Complex Regulation of Gamma-Hemolysin Expression Impacts Staphylococcus aureus Virulence

Staphylococcus aureus gamma-hemolysin CB (HlgCB) is a core-genome-encoded pore-forming toxin that targets the C5a receptor, similar to the phage-encoded Panton-Valentine leucocidin (PVL). Absolute quantification by mass spectrometry of HlgCB in 39 community-acquired pneumonia (CAP) isolates showed considerable variations in the HlgC and HlgB yields between isolates. Moreover, although HlgC and HlgB are encoded on a single operon, their levels were dissociated in 10% of the clinical strains studied. To decipher the molecular basis for the variation in hlgCB expression and protein production among strains, different regulation levels were analyzed in representative clinical isolates and reference strains. Both the HlgCB level and the HlgC/HlgB ratio were found to depend on hlgC promoter activity and mRNA processing and translation. Strikingly, only one single nucleotide polymorphism (SNP) in the 5' untranslated region (UTR) of hlgCB mRNA strongly impaired hlgC translation in the USA300 strain, leading to a strong decrease in the level of HlgC but not in HlgB. Finally, we found that high levels of HlgCB synthesis led to mortality in a rabbit model of pneumonia, correlated with the implication of the role of HlgCB in severe S. aureus CAP. Taken together, this work illustrates the complexity of virulence factor expression in clinical strains and demonstrates a butterfly effect where subtle genomic variations have a major impact on phenotype and virulence. IMPORTANCE S. aureus virulence in pneumonia results in its ability to produce several virulence factors, including the leucocidin PVL. Here, we demonstrate that HlgCB, another leucocidin, which targets the same receptors as PVL, highly contributes to S. aureus virulence in pvl-negative strains. In addition, considerable variations in HlgCB quantities are observed among clinical isolates from patients with CAP. Biomolecular analyses have revealed that a few SNPs in the promoter sequences and only one SNP in the 5' UTR of hlgCB mRNA induce the differential expression of hlgCB, drastically impacting hlgC mRNA translation. This work illustrates the subtlety of regulatory mechanisms in bacteria, especially the sometimes major effects on phenotypes of single nucleotide variation in noncoding regions.

FBXO11 governs macrophage cell death and inflammation in response to bacterial toxins

Staphylococcus aureus causes severe infections such as pneumonia and sepsis depending on the pore-forming toxin Panton-Valentine leukocidin (PVL). PVL kills and induces inflammation in macrophages and other myeloid cells by interacting with the human cell surface receptor, complement 5a receptor 1 (C5aR1). C5aR1 expression is tighly regulated and may thus modulate PVL activity, although the mechanisms involved remain incompletely understood. Here, we used a genome-wide CRISPR/Cas9 screen and identified F-box protein 11 (FBXO11), an E3 ubiquitin ligase complex member, to promote PVL toxicity. Genetic deletion of FBXO11 reduced the expression of C5aR1 at the mRNA level, whereas ectopic expression of C5aR1 in FBXO11-/- macrophages, or priming with LPS, restored C5aR1 expression and thereby PVL toxicity. In addition to promoting PVL-mediated killing, FBXO11 dampens secretion of IL-1β after NLRP3 activation in response to bacterial toxins by reducing mRNA levels in a BCL-6-dependent and BCL-6-independent manner. Overall, these findings highlight that FBXO11 regulates C5aR1 and IL-1β expression and controls macrophage cell death and inflammation following PVL exposure.

LukS-PV inhibits hepatocellular carcinoma cells migration by downregulating HDAC6 expression

BACKGROUND

Hepatocellular carcinoma (HCC) is a clinically common malignant tumor worldwide. LukS-PV is the S component of Panton-Valentine leukocidin secreted by Staphylococcus aureus, which has shown anti-cancer activity. Based on previous findings, this study investigated the effects of LukS-PV on HCC migration and the potential molecular mechanisms involving acetylation pathways.

METHODS

After treating HCC cells with different concentrations of LukS-PV, we used scratch assays to determine the mobility of the cancer cells. Western blots were used to determine the expression levels of migration-related proteins. Quantitative proteomic sequencing was used to evaluate proteomic changes in target proteins. Immunoprecipitation and liquid chromatography coupled with tandem mass spectrometry analyses were used to validate the binding of related target proteins.

RESULTS

LukS-PV inhibited HCC cell migration in a concentration-dependent manner. In addition, LukS-PV attenuated the expression of histone deacetylase (HDAC)6, which is highly expressed in HCC cells. Further studies showed that LukS-PV increased the acetylation level of α-tubulin by down-regulating HDAC6, which resulted in the inhibition of HCC cell migration.

CONCLUSION

Taken together, our data revealed a vital role of LukS-PV in suppressing HCC cell migration by down-regulating HDAC6 and increasing the acetylation level of α-tubulin.

Increased Susceptibility of Humanized NSG Mice to Panton-Valentine Leukocidin and Staphylococcus aureus Skin Infection

Staphylococcus aureus is a leading cause of skin and soft-tissue infections worldwide. Mice are the most commonly used animals for modeling human staphylococcal infections. However a supra-physiologic S. aureus inoculum is required to establish gross murine skin pathology. Moreover, many staphylococcal factors, including Panton-Valentine leukocidin (PVL) elaborated by community-associated methicillin-resistant S. aureus (CA-MRSA), exhibit selective human tropism and cannot be adequately studied in mice. To overcome these deficiencies, we investigated S. aureus infection in non-obese diabetic (NOD)/severe combined immune deficiency (SCID)/IL2rγ^null (NSG) mice engrafted with human CD34⁺ umbilical cord blood cells. These “humanized” NSG mice require one to two log lower inoculum to induce consistent skin lesions compared with control mice, and exhibit larger cutaneous lesions upon infection with PVL⁺ versus isogenic PVL^-S. aureus. Neutrophils appear important for PVL pathology as adoptive transfer of human neutrophils alone to NSG mice was sufficient to induce dermonecrosis following challenge with PVL⁺S. aureus but not PVL^-S. aureus. PMX53, a human C5aR inhibitor, blocked PVL-induced cellular cytotoxicity in vitro and reduced the size difference of lesions induced by the PVL⁺ and PVL^-S. aureus, but PMX53 also reduced recruitment of neutrophils and exacerbated the infection. Overall, our findings establish humanized mice as an important translational tool for the study of S. aureus infection and provide strong evidence that PVL is a human virulence factor.

S. aureus infection has emerged in the past decade as a major burden to public health and is responsible for a surge in preclinical research. Mice are the most commonly studied animals for modeling of human S. aureus infection. However, it is increasingly evident that available murine models poorly mimic human S. aureus disease. Routinely, a supra-physiologic inoculum is required to establish soft-tissue pathology. Additionally, many S. aureus factors exhibit unique human tropism and cannot be adequately investigated in rodents. Here we investigated S. aureus infection in NSG mice engrafted with human umbilical CD34⁺ cells. We showed that a one to two log lower infectious inoculum of S. aureus establishes consistent skin lesions in humanized NSG mice. This inoculum is comparable to published inocula required to induce infection in humans. In addition, we showed that Panton-Valentine Leucocidin, a human tropic factor secreted by S. aureus, contributes to the development of dermonecrosis in the humanized mice, and its interaction with human neutrophils and human C5a receptor appears to be important for immunopathology. Overall our study suggests that humanized mice are an improved tool for modeling of human S. aureus infection.

