SEARCH · PubMed Health

Results for “Integrin”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources

PubMed2006

The alpha4bbeta7-integrin is dynamically expressed on murine eosinophils and involved in eosinophil trafficking to the intestine.

BACKGROUND: Of the numerous adhesion molecules expressed by eosinophils, the alpha4-integrin has been identified as critically involved in eosinophil trafficking in the lung. Most studies have focused on the role of the alpha4beta1-adhesion complex, but eosinophils also express the alpha4beta7-integrin complex. OBJECTIVE: To investigate the role of alpha4beta7, by assessing its membrane expression on eosinophils from different compartments using allergen-challenged mice and IL-4/IL-5 bi-transgenic mice. In addition, we aim to determine the impact of beta7-integrin deficiency on eosinophil recruitment to the lungs and intestine in specific experimental allergic models. RESULTS: Evaluation of alpha4beta7 expression on bronchoalveolar lavage fluid (BALF) and lung tissue eosinophils revealed a down-regulation of this integrin as eosinophils migrate through the lungs. Indeed eosinophils isolated from the BALF and lung of allergic mice had low expression of the alpha4beta7-complex. While expression of the alpha4-chain remained unchanged, a significant decrease in beta7-surface expression was observed. Intestinal eosinophils, isolated from Peyer's patches, also displayed a down-regulation of the alpha4beta7-integrin, albeit only modest. In contrast, circulating eosinophils, isolated from the blood and spleen, expressed high levels of the alpha4beta7-integrin. However, eosinophil trafficking into the lungs of beta7-integrin-deficient mice was not significantly impaired in response to respiratory allergen challenges. In contrast, beta7-deficient mice had impaired eosinophil recruitment to the intestine. CONCLUSION: Taken together, these results identify differential expression of the alpha4beta7-integrin on eosinophils and its critical role in regulating eosinophil responses in the intestine.

Animals↗

PubMed1994

Bio-histochemical aspects of integrins (alpha 2 beta 1, alpha 6 beta 1) in invasive mammary carcinomas: an immunohistochemical study.

Immunohistochemical expression of integrins was examined in 39 human invasive mammary carcinomas, of which 34.2% and 43.6% expressed integrins alpha 2 beta 1 and alpha 6 beta 1, respectively. Immuno-electron microscopy clearly demonstrated that the integrins were in the cell membrane of the carcinoma cells. Similar expression of integrin alpha 2 beta 1 or alpha 6 beta 1 in both the intraductal component and invasive portion of the same tumor was seen in 76.9% and 85.7% of cases, respectively. This suggested that invasive carcinoma cells retained their integrin expression after invasion through the basement membrane. Reciprocal expression of integrins alpha 2 beta 1 and alpha 6 beta 1 was seen in 20 cases. Expression of alpha 2 beta 1 was seen significantly less frequently in scirrhous carcinoma than in the more differentiated papillotubular or solid tubular carcinoma (Chi-squared test, P < 0.05). Intraductal components of carcinoma were present more frequently in cases expressing integrin alpha 2 beta 1 than in those that were negative. This suggests the potential usefulness of integrins as clinical parameters in the surgical treatment of mammary carcinoma, since recent trials of conservative treatment for mammary carcinoma have focused on the intraductal spread of the tumor cells.

Antigens, CD↗

PubMed2005

alphaV integrins are necessary for eutrophic inward remodeling of small arteries in hypertension.

Human essential hypertension is characterized by eutrophic remodeling of small arteries, with little evidence of hypertrophy. Likewise, vessels of young hypertensive TGR(mRen2)27 animals have undergone similar structural alterations. The role of integrins in resistance arteries of TGR(mRen2)27 during the eutrophic-remodeling process was examined as blood pressure rose. Initially, 8 alpha and 3 beta integrins were identified and levels of expression investigated using RT-PCR. As pressure increased and remodeling advanced, integrin expression profiles revealed that only alphaV was significantly raised. In conjunction, we confirmed elevated integrin alphaV protein levels in TGR(mRen2)27 rat arteries and localization to the media using immunofluorescence. beta1 and beta3, but not beta5 integrin subunits were coprecipitated with integrin alphaV and are implicated in the eutrophic remodeling process. Administration of a peptide antagonist of alphaVbeta3 abolished remodeling but enhanced growth, indicating that hypertrophy supervened as a response to hypertension-induced increases in wall stress. We have established that the only upregulated integrin, the alphaV subunit of integrin alphaVbeta3, has a crucial role in the hypertensive remodeling process of TGR(mRen2)27 rat resistance arteries. During hypertensive remodeling, functions of specific alphaVbeta3-extracellular matrix interactions are likely to allow vascular smooth muscle cell-length autoregulation, which includes a migratory process, to maintain a narrowed lumen after a prolonged constricted state.

