Involvement of alpha5beta1 integrins in interleukin 8 production induced by oral viridans streptococcal protein I/IIf in cultured endothelial cells

Oral streptococci: modulators of health and disease

Streptococci are primary colonizers of the oral cavity where they are ubiquitously present and an integral part of the commensal oral biofilm microflora. The role oral streptococci play in the interaction with the host is ambivalent. On the one hand, they function as gatekeepers of homeostasis and are a prerequisite for the maintenance of oral health - they shape the oral microbiota, modulate the immune system to enable bacterial survival, and antagonize pathogenic species. On the other hand, also recognized pathogens, such as oral Streptococcus mutans and Streptococcus sobrinus, which trigger the onset of dental caries belong to the genus Streptococcus. In the context of periodontitis, oral streptococci as excellent initial biofilm formers have an accessory function, enabling late biofilm colonizers to inhabit gingival pockets and cause disease. The pathogenic potential of oral streptococci fully unfolds when their dissemination into the bloodstream occurs; streptococcal infection can cause extra-oral diseases, such as infective endocarditis and hemorrhagic stroke. In this review, the taxonomic diversity of oral streptococci, their role and prevalence in the oral cavity and their contribution to oral health and disease will be discussed, focusing on the virulence factors these species employ for interactions at the host interface.

FAK/IL-8 axis promotes the proliferation and migration of gastric cancer cells

Gastric cancer (GC) is one of the most common malignancies in China and is associated with high mortality. The occurrence and development of gastric cancer are related to genetic and environmental factors. Focal adhesion kinase (FAK) is a cytoplasmic nonreceptor protein tyrosine kinase that is activated by the extracellular matrix and growth factors. FAK is highly expressed in cancer and promotes its development by regulating cancer cell proliferation, migration, and angiogenesis. The expression of IL-8 is increased in many types of malignant tumor cells and is linked to their proliferation, migration, invasion, angiogenesis, and EMT. In this study, we found FAK to be essential for the proliferation, migration, and peritoneal metastasis of gastric cancer cells. To examine the molecular regulatory mechanisms of FAK in the peritoneal dissemination of gastric cancer, we performed RNA-seq analysis of MKN-45-FAK-/- and MKN45 cells and demonstrated that IL-8 was downregulated in FAK-deficient cells. Conversely, we confirmed that IL-8 activates FAK activity. We established that IL-8 promotes the proliferation, colony formation, and migration of gastric cancer cells that are partially mediated by FAK. Thus, we propose that an IL-8-FAK-IL-8 positive feedback loop effects the proliferation and migration of gastric cancer cells.

FAK mediates LPS-induced inflammatory lung injury through interacting TAK1 and activating TAK1-NFκB pathway

Acute lung injury (ALI), characterized by inflammatory damage, is a major clinical challenge. Developing specific treatment options for ALI requires the identification of novel targetable signaling pathways. Recent studies reported that endotoxin lipopolysaccharide (LPS) induced a TLR4-dependent activation of focal adhesion kinase (FAK) in colorectal adenocarcinoma cells, suggesting that FAK may be involved in LPS-induced inflammatory responses. Here, we investigated the involvement and mechanism of FAK in mediating LPS-induced inflammation and ALI. We show that LPS phosphorylates FAK in macrophages. Either FAK inhibitor, site-directly mutation, or siRNA knockdown of FAK significantly suppresses LPS-induced inflammatory cytokine production in macrophages. FAK inhibition also blocked LPS-induced activation of MAPKs and NFκB. Mechanistically, we demonstrate that activated FAK directly interacts with transforming growth factor-β-activated kinase-1 (TAK1), an upstream kinase of MAPKs and NFκB, and then phosphorylates TAK1 at Ser412. In a mouse model of LPS-induced ALI, pharmacological inhibition of FAK suppressed FAK/TAK activation and inflammatory response in lung tissues. These activities resulted in the preservation of lung tissues in LPS-challenged mice and increased survival during LPS-induced septic shock. Collectively, our results illustrate a novel FAK-TAK1-NFκB signaling axis in LPS-induced inflammation and ALI, and support FAK as a potential target for the treatment of ALI.

