Characterization of a novel format scFv×VHH single-chain biparatopic antibody against metal binding protein MtsA

Biparatopic antibodies (bpAbs) are engineered antibodies that bind to multiple different epitopes within the same antigens. bpAbs comprise diverse formats, including fragment-based formats, and choosing the appropriate molecular format for a desired function against a target molecule is a challenging task. Moreover, optimizing the design of constructs requires selecting appropriate antibody modalities and adjusting linker length for individual bpAbs. Therefore, it is crucial to understand the characteristics of bpAbs at the molecular level. In this study, we first obtained single-chain variable fragments and camelid heavy-chain variable domains targeting distinct epitopes of the metal binding protein MtsA and then developed a novel format single-chain bpAb connecting these fragment antibodies with various linkers. The physicochemical properties, binding activities, complex formation states with antigen, and functions of the bpAb were analyzed using multiple approaches. Notably, we found that the assembly state of the complexes was controlled by a linker and that longer linkers tended to form more compact complexes. These observations provide detailed molecular information that should be considered in the design of bpAbs.

Group A Streptococcus cation diffusion facilitator proteins contribute to immune evasion by regulating intracellular metal concentrations

Cation diffusion facilitators (CDFs) are a large family of divalent metal transporters with broad specificities that contribute to intracellular metal homeostasis and toxicity in bacterial pathogens. Streptococcus pyogenes (Group A Streptococcus [GAS]) expresses two homologous CDF efflux transporters, MntE and CzcD, which selectively transport Mn and Zn, respectively. We discovered that the MntE- and CzcD-deficient strains exhibited a marked decrease in the viability of macrophage-differentiated THP-1 cells and neutrophils. In addition, the viability of mice infected with both deficient strains markedly increased. Consistent with a previous study, our results suggest that MntE regulates the PerR-dependent oxidative stress response by maintaining intracellular Mn levels and contributing to the growth of GAS. The maturation and proteolytic activity of streptococcal cysteine protease (SpeB), an important virulence factor in GAS, has been reported to be abrogated by zinc and copper. Zn inhibited the maturation and proteolytic activity of SpeB in the culture supernatant of the CzcD-deficient strain. Furthermore, Mn inhibited SpeB maturation and proteolytic activity in a MntE-deficient strain. Since the host pathogenicity of the SpeB-deficient strain was significantly reduced, maintenance of intracellular manganese and zinc levels in the GAS via MntE and CzcD may not only confer metal resistance to the bacterium, but may also play an essential role in its virulence. These findings provide new insights into the molecular mechanisms of pathogenicity, which allow pathogens to survive under stressful conditions associated with elevated metal ion concentrations during host infection.

Targeting hemoglobin receptors IsdH and IsdB of Staphylococcus aureus with a single VHH antibody inhibits bacterial growth

Methicillin-resistant Staphylococcus aureus, or MRSA, is one of the major causative agents of hospital-acquired infections worldwide. Novel antimicrobial strategies efficient against antibiotic-resistant strains are necessary and not only against S. aureus. Among those, strategies that aim at blocking or dismantling proteins involved in the acquisition of essential nutrients, helping the bacteria to colonize the host, are intensively studied. A major route for S. aureus to acquire iron from the host organism is the Isd (iron surface determinant) system. In particular, the hemoglobin receptors IsdH and IsdB located on the surface of the bacterium are necessary to acquire the heme moiety containing iron, making them a plausible antibacterial target. Herein, we obtained an antibody of camelid origin that blocked heme acquisition. We determined that the antibody recognized the heme-binding pocket of both IsdH and IsdB with nanomolar order affinity through its second and third complementary-determining regions. The mechanism explaining the inhibition of acquisition of heme in vitro could be described as a competitive process in which the complementary-determining region 3 from the antibody blocked the acquisition of heme by the bacterial receptor. Moreover, this antibody markedly reduced the growth of three different pathogenic strains of MRSA. Collectively, our results highlight a mechanism for inhibiting nutrient uptake as an antibacterial strategy against MRSA.

Biological Effect of Streptococcus pyogenes-Released Extracellular Vesicles on Human Monocytic Cells, Induction of Cytotoxicity, and Inflammatory Response

Most bacteria naturally release spherical lipid-bilayered extracellular vesicles (EVs) containing proteins, nucleic acids, and virulence-related molecules, thus contributing to diverse biological functions including transport of virulence factors. The group A streptococcus, Streptococcus pyogenes (GAS), a major human pathogen, also releases EVs; however, it remains unclear how GAS EVs interact physiologically and pathologically with host cells, and what the differences are between invasive and non-invasive strains. The proteome profile in this study revealed that GAS EVs enclosed many virulence-related proteins such as streptolysin O and NAD-glycohydrolase, facilitating their pathogenicity, and invasive GAS EVs were more abundant than non-invasive counterparts. In terms of biological effects, invasive GAS EVs showed slo-dependent cytotoxic activity and the induction of cytokine expression, contributing to GAS pathogenicity directly. Although non-invasive GAS EVs did not show cytotoxic activity, they may be utilized as a means to prevent antibacterial mechanisms such as autophagy, leading to enhancement of their own survival in the intracellular environment after the infection. These results suggest that invasive and non-invasive GAS EVs play different roles in GAS infection strategy and pathogenicity. Our findings also indicate that EVs could be a key factor for GAS pathogenicity in GAS-host interactions.