Animals↗

PubMed1994

Lung epithelial lining fluid T cell subsets defined by distinct patterns of beta 7 and beta 1 integrin expression.

Integrins are heterodimeric cell-surface glycoproteins that mediate cell-cell and cell-matrix adhesion. We previously identified cDNA encoding a novel integrin beta subunit, beta 7, from bronchoalveolar lavage fluid (BALF) leukocytes. The beta 7 subunit protein is now known to associate with at least two integrin alpha subunits on lymphocytes. One beta 7 integrin, alpha 4 beta 7, mediates lymphocyte adhesion to endothelium and to fibronectin. The other known beta 7 integrin, alpha E beta 7, has recently been shown to mediate lymphocyte-epithelial cell adhesion in vitro. We used flow microfluorometry to analyze the expression of alpha 4 beta 7, alpha E beta 7, and other integrins on blood T cells and epithelial lining fluid T cells obtained from five healthy adult volunteers by bronchoalveolar lavage. alpha 4 beta 7 was the predominant beta 7 integrin on blood T cells, whereas alpha E beta 7 was predominant on BALF T cells. BALF T cells could be divided into alpha E beta 7- and alpha E beta 7+ subsets. Between 29 and 61% (mean 42%) of CD3+ T cells were alpha E beta 7+ alpha E beta 7 was more likely to be present on CD8+ T cells (mean 69% alpha E beta 7+) than on CD4+ T cells (mean 29% alpha E beta 7+). The alpha E beta 7- and alpha E beta 7+ BALF T cell subsets were also found to differ in their expression of other integrins.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2004

Immuno-histochemical expression of alpha1, alpha2 and alpha3 integrin subunits during angiogenesis in vitro.

Aortic explants were obtained from mouse fetuses and cultured in collagen gels. Immuno-fluorescence microscopy, antibodies (anti alpha1, alpha2 and alpha3 integrin subunits) were used. Fibroblastic cells migrated from the aortic explant after one day of cultivation. The migrating cells located in the peripheral part of the aortic explant were positive for alpha1 and alpha2 integrin subunit antibodies. Immuno-fluorescence-positive staining for the alpha3 integrin subunit antibody was clearly seen in the migrating cells located near the aortic explant and surrounding tube-like structures. In an immuno-electron microscope study performed by pre-embedding immuno labeling, gold particles associated with the alpha3 integrin subunit were found to reside on the membranes of the cells surrounding the capillary-like tubes. Two synthetic peptides, GRGDSP (Gly-Arg-Gly-Asp-Ser-Pro) and KDGEA (Lys-Asp-Gly-Glu-Ala), were added to the growth medium to study their effects on cell migration. KDGEA, a compound containing the recognition sequence for alpha2beta1 integrin, decreased cell migration, while GRGDSP exhibited no effect. The migration of fibroblastic cells is an important phenomenon for tube formation. The present study suggested that the alpha1 and alpha2 integrin subunits are both involved in the cell migration, and more specifically, that the alpha2 integrin subunit participates in cell migration through the KDGEA sequence. The alpha3 integrin subunit played a role in tube formation.

Animals↗

PubMed1994

Differential expression of integrins alpha 6 and alpha 4 determines pathways in human peripheral CD4+ T cell differentiation.

