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At least 649 records · Page 36Linked to original sources
PubMed2002

Fibronectin mediates Opc-dependent internalization of Neisseria meningitidis in human brain microvascular endothelial cells.

A central step in the pathogenesis of bacterial meningitis caused by Neisseria meningitidis (the meningococcus) is the interaction of the bacteria with cells of the blood-brain barrier. In the present study, we analysed the invasive potential of two strains representing hypervirulent meningococcal lineages of the ET-5 and ET-37 complex in human brain-derived endothelial cells (HBEMCs). In contrast to previous observations made with epithelial cells and human umbilical vein-derived endothelial cells (HUVECs), significant internalization of encapsulated meningococci by HBMECs was observed. However, this uptake was found only for the ET-5 complex isolate MC 58, and not for an ET-37 complex strain. Furthermore, the uptake of meningococci by HBMECs depended on the presence of human serum, whereas serum of bovine origin did not promote the internalization of meningococci in HBMECs. By mutagenesis experiments, we demonstrate that internalization depended on the expression of the opc gene, which is present in meningococci of the ET-5 complex, but absent in ET-37 complex meningococci. Chromatographic separation of human serum proteins revealed fibronectin as the uptake-promoting serum factor, which binds to HBMECs via alpha 5 beta 1 integrin receptors. These data provide evidence for unique molecular mechanisms of the interaction of meningococci with endothelial cells of the blood-brain barrier and contribute to our understanding of the pathogenesis of meningitis caused by meningococci of different clonal lineages.

Antibodies, Monoclonal↗
PubMed2003

BFA-sensitive and insensitive exocytic pathways in Entamoeba histolytica trophozoites: their relationship to pathogenesis.

Entamoeba histolytica manifests its pathogenicity through several cellular processes triggered by external stimuli that activate signal transduction pathways. The intense secretory activity resulting from stimulation is not correlated with a typical endoplasmic reticulum (ER) or Golgi organization, and little is known in this parasite about endocytic/exocytic pathways. The interactions of trophozoites with fibronectin (FN) and cultured mammalian cells, which elicit secretory activities, were chosen to study mechanisms that regulate cytoplamic traffic. Results showed that Brefeldin A (BFA) induced redistribution of the vesicular network recognized by antibodies against amoebic proteins PDI and ERD2. Furthermore, BFA diminished traffic to the plasma membrane of the beta1 integrin-like FN receptor and the heavy subunit of the Gal/GalNAc lectin, required for adhesion to FN and target cells, respectively. However, BFA did not prevent thiol-proteinase secretion or inhibit the traffic of de novo synthesized proteinases. These data suggest that two distinct transport systems occur in E. histolytica, one similar to classical membrane protein transport and another independent of BFA and inducible by external stimuli. Actin-myosin contractility of the cortical cytoskeleton seems necessary for the final release of exported proteinases and the proper function of the surface proteins involved in adhesion.

Actins↗
PubMed2002

Fibronectin fragments active in chondrocytic chondrolysis can be chemically cross-linked to the alpha5 integrin receptor subunit.

OBJECTIVE: To determine whether fibronectin fragments (Fn-f) known to enhance cartilage matrix degradation and to alter chondrocyte metabolism, bind on the chondrocyte cell surface close enough to the alpha(5)beta(1) fibronectin (Fn) receptor to be chemically cross-linked to it. DESIGN: Biotinylated Fn-fs were added to chondrocytes, followed by cross-linking with dithiobissulfosuccinimidyl propionate, and the resultant alpha(5) complexes trapped on to antialpha(5)-agarose. Adherent material was analysed by probing with avidin-HRP. In a more specific approach in which only proximal targets could be cross-linked, photoaffinity labeled Fn-fs or Fn were added to cells, the derivatives activated and the cross-linked material analysed. Interaction of biotinylated Fn-fs and Fn with insolubilized alpha(5)beta(1) receptor was also visualized and quantified. RESULTS: Biotinylated Fn-fs and Fn, but not a control of BSA, were cross-linked to alpha(5) protein in the presence of the propionate. Photoaffinity label Fn-f and Fn, but not BSA, were cross-linked to alpha(5) protein as well. Interaction was decreased by addition of an excess of unlabeled Fn-f or Fn. Fn-fs bound to alpha(5)beta(1)-agarose, although the affinity was 30-fold weaker and the stoichiometry 20-fold greater when the smallest Fn-f was compared to native Fn. CONCLUSIONS: These data are consistent with a role for the alpha(5) subunit in Fn-f activities and suggest that the Fn-fs bind proximal or directly to alpha(5) receptors. The weaker, higher stoichiometry interaction of Fn-fs with receptor suggests that fragmentation has allowed de novo interactions not possible in native Fn.

