In vivo expression of virulence genes of Yersinia pseudotuberculosis

The common virulence plasmid of pathogenic Yersinia species encodes a number of secreted proteins denoted Yops. YopE and YopH are indispensable for virulence and act in concert to mediate resistance to phagocytosis. In vitro all yop genes are coordinately regulated, with maximal expression and secretion at 37 degrees C in medium lacking Ca2+. In order to facilitate studies of in vivo expression of yopE and yopH we constructed operon fusions between these two genes and a promoterless luxAB operon from Vibrio harveyi in Y. pseudotuberculosis. Groups of 10 mice were infected with each fusion strain, and colonization and luciferase expression in Peyer's patches and spleen were followed by sacrificing two mice from each group daily. Peyer's patches were found to be colonized from the first day of infection, whereas the spleen was not colonized until the third day of infection. Luciferase expression could easily be monitored if the sample contained > or = 10(4) bacteria. Expression levels tended to be highest at the early stages of colonization for the respective organ (day 1 for Peyer's patches and day 3 or 4 for spleen). When in vivo expression was compared with in vitro expression, it was found that during infection the expression levels were as high or even higher than the in vitro expression observed for strains grown at 37 degrees C in Ca(2+)-depleted media.

A secreted protein kinase of Yersinia pseudotuberculosis is an indispensable virulence determinant

Phosphorylation of proteins catalysed by protein kinases is associated with central functions in growth and proliferation of the eukaryotic cell, and kinases are particularly important in the signal transduction pathways. Enterobacterial protein kinases are structurally and functionally different from eukaryotic protein kinases, and no prokaryotic kinase has so far been described implicating a direct role for this activity in virulence. Virulent Yersinia possess a common virulence plasmid that encodes a number of secreted proteins (Yops), of which YopH has protein-tyrosine phosphatase activity with a key function in the block of phagocytosis by the pathogen. Here we report that the virulence plasmid of Yersinia pseudotuberculosis encodes a secreted protein kinase (YpkA) with extensive homology to eukaryotic Ser/Thr protein kinases. Specific mutants of ypkA resulted in avirulent strains. Thus, YpkA is, to our knowledge, the first reported prokaryotic secreted protein kinase involved in pathogenicity, presumably by interfering with the signal transduction pathways of the target cell.

Influence of body mass on cross-country ski racing performance

The influence of body mass on cross-country skiing performance was evaluated by (i) a theoretical analysis of the relationship between body mass (M) and on one hand the maximal aerobic power and on the other the power expense of skiing, (ii) timing skiers in varied terrain during ski racing, (iii) comparing racing success between light and heavy skiers, and (iv) relating maximal aerobic power of skiers and power expense of skiing to body mass. The theoretical analysis indicated that the maximal aerobic power scaled with M2/3, while the mass exponent for the power expenses ranged from 1/3 to 1. The net result was that heavy skiers appear to be favored in all types of terrain but the steep uphills. During ski racing, heavy skiers displayed a tendency to be faster in all types of terrain, although no statistically significant effect was found. The racing success tended to be greater in heavy skiers among males but not among females. During skiing, maximal aerobic power and the power expense of skiing scaled with M0.7 and M0.4, respectively, indicating an advantage for the heavy skier. Altogether, these observations indicate that heavy skiers are favored, but also that other factors are more important than body mass for cross-country ski racing performance.

A novel protein, LcrQ, involved in the low-calcium response of Yersinia pseudotuberculosis shows extensive homology to YopH

The plasmid-encoded yop genes of pathogenic yersiniae are regulated by the environmental stimuli calcium and temperature. A novel protein, LcrQ, which exhibits a key function in the negative calcium-controlled pathway, was identified. DNA sequence analysis revealed that LcrQ has a molecular mass of 12,412 daltons and its isoelectric point is 6.51. Overexpression of LcrQ in trans in wild-type Yersinia pseudotuberculosis YPIII(pIB102) changed the phenotype from calcium dependence to calcium independence and inhibited Yop expression. LcrQ is expressed from a monocistronic operon. Trans overexpression of LcrQ in yopN and lcrH mutants affected the phenotype of the yopN mutant (temperature sensitive to calcium independence) but not that of the lcrH mutant (temperature sensitive), suggesting that LcrQ acts between YopN and LcrH in the calcium-regulated pathway. An lcrQ mutant was found to be temperature sensitive for growth and showed derepressed Yop expression at 37 degrees C in the presence of calcium in the growth medium. During these culture conditions, the lcrQ mutant secreted only LcrV and YopD into the culture supernatant. Removal of Ca2+ from the growth medium resulted in a Yop expression pattern of the mutant that was identical to that of the wild-type strain. The LcrQ protein was recovered from the culture supernatant. LcrQ shows 42% identity to the first 128 amino acids of the YopH virulence protein.