Integrins mediate leukocyte adhesion to vascular endothelium and thereby influence leukocyte recirculation. We have explored expression by peripheral blood T cells of beta 1 and beta 7 integrins, particularly alpha 4 beta 1 (VLA-4, CD49d), alpha 4 beta 7 (LPAM-1) and alpha 6 beta 1 (VLA-6, CD49f). Integrin expression differs between CD4+ cells and CD8+ cells in that CD4+ cells 1) are more heterogeneous, particularly for alpha 4; 2) express on the average less alpha 4 and beta 7; and 3) express on the average more alpha 6 and beta 1. 2D gel electrophoretic analysis was combined with flow cytometric analysis to determine which integrin chain pairs are expressed by the CD45RO- (naive) and CD45RO+ (memory) subsets of CD4+ cells. CD45RO- (naive) cells express homogeneously at intermediate levels the three integrin pairs alpha 6 beta 1, alpha 4 beta 1 and alpha 4 beta 7. Although 2D gel analysis suggests similar average integrin chain composition for CD45RO+CD4+ (memory) cells, flow cytometric analysis demonstrates multiple subsets of CD45RO+ cells differing markedly from each other and from naive cells in levels of expression of alpha 6 and alpha 4 integrins. There are a minimum of three CD45RO+ subsets: 1) alpha 4 beta 1hi alpha 6 beta 1hi alpha 4 beta 7neg, which comprises the majority of memory cells; 2) alpha 4 beta 7hi alpha 6 beta 1low presumptive gut-homing memory cells; and 3) alpha 6 beta 1hi alpha 4 beta 7neg alpha 4 beta 1neg, a previously unidentified subset expected to have unique migrational-functional properties. Of particular importance in these results are: the expression by CD4+ naive cells of alpha 6 beta 1, alpha 4 beta 1 and alpha 4 beta 7, the overall prominence and regulation of alpha 6 beta 1 on CD4+ cells, and the selective decreases as well as increases in alpha 4 beta 7 and alpha 4 beta 1 during CD4+ memory specialization. Taken together, these results suggest that differential regulation of expression of alpha 4 and alpha 6 integrin chains that accompany naive-to-memory transition in CD4+ cells are instrumental in generating functional subsets of CD4+ memory cells with specialized recirculation abilities.

CD4-Positive T-Lymphocytes↗

PubMed2004

The alpha 1 beta 1 and alpha E beta 7 integrins define a subset of dendritic cells in peripheral lymph nodes with unique adhesive and antigen uptake properties.

Dendritic cells (DCs) are a heterogeneous population of APCs with critical roles in T cell activation and immune regulation. We report in this study the identification and characterization of a novel subset of DCs resident in skin-draining peripheral lymph nodes of normal mice. This subset of CD11c(high)CD40(high)CD8alpha(intermediate (int)) DCs expresses the collagen-binding integrin, alpha1beta1, and the E-cadherin-binding integrin, alphaEbeta7. Although alpha1beta1 and alphaEbeta7 are also expressed on CD11c(high)CD40(int)CD8alpha(high) lymphoid DCs, CD11c(high)CD40(high)CD8alpha(int) DCs demonstrate preferential integrin-mediated adhesion to collagen and fibronectin. This DC subset most likely acquires expression of these integrins in peripheral lymph node, as this subset is not found in the spleen or mesenteric lymph node, and recent DC migrants from the skin lack expression of alpha1beta1 and alphaEbeta7 integrins. Resident CD40(high) DCs express alpha1beta1 integrin and colocalize with collagen in lymph nodes. When compared with CD11c(high)CD40(high)CD8alpha(int) DCs lacking expression of these integrins, the alpha1beta1+alphaEbeta7+DC subset exhibits more efficient formation of Ag-independent conjugates with T cells, and a decreased ability to acquire soluble Ag. Thus, the alpha1beta1 and alphaEbeta7 integrins define a unique population of peripheral lymph node-derived DCs with altered functional properties and adhesive potential that localizes these cells to sites in lymph nodes where Ag presentation to T cells occurs.

Animals↗

PubMed2002

Differential regulation of a novel variant of the alpha(6) integrin, alpha(6p).

We have reported previously the existence of an M(r) 70,000 form of the alpha(6) integrin called alpha(6p) in a variety of human epithelial cell lines. Four different experimental conditions were used to examine the regulation of alpha(6) and alpha(6p) integrin. The production of the alpha(6) integrin was decreased by 45% using a protein translation inhibitor (2.25 microM puromycin), whereas production of the alpha(6p) variant was unaffected. The alpha(6p) variant was decreased 60% by actin depolymerization (10 microM cytochalasin D) corresponding to a decrease in its surface expression, whereas alpha(6) integrin production was unaffected. The alpha(6p) variant was resistant to endoglycosidase H treatment, whereas the alpha(6) integrin was both sensitive and resistant to endoglycosidase H treatment, indicating retention in the endoplasmic reticulum and processing through the Golgi apparatus. Additionally, digestion by endoglycosidase F demonstrated both alpha(6p) and alpha(6) integrin contained NH(2)-linked glycosylations and both shifted M(r) approximately 10,000 on enzymatic digestion. Finally, inhibition of serine/threonine phosphatases by either calyculin A (15 nM) or okadaic acid (62 microM) did not affect alpha(6p), whereas the production of alpha(6) integrin was decreased by 50%. These data suggest that the production of the alpha(6p) variant is distinct from alpha(6) integrin and may involve a post-translational processing event at the cell surface.

