Selected highlights in immunological research in the last decade

Transcriptome analysis reveals that multidrug efflux genes are upregulated to protect Pseudomonas aeruginosa from pentachlorophenol stress

Through chemical contamination of natural environments, microbial communities are exposed to many different types of chemical stressors; however, research on whole-genome responses to this contaminant stress is limited. This study examined the transcriptome response of a common soil bacterium, Pseudomonas aeruginosa, to the common environmental contaminant pentachlorophenol (PCP). Cells were grown in chemostats at a low growth rate to obtain substrate-limited, steady-state, balanced-growth conditions. The PCP stress was administered as a continuous increase in concentration, and samples taken over time were examined for physiological function changes with whole-cell acetate uptake rates (WAURs) and cell viability and for gene expression changes by Affymetrix GeneChip technology and real-time reverse transcriptase PCR. Cell viability, measured by heterotrophic plate counts, showed a moderately steady decrease after exposure to the stressor, but WAURs did not change in response to PCP. In contrast to the physiological data, the microarray data showed significant changes in the expression of several genes. In particular, genes coding for multidrug efflux pumps, including MexAB-OprM, were strongly upregulated. The upregulation of these efflux pumps protected the cells from the potentially toxic effects of PCP, allowing the physiological whole-cell function to remain constant.

Pyrimidine as constituent of natural biologically active compounds

This review describes the various manifestations of the pyrimidine system (alkylated, glycosylated, benzo-annelated.). These comprise pyrimidine nucleosides as well as alkaloids and antibiotics--some of them have been discovered and isolated from natural sources already long time ago, others have been reported very recently. A short overview on pyrimidine syntheses (prebiotic synthesis, biosynthesis, and metabolism) is given. The biological activities of most of the pyrimidine analogs are briefly described, and, in some cases, syntheses are formulated.

Stereodivergent Syntheses of Anisomycin Derivatives from d-Tyrosine

[structures: see text] Enantiomerically pure 2-alkyl-3-acetoxy-4-iodopyrrolidines with all groups cis, and all adjacent groups trans (10 and 17), important precursors for the synthesis of pyrrolidinediols, have been prepared from D-tyrosine through regio- and diastereoselective reduction of a vinyl ketone and subsequent iodoamidation controlled by minimization of nonbonding steric interactions. Highly stereodivergent Woodward-Prevost methodology, applied to both iodopyrrolidines, yielded enantiomerically pure (2R,3R,4R)-, (2R,3R,4S)-, and (2R,3S,4R)-deacetylanisomycin (3, 4, and 5), each in excellent de. Incorporation of differential protection of the hydroxyl groups led to a one-pot synthesis of (2R,3R,4R)-anisomycin 2.

Dendritic cell aggresome-like induced structures are dedicated areas for ubiquitination and storage of newly synthesized defective proteins

In response to inflammatory stimulation, dendritic cells (DCs) have a remarkable pattern of differentiation (maturation) that exhibits specific mechanisms to control antigen processing and presentation. One of these mechanisms is the sorting of polyubiquitinated proteins in large cytosolic aggregates called dendritic cell aggresome-like induced structures (DALIS). DALIS formation and maintenance are tightly linked to protein synthesis. Here, we took advantage of an antibody recognizing the antibiotic puromycin to follow the fate of improperly translated proteins, also called defective ribosomal products (DRiPs). We demonstrate that DRiPs are rapidly stored and protected from degradation in DALIS. In addition, we show that DALIS contain the ubiquitin-activating enzyme E1, the ubiquitin-conjugating enzyme E225K, and the COOH terminus of Hsp70-interacting protein ubiquitin ligase. The accumulation of these enzymes in the central area of DALIS defines specific functional sites where initial DRiP incorporation and ubiquitination occur. Therefore, DCs are able to regulate DRiP degradation in response to pathogen-associated motifs, a capacity likely to be important for their immune functions.

Triple decoding of hepatitis C virus RNA by programmed translational frameshifting

Ribosomes can be programmed to shift from one reading frame to another during translation. Hepatitis C virus (HCV) uses such a mechanism to produce F protein from the -2/+1 reading frame. We now report that the HCV frameshift signal can mediate the synthesis of the core protein of the zero frame, the F protein of the -2/+1 frame, and a 1.5-kDa protein of the -1/+2 frame. This triple decoding function does not require sequences flanking the frameshift signal and is apparently independent of membranes and the synthesis of the HCV polyprotein. Two consensus -1 frameshift sequences in the HCV type 1 frameshift signal facilitate ribosomal frameshifts into both overlapping reading frames. A sequence which is located immediately downstream of the frameshift signal and has the potential to form a double stem-loop structure can significantly enhance translational frameshifting in the presence of the peptidyl-transferase inhibitor puromycin. Based on these results, a model is proposed to explain the triple decoding activities of the HCV ribosomal frameshift signal.

