Integrin alphavbeta3-mediated endocytosis of immobilized fibrinogen by A549 lung alveolar epithelial cells

Circulating Leukocyte as an Inflammatory Biomarker: Association with Fibrinogen and Neuronal Damage in Acute Ischemic Stroke

Background and Purpose

Leukocytes and fibrinogen are inflammatory markers involved in circulating and central inflammatory response after ischemic stroke. However, the interaction between circulating leukocytes and serum fibrinogen and neuronal injury in acute ischemic stroke (AIS) patients is still unclear. The present study aimed to investigate the association between circulating leukocyte and serum fibrinogen and neuronal injury respectively in AIS.

Methods

A cross-section study with 431 hospitalized AIS patients from department of neurology was performed. Circulating leukocytes and fibrinogen were measured, and neuron-specific enolase (NSE) was detected to evaluate central neuronal damage. A propensity score matching method was used to minimize the effects of confounding factors. The relationship between leukocytes and NSE and fibrinogen was analyzed by linear curve fitting analysis and multiple logistic regression models respectively.

Results

The mean levels of NSE, leukocyte, and fibrinogen were significantly higher in the matched AIS group (n=89) than those of in the healthy control group (n=89) (all p<0.05). Both serum NSE and fibrinogen were increased with the increasing of leukocyte in AIS patients (both p<0.05). Smoothed plots suggested that there are linear relationships between leukocyte and NSE and fibrinogen respectively. Multiple logistic regression analysis showed the OR (95%) for the relationship between leukocyte and high NSE were 1.13 (1.01-1.26, p=0.031) and 1.13 (1.00-1.28, p=0.048), and between leukocyte and high fibrinogen were 1.40 (1.22-1.61, p<0.001) and 1.35 (1.15-1.58, p<0.001) in all AIS patients before and after adjusting for potential confounders.

Conclusion

Our study suggests that elevated circulating leukocyte was associated with high fibrinogen and neuronal injury in AIS. Therefore, there may be potential targets among circulating leukocyte, fibrinogen and NSE that should be intervened to reduce inflammatory reaction after ischemic stroke.

Microvesicle-Mediated Communication Within the Alveolar Space: Mechanisms of Uptake by Epithelial Cells and Alveolar Macrophages

Intra-alveolar microvesicles (MVs) are important mediators of inter-cellular communication within the alveolar space, and are key components in the pathophysiology of lung inflammation such as acute respiratory distress syndrome (ARDS). Despite the abundance of data detailing the pro-inflammatory effects of MVs, it remains unclear how MVs interact or signal with target cells in the alveolus. Using both in vivo and in vitro alveolar models, we analyzed the dynamics of MV uptake by resident alveolar cells: alveolar macrophages and epithelial cells. Under resting conditions, the overwhelming majority of MVs were taken up by alveolar macrophages. However, following lipopolysaccharide (LPS)-mediated inflammation, epithelial cells internalized significantly more MVs (p<0.01) whilst alveolar macrophage internalization was significantly reduced (p<0.01). We found that alveolar macrophages adopted a pro-inflammatory phenotype after internalizing MVs under resting conditions, but reduction of MV uptake following LPS pre-treatment was associated with loss of inflammatory phenotype. Instead, MVs induced significant epithelial cell inflammation following LPS pre-treatment, when MV internalization was most significant. Using pharmacological inhibitors, we interrogated the mechanisms of MV internalization to identify which endocytic pathways and cell surface receptors are involved. We demonstrated that epithelial cells are exclusively dependent on the clathrin and caveolin dependent endocytotic pathway, whereas alveolar macrophage uptake may involve a significant phagocytic component. Furthermore, alveolar macrophages predominantly engulf MVs via scavenger receptors whilst, epithelial cells internalize MVs via a phosphatidylserine/integrin receptor mediated pathway (specifically alpha V beta III), which can be inhibited with phosphatidylserine-binding protein (i.e. annexin V). In summary, we have undertaken a comprehensive evaluation of MV internalization within the alveolar space. Our results demonstrate that different environmental conditions can modulate MV internalization, with inflammatory stimuli strongly enhancing epithelial cell uptake of MVs and inducing epithelial cell activation. Our data reveal the unique mechanisms by which alveolar macrophages and epithelial cells internalize MVs thereby elucidating how MVs exert their pathophysiological effect during lung inflammation and injury. As MVs are potential novel therapeutic targets in conditions such as ARDS, these data provide crucial insights into the dynamics of MV-target cell interactions and highlight potential avenues for researchers to modulate and inhibit their pro-inflammatory actions within the alveolar space.