The Multifaceted Nature of Streptococcal Antigen I/II Proteins in Colonization and Disease Pathogenesis

Streptococci are Gram-positive bacteria that belong to the natural microbiota of humans and animals. Certain streptococcal species are known as opportunistic pathogens with the potential to cause severe invasive disease. Antigen I/II (AgI/II) family proteins are sortase anchored cell surface adhesins that are nearly ubiquitous across streptococci and contribute to many streptococcal diseases, including dental caries, respiratory tract infections, and meningitis. They appear to be multifunctional adhesins with affinities to various host substrata, acting to mediate attachment to host surfaces and stimulate immune responses from the colonized host. Here we will review the literature including recent work that has demonstrated the multifaceted nature of AgI/II family proteins, focusing on their overlapping and distinct functions and their important contribution to streptococcal colonization and disease.

The Role of Functional Amyloids in Bacterial Virulence

Amyloid fibrils are best known as a product of human and animal protein misfolding disorders, where amyloid formation is associated with cytotoxicity and disease. It is now evident that for some proteins, the amyloid state constitutes the native structure and serves a functional role. These functional amyloids are proving widespread in bacteria and fungi, fulfilling diverse functions as structural components in biofilms or spore coats, as toxins and surface-active fibers, as epigenetic material, peptide reservoirs or adhesins mediating binding to and internalization into host cells. In this review, we will focus on the role of functional amyloids in bacterial pathogenesis. The role of functional amyloids as virulence factor is diverse but mostly indirect. Nevertheless, functional amyloid pathways deserve consideration for the acute and long-term effects of the infectious disease process and may form valid antimicrobial targets.

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Functional amyloids are widespread in bacteria, pathogenic and non-pathogenic.

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Bacterial biofilms most commonly function as structural support in the extracellular matrix of biofilms or spore coats, and in cell–cell and cell-surface adherence.

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The amyloid state can be the sole structured and functional state, or can be facultative, as a secondary state to folded monomeric subunits.

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Bacterial amyloids can enhance virulence by increasing persistence, cell adherence and invasion, intracellular survival, and pathogen spread by increased environmental survival.

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Bacterial amyloids may indirectly inflict disease by triggering inflammation, contact phase activation and possibly induce or aggravate human pathological aggregation disorders.

Structural and recovery mechanisms of 3D dental pulp cell microtissues challenged with Streptococcusmutans in extracellular matrix environment

Cariopathogen Streptococcus mutans exists in infected dental pulp of deciduous teeth and is frequently linked with heart diseases. Organotypic (3D) dental pulp stem cell (DPSC) cultures/microtissues, developed to mimic the physiological conditions in vivo, were utilized to assess the bacterial impact on their (i) 3D structural configuration and (ii) recovery mechanisms. The cultures, developed in extracellular matrix (ECM) bio-scaffold (Matrigel™), interacted with WT and GFP-tagged bacterial biofilms by permitting their infiltration through the ECM. Challenged cell constructs were visualized by F-actin/nuclei staining. Their pluripotency (Sox2) and differentiation (osteocalcin) markers were assessed by immunocytochemistry. Secreted mineral was detected by alizarin red, and 3D structural arrangements were analysed by epi-fluorescence and confocal scanning microscopy. Bacterial biofilm/ECM-embedded DPSC interactions appeared in distinct areas of the microtissues. Bacterial attachment to the cell surface occurred without evidence of invasion. Surface architecture of the challenged versus unchallenged microtissues was apparently unaltered. However, significant increases in thickness (138.42 vs 106.51 µm) and bacterial penetration were detected in challenged structures causing canal-like microstructures with various diameters (12.94 -42.88 µm) and average diameter of 20.66 to 33.42 µm per microtissue. Challenged constructs expressed pluripotency and differentiation markers and secreted the mineral. Presented model shows strong potential for assessing pulp-pathogen interactions in vivo. S. mutans infiltrated and penetrated the microtissues but did not invade the cells or compromise major cell repair mechanisms. These findings would suggest reexamining the role of S. mutans as an endodontic pathogen and investigating DPSC resistance to its pathogenicity.

