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At least 1,675 records · Page 93Linked to original sources
PubMed2001

Disruption of the mouse mu-calpain gene reveals an essential role in platelet function.

Conventional calpains are ubiquitous calcium-regulated cysteine proteases that have been implicated in cytoskeletal organization, cell proliferation, apoptosis, cell motility, and hemostasis. There are two forms of conventional calpains: the mu-calpain, or calpain I, which requires micromolar calcium for half-maximal activation, and the m-calpain, or calpain II, which functions at millimolar calcium concentrations. We evaluated the functional role of the 80-kDa catalytic subunit of mu-calpain by genetic inactivation using homologous recombination in embryonic stem cells. The mu-calpain-deficient mice are viable and fertile. The complete deficiency of mu-calpain causes significant reduction in platelet aggregation and clot retraction but surprisingly the mutant mice display normal bleeding times. No detectable differences were observed in the cleavage pattern and kinetics of calpain substrates such as the beta3 subunit of alphaIIbbeta3 integrin, talin, and ABP-280 (filamin). However, mu-calpain null platelets exhibit impaired tyrosine phosphorylation of several proteins including the beta3 subunit of alphaIIbbeta3 integrin, correlating with the agonist-induced reduction in platelet aggregation. These results provide the first direct evidence that mu-calpain is essential for normal platelet function, not by affecting the cleavage of cytoskeletal proteins but by potentially regulating the state of tyrosine phosphorylation of the platelet proteins.

Adenosine Diphosphate↗
PubMed2002

Proximal tubular epithelial cell integrins respond to high glucose by altered cell-matrix interactions and differentially regulate matrixin expression.

Thickening of the tubular basement membrane (TBM) occurs in diabetic nephropathy, but the effects of high glucose on the functional aspects of proximal tubular epithelial cells are not clearly understood. In the present study, we examined the effects of elevated glucose concentrations on (a) integrin expression by human proximal tubular epithelial cells (HK-2) and integrin-mediated interactions with type IV collagen (colIV) and laminin, major components of TBM; (b) the expression of matrixins/matrix metalloproteinases (MMPs), which is regulated by integrins; and (c) the expression of tissue inhibitors of metalloproteinases (TIMPs). HK-2 cells cultured in 25 mM glucose underwent a reduction of the expression of alpha3, beta1, alpha(v)beta3, and alpha5 integrin subunits, with a concomitant increase of the alpha2 subunit, compared with cells grown in 5 mM glucose. Adhesion experiments demonstrated that high glucose led to increased cell adhesion on either colIV or laminin. Experiments of competition of adhesion using anti-integrin antibodies indicated that HK-2 cells in 5 mM glucose used mainly alpha(v)beta3 and alpha5beta1 integrins to adhere to colIV, whereas in 25 mM glucose they additionally used alpha2beta1. In the case of laminin, a beta1-mediated adhesion was observed when HK-2 cells were in 5 mM glucose, whereas in 25 mM glucose, alpha2beta1 and alpha(v)beta3 were also involved. Elevated glucose concentrations resulted in decreased expression of MMP-9 and MMP-2, whereas an increase in TIMP-1 and a decrease in TIMP-2 expression were observed. We also examined which integrins mediated the expression and secretion of matrixins MMP-2 and MMP-9. Ligation of alpha3beta1 with mAbs resulted in induction of MMP-2 expression and secretion, whereas antibody ligation of alpha(v)beta3 led to down-regulation of MMP-9. The above data implicate integrins of proximal tubular epithelial cells in the regulation of MMPs and in the development of TBM thickening in diabetic nephropathy.

Cell Line↗
PubMed2003

Ras oncogene directs expression of a differentially sialylated, functionally altered beta1 integrin.