High Density Display of an Anti-Angiogenic Peptide on Micelle Surfaces Enhances Their Inhibition of αvβ3 Integrin-Mediated Neovascularization In Vitro

Diabetic retinopathy (DR), Retinopathy of Pre-maturity (ROP), and Age-related Macular Degeneration (AMD) are multifactorial manifestations associated with abnormal growth of blood vessels in the retina. These three diseases account for 5% of the total blindness and vision impairment in the US alone. The current treatment options involve heavily invasive techniques such as frequent intravitreal administration of anti-VEGF (vascular endothelial growth factor) antibodies, which pose serious risks of endophthalmitis, retinal detachment and a multitude of adverse effects stemming from the diverse physiological processes that involve VEGF. To overcome these limitations, this current study utilizes a micellar delivery vehicle (MC) decorated with an anti-angiogenic peptide (aANGP) that inhibits αvβ3 mediated neovascularization using primary endothelial cells (HUVEC). Stable incorporation of the peptide into the micelles (aANGP-MCs) for high valency surface display was achieved with a lipidated peptide construct. After 24 h of treatment, aANGP-MCs showed significantly higher inhibition of proliferation and migration compared to free from aANGP peptide. A tube formation assay clearly demonstrated a dose-dependent angiogenic inhibitory effect of aANGP-MCs with a maximum inhibition at 4 μg/mL, a 1000-fold lower concentration than that required for free from aANGP to display a biological effect. These results demonstrate valency-dependent enhancement in the therapeutic efficacy of a bioactive peptide following conjugation to nanoparticle surfaces and present a possible treatment alternative to anti-VEGF antibody therapy with decreased side effects and more versatile options for controlled delivery.

Novel c(RGDyK)-based conjugates of POPAM and 5-fluorouracil for integrin-targeted cancer therapy

Aim: Alkylating agents and antimetabolites are cytotoxic drugs commonly used in cancer treatment. These medications are often associated with serious side effects on normal tissues and organs. Methodology: To improve the pharmacological profile of the alkylating agent POPAM and the antimetabolite 5-fluorouracil, novel integrin-targeted delivery systems based on c(RGDyK) were successfully synthesized. The new conjugates were tested in vitro against different cancer cells such as PC3, SKOV3, A549, MCF7 and MBA-MB-321. Results & conclusion: The c(RGDyK) conjugates of POPAM demonstrated better inhibitory effects and selectivity compared with c(RGDyK) and POPAM. The c(RGDyK) conjugates of 5-FUA demonstrated diverse inhibitory effects compared with c(RGDyK) and 5-FUA related to the levels of integrin expression, the conjugate stability and sensitivity of cancer cells to 5-FUA.