Actins↗

PubMedDate not supplied

Inositol hexaphosphate (IP6) inhibits key events of cancer metastasis: II. Effects on integrins and focal adhesions.

BACKGROUND: We have shown that inositol hexaphosphate (IP6), a natural compound and a potent anti-cancer agent, inhibited cancer cell adhesion to the extracellular matrix (ECM) proteins, thereby leading to inhibition of cell migration and invasion. Cell adhesion to ECM is mediated by specific cell surface integrins, which transduce intracellular signals through their interaction and activation of other proteins that are recruited to the focal adhesion. We hypothesize that IP6 decreases cell adhesion by suppressing the integrin receptors and their subsequent signaling pathway. MATERIALS AND METHODS: We analyzed integrin expressions of the highly invasive estrogen receptor-negative human breast cancer MDA-MB 231 cells exposed to IP6 by flow cytometry. The expression of focal adhesion proteins was investigated by immunocytochemistry and Western blotting. RESULTS: IP6 treatment caused a significant (P < 0.005) decrease in the expression of integrin heterodimers alpha 2 beta 1 (collagen receptor), alpha 5 beta 1 (fibronectin receptor) and alpha v beta 3 (vitronectin receptor); flow cytometry showed that it was the alpha 5 subunit that was down-regulated ( < 0.001). However, the expression of the alpha 2, alpha v, beta 1 and beta 3 subunits were not affected by IP6 treatment. When the expression of integrins on the cell surface was assessed, there was a dramatic 82% decrease in the expression of alpha 5 beta 1 on IP6-treated cells (P < 0.0001), indicating a decrease in cell surface expression of the heterodimers. No effect was seen when inositol hexasulfate (IS6), an analogue of IP6, was used as a control. Immunocytochemistry showed a lack of clustering of paxillin; tyrosine-phosphorylated proteins in IP6-treated cells were discontinuous and scattered around the cell periphery, whereas the patterns were more dense and localized in control cells. Consistent with these observations, focal adhesion kinase (FAK) autophosphorylation at tyrosine-397 residue was suppressed, albeit modestly, by IP6 treatment, suggesting a down-regulation in the integrin-mediated signaling pathway. CONCLUSION: The results of this study indicate that IP6-induced inhibition of cancer cell adhesion, migration and invasion may be mediated through the modulation of integrin dimerization, cell surface expression and integrin-associated signaling pathway.

Breast Neoplasms↗

PubMed1997

Intestinal epithelial restitution. Involvement of specific laminin isoforms and integrin laminin receptors in wound closure of a transformed model epithelium.

Disruptions in the mucosal lining of the gastrointestinal tract reseal by epithelial cell migration, a process termed restitution. We examined the involvement of laminin isoforms and their integrin receptors in restitution using the intestinal epithelial cell line T84. T84 cells express primarily laminins 5, 6, and 7 as indicated by immunostaining using laminin subunit-specific monoclonal antibodies (MAbs). A MAb (BM2) specific for the laminin alpha 3 subunit, a component of laminins 5, 6, and 7, completely inhibited the closure of mechanical wounds in T84 monolayers. Confocal microscopy using MAbs BM2 (laminin alpha 3 subunit) and 6F12 (laminin beta 3 subunit) revealed that laminin-5 is deposited in a basal matrix that extends into the wound. The MAbs 4E10 (laminin beta 1 subunit) and C4 (laminin beta 2 subunit) stained the lateral membranes between T84 cells. This staining was enhanced in cells adjoining wounds. Because T84 cells stained faintly with MAbs 4C7 (laminin alpha 1 subunit) and with MAbs 4F11 and 1B4 (laminin alpha 2 subunit), we suggest that expression of laminins 6 and 7 is enhanced in response to wounding. The alpha 3 beta 1 integrin and the alpha 6-containing integrins function in wound closure because MAbs specific for the beta 1 integrin subunit (MAb13), the alpha 3 subunit (IVA5), and the alpha 6 subunit (2B7) potently inhibited T84 migration into wounds. Immunofluorescence using UMA9, a beta 4-integrin-specific MAb, revealed that alpha 6 beta 4 integrin exists in a Triton-X-100-insoluble structure at the basal surface and that the staining of this structure is enhanced in cells adjoining wounds. In addition, a Triton-X-100-soluble pool of alpha 6 beta 4, as well as alpha 3 beta 1 and presumably alpha 6 beta 1, was found along lateral surfaces of T84 cells. On flattened cells adjoining wounds, staining for these integrins was distributed diffusely, suggesting a redistribution that accompanies cell migration. Taken together, these data suggest that wound-induced epithelial cell migration is a finely tuned process that is dependent upon the regulated function and localization of specific laminins and their integrin receptors.

