Detection of Cleaved Stx2a in the Blood of STEC-Infected Patients

Typical hemolytic uremic syndrome (HUS) is mainly caused by Shiga toxin-producing Escherichia coli (STEC) releasing Shiga toxin 2 (Stx2). Two different structures of this AB5 toxin have been described: uncleaved, with intact B and A chains, and cleaved, with intact B and a nicked A chain consisting of two fragments, A1 and A2, connected by a disulfide bond. Despite having the same toxic effect on sensitive cells, the two forms differ in their binding properties for circulating cells, serum components and complement factors, thus contributing to the pathogenesis of HUS differently. The outcome of STEC infections and the development of HUS could be influenced by the relative amounts of uncleaved or cleaved Stx2 circulating in patients' blood. Cleaved Stx2 was identified and quantified for the first time in four out of eight STEC-infected patients' sera by a method based on the inhibition of cell-free translation. Cleaved Stx2 was present in the sera of patients with toxins bound to neutrophils and in two out of three patients developing HUS, suggesting its involvement in HUS pathogenesis, although in association with other bacterial or host factors.

Enzymatic Cleavage of Stx2a in the Gut and Identification of Pancreatic Elastase and Trypsin as Possible Main Cleavers

Shiga toxins (Stxs), especially the Stx2a subtype, are the major virulence factors involved in enterohemorrhagic Escherichia coli (EHEC)-associated hemolytic uremic syndrome (eHUS), a life-threatening disease causing acute kidney injury, especially in children. After oral transmission and colonization in the gut, EHEC release Stx. Intracellular cleavage of the Stx A subunit, when followed by reduction, boosts the enzymatic activity that causes damage to targeted cells. This cleavage was assumed to be mostly mediated by furin during Stx intracellular trafficking. To investigate whether this cleavage could occur in the intestine, even prior to entering target cells, Stx2a A subunit structure (intact or cleaved) was characterized after its exposure to specific host factors present in human stool. The molecular weight of Stx2a A subunit/fragments was determined by immunoblotting after electrophoretic separation under reducing conditions. In this study, it was demonstrated that Stx2a is cleaved by certain human stool components. Trypsin and chymotrypsin-like elastase 3B (CELA3B), two serine proteases, were identified as potential candidates that can trigger the extracellular cleavage of Stx2a A subunit directly after its secretion by EHEC in the gut. Whether the observed cleavage indeed translates to natural infections and plays a role in eHUS pathogenesis has yet to be determined. If so, it seems likely that a host's protease profile could affect disease development by changing the toxin's biological features.

Shiga Toxin 2 Triggers C3a-Dependent Glomerular and Tubular Injury through Mitochondrial Dysfunction in Hemolytic Uremic Syndrome

Shiga toxin (Stx)-producing Escherichia coli is the predominant offending agent of post-diarrheal hemolytic uremic syndrome (HUS), a rare disorder of microvascular thrombosis and acute kidney injury possibly leading to long-term renal sequelae. We previously showed that C3a has a critical role in the development of glomerular damage in experimental HUS. Based on the evidence that activation of C3a/C3a receptor (C3aR) signaling induces mitochondrial dysregulation and cell injury, here we investigated whether C3a caused podocyte and tubular injury through induction of mitochondrial dysfunction in a mouse model of HUS. Mice coinjected with Stx2/LPS exhibited glomerular podocyte and tubular C3 deposits and C3aR overexpression associated with cell damage, which were limited by C3aR antagonist treatment. C3a promoted renal injury by affecting mitochondrial wellness as demonstrated by data showing that C3aR blockade reduced mitochondrial ultrastructural abnormalities and preserved mitochondrial mass and energy production. In cultured podocytes and tubular cells, C3a caused altered mitochondrial fragmentation and distribution, and reduced anti-oxidant SOD2 activity. Stx2 potentiated the responsiveness of renal cells to the detrimental effects of C3a through increased C3aR protein expression. These results indicate that C3aR may represent a novel target in Stx-associated HUS for the preservation of renal cell integrity through the maintenance of mitochondrial function.

Plasmonic Metasurfaces for Specific SERS Detection of Shiga Toxins

The interest in the development of nanoscale plasmonic technologies has dramatically increased in recent years. The photonic properties of plasmonic nanopatterns can be controlled and tuned via their size, shape, or the arrangement of their constituents. In this work, we propose a 2D hybrid metallic polymeric nanostructure based on the octupolar framework with enhanced sensing property. We analyze its plasmonic features both numerically and experimentally, demonstrating the higher values of their relevant figures of merit: we estimated a surface-enhanced Raman spectroscopy (SERS) enhancement factor of 9 × 10⁷ and a SPR bulk sensitivity of 430 nm/RIU. In addition, our nanostructure exhibits a dual resonance in the visible and near-infrared region, enabling our system toward multispectral plasmonic analysis. Finally, we illustrate our design engineering strategy as enabled by electron beam lithography by the outstanding performance of a SERS-based biosensor that targets the Shiga toxin 2a, a clinically relevant bacterial toxin. To the best of our knowledge, this is the first time that a SERS fingerprint of this toxin has been evidenced.

Bloody Diarrhea and Shiga Toxin-Producing Escherichia coli Hemolytic Uremic Syndrome in Children: Data from the ItalKid-HUS Network

OBJECTIVE

To analyze the results of an enhanced laboratory-surveillance protocol for bloody diarrhea aimed at identifying children with Shiga toxin-producing Escherichia coli (STEC) infection early in the course of the disease toward the early identification and management of patients with hemolytic uremic syndrome (HUS).

STUDY DESIGN

The study (2010-2019) involved a referral population of 2.3 million children. Stool samples of patients with bloody diarrhea were screened for Shiga toxin (Stx) genes. Positive patients were rehydrated and monitored for hemoglobinuria until diarrhea resolved or STEC-HUS was diagnosed.

RESULTS

A total of 4767 children were screened; 214 (4.5%) were positive for either Stx1 (29.0%) or Stx2 (45.3%) or both Stx1+2 (25.7%); 34 patients (15.9%) developed STEC-HUS (0.71% of bloody diarrheas). Hemoglobinuria was present in all patients with HUS. Patients with Stx2 alone showed a greater risk of STEC-HUS (23.7% vs 12.7%) and none of the patients with Stx1 alone developed HUS. During the same period of time, 95 other patients were diagnosed STEC-HUS but were not captured by the screening program (26 had nonbloody diarrhea, 11 came from areas not covered by the screening program, and 58 had not been referred to the screening program, although they did meet the inclusion criteria). At HUS presentation, serum creatinine of patients identified by screening was significantly lower compared with that of the remaining patients (median 0.9 vs 1.51 mg/dL).

