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[Damage to the genome, p53 and cell polyploidization in ontogeny].

The protein p53 is a universal tumor suppressor in humans and negative regulator of cell proliferation, which is induced in cells in response to the damage of DNA and controls arrest of the cell cycle at specific checkpoints. A recently discovered function of gene p53 is the maintenance of the diploid state of the genome and a block of the formation of the population of cycling polyploids. This review examines models of disturbed control of the cell cycle due to loss, inactivation, or hyperexpression of gene p53 or its effector gene p21 in transgenic animals, i.e., homozygous mutant mice (p53-/-), (ERCC-1-/-), as well as in genetically defective cell lines in vitro. We discuss mechanisms responsible for the transition from the diploid to the polyploid state owing to the disturbed control of cell cycle by p53 and arising during the ontogenetic polyploidization of cells in normal animals.

Animals↗

An extensive repertoire of type III secretion effectors in Escherichia coli O157 and the role of lambdoid phages in their dissemination.

Several pathogenic strains of Escherichia coli exploit type III secretion to inject "effector proteins" into human cells, which then subvert eukaryotic cell biology to the bacterium's advantage. We have exploited bioinformatics and experimental approaches to establish that the effector repertoire in the Sakai strain of enterohemorrhagic E. coli (EHEC) O157:H7 is much larger than previously thought. Homology searches led to the identification of >60 putative effector genes. Thirteen of these were judged to be likely pseudogenes, whereas 49 were judged to be potentially functional. In total, 39 proteins were confirmed experimentally as effectors: 31 through proteomics and 28 through translocation assays. At the protein level, the EHEC effector sequences fall into >20 families. The largest family, the NleG family, contains 14 members in the Sakai strain alone. EHEC also harbors functional homologs of effectors from plant pathogens (HopPtoH, HopW, AvrA) and from Shigella (OspD, OspE, OspG), and two additional members of the Map/IpgB family. Genes encoding proven or predicted effectors occur in >20 exchangeable effector loci scattered throughout the chromosome. Crucially, the majority of functional effector genes are encoded by nine exchangeable effector loci that lie within lambdoid prophages. Thus, type III secretion in E. coli is linked to a vast phage "metagenome," acting as a crucible for the evolution of pathogenicity.

Bacteriophage lambda↗

A gene in the Pseudomonas syringae pv. tomato Hrp pathogenicity island conserved effector locus, hopPtoA1, contributes to efficient formation of bacterial colonies in planta and is duplicated elsewhere in the genome.

The ability of Pseudomonas syringae to grow in planta is thought to be dependent upon the Hrp (type III secretion) system and multiple effector proteins that this system injects into plant cells. ORF5 in the conserved effector locus of the P. syringae pv. tomato DC3000 Hrp pathogenicity island was shown to encode a Hrp-secreted protein and to have a similarly secreted homolog encoded in an effector-rich pathogenicity island located elsewhere in the genome. These putative effector genes were designated hopPtoA1 and hopPtoA2, respectively. DNA gel blot analysis revealed that sequences hybridizing with hopPtoA1 were widespread among P. syringae pathovars, and some strains, like DC3000, appear to have two copies of the gene. uidA transcriptional fusions revealed that expression of hopPtoA1 and hopPtoA2 can be activated by the HrpL alternative sigma factor. hopPtoA1 and hopPtoA1/hopPtoA2 double mutants were not obviously different from wild-type P. syringae pv. tomato DC3000 in their ability to produce symptoms or to increase their total population size in host tomato and Arabidopsis leaves. However, confocal laser-scanning microscopy of GFP (green fluorescent protein)-labeled bacteria in Arabidopsis leaves 2 days after inoculation revealed that the frequency of undeveloped individual colonies was higher in the hopPtoA1 mutant and even higher in the hopPtoA1/hopPtoA2 double mutant. These results suggest that hopPtoA1 and hopPtoA2 contribute redundantly to the formation of P. syringae pv. tomato DC3000 colonies in Arabidopsis leaves.

Amino Acid Sequence↗

The Erwinia amylovora avrRpt2EA gene contributes to virulence on pear and AvrRpt2EA is recognized by Arabidopsis RPS2 when expressed in pseudomonas syringae.