Intense investigation has centered on understanding the regulation of integrin cell adhesion receptors. In the present study, we propose that variant N-glycosylation represents an important mechanism for regulation of beta1, but not beta3 or beta5 integrins. We find that expression of oncogenic ras in HD3 colonocytes causes increased alpha2-6 sialylation of beta1 integrins, whereas expression of dominant-negative ras induces decreased alpha2-6 sialylation, relative to cells with wild-type ras. In contrast, neither beta3 nor beta5 integrins are alpha2-6 sialylated, regardless of the state of ras activation. Results from RT-PCR analyses suggest that differential integrin sialylation is due to a ras-dependent alteration in the expression of ST6Gal I, the enzyme that adds alpha2-6-linked sialic acids. Cells that express differentially sialylated beta1 integrins exhibit altered adhesion to collagen I (a beta1 ligand), but not to vitronectin (a beta3 or beta5 ligand). Similarly, the enzymatic removal of cell surface sialic acids from control cells alters binding to collagen, but not to vitronectin. Finally, using a cell-free receptor/ligand-binding assay, we show that purified, desialylated alpha1beta1 integrins have diminished collagen-binding capability, providing strong evidence that sialic acids play a causal role in regulating beta1 integrin function.

Base Sequence↗
PubMed2006

Novel and selective alpha(v)beta3 receptor peptide antagonist: design, synthesis, and biological behavior.

Among RGD-dependent integrins, the alpha(v)beta3 receptor has recently received increasing attention as a therapeutic target because of its critical role in tumor-induced angiogenesis and metastasis formation. Here, we describe a new peptide antagonist of alpha(v)beta3 receptor, designed on the basis of the crystal structure of integrin alpha(v)beta3 in complex with c(RGDf[NMe]V) and the NMR structure of echistatin. Cell adhesion assays have demonstrated that the peptide is a potent and selective antagonist of the alpha(v)beta3 receptor.

Cell Adhesion↗
PubMed2002

Altered expression of ADAMs (A Disintegrin And Metalloproteinase) in fibrillating human atria.

BACKGROUND: ADAMs (A Disintegrin And Metalloproteinase) are ectoproteases that have recently been reported to be expressed in cardiac tissue. Although they are known to regulate cell-cell and cell-matrix interactions, their pathophysiological role in various cardiac diseases is unclear. The purpose of the present study was to determine whether structural remodeling of the atria during atrial fibrillation (AF) is associated with altered ADAM expression. METHODS AND RESULTS: Atrial tissue samples of 30 patients undergoing open-heart surgery were examined. Fifteen patients had persistent AF (> or =6 months), and the remaining 15 patients had no history of AF. ADAM9, ADAM10, and ADAM15 expression was analyzed quantitatively at the mRNA and protein levels. ADAM expression was localized by immunohistochemistry. ADAM expression was correlated with amounts of integrins beta1 and beta3. The amount of ADAM10 protein more than doubled during AF (82+/-15 versus 36+/-8 U; P<0.01). Amounts of ADAM15 protein (102+/-12 versus 40+/-6 U; P<0.01) and mRNA (24.0+/-5.6 versus 10.5+/-2.5 U; P<0.05) increased significantly during AF compared with sinus rhythm. ADAM9 protein was not detected in any sample. ADAM/integrin ratios showed an increase of 4- to 6-fold (P<0.05) in patients with AF who had significantly dilated atria (4.94+/-0.6 versus 4.3+/-0.7 cm; P<0.05). ADAM/integrin ratios correlated with atrial diameter. CONCLUSIONS: AF is associated with an increase in the expression of ADAM10 and ADAM15. Enhanced ADAM-dependent disintegrin and metalloproteinase activity may be a molecular mechanism that contributes to the dilation of fibrillating human atria.

ADAM Proteins↗
PubMed1996

Efficient infection of cells in culture by type O foot-and-mouth disease virus requires binding to cell surface heparan sulfate.