CONCLUSIONS

Nearly 1% of children with bloody diarrhea developed STEC-HUS, and its diagnosis was anticipated by the screening program for Stx. The screening of bloody diarrhea for Stx is recommended, and monitoring patients carrying Stx2 with urine dipstick for hemoglobinuria is suggested to identify the renal complication as early as possible.

Extracellular Vesicles and Renal Endothelial Cells: A Fatal Attraction in Hemolytic Uremic Syndrome

This review focuses on typical hemolytic uremic syndrome (HUS), a life-threatening sequela of human infections caused, particularly in children, by Shiga toxin-producing Escherichia coli strains. Thrombotic microangiopathy of the brain and the kidney is the end point of toxin action, resulting in the hallmarks of HUS (ie, thrombocytopenia, anemia, and acute renal failure). A growing body of evidence points to the role of extracellular vesicles released in the blood of patients by toxin-challenged circulating cells (monocytes, neutrophils, and erythrocytes) and platelets, as a key factor in the pathogenesis of HUS. This review provides i) an updated description of the pathogenesis of Shiga toxin-producing E. coli infections; ii) an analysis of blood cell-derived extracellular vesicles, and of their parent cells, as triggering factors in HUS; and iii) a model explaining why Shiga toxin-containing vesicles dock preferentially to the endothelia of target organs.

Method for the Detection of the Cleaved Form of Shiga Toxin 2a Added to Normal Human Serum

The pathogenesis of Escherichia coli-induced hemolytic uremic syndrome (eHUS) caused by infections with pathogenic Shiga toxin (Stx) producing E. coli (STEC) is centered on bacterial (e.g., Stx) and host factors (circulating cells, complement system, serum proteins) whose interaction is crucial for the immediate outcome and for the development of this life-threatening sequela. Stx2a, associated to circulating cells (early toxemia) or extracellular vesicles (late toxemia) in blood, is considered the main pathogenic factor in the development of eHUS. Recently, it was found that the functional properties of Stx2a (binding to circulating cells and complement components) change according to modifications of the structure of the toxin, i.e., after a single cleavage of the A subunit resulting in two fragments, A1 and A2, linked by a disulfide bridge. Herein, we describe a method to be used for the detection of the cleaved form of Stx2a in the serum of STEC-infected or eHUS patients. The method is based on the detection of the boosted inhibitory activity of the cleaved toxin, upon treatment with reducing agents, on a rabbit cell-free translation system reconstituted with human ribosomes. The method overcomes the technical problem caused by the presence of inhibitors of translation in human serum that have been stalled by the addition of RNAase blockers and by treatment with immobilized protein G. This method, allowing the detection of Stx2a at concentrations similar to those found by ELISA in the blood of STEC-infected patients, could be a useful tool to study the contribution of the cleaved form of Stx2a in the pathogenesis of eHUS.

Is Shigatoxin 1 protective for the development of Shigatoxin 2-related hemolytic uremic syndrome in children? Data from the ItalKid-HUS Network

BACKGROUND

Shigatoxin (Stx)-producing Escherichia coli (STEC) are the most common causes of hemolytic uremic syndrome (STEC-HUS). The aim of our study is to compare the risk of developing STEC-HUS in relation to the type of Stx genes (Stx1, Stx2, or both).

METHODS

This is a prospective, observational, multicenter study involving 63 pediatric units in Northern Italy (ItalKid-HUS Network). STEC-infected children were identified within a screening program for bloody diarrhea during a 10-year period (2010-2019). Stx genes were detected by reverse dot blot or real-time PCR. After the identification of STEC infection, children were followed until diarrhea complete recovery for the possible development of STEC-HUS.

RESULTS

Of the 214 Stx-positive patients, 34 (15.9%) developed STEC-HUS. The risk of HUS in STEC-infected children with Stx1 (n: 62; 29.0%) and Stx2 (n: 97; 45.3%) was respectively 0% and 23.7%, while in patients carrying both Stx1 and Stx2 (n: 55; 25.7%), the risk was 12.7% (p: 0.001).

CONCLUSIONS

Our data confirm that Stx1 is a very rare cause of STEC-HUS and demonstrate that the risk of STEC-HUS halves in the case of Stx1+2-producing Escherichia coli infection compared with infections where Stx2 is present alone. This observation is helpful in assessing the risk of individual STEC-infected patients for the development of HUS and suggests that Stx1, in the presence of Stx2, might exert a protective role possibly by receptor competition.

Particulate Shiga Toxin 2 in Blood is Associated to the Development of Hemolytic Uremic Syndrome in Children

Hemolytic uremic syndrome (HUS), the leading cause of acute renal failure in children (< 3 years), is mainly related to Shiga toxins (Stx)-producing Escherichia coli (STEC) infections. STEC are confined to the gut resulting in hemorrhagic colitis, whereas Stx are delivered in blood to target kidney and brain, with unclear mechanisms, triggering HUS in 5 to 15% of infected children. Stx were found on circulating cells, free in sera (soluble Stx) or in blood cell-derived microvesicles (particulate Stx), whereby the relationship between these forms of circulating toxins is unclear. Here, we have examined 2,846 children with bloody diarrhea and found evidence of STEC infection in 5%. Twenty patients were enrolled to study the natural course of STEC infections before the onset of HUS. In patients, Stx were found to be associated to circulating cells and/or free and functionally active in sera. In most children, Stx were bound to neutrophils when high amounts of toxins were found in feces. Time-course analysis showed that Stx increased transiently in patients' sera while the decrease of toxin amount on leukocytes was observed. Notably, patients who recovered (85%) displayed different settings than those who developed HUS (15%). The distinctive feature of the latter group was the presence in blood of particulate Stx2 (Stx2 sedimented at g-forces corresponding to 1 μm microvesicles) the day before diagnosis of HUS, during the release phase of toxins from circulating cells. This observation strongly suggests the involvement of blood cell-derived particulate Stx2 in the transition from hemorrhagic colitis to HUS.

The structure of the Shiga toxin 2a A-subunit dictates the interactions of the toxin with blood components

Hemolytic uremic syndrome (eHUS) is a severe complication of human infections with Shiga toxins (Stxs)-producing Escherichia coli. A key step in the pathogenesis of eHUS is the interaction of Stxs with blood components before the targeting of renal endothelial cells. Here, we show that a single proteolytic cleavage in the Stx2a A-subunit, resulting into two fragments (A1 and A2) linked by a disulfide bridge (cleaved Stx2a), dictates different binding abilities. Uncleaved Stx2a was confirmed to bind to human neutrophils and to trigger leukocyte/platelet aggregate formation, whereas cleaved Stx2a was ineffective. Conversely, binding of complement factor H was confirmed for cleaved Stx2a and not for uncleaved Stx2a. It is worth noting that uncleaved and cleaved Stx2a showed no differences in cytotoxicity for Vero cells or Raji cells, structural conformation, and contaminating endotoxin. These results have been obtained by comparing two Stx2a batches, purified in different laboratories by using different protocols, termed Stx2a(cl; cleaved toxin, Innsbruck) and Stx2a(uncl; uncleaved toxin, Bologna). Stx2a(uncl) behaved as Stx2a(cl) after mild trypsin treatment. In this light, previous controversial results obtained with purified Stx2a has to be critically re-evaluated; furthermore, characterisation of the structure of circulating Stx2a is mandatory to understand eHUS-pathogenesis and to develop therapeutic approaches.