Separately or combined, LukG/LukH is functionally unique compared to other staphylococcal bicomponent leukotoxins

Staphylococcus aureus is a major human pathogen that elaborates several exotoxins. Among these are the bicomponent leukotoxins (BCLs), which include γ-hemolysin, Panton-Valentine leukocidin (PVL), and LukDE. The toxin components are classified as either F or S proteins, which are secreted individually and assemble on cell surfaces to form hetero-oligomeric pores resulting in lysis of PMNs and/or erythrocytes. F and S proteins of γ-hemolysin, PVL and LukDE have ∼ 70% sequence homology within the same class and several heterologous combinations of F and S members from these three bicomponent toxin groups are functional. Recently, an additional BCL pair, LukGH (also called LukAB) that has only 30% homology to γ-hemolysin, PVL and LukDE, has been characterized from S. aureus. Our results showed that LukGH was more cytotoxic to human PMNs than PVL. However, LukGH-induced calcium ion influx in PMNs was markedly attenuated and slower than that induced by PVL and other staphylococcal BCLs. In contrast to other heterologous BCL combinations, LukG in combination with heterologous S components, and LukH in combination with heterologous F components did not induce calcium ion entry or cell lysis in human PMNs or rabbit erythrocytes. Like PVL, LukGH induced IL-8 production by PMNs. While individual components LukG and LukH had no cytolytic or calcium influx activity, they each induced high levels of IL-8 transcription and secretion. IL-8 production induced by LukG or LukH was dependent on NF-κB. Therefore, our results indicate LukGH differs functionally from other staphylococcal BCLs.

Staphylococcal Panton-Valentine leukocidin induces pro-inflammatory cytokine production and nuclear factor-kappa B activation in neutrophils

Panton-Valentine leukocidin (PVL) is a cytotoxin secreted by Staphylococcus aureus and associated with severe necrotizing infections. PVL targets polymorphonuclear leukocytes, especially neutrophils, which are the first line of defense against infections. Although PVL can induce neutrophil death by necrosis or apoptosis, the specific inflammatory responses of neutrophils to this toxin are unclear. In this study, both in vivo and in vitro studies demonstrated that recombinant PVL has an important cytotoxic role in human neutrophils, leading to apoptosis at low concentrations and necrosis at high concentrations. Recombinant PVL also increased the levels of pro-inflammatory cytokine secretion from neutrophils. The up-regulation of pro-inflammatory cytokines was due to nuclear factor-kappa B (NF-κB) activation induced by PVL. Moreover, blocking NF-κB inhibited the production of inflammatory cytokines. To test the role of neutrophil immune responses during the pathogenesis of PVL-induced acute lung injury, we used immunocompetent or neutropenic rabbits to develop a model of necrotizing pneumonia. Immunocompetent rabbits challenged with PVL demonstrated increased inflammation containing neutrophilic infiltrates. In addition, there were elevated levels of inflammatory cytokines (IL-6, IL-8, TNF-α and IL-10) and NF-κB in the lung homogenate. In contrast, the lung tissues from neutropenic rabbits contained mild or moderate inflammation, and the levels of inflammatory cytokines and NF-κB increased only slightly. Data from the current study support growing evidence that neutrophils play an important role in the pathogenesis of PVL-induced tissue injury and inflammation. PVL can stimulate neutrophils to release pro-inflammatory mediators, thereby causing an acute inflammatory response. The ability of PVL to induce inflammatory cytokine release may be associated with the activation of NF-κB or its pore-forming properties.

[Epidemiology and clinical presentation of Panton-Valentin leukocidin positive methicillin-resistant Staphylococcus aureus]

INTRODUCTION

the aim of our study was to review the epidemiology and clinical manifestations of infections due to Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus (PVL-MRSA).

MATERIAL AND METHODS

Medical history of patients infected by MRSA-PVL admitted to our hospital from January 2007 to July 2009 was reviewed. PVL and the type of cromosomic cassette were determined in all strains by PCR.

RESULTS

A total of 37 cases were included. Seventy percent were males and the median age was 39 years. Sixtytwo percent were Spanish, 14 (37.8%) were HIV-positive and 11 (29.7%) were homosexual. The source of the infection was the skin and soft tissue in 36 cases and pneumonia in 1. Sixteen patients were hospitalized, 5 had bacteremia and 5 developed septic metastasis. The relapse rate was 24% (9 cases). The prevalence during the study period was 11.2% of all MRSA isolated (37 out of 329). All the strains had a cromosomic cassette type IV and were susceptible to cotrimoxazole, rifampin, vancomyin, daptomycin and linezolid. The MIC of vancomycin, measured by E-test, was ≥ 1.5 mg/L in 28 out of 34 cases (82.3%).

CONCLUSIONS

Eleven percent of the MRSA strains isolated in our hospital are PVL positive. In general, skin and soft tissue infections are the most common and bacteremia or septic metastasis are frequent. In contrast to previous Spanish studies, more cases are observed in patients born in Spain and the infections are more severe.

Recombinant immunotoxins for the treatment of chemoresistant hematologic malignancies

Recombinant immunotoxins are proteins composed of fragments of monoclonal antibodies fused to truncated protein toxins. No agents of this class are approved yet for medical use, although a related molecule, denileukin diftitox, composed of interleukin-2 fused to truncated diphtheria toxin, is approved for relapsed/refractory cutaneous T-cell lymphoma. Recombinant immunotoxins which have been tested in patients with chemotherapy-pretreated hematologic malignancies include LMB-2 (anti-CD25), BL22 (CAT-3888, anti-CD22) and HA22 (CAT-8015, anti-CD22), each containing an Fv fragment fused to truncated Pseudomonas exotoxin. Major responses were observed with LMB-2 in adult T-cell leukemia, chronic lymphocytic leukemia (CLL), cutaneous T-cell lymphoma, Hodgkin's disease, and hairy cell leukemia (HCL). BL22 resulted in a high complete remission rate in patients with HCL, particularly those without excessive tumor burden. HA22, an improved version of BL22 with higher affinity to CD22, is now undergoing phase I testing in HCL, CLL, non-Hodgkin's lymphoma, and pediatric acute lymphoblastic leukemia.

Infective Pyomyositis and Myositis in Children in the Era of Community‐Acquired, Methicillin‐ResistantStaphylococcus aureusInfection

BACKGROUND

Cases of pyomyositis and myositis have been increasing in frequency at Texas Children's Hospital (Houston) since 2000. The increase appears to correlate with the emergence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

The medical records of patients with pyomyositis and myositis hospitalized at Texas Children's Hospital during the period from January 2000 through December 2005 were reviewed. Available S. aureus isolates were obtained for susceptibility testing, to determine the presence of pvl (lukS-PV and lukF-PV), and for pulsed-field gel electrophoresis analysis.

