Thrombospondin-1 (TSP-1), a new bone morphogenetic protein-2 and -4 (BMP-2/4) antagonist identified in pituitary cells.

Bone morphogenetic proteins (BMPs) regulate diverse cellular responses during embryogenesis and in adulthood including cell differentiation, proliferation, and death in various tissues. In the adult pituitary, BMPs participate in the control of hormone secretion and cell proliferation, suggesting a potential endocrine/paracrine role for BMPs, but some of the mechanisms are unclear. Here, using a bioactivity test based on embryonic cells (C3H10T1/2) transfected with a BMP-responsive element, we sought to determine whether pituitary cells secrete BMPs or BMP antagonists. Interestingly, we found that pituitary-conditioned medium contains a factor that inhibits action of BMP-2 and -4. Combining surface plasmon resonance and high-resolution mass spectrometry helped pinpoint this factor as thrombospondin-1 (TSP-1). Surface plasmon resonance and co-immunoprecipitation confirmed that recombinant human TSP-1 can bind BMP-2 and -4 and antagonize their effects on C3H10T1/2 cells. Moreover, TSP-1 inhibited the action of serum BMPs. We also report that the von Willebrand type C domain of TSP-1 is likely responsible for this BMP-2/4-binding activity, an assertion based on sequence similarity that TSP-1 shares with the von Willebrand type C domain of Crossveinless 2 (CV-2), a BMP antagonist and member of the chordin family. In summary, we identified for the first time TSP-1 as a BMP-2/-4 antagonist and presented a structural basis for the physical interaction between TSP-1 and BMP-4. We propose that TSP-1 could regulate bioavailability of BMPs, either produced locally or reaching the pituitary via blood circulation. In conclusion, our findings provide new insights into the involvement of TSP-1 in the BMP-2/-4 mechanisms of action.

Identification of the epidermal growth factor receptor as the receptor for Salmonella Rck-dependent invasion.

The Salmonella Rck outer membrane protein binds to the cell surface, which leads to bacterial internalization via a Zipper mechanism. This invasion process requires induction of cellular signals, including phosphorylation of tyrosine proteins, and activation of c-Src and PI3K, which arises as a result of an interaction with a host cell surface receptor. In this study, epidermal growth factor receptor (EGFR) was identified as the cell signaling receptor required for Rck-mediated adhesion and internalization. First, Rck-mediated adhesion and internalization were shown to be altered when EGFR expression and activity were modulated. Then, immunoprecipitations were performed to demonstrate the Rck-EGFR interaction. Furthermore, surface plasmon resonance biosensor and homogeneous time-resolved fluorescence technologies were used to demonstrate the direct interaction of Rck with the extracellular domain of human EGFR. Finally, our study strongly suggests a noncompetitive binding of Rck and EGF to EGFR. Overall, these results demonstrate that Rck is able to bind to EGFR and thereby establish a tight adherence to provide a signaling cascade, which leads to internalization of Rck-expressing bacteria.-Wiedemann, A., Mijouin, L., Ayoub, M. A., Barilleau, E., Canepa, S., Teixeira-Gomes, A. P., Le Vern, Y., Rosselin, M., Reiter, E., Velge, P. Identification of the epidermal growth factor receptor as the receptor for Salmonella Rck-dependent invasion.

Direct regulation of the pefI-srgC operon encoding the Rck invasin by the quorum-sensing regulator SdiA in Salmonella†Typhimurium.