Soluble Toll-Like Receptor 4 Impairs the Interaction of Shiga Toxin 2a with Human Serum Amyloid P Component

Shiga toxin 2a (Stx2a) is the main virulence factor produced by pathogenic Escherichia coli strains (Stx-producing E. coli, STEC) responsible for hemorrhagic colitis and the life-threatening sequela hemolytic uremic syndrome in children. The toxin released in the intestine by STEC targets the globotriaosylceramide receptor (Gb3Cer) present on the endothelial cells of the brain and the kidney after a transient blood phase during which Stx2a interacts with blood components, such as neutrophils, which, conversely, recognize Stx through Toll-like receptor 4 (TLR4). Among non-cellular blood constituents, human amyloid P component (HuSAP) is considered a negative modulating factor that specifically binds Stx2a and impairs its toxic action. Here, we show that the soluble extracellular domain of TLR4 inhibits the binding of Stx2a to neutrophils, assessed by indirect flow cytometric analysis. Moreover, by using human sensitive Gb3Cer-expressing cells (Raji cells) we found that the complex Stx2a/soluble TLR4 escaped from capture by HuSAP allowing the toxin to target and damage human cells, as assayed by measuring translation inhibition, the typical Stx-induced functional impairment. Thus, soluble TLR4 stood out as a positive modulating factor for Stx2a. In the paper, these findings have been discussed in the context of the pathogenesis of hemolytic uremic syndrome.

Human monocytes stimulated by Shiga toxin 1a via globotriaosylceramide release proinflammatory molecules associated with hemolytic uremic syndrome

The life-threatening sequela of hemorrhagic colitis induced by Shiga toxins (Stx)-producing Escherichia coli (STEC) infections in humans is hemolytic uremic syndrome (HUS), the main cause of acute renal failure in early childhood. The key step in the pathogenesis of HUS is the appearance of Stx in the blood of infected patients because these powerful virulence factors are capable of inducing severe microangiopathic lesions in the kidney. During precocious toxemia, which occurs in patients before the onset of HUS during the intestinal phase, Stx bind to several different circulating cells. An early response of these cells might include the release of proinflammatory mediators associated with the development of HUS. Here, we show that primary human monocytes stimulated with Shiga toxin 1a (Stx1a) through the glycolipid receptor globotriaosylceramide released larger amounts of proinflammatory molecules (IL-1β, TNFα, IL-6, G-CSF, CXCL8, CCL2, CCL4) than Stx1a-treated neutrophils. The mediators (except IL-1β) are among the top six proinflammatory mediators found in the sera from patients with HUS in different studies. The molecules appear to be involved in different pathogenetic steps of HUS, i.e. sensitization of renal endothelial cells to the toxin actions (IL-1β, TNFα), activation of circulating monocytes and neutrophils (CXCL8, CCL2, CCL4) and increase in neutrophil counts in patients with poor prognosis (G-CSF). Hence, a role of circulating monocytes in the very early phases of the pathogenetic process culminating with HUS can be envisaged. Impairment of the events of precocious toxemia would prevent or reduce the risk of HUS in STEC-infected children.

Cap-independent protein synthesis is enhanced by betaine under hypertonic conditions

Protein synthesis is one of the main cellular functions inhibited during hypertonic challenge. The subsequent accumulation of the compatible osmolyte betaine during the later adaptive response allows not only recovery of translation but also its stimulation. In this paper, we show that betaine modulates translation by enhancing the formation of cap-independent 48 S pre-initiation complexes, leaving cap-dependent 48 S pre-initiation complexes basically unchanged. In the presence of betaine, CrPV IRES- and sodium-dependent neutral amino acid transporter-2 (SNAT2) 5'-UTR-driven translation is 2- and 1.5-fold stimulated in MCF7 cells, respectively. Thus, betaine could provide an advantage in translation of messengers coding for proteins implicated in the response of cells to different stressors, which are often recognized by ribosomal 40 S subunit through simplified cap-independent mechanisms.

A reconstituted cell-free assay for the evaluation of the intrinsic activity of purified human ribosomes

We describe a cell-free translation system for evaluating the activity of ribosomes stringently purified from human cells. This system is based on in vitro reconstitution of the cellular translation machinery, in which a ribosome-free rabbit reticulocyte lysate (RRL) is reassembled with human ribosomes and in vitro-transcribed reporter mRNAs. The protocol describes the preparation of the RRL-derived fractions, purification of ribosomes devoid of detectable nonribosomal-associated factors, and assembly of the reactions to evaluate ribosomal translational efficiency and fidelity using appropriate reporter transcripts. The whole procedure can be completed in ∼2.5 d (plus 2 weeks for RRL preparation and cell expansion time). This protocol can be applied to study intrinsic functional properties (cis-acting element-mediated translation initiation or translational fidelity) of ribosome populations from different sources (including nonhuman origin). It is therefore useful for the characterization of ribosomal function in ribosomopathies and cancer, and it will be applicable in the emerging fields of ribosome diversity and specialized ribosomes.

Early Volume Expansion and Outcomes of Hemolytic Uremic Syndrome

BACKGROUND

Hemolytic uremic syndrome associated with Shiga toxin-producing Escherichia coli (STEC-HUS) is a severe acute illness without specific treatment except supportive care; fluid management is concentrated on preventing fluid overload for patients, who are often oligoanuric. Hemoconcentration at onset is associated with more severe disease, but the benefits of volume expansion after hemolytic uremic syndrome (HUS) onset have not been explored.

METHODS

All the children with STEC-HUS referred to our center between 2012 and 2014 received intravenous infusion targeted at inducing an early volume expansion (+10% of working weight) to restore circulating volume and reduce ischemic or hypoxic tissue damage. The short- and long-term outcomes of these patients were compared with those of 38 historical patients referred to our center during the years immediately before, when fluid intake was routinely restricted.