RESULTS

Forty-five previously healthy children with bacterial pyomyositis or myositis were analyzed. The causes were S. aureus (in 57.8% of children) and Streptococcus pyogenes (in 2.2%); 40.0% of children had negative culture results. The number of cases increased between 2000 and 2005, primarily as a result of an increase in the prevalence of community-acquired MRSA. The mean patient age was 5.5 years (range, 0.06-15 years). The thigh (40.0% of children) and pelvis (28.9%) were the most commonly affected sites. The mean abscess diameter was 3.5 cm. Eighteen children required at least 1 muscle drainage procedure. Of the 24 available S. aureus isolates (15 community-acquired MRSA isolates and 9 community-acquired, methicillin-susceptible S. aureus [MSSA] isolates), 16 were found to be USA300 by pulsed-field gel electrophoresis, and 17 carried pvl. Patients with community-acquired MRSA, USA300, and/or pvl-positive strains required more drainage procedures than did those with community-acquired MSSA, non-USA300, and/or pvl-negative strains (81% vs. 40% [P=.05], 82% vs. 29% [P=.02], and 81% vs. 38% [P=.07], respectively).

CONCLUSIONS

Community-acquired MRSA is an increasing cause of pyomyositis and myositis in children. Community-acquired MRSA, USA300, pvl-positive S. aureus isolates caused more severe disease than did community-acquired MSSA, non-USA300, and pvl-negative isolates, respectively.

Staphylococcus aureus Panton-Valentine leukocidin directly targets mitochondria and induces Bax-independent apoptosis of human neutrophils

Panton-Valentine leukocidin (PVL) is a pore-forming toxin secreted by Staphylococcus aureus that has recently been associated with necrotizing pneumonia. In the present study, we report that in vitro, PVL induces polymorphonuclear cell death by necrosis or by apoptosis, depending on the PVL concentration. PVL-induced apoptosis was associated with a rapid disruption of mitochondrial homeostasis and activation of caspase-9 and caspase-3, suggesting that PVL-induced apoptosis is preferentially mediated by the mitochondrial pathway. Polymorphonuclear cell exposure to PVL leads to mitochondrial localization of the toxin, whereas Bax, 1 of the 2 essential proapoptotic members of the Bcl-2 family, was still localized in the cytosol. Addition of PVL to isolated mitochondria induced the release of the apoptogenic proteins cytochrome c and Smac/DIABLO. Therefore, we suggest that PVL, which belongs to the pore-forming toxin family, could act at the mitochondrion level by creating pores in the mitochondrial outer membrane. Furthermore, LukS-PV, 1 of the 2 components of PVL, was detected in lung sections of patients with necrotizing pneumonia together with DNA fragmentation, suggesting that PVL induces apoptosis in vivo and thereby is directly involved in the pathophysiology of necrotizing pneumonia.

Staphylococcus aureus leucocidin, a virulence factor in bovine mastitis

The involvement of Staphylococcus aureus exosecretions in bovine udder infection (Younis et al. 2003) suggests that four different monomer protein bands appearing between 36 and 31 kDa, are associated with the severity of the cow's infection response. Three out of these four bands have been identified by means of protein sequencing. Band B, with a MW of 35 kDa was identified as Panton-Valentaine leucocidin LukF'-PV chain- Staph. aureus; band C, with a MW of 32 kDa was identified as leucocidin chain LukM precursor- Staph. aureus; and band D was found to be similar, but not identical, to phosphatidylinositol-specific phospholipase-C-X. Bands B and C were purified by gel filtration using FPLC. The ability of these proteins to induce udder inflammation in vivo, and proliferation response in vitro and cytokine secretion were tested for both the crude exosecretions and purified bands. Three cows were inoculated intracisternally, with three quarters receiving either 0·007–0·008 mg (as total proteins) of Staph. aureus FR2449/1 bacterial exosecretion, pooled fraction 39–41 (bands B and C), or culture broth medium. The fourth quarter was left free as a control. Quarters that received fraction 39–41 of Staph. aureus FR2449/1, exhibited induced inflammation, which was indicated by increased somatic cell count and enhanced NAGase activity that was significantly higher than that of the original Staph. aureus FR2449/1 bacterial exosecretion. Proliferation tests of bovine blood lymphocytes in vitro showed that the pooled fraction 39–41 stimulated bovine proliferation of mononuclear cells much more than the original Staph. aureus FR2449/1 bacterial exosecretion. Secretion of TNF-α, IL-1β, IL-6 and IL-8 was in accordance with the contents of LukF'-PV and LukM precursor in the exosecretions. The results suggest that LukM/LukF' induce inflammation into the udder by a mechanism similar to that of LPS or by a unique mechanism(s) which requires further investigation.

Purification, cloning and characterization of variant LukE-LukD with strong leukocidal activity of staphylococcal bi-component leukotoxin family

Staphylococcus aureus produces bi-component leukotoxins composed of non-associated soluble proteins, S and F. Neither S nor F component alone is cytotoxic, but components together are active. These include Panton-Valentine leukocidin (PVL), gamma-hemolysin, LukE-LukD and others. Purification of leukotoxin from Staphylococcus aureus V8 strain (ATCC 27733) which does not have PVL genes, identified an F component with 100% identical to that of PVL in the first twenty-five N-terminal amino acids. Molecular cloning of this toxin obtained 2,595 nucleotides sequences containing two novel open reading frames for S and F. Deduced amino acid sequences of the S and F were respectively 91 and 94% identical to those of LukE and LukD. These were named variant of LukE-LukD (LukEv-LukDv). The activity of the recombinant LukEv-LukDv to rabbit leukocytes was similar to that of recombinant PVL. LukEv-LukDv was hemolytic to rabbit red blood cells although the activity was only 8% of gamma-hemolysin, but PVL was not. These activities were quite different from the LukE-LukD which was reported no hemolytic and poorly cytotoxic to leukocytes compared to PVL. The lukEv-IukDv was found in 87% of clinical isolates of Staphylococcus aureus but lukE-lukD was not detected. These data demonstrate the existence of variant LukE-LukD in V8 strain (ATCC 27733).

Retrieving biological activity from LukF-PV mutants combined with different S components implies compatibility between the stem domains of these staphylococcal bicomponent leucotoxins

Bicomponent leucotoxins, such as Panton-Valentine leucocidin, are composed of two classes of proteins, a class S protein such as LukS-PV, which bears the cell membrane binding function, and a class F protein such as LukF-PV, which interacts to form a bipartite hexameric pore. These leucotoxins induce cell activation, linked to a Ca(2+) influx, and pore formation as two consecutive and independently inhibitable events. Knowledge of the LukF-PV monomer structure has indicated that the stem domain is folded into three antiparallel beta-strands in the water-soluble form and has to refold into a transmembrane beta-hairpin during pore formation. To investigate the requirements for the cooperative assembly of the stems of the S and F components to produce biological activity, we introduced multiple deletions or single point mutations into the stem domains of LukF-PV and HlgB. While the binding of the mutated proteins was weakly dependent on these changes, Ca(2+) influx and pore formation were affected differently, confirming that they are independent events. Ca(2+) entry into human polymorphonuclear cells requires oligomerization and may follow the formation of a prepore. The activity of some of the LukF-PV mutants, carrying the shorter deletions, was actually improved. This demonstrated that a crucial event in the action of these toxins is the transition of the prefolded stem into the extended beta-hairpins and that this step may be facilitated by small deletions that remove some of the interactions stabilizing the folded structure.