Structural and Functional Analysis of Cell Wall-anchored Polypeptide Adhesin BspA in Streptococcus agalactiae

Streptococcus agalactiae (group B Streptococcus, GBS) is the predominant cause of early-onset infectious disease in neonates and is responsible for life-threatening infections in elderly and immunocompromised individuals. Clinical manifestations of GBS infection include sepsis, pneumonia, and meningitis. Here, we describe BspA, a deviant antigen I/II family polypeptide that confers adhesive properties linked to pathogenesis in GBS. Heterologous expression of BspA on the surface of the non-adherent bacterium Lactococcus lactis confers adherence to scavenger receptor gp340, human vaginal epithelium, and to the fungus Candida albicans Complementary crystallographic and biophysical characterization of BspA reveal a novel β-sandwich adhesion domain and unique asparagine-dependent super-helical stalk. Collectively, these findings establish a new bacterial adhesin structure that has in effect been hijacked by a pathogenic Streptococcus species to provide competitive advantage in human mucosal infections.

Innate Immunity and Biomaterials at the Nexus: Friends or Foes

Biomaterial implants are an established part of medical practice, encompassing a broad range of devices that widely differ in function and structural composition. However, one common property amongst biomaterials is the induction of the foreign body response: an acute sterile inflammatory reaction which overlaps with tissue vascularisation and remodelling and ultimately fibrotic encapsulation of the biomaterial to prevent further interaction with host tissue. Severity and clinical manifestation of the biomaterial-induced foreign body response are different for each biomaterial, with cases of incompatibility often associated with loss of function. However, unravelling the mechanisms that progress to the formation of the fibrotic capsule highlights the tightly intertwined nature of immunological responses to a seemingly noncanonical “antigen.” In this review, we detail the pathways associated with the foreign body response and describe possible mechanisms of immune involvement that can be targeted. We also discuss methods of modulating the immune response by altering the physiochemical surface properties of the biomaterial prior to implantation. Developments in these areas are reliant on reproducible and effective animal models and may allow a “combined” immunomodulatory approach of adapting surface properties of biomaterials, as well as treating key immune pathways to ultimately reduce the negative consequences of biomaterial implantation.

A dual role for β1 integrin in an in vitro Streptococcus mitis/human gingival fibroblasts co-culture model in response to TEGDMA

AIM

To evaluate the effect of TEGDMA on human gingival fibroblasts (HGFs) in vitro co-cultured with Streptococcus mitis, focusing on the signalling pathways underlying cell tissue remodelling and inflammatory response processes.

METHODOLOGY

β1 integrin expression was evaluated by means of imaging flow cytometry. The Western blot technique was used to investigate the expression of protein kinase C (PKC), extracellular signal-regulated kinase (ERK), matrix metalloproteinase 9 (MMP9) and 3 (MMP3). RT-PCR was performed to quantify nuclear factor-kb subunits (Nf-kb1, ReLa), IkB kinase β (IkBkB), cyclooxygenase II (COX-2) and tumour necrosis factor-α (TNF-α) mRNA levels. Statistical analysis was performed using the analysis of variance (anova).

RESULTS

When HGFs are co-cultured with S. mitis, β1 integrin intensity, phosphorylated PKC (p-PKC), activated ERK (p-ERK), IkBkB mRNA level and MMP9 expression increased (for all molecules P < 0.05 HGFs versus HGFs co-cultured with S. mitis). A higher level of MMP3 in HGFs treated with TEGDMA was recorded (P < 0.05 HGFs versus HGFs exposed to TEGDMA). COX-2 inflammatory factor mRNA level appeared higher in HGFs exposed to 1 mmol L(-1) TEGDMA (P < 0.01 HGFs versus HGFs exposed to TEGDMA), whereas TNF-α gene expression was higher in HGFs co-cultured with S. mitis (P < 0.05 HGFs versus HGFs co-cultured with S. mitis).