Adsorbed Fibrinogen stimulates TLR-4 on monocytes and induces BMP-2 expression

Modulation of inflammatory responses to implanted biomaterials towards tissue regeneration has gained prominence as an innovative tissue engineering strategy. Recent in vitro and in vivo studies showed that Fibrinogen (Fg) adsorbed to Chitosan (Ch) substrates modulates immune cell responses, enhances the production of osteogenic factors by monocytes/macrophages and promotes bone regeneration, but the mechanisms involved remain poorly understood. Thus, the present work was conducted to clarify the molecular mechanisms of interaction between primary human monocytes and the above substrates. Cell surface expression of TLR-4 was significantly downregulated in the presence of pre-adsorbed Fg, when compared to Ch control, indicating an interaction via this receptor. The same substrate triggered MAPK activation, specifically the ERK 1/2 and JNK pathways. Importantly, both ERK 1/2 and JNK phosphorylation were reduced when TLR-4 signalling was blocked using a specific pharmacological inhibitor. Functionally, adsorbed Fg induced production of the potent osteogenic mediator BMP-2 by monocytes, while TLR-4 inhibition resulted in a significant decrease of BMP-2 mRNA and protein levels, in response to Fg stimulation. Overall, our data reveals that adsorbed Fg exerts a pro-osteogenic effect on human monocytes through its interaction with TLR-4 and subsequent production of BMP-2, elucidating two key aspects of the immunomodulatory action of adsorbed Fg in bone regeneration.

STATEMENT OF SIGNIFICANCE

Recent studies showed that when Fibrinogen (Fg) is used to modify Chitosan (Ch) substrates, it modulates the immune response, enhances production of osteogenic factors by monocytes/macrophages, and promotes bone regeneration. However, the mechanisms involved in monocyte-Fg interaction, were only partially known. Current work addresses the interaction between primary human monocytes and Ch surfaces modified by Fg adsorption (Ch-Fg) at the molecular level. Results show that monocytes interact specifically with Ch-Fg via TLR-4, triggering particular intracellular signalling pathways (ERK and JNK, but not p38), downstream of TLR-4. Functionally, Ch-Fg induced monocytes to produce the osteogenic mediator BMP-2. Thus, we clarify herein two essential aspects of the interaction between adsorbed Fg and monocytes, with impact on immunomodulation and regeneration, upon biomaterial implantation.

Nuclear monomeric integrin αv in cancer cells is a coactivator regulated by thyroid hormone

Thyroid hormone induces tumor cell and blood vessel cell proliferation via a cell surface receptor on heterodimeric integrin αvβ3. We investigated the role of thyroid hormone-induced internalization of nuclear integrin αv monomer. Physiological concentration of thyroxine (free T4, 10(-10) M), but not 3,5,3'-triiodo-l-thyronine (T3), induced cellular internalization and nuclear translocation of integrin αv monomer in human non-small-cell lung cancer (H522) and ovarian carcinoma (OVCAR-3) cells. T4 did not complex with integrin αv monomer during its internalization. The αv monomer was phosphorylated by activated ERK1/2 when it heterodimerized with integrin β3 in vitro. Nuclear αv complexed with transcriptional coactivator proteins, p300 and STAT1, and with corepressor proteins, NCoR and SMRT. Nuclear αv monomer in T4-exposed cells, but not integrin β3, bound to promoters of specific genes that have important roles in cancer cells, including estrogen receptor-α, cyclooxygenase-2, hypoxia-inducible factor-1α, and thyroid hormone receptor β1 in chromatin immunoprecipitation assay. In summary, monomeric αv is a novel coactivator regulated from the cell surface by thyroid hormone for the expression of genes involved in tumorigenesis and angiogenesis. This study also offers a mechanism for modulation of gene expression by thyroid hormone that is adjunctive to the nuclear hormone receptor (TR)-T3 pathway.

Guiding plant virus particles to integrin-displaying cells

Viral nanoparticles (VNPs) are structurally regular, highly stable, tunable nanomaterials that can be conveniently produced in high yields. Unmodified VNPs from plants and bacteria generally do not show tissue specificity or high selectivity in binding to or entry into mammalian cells. They are, however, malleable by both genetic and chemical means, making them useful scaffolds for the display of large numbers of cell- and tissue-targeting ligands, imaging moieties, and/or therapeutic agents in a well-defined manner. Capitalizing on this attribute, we modified the genetic sequence of the Cowpea mosaic virus (CPMV) coat protein to display an RGD oligopeptide sequence derived from human adenovirus type 2 (HAdV-2). Concurrently, wild-type CPMV was modified via NHS acylation and Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry to attach an integrin-binding cyclic RGD peptide. Both types of particles showed strong and selective affinity for several different cancer cell lines that express RGD-binding integrin receptors.