Foot-and-mouth disease virus (FMDV) enters cells by attaching to cellular receptor molecules of the integrin family, one of which has been identified as the RGD-binding integrin alpha(v)beta3. Here we report that, in addition to an integrin binding site, type O strains of FMDV share with natural ligands of alpha(v)beta3 (i.e., vitronectin and fibronectin) a specific affinity for heparin and that binding to the cellular form of this sulfated glycan, heparan sulfate, is required for efficient infection of cells in culture. Binding of the virus to paraformaldehyde-fixed cells was powerfully inhibited by agents such as heparin, that compete with heparan sulfate or by agents that compete for heparan sulfate (platelet factor 4) or that inactivate it (heparinase). Neither chondroitin sulfate, a structurally related component of the extracellular matrix, nor dextran sulfate appreciably inhibited binding. The functional importance of heparan sulfate binding was demonstrated by the facts that (i) infection of live cells by FMDV could also be blocked specifically by heparin, albeit at a much higher concentration of inhibitor; (ii) pretreatment of cells with heparinase reduced the number of plaques formed compared with that for untreated cells; and (iii) mutant cell lines deficient in heparan sulfate expression were unable to support plaque formation by FMDV, even though they remained equally susceptible to another picornavirus, bovine enterovirus. The results show that entry of type O FMDV into cells is a complex process and suggest that the initial contact with the cell surface is made through heparan sulfate.

Animals↗
PubMed2003

The homeobox transcription factor Hox D3 promotes integrin alpha5beta1 expression and function during angiogenesis.

Neovascularization promotes wound healing, tumor growth, and arthritis. Endothelial cell migration and survival during neovascularization are regulated by adhesion proteins, including integrin alpha5beta1. Integrin alpha5beta1 is poorly expressed on normal quiescent blood vessels, but its expression is induced on tumor blood vessels and in response to angiogenic factors such as basic fibroblast growth factor, interleukin-8, tumor necrosis factor-alpha, and the angiomatrix protein Del-1. We show here that alpha5beta1 expression, and hence function, during angiogenesis is regulated by the transcription factor Hox D3, a homeobox gene that also controls the expression of endothelial cell integrin alphavbeta3 and urokinase-type plasminogen activator. Hox D3 expression in endothelial cells enhances integrin alpha5 protein and message expression, whereas Hox D3 antisense inhibits its expression. Hox D3 promotes alpha5 expression during angiogenesis in vivo, whereas inhibition of alpha5 expression by Hox D3 antisense suppresses angiogenesis. Hox D3 binds directly to the promoters of the integrin alpha5 and beta3 subunits, inducing subunit expression. As Hox D3, integrin alphavbeta3, and integrin alpha5beta1 are expressed on tumor blood vessels but not on normal quiescent vessels, these studies suggest that Hox D3 coordinately regulates the expression of integrin alpha5beta1 and integrin alphavbeta3 during angiogenesis in vivo. These studies also suggest that Hox D3 inhibition could be a useful approach to inhibit tumor angiogenesis.

Animals↗
PubMed2006

Collagen type V enhances matrix contraction by human periodontal ligament fibroblasts seeded in three-dimensional collagen gels.

Extracellular matrix components play an important role in modulating cellular activity. To study such capacities of the matrix, fibroblasts are frequently cultured in a three-dimensional gel and contraction is assessed as a measure of cellular activity. Since a connective tissue contains several types of collagen, we investigated the effect of gels composed of collagen I alone or in combination with 10% collagen III and/or 5% collagen V on contraction by human periodontal ligament fibroblasts. Gels containing collagen V contracted much faster than those without this type of collagen. Blocking of the integrin beta1-subunit with an activity-blocking antibody delayed (gels with collagen V) or almost completely blocked (gels without collagen V) contraction. Use of an antibody directed against integrin alpha2beta1 resulted in delay of gel contraction for gels both with and without collagen V. Anti-integrin alpha v beta3 or RGD peptides partially blocked contraction of gels containing collagen V, but had no effect on gels consisting of collagen I alone. The beta1-containing integrins are involved in the basal contraction by fibroblasts that bind to collagens I and III. The enhanced contraction, stimulated by collagen V, appears to be mediated by integrin alpha v beta3. We conclude that collagen V may play an important modulating role in connective tissue contraction. Such a modulation may occur during the initial stages of wound healing and/or tissue regeneration.

Adult↗
PubMed2001

Disruption of matrix metalloproteinase 2 binding to integrin alpha vbeta 3 by an organic molecule inhibits angiogenesis and tumor growth in vivo.