Animals↗
PubMed2004

Fluid shear of low magnitude increases growth and expression of TGFbeta1 and adhesion molecules in human bone cells in vitro.

Deformation of the bone matrix by mechanical strain causes fluid shifts within the osteocytic canaliculi which affect osteocytic cell metabolism. We applied low fluid shear (1 - 63 micro Pa for 10 - 48 h) to human osteoblastic cells (HOB) in vitro to study its impact on cell proliferation and differentiated functions. Proteins involved in translating the physical force into a cellular response were characterised. Low fluid shear stress stimulated proliferation of HOB 1.2-fold when stress was applied intermittently for 24 h. Shear stress also increased differentiated cellular properties such as alkaline phosphatase (ALP) activity (121 % of control), fibronectin (FN) and fibronectin receptor (FNR) expression (290 % and 200 %, respectively). Prostaglandin E (2) (PGE (2)) and TGFbeta1 release into the medium were significantly stimulated when shear stress was applied for 6 - 12 h and 24 - 48 h, respectively. TGFbeta1 + 2 neutralising antibodies or the presence of indomethacine inhibited the mitogenic effect of fluid shear and reduced ALP activity to its control level. Furthermore, TGFbeta treatment induced a dose-dependent increase in FN and FNR expression. Therefore, fluid shear stress of low magnitude (a) suffices to affect HOB metabolism and (b) regulates anchorage of HOB via FN and FNR by stimulating osteoblastic PGE (2) and TGFbeta secretion.

Aged↗
PubMed2002

Synergistic activity of the ninth and tenth FIII domains of human fibronectin depends upon structural stability.

The ninth and tenth FIII domains (FIII9-10) of human fibronectin act in synergy to promote cell adhesion via the interaction with integrin receptors. Here we describe the functional and structural properties of a set of recombinant FIII9-10 mutants containing various alanine substitutions within the key synergistic site, DRVPHSRN in FIII9, either alone or in combination with another substitution (Leu(1408) to Pro), on the opposite face of FIII9, that increases stability and the functional capacity of FIII9-10. We show that the introduction of mutations into the synergistic sequence of FIII9-10 has a negative effect on the adhesion of baby hamster kidney fibroblasts and results in reduced ability of these ligands to recognize integrin alpha(5)beta(1). Conformational stability of the FIII9 domain in the synergy site mutants is likewise reduced in comparison with native FIII9. The Leu(1408) to Pro substitution in mutant FIII9-10 proteins carrying substitutions in the synergy site results in a substantial recovery of the adhesive activity of the mutants and affinity to alpha(5)beta(1). In keeping with the enhancement of functional activity, the Leu(1408) to Pro substitution in the FIII9-10 synergy site mutants also causes a significant increase in conformational stability of FIII9. These observations imply a strong positive correlation between the biological activity and conformational stability of the assessed FIII9-10 mutants and suggest that a Leu(1408) to Pro substitution restores the biological activity of the mutants via their ability to restore their conformational stability. We conclude that domain stability may be a major determinant of the synergistic potential of FIII9. Our data underscore the value of using more than one approach in such structure-function studies and the requirement for validating the global structural integrity of protein ligands in which sequences that disrupt function have been perturbed.

Animals↗
PubMed2003

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.

Active Transport, Cell Nucleus↗
PubMed2003

Identification of a novel binding site for platelet integrins alpha IIb beta 3 (GPIIbIIIa) and alpha 5 beta 1 in the gamma C-domain of fibrinogen.