MT1-MMP regulates the turnover and endocytosis of extracellular matrix fibronectin

The extracellular matrix (ECM) is dynamically remodeled by cells during development, normal tissue homeostasis and in a variety of disease processes. We previously showed that fibronectin is an important regulator of ECM remodeling. The deposition and/or polymerization of fibronectin into the ECM controls the deposition and stability of other ECM molecules. In addition, agents that inhibit fibronectin polymerization promote the turnover of fibronectin fibrils and enhance ECM fibronectin endocytosis and intracellular degradation. Endocytosis of ECM fibronectin is regulated by β1 integrins, including α5β1 integrin. We have examined the role of extracellular proteases in regulating ECM fibronectin turnover. Our data show that membrane type matrix metalloproteinase 1 (MT1-MMP; also known as MMP14) is a crucial regulator of fibronectin turnover. Cells lacking MT1-MMP show reduced turnover and endocytosis of ECM fibronectin. MT1-MMP regulates ECM fibronectin remodeling by promoting extracellular cleavage of fibronectin and by regulating α5β1-integrin endocytosis. Our data also show that fibronectin polymerization stabilizes fibronectin fibrils and inhibits ECM fibronectin endocytosis by inhibiting α5β1-integrin endocytosis. These data are the first to show that an ECM protein and its modifying enzyme can regulate integrin endocytosis. These data also show that integrin trafficking plays a major role in modulating ECM fibronectin remodeling. The dual dependence of ECM fibronectin turnover on extracellular proteolysis and endocytosis highlights the complex regulatory mechanisms that control ECM remodeling to ensure maintenance of proper tissue function.

Pharmacoproteomic analysis of a novel cell-permeable peptide inhibitor of tumor-induced angiogenesis

P11, a novel peptide ligand containing a PDZ-binding motif (Ser-Asp-Val) with high affinity to integrin α(v)β(3) was identified from a hexapeptide library (PS-SPCL) using a protein microarray chip-based screening system. Here, we investigated the inhibitory mechanism of P11 (HSDVHK) on tumor-induced angiogenesis via a pharmacoproteomic approach. P11 was rapidly internalized by, human umbilical vein endothelial cells (HUVECs) via an integrin α(v)β(3)-mediated event. Caveolin and clathrin appeared to be involved in the P11 uptake process. The cell-penetrating P11 resulted in suppression of bFGF-induced HUVEC proliferation in a dose-dependent manner. Phosphorylation of extracellular-signal regulated kinase (ERK1/2) and mitogen-activated protein kinase kinase (MEK) in bFGF-stimulated HUVECs was inhibited by cell-permeable P11. Proteomic analysis via antibody microarray showed up-regulation of p53 in P11-treated HUVECs, resulting in induction of apoptosis via activation of caspases-3, -8, and -9. Several lines of experimental evidence strongly suggest that the molecular mechanism of P11, a novel anti-angiogenic agent, inhibits bFGF-induced HUVEC proliferation via mitogen-activated protein kinase kinase and extracellular-signal regulated kinase inhibition as well as p53-mediated apoptosis related with activation of caspases.

Type IIB procollagen NH(2)-propeptide induces death of tumor cells via interaction with integrins alpha(V)beta(3) and alpha(V)beta(5)

Cartilage is resistant to tumor invasion. In the present study, we found that the NH(2)-propeptide of the cartilage-characteristic collagen, type IIB, PIIBNP, is capable of killing tumor cells. The NH(2)-propeptide is liberated into the extracellular matrix prior to deposition of the collagen fibrils. This peptide adheres to and kills cells from chondrosarcoma and cervical and breast cancer cell lines via the integrins alpha(v)beta(5) and alpha(v)beta(3). Adhesion is abrogated by blocking with anti alpha(v)beta(5) and alpha(v)beta(3) antibodies. When alpha(v) is suppressed by small intefering RNA, adhesion and cell killing are blocked. Normal chondrocytes from developing cartilage do not express alpha(v)beta(3) and alpha(v)beta(5) integrins and are thus protected from cell death. Morphological, DNA, and biochemical evidence indicates that the cell death is not by apoptosis but probably by necrosis. In an assay for invasion, PIIBNP reduced the number of cells crossing the membrane. In vivo, in a tumor model for breast cancer, PIIBNP was consistently able to reduce the size of the tumor.