RESULTS

Patients undergoing fluid infusion soon after diagnosis showed a mean increase in body weight of 12.5% (vs 0%), had significantly better short-term outcomes with a lower rate of central nervous system involvement (7.9% vs 23.7%, P = .06), had less need for renal replacement therapy (26.3% vs 57.9%, P = .01) or intensive care support (2.0 vs. 8.5 days, P = .02), and needed fewer days of hospitalization (9.0 vs 12.0 days, P = .03). Long-term outcomes were also significantly better in terms of renal and extrarenal sequelae (13.2% vs 39.5%, P = .01).

CONCLUSIONS

Patients with STEC-HUS had great benefit from early volume expansion. It is speculated that early and generous fluid infusions can reduce thrombus formation and ischemic organ damage, thus having positive effects on both short- and long-term disease outcomes.

Serum Shiga toxin 2 values in patients during acute phase of diarrhoea-associated haemolytic uraemic syndrome

AIM

Shiga toxins are delivered via systemic circulation and are considered to be the cause of diarrhoea-associated haemolytic uraemic syndrome (HUS), as they injure endothelial cells, particularly in the glomeruli. This study measured Shiga toxin 2 (Stx2) in the serum of children affected in by HUS due to Stx2 producing Escherichia coli.

METHODS

The concentration of free Stx2 was measured in the serum of 16 children, collected immediately after admission to the clinic in the acute phase of HUS, using a sandwich enzyme-linked immunosorbent assay. The family members of two children were also investigated, with the relative toxicity of Stx2 assessed by a Vero cell-based fluorescent assay.

RESULTS

Stx2 was found in the serum of eight of the 16 children who were investigated. It was also detected in four of the six family members not showing symptomatic HUS, with an extremely high level in two.

CONCLUSION

An absent or rather low concentration of Stx2 was found in the serum of children admitted to the clinic with diarrhoea-associated HUS. The high concentration of Stx2 in family members without HUS, but mostly with watery diarrhoea and raised functional activity, was in line with the concept of early injury by Stx2.

RiboAbacus: a model trained on polyribosome images predicts ribosome density and translational efficiency from mammalian transcriptomes

Fluctuations in mRNA levels only partially contribute to determine variations in mRNA availability for translation, producing the well-known poor correlation between transcriptome and proteome data. Recent advances in microscopy now enable researchers to obtain high resolution images of ribosomes on transcripts, providing precious snapshots of translation in vivo. Here we propose RiboAbacus, a mathematical model that for the first time incorporates imaging data in a predictive model of transcript-specific ribosome densities and translational efficiencies. RiboAbacus uses a mechanistic model of ribosome dynamics, enabling the quantification of the relative importance of different features (such as codon usage and the 5′ ramp effect) in determining the accuracy of predictions. The model has been optimized in the human Hek-293 cell line to fit thousands of images of human polysomes obtained by atomic force microscopy, from which we could get a reference distribution of the number of ribosomes per mRNA with unmatched resolution. After validation, we applied RiboAbacus to three case studies of known transcriptome-proteome datasets for estimating the translational efficiencies, resulting in an increased correlation with corresponding proteomes. RiboAbacus is an intuitive tool that allows an immediate estimation of crucial translation properties for entire transcriptomes, based on easily obtainable transcript expression levels.

Human ribosomes from cells with reduced dyskerin levels are intrinsically altered in translation

Dyskerin is a pseudouridine (ψ) synthase involved in fundamental cellular processes including uridine modification in rRNA and small nuclear RNA and telomere stabilization. Dyskerin functions are altered in X-linked dyskeratosis congenita (X-DC) and cancer. Dyskerin's role in rRNA pseudouridylation has been suggested to underlie the alterations in mRNA translation described in cells lacking dyskerin function, although relevant direct evidences are currently lacking. Our purpose was to establish definitely whether defective dyskerin function might determine an intrinsic ribosomal defect leading to an altered synthetic activity. Therefore, ribosomes from dyskerin-depleted human cells were purified and 1) added to a controlled reticulocyte cell-free system devoid of ribosomes to study mRNA translation; 2) analyzed for protein contamination and composition by mass spectrometry, 3) analyzed for global pseudouridylation levels. Ribosomes purified from dyskerin-depleted cells showed altered translational fidelity and internal ribosome entry site (IRES)-mediated translation. These ribosomes displayed reduced uridine modification, whereas they were not different in terms of protein contamination or ribosomal protein composition with respect to ribosomes from matched control cells with full dyskerin activity. In conclusion, lack of dyskerin function in human cells induces a defect in rRNA uridine modification, which is sufficient to alter ribosome activity.

Dyskerin depletion increases VEGF mRNA internal ribosome entry site-mediated translation

Dyskerin is a nucleolar protein encoded by the DKC1 gene that (i) stabilizes the RNA component of the telomerase complex, and (ii) drives the site-specific pseudouridilation of rRNA. It is known that the partial lack of dyskerin function causes a defect in the translation of a subgroup of mRNAs containing internal ribosome entry site (IRES) elements such as those encoding for the tumor suppressors p27 and p53. In this study, we aimed to analyze what is the effect of the lack of dyskerin on the IRES-mediated translation of mRNAs encoding for vascular endothelial growth factor (VEGF). We transiently reduced dyskerin expression and measured the levels of the IRES-mediated translation of the mRNA encoding for VEGF in vitro in transformed and primary cells. We demonstrated a significant increase in the VEGF IRES-mediated translation after dyskerin knock-down. This translational modulation induces an increase in VEGF production in the absence of a significant upregulation in VEGF mRNA levels. The analysis of a list of viral and cellular IRESs indicated that dyskerin depletion can differentially affect IRES-mediated translation. These results indicate for the first time that dyskerin inhibition can upregulate the IRES translation initiation of specific mRNAs.

Change in conformation with reduction of alpha-helix content causes loss of neutrophil binding activity in fully cytotoxic Shiga toxin 1

Shiga toxins (Stx) play an important role in the pathogenesis of hemolytic uremic syndrome, a life-threatening renal sequela of human intestinal infection caused by specific Escherichia coli strains. Stx target a restricted subset of human endothelial cells that possess the globotriaosylceramide receptor, like that in renal glomeruli. The toxins, composed of five B chains and a single enzymatic A chain, by removing adenines from ribosomes and DNA, trigger apoptosis and the production of pro-inflammatory cytokines in target cells. Because bacteria are confined to the gut, the toxins move to the kidney through the circulation. Polymorphonuclear leukocytes (PMN) have been indicated as the carriers that "piggyback" shuttle toxins to the kidney. However, there is no consensus on this topic, because not all laboratories have been able to reproduce the Stx/PMN interaction. Here, we demonstrate that conformational changes of Shiga toxin 1, with reduction of α-helix content and exposition to solvent of hydrophobic tryptophan residues, cause a loss of PMN binding activity. The partially unfolded toxin was found to express both enzymatic and globotriaosylceramide binding activities being fully active in intoxicating human endothelial cells; this suggests the presence of a distinct PMN-binding domain. By reviewing functional and structural data, we suggest that A chain moieties close to Trp-203 are recognized by PMN. Our findings could help explain the conflicting results regarding Stx/PMN interactions, especially as the groups reporting positive results obtained Stx by single-step affinity chromatography, which could have preserved the correct folding of Stx with respect to more complicated multi-step purification methods.