Single-chain variable fragment (scFv) targeting streptolysin O controls group A Streptococcus infection

Streptococcus pyogenes (Group A Streptococcus, GAS) causes a range of human diseases, including life-threatening and severe invasive GAS infections, such as streptococcal toxic shock syndrome (STSS). Several antibiotics, including penicillin, are effective against GAS. Still, invasive GAS diseases have a high mortality rate (>30%). Clinical isolates from STSS patients show higher expression of pore-forming streptolysin O (SLO). Thus, SLO is an important pathogenic factor for GAS and may be an effective target for treatment of GAS disease. We succeeded in obtaining a single-chain variable fragment (scFv) SLO-I4 capable of recognizing SLO, which significantly inhibited GAS-induced cell lytic activity in erythrocytes, macrophages, and epithelial cells. In epithelial cells, SLO-I4 significantly reduced SLO-mediated endosomal membrane damage, which consequently prevented bacterial escape from the endosome. The effectiveness of anti-SLO scFv in counteracting SLO function suggests that it might be beneficial against GAS infections.

Characterization of a putative maltodextrin-binding protein of Streptococcus pyogenes, SPs0871 and the development of a VHH inhibitor

Streptococcus pyogenes causes a wide range of human infections. Currently, antibiotics are the main treatment for S. pyogenes infection, but serious anti-microbial resistance requires alternative treatment options. To develop a novel strategy for treatment, we physicochemically characterized SPs0871, a putative maltose/maltodextrin-binding protein that is thought to have important roles in the pathogenesis of invasive streptococci. We obtained a variable domain of heavy chain of heavy-chain antibody, the smallest unit of an antibody, which specifically binds to SPs0871. Although the VHH completely inhibited the binding of maltodextrins to SPs0871, the inhibition did not lead to growth suppression of the bacteria. Our results provide important insights for development of VHH as an anti-streptococcal therapeutic.

TBC1D9 regulates TBK1 activation through Ca2+ signaling in selective autophagy

Invading microbial pathogens can be eliminated selectively by xenophagy. Ubiquitin-mediated autophagy receptors are phosphorylated by TANK-binding kinase 1 (TBK1) and recruited to ubiquitinated bacteria to facilitate autophagosome formation during xenophagy, but the molecular mechanism underlying TBK1 activation in response to microbial infection is not clear. Here, we show that bacterial infection increases Ca²⁺ levels to activate TBK1 for xenophagy via the Ca²⁺-binding protein TBC1 domain family member 9 (TBC1D9). Mechanistically, the ubiquitin-binding region (UBR) and Ca²⁺-binding motif of TBC1D9 mediate its binding with ubiquitin-positive bacteria, and TBC1D9 knockout suppresses TBK1 activation and subsequent recruitment of the ULK1 complex. Treatment with a Ca²⁺ chelator impairs TBC1D9-ubiquitin interactions and TBK1 activation during xenophagy. TBC1D9 is also recruited to damaged mitochondria through its UBR and Ca²⁺-binding motif, and is required for TBK1 activation during mitophagy. These results indicate that TBC1D9 controls TBK1 activation during xenophagy and mitophagy through Ca²⁺-dependent ubiquitin-recognition.

Group A Streptococcus NAD-Glycohydrolase Inhibits Caveolin 1-Mediated Internalization Into Human Epithelial Cells

Group A Streptococcus (GAS) invades epithelial cells causing persistent infection. GAS has a variety of effector proteins that modulate host systems to affect their survival in host environments. The main effector proteins of GAS are NAD-glycohydrolase (Nga) and streptolysin O (SLO). Although Nga has NADase activity and shows SLO-dependent cytotoxicity, some clinical isolates harbor NADase-inactive subtypes of Nga, and the function of NADase-inactive Nga is still unclear. In this study, we found that deletion of nga enhanced the internalization of GAS into HeLa and Ca9-22 cells. Amino acid substitution of Nga R289K/G330D (NADase-inactive) does not enhance GAS invasion, suggesting that Nga may inhibit the internalization of GAS into host cells in an NADase-independent manner. Moreover, double deletion of slo and nga showed similar invasion percentages compared with wild-type GAS, indicating the important role of SLO in the inhibition of GAS invasion by Nga. Furthermore, enhanced internalization of the nga deletion mutant was not observed in Cav1-knockout HeLa cells. Altogether, these findings demonstrate an unrecognized NADase-independent function of Nga as a negative regulator of CAV1-mediated internalization into epithelial cells.