Functional single-walled carbon nanotubes based on an integrin alpha v beta 3 monoclonal antibody for highly efficient cancer cell targeting

The application of single-walled carbon nanotubes (SWNTs) in the field of biomedicine is becoming an entirely new and exciting topic. In this study, a novel functional SWNT based on an integrin alpha(v)beta(3) monoclonal antibody was developed and was used for cancer cell targeting in vitro. SWNTs were first modified by phospholipid-bearing polyethylene glycol (PL-PEG). The PL-PEG functionalized SWNTs were then conjugated with protein A. A SWNT-integrin alpha(v)beta(3) monoclonal antibody system (SWNT-PEG-mAb) was thus constructed by conjugating protein A with the fluorescein labeled integrin alpha(v)beta(3) monoclonal antibody. In vitro study revealed that SWNT-PEG-mAb presented a high targeting efficiency on integrin alpha(v)beta(3)-positive U87MG cells with low cellular toxicity, while for integrin alpha(v)beta(3)-negative MCF-7 cells, the system had a low targeting efficiency, indicating that the high targeting to U87MG cells was due to the specific integrin targeting of the monoclonal antibody. In conclusion, SWNT-PEG-mAb developed in this research is a potential candidate for cancer imaging and drug delivery in cancer targeting therapy.

Streptococcal pyrogenic exotoxin B-induced apoptosis in A549 cells is mediated through alpha(v)beta(3) integrin and Fas

Our previous work suggested that streptococcal pyrogenic exotoxin (SPE) B-induced apoptosis is mediated through a receptor-like mechanism. In this study, we have identified alpha(v)beta(3) and Fas as the SPE B receptors for this function. The SPE B fragment without the RGD motif and G308S, a SPE B mutant with the RSD motif, induced less apoptosis than did native SPE B, suggesting that the RGD motif is critical for SPE B-induced apoptosis. Fluorescein isothiocyanate-SPE B binding assays and immunoprecipitation analysis showed that SPE B specifically interacted with alpha(v)beta(3). Anti-alpha(v)beta(3) antibody partially inhibited SPE B-induced apoptosis but had no effect on G308S-induced apoptosis. In addition, Fas binding to SPE B was verified in an affinity column and an immunoprecipitation analysis. Anti-Fas antibody inhibited SPE B- and G308S-induced apoptosis in a dose-dependent manner, suggesting that Fas-mediated SPE B-induced apoptosis also occurs RGD independently. Both anti-alpha(v)beta(3) and anti-Fas antibodies synergistically inhibited SPE B-induced apoptosis. The apoptotic cascades were activated by SPE B and G308S, with a little delay by the latter. After SPE B binding, the cell surface level of alpha(v)beta(3), but not of Fas, was decreased. The decreased alpha(v)beta(3) level was restored by treatment with the proteasome inhibitor MG132, suggesting a SPE B-mediated endocytosis of integrin alpha(v)beta(3) via the ubiquitin-proteasome system. Taken together, our results demonstrate that SPE B-induced apoptosis is mediated through alpha(v)beta(3) integrin and Fas in a synergistic manner.

Fibrinogen synthesized by cancer cells augments the proliferative effect of fibroblast growth factor-2 (FGF-2)

BACKGROUND

Fibroblast growth factor (FGF)-2 is a critical growth factor in normal and malignant cell proliferation and tumor-associated angiogenesis. Fibrinogen and fibrin bind to FGF-2 and modulate FGF-2 functions. Furthermore, we have shown that extrahepatic epithelial cells are capable of endogenous production of fibrinogen.