The interactions of platelets with fibrinogen mediate a variety of responses including adhesion, platelet aggregation, and fibrin clot retraction. Whereas it was assumed that interactions of the platelet integrin alpha IIb beta 3 with the AGDV sequence in the gamma C-domain of fibrinogen and/or RGD sites in the A alpha chains are involved in clot retraction and adhesion, recent data demonstrated that fibrinogen lacking these sites still supported clot retraction. These findings suggested that an unknown site in fibrinogen and/or other integrins participate in clot retraction. Here we have identified a sequence within gamma C that mediates binding of fibrinogen to platelets. Synthetic peptide duplicating the 365-383 sequence in gamma C, designated P3, efficiently inhibited clot retraction in a dose-dependent manner. Furthermore, P3 supported platelet adhesion and was an effective inhibitor of platelet adhesion to fibrinogen fragments. Analysis of overlapping peptides spanning P3 and mutant recombinant gamma C-domains demonstrated that the P3 activity is contained primarily within gamma 370-383. Integrins alpha IIb beta 3 and alpha 5 beta 1 were implicated in recognition of P3, since platelet adhesion to the peptide was blocked by function-blocking monoclonal antibodies against these receptors. Direct evidence that alpha IIb beta 3 and alpha 5 beta 1 bind P3 was obtained by selective capture of these integrins from platelet lysates using a P3 affinity matrix. Thus, these data suggest that the P3 sequence in the gamma C-domain of fibrinogen defines a previously unknown recognition specificity of alpha IIb beta 3 and alpha 5 beta 1 and may function as a binding site for these integrins.

Amino Acid Sequence↗
PubMed2003

Critical role of integrin alpha 5 beta 1 in urokinase (uPA)/urokinase receptor (uPAR, CD87) signaling.

Urokinase-type plasminogen activator (uPA) induces cell adhesion and chemotactic movement. uPA signaling requires its binding to uPA receptor (uPAR/CD87), but how glycosylphosphatidylinositol-anchored uPAR mediates signaling is unclear. uPAR is a ligand for several integrins (e.g. alpha 5 beta 1) and supports cell-cell interaction by binding to integrins on apposing cells (in trans). We studied whether binding of uPAR to alpha 5 beta 1 in cis is involved in adhesion and migration of Chinese hamster ovary cells in response to immobilized uPA. This process was temperature-sensitive and required mitogen-activated protein kinase activation. Anti-uPAR antibody or depletion of uPAR blocked, whereas overexpression of uPAR enhanced, cell adhesion to uPA. Adhesion to uPA was also blocked by deletion of the growth factor domain (GFD) of uPA and by anti-GFD antibody, whereas neither the isolated uPA kringle nor serine protease domain supported adhesion directly. Interestingly, anti-alpha 5 antibody, RGD peptide, and function-blocking mutations in alpha 5 beta 1 blocked adhesion to uPA. uPA-induced cell migration also required GFD, uPAR, and alpha 5 beta 1, but alpha 5 beta 1 alone did not support uPA-induced adhesion and migration. Thus, binding of uPA causes uPAR to act as a ligand for alpha 5 beta 1 to induce cell adhesion, intracellular signaling, and cell migration. We demonstrated that uPA induced RGD-dependent binding of uPAR to alpha 5 beta 1 in solution. These results suggest that uPA-induced adhesion and migration of Chinese hamster ovary cells occurs as a consequence of (a) uPA binding to uPAR through GFD, (b) the subsequent binding of a uPA.uPAR complex to alpha 5 beta 1 via uPAR, and (c) signal transduction through alpha 5 beta 1.

Animals↗
PubMed2003

Role of ADMIDAS cation-binding site in ligand recognition by integrin alpha 5 beta 1.

