A novel peptide derived from vascular endothelial growth factor prevents amyloid beta aggregation and toxicity

Amyloid-β oligomers (Aβo) are the most pathologically relevant Aβ species in Alzheimer's disease (AD), because they induce early synaptic dysfunction that leads to learning and memory impairments. In contrast, increasing VEGF (Vascular Endothelial Growth Factor) brain levels have been shown to improve learning and memory processes, and to alleviate Aβ-mediated synapse dysfunction. Here, we designed a new peptide, the blocking peptide (BP), which is derived from an Aβo-targeted domain of the VEGF protein, and investigated its effect on Aβ-associated toxicity. Using a combination of biochemical, 3D and ultrastructural imaging, and electrophysiological approaches, we demonstrated that BP strongly interacts with Aβo and blocks Aβ fibrillar aggregation process, leading to the formation of Aβ amorphous aggregates. BP further impedes the formation of structured Aβo and prevents their pathogenic binding to synapses. Importantly, acute BP treatment successfully rescues long-term potentiation (LTP) in the APP/PS1 mouse model of AD, at an age when LTP is highly impaired in hippocampal slices. Moreover, BP is also able to block the interaction between Aβo and VEGF, which suggests a dual mechanism aimed at both trapping Aβo and releasing VEGF to alleviate Aβo-induced synaptic damage. Our findings provide evidence for a neutralizing effect of the BP on Aβ aggregation process and pathogenic action, highlighting a potential new therapeutic strategy.

Long-term Outcomes of Critically Ill Patients With Stroke Requiring Mechanical Ventilation

BACKGROUND

Data on outcomes of critically ill patients requiring mechanical ventilation at the onset of stroke are limited.

OBJECTIVE

To assess the hospital and long-term functional outcomes of patients with stroke who require mechanical ventilation.

METHODS

This retrospective single-center cohort study performed from 1994 to 2008 involved adult patients within 7 days of stroke onset and who required intensive care unit admission and mechanical ventilation.

RESULTS

A total of 274 patients requiring mechanical ventilation at the onset of stroke were analyzed. Indications for intubation included coma in 195 patients (71%). The median (interquartile range) score on the Glasgow Coma Scale at admission to the intensive care unit was 6 (3-9). Forty-four patients (16%) had sepsis at intensive care unit admission. The overall hospital mortality rate was 53%. After adjustment for confounders, severity of illness at admission as assessed by the Simplified Acute Physiology Score II (odds ratio, 1.07; 95% CI, 1.05-1.10), anisocoria (odds ratio, 5.26; 95% CI, 1.76-15.80), and sepsis at intensive care unit admission (odds ratio, 0.40; 95% CI, 0.19-0.85) were associated with outcome. At 1 year, median (interquartile range) modified Rankin Scale score was 6 (2-6). Only 89 patients (32%) exhibited mild to moderate neurologic impairment.

CONCLUSION

In this study, adult patients requiring mechanical ventilation at the onset of stroke experienced high 1-year mortality, with survivors having poor functional status.

Correction: Energy-dependent nucleolar localization of p53 in vitro requires two discrete regions within the p53 carboxyl terminus

Following the publication of this article the authors noted that two images were duplicated in Figure 2B. The corrected figure 2B is below. The authors wish to apologize for any inconvenience caused.

Labeling of native proteins with fluorescent RAFT polymer probes: application to the detection of a cell surface protein using flow cytometry

Fluorescent RAFT polymer probes with an activated ester reactive end-group can be advantageously used to label native proteins.

First case report of a human sepsis involving a recently identified anaerobic agent: Bacteroides faecis

Up until now, Bacteroides faecis, a Gram-negative, anaerobic, non-motile, nonsporeforming rod has been principally described as a commensal microbe isolated from the feces of healthy adults. We report the first case of human Bacteroides faecis sepsis after removal of suspected post-colonic ischemia colonized epicardic electrodes. Electrodes and blood cultures both grew Gram-negative anaerobic rods but usual phenotypic methods and 16S rARN gene sequencing failed to ensure its species identification. B. faecis was finally identified using hsp60 gene sequencing. Because this species is not well-known and is difficult to identify, it may have been overlooked or misidentified in previous studies.

A penicillin- and metronidazole-resistant Clostridium botulinum strain responsible for an infant botulism case

The clinical course of a case of infant botulism was characterized by several relapses despite therapy with amoxicillin and metronidazole. Botulism was confirmed by identification of botulinum toxin and Clostridium botulinum in stools. A C. botulinum A2 strain resistant to penicillins and with heterogeneous resistance to metronidazole was isolated from stool samples up to 110 days after onset. Antibiotic susceptibility was tested by disc agar diffusion and MICs were determined by Etest. Whole genome sequencing allowed detection of a gene cluster composed of blaCBP for a novel penicillinase, blaI for a regulator, and blaR1 for a membrane-bound penicillin receptor in the chromosome of the C. botulinum isolate. The purified recombinant penicillinase was assayed. Resistance to β-lactams was in agreement with the kinetic parameters of the enzyme. In addition, the β-lactamase gene cluster was found in three C. botulinum genomes in databanks and in two of 62 genomes of our collection, all the strains belonging to group I C. botulinum. This is the first report of a C. botulinum isolate resistant to penicillins. This stresses the importance of antibiotic susceptibility testing for adequate therapy of botulism.