OBJECTIVE

Herein we examined the role of fibrinogen and FGF-2 interactions on prostate and lung adenocarcinoma cell growth in vitro.

METHODS

Cell proliferation was measured by (3)H-thymidine uptake and the specificity of FGF-2-fibrinogen interactions was measured using wild-type and mutant FGF-2s, fibrinogen gamma-chain (FGG) RNAi and co-immunoprecipitation. Metabolic labeling, immunopurification and fluorography demonstrated de novo fibrinogen production.

RESULTS

FGF-2 stimulated DU-145 cell proliferation, whereas neither FGF-2 nor fibrinogen affected the growth of PC-3 or A549 cells. Fibrinogen augmented the proliferative effect of FGF-2 on DU-145 cells. The role of fibrinogen in FGF-2-enhanced DNA synthesis was confirmed using an FGF-2 mutant that exhibits no binding affinity for fibrinogen. FGG transcripts were present in PC-3, A549 and DU-145 cells, but only PC-3 and A549 cells produced detectable levels of intact protein. RNAi-mediated knockdown of FGG expression resulted in decreased production of fibrinogen protein and inhibited (3)H-thymidine uptake in A549 and PC-3 cells by 60%, which was restored by exogenously added fibrinogen. FGF-2 and fibrinogen secreted by the cells were present in the medium as a soluble complex, as determined by coimmunoprecipitation studies.

CONCLUSIONS

These data indicate that endogenously synthesized fibrinogen promotes the growth of lung and prostate cancer cells through interaction with FGF-2.

Targeting Beta-3 integrin using a linear hexapeptide labeled with a near-infrared fluorescent molecular probe

Biomolecules containing the RGD peptide sequence are known to bind integrins with high affinity. Studies of hexa-and hepta-peptides labeled with a near-infrared fluorescent probe (cypate) showed that rearranging the glycine in a linear RGD peptide sequence to form the GRD analogue favored the uptake of the GRD compound by alphavbeta3 integrin receptor (ABIR)-positive A549 tumor cells and tissue. The internalization of the GRD compound in A549 cells and tumor uptake in mice were inhibited by ABIR-avid peptides, suggesting its recognition by this receptor. Further studies with functional blocking antibodies and beta3 knockout cells revealed that beta3 integrin mediates the internalization of the cypate-GRD peptide. Molecular modeling studies supported preferential interaction of the probe with the beta3 subunit of integrins relative to the alphav subunit. The results demonstrate that the cypate-GRD peptide targets beta3 integrin, thereby providing a strategy to monitor drug delivery and efficacy, and physiopathologic processes mediated by this protein.

Whole-body fluorescence lifetime imaging of a tumor-targeted near-infrared molecular probe in mice

Fluorescence lifetime imaging can provide valuable diagnostic information relating to the functional status of diseases. In this study, a near-infrared (NIR) dye-labeled hexapeptide (abbreviated Cyp-GRD) was synthesized. In vitro, Cyp-GRD internalized in nonsmall cell lung cancer cells (A549) without observable cytotoxic or proliferative effects to the cells at a concentration up to 1x10(-4) M. Time-domain fluorescence intensity and lifetime imaging of Cyp-GRD injected into A549 tumor-bearing mice revealed that the probe preferentially accumulated in the tumor and the major excretion organs. The fluorescence lifetime of the conjugate at the tumor site was mapped, showing the spatial distribution of the lifetime related to its environment. Additionally, fluorescence intensity image reconstruction obtained by integrating the time-resolved intensities enabled the contrast ratios of tumor-to-kidney or liver in slices at different depths to be displayed. The mean lifetime was 1.03 ns for the tumor and 0.80 ns for the liver when averaging those pixels exhibiting adequate signal-to-noise ratio, showing the tumor had a higher lifetime average and reflecting the altered physiopathology of the tumor. This study clearly demonstrated the feasibility of whole-body NIR fluorescence lifetime imaging for tumor localization and its spatial functional status in living small animals.