CONCLUSIONS

β1 integrin triggered the signalling pathway, transduced by p-PKCα and involving ERK 1 and 2 and MMPs. This pathway resulted in an unbalanced equilibrium in tissue remodelling process, along with inflammatory response when HGFs are exposed to bacteria or biomaterial alone. On the contrary, the TEGDMA/S. mitis combination restored the balance between extracellular matrix deposition and degradation and prevented an inflammatory response.

Bacterial Pili exploit integrin machinery to promote immune activation and efficient blood-brain barrier penetration

Group B Streptococcus (GBS) is the leading cause of meningitis in newborn infants. Bacterial cell surface appendages, known as pili, have been recently described in streptococcal pathogens, including GBS. The pilus tip adhesin, PilA, contributes to GBS adherence to blood-brain barrier (BBB) endothelium; however, the host receptor and the contribution of PilA in central nervous system (CNS) disease pathogenesis are unknown. Here we show that PilA binds collagen, which promotes GBS interaction with the α₂β₁ integrin resulting in activation of host chemokine expression and neutrophil recruitment during infection. Mice infected with the PilA-deficient mutant exhibit delayed mortality, a decrease in neutrophil infiltration and bacterial CNS dissemination. We find that PilA-mediated virulence is dependent on neutrophil influx as neutrophil depletion results in a decrease in BBB permeability and GBS-BBB penetration. Our results suggest that the bacterial pilus, specifically the PilA adhesin, has a dual role in immune activation and bacterial entry into the CNS.

Streptococcus cristatus modulates the Fusobacterium nucleatum-induced epithelial interleukin-8 response through the nuclear factor-kappa B pathway

BACKGROUND AND OBJECTIVE

We previously reported that the interleukin-8 (IL-8) response to Fusobacterum nucleatum was attenuated in the presence of Streptococcus cristatus. Here, we further examined the underlying mechanism(s) involved in the modulating effect of S. cristatus by looking specifically at its impact on the nuclear factor-kappa B (NF-κB) pathway under the toll-like receptor (TLR) signaling background.

MATERIAL AND METHODS

OKF6/TERT-2 and KB cells were co-cultured with F. nucleatum and S. cristatus, either alone or in combination. Secretion of IL-8 protein was measured by ELISA. The nuclear translocation of NF-κB was evaluated by confocal microscopy, while DNA-binding activity was quantified using TransAM™ ELISA kits. Western blot analysis was performed to determine whether the anti-inflammatory effect of S. cristatus is related to the modulation of the NF-κB inhibitory protein IκB-α.

RESULTS

Incubation with F. nucleatum significantly enhanced the nuclear translocation of NF-κB. Exposure to S. cristatus alone did not cause detectable NF-κB translocation and was able to inhibit the F. nucleatum-induced NF-κB nuclear translocation. The TransAM assay further confirmed that S. cristatus blocked the nuclear translocation of NF-κB in response to F. nucleatum stimulation. In contrast to the nearly complete degradation of IκB-α induced by F. nucleatum alone, the presence of S. cristatus stabilized IκB-α. Pre-incubation with TLR2 and TLR4 antibodies, however, did not affect the epithelial response to either species alone or in combination.

CONCLUSION

The mechanism by which S. cristatus attenuates F. nucleatum-induced proinflammatory responses in oral epithelial cells appears to involve blockade of NF-κB nuclear translocation at the level of IκB-α degradation.

Streptococcus adherence and colonization

Streptococci readily colonize mucosal tissues in the nasopharynx; the respiratory, gastrointestinal, and genitourinary tracts; and the skin. Each ecological niche presents a series of challenges to successful colonization with which streptococci have to contend. Some species exist in equilibrium with their host, neither stimulating nor submitting to immune defenses mounted against them. Most are either opportunistic or true pathogens responsible for diseases such as pharyngitis, tooth decay, necrotizing fasciitis, infective endocarditis, and meningitis. Part of the success of streptococci as colonizers is attributable to the spectrum of proteins expressed on their surfaces. Adhesins enable interactions with salivary, serum, and extracellular matrix components; host cells; and other microbes. This is the essential first step to colonization, the development of complex communities, and possible invasion of host tissues. The majority of streptococcal adhesins are anchored to the cell wall via a C-terminal LPxTz motif. Other proteins may be surface anchored through N-terminal lipid modifications, while the mechanism of cell wall associations for others remains unclear. Collectively, these surface-bound proteins provide Streptococcus species with a "coat of many colors," enabling multiple intimate contacts and interplays between the bacterial cell and the host. In vitro and in vivo studies have demonstrated direct roles for many streptococcal adhesins as colonization or virulence factors, making them attractive targets for therapeutic and preventive strategies against streptococcal infections. There is, therefore, much focus on applying increasingly advanced molecular techniques to determine the precise structures and functions of these proteins, and their regulatory pathways, so that more targeted approaches can be developed.

