Entry of spores into intestinal epithelial cells contributes to recurrence of Clostridioides difficile infection.

Clostridioides difficile spores produced during infection are important for the recurrence of the disease. Here, we show that C. difficile spores gain entry into the intestinal mucosa via pathways dependent on host fibronectin-α5ß1 and vitronectin-αvß1. The exosporium protein BclA3, on the spore surface, is required for both entry pathways. Deletion of the bclA3 gene in C. difficile, or pharmacological inhibition of endocytosis using nystatin, leads to reduced entry into the intestinal mucosa and reduced recurrence of the disease in a mouse model. Our findings indicate that C. difficile spore entry into the intestinal barrier can contribute to spore persistence and infection recurrence, and suggest potential avenues for new therapies.

Characterization of a novel protein of Leptospira interrogans exhibiting plasminogen, vitronectin and complement binding properties.

Leptospirosis is a severe zoonosis caused by pathogenic species of the genus Leptospira. This work focuses on a hypothetical protein of unknown function, encoded by the gene LIC13259, and predicted to be a surface protein, widely distributed among pathogenic leptospiral strain. The gene was amplified from L. interrogans serovar Copenhageni, strain Fiocruz L1-130, cloned and the protein expressed using Escherichia coli as a host system. Immunofluorescence assay showed that the protein is surface-exposed. The recombinant protein LIC13259 (rLIC13259) has the ability to interact with the extracellular matrix (ECM) laminin, in a dose-dependent manner but saturation was not reach. The rLIC13259 protein is a plasminogen (PLG)-binding protein, generating plasmin, in the presence of urokinase PLG-activator uPA. The recombinant protein is able to mediate the binding to human purified terminal complement route vitronectin, C7, C8 and C9, and to recruit and interact with these components from normal human serum (NHS). These interactions are dose-dependent on NHS increased concentration. The binding of rLIC13259 to C8 and vitronectin was slight and pronounced inhibited in the presence of increasing heparin concentration, respectively, suggesting that the interaction with vitronectin occurs via heparin domain. Most interesting, the interaction of rLIC13259 with C9 protein was capable of preventing C9 polymerization, suggesting that the membrane attack complex (MAC) formation was inhibited. Thus, we tentatively assign the coding sequence (CDS) LIC13259, previously annotated as unknown function, as a novel protein that may play an important role in the host's invasion and immune evasion processes, contributing to the establishment of the leptospiral infection.

Binding of human complement C1 sterase inhibitor to Leptospira spp.

Leptospirosis is an important zoonosis of global importance caused by bacteria Leptospira spp. Pathogenic Leptospira is resistant to Complement System killing while non-pathogenic Leptospira is rapidly killed by exposure to normal human serum (NHS). Pathogenic Leptospira interact with Complement Regulators such as Factor H, C4b binding protein and Vitronectin avoiding Complement activation and killing by Alternative and Classical Pathways. One important regulator is C1-inhibitor (C1INH) that interacts with C1s or MASPs controlling the cleavage of C4 and C2 molecules, thereby inhibiting the activation of the Classical and Lectin Pathways. In this study, we demonstrate that attenuated, saprophytic and pathogenic Leptospira interact with C1INH that maintain its regulatory capacity of interaction with C1s preventing the activation of Complement system. Although the interaction with C1INH is not crucial for pathogenic Leptospira survival, it seems to be important for the survival of attenuated and saprophytic Leptospira in normal human serum.

Characterization of the Adherence of Clostridium difficile Spores: The Integrity of the Outermost Layer Affects Adherence Properties of Spores of the Epidemic Strain R20291 to Components of the Intestinal Mucosa.

Clostridium difficile is the causative agent of the most frequently reported nosocomial diarrhea worldwide. The high incidence of recurrent infection is the main clinical challenge of C. difficile infections (CDI). Formation of C. difficile spores of the epidemic strain R20291 has been shown to be essential for recurrent infection and transmission of the disease in a mouse model. However, the underlying mechanisms of how these spores persist in the colonic environment remains unclear. In this work, we characterized the adherence properties of epidemic R20291 spores to components of the intestinal mucosa, and we assessed the role of the exosporium integrity in the adherence properties by using cdeC mutant spores with a defective exosporium layer. Our results showed that spores and vegetative cells of the epidemic R20291 strain adhered at high levels to monolayers of Caco-2 cells and mucin. Transmission electron micrographs of Caco-2 cells demonstrated that the hair-like projections on the surface of R20291 spores are in close proximity with the plasma membrane and microvilli of undifferentiated and differentiated monolayers of Caco-2 cells. Competitive-binding assay in differentiated Caco-2 cells suggests that spore-adherence is mediated by specific binding sites. By using spores of a cdeC mutant we demonstrated that the integrity of the exosporium layer determines the affinity of adherence of C. difficile spores to Caco-2 cells and mucin. Binding of fibronectin and vitronectin to the spore surface was concentration-dependent, and depending on the concentration, spore-adherence to Caco-2 cells was enhanced. In the presence of an aberrantly-assembled exosporium (cdeC spores), binding of fibronectin, but not vitronectin, was increased. Notably, independent of the exosporium integrity, only a fraction of the spores had fibronectin and vitronectin molecules binding to their surface. Collectively, these results demonstrate that the integrity of the exosporium layer of strain R20291 contributes to selective spore adherence to components of the intestinal mucosa.