Identification of serine138 residue in the 4-residue segment K135K1361137S138 of LukS-I component of Staphylococcus intermedius leukocidin crucial for the LukS-I-specific function of staphylococcal leukocidin

Luk-I produced by Staphylococcus intermedius was found to be a new member of the staphylococcal bi-component pore-forming toxin family, in which staphylococcal leukocidin, Panton-Valentine leukocidin, and gamma-hemolysin are included. Luk-I consists of LukS-I and LukF-I. From the deduced amino acid sequence of LukS-I, a 4-residue sequence, K135K1361137S138, at the root of the stem region was found to be identical with that of the phosphorylated segment of a protein phosphorylated by protein kinase A. A mutant of LukS-I (MLSI-SA), in which the Ser138 residue was replaced by an alanine residue, was created, purified, and assayed for its leukocytolytic and pore-forming activities with LukF-I. Both LukS-I and MLSI-SA formed a ring-shaped complex with LukF-I on rabbit erythrocytes and human polymorphonuclear leukocytes (HPMNLs) membrane. However, MLSI-SA showed no leukocytolytic activity with LukF-I. LukS-I was phosphorylated by protein kinase A in the presence of [gamma-32P] ATP in a cell-free system, but MLSI-SA was not phosphorylated significantly. A potent and selective inhibitor of protein kinase A (N-[2(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89)) showed 50% inhibition of the Luk-I-induced cell lysis at 0.5 nM. Thus, it is concluded that the phosphorylation of the Ser138 residue in the 4-residue segment K135K1361137S138 of LukS-I is important for the leukocytolysis of HPMNLs.

[Leukocyanidines and collagenases: in vitro enzyme inhibition activity]

OBJECTIVE

The matrix metalloproteinases (MMPs) play a key role in the extracellular matrix turnover. This protein family has been involved in some ocular pathologies such as glaucoma, diabetic retinopathy, macular degeneration, vitreous degeneration and corneal stroma ulceration cleaving all the matrix components. In the present study we evaluated the action of leucocyanidin from Vitis vinifera seeds as non toxic inhibitor of these proteinases.

MATERIALS AND METHODS

To this purpose we used a fluorimetric method to evaluate the effect of this substance on the collagenase activity. We evaluated "in vitro" the inhibitory potency of the tested drug on type III collagenase activity, and the recover of the metalloprotease activity upon removal by dialysis of the inhibitor.

RESULTS

The leucocyanidines extract (minimum procyanidines value of 95.0) resulted to be a good collagenase activity inhibitor showing an inhibition constant value, Ki, of 82 microM, evident index of affinity between the extract and the enzyme. Furthermore, the dialysis experiments demonstrated that the inhibitory effect persisted 24 h later, probably because the extract forms a stable complex with the enzyme.

CONCLUSIONS

These results should be related to the pharmacokinetic profile of leucoanthocyanins, a family of natural polyphenols belonging to the class of bioflavonoids of grape seds extract (Vitis vinifera L.).

The structure of a Staphylococcus aureus leucocidin component (LukF-PV) reveals the fold of the water-soluble species of a family of transmembrane pore-forming toxins

BACKGROUND

Leucocidins and gamma-hemolysins are bi-component toxins secreted by Staphylococcus aureus. These toxins activate responses of specific cells and form lethal transmembrane pores. Their leucotoxic and hemolytic activities involve the sequential binding and the synergistic association of a class S and a class F component, which form hetero-oligomeric complexes. The components of each protein class are produced as non-associated, water-soluble proteins that undergo conformational changes and oligomerization after recognition of their cell targets.

RESULTS

The crystal structure of the monomeric water-soluble form of the F component of Panton-Valentine leucocidin (LukF-PV) has been solved by the multiwavelength anomalous dispersion (MAD) method and refined at 2.0 A resolution. The core of this three-domain protein is similar to that of alpha-hemolysin, but significant differences occur in regions that may be involved in the mechanism of pore formation. The glycine-rich stem, which undergoes a major rearrangement in this process, forms an additional domain in LukF-PV. The fold of this domain is similar to that of the neurotoxins and cardiotoxins from snake venom.

CONCLUSIONS

The structure analysis and a multiple sequence alignment of all toxic components, suggest that LukF-PV represents the fold of any water-soluble secreted protein in this family of transmembrane pore-forming toxins. The comparison of the structures of LukF-PV and alpha-hemolysin provides some insights into the mechanism of transmembrane pore formation for the bi-component toxins, which may diverge from that of the alpha-hemolysin heptamer.

Partial characterization and cloning of leuconocin J, a bacteriocin produced by Leuconostoc sp. J2 isolated from the Korean fermented vegetable Kimchi

Leuconostoc sp. J2, isolated from naturally fermented Kimchi, produced a bacteriocin which was named leuconocin J. This bacteriocin exhibited an inhibitory activity against several lactic acid bacteria and some food-borne pathogens. The antimicrobial substance was secreted into the medium during the late log phase. It appears to be proteinaceous since its activity was completely inactivated by a range of proteolytic enzymes, and it was also relatively heat-stable. The bacteriocin was partially purified by ammonium sulphate precipitation, following dialysis. The apparent molecular mass of partially purified bacteriocin, as indicated by activity detection after Tricine-SDS-PAGE, was 2.5-3.5 kDa. Leuconostoc sp. J2 plasmid DNA digested by EcoRI was cloned into pUC118 and transformed into Escherichia coli DH5 alpha. Phenotypic expression of the bacteriocin production was detected in transformants harboring pULBJ5.5. Finally, Southern blotting with the 2.3 kb insert as a probe against plasmid digests of Leuconostoc sp. J2 revealed that the cloned foreign DNA originated from Leuconostoc sp. J2.

The interaction of Staphylococcus aureus bi-component gamma-hemolysins and leucocidins with cells and lipid membranes

Staphylococcus aureus gamma-hemolysins (HlgA, HlgB and HlgC) and Panton-Valentine leucocidins (LukS-PV and LukF-PV) are bi-component toxins forming a protein family with some relationship to alpha-toxin. Active toxins are couples formed by taking one protein from each of the two subfamilies of the S-components (LukS-PV, HlgA and HlgC) and the F-components (LukF-PV and HlgB). We compared the mode of action of the six possible couples on leukocytes, red blood cells and model lipid membranes. All couples were leucotoxic on human monocytes, whereas only four couples (HlgA+HlgB, HlgC+HlgB, LukS-PV+HlgB and HlgA+LukF-PV) were hemolytic. Toxins HlgA+HlgB and HlgC+HlgB were also able to induce permeabilisation of model membranes by forming pores via oligomerisation. The presence of membrane-bound aggregates, the smallest and most abundant of which had molecular weight and properties similar to that formed by alpha-toxin, was detected by SDS-PAGE. By infrared spectroscopy in the attenuated total reflection configuration (FTIR-ATR), the secondary structure of both components and of the aggregate were determined to be predominantly beta-sheet and turn with small variations among different toxins. Polarisation experiments indicated that the structure of the membrane complex was compatible with the formation of a beta-barrel oriented perpendicularly to the plane of the membrane, similar to that of porins. The couple LukS-PV+LukF-PV was leucotoxic, but not hemolytic. When challenged against model membranes it was able to bind to the lipid vesicles and to form the aggregate with the beta-barrel structure, but not to increase calcein permeability. Thus, the pore-forming effect correlated with the hemolytic, but not with the complete leucotoxic activity of these toxins, suggesting that other mechanisms, like the interaction with endogenous cell proteins, might also play a role in their pathogenic action.