One important step for the pathogenesis of Salmonella is its ability to penetrate host cells. Recently, a new entry system involving the outer membrane protein Rck has been characterized. Previous studies have shown that the pefI-srgC locus, which contains rck, was regulated by the temperature and SdiA, the transcriptional regulator of quorum sensing in Salmonella. To decipher the regulation of rck by SdiA, we first confirmed the operon organization of the pefI-srgC locus. Using plasmid-based transcriptional fusions, we showed that only the predicted distal promoter upstream of pefI, PefIP2, displays an SdiA- and acyl-homoserine lactones-dependent activity while the predicted proximal PefIP1 promoter exhibits a very low activity independent on SdiA in our culture conditions. A direct and specific interaction of SdiA with this PefIP2 region was identified using electrophoretic mobility shift assays and surface plasmon resonance studies. We also observed that Rck expression is negatively regulated by the nucleoid-associated H-NS protein at both 25°C and 37°C. This work is the first demonstration of a direct regulation of genes by SdiA in Salmonella and will help further studies designed to identify environmental conditions required for Rck expression and consequently contribute to better characterize the role of this invasin in vivo.

Bile-mediated activation of the acrAB and tolC multidrug efflux genes occurs mainly through transcriptional derepression of ramA in Salmonella enterica serovar Typhimurium.

OBJECTIVES: In Salmonella Typhimurium, the genes encoding the AcrAB-TolC multidrug efflux system are mainly regulated by the ramRA locus, composed of the divergently transcribed ramA and ramR genes. The acrAB and tolC genes are transcriptionally activated by RamA, the gene for which is itself transcriptionally repressed by RamR. Previous studies have reported that bile induces acrAB in a ramA-dependent manner, but none provided evidence for an induction of ramA expression by bile. Therefore, the objective of this study was to clarify the regulatory mechanism by which bile activates acrAB and tolC. METHODS: qRT-PCR was used to address the effects of bile (using choleate, an ox-bile extract) on the expression of ramA, ramR, acrB and tolC. Electrophoretic mobility shift assays and surface plasmon resonance experiments were used to measure the effect of bile on RamR binding to the ramA promoter (PramA) region. RESULTS: We show that ramA is transcriptionally activated by bile and is strictly required for the bile-mediated activation of acrB and tolC. Additionally, bile is shown to specifically inhibit the binding of RamR to the PramA region, which overlaps the putative divergent ramR promoter, thereby explaining our observation that bile also activates ramR transcription. CONCLUSIONS: We propose a regulation model whereby the bile-mediated activation of the acrAB and tolC multidrug efflux genes occurs mainly through the transcriptional derepression of the ramA activator gene.

Novel feature of Mycobacterium avium subsp. paratuberculosis, highlighted by characterization of the heparin-binding hemagglutinin adhesin.

Mycobacterium avium subsp. paratuberculosis comprises two genotypically defined groups, known as the cattle (C) and sheep (S) groups. Recent studies have reported phenotypic differences between M. avium subsp. paratuberculosis groups C and S, including growth rates, infectivity for macrophages, and iron metabolism. In this study, we investigated the genotypes and biological properties of the virulence factor heparin-binding hemagglutinin adhesin (HBHA) for both groups. In Mycobacterium tuberculosis, HBHA is a major adhesin involved in mycobacterium-host interactions and extrapulmonary dissemination of infection. To investigate HBHA in M. avium subsp. paratuberculosis, we studied hbhA polymorphisms by fragment analysis using the GeneMapper technology across a large collection of isolates genotyped by mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) and IS900 restriction fragment length polymorphism (RFLP-IS900) analyses. Furthermore, we analyzed the structure-function relationships of recombinant HBHA proteins of types C and S by heparin-Sepharose chromatography and surface plasmon resonance (SPR) analyses. In silico analysis revealed two forms of HBHA, corresponding to the prototype genomes for the C and S types of M. avium subsp. paratuberculosis. This observation was confirmed using GeneMapper on 85 M. avium subsp. paratuberculosis strains, including 67 strains of type C and 18 strains of type S. We found that HBHAs from all type C strains contain a short C-terminal domain, while those of type S present a long C-terminal domain, similar to that produced by Mycobacterium avium subsp. avium. The purification of recombinant HBHA from M. avium subsp. paratuberculosis of both types by heparin-Sepharose chromatography highlighted a correlation between their affinities for heparin and the lengths of their C-terminal domains, which was confirmed by SPR analysis. Thus, types C and S of M. avium subsp. paratuberculosis may be distinguished by the types of HBHA they produce, which differ in size and adherence properties, thereby providing new evidence that strengthens the genotypic differences between the C and S types of M. avium subsp. paratuberculosis.