Inhibition of the Membrane Attack Complex by Dengue Virus NS1 through Interaction with Vitronectin and Terminal Complement Proteins.

Dengue virus (DENV) infects millions of people worldwide and is a major public health problem. DENV nonstructural protein 1 (NS1) is a conserved glycoprotein that associates with membranes and is also secreted into the plasma in DENV-infected patients. The present study describes a novel mechanism by which NS1 inhibits the terminal complement pathway. We first identified the terminal complement regulator vitronectin (VN) as a novel DENV2 NS1 binding partner by using a yeast two-hybrid system. This interaction was further assessed by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) assay. The NS1-VN complex was also detected in plasmas from DENV-infected patients, suggesting that this interaction occurs during DENV infection. We also demonstrated that the DENV2 NS1 protein, either by itself or by interacting with VN, hinders the formation of the membrane attack complex (MAC) and C9 polymerization. Finally, we showed that DENV2, West Nile virus (WNV), and Zika virus (ZIKV) NS1 proteins produced in mammalian cells inhibited C9 polymerization. Taken together, our results points to a role for NS1 as a terminal pathway inhibitor of the complement system. IMPORTANCE: Dengue is the most important arthropod-borne viral disease nowadays and is caused by dengue virus (DENV). The flavivirus NS1 glycoprotein has been characterized functionally as a complement evasion protein that can attenuate the activation of the classical, lectin, and alternative pathways. The present study describes a novel mechanism by which DENV NS1 inhibits the terminal complement pathway. We identified the terminal complement regulator vitronectin (VN) as a novel DENV NS1 binding partner, and the NS1-VN complex was detected in plasmas from DENV-infected patients, suggesting that this interaction occurs during DENV infection. We also demonstrated that the NS1-VN complex inhibited membrane attack complex (MAC) formation, thus interfering with the complement terminal pathway. Interestingly, NS1 itself also inhibited MAC activity, suggesting a direct role of this protein in the inhibition process. Our findings imply a role for NS1 as a terminal pathway inhibitor of the complement system.

Vitronectin expression in the airways of subjects with asthma and chronic obstructive pulmonary disease.

Vitronectin, a multifunctional glycoprotein, is involved in coagulation, inhibition of the formation of the membrane attack complex (MAC), cell adhesion and migration, wound healing, and tissue remodeling. The primary cellular source of vitronectin is hepatocytes; it is not known whether resident cells of airways produce vitronectin, even though the glycoprotein has been found in exhaled breath condensate and bronchoalveolar lavage from healthy subjects and patients with interstitial lung disease. It is also not known whether vitronectin expression is altered in subjects with asthma and COPD. In this study, bronchial tissue from 7 asthmatic, 10 COPD and 14 control subjects was obtained at autopsy and analyzed by immunohistochemistry to determine the percent area of submucosal glands occupied by vitronectin. In a separate set of experiments, quantitative colocalization analysis was performed on tracheobronchial tissue sections obtained from donor lungs (6 asthmatics, 4 COPD and 7 controls). Vitronectin RNA and protein expressions in bronchial surface epithelium were examined in 12 subjects who undertook diagnostic bronchoscopy. Vitronectin was found in the tracheobronchial epithelium from asthmatic, COPD, and control subjects, although its expression was significantly lower in the asthmatic group. Colocalization analysis of 3D confocal images indicates that vitronectin is expressed in the glandular serous epithelial cells and in respiratory surface epithelial cells other than goblet cells. Expression of the 65-kDa vitronectin isoform was lower in bronchial surface epithelium from the diseased subjects. The cause for the decreased vitronectin expression in asthma is not clear, however, the reduced concentration of vitronectin in the epithelial/submucosal layer of airways may be linked to airway remodeling.

Recombinant disintegrin targets α(v) ß(3) integrin and leads to mediator production.