The enterobacterium Erwinia amylovora is a devastating plant pathogen causing necrotrophic fire blight disease of apple, pear, and other rosaceous plants. In an attempt to identify genes induced during infection of host plants, we identified and cloned a putative effector gene, avrRpt2EA. The deduced amino-acid sequence of the translated AvrRpt2EA protein is homologous to the effector protein AvrRpt2 previously reported in Pseudomonas syringae pv. tomato. These two proteins share 58% identity (70% similarity) in the functional domain; however, the secretion and translocation signal domain varied. The avrRpt2EA promoter region contains a typical 'hrp box,' which suggests that avrRpt2EA is regulated by the alternative sigma factor, HrpL. avrRpt2EA was detected in all E. amylovora strains tested but not in other closely related Erwinia species. An avrRpt2EA deletion mutant was reduced in its ability to cause systemic infection on immature pear fruits as compared with the wild-type strain, indicating that avrRpt2EA acts as a virulence factor on its native host. Growth of P. syringae pv. tomato DC3000 expressing avrRpt2EA was 10-fold higher than that of P. syringae pv. tomato DC3000 in an Arabidopsis rps2 mutant, indicating that avrRpt2EA promotes virulence of P. syringae pv. tomato DC3000 on Arabidopsis similar to P. syringae pv. tomato avrRpt2. When avrRpt2EA was expressed in P. syringae pv. tomato DC3000 in its native form, a weak hypersensitive response (HR) was induced in Arabidopsis; however, a hybrid protein containing the P. syringae pv. tomato avrRpt2 signal sequence, when expressed from the P syringae pv. tomato avrRpt2 promoter, caused a strong HR. Thus, the signal sequence and promoter of avrRpt2EA may affect its expression, secretion, or translocation, singly or in combination, in P. syringae pv. tomato DC3000. These results indicated that avrRpt2EA is genetically recognized by the RPS2 disease resistance gene in Arabidopsis when expressed in P. syringae pv. tomato DC3000. The results also suggested that although distinct pathogens such as E. amylovora and P. syringae may contain similar effector genes, expression and secretion of these effectors can be under specific regulation by the native pathogen.

Amino Acid Sequence↗

Medical applications of single-chain antibodies.

A single-chain antibody or single-chain Fv (sFv) incorporates the complete antibody binding site in a single polypeptide chain of minimal size, with an approximate molecular weight of 26,000. In antibodies, the antigen combining site is part of the Fv region, which is composed of the VH and VL variable domains on separate heavy and light chains. Efforts over nearly two decades have indicated that Fv fragments can only rarely be prepared from IgG and IgA antibodies by proteolytic dissection. Beginning in 1988, single-chain analogues of Fv fragments and their fusion proteins have been reliably generated by antibody engineering methods. The first step involves obtaining the genes encoding VH and VL domains with desired binding properties; these V genes may be isolated from a specific hybridoma cell line, selected from a combinatorial V-gene library, or made by V gene synthesis. The single-chain Fv is formed by connecting the component V genes with an oligonucleotide that encodes an appropriately designed linker peptide, such as (Gly4-Ser)3. The linker bridges the C-terminus of the first V region and N-terminus of the second, ordered as either VH-linker-VL or VL-linker-VH. In principle, the sFv binding site can faithfully replicate both the affinity and specificity of its parent antibody combining site, as demonstrated in our model studies with the 26-10 anti-digoxin sFv. Furthermore, the sFv remains stable at low concentrations that promote VH and VL dissociation from the Fv heterodimer, resulting in loss of Fv binding. Intravenously administered sFv proteins exhibit accelerated biodistribution and exceptionally fast clearance compared to IgG or Fab. These pharmacokinetic properties allow rapid imaging by sFv, which therefore may be labeled with a short-lived isotope such as Tc-99m. Expression of a single gene product from fused sFv and effector genes facilitates immunotargeting of the effector protein, as shown for single-chain Fv toxin fusion proteins.

Amino Acid Sequence↗

Transformation effector and suppressor genes.