Deleted in malignant brain tumor 1 is secreted in the oviduct and involved in the mechanism of fertilization in equine and porcine species.

Oviductal environment affects preparation of gametes for fertilization, fertilization itself, and subsequent embryonic development. The aim of this study was to evaluate the effect of oviductal fluid and the possible involvement of deleted in malignant brain tumor 1 (DMBT1) on IVF in porcine and equine species that represent divergent IVF models. We first performed IVF after pre-incubation of oocytes with or without oviductal fluid supplemented or not with antibodies directed against DMBT1. We showed that oviductal fluid induces an increase in the monospermic fertilization rate and that this effect is canceled by the addition of antibodies, in both porcine and equine species. Moreover, pre-incubation of oocytes with recombinant DMBT1 induces an increase in the monospermic fertilization rate in the pig, confirming an involvement of DMBT1 in the fertilization process. The presence of DMBT1 in the oviduct at different stages of the estrus cycle was shown by western blot and confirmed by immunohistochemical analysis of ampulla and isthmus regions. The presence of DMBT1 in cumulus-oocyte complexes was shown by western blot analysis, and the localization of DMBT1 in the zona pellucida and cytoplasm of equine and porcine oocytes was observed using immunofluorescence analysis and confocal microscopy. Moreover, we showed an interaction between DMBT1 and porcine spermatozoa using surface plasmon resonance studies. Finally, a bioinformatic and phylogenetic analysis allowed us to identify the DMBT1 protein as well as a DMBT1-like protein in several mammals. Our results strongly suggest an important role of DMBT1 in the process of fertilization.

Kallikrein-related peptidase 12 hydrolyzes matricellular proteins of the CCN family and modifies interactions of CCN1 and CCN5 with growth factors.

Kallikrein-related peptidases (KLKs) are an emerging group of secreted serine proteases involved in several physiological and pathological processes. We used a degradomic approach to identify potential substrates of KLK12. MDA-MB-231 cells were treated either with KLK12 or vehicle control, and the proteome of the overlying medium was analyzed by mass spectrometry. CCN1 (cyr61, ctgf, nov) was among the proteins released by the KLK12-treated cells, suggesting that KLK12 might be responsible for the shedding of this protein from the cell surface. Fragmentation of CCN1 by KLK12 was further confirmed in vitro, and the main cleavage site was localized in the hinge region between the first and second half of the recombinant protein. KLK12 can target all six members of the CCN family at different proteolytic sites. Limited proteolysis of CCNs (cyr61, ctgf, nov) was also observed in the presence of other members of the KLK family, such as KLK1, KLK5, and KLK14, whereas KLK6, KLK11, and KLK13 were unable to fragment CCNs. Because KLK12 seems to have a role in angiogenesis, we investigated the relations between KLK12, CCNs, and several factors known to be involved in angiogenesis. Solid phase binding assays showed that fragmentation of CCN1 or CCN5 by KLK12 prevents VEGF(165) binding, whereas it also triggers the release of intact VEGF and BMP2 from the CCN complexes. The KLK12-mediated release of TGF-ß1 and FGF-2, either as intact or truncated forms, was found to be concentration-dependent. These findings suggest that KLK12 may indirectly regulate the bioavailability and activity of several growth factors through processing of their CCN binding partners.

Regulation of fructooligosaccharide metabolism in an extra-intestinal pathogenic Escherichia coli strain.