Microparticle-induced release of B-lymphocyte regulators by rheumatoid synoviocytes

Introduction

In the present study, we investigated the ability of microparticles isolated from synovial fluids from patients with rheumatoid arthritis or osteoarthritis to induce the synthesis and release of key cytokines of B-lymphocyte modulation such as B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor by rheumatoid fibroblast-like synoviocytes.

Methods

Microparticles were analyzed in synovial fluids from patients with rheumatoid arthritis, osteoarthritis, microcristalline arthritis, and reactive arthritis. In addition, microparticle release after activation from various cell lines (CEM lymphocyte and THP-1 cells) was assessed. Microparticles were isolated by differential centrifugation, and quantitative determinations were carried out by prothrombinase assay after capture on immobilized annexin V. B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor release was evaluated by enzyme-linked immunosorbent assay.

Results

Microparticles isolated from synovial fluids obtained from rheumatoid arthritis and osteoarthritis patients or microparticles derived from activated THP-1 cells were able to induce B cell-activating factor, thymic stroma lymphopoietin, and secretory leukocyte protease inhibitor release by rheumatoid arthritis fibroblast-like synoviocytes. Conversely, CEM-lymphocytes-derived microparticles generated by treatment with a combination of PHA, PMA and Adt-D did not promote the release of B cell-activating factor but favored the secretion of thymic stroma lymphopoietin and secretory leukocyte protease inhibitor by rheumatoid arthritis fibrobast-like synoviocytes. However, microparticles isolated from actinomycin D-treated CEM lymphocytes were not able to induce B cell-activating factor, thymic stroma lymphopoietin, or secretory leukocyte protease inhibitor release, indicating that microparticles derived from apoptotic T cells do not function as effectors in B-cell activation.

Conclusions

These results demonstrate that microparticles are signalling structures that may act as specific conveyors in the triggered induction and amplification of autoimmunity. This study also indicates that microparticles have differential effects in the crosstalk between B lymphocytes and target cells of autoimmunity regarding the parental cells from which they derive.

BAFF synthesis by rheumatoid synoviocytes is positively controlled by alpha5beta1 integrin stimulation and is negatively regulated by tumor necrosis factor alpha and Toll-like receptor ligands

OBJECTIVE

It was recently demonstrated that synoviocytes (FLS) from rheumatoid arthritis (RA) patients express BAFF transcripts that are up-regulated by tumor necrosis factor alpha (TNFalpha) and interferon-gamma (IFNgamma). Thus, BAFF increases in RA target cells might be related to activation of the receptors of innate immunity. The purpose of this study was to determine whether ligands of Toll-like receptor 2 (TLR-2), TLR-4, TLR-9, and alpha5beta1 integrin are able to induce BAFF synthesis by RA FLS.

METHODS

Quantitative reverse transcription-polymerase chain reaction analyses and enzyme-linked immunosorbent assays were performed to evaluate BAFF messenger RNA induction and BAFF release from FLS after stimulation by ligands for TLR-2, TLR-4, TLR-9, alpha5beta1 integrin (bacterial lipopeptide [BLP] palmitoyl-3-cysteine-serine-lysine-4, lipopolysaccharide [LPS], CpG, and protein I/II, respectively), TNFalpha, and IFNgamma.