[Pore-forming leukotoxins from Staphylococcus aureus: variability of the target cells and 2 pharmacological processes]

The staphylococcal bi-component leukotoxins constitute a family included in the super-family of the beta-sheet-structured pore-forming toxins. They may be produced by Staphylococcus aureus and by Staphylococcus intermedius and their target cells vary according to the molecules. The mode of action proceeds by the sequential binding of the class S proteins, then by that of the class F proteins at the surface of the membranes. Then, the activation of cellular calcium-channels precedes the pore formation which seems to be sensitive to several monovalent cations. The cell response is inflammatory and includes the neosynthesis as well as the secretion of leukotriene B4, interleukin -8, histamine. The injection of leukotoxins to rabbits generates cell chemotaxis , vasodilatation, and tissue necrosis. The association of the production of leukotoxins with clinical syndromes concerns several aspects of the pathology of S. aureus, and confers to these leukotoxins an important role of virulence factors.

The staphylococcal pore-forming leukotoxins open Ca2+ channels in the membrane of human polymorphonuclear neutrophils

The ability of leukotoxins secreted by Staphylococcus aureus to modify the permeability of the membrane of human polymorphonuclear neutrophils has been studied by spectrofluorometry and appropriate fluorescent probes. This family of bicomponent leukotoxins is constituted by, at least, three pairs of proteins: LukS-PV/LukF-PV, HlgA/HlgB, HlgC/HlgB. After binding of both components to the membrane, each pair induces influxes of divalent cations and ethidium in polymorphonuclear neutrophils, although with different intensities. The influx of divalent cations appears sooner than the influx of ethidium. The pathway for divalent cations is not permeable to monovalent cations (Na+, K+, ethidium+) and is blocked by Ca2+ channel inhibitors that do not block the fluxes of ethidium and monovalent cations. It is concluded that the leukotoxins bind to a receptor linked to a divalent cation-selective channel or to the channel itself which is activated. Then, the leukotoxins open a second pathway by insertion into the membrane and subsequent formation of aspecific pores allowing an influx of ethidium.

Identification of the essential amino acid residues in lukS for the hemolytic activity of staphylococcal leukocidin towards rabbit erythrocytes

Staphylococcus aureus V8 (ATCC 49775) produces Panton-Valentine leukocidin (PVL) and leukocidin (Luk). PVL and Luk consist of LukF-PV and LukS-PV, and LukF and LukS, respectively. LukF and LukS cooperatively and strongly lyse rabbit erythrocytes besides human and rabbit polymorphonuclear leukocytes. LukF and LukS-PV also cooperatively lysed rabbit erythrocytes, but its activity was only 4% of that in combination [LukF-LukS] after 15 min of incubation. To identify the pivotal region responsible for the hemolytic function of LukS towards rabbit erythrocytes, we created a series of chimeric genes (lukS-PV/lukS) and mutant genes of lukS-PV and had them expressed in Escherichia coli. The chimeric and mutant proteins purified from the sonicated extract from the cells of E. coli were assayed for their hemolytic activities towards rabbit erythrocytes in combination with LukF or LukF-PV. The results indicate that a 2-residue segment (D12I13) of lukS is the minimum region essential for the hemolytic function of LukS towards rabbit erythrocytes.

Composition of staphylococcal bi-component toxins determines pathophysiological reactions

Staphylococcus aureus produces numerous bi-component toxins, e.g., Panton-Valentine leukocidin (Luk-PVL) and gamma-haemolysin, which consist of type S and F proteins. Previous studies showed that Luk-PVL induces inflammatory mediator release from human granulocytes that might reflect the in-vivo effects, e.g., dermonecrosis by Luk-PVL. Clinical isolates not only harbour the two genes coding for Luk-PVL (S-protein: LukS-PVL, F-protein: LukF-PVL) but also the three genes encoding gamma-haemolysin (S-protein: HlgA, HlgB; F-protein: HlgC). The interaction of all the possible potential toxins with human granulocytes was studied with regard to the generation of oxygen metabolites (chemiluminescence response), enzyme activity (beta-glucuronidase) and histamine release as well as interleukin (IL)-8 generation. The data clearly show that the individual subunits (S, F) differ in their activities. The following activities were obtained for the S components: LukS-PVL > HlgC > HlgA; the F components LukF-PVL and HlgB were similarly active. Thus, the toxins LukS-PVL/LukF-PVL and LukS-PVL/HlgB were the most potent inducers of inflammatory mediator release from human granulocytes, followed by HlgC/LukF-PVL and HlgC/HlgB and to a lesser degree by the toxins HlgA/LukF-PVL and HlgA/HlgB. The data indicate that class S components and class F components are interchangeable and give toxins with genuine biological activities.

Effects of Staphylococcus aureus leukocidins on inflammatory mediator release from human granulocytes

The secretion of the Panton-Valentine leukocidin (Luk-PV) but not of another leukocidin (Luk-R) from Staphylococcus aureus strains is correlated with severe pyodermic infections (dermonecrosis). The effects of both Luk-PV and Luk-R in amounts of 0-5000 ng on inflammatory mediator release from human leukocytes were studied. Luk-PV but not Luk-R induced a pronounced release of the vasodilator histamine from human basophilic granulocytes (up to 55% +/- 7%) and of enzymes (beta-glucuronidase, up to 45% +/- 10%; lysozyme, up to 35% +/- 7%), chemotactic components leukotriene B4 (42 +/- 8 ng/10(7) cells) and interleukin-8 (up to 33 +/- 5 ng/10(7) cells), and oxygen metabolites from human neutrophilic granulocytes. The results indicate that granulocytes play a central role in dermonecrosis; these in vitro data account for the histologic picture of Luk-PV infections, characterized by local vasodilation, infiltration of granulocytes, and a central necrotic area.

GTP-binding proteins are involved in the modulated activity of human neutrophils treated with the Panton-Valentine leukocidin from Staphylococcus aureus

Significant amounts of leukotriene B4 (LTB4) are generated by human polymorphonuclear neutrophils (PMNs) after incubation with the Panton-Valentine leukocidin (Luk-PV) from Staphylococcus aureus V8 strains. We showed that GTP-binding proteins (G proteins) are involved in the Luk-PV-activated signal transduction of PMNs. ADP-ribosylation of heterotrimeric G proteins by cholera and pertussis toxins decreased the Luk-PV-induced LTB4-generation. In contrast, ADP-ribosylation of the low-molecular-weight G proteins rho and rac by Clostridium botulinum exoenzyme C3 increased the Luk-PV-induced LTB4 synthesis. The subsequent stimulation of Luk-PV-treated PMNs by either calcium ionophore A23187, sodium fluoride, or formylmethionyl-leucyl-phenylalanine was significantly inhibited. This decrease was paralleled by a loss of G-protein functions, including GTPase activity and GTP-binding capacity. An increase of G-protein functions was obtained with low amounts of Luk-PV. In addition to the modulated G-protein functions, ADP-ribosylation of 24-, 40-, and 45-kDa proteins by Luk-PV was detected. As shown in control experiments, the ADP-ribosylated 24-kDa proteins were not substrates for C. botulinum exoenzyme C3. Introduction of ras p21 into digitonin-permeabilized PMNs was without effect on subsequent Luk-PV stimulation. In addition, the translocation of ras p21, ras GAP, and 5-lipoxygenase into the membrane of Luk-PV-treated PMNs, as well as the expression of chemotactic membrane receptors for LTB4 and formylmethionyl leucyl phenylalanine, was significantly diminished.