Much has been learned about the molecular basis of cancer from the study of the dominantly acting viral and cellular oncogenes and their normal progenitors, the proto-oncogenes. More recent studies have resulted in the isolation and characterization of several genes prototypic of a second class of cancer genes. Whereas oncogenes act to promote the growth of cells, members of this latter class of genes act to inhibit cellular growth and are believed to contribute to the tumorigenic phenotype only when their activities are absent. This new class of cancer genes is referred to by a number of different names including; anti-oncogenes, recessive oncogenes, growth suppressor genes, tumor suppressor genes and emerogenes. Although only a few of these cancer genes have been identified, to date, it is likely that many additional genes of this class await identification. A third class of genes, necessary for the development of the cancer phenotype, is comprised of the transformation effector genes. These are normal cellular genes that encode proteins that cooperate with or activate oncogene functions and thereby induce the development of the neoplastic phenotype. The inactivation of transformation effector functions would therefore inhibit the ability of certain dominantly acting oncogenes to transform cells. The approaches outlined here describe functional assays for the isolation and molecular characterization of transformation effector and suppressor genes.

Animals↗

Apoptosis and cancer chemotherapy.

Apoptosis is a fundamental mechanism of cell death that can be engaged by a range of cellular insults. One of the major modes of action of chemotherapeutic drugs may be via the activation of apoptosis. Understanding how the cell death program is engaged following an insult, and hence why it fails to be engaged in certain settings, offers a novel approach to overcoming the clinical problem of drug resistance. The tumour suppressor gene p53 and its downstream effector genes p21, mdm-2, and gadd45 seem to be important in the cellular response to genotoxic drug induced damage. Considerable evidence has accrued about the effect of mutations of this pathway on drug sensitivity and this is discussed. The expanding Bcl-2 family of proteins also play an important role in the cell death program. Evidence suggests that these proteins may function as integrators of damage signals, and may be the final decision point as to whether a cell lives or dies. These proteins may thus represent a logical target for new approaches to overcoming drug resistance.

Animals↗

Intrathecal injection of cAMP response element binding protein (CREB) antisense oligonucleotide attenuates tactile allodynia caused by partial sciatic nerve ligation.

The transcription factor cAMP responsive element binding protein (CREB) is important in regulating immediate-early genes and some late-effector genes involved in neuroplasticity in response to peripheral injury and stressful insults. Partial nerve injury elicited neuropathic pain is accompanied by increased phosphorylation of CREB in the ipsilateral spinal cord dorsal horn (Ma and Quirion, Pain 93 (2001) 295; Miletic et al., Pain 99 (2002) 493). The aim of this study is to determine whether increased phosphorylation of CREB in the dorsal horn contributes to the pathogenesis of neuropathic pain. Three weeks following partial sciatic nerve ligation (PSNL), daily intrathecal injection of antisense CREB oligodeoxynucleotide (ODN, 20 microg/day) for 5 days significantly attenuated tactile allodynia. The attenuation lasted for more than 4 days. Total CREB and phosphorylated CREB in both ipsilateral and contralateral dorsal horn neurons were dramatically reduced in antisense ODN injected PSNL rats 1 week after injection. The extent of reduction of total CREB and phosphorylated CREB containing cells in the dorsal horn ipsilateral to injury was greater than in the contralateral dorsal horn. These data suggest that phosphorylation of CREB is an important contributing event in the central plasticity of nerve injury and in the pathogenesis of neuropathic pain.

Animals↗

Genome-wide association study meta-analysis provides insights into the etiology of heart failure and its subtypes.

Heart failure (HF) is a major contributor to global morbidity and mortality. While distinct clinical subtypes, defined by etiology and left ventricular ejection fraction, are well recognized, their genetic determinants remain inadequately understood. In this study, we report a genome-wide association study of HF and its subtypes in a sample of 1.9 million individuals. A total of 153,174 individuals had HF, of whom 44,012 had a nonischemic etiology (ni-HF). A subset of patients with ni-HF were stratified based on left ventricular systolic function, where data were available, identifying 5,406 individuals with reduced ejection fraction and 3,841 with preserved ejection fraction. We identify 66 genetic loci associated with HF and its subtypes, 37 of which have not previously been reported. Using functionally informed gene prioritization methods, we predict effector genes for each identified locus, and map these to etiologic disease clusters through phenome-wide association analysis, network analysis and colocalization. Through heritability enrichment analysis, we highlight the role of extracardiac tissues in disease etiology. We then examine the differential associations of upstream risk factors with HF subtypes using Mendelian randomization. These findings extend our understanding of the mechanisms underlying HF etiology and may inform future approaches to prevention and treatment.