RESULTS

In contrast to IFNgamma, neither TNFalpha, LPS, BLP, nor CpG induced the de novo synthesis and release of BAFF by FLS. Priming of cells with IFNgamma did not have a synergistic effect on BAFF synthesis by FLS stimulated with bacterial products known as pathogen-associated molecular patterns. Moreover, we found that IFNgamma-induced BAFF synthesis is inhibited by simultaneous stimulation with either TLR ligands or TNFalpha. We also showed that interplay between TLRs, TNF receptors, and IFNgamma signaling induces the expression of suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 and reduces IFNgamma-dependent STAT-1 phosphorylation, which might explain this inhibition. In contrast, we demonstrated that stimulation of alpha5beta1 integrin can induce BAFF synthesis and release per se and that stimulation of this pathway has no inhibitory effect on IFNgamma-induced BAFF synthesis.

CONCLUSION

Our findings indicate that BAFF secretion by resident cells in target organs of autoimmunity is tightly regulated by innate immunity, with positive and negative controls, depending on the receptors and the pathways triggered.

Histone-like DNA binding protein of Streptococcus intermedius induces the expression of pro-inflammatory cytokines in human monocytes via activation of ERK1/2 and JNK pathways

Streptococcus intermedius is a commensal associated with serious, deep-seated purulent infections in major organs, such as the brain and liver. Histone-like DNA binding protein (HLP) is an accessory architectural protein in a variety of bacterial cellular processes. In this study, we investigated the mechanisms of pro-inflammatory cytokine inductions in THP-1 cells by stimulation with recombinant HLP of S. intermedius (rSi-HLP). rSi-HLP stimulation-induced production of pro-inflammatory cytokines (IL-8, IL-1 beta and TNF-alpha) occurred in a time- and dose-dependent manner. In contrast with the heat-stable activity of DNA binding, the induction activity of rSi-HLP was heat-unstable. In subsequent studies, rSi-HLP acted cooperatively with lipoteichoic acid, the synthetic Toll-like receptor 2 agonist, Pam3CSK4, and the cytosolic nucleotide binding oligomerization domain 2 receptor agonist, muramyldipeptide. Furthermore, Western blot and blocking assays with specific inhibitors showed that rSi-HLP stimulation induced the activation of cell signal transduction pathways, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK). In addition to its physiological role in bacterial growth through DNA binding, these results indicate that Si-HLP can trigger a cascade of events that induce pro-inflammatory responses via ERK1/2 and JNK signal pathways, and suggest that bacterial HLP may contribute to the activation of host innate immunity during bacterial infection.

Adherence and internalization of Streptococcus gordonii by epithelial cells involves beta1 integrin recognition by SspA and SspB (antigen I/II family) polypeptides

Streptococcus gordonii is a commensal bacterium that colonizes the hard and soft tissues present in the human mouth and nasopharynx. The cell wall-anchored polypeptides SspA and SspB expressed by S. gordonii mediate a wide range of interactions with host proteins and other bacteria. In this article we have determined the role of SspA and SspB proteins, which are members of the streptococcal antigen I/II (AgI/II) adhesin family, in S. gordonii adherence and internalization by epithelial cells. Wild-type S. gordonii DL1 expressing AgI/II polypeptides attached to and was internalized by HEp-2 cells, whereas an isogenic AgI/II- mutant was reduced in adherence and was not internalized. Association of S. gordonii DL1 with HEp-2 cells triggered protein tyrosine phosphorylation but no significant actin rearrangement. By contrast, Streptococcus pyogenes A40 showed 50-fold higher levels of internalization and this was associated with actin polymerization and interleukin-8 upregulation. Adherence and internalization of S. gordonii by HEp-2 cells involved beta1 integrin recognition but was not fibronectin-dependent. Recombinant SspA and SspB polypeptides bound to purified human alpha5beta1 integrin through sequences present within the NAV (N-terminal) region of AgI/II polypeptide. AgI/II polypeptides blocked interactions of S. gordonii and S. pyogenes with HEp-2 cells, and S. gordonii DL1 cells expressing AgI/II proteins inhibited adherence and internalization of S. pyogenes by HEp-2 cells. Conversely, S. gordonii AgI/II- mutant cells did not inhibit internalization of S. pyogenes. The results suggest that AgI/II proteins not only promote integrin-mediated internalization of oral commensal streptococci by host cells, but also potentially influence susceptibility of host tissues to more pathogenic bacteria.