Leukotriene B4 generation and DNA fragmentation induced by leukocidin from Staphylococcus aureus: protective role of granulocyte-macrophage colony-stimulating factor (GM-CSF) and G-CSF for human neutrophils

We studied the effect of leukocidin from Staphylococcus aureus V8 strains (Luk-PV) on the generation of Leukotriene B4 (LTB4) and its metabolites from human polymorphonuclear neutrophils (PMNs). Significant amounts of LTB4 were generated by PMNs after leukocidin exposure in a time- and dose-dependent manner, as shown by reversed-phase high-performance liquid chromatography analysis. In this regard, the S and F components of leukocidin acted synergistically. The calcium ionophore A23187 induced LTB4 generation, and the metabolism of exogenously added LTB4 into biologically less active omega-oxidated compounds was significantly decreased after leukocidin exposure. Priming of PMNs with granulocyte-macrophage colony-stimulating factor (GM-CSF) or G-CSF prior to leukocidin exposure substantially increased toxin- and calcium ionophore A23187-induced LTB4 formation. The inhibitory effects of leukocidin on mediator release were accompanied by membrane damage and DNA fragmentation, which were both restored after pretreatment with GM-CSF. The data suggest that the presence of costimulatory priming factors such as GM-CSF or G-CSF in the microenvironment of an inflammatory focus determines the pathophysiological effects induced by S. aureus leukocidin.

Pore formation by a two-component leukocidin from Staphylococcus aureus within the membrane of human polymorphonuclear leukocytes

The effects of the Staphylococcus aureus leukocidin (PVL), a two-component non-hemolytic toxin, were investigated on the membrane permeability of human polymorphonuclear leukocytes (PMNs). In the absence of extracellular Ca2+, the fluorescence of ethidium bromide added to the extracellular medium increased after PVL application in a concentration-dependent manner and no variations in the free intracellular [Ca2+] of Fura2-loaded PMNs were detected. In the presence of extracellular Ca2+, the fluorescence of ethidium was not modified but the free intracellular [Ca2+] of PMNs increased after application of PVL in a concentration-dependent manner. The time lag observed before an increase in the ethidium fluorescence was longer than the time lag observed before a Fura2 fluorescence increase. Simultaneous recordings of the two probes fluorescence variations have shown the protective effect of Ca2+ and Zn2+ and the closing of the pore by 50 mM Ca2+ or 2 mM Zn2+. Moreover, the effect of Ca2+ could be reversed by the addition of EGTA. In the presence of 1 mM extracellular Ca2+ or 0.8 mM extracellular Zn2+, the pore induced by PVL had an ionic size allowing Ca2+, Mn2+, Zn2+ and Mg2+ fluxes. The addition of antibodies against either component of PVL inhibits the permeabilization provoked by the toxin even after it was initiated. It is concluded that leukocidin from S. aureus is a pore-forming toxin which, under physiological conditions ([Ca2+] = 1 to 1.5 mM), provokes the formation of an ion-sized pore inducing an increase in the free intracellular Ca2+ which may activate PMN functions.

Priming effect of pseudomonal leukocidin on chemiluminescence response of rabbit polymorphonuclear leukocytes

To clarify effects of pseudomonal leukocidin (42.5 kd) on chemiluminescence (CL) production of polymorphonuclear leukocytes (PMNs), rabbit PMNs were stimulated by zymosan or phorbol myristate acetate (PMA) after pretreatment with the leukocidin, which by itself stimulated little chemiluminescence response. The extent of CL responses stimulated by zymosan or PMA was respectively 5.3- or 3.5-fold greater in leukocidin (1.5 micrograms/ml)-pretreated PMNs than in non-pretreated ones. The priming effect of the leukocidin was greater than that of G-CSF and related to some steps before NADPH oxidase activation. The increased CL productions might be related to tissue damages caused by pseudomonal infections in vivo.

Changes in the susceptibility of 12-O-tetradecanoylphorbol 13-acetate (TPA)-treated HL-60 cells to staphylococcal leukocidin

Susceptibility of human promyelocytic leukemia HL-60 cells to staphylococcal leukocidin following treatment of cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) was examined. TPA treatment for 6 hr rendered the cells very resistant transiently to leukocidin. There was no change in binding of leukocidin to the cells, but leukocidin-induced 45CaCl2 influx, phospholipase A2 and C activities were inhibited. Further incubation with TPA rendered the cells sensitive again and then more sensitive than original HL-60 cells following increase of the binding, and leukocidin-induced activities described above appeared again. Those cells treated with TPA for more than 18 hr started to differentiate to macrophages morphologically and functionally. These data suggest that the differentiated cells were more sensitive than original HL-60 cells because of increased binding of leukocidin and that treatment of TPA for 6 hr may transiently impair the signal transduction system of leukocidin after binding of leukocidin to the specific receptor of the cell membrane. Using these TPA-treated cells, it was shown in this report that calcium influx, phospholipase A2 and C activities were important to induce cytotoxic action of leukocidin after binding of leukocidin to specific receptors on the cells.

Improved purification of leukocidin from Staphylococcus aureus and toxin distribution among hospital strains

For purification of F and S components of the Panton-Valentine leukocidin, an easy three-step method using fast protein liquid chromatography was developed to replace the time-consuming purification procedures previously published. This technique enabled the recovery of 13 and 17 mg of purified F and S, respectively, per litre of culture supernatant. Affinity-purified neutralizing polyclonal antibodies were obtained against each individual component. One hundred and thirty-nine Staphylococcus aureus strains isolated from various clinical samples of hospitalized patients were screened by immunoprecipitation for Panton-Valentine leukocidin (PVL) production. Only 8 strains produced PVL; all originated from injured superficial soft tissues. Contrary to widespread opinion, the 8 PVL-producing strains were never associated with severe infection.

Stimulatory effect of staphylococcal leukocidin on phosphoinositide metabolism in rabbit polymorphonuclear leukocytes

When rabbit polymorphonuclear leukocytes (PMNs) were incubated with staphylococcal leukocidin (F and S components) in the presence of 32Pi at 37 degrees C, incorporation of 32Pi into phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) occurred after a lag phase of 10 s and reached a maximal level at 60 s of 50- and 30-fold increase, respectively, compared with that of the control in the absence of the toxin. Whereas the amount of 32P radioactivity incorporated in PIP and PIP2 decreased to control levels in a few minutes, 32P incorporation into phosphatidic acid (PA) continuously increased over 3 min. These findings suggested an early activation of phosphoinositide-specific phospholipase C in rabbit PMNs by leukocidin as shown by the rapid breakdown of PIP and PIP2 accompanied by the appearance of PA. The stimulatory effect of leukocidin on some enzymatic activities of the phosphatidylinositol pathway was further investigated by using PMN cell membrane preparations. In the presence of both the F and S components, enhanced 32P incorporation was observed not only in PIP2 and PA but also in PIP. While the F component mainly enhanced 32P incorporation into PIP2 and PA, the S component alone had no effect on 32P incorporation into PIP, PIP2, and PA. The F component alone enhanced conversion of PIP to [32P]PIP2 in the presence of unlabeled PIP and [gamma-32P]ATP, through the activation of PIP kinase. PIP kinase activity was potentiated by the addition of NAD and GTP. Subsequent formation of [32P]PA was also enhanced by the F component, resulting from activation of the phosphoinositide-specific phospholipase C. These results suggested that the F component of staphylococcal leukocidin is responsible for the enhancement of phosphoinositide metabolism in rabbit PMN cell membranes.