Intracellular targeting of the Yersinia YopE cytotoxin in mammalian cells induces actin microfilament disruption

Pathogenic Yersinia spp., including the etiological agent of plague, Y. pestis, all carry a common plasmid that encodes a number of essential virulence determinants, the Yop proteins. One of these, YopE, has been shown to be involved in the obstruction of the primary host defense by a molecular mechanism leading to inhibition of phagocytosis (R. Rosqvist, A. Forsberg, M. Rimpiläinen, T. Bergman, and H. Wolf-Watz, Mol. Microbiol. 4:657-667, 1990). Although the Yop proteins are secreted into the culture supernatant in vast amounts, in vitro studies of the function of the Yop proteins have so far been unsuccessful. We show that isolated Yop proteins indeed can cause cytotoxic effects in vitro if the proteins are introduced intracellularly into the eukaryotic cell. Isolated Yop proteins of Yersinia pseudotuberculosis were found to disrupt the microfilament structure when microinjected intracellularly into the host cell. In particular, YopE was demonstrated to be directly involved in the cytotoxic action, whereas YopD seems to have a critical role in translocating the YopE protein through the host cell membrane. These results elucidate the requirement for at least some of the Yop proteins to leave the pathogen during infection.

The surface-located YopN protein is involved in calcium signal transduction in Yersinia pseudotuberculosis

The low-calcium response (lcr) is strongly conserved among the pathogenic Yersinia species and is observed when the pathogen is grown at 37 degrees C in Ca(2+)-depleted medium. This response is characterized by a general metabolic downshift and by a specific induction of virulence-plasmid-encoded yop genes. Regulation of yop expression is exerted at transcriptional level by a temperature-regulated activator and by Ca(2+)-regulated negative elements. The yopN gene was shown to encode a protein (formerly also designated Yop4b) which is surface-located when Yersinia is grown at 37 degrees C. yopN was found to be part of an operon that is induced during the low-calcium response. Insertional inactivation of the yopN gene resulted in derepressed transcription of yop genes. A hybrid plasmid containing the yopN gene under the control of the tac promoter fully restored the wild-type phenotype of the yopN mutant. Thus the surface-located YopN somehow senses the calcium concentration and transmits a signal to shut off yop transcription when the calcium concentration is high.

Analysis of the V antigen lcrGVH-yopBD operon of Yersinia pseudotuberculosis: evidence for a regulatory role of LcrH and LcrV

Virulent Yersinia species possess a common plasmid that encodes essential virulence determinants (Yops) which are regulated by the extracellular stimuli Ca2+ and temperature. The V antigen operon was recently shown to be involved in the Ca2(+)-regulated negative pathway (A. Forsberg and H. Wolf-Watz, Mol. Microbiol. 2:121-133, 1988). We show here that the V antigen-containing operon of Yersinia pseudotuberculosis is a polycistronic operon having the gene order lcrGVH-yopBD. DNA sequencing analysis of lcrGVH revealed a high homology to the corresponding genes of Yersinia pestis. LcrG was conserved and LcrH showed only one amino acid difference, while LcrV showed only 96.6% identity. The amino acid substitutions of LcrV occurred in the central domain of the protein, while the two ends of the protein were conserved. Northern (RNA) blotting experiments showed that the operon is regulated at the transcriptional level by the extracellular stimuli temperature and calcium. One 4.6-kb transcriptional product of the operon was identified. This mRNA is rapidly processed at its 5' end, resulting in different mRNA species of variable stability. By genetic analysis, the lcrV and lcrH gene products were found to be regulatory proteins having important roles in the Ca2(+)-controlled regulation of Yop expression. The activity of LcrH is modulated by a gene product of the operon that inhibits the negative action of LcrH on yop transcription in the absence of Ca2+.

The relationship between body mass and oxygen uptake during running in humans

Oxygen uptake during treadmill running was measured at submaximal and maximal intensities in six different groups of endurance athletes (N = 134) and in seven endurance-trained men. The relationship between body mass (M) and oxygen uptake (VO2) was evaluated by deriving the exponent b in the equation VO2 = a.Mb. Thus, if b = 1, the oxygen uptake increases in proportion to body mass and oxygen uptake per kg is independent of body mass; if b less than 1, than the oxygen uptake per kg is inversely related to body mass. The exponent b was found to be less than unity for all groups for both submaximal (b = 0.76, s = 0.06) and maximal oxygen uptake (b = 0.71, s = 0.05). These results indicate that neither submaximal nor maximal oxygen uptake increases in proportion to body mass during running. The relationship between submaximal oxygen uptake and body mass observed in this study may explain why the oxygen uptake per kg of body mass has been found to be higher for children than for adults.