Group A Streptococcus modulates RAB1- and PIK3C3 complex-dependent autophagy

Autophagy selectively targets invading bacteria to defend cells, whereas bacterial pathogens counteract autophagy to survive in cells. The initiation of canonical autophagy involves the PIK3C3 complex, but autophagy targeting Group A Streptococcus (GAS) is PIK3C3-independent. We report that GAS infection elicits both PIK3C3-dependent and -independent autophagy, and that the GAS effector NAD-glycohydrolase (Nga) selectively modulates PIK3C3-dependent autophagy. GAS regulates starvation-induced (canonical) PIK3C3-dependent autophagy by secreting streptolysin O and Nga, and Nga also suppresses PIK3C3-dependent GAS-targeting-autophagosome formation during early infection and facilitates intracellular proliferation. This Nga-sensitive autophagosome formation involves the ATG14-containing PIK3C3 complex and RAB1 GTPase, which are both dispensable for Nga-insensitive RAB9A/RAB17-positive autophagosome formation. Furthermore, although MTOR inhibition and subsequent activation of ULK1, BECN1, and ATG14 occur during GAS infection, ATG14 recruitment to GAS is impaired, suggesting that Nga inhibits the recruitment of ATG14-containing PIK3C3 complexes to autophagosome-formation sites. Our findings reveal not only a previously unrecognized GAS-host interaction that modulates canonical autophagy, but also the existence of multiple autophagy pathways, using distinct regulators, targeting bacterial infection.Abbreviations: ATG5: autophagy related 5; ATG14: autophagy related 14; ATG16L1: autophagy related 16 like 1; BECN1: beclin 1; CALCOCO2: calcium binding and coiled-coil domain 2; GAS: group A streptococcus; GcAV: GAS-containing autophagosome-like vacuole; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTORC1: mechanistic target of rapamycin kinase complex 1; Nga: NAD-glycohydrolase; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns4P: phosphatidylinositol-4-phosphate; RAB: RAB, member RAS oncogene GTPases; RAB1A: RAB1A, member RAS oncogene family; RAB11A: RAB11A, member RAS oncogene family; RAB17: RAB17, member RAS oncogene family; RAB24: RAB24, member RAS oncogene family; RPS6KB1: ribosomal protein S6 kinase B1; SLO: streptolysin O; SQSTM1: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1; WIPI2: WD repeat domain, phosphoinositide interacting 2.

NLRX1 Negatively Regulates Group A Streptococcus Invasion and Autophagy Induction by Interacting With the Beclin 1-UVRAG Complex

Group A Streptococcus (GAS) can invade epithelial cells; however, these bacteria are targeted and eventually destroyed by autophagy. Members of the Nod-like receptor (NLR) family are thought to be critical for the autophagic response to invasive bacteria. However, the intracellular sensors within host cells that are responsible for bacterial invasion and the induction of autophagy are largely unknown. Thus, our aim was to examine the role of one such NLR, namely NLRX1, in invasion and autophagy during GAS infection. We found that GAS invasion was markedly increased in NLRX1 knockout cells. This led to the potentiation of autophagic processes such as autophagosome and autolysosome formation. NLRX1 was found to interact with Beclin 1 and UVRAG, members of Beclin1 complex, and knockout of these proteins inhibited invasion and autophagy upon GAS infection. Especially, NLRX1 interacted with Beclin 1 via its NACHT domain and this interaction was responsible for the NLRX1-mediated inhibition of invasion and autophagic processes including autophagosome and autolysosome formation during GAS infection. These findings demonstrate that NLRX1 functions as a negative regulator to inactivate the Beclin 1–UVRAG complex, which regulates invasion and autophagy during GAS infection. Thus, our study expands our knowledge of the role of NLRX1 during bacterial invasion and autophagy and could lead to further investigations to understand pathogen–host cell interactions, facilitating novel targeted therapeutics.