Energy-dependent nucleolar localization of p53 in vitro requires two discrete regions within the p53 carboxyl terminus

The p53 tumor suppressor is a nucleocytoplasmic shuttling protein that is found predominantly in the nucleus of cells. In addition to mutation, abnormal p53 cellular localization is one of the mechanisms that inactivate p53 function. To further understand features of p53 that contribute to the regulation of its trafficking within the cell, we analysed the subnuclear localization of wild-type and mutant p53 in human cells that were either permeabilized with detergent or treated with the proteasome inhibitor MG132. We, here, show that either endogenously expressed or exogenously added p53 protein localizes to the nucleolus in detergent-permeabilized cells in a concentration- and ATP hydrolysis-dependent manner. Two discrete regions within the carboxyl terminus of p53 are essential for nucleolar localization in permeabilized cells. Similarly, localization of p53 to the nucleolus after proteasome inhibition in unpermeabilized cells requires sequences within the carboxyl terminus of p53. Interestingly, genotoxic stress markedly decreases the association of p53 with the nucleolus, and phosphorylation of p53 at S392, a site that is modified by such stress, partially impairs its nucleolar localization. The possible significance of these findings is discussed.

Two outbreaks of Salmonella enteritidis phage type 8 linked to the consumption of Cantal cheese made with raw milk, France, 2001

Salmonelloses are one are the main causes of foodborne infections in industrialised countries. In France, the incidence of human salmonellosis recorded by the National Reference Centre for Salmonella and Shigella (CNRSS) in 2001 was 21 cases per 100,000 inhabitants, and Salmonella serotype Enteritidis represented 39% of cases (1). This article reports the investigation results of two community outbreaks of salmonellosis that occurred simultaneously in the south west of France, and which were linked to the consumption of cheese made from raw milk.

An increased expression of nucleolin is associated with a physiological nucleolar segregation

Nucleolar segregation is the most striking cellular phenotypic feature of cold-acclimatized carp and depicts the cyclical reprogramming that the physiology of the fish undergoes between summer and winter, where a clear differential expression of some nucleolar related genes occurs. We characterized carp nucleolin, a nucleolar protein involved in multiple steps of ribosome biogenesis, and evaluated its expression upon fish acclimatization. We show that the carp cDNA deduced amino acid sequence exhibits the same tripartite structural organization found in other species. Nevertheless, we observed that nucleolin mRNA expression was strongly induced in the cold-adapted carp as was the nuclear protein content, assessed by immunocytochemistry in liver sections. The physiological up-regulation of nucleolin in the cold-acclimatized carp, where rRNA transcription and processing are depressed concomitantly with the nucleolus segregation, is consistent with the notion that nucleolin plays a fundamental role in repressing rRNA synthesis.

Recognition of pre-formed and flexible elements of an RNA stem-loop by nucleolin

Nucleolin is an abundant nucleolar protein which is essential for ribosome biogenesis. The first two of its four tandem RNA-binding domains (RBD12) specifically recognize a stem-loop structure containing a conserved UCCCGA sequence in the loop called the nucleolin-recognition element (NRE). We have determined the structure of the consensus SELEX NRE (sNRE) by NMR spectroscopy. In both the free and bound RNA the top part of the stem forms a loop E (or S-turn) motif. In the absence of protein, the structure of the hairpin loop is not well defined due to conformational heterogeneity, and appears to be in equilibrium between two families of conformations. Titrations of RBD1, RBD2, and RBD12 with the sNRE show that specific binding requires RBD12. In complex with RBD12, the hairpin loop interacts specifically with the protein and adopts a well-defined structure which shares some of the features of the free form. The loop E motif also has specific interactions with the protein. Implications of these findings for the mechanism of recognition of RNA structures by modular proteins are discussed.

RNA-binding strategies common to cold-shock domain- and RNA recognition motif-containing proteins

Numerous RNA-binding proteins have modular structures, comprising one or several copies of a selective RNA-binding domain generally coupled to an auxiliary domain that binds RNA non-specifically. We have built and compared homology-based models of the cold-shock domain (CSD) of the Xenopus protein, FRGY2, and of the third RNA recognition motif (RRM) of the ubiquitous nucleolar protein, nucleolin. Our model of the CSD(FRG)-RNA complex constitutes the first prediction of the three-dimensional structure of a CSD-RNA complex and is consistent with the hypothesis of a convergent evolution of CSD and RRM towards a related single-stranded RNA-binding surface. Circular dichroism spectroscopy studies have revealed that these RNA-binding domains are capable of orchestrating similar types of RNA conformational change. Our results further show that the respective auxiliary domains, despite their lack of sequence homology, are functionally equivalent and indispensable for modulating the properties of the specific RNA-binding domains. A comparative analysis of FRGY2 and nucleolin C-terminal domains has revealed common structural features representing the signature of a particular type of auxiliary domain, which has co-evolved with the CSD and the RRM.

Two different combinations of RNA-binding domains determine the RNA binding specificity of nucleolin

Nucleolin is an abundant nucleolar protein involved in several steps of ribosome biogenesis. The protein is highly conserved through evolution and possesses four RNA-binding domains (RBD), which are likely to determine its RNA binding specificity. Previous studies have shown that nucleolin interacts with two different RNA targets. The first is a small stem-loop structure, the nucleolin recognition element (NRE), found all along the pre-ribosomal RNA. The second is a short single-stranded RNA sequence, the evolutionary conserved motif (ECM), located five nucleotides downstream of the first processing site in the pre-ribosomal RNA 5' external transcribed spacer. Biochemical, genetic, and structural studies have shown that the first two RBD of nucleolin are necessary and sufficient for the specific interaction of nucleolin with the NRE motif. In this work, we have studied the interaction of nucleolin with the ECM sequence. Deletion and mutational analyses showed that all four RBDs of hamster nucleolin were required for the interaction with the ECM sequence. This RNA binding specificity is conserved between hamster and Xenopus laevis, whereas the Xenopus protein does not interact with the NRE. Nucleolin is the first example of a protein that requires four RBDs for its interaction with an RNA target, demonstrating that a single protein can use different combinations of RBD to interact specifically with several RNA sequences.