Gene Transfer Mediated by Native versus Fibroblast Growth Factor–Retargeted Adenoviral Vectors into Lung Cancer Cells

We compared native Adenoviral (Ad) vectors to a basic Fibroblast Growth Factor-retargeted Adenovirus (FGF2-Ad) for gene delivery into a diverse panel of lung cancer cells in vitro and xenografts in vivo. Cells were first evaluated for vector-specific receptor expression. Marked variations of surface coxsackie-adenovirus receptor (CAR), but relatively similar levels of alpha v integrin and FGF receptor expression were evident. Transduction efficiency by Ad directly correlated (R = 0.77, 95% CI 0.28-0.94, P = 0.0085) with CAR, but not with alpha v integrin expression. Transduction efficiency by FGF2-Ad did not correlate with the measured FGF receptor expression. Blocking studies indicated that gene transfer by FGF2-Ad occurred by a CAR-independent pathway, and could be inhibited by free FGF in a dose-dependent manner. Ad-antiserum inhibited FGF2-Ad gene transfer, suggesting that the Ad-component was needed for post-entry DNA-delivery. Soluble heparin sulfate proteoglycans (HSPG) or alpha v integrin blockers marginally decreased FGF2-Ad transduction. Both Ad and FGF2-Ad equally transduced CAR-positive non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cells. By contrast, FGF2-Ad had a distinct transduction advantage in CAR-deficient NSCLC cells. This improvement in transduction of CAR-deficient cells by FGF2-Ad persisted in vivo. These data justify the need for an improved FGF2-Ad vector for clinical use in CAR-deficient lung cancer.

The novel fibrinogen-binding protein FbsB promotes Streptococcus agalactiae invasion into epithelial cells

Streptococcus agalactiae is a major cause of bacterial sepsis and meningitis in human newborns. The interaction of S. agalactiae with host proteins and the entry into host cells thereby represent important virulence traits of these bacteria. The present report describes the identification of the fbsB gene, encoding a novel fibrinogen-binding protein that plays a crucial role in the invasion of S. agalactiae into human cells. In Western blots and enzyme-linked immunosorbent assay (ELISA) experiments, the FbsB protein was demonstrated to interact with soluble and immobilized fibrinogen. Binding studies showed the N-terminal 388 residues of FbsB and the Aalpha-subunit of human fibrinogen to recognize each other. By reverse transcription (RT)-PCR, the fbsB gene was shown to be cotranscribed with the gbs0851 gene in S. agalactiae. Deletion of the fbsB gene in the genome of S. agalactiae did not influence the binding of the bacteria to fibrinogen, suggesting that FbsB does not participate in the attachment of S. agalactiae to fibrinogen. In tissue culture experiments, however, the fbsB deletion mutant was severely impaired in its invasion into lung epithelial cells. Bacterial invasion could be reestablished by introducing the fbsB gene on a shuttle plasmid into the fbsB deletion mutant. Furthermore, treatment of lung epithelial cells with FbsB fusion protein blocked S. agalactiae invasion of epithelial cells in a dose-dependent fashion. These results suggest an important role of the FbsB protein in the overall process of host cell entry by S. agalactiae.

Matrix-fibrinogen enhances wound closure by increasing both cell proliferation and migration