The cytotoxic protein YopE of Yersinia obstructs the primary host defence

It has previously been shown that the plasmid-encoded YopE protein of Yersinia pseudotuberculosis is a virulence determinant. In this study, HeLa cells, macrophages and mice were used as different model systems to determine the actual role of YopE in the virulence process. The YopE protein mediates a cytotoxic response on a confluent layer of HeLa cells. A prerequisite of this activity is that the pathogen binds to the cell surface. YopE also induces a cytotoxic response on mouse macrophages where it influences the ability of the pathogen to resist phagocytosis. Bacterial mutants defective in their ability to express YopE are avirulent after oral or intraperitoneal infection but virulent following intravenous injection. On the basis of these results, we propose a role for YopE in the virulence process of Yersinia.

Genetic analysis of the yopE region of Yersinia spp.: identification of a novel conserved locus, yerA, regulating yopE expression

The yopE gene of Yersinia pseudotuberculosis was recently sequenced, and YopE was identified as an indispensable virulence determinant when tested in a mouse model (A. Forsberg and H. Wolf-Watz, Mol. Microbiol. 2:121-133, 1988). In the study described here, the DNA sequences of the yopE genes of Yersinia pestis EV76 and Yersinia enterocolitica 8081 were determined and compared with that of the Y. pseudotuberculosis gene. Only two codons were found to differ, both leading to amino acid replacements, when the gene from Y. pestis was compared. These two replacements were also present in the gene from Y. enterocolitica; in addition, 18 other codons were found to differ. Thirteen of these substitutions led to amino acid replacements. Downstream of the yopE gene, the plasmid partition locus par was found to be conserved in all three species. In Y. enterocolitica 8081, the sequence homology was interrupted by a putative insertion sequence element inserted between the yopE gene and the par region at a position only 5 base pairs downstream of the yopE stop codon. Upstream of the yopE gene, 620 base pairs were conserved in the three species. This region contained a 130-amino-acid-long open reading frame reading in the opposite direction to the yopE gene and expressed a 14-kilodalton protein in minicells. An insertion mutation in this region constructed in Y. pseudotuberculosis expressed significantly lower amounts of YopE protein in vitro than did the corresponding wild type. The expression level could be restored by transcomplementation. This new locus was designated yerA, for yopE-regulating gene A. The yerA mutant was avirulent when mice were challenged by oral infection.

Identification and mapping of the temperature-inducible, plasmid-encoded proteins of Yersinia spp

The structural genes of the outer membrane polypeptides of Yersinia spp. (YOPs) and the V antigen of plasmid pIB1 of Yersinia pseudotuberculosis were recently cloned and mapped (A. Forsberg, I. Bölin, L. Norlander, and H. Wolf-Watz, Microb. Pathogen. 2:123-137, 1987). The corresponding genes were localized on pYV019 and pYV8081 of Yersinia pestis and Yersinia enterocolitica, respectively. No obvious differences were observed on comparison of pIB1 and pYV019, whereas pYV8081 showed intragenic as well as extragenic changes. However, one region of plasmid pYV8081, which coded for the V antigen, YOP3, and YOP4a, was essentially conserved among the three plasmids. Since this region is connected with the Ca2+ region, we suggest that the conserved region of the virulence plasmids of Yersinia spp. be extended to include both of these regions. Low amounts of the YOPs were detected in the membrane fraction at 37 degrees C in the presence of 2.5 mM calcium. Only minor differences were noticed when the individual YOPs of Y. pestis and Y. pseudotuberculosis were compared. Several differences were observed when the YOPs of Y. enterocolitica were included for comparison. All Y. enterocolitica proteins, except YOP1, YOP4b, and the V antigen, exhibited changes in their characteristic molecular sizes. Although these differences were within a range of +/- 2 kilodaltons, the isoelectric point was retained for each protein type.