Matrix metalloproteinase 2 (MMP2) can associate with integrin alpha(v)beta3 on the surface of endothelial cells, thereby promoting vascular invasion. Here, we describe an organic molecule (TSRI265) selected for its ability to bind to integrin alphav(v)beta3 and block alpha(v)beta3 interaction with MMP2. Although disrupting alpha(v)beta3/MMP2 complex formation, TSRI265 has no effect on alpha(v)beta3 binding to its extracellular matrix ligand vitronectin and does not influence MMP2 activation or catalytic activity directly. However, TSRI265 acts as a potent antiangiogenic agent and thereby blocks tumor growth in vivo. These findings suggest that activated MMP2 does not facilitate vascular invasion during angiogenesis unless it forms a complex with alpha(v)beta(3) on the endothelial cell surface. By disrupting endothelial cell invasion without broadly suppressing cell adhesion or MMP function, the use of compounds such as TSRI265 may provide a novel therapeutic approach for diseases associated with uncontrolled angiogenesis.

Angiogenesis Inhibitors↗
PubMed1998

Vitronectin decreases microvascular endothelial cell apoptosis.

Angiogenesis after tissue injury occurs in a matrix environment consisting of fibrin, fibronectin, and vitronectin as the major extracellular matrix (ECM) constituents. ECM-integrin interactions is critical for angiogenesis and failure to bind a ligand to certain integrin receptors (alpha[v]beta3 or alpha[v]beta5) inhibits angiogenesis. The ligand that binds to alpha(v)beta3 or alpha(v)beta5 integrin receptors during microvascular angiogenesis has not been identified. Our hypothesis is that provisional matrix molecules provide the environmental context cues to microvascular endothelial cells and promote angiogenesis by decreased programmed cell death. Using cultured human microvascular endothelial cells, we show that vitronectin, in comparison to growth on alternative provisional matrix molecules (fibronectin, fibrinogen plus thrombin), collagen I, and basement membrane molecules (collagen IV), significantly reduces microvascular endothelial cell death in vitro. This reduction was observed using morphologic criteria, TdT-mediated dUTP nick end labeling (TUNEL) assay, histone release into the cytoplasm, and thymidine release into the supernatant. Though our data confirm that vitronectin may bind to more than one integrin receptor to reduce MEC apoptosis, binding to the alpha(v) component appears to be the critical integrin subcomponent for reducing apoptosis.

Apoptosis↗
PubMed2002

Unique ability of integrin alpha(v)beta 3 to support tumor cell arrest under dynamic flow conditions.

Shear-resistant arrest of circulating tumor cells is required for metastasis from the blood stream. Arrest during blood flow can be supported by tumor cell interaction with attached, activated platelets. This is mediated by tumor cell integrin alpha(v)beta3 and cross-linking plasma protein ligands. To analyze the mechanism of tumor cell ligand interactions under dynamic flow conditions, we used real-time video microscopy and tested human melanoma cell binding to fibrinogen, von Willebrand Factor, or fibronectin matrices in a buffer perfusion system. When perfused at venous flow, melanoma cells arrested abruptly and began to spread immediately. This was uniquely mediated by integrin alpha(v)beta3 on all tested ligands, and required alpha(v)beta3 activation and actin polymerization. Under static conditions, alpha(v)beta3 cooperated with alpha(v)beta1 and alpha5beta1 in supporting melanoma cell adhesion to fibronectin. But even when activated, beta1 integrins did not contribute to melanoma cell arrest during flow. Soluble ligand served as a cross-linker between attached and circulating tumor cells and enhanced melanoma cell arrest. Cohesion of activated melanoma cells was restricted to the matrix surface and did not occur in suspension. We conclude that the presence of alpha(v)beta3 in a functionally activated state provides a unique advantage for circulating tumor cells by promoting tumor cell arrest in the presence of flow-dependent shear forces.

Actins↗
PubMed2001

gp49B1-alpha(v)beta3 interaction inhibits antigen-induced mast cell activation.