Novel dyskerin-mediated mechanism of p53 inactivation through defective mRNA translation

In up to 60% of human cancers, p53 gene mutations are responsible for direct inactivation of the tumor suppressor function of p53. Alternative mechanisms of p53 inactivation described thus far mainly affect its posttranslational regulation. In X-linked dyskeratosis congenita, a multisystemic syndrome characterized by increased cancer susceptibility, mutations of the DKC1 gene encoding dyskerin cause a selective defect in the translation of a subgroup of internal ribosome entry site (IRES)-containing cellular mRNAs. In this study, we show that impairment of dyskerin function can cause p53 inactivation due to a defect in p53 mRNA translation. siRNA-mediated reduction of dyskerin levels caused a decrease of p53 mRNA translation, protein levels, and functional activity, both in human breast cancer cells and in primary mammary epithelial progenitor cells. These effects seemed to be independent of the known role of dyskerin in telomerase function, and they were associated with a specific impairment of translation initiation mediated by IRES elements present in p53 mRNA. In a series of human primary breast cancers retaining wild-type p53, we found that low levels of dyskerin expression were associated with reduced expression of p53-positive target genes. Our findings suggest that a dyskerin-mediated mechanism of p53 inactivation may occur in a subset of human tumors.

Molecular damage and induction of proinflammatory cytokines in human endothelial cells exposed to Shiga toxin 1, Shiga toxin 2, and alpha-sarcin

Treatment of human endothelial cells with Shiga toxin 1 and 2 leads to the upregulation of genes encoding proinflammatory molecules involved in the pathogenesis of hemolytic-uremic syndrome. The paradoxical effect of inhibitors of mRNA translation, such as Shiga toxins, that at the same time induce protein expression was investigated by studying the relationship between their enzymatic activity (abstraction of adenine from nucleic acids) and the induction of interleukin-8 and granulocyte-macrophage colony-stimulating factor in human endothelial cells. As a positive control, the fungal toxin alpha-sarcin, acting on the same rRNA sequence targeted by Shiga toxins with a different mechanism (RNase activity), was used. The three toxins caused ribosomal lesions that, in turn, induced the activation of p38 stress kinase with kinetics that paralleled the inhibition of translation. Alpha-sarcin was devoid of activity on DNA. Shiga toxin 2 targeted nuclear DNA with more rapid kinetics than did Shiga toxin 1. Since the fungal ribotoxin was fully effective in the induction of proinflammatory proteins, we conclude that damage to ribosomes is indispensable and sufficient to activate protein expression via induction of the stress-kinase cascade. However, gene upregulation events induced by Shiga toxin 2 were much more efficient than those triggered by Shiga toxin 1, although the two toxins impaired translation to the same extent and had overlapping time courses of stress kinase activation. Regulations independent of the ribotoxic stress were assumed to operate in intoxicated cells. We hypothesized that the two bacterial toxins recognize different DNA sequences inducing different regulating effects on gene expression.

Dyskerin expression influences the level of ribosomal RNA pseudo-uridylation and telomerase RNA component in human breast cancer

Dyskerin is a nucleolar protein, altered in dyskeratosis congenita, which carries out two separate functions, both fundamental for proliferating cells. One function is the pseudo-uridylation of ribosomal RNA (rRNA) molecules, necessary for their processing, and the other is the stabilization of the telomerase RNA component, necessary for telomerase activity. A significant feature of dyskeratosis congenita is an increased susceptibility to cancer; so far, however, no data have been reported on dyskerin changes in human tumours. Therefore, in this study, the distribution of dyskerin in a large series of human tumours from the lung, breast, and colon, as well as from B-cell lymphomas, was analysed by immunohistochemistry. Dyskerin proved never to be lost or delocalized outside the nucleolus. A quantitative analysis of dyskerin mRNA expression was then performed in 70 breast carcinomas together with the evaluation of telomerase RNA component levels and rRNA pseudo-uridylation. Dyskerin mRNA levels were highly variable and directly associated with both telomerase RNA component levels and rRNA pseudo-uridylation. Dyskerin gene silencing in the MCF-7 human breast carcinoma cell line reduced telomerase activity and rRNA pseudo-uridylation. Significantly, patients with low dyskerin expression were characterized by a better clinical outcome than those with a high dyskerin level. These data indicate that dyskerin is not lost in human cancers and that the levels of its expression and function are associated with tumour progression.

Creatine as a compatible osmolyte in muscle cells exposed to hypertonic stress

Exposure of C2C12 muscle cells to hypertonic stress induced an increase in cell content of creatine transporter mRNA and of creatine transport activity, which peaked after about 24 h incubation at 0.45 osmol (kg H(2)O)(-1). This induction of transport activity was prevented by addition of either cycloheximide, to inhibit protein synthesis, or of actinomycin D, to inhibit RNA synthesis. Creatine uptake by these cells is largely Na(+) dependent and kinetic analysis revealed that its increase under hypertonic conditions resulted from an increase in V(max) of the Na(+)-dependent component, with no significant change in the K(m) value of about 75 mumol l(-1). Quantitative real-time PCR revealed a more than threefold increase in the expression of creatine transporter mRNA in cells exposed to hypertonicity. Creatine supplementation significantly enhanced survival of C2C12 cells incubated under hypertonic conditions and its effect was similar to that obtained with the well known compatible osmolytes, betaine, taurine and myo-inositol. This effect seemed not to be linked to the energy status of the C2C12 cells because hypertonic incubation caused a decrease in their ATP content, with or without the addition of creatine at 20 mmol l(-1) to the medium. This induction of creatine transport activity by hypertonicity is not confined to muscle cells: a similar induction was shown in porcine endothelial cells.

Inhibition by suramin of protein synthesis in vitro. Ribosomes as the target of the drug

Suramin, a drug widely used both as a therapeutic agent and in research, inhibits translation in eukaryotic cell-free systems from rabbit reticulocyte lysate (IC(50)=142-241 microM). Suramin affects both initiation (block of 43S pre-initiation complex formation) and elongation (impairment of poly(U) translation). The drug induces an increase in the pools of ribosomal subunits and the formation of high molecular weight ribosomal complexes, thus causing the disappearance of polysomes. Ribosomes isolated from suramin-treated translating mixtures are inactivated. [(3)H]Suramin binds to ribosomes and to isolated 60S and 40S ribosomal subunits (116, 106 and 3 binding sites, respectively) showing higher affinity for the small subunit (K(d)=2 microM).