The virulence protein Yop5 of Yersinia pseudotuberculosis is regulated at transcriptional level by plasmid-plB1-encoded trans-acting elements controlled by temperature and calcium

The DNA sequence of the structural gene (yopE) of one of the Yersinia pseudotuberculosis virulence plasmid-plB1-encoded proteins, Yop5, is presented. The deduced protein showed a molecular weight of 22,971 Daltons. A specific mutant, having a kanamycin-resistance fragment inserted within the yopE gene was no longer virulent for mice. The expression of the Yop5 protein is regulated at the level of transcription by temperature as well as by the Ca2+-concentration of the medium. A significant increase in the level of transcription was not detected until 45 min after a temperature shift from 26 degrees C to 37 degrees C in the absence of calcium; addition of Ca2+ inhibited the expression. The yopE promoter is under positive, as well as negative, plB1-encoded control. The positive function is solely regulated by temperature, while the regulation of the negative function involves at least five different plasmid-encoded gene loci; one of these genes encodes the V-antigen.

Studies on metal content in the brown seaweed, Fucus vesiculosus, from the Archipelago of Stockholm

Concentrations of eleven metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn) were determined in the brown seaweed Fucus vesiculosus collected from the Archipelago of Stockholm. Several factors which influence the metal content in the seaweed have been studied, including errors caused by epiphytes, sea exposure and differences depending on which part of the seaweed is analysed. It is concluded that, if all these factors are considered, Fucus vesiculosus plants are excellent bio-indicators of metal pollution. This is also demonstrated by a significant increase in metal content in transplanted Fucus vesiculosus near the city of Stockholm. The results from this investigation also indicate increasing metal concentrations, especially Cd, in samples from the northern parts of the Archipelago and the reason for this is discussed.

Concentrations of cadmium and other metals in Fucus vesiculosus L. and Fontinalis dalecarlica Br. Eur. from the northern Baltic Sea and the southern Bothnian Sea

Concentrations of Cd and ten other metals (Al, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn) were determined in the brown seaweed Fucus vesiculosus L. and the aquatic moss, Fontinalis dalecarlica Br. Eur. from the northern Baltic Sea and the southern Bothnian Sea. Elevated concentrations of metals were found in samples taken close to densely populated areas, such as Stockholm and Nynäshamn. Very high concentrations of especially Zn were found in both Fucus and Fontinalis samples taken from the area south of the Gulf of Gävle. The results indicate that mining and industrial activities along the river Dalälven are the main sources of Zn and several other metals. Cd concentrations in Fucus plants reached maximum values (24.5 mg kg(-1)) at the northern site. The gradual increase of Cd concentrations in Fucus plants northward could not be totally explained by the salinity gradient in the Baltic Sea; reasons for this are discussed in this paper.

Immunologic aberrations, HIV seropositivity and seroconversion rates in patients with hemophilia B

Because there have been reports that factor IX concentrate is less immunosuppressive and therefore factor IX users have less immunologic aberrations, we have studied a group of 22 patients with hemophilia B and six patients with factor VIII deficiency and high titer inhibitors with respect to lymphocyte numbers and function, human immunodeficiency virus (HIV) serology, and factor usage. This group was compared to 111 patients with hemophilia A and a group of 28 healthy male volunteer controls. When the study began in 1983, the majority of patients with hemophilia B and with higher titer factor VIII inhibitors were seronegative, 77% and 83% respectively, as compared to only 30% of patients with hemophilia A. At that time the factor IX users also had milder immune aberrations than the hemophilia A group. However, with time and increasing clotting factor concentrate usage, seroconversion and more striking abnormalities in immune function have occurred in the hemophilia B group. In a subgroup of 16 patients with hemophilia B studied twice, the incidence of seropositivity increased from 31% in 1983 to 69% in 1985. We thus conclude that factor IX concentrate in itself is not less immunosuppressive than factor VIII concentrate. Seroconversion in factor IX concentrate users appears to be lagging behind seroconversion in factor VIII concentrate users, perhaps secondary to the lower cumulative dosage of concentrate that patients with hemophilia B utilize.

Molecular cloning and expression of calcium-regulated, plasmid-coded proteins of Y. pseudotuberculosis

A number of plasmid-associated proteins (YOPs) of Y. pseudotuberculosis are induced and expressed at high levels when the pathogen is grown at 37 degrees C in absence of Ca2+ ions. These proteins were recovered both from the outer membrane fraction and the culture supernatant. Two hours after a temperature-shift the YOPs were only found in the culture supernatant, amounting to about 5% of the total cell protein. After 4 h of incubation they were also detected in the outer membrane fraction. Separation by 2-D gel electrophoresis revealed that the YOPs could be separated into 6 different polypeptides; YOP2a (45 kDa), YOP2b (45 kDa), YOP3 (41-42 kDa), YOP4a (34 kDa), YOP4b (34 kDa) and YOP5 (26 kDa). The structural genes of all of these YOPs, except the YOP2a gene, were cloned to pBR322 and their respective genetic localization was established. It was found that the genes were not part of a common operon but scattered around plasmid plB1. Only the YOP4b protein was found to map within the Ca2+ region. The hybrid plasmid plB572 coded for a number of plasmid plB1 specific proteins, one of which showed a molecular weight of 38 kDa. This polypeptide could be precipitated by monospecific V-antiserum, showing that this protein is the V-antigen.