RAB30 regulates PI4KB (phosphatidylinositol 4-kinase beta)-dependent autophagy against group A Streptococcus

Macroautophagy/autophagy plays an important role in the immune response to invasion by intracellular pathogens such as group A Streptococcus (GAS; Streptococcus pyogenes). We previously identified RAB30, a Golgi-resident GTPase, as a novel anti-bacterial autophagic regulator in the formation of GAS-containing autophagosome-like vacuoles (GcAVs); however, the precise mechanism underlying this process remains elusive. Here, we elucidate a novel property of RAB30: the ability to recruit PI4KB (phosphatidylinositol 4-kinase beta) to the Golgi apparatus and GcAVs. We found that trans-Golgi network (TGN) vesicles were incorporated into GcAVs via RAB30 to promote GcAV formation. Moreover, depletion of phosphatidylinositol-4-phosphate (PtdIns4P), a phosphatidylinositol enriched in the TGN, by wortmannin and phenylarsine oxide, followed by subsequent repletion with exogenous PtdIns4P revealed that PtdIns4P is crucial for GcAV formation. Furthermore, we identify an interaction between RAB30 and PI4KB, in which the knockdown of RAB30 decreased the localization of PI4KB to the TGN and GcAVs. Finally, PI4KB knockout suppressed autophagy by inhibiting GcAV formation, resulting in the increased survival of GAS. Our results demonstrate a novel autophagosomal formation mechanism involving coordinative functions of RAB30 and PI4KB distinct from those utilized in canonical autophagy. Abbreviations: GAS: group A Streptococcus; GcAVs: GAS-containing autophagosome-like vacuoles; PI4KB: phosphatidylinositol 4-kinase beta; PtdIns: phosphatidylinositol; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns4P: phosphatidylinositol-4-phosphate; PtdIns5P: phosphatidylinositol-5-phosphate; SLO: streptolysin O; TGN: trans-Golgi network; TGOLN2: trans-golgi network protein 2; PH: plekstrin homology; OSBP: oxysterol binding protein.

The intracellular microbial sensor NLRP4 directs Rho-actin signaling to facilitate Group A Streptococcus-containing autophagosome-like vacuole formation

Xenophagy, also known as antibacterial autophagy, functions as a crucial defense system that can utilize intracellular pattern recognition sensors, such as NLRP4, to recognize and selectively eliminate bacterial pathogens. However, little is known about how NLRP4 regulates xenophagy. Here, we report that NLRP4 binds ARHGDIA (Rho GDP dissociation inhibitor α) to regulate Rho GTPase signaling and facilitate actin-mediated xenophagy. Specifically, NLRP4 is recruited to Group A Streptococcus (GAS) and colocalizes with GAS-containing autophagosome-like vacuoles (GcAVs), where it regulates ARHGDIA-Rho GTPase recruitment to promote autophagosome formation. The interaction between NLRP4, ARHGDIA, and Rho GTPases is regulated by ARHGDIA Tyr156 phosphorylation, which acts as a gate to induce Rho-mediated xenophagy. Moreover, ARHGDIA and Rho GTPase are involved in actin-mediated ATG9A recruitment to phagophores, facilitating elongation to form autophagosomes. Collectively, these findings demonstrate that NLRP4 functions as a Rho receptor complex to direct actin dynamics regulating xenophagy.

YvqE and CovRS of Group A Streptococcus Play a Pivotal Role in Viability and Phenotypic Adaptations to Multiple Environmental Stresses

Streptococcus pyogenes (group A Streptococcus, or GAS) is a human pathogen that causes a wide range of diseases. For successful colonization within a variety of host niches, GAS utilizes TCSs to sense and respond to environmental changes and adapts its pathogenic traits accordingly; however, many GAS TCSs and their interactions remain uncharacterized. Here, we elucidated the roles of a poorly characterized TCS, YvqEC, and a well-studied TCS, CovRS, in 2 different GAS strain SSI-1 and JRS4, respectively. Deletion of yvqE and yvqC in JRS4 resulted in lower cell viability and abnormality of cell division when compared to the wild-type strain under standard culture conditions, demonstrating an important role for YvqEC. Furthermore, a double-deletion of yvqEC and covRS in SSI-1 and JRS4 resulted in a significantly impaired ability to survive under various stress conditions, as well as an increased sensitivity to cell wall-targeting antibiotics compared to that observed in either single mutant or wild-type strains suggesting synergistic interactions. Our findings provide new insights into the impact of poorly characterized TCS (YvqEC) and potential synergistic interactions between YvqEC and CovRS and reveal their potential role as novel therapeutic targets against GAS infection.

Bcl-xL Affects Group A Streptococcus-Induced Autophagy Directly, by Inhibiting Fusion between Autophagosomes and Lysosomes, and Indirectly, by Inhibiting Bacterial Internalization via Interaction with Beclin 1-UVRAG

