies. Although the etiology and biologic significance of NK cells remain obscure, there is suggestive evidence that these cells may be in volved in resistance to and immunosurveillance of malignancies, since there is experimental evidence for a correlation between in vivo and in vitro NK cell activities. The fact that athymic mice do not have a higher incidence of malignancies than conventional mice and express delayed appearance and higher resistance to virally and chemically induced tumors (Stutman, 1975) is consistent with a protective role of the NK cell effector mechanism. In addition, their spontaneous occurrence without any necessity for priming and their ability to recognize and kill malignant cells makes NK cells almost perfect candidates for the part of immunosurveillors. The similarity between bone marrow effector cells and NK cells also seems unlikely to be fortuitous. In summary, this interesting cell requires further attention.