Glucosyltransferases of viridans group streptococci modulate interleukin-6 and adhesion molecule expression in endothelial cells and augment monocytic cell adherence

Recruitment of monocytes plays important roles during vegetation formation and endocardial inflammation in the pathogenesis of infective endocarditis (IE). Bacterial antigens or modulins can activate endothelial cells through the expression of cytokines or adhesion molecules and modulate the recruitment of leukocytes. We hypothesized that glucosyltransferases (GTFs), modulins of viridans group streptococci, may act directly to up-regulate the expression of adhesion molecules and also interleukin-6 (IL-6) to augment monocyte attachment to endothelial cells. Using primary cultured human umbilical vein endothelial cells (HUVECs) as an in vitro model, we demonstrated that GTFs (in the cell-bound or free form) could specifically modulate the expression of IL-6, and also adhesion molecules, in a dose- and time-dependent manner. Results of inhibition assays suggested that enhanced expression of adhesion molecules was dependent on the activation of nuclear factor kappaB (NF-kappaB) and extracellular signal-regulated kinase and that p38 mitogen-activated protein kinase pathways also contributed to the release of IL-6. Streptococcus-infected HUVECs or treatment with purified IL-6 plus soluble IL-6 receptor alpha enhanced the expression of ICAM-1 and the adherence of the monocytic cell line U937. These results suggest that streptococcal GTFs might play an important role in recruiting monocytic cells during inflammation in IE through induction of adhesion molecules and IL-6, a cytokine involved in transition from neutrophil to monocyte recruitment.

Cross Talk between MyD88 and Focal Adhesion Kinase Pathways

Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase involved in signaling downstream of integrins, linking bacterial detection, cell entry, and initiation of proinflammatory response through MAPKs and NF-kappaB activation. In this study, using protein I/II from Streptococcus mutans as a model activator of FAK, we investigated the potential link between FAK and TLR pathways. Using macrophages from TLR- or MyD88-deficient mice, we report that MyD88 plays a major role in FAK-dependent protein I/II-induced cytokine release. However, response to protein I/II stimulation was independent of TLR4, TLR2, and TLR6. The data suggest that there is a cross talk between FAK and MyD88 signaling pathways. Moreover, MyD88-dependent, LPS-induced IL-6 secretion by human and murine fibroblasts required the presence of FAK, confirming that MyD88 and FAK pathways are interlinked.

Insertional inactivation of pac and rmlB genes reduces the release of tumor necrosis factor alpha, interleukin-6, and interleukin-8 induced by Streptococcus mutans in monocytic, dental pulp, and periodontal ligament cells

Streptococcus mutans possesses different cell wall molecules, such as protein of the I/II family, the serotype f polysaccharide rhamnose glucose polymer (RGP), and lipoteichoic acid (LTA), which act as adhesins and modulins, allowing S. mutans to colonize teeth and cause dental caries and pulpitis. We tested several isogenic mutants of S. mutans defective in protein I/II and/or RGP, as well as purified modulins such as protein I/II, RGP, and LTA, for their binding and activation abilities on monocytic, dental pulp (DP), and periodontal ligament (PDL) cells. Our results demonstrate that both protein I/II and RGP play important roles in streptococcal adherence to human monocytic and fibroblastic cells, whereas LTA is only a minor adhesin. In the activation process, the cytokine response elicited is polarized toward a Th1 response which seems principally due to protein I/II and RGP. Even if protein I/II seems to be more efficient in its purified form in triggering cells to release interleukin-8 (IL-8), RGP is the most efficient cytokine-stimulating component in intact bacteria, while LTA plays only a minor role. In cell activation, we showed, by using either cytochalasin D or coated ligands, that internalization of either S. mutans, S. mutans isogenic mutants, or purified ligands is not necessary to trigger cells to release IL-8. We also showed that, besides the implication of monocytes in pulpal inflammation, fibroblast-like cells such as DP and PDL cells are also actively implicated in local inflammation and in the generation of a Th1 response after stimulation with S. mutans cells or antigens.