We have identified the integrin alpha(v)beta3 as a ligand for mouse gp49B1, thus identifying a new class of ligand for a member of the family of inhibitory immunoreceptors that bear C2-type immunoglobulin-like domains. The specific interaction was shown by both cell-protein and cell-cell binding assays. In addition, we found that the interaction of alpha(v)beta3 with gp49B1 on bone marrow-derived mouse mast cells inhibited antigen-induced immunoglobulin E-mediated cell activation. Because neither gp49B1 nor alpha(v)beta3 exhibit substantive allelic variation, their newly appreciated interaction may reflect an innate pathway for down-regulating the activity of mast cells.

Animals↗
PubMed2005

Association of polymorphisms of platelet membrane integrins alpha IIb(beta)3 (HPA-1b/Pl) and alpha2(beta)1 (alpha807TT) with premature myocardial infarction.

Conflicting results of an association of the human platelet antigen 1b (HPA-1b/PlA2), localized on the beta-subunit of the integrin alpha(IIb)beta3, and the alpha(2)807TT genotype of the integrin alpha2beta1 with coronary atherosclerosis and myocardial infarction have been reported. Both platelet receptor polymorphisms were genotyped in 3261 patients who had undergone coronary angiography, including 1175 survivors of a myocardial infarction, 1211 individuals with coronary artery disease but no history of myocardial infarction, and 571 control patients without angiographic coronary artery disease, and in 793 blood donors. In a case-control design, the prevalence of HPA-1b and alpha(2)807TT genotypes did not differ significantly between the patient groups with coronary artery disease or myocardial infarction and patient controls or blood donors. By contrast, using a multivariate case-only design, it was found that the median age of onset of myocardial infarction was 5.2 years earlier (P = 0.006) in carriers of the HPA-1b allele and 6.3 years earlier (P = 0.006) in carriers of the alpha(2)807TT genotype in the 264 survivors of myocardial infarction of recent onset with one- or two-vessel coronary artery disease. A significant interaction with the conventional risk factors hypercholesterolemia, smoking, diabetes, hypertension, and hyperfibrinogenemia was excluded. Human platelet antigen 1b and alpha(2)807TT are associated with premature myocardial infarction but not with coronary artery disease, suggesting a role of distinct integrin genotypes for increased platelet thrombogenicity. This association requires confirmation in follow-up studies.

Age of Onset↗
PubMed2001

Unusually stable and long-lived ligand-induced conformations of integrins.

Integrins are a large family of cell surface receptors that are involved in a wide range of biological processes. The integrin alpha(IIb)beta3 (glycoprotein IIb-IIIa) is a major platelet glycoprotein heterodimeric receptor that mediates platelet aggregation and is currently a target for pharmaceutical intervention. Ligand binding to the receptor has been shown to induce conformational changes by physical methods and the exposure of neoepitopes (the ligand-induced binding sites). Here we show that the antagonist XP280 induces a conformation that is stable to treatment with SDS and that the protein retains this conformation for several days even after dissociation of the inhibitor. These ligand-induced conformational changes take place with purified protein and on intact platelets. They are competable with an RGDS peptide and are stable to reduction but not boiling or treatment with EDTA. The retention of an altered conformation in the absence of the ligand implies the possibility of ligand-induced alteration of biological function even in the absence of ligand. Finally, similar behavior is observed with the integrin alpha(v)beta3, suggesting that access to SDS stable conformations may be conserved throughout the integrin superfamily. The unusual stability, long-lived nature, and potential generality of these conformations could have profound implications for integrin biology.

Alanine↗
PubMed2001

A novel synthetic Arg-Gly-Asp-containing peptide cyclo(-RGDf==V-) is the potent inhibitor of angiogenesis.