Fibrinogen (FBG) assembles into matrix fibrils of fibroblasts, lung and mammary epithelial cells, but not endothelial cells. Furthermore, cryptic beta15-21 residues are exposed in FBG fibrils with no evidence of thrombin or plasmin proteolysis. Herein, the effects of FBG on migration and proliferation of wounded dermal fibroblasts were investigated. FBG preassembled into matrix prior to scrape-wounding induced 3H-thymidine incorporation 8-fold and shortened the time to wound closure 1.6-fold +/- 0.1-fold. FBG added immediately after wounding did not enhance either response. Fibroblast growth factor-2/platelet-derived growth factor (FGF-2/PDGF) stimulated cell proliferation 2.2-fold for FGF-2 and 3.2-fold for PDGF and wound closure 1.5-fold +/- 0.1-fold in the absence of matrix-FBG. Surprisingly, exogenous growth factors had negligible effect on wound closure and cell proliferation already enhanced by matrix-FBG. Matrix-FBG-enhanced wound closure required active assembly of an FBG-fibronectin matrix, engagement of alphavbeta3, and FBG Aalpha-RGDS572-575 integrin recognition sites; Aalpha-RGDF95-98 sites were not sufficient for matrix-FBG assembly, enhanced wound closure, or cell proliferation. Although Bbeta1-42 was not necessary for matrix assembly, it was required for matrix-FBG-enhanced cell migration. These data indicate that FBG serves as an important matrix constituent in the absence of fibrin formation to enhance wound repair and implicate Bbeta1-42 as a physiologic inducer of signal transduction to promote an intermediate state of cell adhesion and a migratory cell phenotype.

The integrin alphavbeta3 is a receptor for the latency-associated peptides of transforming growth factors beta1 and beta3

The integrins alpha(v)beta(1), alpha(v)beta(5), alpha(v)beta(6) and alpha(v)beta(8) have all recently been shown to interact with the RGD motif of the latency-associated peptide (LAPbeta(1)) of transforming growth factor beta(1) (TGFbeta(1)), with binding to alpha(v)beta(6) and alpha(v)beta(8) leading to TGFbeta(1) activation. Previously it has been suggested that the remaining alpha(v) integrin, alpha(v)beta(3,) does not interact with LAPbeta(1). However, here we show clearly that alpha(v)beta(3) does indeed interact with the LAPbeta(1) RGD motif. This interaction is similar to other alpha(v)beta(3) ligands in terms of the cations required for adhesion, the concentrations of LAPbeta(1) required for binding and the ability of a small-molecule inhibitor of alpha(v)beta(3), SB223245, to block the interaction. Using glutathione S-transferase fusion proteins we have mapped a minimal integrin-binding loop in LAPbeta(1) and then used this approach to probe the integrin-binding properties of the equivalent loops in LAPbeta(2) and LAPbeta(3). We show that the RGD motif of LAPbeta(3) also interacts with alpha(v)beta(3), in addition to alpha(v)beta(6), alpha(v)beta(1) and alpha(v)beta(5), whereas the corresponding loop in LAPbeta(2) does not interact with these integrins. These observations therefore correct a previously reported inaccuracy in the literature. Furthermore, they are important as they link alpha(v)beta(3) and TGFbeta, which may have implications in cancer and a number of inflammatory and fibrotic diseases where expression of both proteins has been documented.

The incorporation of fibrinogen into extracellular matrix is dependent on active assembly of a fibronectin matrix

Fibrinogen is a soluble protein produced by hepatocytes and secreted into plasma, where it functions in hemostasis. During inflammation, the hepatic synthesis of fibrinogen is induced 2-10 fold. Recent studies demonstrate that after an inflammatory stimulus, fibrinogen gene expression and protein production is upregulated in lung epithelial cells, where it is secreted basolaterally and consequently deposited into the extracellular matrix in fibrils that extensively colocalize with fibronectin fibrils. In this study, we show that the deposition of fibrinogen into the matrix of fibroblasts occurred rapidly and in a Rho-dependent manner in response to serum or lysophosphatidic acid; RhoA GTPase signaling is also required for fibronectin matrix assembly. Using mouse embryonic fibronectin-null cells, we show that incorporation of exogenous fibrinogen into matrix fibrils occurred only in the presence of exogenous fibronectin, which is also assembled into matrix fibrils. Furthermore, treatment of fibroblasts and fibronectin-null cells with an antibody that inhibits fibronectin matrix assembly impaired incorporation of fibrinogen into matrix fibrils. Collectively, these data suggest that incorporation of fibrinogen into the extracellular matrix requires active fibronectin polymer elongation into matrix fibrils. From these data, we hypothesize that fibrinogen deposition rapidly changes the topology of the extracellular matrix to provide a surface for cell migration and matrix remodeling during tissue repair.