Minced beef and human salmonellosis: review of the investigation of three outbreaks in France

The synthesis of investigations of three salmonellosis outbreaks which occured in France between 1998 and 2000 confirms the role of the consumption of minced beef and highlights the importance of prevention measures.

Molecular and phenotypic characterization of potentially new Shigella dysenteriae serotype

From September 1997 to November 1998, the French National Center for Salmonella and Shigella received 22 Shigella isolates recovered from 22 different patients suffering from dysentery. None of these isolates reacted with any of the antisera used to identify established Shigella serotypes, but all of them agglutinated in the presence of antisera to a previously described potentially new Shigella dysenteriae serotype (represented by strain 96-204) primarily isolated from stool cultures of imported diarrheal cases in Japan. All French isolates, as well as strain 96-204, showed biochemical reactions typical of S. dysenteriae and gave positive results in a PCR assay for detection of the plasmid ipaH gene coding for invasiveness. No Shiga toxin gene was detected by PCR. These isolates were indistinguishable by molecular analysis of ribosomal DNA (ribotyping) and seemed to be related to S. dysenteriae serotypes 3 and 12. However, further characterization by restriction of the amplified O-antigen gene cluster clearly distinguished this new serotype from all other Shigella or Escherichia coli serotypes.

Molecular basis of sequence-specific recognition of pre-ribosomal RNA by nucleolin

The structure of the 28 kDa complex of the first two RNA binding domains (RBDs) of nucleolin (RBD12) with an RNA stem-loop that includes the nucleolin recognition element UCCCGA in the loop was determined by NMR spectroscopy. The structure of nucleolin RBD12 with the nucleolin recognition element (NRE) reveals that the two RBDs bind on opposite sides of the RNA loop, forming a molecular clamp that brings the 5' and 3' ends of the recognition sequence close together and stabilizing the stem-loop. The specific interactions observed in the structure explain the sequence specificity for the NRE sequence. Binding studies of mutant proteins and analysis of conserved residues support the proposed interactions. The mode of interaction of the protein with the RNA and the location of the putative NRE sites suggest that nucleolin may function as an RNA chaperone to prevent improper folding of the nascent pre-rRNA.

Solution structure of the two N-terminal RNA-binding domains of nucleolin and NMR study of the interaction with its RNA target

Nucleolin is an abundant 70 kDa nucleolar protein involved in many aspects of ribosomal RNA biogenesis. The central region of nucleolin contains four tandem consensus RNA-binding domains (RBD). The two most N-terminal domains (RBD12) bind with nanomolar affinity to an RNA stem-loop containing the consensus sequence UCCCGA in the loop. We have determined the solution structure of nucleolin RBD12 in its free form and have studied its interaction with a 22 nt RNA stem-loop using multidimensional NMR spectroscopy. The two RBDs adopt the expected beta alpha beta beta alpha beta fold, but the position of the beta 2 strand in both domains differs from what was predicted from sequence alignments. RBD1 and RBD2 are significantly different from each others and this is likely important in their sequence specific recognition of the RNA. RBD1 has a longer alpha-helix 1 and a shorter beta 2-beta 3 loop than RBD2, and differs from most other RBDs in these respects. The two RBDs are separated by a 12 amino acid flexible linker and do not interact with one another in the free protein. This linker becomes ordered when RBD12 binds to the RNA. Analysis of the observed NOEs between the protein and the RNA indicates that both RBDs interact with the RNA loop via their beta-sheet. Each domain binds residues on one side of the loop; specifically, RBD2 contacts the 5' side and RBD1 contacts the 3'.

Risk factors for the occurrence of sporadic Salmonella enterica serotype typhimurium infections in children in France: a national case-control study

To determine risk factors for the occurrence of sporadic Salmonella typhimurium infections among children in France, we conducted a matched case-control study. Cases were identified between 15 June and 30 September 1996. We interviewed 101 pairs of case patients and control subjects, matched for age and place of residence. The risk of illness was greater for children who ate undercooked ground beef than for those who did not (odds ratio [OR], 5.0; 95% confidence interval [CI], 1.9-13.1). Case patients were more likely than control subjects to have taken antibiotics during the month before onset of disease (OR, 2.2; 95% CI, 1.0-4.9). Case patients <5 years of age were more likely to have been in contact with a household member with diarrhea 3-10 days before onset (P=.05). Consumption of undercooked ground beef is a risk factor for the sporadic occurrence of S. typhimurium infection among children, and antibiotics may facilitate the occurrence of illness. The possibility of person-to-person transmission among young children needs to be considered.

How many foodborne outbreaks of Salmonella infection occurred in France in 1995? Application of the capture-recapture method to three surveillance systems

Despite control measures, foodborne outbreaks of non-typhi Salmonella infection continue to occur in developed countries. The authors aimed to assess the number of foodborne Salmonella outbreaks that occurred in France in 1995 using a capture-recapture approach. Data from three sources--the National Public Health Network (NPHN), the Ministry of Agriculture (MA), which receives mandatory notification, and the National Salmonella and Shigella Reference Center (NRC)-were collected. Matching algorithms permitted identification of matched outbreaks. The total number of outbreaks was estimated by log-linear modeling taking into account source dependencies and the variable catchability. The final estimate was adjusted for the positive predictive value (66%) of the NRC case definition. The dependence between the NPHN and the MA was also evaluated by means of a qualitative survey. A total of 716 foodborne Salmonella outbreaks were reported to the three sources, and 108 matches were identified. The best-fitting model, taking into account a positive dependence between the NPHN and MA sources, gave an estimate of 757 outbreaks. The sensitivity was 15% for the NPHN, 10% for the MA, and 50% for the NRC. In France, routine mandatory reporting of foodborne Salmonella outbreaks is very incomplete, and it is not representative of the serotype and the type of outbreak.