Integrin αvß3 is most likely the foremost modulator of angiogenesis among all known integrins. Recombinant disintegrin DisBa-01, originally obtained from snake venom glands, binds to αvß3, thereby significantly inhibiting adhesion and generating in vivo anti-metastatic ability. However, its function in mediator production is not clear. Here, we observed that the mediators VEGF-A, IL-8, and TGF-ß are not produced by human umbilical vein endothelial cells (HUVEC cell line) or monocyte/macrophage cells (SC cell line) when cells adhered to vitronectin. However, when exposed to DisBa-01, HUVECs produced higher levels of TGF-ß, and SC cells produced higher levels of VEGF-A. Nonetheless, HUVECs also showed an enhancement of apoptosis after losing adherence when exposed to disintegrin, which is a characteristic of anoikis. We propose that disintegrin DisBa-01 could be used to modulate integrin αvß3 functions.

Cell adhesion glycoprotein vitronectin during Xenopus laevis embryogenesis.

Vitronectin (vn) is a cell-adhesive glycoprotein present in blood and extracellular matrix of all vertebrates. In the present study we reported the cDNA cloning of Xenopus laevisvitronectin and its spatial and temporal expression pattern during the embryonic development of this important model organism. The deduced amino acid sequence of Xenopus laevis vn showed 49%, 47% and 43% identity with human, chicken and zebrafish orthologs, respectively, whereas the comparison with Xenopus tropicalis vn presented 85% identity. The structural organization consisting of a somatomedin B domain and two hemopexin-like domains was similar to higher vertebrate vitronectins. The vn transcripts were detected from stage 28 onward. At tadpole stages, vn is expressed in heart, gut derivatives and in the notochord. The protein was detected in heart, liver, foregut, pronephros and notochord at stages 43 and 47 of Xenopus embryos. Our results suggest that vitronectin is developmentally regulated and could participate in embryo organogenesis.

Developmental expression of prion protein and its ligands stress-inducible protein 1 and vitronectin.

Prion protein (PrP(C)) is the normal isoform of PrP(Sc), a protein involved in neurodegenerative disorders. PrP(C) participates in neuritogenesis, neuroprotection, and memory consolidation through its interaction with the secreted protein stress-inducible protein 1 (STI1) and the extracellular matrix protein vitronectin (Vn). Although PrP(C) mRNA expression has been documented during embryogenesis, its protein expression patterns have not been evaluated. Furthermore, little is known about either Vn or STI protein expression. In this study, PrP(C), STI1, and Vn protein expression was explored throughout mouse embryonic life. We found that the distributions of the three proteins were spatiotemporally related. STI1 and Vn expression became evident at E8, earlier than PrP(C), in the nervous system and heart. At E10, we observed, in the spinal cord, a gradient of expression of the three proteins, more abundant in the notochord and floor plate, suggesting that they can have a role in axonal growth. As development proceeded, the three proteins were detected in other organs, suggesting that they may play a role in the development of nonneural tissues as well. Finally, although STI1 and Vn are PrP(C) ligands, their expression was not altered in PrP(C)-null mice.

Effects of Himatanthus lancifolius on human leukocyte chemotaxis and their adhesion to integrins.

The aim of this work was to investigate the anti-inflammatory activities of the uleine-rich fraction extracted from the barks of Himatanthus lancifolius (Muell. Arg.) Woodson (Apocynaceae). To achieve this, we focused on its in vitro effects on some steps of the inflammatory response using peripheral human leukocytes. The results presented herein show that the uleine-rich fraction significantly inhibits the migration of casein-induced granulocytes and their adhesion to fibronectin and vitronectin, along with mononuclear cells, by down-regulating the expression of alpha 4beta1 and alpha5beta1 integrins. The data suggest that H. LANCIFOLIUS has the potential of interferring with leukocyte trafficking through its uleine-rich fraction, emphasizing its usefulness in inflammatory conditions. DEXA:dexamethasone disodium phosphate FN:fibronectin PMN:polymorphonuclear URF:uleine-rich fraction VN:vitronectin.

Cellular prion protein interaction with vitronectin supports axonal growth and is compensated by integrins.

The physiological functions of the cellular prion protein, PrP(C), as a cell surface pleiotropic receptor are under debate. We report that PrP(C) interacts with vitronectin but not with fibronectin or collagen. The binding sites mediating this PrP(C)-vitronectin interaction were mapped to residues 105-119 of PrP(C) and the residues 307-320 of vitronectin. The two proteins were co-localized in embryonic dorsal root ganglia from wild-type mice. Vitronectin addition to cultured dorsal root ganglia induced axonal growth, which could be mimicked by vitronectin peptide 307-320 and abrogated by anti-PrP(C) antibodies. Full-length vitronectin, but not the vitronectin peptide 307-320, induced axonal growth of dorsal root neurons from two strains of PrP(C)-null mice. Functional assays demonstrated that relative to wild-type cells, PrP(C)-null dorsal root neurons were more responsive to the Arg-Gly-Asp peptide (an integrin-binding site), and exhibited greater alphavbeta3 activity. Our findings indicate that PrP(C) plays an important role in axonal growth, and this function may be rescued in PrP(C)-knockout animals by integrin compensatory mechanisms.