Integrin-ligand interactions are regulated in a complex manner by divalent cations, and multiple cation-binding sites are found in both alpha and beta integrin subunits. A key cation-binding site that lies in the beta subunit A-domain is known as the metal-ion dependent adhesion site (MIDAS). Recent x-ray crystal structures of integrin alpha V beta 3 have identified a novel cation binding site in this domain, known as the ADMIDAS (adjacent to MIDAS). The role of this novel site in ligand recognition has yet to be elucidated. Using the interaction between alpha 5 beta 1 and fibronectin as a model system, we show that mutation of residues that form the ADMIDAS site inhibits ligand binding but this effect can be partially rescued by the use of activating monoclonal antibodies. The ADMIDAS mutants had decreased expression of activation epitopes recognized by 12G10, 15/7, and HUTS-4, suggesting that the ADMIDAS is important for stabilizing the active conformation of the integrin. Consistent with this suggestion, the ADMIDAS mutations markedly increased the dissociation rate of the integrin-fibronectin complex. Mutation of the ADMIDAS residues also reduced the allosteric inhibition of Mn2+-supported ligand binding by Ca2+, suggesting that the ADMIDAS is a Ca2+-binding site involved in the inhibition of Mn2+-supported ligand binding. Mutations of the ADMIDAS site also perturbed transduction of a conformational change from the MIDAS through the C-terminal helix region of the beta A domain to the underlying hybrid domain, implying an important role for this site in receptor signaling.

Allosteric Regulation↗
PubMed2005

Integrin alpha5/beta1 expression mediates HER-2 down-regulation in colon cancer cells.

HER-2 is constitutively activated and overexpressed in many cancers, and its inhibition in colon cancer cells diminishes tumorigenicity and induces apoptosis. Little is known about the regulation of HER-2 signaling in colon cancer cells. Integrin alpha5/beta1 expression is frequently lost in colorectal cancer cells compared with normal intestinal epithelium, and colon cancer cells lacking integrin alpha5/beta1 expression utilize HER-2 signaling for proliferation and tumorigenicity. Re-expression of integrin alpha5/beta1 in colon cancer cells abrogated their tumorigenicity, but how this occurs is not well known. Stable expression of integrin alpha5/beta1 in colon cancer cells with little or no detectable integrin alpha5/beta1 protein expression resulted in the post-transcriptional down-regulation of HER-2 protein. Integrin alpha5/beta1 was found to interact with HER-2, and the cytoplasmic domain of integrin alpha5/beta1 was sufficient to mediate HER-2 down-regulation. Integrin alpha5/beta1-mediated down-regulation of HER-2 was the result of increased lysosomal targeting. The inhibition of HER-2 signaling represents a potential mechanism by which integrin alpha5/beta1 exerts its tumor suppressor-like activity in colon cancer cells. These results also suggest that a novel function for integrin alpha5/beta1 is the control of HER-2 expression.

Agar↗
PubMed2006

N-acetylglucosaminyltransferase III antagonizes the effect of N-acetylglucosaminyltransferase V on alpha3beta1 integrin-mediated cell migration.

N-acetylglucosaminyltransferase V (GnT-V) catalyzes the addition of beta1,6-GlcNAc branching of N-glycans, which contributes to metastasis. N-acetylglucosaminyltransferase III (GnT-III) catalyzes the formation of a bisecting GlcNAc structure in N-glycans, resulting in the suppression of metastasis. It has long been hypothesized that the suppression of GnT-V product formation by the action of GnT-III would also exist in vivo, which will consequently lead to the inhibition of biological functions of GnT-V. To test this, we draw a comparison among MKN45 cells, which were transfected with GnT-III, GnT-V, or both, respectively. We found that alpha3beta1 integrin-mediated cell migration on laminin 5 was greatly enhanced in the case of GnT-V transfectant. This enhanced cell migration was significantly blocked after the introduction of GnT-III. Consistently, an increase in bisected GlcNAc but a decrease in beta1,6-GlcNAc-branched N-glycans on integrin alpha3 subunit was observed in the double transfectants of GnT-III and GnT-V. Conversely, GnT-III knockdown resulted in increased migration on laminin 5, concomitant with an increase in beta1,6-GlcNAc-branched N-glycans on the alpha3 subunit in CHP134 cells, a human neuroblastoma cell line. Therefore, in this study, the priority of GnT-III for the modification of the alpha3 subunit may be an explanation for why GnT-III inhibits GnT-V-induced cell migration. Taken together, our results demonstrate for the first time that GnT-III and GnT-V can competitively modify the same target glycoprotein and furthermore positively or negatively regulate its biological functions.