Humans↗

[Criteria defining antimanic drugs (psychopharmacological specificity and/or nonspecificity?)].

The question as to whether specific antimanic drugs differ in their action profile from nonspecific drugs is addressed in regard to symptomatic, nosographic, regulatory and physiopathological issues. Results from clinical studies have shown that mood stabilizers and typical neuroleptics differ as regards improvement of manic symptoms: the former appear to act more evenly on all symptoms of mania, showing a more total normalization of affect, ideation and behaviour whereas the latter tend to sedate patients or to cause a psychomotor retardation, leaving the core manic symptoms unaffected. This has been many times underlined, in particular for lithium, notwithstanding the fact that rating scales employed in clinical trials have often been charged to fall far short of being sensitive enough to pick up the qualitative changes in manic psychopathology. Antimanic drugs may also be more or less specific in their capacities to treat all facets of the manic episode (psychotic, depressive, irritable) whatever the bipolar subtype (bipolar I, II, rapid and non-rapid cycling, secondary bipolar disorder) or the disease stage (early and late episodes). In this respect divalproate seems to have a broader spectrum of efficacy than other available agents. Newer antipsychotics such as olanzapine are promising too. From a regulatory point of view, the current European requirements for a specific antimanic drug are more stringent than the US requirements of the Food and Drug Administration (FDA). Efficacy must be demonstrated in short-term studies showing an effect in acute mania; moreover it has to be shown that efficacy is to be maintained during the episode. So far, three armed randomized controlled trials are required, in which the test product is compared both with placebo and with a standard treatment. A possible design is a comparison of test product, placebo and active control for 3 weeks followed by a two-arm phase for the remaining 9 weeks, comparing only test product and active control. In addition, a specific antimanic has to demonstrate that it does not cause switching to depression. As regards physiopathology, integrative models of bipolar disorder, ie kindling and behavioural sensitization, offer an exciting perspective on the specificity issue; agents active in these models initialize a cascade of intracellular signaling that leads to changes in the expression of immediate early genes as well as late effector genes in corticolimbic structures: the former may contribute to acute symptomatology whereas the latter give rise to neuroanatomical reorganization which could underlie more stable changes in mood and cognition. Due to their action on intracellular messaging systems, dopamine D(1) receptors, serotonin 5HT(1a) or 5HT(2a) receptors, especially in orbitofrontal circuit, antimanic agents may exhibit a more specific activity than other drugs. This specificity could concern a whole spectrum of bipolarity which might be characterized by impulsivity.

Antimanic Agents↗

[Study of single nucleotide polymorphism of A-FABP gene and its association with fatness traits in chicken].

In this experiment, Beijing-You chicken was used to detect single nucleotide polymorphisms (SNPs) in A-FBAP gene and to study the correlation between its genotype and the trait of fat accumulation. The first exon of the gene was amplified by one pair of primers, and SNPs were detected by the technique of single strand conformation polymorphism (SSCP) and finally confirmed by sequencing. Results of analysis of variance showed that a significant difference existed among abdominal fat percentage, subcutaneous fat thickness and intramuscular fat contents in breast musculature with different genotypes (P<0.01). It implied that A-FABP gene could be a major effector gene or could be linked to gene(s) which significantly affect fat metabolism in chicken.

Adipocytes↗

Natural killer cells and gene therapy: potential of gene transfection for optimizing effector cell functions and for targeting gene products into tumor metastases.

Fluorescently labeled, adoptively transferred interleukin (IL)-2 activated natural killer (A-NK) cells have the ability to selectively accumulate within established pulmonary or hepatic metastases, binding to tumor cells and/or to microvascular endothelial cells. A-NK cells have also been shown to exert antimetastatic therapy in animal models and in the clinic. Transfection of genes for cytokines or possibly other molecules has the potential to improve the therapeutic potency and efficacy of the effector cells. Gene transfection to induce autocrine production of IL-2 and/or other cytokines is expected to augment their antimetastatic activities, while avoiding toxicity from systemic administration of high doses of cytokines. An alternative or complementary strategy for gene therapy is to transfect A-NK cells with genes for cytotoxic molecules, to selectively target them to metastatic sites.