Anti-apoptotic Bcl-2 and Bcl-xL are proposed to regulate starvation-induced autophagy by directly interacting with Beclin 1. Beclin 1 is also thought to be involved in multiple vesicle trafficking pathways such as endocytosis by binding to Atg14L and UVRAG. However, how the interaction of Bcl-2 family proteins and Beclin 1 regulates anti-bacterial autophagy (xenophagy) is still unclear. In this study, we analyzed these interactions using Group A Streptococcus (GAS; Streptococcus pyogenes) infection as a model. GAS is internalized into epithelial cells through endocytosis, while the intracellular fate of GAS is degradation by autophagy. Here, we found that Bcl-xL but not Bcl-2 regulates GAS-induced autophagy. Autophagosome-lysosome fusion and the internalization process during GAS infection were promoted in Bcl-xL knockout cells. In addition, knockout of Beclin 1 phenocopied the internalization defect of GAS. Furthermore, UVRAG interacts not only with Beclin 1 but also with Bcl-xL, and overexpression of UVRAG partially rescued the internalization defect of Beclin 1 knockout cells during GAS infection. Thus, our results indicate that Bcl-xL inhibits GAS-induced autophagy directly by suppressing autophagosome-lysosome fusion and indirectly by suppressing GAS internalization via interaction with Beclin 1-UVRAG.

The STX6-VTI1B-VAMP3 complex facilitates xenophagy by regulating the fusion between recycling endosomes and autophagosomes

Macroautophagy/autophagy plays a critical role in immunity by directly degrading invading pathogens such as Group A Streptococcus (GAS), through a process that has been named xenophagy. We previously demonstrated that autophagic vacuoles directed against GAS, termed GAS-containing autophagosome-like vacuoles (GcAVs), use recycling endosomes (REs) as a membrane source. However, the precise molecular mechanism that facilitates the fusion between GcAVs and REs remains unclear. Here, we demonstrate that STX6 (syntaxin 6) is recruited to GcAVs and forms a complex with VTI1B and VAMP3 to regulate the GcAV-RE fusion that is required for xenophagy. STX6 targets the GcAV membrane through its tyrosine-based sorting motif and transmembrane domain, and localizes to TFRC (transferrin receptor)-positive punctate structures on GcAVs through its H2 SNARE domain. Knockdown and knockout experiments revealed that STX6 is required for the fusion between GcAVs and REs to promote clearance of intracellular GAS by autophagy. Moreover, VAMP3 and VTI1B interact with STX6 and localize on the TFRC-positive puncta on GcAVs, and are also involved in the RE-GcAV fusion. Furthermore, knockout of RABGEF1 impairs the RE-GcAV fusion and STX6-VAMP3 interaction. These findings demonstrate that RABGEF1 mediates RE fusion with GcAVs through the STX6-VAMP3-VTI1B complex, and reveal the SNARE dynamics involved in autophagosome formation in response to bacterial infection.

DNA-based culture-independent analysis detects the presence of group a streptococcus in throat samples from healthy adults in Japan

Background

Group A Streptococcus (GAS; Streptococcus pyogenes) causes a range of mild to severe infections in humans. It can also colonize healthy persons asymptomatically. Therefore, it is important to study GAS carriage in healthy populations, as carriage of it might lead to subsequent disease manifestation, clonal spread in the community, and/or diversification of the organism. Throat swab culture is the gold standard method for GAS detection. Advanced culture-independent methods provide rapid and efficient detection of microorganisms directly from clinical samples. We investigated the presence of GAS in throat swab samples from healthy adults in Japan using culture-dependent and culture-independent methods.

Results

Two throat swab samples were collected from 148 healthy volunteers. One was cultured on selective medium, while total DNA extracted from the other was polymerase chain reaction (PCR) amplified with two GAS-specific primer pairs: one was a newly designed 16S rRNA-specific primer pair, the other a previously described V-Na⁺-ATPase primer pair. Although only 5 (3.4 %) of the 148 samples were GAS-positive by the culture-dependent method, 146 (98.6 %) were positive for the presence of GAS DNA by the culture-independent method. To obtain serotype information by emm typing, we performed nested PCR using newly designed emm primers. We detected the four different emm types in 25 (16.9 %) samples, and these differed from the common emm types associated with GAS associated diseases in Japan. The different emm types detected in the healthy volunteers indicate that the presence of unique emm types might be associated with GAS carriage.

Conclusions

Our results suggest that culture-independent methods should be considered for profiling GAS in the healthy hosts, with a view to obtaining better understanding of these organisms. The GAS-specific primers (16S rRNA and V-Na⁺-ATPase) used in this study can be used to estimate the maximum potential GAS carriage in people.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0858-5) contains supplementary material, which is available to authorized users.

[New insights from infection-specific gene expression network]

Most of our current knowledge about the gene regulation of pathogen comes from studies with in vitro conditions that mimic their host environments, revealing many types of virulence genes and their regulatory network. Recent advances in DNA sequencing and techniques for transcriptome analysis allow us to identify pathogenic genes specifically expressed in vivo. Analyses for gene expression of pathogens in response to the host environment, including immune response and change of bacterial flora during infection, provide clues to understanding the underlying events to establish the infectious diseases. Here, we would like to introduce next epoch-making ideas and concepts to understand the real picture of microbial infection through the recent works of gene regulation in host environments.