A gene cluster involved in the metabolism of prebiotic short-chain fructooligosaccharides (scFOS) has recently been identified in the extra-intestinal avian pathogenic Escherichia coli strain BEN2908. This gene cluster, called the fos locus, plays a major role in the initiation stage of chicken intestinal colonization. This locus is composed of six genes organized as an operon encoding a sugar transporter and enzymes involved in scFOS metabolism, and of a divergently transcribed gene encoding a transcriptional regulator, FosR, belonging to the LacI/GalR family. To decipher the regulation of scFOS metabolism, we monitored the fos operon promoter activity using a luciferase reporter gene assay. We demonstrated that the expression of fos genes is repressed by FosR, controlled by catabolite repression and induced in the presence of scFOS. Using electrophoretic mobility shift assays and surface plasmon resonance experiments, we showed that FosR binds to two operator sequences of the fos operon promoter region. This binding to DNA was inhibited in the presence of scFOS, especially by GF2. We then propose a model of scFOS metabolism regulation in a pathogenic bacterium, which will help to identify the environmental conditions required for fos gene expression and to understand the role of this locus in intestinal colonization.

Binding of the RamR repressor to wild-type and mutated promoters of the RamA gene involved in efflux-mediated multidrug resistance in Salmonella enterica serovar Typhimurium.

The transcriptional activator RamA is involved in multidrug resistance (MDR) by increasing expression of the AcrAB-TolC RND-type efflux system in several pathogenic Enterobacteriaceae. In Salmonella enterica serovar Typhimurium (S. Typhimurium), ramA expression is negatively regulated at the local level by RamR, a transcriptional repressor of the TetR family. We here studied the DNA-binding activity of the RamR repressor with the ramA promoter (P(ramA)). As determined by high-resolution footprinting, the 28-bp-long RamR binding site covers essential features of P(ramA), including the -10 conserved region, the transcriptional start site of ramA, and two 7-bp inverted repeats. Based on the RamR footprint and on electrophoretic mobility shift assays (EMSAs), we propose that RamR interacts with P(ramA) as a dimer of dimers, in a fashion that is structurally similar to the QacR-DNA binding model. Surface plasmon resonance (SPR) measurements indicated that RamR has a 3-fold-lower affinity (K(D) [equilibrium dissociation constant] = 191 nM) for the 2-bp-deleted P(ramA) of an MDR S. Typhimurium clinical isolate than for the wild-type P(ramA) (K(D) = 66 nM). These results confirm the direct regulatory role of RamR in the repression of ramA transcription and precisely define how an alteration of its binding site can give rise to an MDR phenotype.

The secretions of oviduct epithelial cells increase the equine in vitro fertilization rate: are osteopontin, atrial natriuretic peptide A and oviductin involved?

BACKGROUND: Oviduct epithelial cells (OEC) co-culture promotes in vitro fertilization (IVF) in human, bovine and porcine species, but no data are available from equine species. Yet, despite numerous attempts, equine IVF rates remain low. Our first aim was to verify a beneficial effect of the OEC on equine IVF. In mammals, oviductal proteins have been shown to interact with gametes and play a role in fertilization. Thus, our second aim was to identify the proteins involved in fertilization in the horse. METHODS & RESULTS: In the first experiment, we co-incubated fresh equine spermatozoa treated with calcium ionophore and in vitro matured equine oocytes with or without porcine OEC. We showed that the presence of OEC increases the IVF rates. In the subsequent experiments, we co-incubated equine gametes with OEC and we showed that the IVF rates were not significantly different between 1) gametes co-incubated with equine vs porcine OEC, 2) intact cumulus-oocyte complexes vs denuded oocytes, 3) OEC previously stimulated with human Chorionic Gonadotropin, Luteinizing Hormone and/or oestradiol vs non stimulated OEC, 4) in vivo vs in vitro matured oocytes. In order to identify the proteins responsible for the positive effect of OEC, we first searched for the presence of the genes encoding oviductin, osteopontin and atrial natriuretic peptide A (ANP A) in the equine genome. We showed that the genes coding for osteopontin and ANP A are present. But the one for oviductin either has become a pseudogene during evolution of horse genome or has been not well annotated in horse genome sequence. We then showed that osteopontin and ANP A proteins are present in the equine oviduct using a surface plasmon resonance biosensor, and we analyzed their expression during oestrus cycle by Western blot. Finally, we co-incubated equine gametes with or without purified osteopontin or synthesized ANP A. No significant effect of osteopontin or ANP A was observed, though osteopontin slightly increased the IVF rates. CONCLUSION: Our study shows a beneficial effect of homologous and heterologous oviduct cells on equine IVF rates, though the rates remain low. Furthers studies are necessary to identify the proteins involved. We showed that the surface plasmon resonance technique is efficient and powerful to analyze molecular interactions during fertilization.