Antigens, CD↗

PubMed1998

The selective inhibition of beta 1 and beta 7 integrin-mediated lymphocyte adhesion by bacitracin.

Integrins play an important role in lymphocyte adhesion to cellular and extracellular components of their microenvironment. The regulation of such adhesion often involves changes in the functional state of the integrins rather than alterations in their expression levels. Although the functional basis for such transitions is unknown, a possible role for disulfide exchange might be postulated based on the observations that integrin function can be activated by bifunctional reducing agents or by Abs that react with areas adjacent to predicted long-range disulfide bonds in integrins. Recently, it has been reported that enzymes that catalyze disulfide exchanges such as protein disulfide isomerase (PDI) are present on the surface of lymphoid cells, raising the possibility that such enzymes might be involved in the control of lymphocyte adhesion. A number of inhibitors of PDI function were examined for their effects on integrin-mediated adherence of T cells. The results did not support role for PDI in the regulation of integrin function, as the inhibitors somatostatin A, tocinoic acid, dithiobisnitrobenzoic acid, and anti-PDI mAb did not interfere with adherence. However, one of the PDI inhibitors, bacitracin, selectively interfered with the beta1 integrin-mediated adherence of lymphoid cells to collagen, fibronectin, laminin, and VCAM-1, and with alpha4beta7-dependent adherence to fibronectin and to VCAM-1. In contrast, alpha(v)beta3- and alpha(L)beta2-mediated adherence were not inhibited. Thus, it appears that bacitracin may be a selective inhibitor of beta1 and beta7 integrin functions by an as yet unknown mechanism.

B-Lymphocytes↗

PubMed1998

Association of the decreased expression of alpha3beta1 integrin with the altered cell: environmental interactions and enhanced soft agar cloning ability of c-myc-overexpressing small cell lung cancer cells.

Small cell lung cancer (SCLC) is a highly invasive and metastatic tumor, and the decreased expression of alpha3beta1 integrin may contribute to its virulence. Alpha3beta1 is a critical integrin for pulmonary development and epithelial integrity, and its reduced expression has been linked to the increased malignancy and invasion of other cancers. The amplification of the c-myc oncogene is seen frequently in relapsed SCLC tumors and is associated with a worsened prognosis. In the present study using a model of SCLC tumor progression, overexpression of c-myc in a classic SCLC cell line, NCI H209, enhanced in vitro features of tumorigenesis, altered the relationships between cell and environment, and markedly down-regulated the expression of the alpha3 integrin subunit at both the transcript and protein levels. This inverse relationship between the expression of the alpha3 integrin subunit and c-myc is mimicked by other c-myc-overexpressing SCLC cell lines. Restoring alpha3 expression in the myc-transfected 209 cells reversed the effects of c-myc: alpha3 transfection increased cell:cell adhesion and reduced soft agar cloning without affecting the in vitro doubling time. The diminished soft agar cloning produced by alpha3 transfection was reversed by an antibody that specifically engages alpha3beta1 integrins, P1B5. These results suggest first, that alpha3beta1 integrin mediates homotypic adhesion of SCLC cells, and second, that unengaged alpha3beta1 integrin suppresses the growth of disaggregated SCLC cells. Thus, the down-regulation of the alpha3 integrin subunit may contribute to the enhanced tumorigenicity of c-myc-overexpressing SCLCs by allowing the growth of tumor cells that have reduced contact with ligand-expressing substratum or cells, a condition that occurs during the growth of the primary tumor, tumor invasion, and metastasis.