Interaction of nucleolin with an evolutionarily conserved pre-ribosomal RNA sequence is required for the assembly of the primary processing complex

The first processing event of the precursor ribosomal RNA (pre-rRNA) takes place within the 5' external transcribed spacer. This primary processing requires conserved cis-acting RNA sequence downstream from the cleavage site and several nucleic acids (small nucleolar RNAs) and proteins trans-acting factors including nucleolin, a major nucleolar protein. The specific interaction of nucleolin with the pre-rRNA is required for processing in vitro. Xenopus laevis and hamster nucleolin interact with the same pre-rRNA site and stimulate the processing activity of a mouse cell extract. A highly conserved 11-nucleotide sequence located 5-6 nucleotides after the processing site is required for the interaction of nucleolin and processing. In vitro selection experiments with nucleolin have identified an RNA sequence that contains the UCGA motif present in the 11-nucleotide conserved sequence. The interaction of nucleolin with pre-rRNA is required for the formation of an active processing complex. Our findings demonstrate that nucleolin is a key factor for the assembly and maturation of pre-ribosomal ribonucleoparticles.

Haemolytic uraemic syndrome and Shiga toxin-producing Escherichia coli infection in children in France. The Société de Néphrologie Pédiatrique

We conducted a study to determine the incidence of haemolytic uraemic syndrome (HUS) in children in France and to assess the role of Shiga-toxin-producing Escherichia coli (STEC) infection in the aetiology of HUS. In collaboration with the Société de Néphrologie Pédiatrique we undertook a retrospective review of all cases of HUS hospitalized from January 1993 to March 1995 and a 1-year prospective study (April 1995-March 1996) of epidemiological and microbiological features of cases of HUS. The polymerase chain reaction (PCR) procedure was used to detect stx, eae, e-hlyA genes directly from case stool samples. Serum samples from cases were examined for antibodies to lipopolysaccharide (LPS) of 26 major STEC serogroups. Two hundred and eighty-six cases were reported. The average incidence per year was 0.7/10(5) children < 15 years and 1.8/10(5) children < 5 years. During the prospective study, 122/130 cases were examined for evidence of STEC infection using PCR and/or serological assays and 105 (86%) had evidence of STEC infection. Serum antibodies to E. coli O157 LPS were detected in 79 (67%) cases tested. In conclusion, this study showed that STEC infection is an important cause of HUS in children in France, with a high proportion related to the O157 serogroup.

Urokinase-induced mitogenesis is mediated by casein kinase 2 and nucleolin

BACKGROUND

Urokinase (uPA) and the urokinase receptor (uPAR) form a multifunctional system capable of concurrently regulating pericellular proteolysis, cell-surface adhesion, and mitogenesis. The role of uPA and uPAR in directed proteolysis is well established and its function in cellular adhesiveness has recently been clarified by numerous studies. The molecular mechanisms underlying the mitogenic effects of uPA and uPAR are still unclear, however.

RESULTS

We identified mechanisms that might participate in uPA-related mitogenesis in human vascular smooth muscle cells and demonstrated that uPA induces activation of a unique signaling complex. This complex contains uPAR and two additional proteins, nucleolin and casein kinase 2, which are implicated in cell proliferation. Both proteins were isolated by affinity chromatography on uPA-conjugated cyanogen-bromide-activated Sepharose 4B and were identified using nano-electrospray mass spectrometry and immunoblotting. We used laser scanning and immunoelectron microscopy studies to further demonstrate that nucleolin and casein kinase 2 are located on the cell surface where they colocalize with the uPAR. Moreover, the proteins were co-internalized into the cell as an entire complex. Immunoprecipitation experiments in combination with an in vitro kinase assay demonstrated a specific association of uPAR with nucleolin and casein kinase 2 and revealed a uPA-induced activation of casein kinase 2, which presumably led to phosphorylation of nucleolin. Blockade of nucleolin and casein kinase 2 with specific modulators led to the inhibition of uPA-induced cell proliferation.

CONCLUSIONS

We conclude that in human vascular smooth muscle cells, uPA induces the formation and activation of a newly identified signaling complex comprising uPAR, nucleolin, and casein kinase 2, that is responsible for the uPA-related mitogenic response. The complex is not a unique feature of vascular smooth muscle cells, as it was also found in other uPAR-expressing cell types.

Systemic lupus erythematosus-associated catastrophic antiphospholipid syndrome occurring after typhoid fever: a possible role of Salmonella lipopolysaccharide in the occurrence of diffuse vasculopathy-coagulopathy

We report a case of well-documented typhoid fever in a 30-year-old woman with inactive systemic lupus erythematosus with asymptomatic lupus anticoagulant and high-titer anticardiolipin antibody (aCL). Despite prompt eradication of the Salmonella typhi obtained with appropriate antibiotic therapy, multiple organ system dysfunction occurred. The central nervous system was involved, with ischemic infarcts in the occipital lobes. High-dose corticosteroid therapy failed to improve the neurologic manifestations, which responded to repeated plasmapheresis. A sharp fall in aCL and anti-beta2-glycoprotein I antibody titers was recorded before the start of plasmapheresis. At the same time, IgM and IgG antibodies to Salmonella group O:9 lipopolysaccharide became detectable; the IgM antibodies disappeared within 4 months, whereas the IgG antibodies remained detectable during the next 13 months. Despite treatment with high-dose corticosteroids and cyclophosphamide, rapidly progressive glomerulonephritis developed, leading to chronic renal failure. There is convincing evidence of a link between the S. typhi infection and the ensuing catastrophic syndrome in this patient, probably precipitated by bacterial antigens.