ADP-ribosylation of cell membrane proteins by staphylococcal alpha-toxin and leukocidin in rabbit erythrocytes and polymorphonuclear leukocytes

Staphylococcal alpha-toxin resulted in ADP-ribosylation of the 37 and 41 kDa proteins of a membrane preparation from rabbit erythrocytes. In the presence of 100 microM GTP, the toxin ADP-ribosylated proteins of 54 and 59 kDa and potentiated ADP-ribosylation of the 37 and 41 kDa forms. GTP had no effect on ADP-ribosylation of membrane proteins in the absence of alpha-toxin. Incubation of a membrane preparation of rabbit polymorphonuclear leukocytes with the S and F components of staphylococcal leukocidin resulted in ADP-ribosylation of the 37 and 41 kDa proteins, respectively. Furthermore, the 37, 41, 54 and 59 kDa proteins were ADP-ribosylated by leukocidin in the presence of GTP. The ADP-ribosylation of these proteins was observed to be dependent on the incubation time and toxin dose and was abolished by prior boiling. Addition of agmatine did not attenuate ADP-ribosylation of these proteins. These results demonstrate that staphylococcal alpha-toxin and leukocidin possess ADP-ribosyltransferase activities which are potentiated by GTP and suggest that ADP-ribosylation reactions are responsible for development of the cytolytic activities of these staphylococcal toxins.

Effects of leukocidin from Fusobacterium necrophorum on bovine peripheral leukocytes in vitro

Partially purified leukocidin from Fusobacterium necrophorum damaged bovine peripheral leukocytes as demonstrated by trypan blue staining. Granulocytes were most and T-lymphocytes least sensitive to the leukocidin. Heating for 30 min at 60 degrees C completely inactivated the leukocidin. The cytotoxicity of the leukocidin could be neutralized by homologous anti-leukocidin. Scanning electron microscopy of the exposed cells revealed an apparent destruction of the cell membranes, loss of the microvilli and smoothing of the cell surfaces.

Non-thiol-activated cytolytic bacterial toxins: current status

Among non-thiol-activated cytolytic toxins, staphylococcal alpha-toxin, staphylococcal leucocidin, and pseudomonal leucocidin are characterized by their interaction (with susceptible cell membranes) as a biomembrane response modifier. The transmembrane signalling by the receptor-toxin complex follows the activities of membrane-associated enzymes, which lead to changes in membrane ion-permeability.

Cytotoxic effects of a leukocidin from Fusobacterium necrophorum on bovine hepatic cells

Cytotoxic effects of a leukocidin from Fusobacterium necrophorum were demonstrated on bovine hepatic cells. The cytotoxic response was dose-dependent and could be inhibited by homologous antiserum. Scanning electron microscopy revealed damaged hepatic cell surface. These findings indicated a pathogenic role of the leukocidin in F. necrophorum infections.

Partial characterization of leukocidin from Fusobacterium necrophorum

Leukocidin from Fusobacterium necrophorum was produced in the diffusate of a dialysis culture. It was free from deoxyribonuclease, fibrinolysin, gelatinase, haemolysin, lipase, caseinase and endotoxin. The leukocidin had a molecular weight between 10,000 and 5,000 as estimated by membrane partition chromatography. It formed precipitin lines with anti-leukocidin-serum in double immunodiffusion tests. Mouse peritoneal cells were characteristically damaged by the leukocidin, as revealed by scanning electron microscopy. The damaged cells lost microvilli and suffered partial destruction of their cell membranes.

Use of 51Cr release to measure the cytotoxic effects of staphylococcal leukocidin and toxin neutralization on bovine leukocytes

Leukocidin toxin from Staphylococcus aureus produces specific cytolytic effects on neutrophils and macrophages. The most commonly used method for determination of leukocidin activity is microscopic examination for characteristic morphological changes in toxin-treated cells. The 51Cr release assay was modified to allow quantitation of the cytolytic effects of leukocidin on bovine peripheral blood neutrophils and lymphocytes. Toxin neutralization by serum and milk samples was quantitated by this method. The neutralizing abilities of the various samples were found to correlate with the levels of immunoglobulin G (IgG1) specific for leukocidin. Undiluted normal serum samples, however, were capable of partially preventing the cytotoxic effects of leukocidin. The assay was shown to be an effective means of quantitating the cytotoxic activity of leukocidin on neutrophils as well as demonstrating neutralization of cytotoxicity by milk and serum samples.

Properties of the leak permeability induced by a cytotoxic protein from Pseudomonas aeruginosa (PACT) in rat erythrocytes and black lipid membranes

A cytotoxic protein, isolated from Pseudomonas aeruginosa (PACT), was tested on red blood cells of rats and on black lipid membranes for changes of membrane permeability. In rat erythrocytes PACT induces lysis indicative of the formation of a leak permeable to monovalent ions. The dose response curve for the PACT-induced hemolysis demonstrates that the rate of lysis as well as the fraction of lytic cells increases with increasing toxin concentration. Furthermore, the leak pathway discriminates hydrophilic non-electrolytes according to their molecular weight. The findings indicate formation by PACT of a pore with an apparent radius of about 1.2 nm. In pure lipid membranes PACT forms hydrophilic pathways with moderate selectivity for small cations over small anions. The presence of cholesterol is a prerequisite for the occurrence of these PACT-induced permeability changes.

An early effect of the S component of staphylococcal leukocidin on methylation of phospholipid in various leukocytes

On incubation of rabbit polymorphonuclear leukocytes with the S component of staphylococcal leukocidin at 37 degrees C, the 3H-labeled methyl group of S-adenosyl[methyl-3H]methionine was rapidly incorporated into phospholipid. Subsequently, the methylated phosphatidylcholine was degraded by activated phospholipase A2. Complete blockage of the methylation of phospholipid by a mixture of erythro-9-[2-hydroxy-3-nonyl]adenine, adenosine, and L-homocysteine thiolactone markedly inhibited the activation of phospholipase A2 by the S component. It also inhibited the binding of 125I-labeled F component to the cells, but not that of the labeled S component. These results suggest that methylation of phospholipid in the cell membranes by the S component results in activation of phospholipase A2, which induces the binding of the F component to the cells.

Action of a cytotoxin from Pseudomonas aeruginosa on human leukemic cell lines. Increase in cell permeability to Ca2+ and Mn2+ and lack of stimulation of inositol lipid turnover

Quin2 loaded human leukemic, JURKAT and K562 cells, were exposed to various doses of Pseudomonas aeruginosa cytotoxin. This cytotoxin induced an increase in quin2 fluorescence indicating an increase in the cytoplasmic free Ca2+ concentration. The rate of the fluorescence increase and the lag time before the response were dependent on the doses of the cytotoxin. Addition of MnCl2 to the cytotoxin-treated cells induced a decrease in the quin2 fluorescence at rates dependent on the doses of the cytotoxin. The cytotoxin did not stimulate the inositol lipid turnover in JURKAT cells, which was determined by the accumulation of [3H]inositol phosphates in myo-[2-3H]inositol-prelabeled cells in the presence of LiCl. These results indicate that the cytotoxin increases cell permeability to both Ca2+ and Mn2+ by direct breakdown of the permeability barrier of the plasma membrane.