Animals↗

Transcriptional regulation of components of the type III secretion system and effectors in Pseudomonas syringae pv. phaseolicola.

Quantitative real-time polymerase chain reaction was used with specific TaqMan probes to examine transcription of selected hrp and effector genes in Pseudomonas syringae pv. phaseolicola strains 1448A (race 6) and 1449B (race 7). Transcripts examined were from genes encoding the regulators hrpR and hrpL, core structural components of the type III secretion system (TTSS) hrcC, hrcJ, hrcN, hrcU, and hrpA; the first open-reading frame of each hrp operon, including hrpF, hrpJ, hrpP, and hrpY, and also secreted effectors hrpZ, avrPphE, avrPphF, and virPphA. All genes were induced by incubation in a minimal medium and showed patterns of expression indicating regulation by HrpRS and HrpL. Basal mRNA levels and the timing of accumulation of transcripts after induction differed significantly, suggesting the operation of additional regulatory elements. However, no clear transcriptional hierarchy emerged to explain the ordered construction of the TTSS. Quantitative analysis confirmed that the rates and levels of transcript accumulation within the first 2 h after inoculation were considerably higher in planta than in vitro, and indicated that plant cell wall contact may enhance transcription of TTSS and effector genes in P. syringae pv. phaseolicola. The low-abundance hrcU mRNA had a half-life of 16.5 min, whereas other transcripts had half-lives between 3 and 8 min.

Bacterial Proteins↗

Iron-induced oxidative damage and apoptosis in cerebellar granule cells: attenuation by tetramethylpyrazine and ferulic acid.

Tetramethylpyrazine and ferulic acid are two active ingredients of a Chinese herbal medicine Ligusticum wallichi Franchat. In the present investigation, iron-induced oxidative neuronal damage and the protective effects of tetramethylpyrazine and ferulic acid against this induction were studied in primary cultures of rat cerebellar granule cells. When neurons were treated with 200 microM of FeSO(4) for 1 h, lipid peroxidation in neurons increased time dependently, as measured with the thiobarbituric acid assay. Thirty-six hours after iron treatment, the cell viability decreased to 43.6% and the percentage of apoptotic cells increased to 50.6%. Transmission electron microscopic examination showed a disrupted nuclear envelope and condensed chromatin in iron-treated neurons. Analysis of DNA extracted from iron-treated cells by agarose gel electrophoresis showed the typical "ladder pattern", which indicated the formation of mono- and oligonucleosomes. After iron treatment, caspase 3 activity increased significantly, as measured in a fluoregenic assay. The results above suggested that iron treatment triggered oxidative stress and apoptosis in neurons. Western blot revealed that iron treatment up-regulated the apoptosis-related gene p53 as well as its effector gene p21(waf1/cip1). Pretreatment of the cells with 100 microM of tetramethylpyrazine or ferulic acid effectively decreased the activation of caspase 3 as well as the expression of p53 and p21(waf1/cip1), and attenuated iron-induced oxidative damage and apoptosis. The results suggest that tetramethylpyrazine and ferulic acid might be used as preventive agents against neuronal diseases associated with oxidative stress.

Animals↗

Do the epilepsies, pain syndromes, and affective disorders share common kindling-like mechanisms?