Cell Line, Tumor↗
PubMed2002

Adhesion molecule-dependent mechanisms regulate the rate of macrophage clearance during the resolution of peritoneal inflammation.

Macrophage clearance is essential for the resolution of inflammation. Much is known about how monocytes enter the inflammatory site but little is known about how resultant macro-phages are cleared. We have previously demonstrated that macrophage clearance from resolving peritonitis occurs by emigration into draining lymphatics rather than local apoptosis. We now examine mechanisms for this process, in particular by evaluating the hypothesis that modulation of adhesion interactions between macrophages and cells lining the lymphatics regulates the rate of macrophage clearance. We demonstrate in vivo that macrophages adhere specifically to mesothelium overlying draining lymphatics and that their emigration rate is regulated by the state of macrophage activation. We observed that macrophage-mesothelial adhesion is Arg-Gly-Asp (RGD) sensitive and partially mediated by very late antigen (VLA)-4 and VLA-5 but not alpha(v) or beta(2) integrins. Moreover, macrophage clearance into lymphatics can be blocked in vivo by RGD peptides and VLA-4 and VLA-5 but not beta(2) blocking antibodies. This is the first evidence that macrophage emigration from the inflamed site is controlled and demonstrates that this is exerted through specific adhesion molecule regulation of macrophage-mesothelial interactions. It highlights the importance of adhesion molecules governing entry of cells into the lymphatic circulation, thus opening a new avenue for manipulating the resolution of inflammation.

Animals↗
PubMed2002

Concerted action of androgens and mechanical strain shifts bone metabolism from high turnover into an osteoanabolic mode.

Adhesion of bone cells to the extracellular matrix is a crucial requirement for osteoblastic development and function. Adhesion receptors connect the extracellular matrix with the cyto-skeleton and convey matrix deformation into the cell. We tested the hypothesis that sex hormones modulate mechanoperception of human osteoblastic cells (HOB) by affecting expression of adhesion molecules like fibronectin and the fibronectin receptor. Only dihydrotestosterone (DHT), but not 17beta-estradiol, stimulated fibronectin (137%) and fibronectin receptor (252%) protein expression. The effects of deformation strain on HOB metabolism were investigated in a FlexerCell strain unit. Cyclically applied strain (2.5% elongation) increased DNA synthesis (125%) and interleukin-6 (IL-6) production (170%) without significantly affecting alkaline phosphatase (AP) activity, type I collagen (PICP), or osteoprotegerin (OPG) secretion. 10 nM DHT pretreatment abolished the mitogenic response of HOB to strain and increased AP activity (119%), PICP (163%), and OPG production (204%). In conclusion, mechanical strain stimulates bone remodeling by increasing HOB mitosis and IL-6 production. DHT enhances the osteoanabolic impact of deformation strain by increasing bone formation via increased AP activity and PICP production. At the same time, bone resorption is inhibited by decreased IL-6 and increased OPG secretion into the bone microenvironment.

Alkaline Phosphatase↗
PubMed2001

Quantitative expression of adhesion molecules on granulocyte colony-stimulating factor-mobilized peripheral blood, bone marrow, and cord blood CD34+ cells.