Agar↗

PubMed2002

Integrin expression in the dermis during scar formation in humans.

To evaluate changes leading to human wound reorganization we examined by immunohistochemistry the expression of several extracellular matrix (ECM) receptors (alpha2 chain of VLA-2, alpha3 chain of VLA-3, alpha6 chain of VLA-6, alphav, and beta1/beta3 chains of integrins) in a series of biopsies of human skin wounds healing by primary intention. The first time point investigated in this study was day 6 after injury, i.e. when a fibrin clot has been almost completely replaced by the granulation tissue. Gradual changes in integrin expression in granulation tissue and in the dermal scar were observed from the first time point investigated and were characterized by an up-regulation of alpha2beta1 complex, alphav integrin subunit, and beta1 integrin subunit. At day 27, the expression of the alpha2 chain of VLA-2 in the scar decreased. The expression of alphav and beta1 integrin subunits decreased but was still detectable by day 35. Vitronectin expression from day 7 onwards was also increased and colocalized to the area of the wounded dermis, and decreased by day 27. Our data suggests that, during the remodelling of the provisional matrix of the wound, dermal fibroblasts express transiently mainly alpha2 and alphav subunits of integrins associated with up-regulation of the beta1 subunit. It seems that up-regulation of some chains of integrins may be involved in the control of deposition of ECM components associated with wound healing.

Cicatrix↗

PubMed1999

Integrin alpha(v)beta(3)-mediated activation of apoptosis.

The alpha(v)beta(3) integrin mediates endothelial cell binding to the extracellular matrix and transduces an intracellular signal promoting survival of endothelial cells and various tumor cells. While the alpha(v)beta(3) integrin-mediated survival signal has been shown to be adhesion dependent, a thorough analysis has not been performed comparing the biochemical effects of antagonist binding to alpha(v)beta(3) integrin with the effects induced by the growth of cells in suspension. In this study we demonstrate that expression of alpha(v)beta(3) integrin in human embryonic kidney 293 cells transfers the alpha(v)beta(3) integrin survival pathway to an epithelial cell line. Furthermore, we show that alpha(v)beta(3) integrin-expressing cells respond differently to alpha(v)beta(3) integrin-specific antagonist treatment and growth in suspension conditions. Treatment with the alpha(v)beta(3) antagonist echistatin resulted in an apoptotic response occurring prior to cell detachment and was not observed in either suspended cells or antagonist-treated suspended cells. These data suggest that the death induced by antagonist binding to alpha(v)beta(3) integrin results in an apoptotic signal with different kinetics than the apoptotic signal induced by matrix detachment (anoikis). Since aberrant alpha(v)beta(3) integrin expression in tumor models is thought to play a role in tumor cell survival, these data have implications for the use of alpha(v)beta(3) antagonists as anti-tumor agents.

Annexin A5↗

PubMed1999

The integrin specificity of human recombinant osteopontin.

The ability of full-length human recombinant osteopontin (OPN) to support the adhesion of various alphav integrin-expressing cell lines was determined in order to characterize its integrin selectivity. The identity of this protein was assessed by cDNA sequence and mass spectroscopic analysis, and confirmed as full-length OPN. Neither the human embryonic kidney 293 cell line, which expresses the alphavbeta1 integrin, nor the human colonic adenocarcinoma HT-29 cell line, which expresses the alphavbeta5 integrin, were able to adhere to OPN; both of these cell lines are deficient in the beta3 subunit. In contrast, an alphavbeta3 integrin-expressing cell line, SK-MEL-24, was able to adhere to OPN in an arginine-glycine-aspartic acid dependent manner. In addition, this OPN-mediated cellular adhesion was completely blocked with an anti-alphavbeta3 integrin antibody (LM609), confirming that only the alphavbeta3 integrin mediated this cellular adhesion. These data demonstrate that, at least among the alphav integrins, only the alphavbeta3 is able to support cellular adhesion to osteopontin. This finding may have implications for the design of therapeutics targeting OPN-integrin interactions.

Cell Adhesion↗

PubMed2001

Functional blocking of integrin-associated protein impairs memory retention and decreases glutamate release from the hippocampus.