Shiga toxins present in the gut and in the polymorphonuclear leukocytes circulating in the blood of children with hemolytic-uremic syndrome

Hemolytic-uremic syndrome, the main cause of acute renal failure in early childhood, is caused primarily by intestinal infections from some Escherichia coli strains that produce Shiga toxins. The toxins released in the gut are targeted to renal endothelium after binding to polymorphonuclear leukocytes. The presence of Shiga toxins in the feces and the circulating neutrophils of 20 children with hemolytic uremic syndrome was evaluated by the Vero cell cytotoxicity assay and flow cytometric analysis, respectively. The latter showed the presence of Shiga toxins on the polymorphonuclear leukocytes of 13 patients, 5 of whom had no other microbiologic or serologic evidence of infection by Shiga toxin-producing Escherichia coli. A positive relationship was observed between the amounts of Shiga toxins released in the intestinal lumen and those released in the bloodstream. The toxins were detectable on the neutrophils for a median period of 5 days after they were no longer detectable in stools. This investigation confirms that the immunodetection of Shiga toxins on neutrophils is a valuable tool for laboratory diagnosis of Shiga toxin-producing Escherichia coli infection in hemolytic-uremic syndrome and provides clues for further studies on the role of neutrophils in the pathogenesis of this syndrome.

Shiga toxin 1 and ricin inhibit the repair of H2O2-induced DNA single strand breaks in cultured mammalian cells

A growing body of evidence suggests that ribosome-inactivating proteins (RIPs) remove adenine moieties not only from rRNA, but also from DNA--an effect leading to DNA damage in cultured cells. We herein report that two distinct RIPs of bacterial (shiga toxin 1, Stx1) and plant (ricin) origin, inhibit the repair of the DNA lesions generated by hydrogen peroxide in cultured human cells. This effect is unrelated either to inhibition of protein synthesis or to depletion of cellular antioxidant defenses and is likely to derive from direct interactions with cellular DNA repair machinery. Therefore, the genotoxicity of these toxins on mammalian cells seems to be a complex phenomenon resulting from the balance between direct (DNA damaging activity), indirect (DNA repair inhibition) effects and the eventual presence of other DNA damaging species. In particular, with regard to Stx1, it could be hypothesized that Stx-producing bacteria increase the risk of transformation of surrounding, inflamed tissues in the course of human infections.

Shiga toxin 1 acting on DNA in vitro is a heat-stable enzyme not requiring proteolytic activation

Shiga toxin 1 (Stx1) catalyses the removal of a specific adenine from 28S rRNA within ribosomes (RNA-N-glycosylase activity) and the removal of multiple adenines from DNA (DNA-glycosylase activity). For the in vitro activity the toxin requires activation by trypsin, urea and DTT which releases the enzymatically active A1 fragment. We show that activated Stx1 acts on DNA as a heat-stable enzyme. Moreover, heat-treatment of the pro-enzyme at acidic pH turns it into an enzymatically active species which efficiently depurinates DNA. Although the effect of this treatment is centred on the enzyme and not on DNA, we found no evidence for covalent modification of the holotoxin. We suggest that high temperatures and acidic buffer induce unfolding of the holotoxin allowing the substrate to gain access to the active site. Possible practical applications (rapid assay for Stx1 detection, use of the toxin for DNA sequencing) are discussed.

Flow cytometry detection of Shiga toxins in the blood from children with hemolytic uremic syndrome

BACKGROUND

Hemolytic uremic syndrome (HUS) is the main cause of acute renal failure in early childhood. Most cases are due to intestinal infections from Escherichia coli strains (STEC) which produce by Shiga toxin (Stxs). Stx1 and Stx2 produced by STEC in the gut are absorbed into the circulation and, after binding on polymorphonuclear leukocytes (PMNs), are targeted to renal endothelium. The aim of the present work was the development of a method to detect Stxs bound on circulating PMNs and to diagnose STEC infections in patients with HUS.

METHODS

White blood cells isolated after erythrocytic lysis were incubated with anti-Stxs mouse monoclonal antibodies in the presence of human serum to saturate Fc receptors on PMNs. After incubation with fluorescein isothiocyanate-goat anti-mouse immunoglobulin G, flow cytometric analysis was used to demonstrate the cell-bound fluorescence.

RESULTS

The method was quick (3 h), sensitive (femtomoles), and capable of detecting both Stxs. The presence of Stxs was detected on PMNs from six patients with HUS: four patients had serologic or microbiological evidence of STEC infection, whereas the other two patients had no evidence of STEC infection when employing the standard diagnostic methods.

CONCLUSIONS

The method described is rapid, simple, and based on commercially available reagents, and it might be more sensitive than the standard methods for diagnosis of STEC infection. It also allows the detection of Stxs in blood, a key step to monitor the pathogenesis of HUS.

Ribosome-inactivating proteins depurinate poly(ADP-ribosyl)ated poly(ADP-ribose) polymerase and have transforming activity for 3T3 fibroblasts

It has been known that ribosome-inactivating proteins (RIPs) from plants damage ribosomes by removing adenine from a precise position of rRNA. Subsequently it was observed that all tested RIPs depurinate DNA, and some of them also non-ribosomal RNAs and poly(A), hence the denomination of adenine polynucleotide glycosylases was proposed. We report now that ricin, saporin-L2, saporin-S6, gelonin and momordin depurinate also poly(ADP-ribosyl)ated poly(ADP-ribose) polymerase (auto modified enzyme), an enzyme involved in DNA repair. We observed also that all RIPs but gelonin induce transformation of fibroblasts, possibly as a consequence of damage to DNA and of the altered DNA repair system.

Effects of osmolarity, ions and compatible osmolytes on cell-free protein synthesis

To mimic what might happen in cells exposed to hypertonicity, the effects of increased osmolarity and ionic strength on cell-free protein synthesis have been examined. Translation of globin mRNA by rabbit reticulocyte lysate decreased by 30-60% when osmolality was increased from 0.35 to 0.53 osmol/kg of water by the addition of NaCl, KCl, CH(3)CO(2)Na or CH(3)CO(2)K. In contrast, equivalent additions of the compatible osmolytes betaine or myo -inositol caused a 40-50% increase in the rate of translation, whereas amino acids (50-135 mM) that are transported via system A had no significant effect. Addition of 75 mM KCl caused a dramatic fall in the amount of the 43 S pre-initiation complex, whereas it was totally preserved when osmolarity was similarly increased by the addition of 150 mM betaine. The formation of a non-enzymic initiation complex between rabbit [(3)H]Phe-tRNA, poly(U) and the 80 S ribosomes was unaffected by the addition of 75 mM NaCl or KCl, but translation of the complex decreased by 70%. Density-gradient centrifugation of reticulocyte extracts translating endogenous mRNA revealed that addition of 150 mM betaine had no effect, whereas addition of 75 mM KCl caused a marked decrease in the polysome peak, concomitant with an increase in the proportion of 80 S ribosomes and ribosomal subunits, even when elongation was inhibited with fragment A of diphtheria toxin. These results are consistent with the notion that both initiation and elongation are inhibited by unusually high concentrations of inorganic ions, but not by the compatible osmolytes betaine or myo -inositol.