Intraindividual variation in core microbiota in peri-implantitis and periodontitis

The oral microbiota change dramatically with each part of the oral cavity, even within the same mouth. Nevertheless, the microbiota associated with peri-implantitis and periodontitis have been considered the same. To improve our knowledge of the different communities of complex oral microbiota, we compared the microbial features between peri-implantitis and periodontitis in 20 patients with both diseases. Although the clinical symptoms of peri-implantitis were similar to those of periodontitis, the core microbiota of the diseases differed. Correlation analysis revealed the specific microbial co-occurrence patterns and found some of the species were associated with the clinical parameters in a disease-specific manner. The proportion of Prevotella nigrescens was significantly higher in peri-implantitis than in periodontitis, while the proportions of Peptostreptococcaceae sp. and Desulfomicrobium orale were significantly higher in periodontitis than in peri-implantitis. The severity of the peri-implantitis was also species-associated, including with an uncultured Treponema sp. that correlated to 4 clinical parameters. These results indicate that peri-implantitis and periodontitis are both polymicrobial infections with different causative pathogens. Our study provides a framework for the ecologically different bacterial communities between peri-implantitis and periodontitis, and it will be useful for further studies to understand the complex microbiota and pathogenic mechanisms of oral polymicrobial diseases.

Rab17-mediated recycling endosomes contribute to autophagosome formation in response to Group A Streptococcus invasion

Autophagy plays a crucial role in host defence by facilitating the degradation of invading bacteria such as Group A Streptococcus (GAS). GAS-containing autophagosome-like vacuoles (GcAVs) form when GAS-targeting autophagic membranes entrap invading bacteria. However, the membrane origin and the precise molecular mechanism that underlies GcAV formation remain unclear. In this study, we found that Rab17 mediates the supply of membrane from recycling endosomes (REs) to GcAVs. We showed that GcAVs contain the RE marker transferrin receptor (TfR). Colocalization analyses demonstrated that Rab17 colocalized effectively with GcAV. Rab17 and TfR were visible as punctate structures attached to GcAVs and the Rab17-positive dots were recruited to the GAS-capturing membrane. Overexpression of Rab17 increased the TfR-positive GcAV content, whereas expression of the dominant-negative Rab17 form (Rab17 N132I) caused a decrease, thereby suggesting the involvement of Rab17 in RE-GcAV fusion. The efficiency of GcAV formation was lower in Rab17 N132I-overexpressing cells. Furthermore, knockdown of Rabex-5, the upstream activator of Rab17, reduced the GcAV formation efficiency. These results suggest that Rab17 and Rab17-mediated REs are involved in GcAV formation. This newly identified function of Rab17 in supplying membrane from REs to GcAVs demonstrates that RE functions as a primary membrane source during antibacterial autophagy.

The staphylococcal elastin-binding protein regulates zinc-dependent growth/biofilm formation

Staphylococcus aureus is one of the most important human pathogens because it is a common cause of nosocomial infections. The elastin-binding protein of Staphylococcus aureus (EbpS) is an adhesin that is responsible for attachment to host cells via its binding to elastin. Despite its relatively weak contribution to adhesion, the ebpS gene is highly conserved among S. aureus isolates, suggesting that EbpS may have other crucial functions. Here, we found that EbpS binds Zn(2+) with its N-terminal region, which leads to local conformational changes that result in the assembly of the EbpS protein. The growth rate of the EbpS-deficient strain was considerably decreased. Zn(2+) chelation decreased the growth rate of the wild-type strain but did not alter that of the EbpS-deficient strain. Furthermore, biofilm formation by the EbpS-deficient strain was abnormally enhanced in the Zn(2+) concentration-dependent manner. All the results suggest that ebpS deficiency led to a zinc concentration-dependent inability to modulate the growth/biofilm maturation phase appropriately. Given the high conservation of ebpS and that appropriate regulation of biofilm formation is thought to be essential for effective staphylococcal infection, inhibition of EbpS binding to Zn(2+) could lead to the development of novel therapeutic strategies for controlling S. aureus infections.

CRISPR regulation of intraspecies diversification by limiting IS transposition and intercellular recombination