Chloramphenicol is an inhibitor of photosynthesis

Chloramphenicol inhibited significantly but incompletely photosynthesis in leaf segments of rice. Fluorescence and polarographic experiments indicated that chloramphenicol competes with the CO2 reducing cycle for electrons from photosystem I because it serves as an electron acceptor of photosystem I and its reduction intermediate transfers its electron to molecular oxygen.

Biochemical studies carried out on different groups of Candida parapsilosis and Candida rhagii strains by comparing some cellular and mitochondrial activities

A comparative biochemical study was performed on some strains of Candida rhagii and on strains belonging to different subgroups of Candida parapsilosis. Measurements of alcohol dehydrogenase activity, resistance to drugs and occurrence of an alternative pathway enabled us to confirm the classification between several subgroups within the C. parapsilosis species.

Differential inhibition of protein synthesis: a possible biochemical mechanism of thalidomide teratogenesis

A theory concerning the chemical and biochemical mechanisms of thalidomide teratogenesis is presented. A considerable body of evidence suggests that the glutarimide ring of thalidomide may exert its biological activity because of its resemblance to the imide pyrimidines thymine and uracil. In addition to the glutarimide ring, thalidomide contains a moderately reactive phthalimide moiety, which allows the spontaneous formation of various glutarimide derivatives in fetal tissues. A model is proposed in which the phthalimide group reacts with small nucleophiles, most likely the polyamines, to produce a derivative(s) having a similar biochemical potential to that of cycloheximide, a glutarimide which is a powerful inhibitor of the elongation phase of protein synthesis. Interference in the elongation phase results in the selective inhibition of the translation of messages which have a high translational efficiency. Evidence is reviewed concerning the differential inhibition or protein synthesis by cycloheximide and the effects of this inhibition on various biochemical and biological processes which are critical during development and differentiation. A similar biochemical activity by the putative thalidomide derivative(s) could explain its extreme teratogenic potential. A number of parallels between the biological effects of thalidomide and cycloheximide are discussed which support the idea that a similar biochemical activity is involved. The theory readily explains many of the observed biological effects of thalidomide including the large difference between fetal and adult toxicity. In addition, evidence is reviewed which suggests that the teratogenic properties of a number of drugs which are structurally related to thalidomide may have a common chemical basis due to the similarity of their imide core structures to thymine and uracil.

Biphasic modulation by ACTH-like peptides of protein synthesis in a cell-free system from rat brain

Brain protein synthesis in a cell-free system was stimulated by 10(-8) M-ACTH1-24. This stimulatory effect was completely inhibited by aurintricarboxylic acid (ATA), an inhibitor of reinitiation of new peptide chains. The N-terminal peptide sequence 4-10 exerted a biphasic modulation of cell-free protein synthesis, i.e., a stimulation at low concentrations (10(-8) and 10(-10) M) and an inhibition at a high concentration (10(-4) M). The D-isomer, ACTH4-10-7-D-phe, also showed a biphasic modulation that, however, was in a direction opposite to that shown by ACTH4-10-7-L-phe at 10(-8) M and 10(-4) M.

Pactamycin resistance in CHO cells: morphological changes induced by the drug in the wild-type and mutant cells

Stable mutants resistant to pactamycin (PacR), a polypeptide chain initiation inhibitor, have been selected in a single step in Chinese hamster ovary (CHO) cells. The sensitivity of protein synthesis in mutant cell extracts to pactamycin indicates that resistance involves an alteration in the permeability of this drug. The failure of PacR mutants to show cross-resistance to other compounds provides further indication that the lesion is presumably specific for pactamycin. Cell hybrids formed between PacR X PacS lines show intermediate sensitivity towards pactamycin, suggesting that the PacR lesion behaves codominantly under these conditions. In the presence of subinhibitory concentrations of pactamycin, CHO cells, which are normally short, polygonal and disoriented, became greatly elongated and aligned themselves in parallel fashion to produce highly oriented colony morphologies, reminiscent of normal diploid fibroblasts. This effect of pactamycin on cellular morphology was seen much more clearly with the PacR mutants, although somewhat higher concentrations of the drug were required to produce this change.