A new method to discriminate immunogen-specific heavy-chain homodimer from heterotetramer immunoglobulin G directly in immunized dromedary whole plasma proteins: Western ligand blotting.

The variable domain of heavy-chain camelid antibodies (VHH), exclusively present in the homodimer IgGs (HC IgG), provides valuable ligands for diagnosis, imaging and therapy. These VHHs are efficiently produced from lymphocytes of immunized animals through phage display and recombination biotechnology. For VHH development it is desirable to identify animals with high affinity HC IgG response by monitoring antigen-binding in the course of immunization. The aim of this study was to propose a direct approach on whole plasma samples to distinguish between homodimer IgG and heterotetramer (IgG(1)) responses, and quantify them, using western ligand blotting (WLB). WLB consists here in electrophoretic separation of the target IgG subclasses on the basis of molecular size and binding of (125)I labeled antigen. First, we established the WLB parameters for titration of antigen-binding homodimers in relation to antigen-binding total IgGs in ovalbumin-immunized dromedary plasma samples and demonstrated that the WLB is an alternative to ELISA for IgG subclass titration. As purification of IgG subclasses or availability of IgG subclass-specific antibodies is not necessary, WLB is more direct and practical for screening a large number of samples. Second, WLB was applied to study the pattern of homodimer and heterotetramer responses during the time-course of immunizations against three different types of immunogens. As these patterns can differ between animals and immunogens, the method may be useful for identifying animals displaying the desired antigen-specific homodimer IgG response. Lastly, WLB was also described in its variant form of dot ligand blotting for identifying antigen-binding phages at the final step of a phage display experiment.

A one-step exclusion-binding procedure for the purification of functional heavy-chain and mammalian-type gamma-globulins from camelid sera.

A new approach has recently been proposed for the purification of 'mammalian-type' IgG, consisting of exclusion binding. The technique uses a gel ('Melon gel'; Pierce) that binds to all plasma proteins, but not to IgGs, thus allowing IgGs to be recovered in the FT (flow-through) fraction. Here, the technique was applied to camelid IgGs, which are known to be composed of not only classic mammalian-type IgGs (IgG1) but also HC-IgGs (heavy chain IgGs). Both mammalian type and HC-IgGs can be purified in the FT fraction of dromedary (Camelus dromedarius) plasma samples with less than 8.5% contamination, by making minor improvements to the conditions recommended by the manufacturer. The contaminant proteins, as determined by LC-MS/MS (liquid chromatography-tandem MS), are mainly transferrin and albumin. The recovery rate is elevated for both types of IgGs (95+/-14% and 88+/-25% for IgG1 and HC-IgGs respectively). IgGs thus purified maintain their ability to bind to their antigen, as measured by surface plasmon resonance and Western ligand blotting. Furthermore, IgGs can be purified from plasma samples of all camelid species in a similar manner, although the ratio of HC-IgGs to total IgGs was lower for Lama (llama) and Vicugna (vicuña) than for Camelus species. The 'Melon gel' technique can thus be used to satisfactorily purify IgG1 and HC-IgGs from all camelid species.