Structure and functions of nucleolin

Nucleolin is an abundant protein of the nucleolus. Nucleolar proteins structurally related to nucleolin are found in organisms ranging from yeast to plants and mammals. The association of several structural domains in nucleolin allows the interaction of nucleolin with different proteins and RNA sequences. Nucleolin has been implicated in chromatin structure, rDNA transcription, rRNA maturation, ribosome assembly and nucleo-cytoplasmic transport. Studies of nucleolin over the last 25 years have revealed a fascinating role for nucleolin in ribosome biogenesis. The involvement of nucleolin at multiple steps of this biosynthetic pathway suggests that it could play a key role in this highly integrated process.

Phylogenetic analysis of proteolytic Acinetobacter strains based on the sequence of genes encoding aminoglycoside 6'-N-acetyltransferases

The sequence of seven aac(6')-I genes encoding aminoglycoside 6'-N-acetyltransferases from proteolytic Acinetobacter strains including genomic species 14, 15, 16, and 17 and from ungrouped proteolytic strains 631, 640, and BM2722 was determined. Pulsed-field gel electrophoresis of genomic DNA of these strains and of Acinetobacter sp. 6 CIP A165 digested with SfiI followed by hybridization with rRNA and aac(6')-I specific probes indicated that these genes were located in the chromosome. Phylogenetic analysis of the genes indicated that aac(6')-I of A. baumannii, Acinetobacter ungrouped strain 631, and Acinetobacter sp. 16 formed a cluster (91.5 to 92.3% identity) whereas aac(6')-I of Acinetobacter sp. 15, sp. 17, and Acinetobacter ungrouped strain BM2722 formed another cluster (90.7 to 94.6% identity). A third cluster was constituted by A. haemolyticus and Acinetobacter sp. 6 (83.6% identity). The phylogeny drawn from aac(6')-I sequences was consistent with that based on DNA-DNA hybridization and phenotype comparison. The aac(6')-I genes were all species specific except for aac(6')-Ih located in a 13.7-kb non conjugative plasmid from A. baumannii BM2686. We conclude that aac(6')-I genes may be suitable for identification at the species level and for analysis of the phylogenetic relationships of Acinetobacter.

Risk factors for the occurrence of sporadic Salmonella enterica serotype enteritidis infections in children in France: a national case-control study

To determine risk factors associated with the occurrence of sporadic cases of Salmonella enteritidis infections among children in France, we conducted a matched case-control study. Cases were identified between 1 March and 30 September 1995. One hundred and five pairs of cases and controls matched for age and place of residence were interviewed. In the 1-5 years age group, illness was associated with the consumption of raw eggs or undercooked egg-containing foods (OR 2.4, 95% CI 1.2-4.8). Storing eggs more than 2 weeks after purchase was associated with Salmonella enteritidis infection (OR 3.8, 95% CI 1.4-10.2), particularly during the summer period (OR 6.0, 95% CI 1.3-26.8). Cases were more likely to report a case of diarrhoea in the household 10-3 days before the onset of symptoms, particularly in the age group < or = 1 year (P = 0.01). This study confirms the link between eggs and the occurrence of sporadic cases of Salmonella enteritidis among children, highlights the potential role of prolonged egg storage and underlines the role of person-to-person transmission in infants.

Cellular adhesion mediated by factor J, a complement inhibitor. Evidence for nucleolin involvement

Factor J (FJ) is a complement inhibitor that acts on the classical and the alternative pathways. We demonstrated FJ-cell interactions in fluid phase by flow cytometry experiments using the cell lines Jurkat, K562, JY, and peripheral blood lymphocytes. FJ bound to plastic plates was able to induce in vitro adhesion of these cells with potency equivalent to fibronectin. As evidence for the specificity of this reaction, the adhesion was blocked by MAJ2, an anti-FJ monoclonal antibody, and by soluble FJ. Attachment of the cells required active metabolism and cytoskeletal integrity. The glycosaminoglycans heparin, heparan sulfate, or chondroitin sulfates A, B, and C inhibited to varying degrees the binding of FJ to cells, as did treatment with chondroitinase ABC. In the search for a putative receptor, a protein of 110 kDa was isolated by affinity chromatography, and microsequence analysis identified this protein as nucleolin. Confocal microscopy evidenced the presence of nucleolin in cell membrane by immunofluorescence with monoclonal (D3) and polyclonal anti-nucleolin antibodies in Jurkat cells. The interaction FJ-nucleolin was evidenced by Western blot and enzyme-linked immunosorbent assay. Furthermore, purified nucleolin and D3 inhibited adhesion of Jurkat cells to immobilized FJ, suggesting that the interaction was specific and that nucleolin mediated the binding.

Nucleolin interacts with several ribosomal proteins through its RGG domain

Nucleolin is one of the major nonribosomal proteins of the nucleolus. Through its four RNA-binding domains, nucleolin interacts specifically with pre-rRNA as soon as synthesis begins, but it is not found in mature cytoplasmic ribosomes. Nucleolin is able to shuttle between the cytoplasm and the nucleus. These data suggest that nucleolin might be involved in the nucleolar import of cytoplasmic components and in the assembly of pre-ribosomal particles. Here we show, using two-dimensional blots in a ligand blotting assay, that nucleolin interacts with 18 ribosomal proteins from rat (14 and 4 from the large and small subunit, respectively). The C-terminal domain of nucleolin (p50) interacts with 10 of these identified ribosomal proteins. In vitro binding assays show that the glycine-arginine rich domain of nucleolin (RGG domain) is sufficient for the interaction with one of these proteins. Interestingly, most of the proteins that interact with p50 belong to the core ribosomal proteins, which are resistant to extraction with high salt concentration. These findings suggest that nucleolin might be involved in the nucleolar targeting of some ribosomal proteins and in their assembly within pre-ribosomal particles.