High doses of fluoride do not affect cyclic AMP levels in human and rat plasma or urine

The effect of fluoride ingestion on plasma and urinary cyclic AMP levels was studied in healthy volunteers, children undergoing prophylactic fluoride treatment and in rats. In the first series of experiments fluoride ingestion led to a 20-fold increase in plasma fluoride concentration, which was unrelated to changes in plasma cyclic AMP. The only significant effect on plasma cyclic AMP occurred prior to fluoride, an effect attributed to stress. In the second series performed in children increases in urinary F- of up to 200-fold were associated with slight but nonsignificant changes in cyclic AMP excretion. In rat experiments the blood sampling procedure was associated with a rise in plasma cyclic AMP. When this was prevented by pretreatment with propranolol (3 mg/kg), the effect of fluoride (50 ppm in the drinking water) was tested. A fall in urine production was not associated with any change in cyclic AMP excretion or in nephrogenic cyclic AMP. It is concluded that if fluoride alters cyclic AMP in rats and man the effect is small and easily masked by other factors such as catecholamine release following stress.

Anterior tibial compartment pressure during race walking

In 14 race walkers the intramuscular pressure in the anterior tibial muscle was measured with a wick catheter. At rest the pressure was 10 to 15 mmHg and increased by a factor of 10 during full speed walking. Those walkers who experienced pain in the anterior tibial muscle also had a higher than average pressure. Fasciotomy decreased the intramuscular pressure and relieved the pain.

Kinetics for the inhibition of acetylcholinesterase from the electric eel by some organophosphates and carbamates

The inhibition kinetics for some organophosphates (paroxon, diisopropylfluorophosphate, sarin, VX, soman and soman isomers) and carbamates (physostigmine, neostigmine, pyridostigmine and carbaryl) in the reaction with acetylcholinesterase from electric eel have been studied. Dissociation constants and rate constants for the irreversible step were determined. The great differences in inhibitory power of the organophosphates were almost entirely due to differences in affinity. A possible correlation between affinity and bonding rate is discussed.

Platelet activation and mitral valve prolapse

Mitral valve prolapse (MVP) is a predisposing factor for cerebral ischemia, especially in young adults. Cerebral embolization of intracardiac thrombi is the probable mechanism in many cases. Platelets play a key role in the development of thrombi. We found that platelet factor 4, a marker protein of platelet activation, was elevated in 12 of 33 MVP patients (36%) without a history of stroke. This finding indicates that platelets are frequently activated in asymptomatic MVP patients and may allow identification of a subgroup of MVP patients with activated platelets who are at increased risk for emboli.

Marker proteins of platelet activation in patients with cerebrovascular disease

Platelet activation is assumed to occur in many patients with strokes of transient ischemic attacks (TIAs). Determination of this activity can now be measured by assaying the platelet-specific proteins, platelet factor 4 and beta-thromboglobulin. These proteins are platelet specific and are released during irreversible aggregation. The plasma level of these proteins was measured in patients with strokes and TIAs and both groups had significantly greater values than healthy control subjects. These markers of platelet activation may provide further understanding of the role of platelets in the etiology, diagnosis, and treatment of cerebrovascular disease.

Morphological muscle characteristics in rowers

Biopsies were taken from the vastus lateralis and deltoid muscle in twelve major senior rowers. Histochemical analyses showed a predominance of the oxidative type I fiber, a low content of the highly glycolytic type IIB fiber, large fiber areas, and a large number of capillaries surrounding the fibers. All these trends were more pronounced in the internationally competitive compared to the nationally competitive rowers. Exceptionally high aerobic capacities and muscular strengths, in competitive rowers, have been reported in previous papers as well as confirmed in the present study. The muscle morphology reported here is in line with the high aerobic demand in race rowing. However, strength has been shown to be more favoured by a high content of type II fibers which may appear contradictory to the present results. This question together with possible effects of physical training on the muscle morphology is discussed.