Effect of Pseudomonas aeruginosa cytotoxin on thymidine incorporation by murine splenocytes

The interaction of highly purified Pseudomonas aeruginosa cytotoxin (PAC) with murine splenocytes was examined. Added at culture initiation, PAC (0.1 to 0.5 microgram/ml) inhibited subsequent [3H]deoxythymidine incorporation measured between 42 to 48 h. Incorporation of [3H]deoxythymidine was inhibited 50% in lipopolysaccharide-, phytohemagglutinin-, and concanavalin A-stimulated cultures by 0.20, 0.32, and 0.39 microgram of PAC per ml, respectively. It is concluded that PAC exhibits a narrow inhibitory concentration response range of 0.1 to 0.5 microgram/ml which, secondarily, is affected by the presence of mitogens. Antitoxin added at splenocyte culture initiation, directly after PAC, yielded greater than or equal to 86% protection against PAC inhibition of [3H]deoxythymidine incorporation. Addition of antitoxin to cultures at different times after PAC demonstrated a time-dependent loss of antitoxin protective effect over a 12-h period, indicating that PAC became cell associated and refractory to antitoxin within this time period. PAC preincubated with splenocytes at 4 degrees C for less than or equal to 1 h could not be removed by washing of cells and was fully inhibitory to [3H]deoxythymidine incorporation when these cells were cultured at 37 degrees C. This finding was confirmed by demonstrating that 125I-labeled PAC bound immediately to cells. It is concluded that PAC action on splenocytes is dose- and time-dependent and consists of a two-phase process: (i) a very rapid binding of PAC to the cell surface available to antitoxin, and (ii) a slower toxicity development phase of ca. 12 h, during which PAC becomes refractory to antitoxin.

Mode of cytotoxic action of pseudomonal leukocidin on phosphatidylinositol metabolism and activation of lysosomal enzyme in rabbit leukocytes

The cytotoxic action of leukocidin from Pseudomonas aeruginosa was supported by the following observations. (i) The destruction of rabbit leukocytes by the toxin was reduced in the absence of Ca2+ and stimulated by the addition of calcium ionophore A23187 but inhibited by EDTA, EGTA, and TMB-8, an antagonist of intracellular Ca2+ transport. (ii) Uptake of 45Ca into leukocytes exposed to the toxin was enhanced about threefold the rate of uptake into untreated cells. The increased 45Ca uptake into the cells was slightly inhibited by trifluoperazine, an inhibitor of Ca2+-calmodulin activity, but not by ruthenium red. (iii) Pseudomonal leukocidin enhanced rapidly the labeling of phosphatidylinositol, polyphosphoinositides, phosphatidic acid, and lysophosphatidic acid from [32P]phosphate. The time course experiments of the labeling and breakdown of these phospholipids suggested that the initial action of this toxin was to stimulate phosphatidic acid production, presumably causing a rapid metabolic change of phosphatidylinositol correlating with the activities of phosphatidylinositol-specific phospholipase C and 1,2-diacylglycerol kinase. It was considered that a rapid formation of phosphatidic acid and degradation of polyphosphoinositides might be related to a Ca2+ movement from extra- and intracellular space. (iv) In leukocytes exposed to the toxin, acid phosphatase activity as a marker enzyme of lysosome was activated up to 75% of the lysosomal enzyme before cell destruction. The leakage of lysosomal enzyme from the cells occurred at the almost same time as leukocyte destruction. The mode of cytotoxic action of pseudomonal leukocidin is discussed.

A rapid stimulation of phosphatidylinositol metabolism in rabbit leukocytes by pseudomonal leukocidin

The time course experiments of 32Pi-labelling and breakdown of phospholipids in rabbit leukocytes exposed to leukocidin from Pseudomonas aeruginosa suggested that the initial action of this toxin was to stimulate phosphatidic acid production, presumably by causing a rapid metabolic change of phosphatidylinositol (PI response) correlating with phosphatidylinositol-specific phospholipase C and 1,2-diacylglycerol kinase. It appears that a rapid formation of phosphatidic acid and degradation of polyphosphoinositides in leukocytes treated with the toxin might be related a Ca2+-movement from extra- and intracellular spaces, resulting in the activation of Ca2+-dependent enzymes involved in the leukocidic process.

Mode of action of staphylococcal leukocidin: effects of the S and F components on the activities of membrane-associated enzymes of rabbit polymorphonuclear leukocytes

The cytotoxic action of the S component of leukocidin from Staphylococcus aureus on rabbit polymorphonuclear leukocytes was supported by the following observations, (i) Leukocytes displayed a large chemotactic response to the S component (10(-10) M) as well as to the chemotactic factor N-formylmethionylleucylphenylalanine (10(-11) M). (ii) The S component stimulated high levels of phospholipase A2 activity in the cell membranes, with concomitant synthesis and release of prostaglandins. (iii) Uptake of 45Ca into leukocytes exposed to the S component was about double the rate of uptake into untreated cells. The increased 45Ca uptake into the cells was not inhibited by trifluoperazine and ruthenium red. (iv) Indomethacin and alloxazine, which had no effects on the binding of the S component to the cells, attenuated markedly the stimulation of phospholipase A2 activity, the syntheses of prostaglandins, and the increased uptake of 45Ca caused by the S component. The F component of leukocidin, bound to rabbit leukocytes with the aid of the S component, rapidly induced complete release of 86Rb from preloaded leukocytes. This release resulted from stimulation of ouabain-insensitive (Na+ + K+)-adenosine triphosphatase activity and inhibition of cyclic AMP-dependent protein kinase.

Effects of diphtheria toxin and other exotoxins on oxidant generation by human and murine phagocytes

Bacterial exotoxins such as diphtheria toxin (D.T.), staphylococcal alpha toxin and Leucocidin can powerfully activate granulocytes and macrophages as detected by production of chemiluminescence in presence of Luminol. Production of superoxide by granulocytes and of prostaglandin E2 in macrophages is also stimulated by D.T. In contrast with the known resistance of rodent parenchymal cells to the diphtheria toxin, human and rodent leucocytes have similar sensitivities to D.T.

Effect of staphylococcal leukocidin on mouse leukocyte system

Staphylococcal Panton-Valentine leukocidin has been purified and tested in mice for its biological properties. Applied even in high doses the leukocidin was not lethal. It caused however, disturbances in the peripheral blood occurring in several phases. First reaction after leukocidin injection was seen as marked granulocytosis persisting for 16-20 hours and accompanied by lymphopenia. At the same time, decrease in serum lysozyme activity and increase of intracellular digestion by mature granulocytes, was observed. In the second phase, these phenomena have reversed. 131I-labelled leukocidin has been used for the study of distribution of this toxin in the mouse. Accumulation of leukocidin in some tissues was observed. The leukocidin affected not only granulocytes but also other peripheral blood cells.