Nucleolin functions in the first step of ribosomal RNA processing

The first processing step of precursor ribosomal RNA (pre-rRNA) involves a cleavage within the 5' external transcribed spacer. This processing requires sequences downstream of the cleavage site which are perfectly conserved among human, mouse and Xenopus and also several small nucleolar RNAs (snoRNAs): U3, U14, U17 and E3. In this study, we show that nucleolin, one of the major RNA-binding proteins of the nucleolus, is involved in the early cleavage of pre-rRNA. Nucleolin interacts with the pre-rRNA substrate, and we demonstrate that this interaction is required for the processing reaction in vitro. Furthermore, we show that nucleolin interacts with the U3 snoRNP. Increased levels of nucleolin, in the presence of the U3 snoRNA, activate the processing activity of a S100 cell extract. Our results suggest that the interaction of nucleolin with the pre-rRNA substrate might be a limiting step in the primary processing reaction. Nucleolin is the first identified metazoan proteinaceous factor that interacts directly with the rRNA substrate and that is required for the processing reaction. Potential roles for nucleolin in the primary processing reaction and in ribosome biogenesis are discussed.

Discrimination of Acinetobacter genomic species by AFLP fingerprinting

AFLP is a novel genomic fingerprinting method based on the selective PCR amplification of restriction fragments. The usability of this method for the differentiation of genomic species in the genus Acinetobacter was investigated. A total of 151 classified strains (representing 18 genomic species, including type, reference, and field strains) and 8 unclassified strains were analyzed. By using a single set of restriction enzymes (HindIII and TaqI) and one particular set of selective PCR primers, all strains could be allocated to the correct genomic species and all groups were properly separated, with minimal intraspecific similarity levels ranging from 29 to 74%. Strains belonging to genomic species 8 (Acinetobacter lwoffii sensu stricto) and 9 grouped together in one cluster. The closely related DNA groups 1 (Acinetobacter calcoaceticus), 2 (Acinetobacter baumannii), 3 and 13TU (sensu Tjernberg & Ursing 1989) were clearly distinguishable, with intraspecific linkage levels above 50%. Strains of the independently described genomic species 13BJ (sensu Bouvet & Jeanjean 1989) and 14TU linked together at a relatively low level (33%). Although a previous DNA-DNA hybridization study seemed to justify the unification of these genomic species, AFLP analysis actually divides the 13BJ-14TU group into three well-separated subgroups. Finally, four unclassified strains obtained from diverse sources and origins grouped convincingly together, with a similarity linkage level of approximately 50%. These strains showed no similarities in their AFLP patterns with any of the other 155 strains studied and may represent a thus-far-undescribed Acinetobacter species. Based on these results, AFLP should be regarded as an important auxiliary method for the delineation of genomic species. Furthermore, because AFLP provides a detailed insight into the infraspecific structure of Acinetobacter taxa, the method also represents a highly effective means for the confirmation of strain identity in the epidemiology of acinetobacters.

RNA recognition by the joint action of two nucleolin RNA-binding domains: genetic analysis and structural modeling

The interaction of nucleolin with a short stem-loop structure (NRE) requires two contiguous RNA-binding domains (RBD 1+2). The structural basis for RNA recognition by these RBDs was studied using a genetic system in Escherichia coli. Within each of the two domains, we identified several mutations that severely impair interaction with the RNA target. Mutations that alter RNA-binding specificity were also isolated, suggesting the identity of specific contacts between RBD 1+2 amino acids and nucleotides within the NRE stem-loop. Our data indicate that both RBDs participate in a joint interaction with the NRE and that each domain uses a different surface to contact the RNA. The constraints provided by these genetic data and previous mutational studies have enabled us to propose a three-dimensional model of nucleolin RBD 1+2 bound to the NRE stem-loop.

Two RNA-binding domains determine the RNA-binding specificity of nucleolin

Nucleolin is an abundant nucleolar RNA-binding protein that seems to be involved in many aspects of ribosome biogenesis. Nucleolin contains four copies of a consensus RNA-binding domain (CS-RBD) found in several other proteins. In vitro RNA-binding studies previously determined that nucleolin interacts specifically with a short RNA stem-loop structure. Taken individually, none of the four CS-RBDs interacts significantly with the RNA target, but a peptide that contains the first two adjacent CS-RBDs (R12) is sufficient to account for nucleolin RNA-binding specificity and affinity. The full integrity of these two domains is required, since N- or C-terminal deletion abolishes the specific interaction with the RNA. Mutation of conserved amino acids within the RNP-1 sequence of CS-RBD 1 or 2 drastically reduces the interaction with the RNA, whereas mutation of the analogous residues in CS-RBDs 3 and 4 has no effect in the context of the R1234G protein (which corresponds to the C-terminal end of nucleolin). Our results demonstrate that nucleolin RNA-binding specificity is the result of a cooperation between two CS-RBDs (RBDs 1 and 2) and also suggests a direct or indirect involvement of the RNP-1 consensus sequence of both CS-RBDs in the recognition of the RNA target.