Selection and characterization of recombinant dromedary antiovalbumin antibody fragments that do not cross-react with ovalbumin-related protein X: use for immunoaffinity.

Ovalbumin-related protein X (OVAX) and ovalbumin are two very close ovalbumin-related serpins. As primary data on OVAX remain recent, information about possible cross-reaction of available antiovalbumin antibodies with OVAX is still missing. Using labeled purified OVAX and dot ligand blotting, we identified 49 recombinant dromedary antiovalbumin single domain antibody (sdAb) fragments that were unable to bind OVAX. Discrimination between OVAX and ovalbumin was confirmed for two of the corresponding sdAb fragments by surface plasmon resonance and Western ligand blotting (WLB) characterizations. Furthermore, they were covalently linked to Sepharose and used as an affinity matrix for ovalbumin depletion. At least 90% of the original ovalbumin was eliminated from the allantoic fluid of 14 day old chicken embryo in one step. These sdAb fragments, which bind ovalbumin with nanomolar affinity, should also contribute to a better characterization of ovalbumin preparations.

Dimeric transferrin inhibits phagocytosis of residual bodies by testicular rat Sertoli cells.

Transferrin is well known as an iron transport glycoprotein. Dimeric or tetrameric transferrin forms have recently been reported to modulate phagocytosis by human leukocytes. It is mainly synthesized by the liver, and also by other sources, such as Sertoli cells of the testis. Sertoli cells show a strong phagocytic activity toward apoptotic germ cells and residual bodies. Here, we provide evidence that purified human dimeric transferrin from commercial sources decreased residual body phagocytosis, unlike monomeric transferrin. The presence of iron appeared essential for dimeric transferrin inhibitory activity. Importantly, dimeric transferrin could be visualized by immunoblotting in Sertoli cell lysates as well as in culture media, indicating that dimeric transferrin could be physiologically secreted by Sertoli cells. By siRNA-mediated knockdown, we show that endogenous transferrin significantly inhibited residual body ingestion by Sertoli cells. These results are the first to identify dimeric transferrin in Sertoli cells and to demonstrate its implication as a physiological modulator of residual body phagocytosis by Sertoli cells.

Activin signaling pathways in ovine pituitary and LbetaT2 gonadotrope cells.

In the pituitary, activin stimulates the synthesis and release of FSH. However, the activin receptor signaling pathways that mediate these effects are poorly known. We investigated these mechanisms in primary ovine pituitary cells (POP) and in the murine LbetaT2 gonadotrope cell line. POP cells and LbetaT2 cells express the different activin receptors (types IA, IB, IIA, and IIB) and the Smad proteins (Smad-2, -3, -4, and -7). In both POP and LbetaT2 cells, activin activated several signaling pathways: Smad-2, extracellular regulated kinase-1/2 (ERK1/2), p38, and phosphatidylinositol 3'-kinase (PI3K)/Akt. Phosphorylation of ERK1/2 and p38 were stimulated (3- to 6-fold) rapidly in 5 min, whereas activation of both Smad-2 and Akt (3- to 5-fold) occurred later, in 60 min. Activin also increased the association of activin receptor IIB with PI3K. Using specific inhibitors, we demonstrated that the activation of Smad-2 was partially blocked by the inhibition of PI3K but not by the inhibition of ERK1/2 or p38, suggesting a cross-talk between the Smad and PI3K/Akt pathways. In both POP and LbetaT2 cells, FSH expression and secretion in response to activin were not altered by the inhibition of PI3K/Akt, ERK1/2, or p38 pathways, whereas they were reduced by about 2-fold by expression of a dominant negative of Smad-2 or the natural inhibitory Smad-7 in LbetaT2 cells. These results indicate that activin activates several signaling pathways with different time courses in both POP and LbetaT2 cells, but only the Smad-2 pathway appears to be directly implicated in FSH expression and release in LbetaT2 cells.