Damage to nuclear DNA induced by Shiga toxin 1 and ricin in human endothelial cells

Ribosome-inactivating proteins (RIPs) remove a specific adenine from 28S rRNA leading to inactivation of ribosomes and arrest of translation. Great interest as to a possible second physiological substrate for RIPs came from the observation that in vitro RIPs remove adenine from DNA. This paper addresses the problem of nuclear lesions induced by RIPs in human endothelial cells susceptible to the bacterial RIP Shiga toxin 1 and the plant RIP ricin. With both toxins, nuclear DNA damage as evaluated by two independent techniques (alkaline-halo assay and alkaline filter elution) appears early, concomitant with (ricin) or after (Shiga toxin 1) the inhibition of protein synthesis. At this time, the annexin V binding assay, caspase 3 activity, the formation of typical < or = 50 Kb DNA fragments, and changes in morphology associated with apoptosis were negative. Furthermore, a block of translation comparable to that induced by RIPs, but obtained with cycloheximide, did not induce nuclear damage. Such damage is consistent with the enzymatic activity (removal of adenine) of RIPs acting in vitro on RNA-free chromatin and DNA. The results unequivocally indicate that RIPs can damage nuclear DNA in whole cells by means that are not secondary to ribosome inactivation or apoptosis.

Nucleotides U28-A42 and A37 in unmodified yeast tRNA(Trp) as negative identity elements for bovine tryptophanyl-tRNA synthetase

Wild-type bovine and yeast tRNA(Trp) are efficiently aminoacylated by tryptophanyl-tRNA synthetase both from beef and from yeast. Upon loss of modified bases in the synthetic transcripts, mammalian tRNA(Trp) retains the double recognition by the two synthetases, while yeast tRNA(Trp) loses its substrate properties for the bovine enzyme and is recognised only by the cognate synthetase. By testing chimeric bovine-yeast transcripts with tryptophanyl-tRNA synthetase purified from beef pancreas, the nucleotides responsible for the loss of charging of the synthetic yeast transcript have been localised in the anticodon arm. A complete loss of charging akin to that observed with the yeast transcript requires substitution in the bovine backbone of G37 in the anticodon loop with yeast A37 and of C28-G42 in the anticodon stem with yeast U28-A42. Since A37 does not prevent aminoacylation of the wild-type yeast tRNA(Trp) by the beef enzyme, a negative combination apparently emerges in the synthetic transcript after unmasking of U28 by loss of pseudourydilation.

Shiga toxin 1: damage to DNA in vitro

Shiga toxins share with plant ribosome-inactivating proteins the same enzymatic mechanism of action: the removal of a specific adenine from 28S RNA when acting on ribosomes and the removal of multiple adenines when acting on DNA in vitro. The activity on DNA, only recently reported, is particularly evident, and has been studied mostly at acidic pH. For the in vitro activity, on both ribosomes and DNA, Shiga toxins require activation by trypsin, urea and dithiothreitol which release the enzymatically active A(1) fragment. Activation by the classical procedure leaves large amounts of urea and DTT which interfere in the DNA depurination assay and completely abolish depurination at physiological pH. A consistent release of [3H]adenine from DNA at neutral pH is instead observed when the toxin is activated in vitro by an improved method which removes most of the drastic reagents required for proteolytic cleavage and reduction. Damage to single-stranded DNA by Shiga toxin 1 (Stx1) primarily involves depurination. A spontaneous DNA breakdown appears in fact only after extensive base removal, a behavior similar to that observed with uracil-DNA glycosylase, a simple glycosylase devoid of lyase activity. NaCl inhibits the activity of Stx1, probably by minimizing the sliding distance traveled by the enzyme along DNA in search of its target sites and promoting dissociation of the substrate-enzyme complex.

A survey of adenine and 4-aminopyrazolo[3,4-d]pyrimidine (4-APP) as inhibitors of ribosome-inactivating proteins (RIPs)

The inhibitory power of adenine and 4-aminopyrazolo[3,4-d]pyrimidine (4-APP) on the RNA-N-glycosidase activity catalyzed by bacterial (Shiga toxin 1) and plant (ricin, gelonin, momordin, bryodin-R, PAP-S, luffin, trichosantin, saporin 6 and barley) RIPs has been compared. The behavior of the two inhibitors is largely variable. While Shiga toxin 1 is preferentially inhibited by 4-APP, plant RIPs are either preferentially inhibited by adenine, or equally inhibited by the two compounds or, finally, only slightly more by 4-APP. Sequence variabilities involved in these different behaviors are discussed. The experimental data clearly indicate that, in spite of the same mechanism of action, RIPs differ widely in the ability to fit small ring molecules in the active cleft. While the strong inhibitory power of 4-APP on Shiga toxin 1 opens perspectives of therapeutic interventions, the ineffectiveness of the compound on ricin precludes its use as a suitable antidote in poisoning.

4-Aminopyrazolo[3,4-d]pyrimidine (4-APP) as a novel inhibitor of the RNA and DNA depurination induced by Shiga toxin 1

Shiga toxin 1 (Stx1) catalyses the removal of a unique and specific adenine from 28S RNA in ribosomes (RNA-N-glycosidase activity) and the release of multiple adenines from DNA (DNA glycosylase activity). Added adenine behaves as an uncompetitive inhibitor of the RNA-N-glycosidase reaction binding more tightly to the Stx1-ribosome complex than to the free enzyme. Several purine derivatives and analogues have now been assayed as inhibitors of Stx1. Most of the compounds showed only minor differences in the rank order of activity on the two enzymatic reactions catalysed by Stx1. The survey highlights the importance of the amino group in the 6-position of the pyrimidine ring of adenine. Shifting (2-aminopurine) or substituting (hypoxanthine, 6-mercapto-purine, 6-methylpurine) the group greatly decreases the inhibitory power. The presence of a second ring, besides the pyrimidine one, is strictly required. Substitution, by introducing an additional nitrogen, of the imidazole ring of adenine with triazole leads to loss of inhibitory power, while rearrangement of the nitrogen atoms of the ring from the imidazole to the pyrazole configuration greatly enhances the inhibitory power. Thus 4-aminopyrazolo[3,4-d]pyrimidine (4-APP), the isomer of adenine with the five-membered ring in the pyrazole configuration, is by far the most potent inhibitor of both enzymatic reactions catalysed by Stx1. This finding opens perspectives on therapeutic strategies to protect endothelial renal cells once endocytosis of Stx1 has occurred (haemolytic uraemic syndrome). In the RNA-N-glycosidase reaction 4-APP binds, as adenine, predominantly to the Stx1-ribosome complex (uncompetitive inhibition), while inhibition of the DNA glycosylase activity by both inhibitors is of the mixed type.