Mobile genetic elements (MGEs) and genetic rearrangement are considered as major driving forces of bacterial diversification. Previous comparative genome analysis of Porphyromonas gingivalis, a pathogen related to periodontitis, implied such an important relationship. As a counterpart system to MGEs, clustered regularly interspaced short palindromic repeats (CRISPRs) in bacteria may be useful for genetic typing. We found that CRISPR typing could be a reasonable alternative to conventional methods for characterizing phylogenetic relationships among 60 highly diverse P. gingivalis isolates. Examination of genetic recombination along with multilocus sequence typing suggests the importance of such events between different isolates. MGEs appear to be strategically located at the breakpoint gaps of complicated genome rearrangements. Of these MGEs, insertion sequences (ISs) were found most frequently. CRISPR analysis identified 2,150 spacers that were clustered into 1,187 unique ones. Most of these spacers exhibited no significant nucleotide similarity to known sequences (97.6%: 1,158/1,187). Surprisingly, CRISPR spacers exhibiting high nucleotide similarity to regions of P. gingivalis genomes including ISs were predominant. The proportion of such spacers to all the unique spacers (1.6%: 19/1,187) was the highest among previous studies, suggesting novel functions for these CRISPRs. These results indicate that P. gingivalis is a bacterium with high intraspecies diversity caused by frequent insertion sequence (IS) transposition, whereas both the introduction of foreign DNA, primarily from other P. gingivalis cells, and IS transposition are limited by CRISPR interference. It is suggested that P. gingivalis CRISPRs could be an important source for understanding the role of CRISPRs in the development of bacterial diversity.

The small GTPases Rab9A and Rab23 function at distinct steps in autophagy during Group A Streptococcus infection

Autophagy mediates the degradation of cytoplasmic contents in the lysosome and plays a significant role in immunity. Here we identified the small GTPases Rab9A and Rab23 as novel autophagy regulators during Group A streptococcus (GAS) infection. Rab9A was recruited to GAS-containing autophagosome-like vacuoles (GcAVs) after autophagosomal maturation and its activity was required for GcAV enlargement and eventual lysosomal fusion. GcAV enlargement appeared to be related to homotypic fusion of GcAVs with Rab9A. Rab23 was recruited to GAS-capturing forming autophagosomes. Knockdown of Rab23 expression decreased both LC3- and Atg5-positive GAS formation and caused the accumulation of LC3-positive structures that did not associate with intracellular GAS. It was suggested, therefore, that Rab23 is required for GcAV formation and is involved in GAS targeting of autophagic vacuoles. Furthermore, knockdown of Rab9A or Rab23 expression impaired the degradation of intracellular GAS. Therefore, our data reveal that the Rab9A and Rab23 GTPases play crucial roles in autophagy of GAS. However, neither Rab9A nor Rab23 were localized to starvation-induced autophagosomes. Not only Rab9A but also Rab23 was dispensable for starvation-induced autophagosome formation. These findings demonstrate that specific Rab proteins function at distinct steps during autophagy in response to GAS infection.

CRISPR inhibition of prophage acquisition in Streptococcus pyogenes

Streptococcus pyogenes, one of the major human pathogens, is a unique species since it has acquired diverse strain-specific virulence properties mainly through the acquisition of streptococcal prophages. In addition, S. pyogenes possesses clustered regularly interspaced short palindromic repeats (CRISPR)/Cas systems that can restrict horizontal gene transfer (HGT) including phage insertion. Therefore, it was of interest to examine the relationship between CRISPR and acquisition of prophages in S. pyogenes. Although two distinct CRISPR loci were found in S. pyogenes, some strains lacked CRISPR and these strains possess significantly more prophages than CRISPR harboring strains. We also found that the number of spacers of S. pyogenes CRISPR was less than for other streptococci. The demonstrated spacer contents, however, suggested that the CRISPR appear to limit phage insertions. In addition, we found a significant inverse correlation between the number of spacers and prophages in S. pyogenes. It was therefore suggested that S. pyogenes CRISPR have permitted phage insertion by lacking its own spacers. Interestingly, in two closely related S. pyogenes strains (SSI-1 and MGAS315), CRISPR activity appeared to be impaired following the insertion of phage genomes into the repeat sequences. Detailed analysis of this prophage insertion site suggested that MGAS315 is the ancestral strain of SSI-1. As a result of analysis of 35 additional streptococcal genomes, it was suggested that the influences of the CRISPR on the phage insertion vary among species even within the same genus. Our results suggested that limitations in CRISPR content could explain the characteristic acquisition of prophages and might contribute to strain-specific pathogenesis in S. pyogenes.

The dawning era of comprehensive transcriptome analysis in cellular microbiology

Bacteria rapidly change their transcriptional patterns during infection in order to adapt to the host environment. To investigate host–bacteria interactions, various strategies including the use of animal infection models, in vitro assay systems and microscopic observations have been used. However, these studies primarily focused on a few specific genes and molecules in bacteria. High-density tiling arrays and massively parallel sequencing analyses are rapidly improving our understanding of the complex host–bacterial interactions through identification and characterization of bacterial transcriptomes. Information resulting from these high-throughput techniques will continue to provide novel information on the complexity, plasticity, and regulation of bacterial transcriptomes as well as their adaptive responses relative to pathogenecity. Here we summarize recent studies using these new technologies and discuss the utility of transcriptome analysis.