Genetic and biochemical characterization of mutants of CHO cells resistant to the protein synthesis inhibitor trichodermin

Mutants resistant to the protein synthesis inhibitor trichodermin have been selected in Chinese hamster ovary (CHO) cells. The mutants vary in their stability from those which rapidly lose their resistance to others which are relatively stable after prolonged growth in nonselective medium. Protein synthesis in extracts from the latter class of mutants (Trir) is resistant to the inhibitory action of trichodermin as compared to similar extracts from wild-type cells. After dissociation into subunits, the ability of the 60S ribosomal subunits from Trir cells to function in a protein-synthesizing system is greatly diminished. This subunit also shows reduced binding of [acetyl-14C]TRICHODERMIN. The lesion in Trir mutants therefore seems to have affected this ribosomal subunit. Trir X Tris hybrids are sensitive to trichodermin indicating that the Trir mutation behaves recessively to Tris in hybrids. The Emtr and Trir markers segregate independently from hybrid cells showing that the Trir mutation is probably not linked to the Emtr locus, which as we have shown earlier affects the 40S ribosomal subunit.

Genetics and biochemistry of cryptopleurine resistance in the yeast Saccharomyces cerevisiae

Protein synthesis by ribosomes from several cryptopleurine-resistant yeast mutants is also resistant to emetine and tubulosine. These mutants can be classified into two different types: Class I mutants which display high levels of resistance to emetine and tubulosine and Class II mutants that are only weakly resistant to tubulosine and are slightly more sensitive to emetine than those of Class I. Apparently all mutants have similar levels of resistance to cryptopleurine. The distinct phenotypes of Class I and Class II strains are expressed through their 40S ribosomal subunit. Genetic analysis has shown that the mutations to cryptopleuring resistance are allelic and that in a particular case (strain CRY6) the pleiotropic phenotype is a result of the expression of the cry1 locus. It is suggested that Class I and Class II mutants arise from two independent mutational events within The cry1 allel. In heterozygous (+/cry1) diploids both the sensitive and the resistant genes are expressed as shown by studies of the action of cryptopleurine on polyphenylalanine-synthesizing systems derived from each parental sensitive and resistant haploid strain and heterozygous diploid strains. The apparent dominance of sensitivity over resistance which may be observed in vivo in heterozygous (+/cry1) diploids has been explained in terms of the mode of action of the inhibitors.

Mutants of CHO cells resistant to the protein synthesis inhibitors, cryptopleurine and tylocrebrine: genetic and biochemical evidence for common site of action of emetine, cryptopleurine, tylocrebine, and tubulosine

Stable mutants resistant to the protein synthesis inhibitors cryptopleurine and tylocrebine can be isolated in Chinese hamster ovary (CHO) cells, in a single step. The frequency of occurrence of cryptopleurine (CryR) and tylocrebrine (TylR) resistant mutants in normal and mutagenized cell populations is similar to that observed for emetine resistant (EmtR) mutants. The CryR, TylR, and EmtR mutants exhibit strikingly similar cross-resistance to the three drugs used for selection, to tubulosine and also to two emetine derivatives cephaeline and dehydroemetine, based on assays of in vivo cytotoxicity and on assays of protein synthesis in cell-free extracts. The identity of cross-resistance patterns of the CryR, TylR, and EmtR mutants indicates that the resistance to all these compounds results from the same primary lesion, which in the case of EmtR cells has been shown to affect the 40S ribosomal subunit. This conclusion is strongly supported by the failure of EmtR, TylR, and CryR mutants to complement each other in somatic cell hybrids. Based on these results it is suggested that the above group of compounds possesses common structural determinants which are responsible for their activity. The above mutants, however, do not show any cross-resistance to other inhibitors of protein synthesis such as cycloheximide, trichodermin, anisomycin, pactamycin, and sparsomycin, either in vivo or in vitro, indicating that the site of action of these inhibitors is different from that of the emetine-like compounds.

Indolmycin inhibits prokaryotic tryptophanyl-tRNA ligase

Indolmycin specifically prevents the formation of tryptophanyl-tRNA in a prokaryotic system in vitro using Escherichia coli enzymes. However, the drug has little effect in an eukaryotic system in vitro (rat liver enzymes). Analysis of the type of inhibition revealed that indolmycin competes with tryptophan as a pure competitive inhibitor of prokaryotic tryptophanyl-tRNA ligase.