Nucleolin is a sequence-specific RNA-binding protein: characterization of targets on pre-ribosomal RNA

Nucleolin is an abundant nucleolar protein, which plays an essential, but largely unknown role in ribosome biogenesis. Nucleolin contains four consensus RNA-binding domains (CS-RBD), the presence of which suggests that the molecular function of this protein is likely reflected by its RNA-binding properties. Indeed, by immunocytological analysis performed on ribosomal transcription units, we have found several nucleolin molecules associated with nascent pre-rRNA. In mouse, two high-affinity binding sites with an apparent dissociation constant (Kd) of 50 to 100 nM have been mapped in the 5' ETS upstream from the early pre-rRNA processing site. Interestingly, nucleolin of mouse origin has recognized analogous sequences in the 5' ETS of human pre-rRNA. In parallel, selection-amplification (SELEX) experiments have identified an 18-nucleotide long RNA sequence that binds nucleolin with high affinity (Kd 5 to 20 nM) and shares a common UCCCGA motif with the characterized pre-rRNA binding sites. By mutagenesis and a structural analysis, we have characterized the nucleolin RNA binding site and found that it is constituted by a minimal 18-nucleotide long stem-loop structure. The sequence UCCCGA that is found within the hairpin loop is necessary for the specific interaction. Mutation of any of the C or G residues within this motif abolishes nucleolin interaction. Furthermore, point mutation in the stem that completely disrupt the hairpin structure also prevents nucleolin binding. By determining the minimal 5' and 3' ends of the RNA that is bound to the protein we concluded that nucleolin binding site is constituted by a short four to five-base-pair stem and an eight-nucleotide loop. This structural motif is very similar to hairpins recognized by two other CS-RBD-containing proteins (U1 snRNP A and U2 snRNP B"). Possible functional implications of our findings are discussed.

Outbreak of Salmonella dublin infection in France, November - December 1995

On 20 December 1995, the National Network of Public Health (Reseau National de Sante Publique - RNSP) was notified by the Salmonella and Shigella National Reference Centre (Centre National de Reference - CNR) that a greater than expected number of human i

Large outbreak of Salmonella enterica serotype paratyphi B infection caused by a goats' milk cheese, France, 1993: a case finding and epidemiological study

OBJECTIVE

To assess the magnitude of a nationwide outbreak of infection with Salmonella enterica serotype paratyphi B and identify the vehicle and source of infection.

DESIGN

A case finding study of S paratyphi B infection between 15 August and 30 November 1993; a pair matched case-control study; an environmental investigation at a processing plant that produced a raw goats' milk cheese incriminated in the outbreak; phage typing and genotyping of food and human S paratyphi B isolates.

SETTING

France, 15 August to 30 November 1993.

SUBJECTS

273 patients with S paratyphi B infection; 59 pairs of cases and controls matched for age, sex, and city of residence.

MAIN OUTCOME MEASURES

Numbers of cases and incidence rates by region of residence and age; matched odds ratios for dairy food preferences.

RESULTS

Among the 273 cases there was one death; 203 (78%) strains belonged to phage type 1 var 3. The incidence of infection was greatest in the region where goats' milk cheese is commonly produced. Comparison of cases and controls showed a 12-fold greater risk of illness (95% confidence interval 1.6 to 92.3) from eating brand A unpasteurised goats' milk cheese. S paratyphi B isolates of phage type 1 var 3 were recovered from cheese A, goats' milk at the plant processing cheese A, and goats' milk supplied to the plant by a single farm. Genotypic IS 200 typing of food and human 1 var 3 phage type isolates showed a common IS 200 pattern.

CONCLUSION

This outbreak emphasises the potential health hazards of widely distributed unpasteurised milk products in France and the need for their close bacterial monitoring.

Localization of nucleolin binding sites on human and mouse pre-ribosomal RNA

Nucleolin, a major RNA binding protein of the nucleolus is found associated mainly to the pre-ribosomal particles and is absent from the cytoplasmic mature ribosomes. The role of this protein in ribosome biogenesis remains largely unknown, and is likely to be reflected by its RNA binding properties. Nucleolin contains in its central domain four RNA recognition motifs (RRM, also called RBD for RNA binding domain) which are conserved among different species. RNA binding studies have revealed that nucleolin interacts specifically with a short stem loop structure called NRE (nucleolin recognition element). We show that nucleolin extracted from human, hamster and mouse cells interacts with the same specificity and affinity to a mouse 5'ETS (external transcribed spacer) RNA fragment which contains a NRE motif. A similar structure within the human 5'ETS is also efficiently recognized by mouse nucleolin. We identified putative NRE not only in the 5'ETS but also in the 3'ETS, ITS (internal transcribed spacer) and in the 18S and 28S RNA sequences. This is in agreement with in vivo cross-linking data and a previous immunocytological analysis of ribosomal transcription units. Interestingly, we found that all the NRE localized in the 28S region are within the variable domains. Despite considerable sequence divergence of these domains, several of the NRE have sequences perfectly conserved between these two species. This suggests that these nucleolin binding sites might be functionally important, in particular for ribosome biogenesis.

Acinetobacter baumannii outbreak isolates characterized by three typing methods

Forty-two strains of Acinetobacter baumannii were isolated from 15 patients hospitalized in a French intensive care unit. An epidemiological study based on the typing of these isolates was carried out using biotyping, antibiotyping, and ribotyping to recognize the transmission of multiresistant strains by transfer of a patient from one hospital to another. Fifteen strains from the outbreak (1 strain for each patient), five Acinetobacter baumannii strains isolated before the outbreak in Bellevue Hospital (St. Etienne), and five strains isolated in Cochin Hospital (Paris) were included. The three methods gave a good correlation: the epidemic strains had the same antibiotic resistance pattern, the same biotype, and the same ribotypes obtained with three different endonucleases.