Arg-Gly-Asp (RGD)-containing peptide is a ligand for integrin alpha(V)beta3 and acts as an angiogenic inhibitor. A novel cyclic RGD peptide, cyclo(-RGDf==V-) (f==V), was synthesized and its biological activities were characterized and compared with its analogs, cyclo(-RGDfV-) (fV) and cyclo(-RGDf-MeV-) (fMeV). It bound to integrin alpha(V)beta3 with almost the same affinity as the fV and fMeV analogs. All three compounds inhibited the adhesion and growth of HUVEC cells in a dose-dependent manner in vitro. Out of three, fMeV had the strongest effect, f==V was almost as strong as fMeV, and fV had the least effect. However, in vivo, f==V significantly decreased the intratumoral microvessel density (MVD) in the DLD-1 (human colon cancer cell) inoculated mice, while fMeV had little effect. These results suggest the potential usefulness of the cyclo(-RGDf==V-) as an antiangiogenic agent for clinical use in the future.

Animals↗
PubMed2003

PYK2 and FAK in osteoclasts.

Integrin alpha(v)beta3 plays a pivotal role in osteoclastic bone resoprtion by mediating both osteoclast attachments on bone matrix and cytoskeleton reorganization. The focal adhesion kinase (FAK) family kinases including FAK and proline-rich tyrosine kinase 2 (PYK2) are major tyrosine kinases activated by integrin engagement. In osteoclasts, although FAK is expressed, PYK2 appears to be the predominant mediator of integrin alpha(v)beta3 signaling events that influence osteoclast physiology and pathology. Recent progress in the understanding of the role of PYK2/FAK kinases in the regulation of osteoclastic actin cytoskeletal organization, cell migration, and bone resorption will be discussed in this review.

Animals↗
PubMed1998

Chloramine T-induced structural and biochemical changes in echistatin.

Echistatin is a member of the disintegrin family of peptides and a potent inhibitor of platelet aggregation and cell adhesion. Echistatin binds to integrin alpha(v)beta3 and alpha(IIb)beta3 receptors with high affinity. Binding is mediated by an RGD-containing loop maintained in an appropriate conformation by disulfide bridges. In this study, we have compared the binding characteristics of echistatin iodinated by either lactoperoxidase or chloramine T method. We show that echistatin labeled by lactoperoxidase method binds to integrin alpha(v)beta3 receptor with high affinity and in a non-dissociable manner very similar to native echistatin. In contrast, chloramine T-labeled echistatin can rapidly dissociate from the receptor. We demonstrate that chloramine T reaction results in the addition of an extra oxygen to the methionine residue adjacent to the RGD motif in echistatin. Modeling studies and molecular dynamic simulation studies show that the extra oxygen atom on the methionine residue can form hydrogen bonds with the glycine and aspartic acid residues of the RGD motif. These structural changes in echistatin help explain the changes in the binding characteristics of the molecule following chloramine T reaction.

Chloramines↗
PubMed2001

X-rays modulate extracellular matrix in vivo.

X-rays have an antiangiogenic effect in the chicken embryo chorioallantoic membrane (CAM) model of in vivo angiogenesis. Our study demonstrates that X-rays induce an early apoptosis of CAM cells, modulate the synthesis and deposition of extracellular matrix (ECM) proteins involved in regulating angiogenesis and affect angiogenesis induced by tumour cells implanted onto the CAM. Apoptosis was evident within 1-2 hr, but not later than 6 hr after irradiation. Fibronectin, laminin, collagen type I, integrin alpha(v)beta3 and MMP-2 protein amounts were all decreased 6 hr after irradiation. In contrast, collagen type IV, which is restricted to basement membrane, was not affected by irradiation of the CAM. There was a similar decrease of gene expression for fibronectin, laminin, collagen type I and MMP-2, 6 hr after irradiation. The levels of mRNA for integrin alpha(v)beta3 and collagen type IV were unaffected up to 24 hr after irradiation. The decrease in both protein and mRNA levels was reversed at later time points and 48 hr after irradiation, there was a significant increase in the expression of all the genes studied. When C6 glioma tumour cells were implanted on irradiated CAMs, there was a significant increase in the angiogenesis induced by tumour cells, compared to that in non-irradiated CAMs. Therefore, although X-rays have an initial inhibitory effect on angiogenesis, their action on the ECM enhances new vessel formation induced by glioma cells implanted on the tissue.

Animals↗