We have previously demonstrated that integrin-associated protein is involved in memory consolidation of one-way inhibitory avoidance learning in rats and mice. In the present study, we examined the effects of functional blocking of integrin-associated protein on memory retention, long-term potentiation and glutamate release in mice as well as on cell attachment to extracellular matrix protein in primary cultures. The results indicated that integrin-associated protein monoclonal antibody miap301, when directly injected into the dentate gyrus of the hippocampus at moderate doses, significantly impairs memory retention in mice in the same one-way inhibitory avoidance task and decreases the amplitude of tetanic stimulation-induced long-term potentiation in dentate gyrus neurons. At a dose that effectively impairs both memory retention and long-term potentiation, integrin-associated protein monoclonal antibody also significantly blocks potassium chloride-induced glutamate release from the hippocampus in vivo. Results from western blot confirmed the presence of integrin-associated protein at the synaptic area. Cell adhesion experiments further revealed that integrin-associated protein monoclonal antibody markedly inhibits granular cell attachment to thrombospondin, the extracellular matrix protein known to bind integrin-associated protein, but not to collagen and laminin, the extracellular matrix proteins known to bind integrin. From these results we suggest that integrin-associated protein monoclonal antibody may impair synaptic plasticity and behavioral plasticity in mice through blockade of granular cell attachment to extracellular matrix protein and the subsequent signal transduction, and through inhibition of glutamate release from the hippocampus.

Animals↗

PubMed2001

Mechanism of integrin activation by disulfide bond reduction.

Integrin alphaIIbbeta3 plays a pivotal role in hemostasis and thrombosis by mediating platelet adhesion and platelet aggregation. Integrin alphaIIbbeta3 contains an on/off switch that regulates its ligand binding affinity. The switch from "off" to "on" is commonly referred to as integrin activation. We recently identified a redox site within the extracellular domain of the platelet integrin alphaIIbbeta3 that exhibits many properties that one might expect of the on/off switch [Yan, B., and Smith, J. W. (2000) J. Biol. Chem. 275, 39964-39972]. Several independent reports show that reducing agents, such as dithiothreitol, can activate integrins. The objective of the present study was to determine if the effects of DTT can be attributed to a perturbation at the integrin redox site. Indeed, we find that DTT reduces two disulfide bonds within the integrin's cysteine-rich domain. Such bond reduction leads to global conformational changes within both alphaIIb and beta3 and the opening of the RGD and fibrinogen binding sites. These findings causally link the reduction of disulfide bonds within the integrin's redox site to transitions in the integrin's activation state.

Alkylating Agents↗

PubMed1997

Integrin alphaIIb beta3 reconstituted into lipid bilayers is nonclustered in its activated state but clusters after fibrinogen binding.

Integrin activation, ligand binding, and integrin clustering were analyzed using alphaIIb beta3 reconstituted into phospholipid vesicles and into supported planar lipid bilayers. Strong and specific binding of fibrinogen and the gamma-chain dodecapeptide of fibrinogen to alphaIIb beta3 indicated that the integrin is in an activated state after membrane reconstitution. Cryoelectron and fluorescence microscopy suggested a nonclustered state of the protein in the vesicle membrane. Supported planar lipid membranes were generated by fusion of vesicles in which approximately equal fractions of integrins were pointing inside-out and outside-in. This distribution led to an immobilization of about 40% of the integrin in supported bilayers due to attachment of the large extracellular domains to the quartz support. Fluorescence recovery after photobleaching indicated a diffusion coefficient of D = (0.70 +/- 0.06) x 10(-8) cm2/s, consistent with a nonclustered state of the mobile integrin. Upon fibrinogen binding, the integrins became immobile, and fluorescence micrographs showed a patchy distribution of fibrinogen-integrin complexes consisting of approximately 250 molecules. In addition to the expected dimer formation by bivalent fibrinogen, additionally induced fibrinogen clustering may account for the large size of the complexes. In contrast, binding of monovalent GRGDS pentapeptide or the gamma-chain dodecapeptide of fibrinogen altered neither the mobile fraction nor the association state of alphaIIb beta3. Our data indicate that integrin alphaIIbb3 is activated while monodisperse, and became clustered upon fibrinogen binding, leading to an irreversibly bound state.

Amino Acid Sequence↗