Sequence-specific RNA recognition by the Xenopus Y-box proteins. An essential role for the cold shock domain

The Xenopus Y-box protein FRGY2 has a role in the translational silencing of masked maternal mRNA. Here, we determine that FRGY2 will recognize specific RNA sequences. The evolutionarily conserved nucleic acid-binding cold shock domain is required for sequence-specific interactions with RNA. However, RNA binding by FRGY2 is facilitated by N- and C-terminal regions flanking the cold shock domain. The hydrophilic C-terminal tail domain of FRGY2 interacts with RNA independent of the cold shock domain but does not determine sequence specificity. Thus, both sequence-specific and nonspecific RNA recognition domains are contained within the FRGY2 protein.

A role for transcription and FRGY2 in masking maternal mRNA within Xenopus oocytes

We find that mRNA synthesized within the Xenopus oocyte nucleus is translated with an efficiency 50 times less than that of mRNA injected into the oocyte cytoplasm. For histone H1 mRNA this effect is independent of mRNA splicing, nuclear export, and the promoter driving transcription. The mRNA synthesized in vivo is translationally competent but is masked from the translational machinery in the cytoplasm through association with proteins including frog Y-box protein 2 (FRGY2). We find that overexpression of FRGY2 facilitates the translational repression of mRNA synthesized within Xenopus oocytes. The requirement for transcription to occur in vivo before a translationally repressed state can be established suggests that these two events are functionally coupled in Xenopus oocytes.

Specific regulation of Xenopus chromosomal 5S rRNA gene transcription in vivo by histone H1

The incorporation of histone H1 into chromatin during embryogenesis directs the specific repression of the Xenopus oocyte 5S rRNA genes. An increase in histone H1 content specifically restricts TFIIIA-activated transcription, and a decrease in histone H1 within chromatin facilitates the activation of the oocyte 5S rRNA genes by TFIIIA. Variation in the amount of histone H1 in chromatin does not significantly influence somatic 5S rRNA gene transcription. Thus, the regulated expression of histone H1 during Xenopus development has a specific and dominant role in mediating the differential expression of the oocyte and somatic 5S rRNA genes. This example demonstrates that histones can exert dominant repressive effects on the transcription of a gene in vivo in spite of an abundance of transcription factors for that gene.

The deadenylation conferred by the 3' untranslated region of a developmentally controlled mRNA in Xenopus embryos is switched to polyadenylation by deletion of a short sequence element

The maternal Xenopus Eg mRNAs are adenylated and translated in the mature oocyte and then, after fertilization, are deadenylated and released from polysomes. Therefore, after fertilization, a change occurs in the cellular mechanisms that control mRNA adenylation. In the study reported here, we show that the 3' untranslated region of Eg2 mRNA contains a cis-acting element that is required for the deadenylation of chimeric RNAs after fertilization. This cis-acting element is contained within a single 17-nucleotide portion of the Eg2 mRNA. Disruption of this deadenylation element allows adenylation of the chimeric transcripts in the embryo. Therefore, this cis-acting element is part of the sequence information required for the developmental switch from adenylation to deadenylation of the maternal Eg2 mRNA in Xenopus embryos.

Control of RNase E-mediated RNA degradation by 5'-terminal base pairing in E. coli

Despite the variety of messenger RNA half-lives in bacteria (0.5-30 min in Escherichia coli) and their importance in controlling gene expression, their molecular basis remains obscure. The lifetime of an entire mRNA molecule can be determined by features near its 5' end, but no 5' exoribonuclease has been identified in any prokaryotic organism. A mutation that inactivates E. coli RNase E also increases the average lifetime of bulk E. coli mRNA and of many individual messages, suggesting that cleavage by this endonuclease may be the rate-determining step in the degradation of most mRNAs in E. coli. We have investigated the substrate preference of RNase E in E. coli by using variants of RNA I, a small untranslated RNA whose swift degradation in vivo is initiated by RNase E cleavage at an internal site. We report here that RNase E has an unprecedented substrate specificity for an endoribonuclease, as it preferentially cleaves RNAs that have several unpaired nucleotides at the 5' end. The sensitivity of RNase E to 5'-terminal base pairing may explain how determinants near the 5' end can control rates of mRNA decay in bacteria.

Identification of RNA-binding proteins specific to Xenopus Eg maternal mRNAs: association with the portion of Eg2 mRNA that promotes deadenylation in embryos

Maternal Xenopus Eg mRNAs have been previously identified as transcripts that are specifically deadenylated after fertilization and degraded after the mid blastula transition. Destabilizing cis sequences were previously localised in the 3′ untranslated region of Eg2 mRNA. In order to characterize possible trans-acting factors which are involved in the post-transcriptional regulation of Eg mRNAs, gel-shift and u.v. cross-linking experiments were performed, which allowed the identification of a p53-p55 RNA-binding protein doublet specific for the 3′ untranslated regions of Eg mRNAs. These p53-p55 proteins do not bind to the 3′ untranslated regions of either ornithine decarboxylase or phosphatase 2Ac mRNAs, which remain polyadenylated in embryos. These novel RNA-binding proteins are distinct from the cytoplasmic polyadenylation element-binding protein that controls the polyadenylation of maternal mRNAs in maturing Xenopus oocytes, and from previously identified thermoresistant RNA-binding proteins present in oocyte mRNP storage particles. The p53-p55 bind a portion of the Eg2 mRNA 3′ untranslated region, distinct from the previously identified destabilizing region, that is able to confer the postfertilization deadenylation of CAT-coding chimeric mRNAs. This suggests that the p53-p55 RNA-binding proteins are good candidates for trans-acting factors involved in the deadenylation of Eg mRNAs in Xenopus embryos.