Potential role for insulin-like growth factor II and vitronectin in the endothelial-mesenchymal transition process.

Endothelial-to-mesenchymal transition (EndoMT) is a process through which certain subsets of endothelial cells lose endothelial characteristics and transform into mesenchymal or smooth muscle-like cells. Emerging evidence suggests that this process plays an important role during vascular development and in many vascular pathologies. As in epithelial-mesenchymal transition, EndoMT seems to progress through a series of important steps whose interdependence and order are not clear, and that some of them are regulated by soluble growth factors. Insulin-like growth factor II (IGFII), apart from being considered important in cancer, angiogenesis, and atherosclerotic lesions, is also considered as essential to embryonic development. Here, we report that addition of IGFII promoted the EndoMT process in the presence of very low amounts of chicken serum to arrested primary embryonic aortic chicken endothelial cells attached to fibronectin (FN), gelatin, or native type I collagen. This was demonstrated by cell spreading, loss of cell-cell contacts, detachment, migration, and transformation. These cellular events also occurred when IGFII was added to medium containing vitronectin (VN). Additionally, we demonstrated that these proteins were present in the spontaneous intimal thickenings that are observed at day 11-13 of chicken embryo development. We also show that alterations in the distribution of VE-cadherin and beta-catenin occur after IGFII and serum or VN stimulation, and propose that the via VN IGFII effects may be facilitated by interaction of the mannose-6-phosphate/IGFII receptor (M6P/IGFIIR) with the urokinase-type plasminogen activator receptor (uPAR) and its ligand (uPA). Collectively, these findings provide the first evidence for a potential role of the IGFII-VN complex during the EndoMT process. From our observations and previous studies, we postulate a working hypothesis supporting a fundamental role for these molecules during EndoMT.

Integrin alpha(v)beta(3) mediates rotavirus cell entry.

Rotavirus strains differ in their need for sialic acid (SA) for initial binding to the cell surface; however, the existence of a postattachment cell receptor, common to most, if not all, rotavirus strains, has been proposed. In the present study, antibodies to the alpha(v) and beta(3) integrin subunits, and the alpha(v)beta(3) ligand, vitronectin, efficiently blocked the infectivity of the SA-dependent rhesus rotavirus RRV, its SA-independent variant nar3, and the neuraminidase-resistant human rotavirus strain Wa. Vitronectin and anti-beta(3) antibodies, however, did not block the binding of virus to cells, indicating that rotaviruses interact with alpha(v)beta(3) at a postbinding step, probably penetration. This interaction was shown to be independent of the tripeptide motif arginine-glycine-aspartic acid present in the natural ligands of this integrin. Transfection of CHO cells with alpha(v)beta(3) genes significantly increased their permissiveness to all three rotavirus strains, and the increment of virus infectivity was reverted by incubation of these cells either with antibodies to beta(3) or with vitronectin. These findings implicate alpha(v)beta(3) integrin as a cellular receptor common to neuraminidase-sensitive and neuraminidase-resistant rotaviruses, and support the hypothesis that this integrin could determine, at least in part, the cellular susceptibility to rotaviruses.

Amphibian Bufo arenarum vitronectin-like protein: its localization during oogenesis.

In the present study, we analyzed the localization of vitronectin-like protein in oocytes during oogenesis as well as in the serum and liver tissue of the amphibian Bufo arenarum. Vitronectin-like protein was purified from serum by heparin-affinity chromatography and showed to have the two biological properties in common with most animal vitronectins (VN): heparin binding activity and an RGD-dependent cell-spreading activity. SDS-PAGE of vitronectin-like protein revealed that it consists of two bands of 64 kDa and 72 kDa, while immunoblotting analyses showed that this protein strongly cross-reacts with two monoclonal antibodies against human VN. No immunofluorescent staining of vitronectin-like protein was observed in previtellogenic oocytes (stages I and II). In vitellogenic oocytes (stages III, IV and V) fluorescence was observed in the cortical cytoplasm localized in yolk platelets, extending concomitantly with the vitellogenic process. When we examined the yolk platelet formation pathway by immunoelectron microscopy, gold particles indicated that vitronectin-like protein was located on the yolk platelet precursors: multivesicular bodies and primordial yolk platelets. Gold particles also were seen sparsely distributed in all oocyte investing layers. The mean serum vitronectin-like protein concentration in amphibian animals was 127.8 +/- 11.6 micrograms/ml in adult males and 181.5 +/- 14.3 micrograms/ml in adult females. Serum vitronectin-like protein of males and females was susceptible to hormonal stimulation (17-beta estradiol). These results suggest that vitronectin-like protein is stored in the yolk platelets and may be involved in the later events of amphibian development.