The purpose of this study is to investigate the function of the main adhesion receptors on CD34(+) cells during hematopoietic stem cell transplantation. Expression was quantified by flow cytometry using calibration beads. CD34(+) cells were isolated from either bone marrow (BM), cord blood (CB), or peripheral blood (PB) from study patients and a control group after granulocyte colony-stimulating factor (G-CSF) administration. The study of the CD34(+) cell differentiation showed that CD34(+) cells are mainly CD38(+) and HLA-DR(+), whatever the type of harvest. However, quantitative analysis elicited a weaker expression of CD38 on PB and CB CD34(+) cells in comparison to BM CD34(+) cells. The proportions of CD34(+)/CD49d(+) and CD34(+)/CD49e(+) were smaller on PB cells, without quantitative expression variation. This phenotypic variation promotes CD34(+) cells to exit from BM into circulation, inducing the mobilization. The homing of the CD34(+) cells to the BM involves the CD62L receptor. The expression of this receptor was found to be more frequent and stronger on PB cells than on BM or CB cells. The CD11b, CD18, and CD54 receptors are implicated in CD34(+) cell adhesion to BM microenvironment. No significant variation in CD34(+)/CD11b(+) and CD34(+)/CD18(+) cell frequency was noted. Moreover, the CD54 receptor was more frequently expressed on CB and PB cells. Quantitative analysis revealed that CD18 was more strongly expressed on BM than on PB cells to promote progenitors adhesion by interacting with stromal cells. Finally, the quantitative expression of the main receptors on CD34(+) cells explained cellular functions during the different steps of hematopoietic stem cells transplantation.

ADP-ribosyl Cyclase↗
PubMed2002

Suppression of integrin activation by activated Ras or Raf does not correlate with bulk activation of ERK MAP kinase.

The rapid modulation of ligand-binding affinity ("activation") is a central property of the integrin family of cell adhesion receptors. The Ras family of small GTP-binding proteins and their downstream effectors are key players in regulating integrin activation. H-Ras can suppress integrin activation in fibroblasts via its downstream effector kinase, Raf-1. In contrast, to H-Ras, a closely related small GTP-binding protein R-Ras has the opposite activity, and promotes integrin activation. To gain insight into the regulation of integrin activation by Ras GTPases, we created a series of H-Ras/R-Ras chimeras. We found that a 35-amino acid stretch of H-Ras was required for full suppressive activity. Furthermore, the suppressive chimeras were weak activators of the ERK1/2 MAP kinase pathway, suggesting that the suppression of integrin activation may be independent of the activation of the bulk of ERK MAP kinase. Additional data demonstrating that the ability of H-Ras or Raf-1 to suppress integrin activation was unaffected by inhibition of bulk ERK1/2 MAP kinase activation supported this hypothesis. Thus, the suppression of integrin activation is a Raf kinase induced regulatory event that can be mediated independently of bulk activation of the ERK MAP-kinase pathway.

Amino Acid Sequence↗
PubMed2004

The role of alpha(5)beta(1)-integrin in the IGF-I-induced migration of extravillous trophoblast cells during the process of implantation.

The role of integrins in the processes of adhesion and migration makes them attractive potential participants in the complex events of embryo implantation and placentation. Recently, the role of the alpha(v)beta(3)-integrin pathway was shown in the insulin-like growth factor-I (IGF-I)-stimulated migration of extravillous trophoblast (EVT) cells. This study was designed to investigate the role of alpha(5)beta(1)-integrin in this respect. Using cultured EVT cells, migration assays were carried out for IGF-I-treated or untreated cells in the presence or absence of the GRGDSP and GRGESP hexapeptides, alphaIR3, and a blocking antibody against alpha(5)beta(1)-integrin. Immuno-electron microscopy and immunofluorescent staining were performed to localize the distribution of alpha(5)beta(1)- and alpha(v)beta(3)-integrins, Rab5a, paxillin, phospho-FAK (pFAK), and vinculin. The results showed that IGF-I-induced migration of EVT cells was abolished following treatment with GRGDSP hexapeptide, alphaIR3, and a blocking antibody against alpha(5)beta(1)-integrin. Further, statistical analysis showed that the area-related numerical density of the alpha(5)beta(1)-integrin in the perinuclear regions was significantly higher than in the cell extensions. Immunocytochemical experiments demonstrated an up-regulation in internalization rate of alpha(5)beta(1)-integrin in IGF-I-stimulated EVT cells. Furthermore, alpha(5)beta(1)-integrin exhibited co-localization with Rab5a, but not with alpha(v)beta(3)-integrin, pFAK, paxillin, and vinculin at the focal adhesions of the EVT cells. Taken together, these findings suggest an essential role for alpha(5)beta(1)-integrin in IGF-I-promoted migration of EVT cells. It is possible therefore that IGF-I-induced internalization of alpha(5)beta(1)-integrin may be an important event during the migration of EVT cells in the complex processes of implantation and placentation.