Kindling, in the classical sense, involves progressively increasing responsivity to the intermittent repetition of the same 1-s subthreshold electrical stimulation over time, with the amygdala being the area most frequently studied. Such repeated subthreshold stimulation is associated with: lowering of the after-discharge (AD) threshold; lengthening and spread of the AD; marked seizure stage progression culminating in full-blown tonic-clonic forelimb convulsions with rearing and falling; and evolution from triggered to spontaneous seizures. This evolving process concomitantly involves changes in the spatio-temporal expression of immediate early genes (IEGs), neurotrophic factors, and late effector genes (LEGs), and an associated changing pattern of effectiveness of different pharmacological interventions. Since seizures are the paradigmatic behavioral manifestation of kindling, some types of pharmacological seizures, such as those induced by the local anesthetics cocaine and lidocaine, and some epileptic syndromes, are most likely homologously modeled by kindling. However, since non-epileptiform syndromes, such as recurrent episodes of affective illness and some pain syndromes possess non-homogenous elements of kindling-like evolution, some of the principles involved in kindling progression may, nonetheless, be pertinent to the understanding and treatment of these syndromes. For example, one could attempt to distinguish between the genes involved in the primary pathological processes of syndrome evolution versus those that are secondary and adaptive; such a differentiation could have important implications for the development of therapeutic approaches targeted to suppressing or enhancing these alterations, respectively. In these instances, inferences drawn from the kindling model are necessarily indirect and circumscribed because different neuroanatomical and biochemical processes are likely involved in the evolution of each neuropsychiatric syndrome. Given these recognized limitations of non-homologous models, kindling may still provide insights into the longitudinal course, progression, and treatment of some neuropsychiatric syndromes that can then be directly tested in the clinic.

Amygdala↗

Innate immunity in plants.

Studies of receptors and signal-transduction components that play a role in plant disease resistance have revealed remarkable similarities with innate immunity pathways in insects and mammals. In plants, specific receptors encoded by disease-resistance genes interact with products of microbial effector genes to activate defence responses. Resistance proteins have been found to have motifs in common with components of immune response pathways in mammals and invertebrates, and to rely on similar downstream signalling components. In the future, the sharing of ideas among plant and animal biologists is likely to broaden our understanding of defence responses in diverse organisms.

Animals↗

Kips off to Myc: implications for TGF beta signaling.

Loss of sensitivity to the negative growth regulator transforming growth factor beta (TGF beta) is a feature of many different tumor types and is likely involved in tumor progression. In some cases this loss of sensitivity to TGF beta has been shown to be manifest in the absence of membrane-associated TGF beta receptor complexes, thus preventing initiation of antiproliferative signals from the cell surface. In others, loss of sensitivity to TGF beta-induced inhibitory signals has been attributed to loss of function of intracellular effectors of TGF beta-induced inhibitory signals due to mutation or allelic loss of effector genes and their products. The intracellular effectors of TGF beta inhibitory signals have been shown to be involved in the normal regulation of progression through the cell cycle, specifically during G1 phase. In this manner, elucidation of the mechanisms by which TGF beta inhibits cell growth not only helps us identify steps involved in tumor progression, but also allows us to better understand how cells regulate progression through the cell cycle.

Cyclin-Dependent Kinases↗

Distinct patterns of Fas cell surface expression during development of T- or B-lymphocyte lineages in normal, scid, and mutant mice lacking or overexpressing p53, bcl-2, or rag-2 genes.

Fas is a cell membrane protein involved in programmed cell death. In normal young mice, Fas was expressed on pluripotent stem cells, multipotent progenitors, pro-T and pre-T cells, most thymocytes, and a subset of CD4 and CD8 mature T lymphocytes. In contrast, Fas expression was switched off in B-cell and myelocytic progenitors and most pro-B and a proportion of pre-B cells and was switched on again later, but this occurred only in a subset of mature B lymphocytes. A lack of bcl-2 increased the proportion of Fas+ B-lymphocyte lineage cells and Fas+ CD4+ cells and decreased the percentage of Fas- CD8+ mature T-cell subsets. Overexpression of bcl-2 reversed this pattern of Fas cell surface expression. Interestingly, lack of p53 increased the proportions of Fas-expressing CD4 and CD8 mature T-cell subsets and of Fas- B-cell precursors but decreased that of Fas- mature B-lymphocyte populations. We conclude that the expression of Fas is regulated distinctly during the development of T and B lymphocytes. Although the products of neither bcl-2 nor p53 genes are essential for Fas cell surface expression on hematopoietic cells, these repressor and effector genes, respectively, of programmed cell death affect distinct subsets of lymphoid lineage cells at different stages of lymphopoiesis. Our results suggest that distinct combinations of effector and suppressor genes of programmed cell death act on distinct cell populations and at different stages of differentiation within the same cell lineage in the hematopoietic system.

Animals↗