Attenuated expression of 70-kDa heat shock protein in WI-38 human fibroblasts during aging in vitro

We examined the effects of cellular aging on the expression of the heat shock-inducible HSP70 gene in WI-38 diploid human fibroblasts serially passaged in vitro. The senescence of the cells was established by evaluating population doubling level, cell density at confluency, and cell morphology along with the detection of senescence-associated beta-galactosidase activity (histochemically detectable at pH 6), a reliable marker of aging in low-density cultures. A marked decrease in the synthesis and accumulation of the inducible HSP70 protein was observed in serum-fed late passage cells exposed to a severe heat shock (30 min at 45 degrees C) in comparison to early passage cells. However, the degree of HSF-DNA binding, monitored by gel retardation assay was similar in both early and late passage cells. Similarly, Northern blotting analysis indicated that comparable amounts of inducible HSP70 mRNA were present in the total RNA fraction, in the total polyadenylated RNA fraction, or in the nuclear polyadenylated RNA fraction extracted from both early and late passage cells. In contrast, much less inducible HSP70 mRNA was detected in the total cytoplasmic RNA fraction or in the polyadenylated cytoplasmic RNA fraction of late passage cells. Thus age-related differences in heat-induced HSP70 synthesis and accumulation observed in serum-fed WI-38 cells appeared to result from an impairment in the posttranscriptional processing of the HSP70 mRNA at a level following the polyadenylation step and preceding translocation from the nucleus to the cytoplasm. When HF were serum deprived for 20 h before heat shock, the induction of HSP70 mRNA was less than 30% reduced in early passage cells in comparison to serum-fed cells; however, the level of HSP70 mRNA was markedly (over 80%) decreased in serum-deprived late passage cells. This result indicated that the presence of serum has a strong influence on heat shock-induced HSP70 gene expression in human fibroblasts aging in vitro.

Identity elements in bovine tRNA(Trp) required for the specific stimulation of gelonin, a plant ribosome-inactivating protein

Ribosome-inactivating proteins (RIPs) are RNA-N-glycosidases widely present in plants that depurinate RNA in ribosomes at a specific universally conserved position, A4324, in the rat 28S rRNA. A small group of RIPs (cofactor-dependent RIPs) require ATP and tRNA to reach maximal activity on isolated ribosomes. Among cofactor-dependent RIPs, gelonin is specifically and uniquely stimulated by tRNA(Trp). The active species are avian (chicken) and mammalian (beef, rat, and rabbit) tRNA(Trp), whereas yeast tRNA(Trp) is completely devoid of stimulating activity. In the present article, bovine and yeast tRNA(Trp) with unmodified bases were prepared by assembly of the corresponding genes from synthetic oligonucleotides followed by PCR and T7 RNA polymerase transcription of the amplified products. The two synthetic tRNAs were fully active (bovine) or inactive (yeast) as the wild-type tRNAs. Construction of chimeric tRNA(Trp) transcripts identified the following bovine nucleotides as recognition elements for gelonin-stimulating activity: G26 and bp G12-C23 in the D arm and G57, A59, and bp G51-C63 and U52-A62 in the T arm. Among single-stranded nucleotides, A59 has a prominent role, but full expression of the gelonin-stimulating activity requires an extensive cooperation between nucleotides in both arms.

A polymerase chain reaction (PCR) method for the identification of collagen adhesin gene (CNA) in Staphylococcus-induced prosthesis infections

Staphylococci are well-recognized pathogens of foreign body-associated infections. The pathogenesis of such infections involves an initial step of contact between the colonizing bacterium and the biomaterial, with subsequent colony formation. Several studies have been devoted to identify adhesion mechanisms for these bacteria. Slime in particular has been extensively investigated. Recently, considerable attention has been given to the host protein receptors that have been shown in in vitro assays to serve as substrates for bacterial adherence. To determine the importance of the collagen adhesin as virulence factor in Staphylococcus-induced prosthesis infection, a simple and reliable method using a polymerase chain reaction (PCR) was devised to identify collagen adhesin gene (cna). By using lysates of ten strains from orthopedic prostheses (5 Staphylococcus aureus and 5 Staphylococcus epidermidis) and two 20-oligonucleotides as primers, a 192-bp region of the cna gene was amplified by PCR and detected by agarose gel electrophoresis. Results obtained by this method were in accordance with those obtained by the in vitro phenotypic characterization of binding ability to collagen of Staphylococcus strains.

A rapid and sensitive method to measure the enzymatic activity of ribosome-inactivating proteins

A method is described in which the adenosine- N -glycosidase activity of ribosome-inactivating proteins (RIPs) is measured using as substrate a 2251 bp [3H]DNA obtained by PCR amplification of the 731-2981 region of the pBR322 plasmid. The DNA, labelled in the purine ring of adenine, proved a good substrate for all three RIPs tested (PAP-S, ricin and shiga-like toxin I). The method, which measures directly the [3H]adenine released, is highly specific, extremely rapid and quantitative in a wide range of RIP concentrations.

Identification of the tRNAs which up-regulate agrostin, barley RIP and PAP-S, three ribosome-inactivating proteins of plant origin

Ribosome-inactivating proteins (RIP) are RNA-N-glycosidases widely diffused in plants which depurinate ribosomal RNA at a specific universally conserved position, A4324 in rat ribosomes. A small group of RIPs (cofactor-dependent RIPs) require ATP and tRNA to reach maximal activity on isolated ribosomes. The tRNA which stimulates gelonin was identified as tRNA(Trp). The present paper reports the identification of three other tRNAs which stimulate agrostin (tRNA(Ala)), barley RIP (tRNA(Ala), tRNA(Val)) and PAP-S (tRNA(Gly)), while for tritin-S no particular stimulating tRNA emerged. The sequences of tRNA(Val) and tRNA(Gly) correspond to the already known ones (rabbit and man, respectively). The tRNA(Ala) (anticodon IGC) identifies a new isoacceptor. Only the stimulating activity of the tRNA(Ala) for agrostin approaches the specificity previously observed for the couple gelonin-tRNA(Trp).