Cell Movement↗
PubMed2003

Bacillus Calmette-Guerin initiates intracellular signaling in a transitional carcinoma cell line by cross-linking alpha 5 beta 1 integrin.

PURPOSE: The adherence of bacillus Calmette-Guerin (BCG) to the surface of transitional carcinoma tumor cells initiates nuclear factor (NF)-kappa B signal transduction pathways that modulate the expression of proteins important in the antitumor response to BCG. We tested the hypothesis that BCG initiates NF-kappa B signaling as a consequence of cross-linking alpha 5 beta 1 integrin receptors present on the tumor cell surface. MATERIALS AND METHODS: The effect of alpha 5 beta 1 antibody mediated cross-linking on interleukin (IL)-6 mRNA expression, IL-6 promoter activation and activation of a specific NF-kappa B reporter construct was determined. A series of reporter constructs containing nonfunctional mutations in the AP-1, NF-IL-6 and NF-kappa B sites were used to determine the relative importance of these response elements in alpha 5 beta 1 cross-linking mediated activation of the IL-6 promoter. A final series of experiments assessed the role of alpha 5 beta 1 receptor occupancy by fibronectin (FN) in initiating antibody or BCG mediated signaling. RESULTS: Anti alpha 5 and anti beta 1 mediated cross-linking of alpha 5 beta 1 integrin initiated NF-kappa B signaling, IL-6 promoter activation and IL-6 mRNA expression. Deletion mutants demonstrated that alpha 5 beta 1 cross-link initiated, IL-6 promoter transactivation required intact NF-kappa B and AP-1 response elements. Receptor occupancy by FN was required for BCG but not for antibody initiated signaling. CONCLUSIONS: Cross-linking the alpha 5 beta 1 receptor present on the surface of human transitional carcinoma cells lines initiates signal transduction in a manner identical to that observed for BCG. We propose a model in which multiple FN binding sites present on BCG interact with alpha 5 beta 1 receptor bound FN molecules to cross-link alpha 5 beta 1 receptors and initiate intracellular signaling.

Bacterial Adhesion↗
PubMed2005

Gangliosides inhibit urokinase-type plasminogen activator (uPA)-dependent squamous carcinoma cell migration by preventing uPA receptor/alphabeta integrin/epidermal growth factor receptor interactions.

The interaction of the urokinase-type plasminogen activator (uPA) receptor (uPAR) with integrins plays a critical role in the regulation of cell adhesion and migration. However, the molecular events underlying the modulation of the interaction of uPAR and integrin are poorly understood. Gangliosides are thought to regulate epithelial cell adhesion and migration by inhibiting alpha(5)beta(1) integrin and epidermal growth factor receptor (EGFR) signaling. We report here that increases in the expression of ganglioside NeuAcalpha2-->3Galbeta1-->3GalNAcbeta1-->4(NeuAcalpha2-->8NeuAcalpha2-->3)Galbeta1-->4Glcbeta1-Cer (GT1b) or NeuAcalpha2-->3Galbeta1-->4Glcbeta1-Cer (GM3) inhibit uPA-dependent cell migration by preventing the association of uPAR with alpha(5)beta(1) integrin or uPAR/alpha(5)beta(1) integrin with the EGFR, respectively. As a result, uPA-dependent focal adhesion kinase (FAK) and integrin-mediated EGFR signaling are suppressed. Both gangliosides inhibit uPAR signaling-stimulated migration; however, GM3 inhibits uPA-induced EGFR phosphorylation by blocking the crosstalk between integrin and EGFR, whereas GT1b suppresses both uPA-induced FAK and EGFR activation by preventing the activation of integrin alpha(5)beta(1).

Carcinoma, Squamous Cell↗