Specific behavior of intracellular Streptococcus pyogenes that has undergone autophagic degradation is associated with bacterial streptolysin O and host small G proteins Rab5 and Rab7

Streptococcus pyogenes (group A streptococcus (GAS)) is a pathogen that invades non-phagocytic host cells, and causes a variety of acute infections such as pharyngitis. Our group previously reported that intracellular GAS is effectively degraded by the host-cell autophagic machinery, and that a cholesterol-dependent cytolysin, streptolysin O (SLO), is associated with bacterial escape from endosomes in epithelial cells. However, the details of both the intracellular behavior of GAS and the process leading to its autophagic degradation remain unknown. In this study, we found that two host small G proteins, Rab5 and Rab7, were associated with the pathway of autophagosome formation and the fate of intracellular GAS. Rab5 was involved in bacterial invasion and endosome fusion. Rab7 was clearly multifunctional, with roles in bacterial invasion, endosome maturation, and autophagosome formation. In addition, this study showed that the bacterial cytolysin SLO supported the escape of GAS into the cytoplasm from endosomes, and surprisingly, a SLO-deficient mutant of GAS was viable longer than the wild-type strain although it failed to escape the endosomes. This intracellular behavior of GAS is unique and distinct from that of other types of bacterial invaders. Our results provide a new picture of GAS infection and host-cell responses in epithelial cells.

Reactive oxygen species induced by Streptococcus pyogenes invasion trigger apoptotic cell death in infected epithelial cells

Streptococcus pyogenes (group A streptococcus, GAS), one of the most common pathogens of humans, attaches and invades into human pharyngeal or skin epithelial cells. We have previously reported that induction of apoptosis is associated with GAS invasion, which induces mitochondrial dysfunction and apoptotic cell death. We demonstrate here that GAS-induced apoptosis is mediated by reactive oxygen species (ROS) production. Both the induction of apoptosis and ROS production markedly increased upon invasion of wild-type GAS strain JRS4 into HeLa cells; however, the apoptotic response was not observed in fibronectin-binding protein F1-disrupted mutant SAM1-infected cells. In Bcl-2-overexpressing HeLa cells (HBD98-2-4), the induction of apoptosis, ROS production and mitochondrial dysfunction were significantly suppressed, whereas the numbers of invaded GAS was not different between HeLa (mock cells) and the HeLa HBD98-2-4 cells. Whereas Rac1 activation occurred during GAS invasion, ROS production in GAS-infected cells was clearly inhibited by transfection with the Rac1 mutants (L37 or V12L37), but not by the dominant active mutant (V12L61) or by the dominant negative mutant (N17). These observations indicate that GAS invasion triggers ROS production through Rac1 activation and generated ROS induced mitochondrial dysfunction leading to cellular apoptosis.

Cost effective DNA sequencing and template preparation from bacterial colonies and plasmids

Cost-effective DNA sequencing and template preparation were evaluated for high-throughput screening of bacterial colonies. The rolling-circle amplification to generate template for DNA sequencing was carried out using 10-fold smaller amount of phi29 DNA polymerase and excluding two other enzymes (yeast pyrophosphatase and calf intestine alkaline phosphatase) used previously. Then, a 1/40 volume of the fluorescent terminator mix recommended by the manufacturer gave a usable sequencing result although a 1/26.7 volume of the mix was used to compare the protocol more accurately with manufacturer's protocol.

Microcirculatory alteration in low-grade gastric mucosa-associated lymphoma by Helicobacter heilmannii infection: its relation to vascular endothelial growth factor and cyclooxygenase-2

BACKGROUND

There are clinical reports that Helicobacter heilmannii, as well as Helicobacter pylori, has been clinically reported to cause gastric low-grade mucosa-associated lymphoid tissue-type (MALT) lymphoma, although its precise mechanism remains to be clarified. Thus, the present study was undertaken to elucidate the alteration of the microcirculatory structure and the relation to angiogenetic factors in mice infected with H. heilmannii for 3 and 6 months.

METHODS

Immunohistochemical studies have been performed by FITC-dextran intra-aortic infusion or CD31, vascular endothelial growth factor-A, cyclooxygenase 2 antibodies using our recently established model of gastric mucosa-associated lymphoid tissue-type gastric B-cell lymphoma in C57BL/6 mice.

RESULTS

Increased microcirculatory network was recognized surrounding the MALT lymphoma tissues by both the FITC-dextran infusion method and CD31 immunoreactivity. Vascular endothelial growth factor-A immunoreactivity was recognized within the lymphoma tissues as well as in the marginal area, while cyclooxygenase-2 immunoreactivity was localized in the area surrounding the MALT lymphoma tissues.

CONCLUSION

Increased microvascular network as well as enhanced VEGF-A immunoreactivity was shown to be related to expansion of the MALT lymphoma formed by Helicobacter heilmannii infection.