ERK 1/2- and JNKs-dependent synthesis of interleukins 6 and 8 by fibroblast-like synoviocytes stimulated with protein I/II, a modulin from oral streptococci, requires focal adhesion kinase

Protein I/II, a pathogen-associated molecular pattern from oral streptococci, is a potent inducer of interleukin-6 (IL-6) and IL-8 synthesis and release from fibroblast-like synoviocytes (FLSs), cells that are critically involved in joint inflammation. This synthesis implicates ERK 1/2 and JNKs as well as AP-1-binding activity and nuclear translocation of NF-kappaB. The mechanisms by which protein I/II activates MAPKs remain, however, elusive. Because focal adhesion kinase (FAK) was proposed to play a role in signaling to MAPKs, we examined its ability to contribute to the MAPKs-dependent synthesis of IL-6 and IL-8 in response to protein I/II. We used FAK-/- fibroblasts as well as FAK+/+ fibroblasts and FLSs transfected with FRNK, a dominant negative form of FAK. The results demonstrate that IL-6 and IL-8 release in response to protein I/II was strongly inhibited in both protein I/II-stimulated FAK-/- and FRNK-transfected cells. Cytochalasin D, which inhibits protein I/II-induced phosphorylation of FAK (Tyr-397), had no effect either on activation of ERK 1/2 and JNKs or on IL-6 and IL-8 release. Taken together, these results indicate that IL-6 and IL-8 release by protein I/II-activated FLSs is regulated by FAK independently of Tyr-397 phosphorylation.

NF-kappaB and the MAP kinases/AP-1 pathways are both involved in interleukin-6 and interleukin-8 expression in fibroblast-like synoviocytes stimulated by protein I/II, a modulin from oral streptococci

As in rheumatoid arthritis (RA), it was demonstrated recently that bacterial fragments of DNA or rRNA are present in the joint and therefore could play a role in inducing or perpetuating the disease, this work was initiated to define mechanisms that account for the stimulatory activities of the oral streptococcal modulin, protein I/II, on fibroblast-like synoviocytes (FLSs) from RA patients. FLSs from RA patients were stimulated with protein I/II, and expression of interleukin (IL)-6 and IL-8 mRNA was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Immunoblotting by antibodies specific for activated forms of MAPKs and electrophoretic mobility shift assays (EMSAs) were performed to study downstream signalling, which allowed the synthesis of IL-6 and IL-8. We reported that protein I/II interactions with FLSs from RA patients trigger the synthesis and release of IL-6 and IL-8. We also demonstrated that protein I/II enhances the phosphorylation of ERK 1/2, p38 and JNKs and that ERK 1/2 and JNK MAPKs seem to play a more important role than p38 in protein I/II-mediated synthesis of IL-6 and IL-8. Our experiments also indicated that stimulation of FLSs with protein I/II induces nuclear translocation of NF-kappaB, AP-1-binding activity and that NF-kappaB plays a major role in IL-6 and IL-8 secretion from activated cells.

Expression and functional properties of the Streptococcus intermedius surface protein antigen I/II

Streptococcus intermedius is associated with deep-seated purulent infections. In this study, we investigated expression and functional activities of antigen I/II in S. intermedius. The S. intermedius antigen I/II appeared to be cell surface associated, with a molecular mass of approximately 160 kDa. Northern blotting indicated that the S. intermedius NCTC 11324 antigen I/II gene was transcribed as a monocistronic message. Maximum expression was seen during the early exponential phase. Insertional inactivation of the antigen I/II gene resulted in reduced hydrophobicity during early exponential phase, whereas no effect was detected during mid- and late exponential phases. Binding to human fibronectin and laminin was reduced in the isogenic mutant, whereas binding to human collagen types I and IV and to rat collagen type I was not significant for either the wild type or the mutant. Compared to the wild type, the capacity of the isogenic mutant to induce interleukin 8 (IL-8) release by THP-1 monocytic cells was significantly reduced. The results indicate that the S. intermedius antigen I/II is involved in adhesion to human receptors and in IL-8 induction.