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Results for “Integrin alpha4”

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At least 289 records · Page 16Linked to original sources

PubMed2006

Sustained alterations in biodistribution of stem/progenitor cells in Tie2Cre+ alpha4(f/f) mice are hematopoietic cell autonomous.

We have generated Tie2Cre+alpha4(f/f) mice with documented alpha4-integrin ablation in hematopoietic and endothelial cells. A prominent feature in this model is a sustained, significant increase in circulating progenitors at levels higher than the levels seen with Tie2Cre+VCAM-1(f/f) mice. To test whether phenotypic differences are due to contributions by ligands other than VCAM-1 in bone marrow, or to alpha4-deficient endothelial cells or pericytes, we carried out transplantation experiments using these mice as donors or as recipients. Changes in progenitor biodistribution after transplantation were seen only with alpha4-deficient donor cells, suggesting that these cells were necessary and sufficient to reproduce the phenotype with no discernible contribution by alpha4-deficient nonhematopoietic cells. Because several similarities are seen after transplantation between our results and those with CXCR4-/- donor cells, the data suggest that VLA4/VCAM-1 and CXCR4/CXCL12 pathways contribute to a nonredundant, ongoing signaling required for bone marrow retention of progenitor cells during homeostasis.

Animals↗

PubMed1999

Cooperative activity of alpha4beta1 and alpha4beta7 integrins in mediating human B-cell lymphoma adhesion and chemotaxis on fibronectin through recognition of multiple synergizing binding sites within the central cell-binding domain.

We have quantitated the relative contributions of the constitutively active alpha4beta1 and alpha4beta7 integrins and the domains embodying their cognate binding sites in mediating human B-cell lymphoma adhesion and chemotaxis on fibronectin. By cooperating, the central cell-binding and IIICS carboxy-terminal domains were entirely responsible for the adhesion activity displayed by fibronectin, and their relative contribution to this process was estimated to be 30% versus 70%. Assessment of the leukocyte-substrate binding strength (ie, dynes/cell) indicated a 10-fold higher avidity of the cell-IIICS domain interaction. The two integrins interchangeably recognized both domains, but differed quantitatively in their participation in the adhesive event, as well as in domain preference. The use of 3Fn (according to the nomenclature proposed by Bork and Koonin [Curr Opin Struct Biol 6:366, 1996] for the type III fibronectin modules) module-specific antibodies and recombinant polypeptides showed that alpha4 integrins recognized both the RGD sequence (3Fn10) and an apparently novel synergistic site located within the 3Fn8 module; even in this case, the integrins displayed a distinct binding site preference. Interleukin-1beta (IL-1beta)/IL-2-induced chemotaxis also involved cooperative function of the central cell-binding and IIICS domains, but the mechanisms regulating this phenomenon differed markedly from those controlling cell adhesion. First, the relative contribution of the individual domains was comparable, but neither of the individual domains promoted migration to the extent observed on intact fibronectin. Secondly, alpha4beta1 and alpha4beta7 integrins were both involved in the domain-binding necessary for initiation of migration, but the relative contribution of each receptor in the chemotactic process was less disparate than for initial cell adhesion. Thirdly, the mode by which chemotactic B-lymphoma movement was supported by the central cell-binding domain differed from that sustaining cell adhesion in that it involved independent recognition of either the 3Fn8 or the 3Fn9 module, which acted in synergy with the 3Fn10 module. Our data provide novel evidence concerning the relative importance of the constitutively active alpha4beta1 and alpha4beta7 integrins for the interaction of B-cell lymphoma cells with fibronectin, and they emphasize a multiple and diverse recognition of sites responsible for either anchorage or locomotion of tumor leukocytes on this matrix molecule.

Binding Sites↗

PubMed2000

Alpha4beta1-integrin activation is necessary for high-efficiency T-cell subset interactions with VCAM-1 under flow.

OBJECTIVE: The purpose of this study was to examine the relationship between alpha4beta1-integrin state of activation on CD4+ T-cell subsets and their adhesive interaction to VCAM-1 under flow. METHODS: Human CD4+ memory and naive T-cells were freshly isolated and effector-helper T-cell subsets. Th1 and Th2 cells, were differentiated in vitro from CD4+ naive T-cells. The expression of activation/ligand induced epitopes on beta1-integrins of each T-cell subset was assessed using mAb HUTS21 and mAb 15/7. T-cell subsets attachment and rolling on VCAM-1 was determined under defined flow conditions and the rates of attachment (ka), accumulation, and instantaneous rolling velocities were correlated to their beta1-integrin activation epitope expression. RESULTS: A subset of memory T-cells constitutively express activation/ligand induced epitopes on beta1-integrins recognized by mAb HUTS21 and 15/7, whereas expression levels on naive T-cells is low or not detectable. Consistent with an activated phenotype, memory T-cells exhibit significantly higher rates of attachment and accumulation on VCAM-1 under flow as compared to naive T-cells. Interestingly, the expression of activation/ligand induced epitopes on beta1-integrins on Th2 cells and the ability of these cells to interact with VCAM-1 are comparable to memory T-cells. In contrast, Th1 cells did not interact as efficiently with VCAM-1, which correlated with lower expression of activation/ligand induced epitopes on these cells. VCAM-1 interactions are inhibited completely by pretreatment of the T-cells with blocking mAb to alpha4-integrins or beta1-integrins, indicating that alpha4beta1 is the predominant T-cell integrin involved. CONCLUSIONS: Memory T-cells express constitutively active alpha4beta1-integrins, as compared to naive T-cells, which mediate high rates of initial attachment and sustained high-affinity adhesive interactions with VCAM-1 under flow conditions in vitro. Similarly, in vitro differentiated Th2 cells but not Th1 cells, which also express elevated levels of activated alpha4beta1-integrins, are capable of sustaining high-affinity adhesive interactions with VCAM-1. The differences observed in beta1-integrin activation on T-cell subsets may underlie selective recruitment patterns of T-cell subsets in vivo.

Cell Adhesion↗

PubMed1998

The beta7 integrin gene (Itgb-7) promoter is responsive to TGF-beta1: defining control regions.

The beta7 integrins LPAM-1 (alpha4beta7) and M290 (alphaEbeta7) mediate the homing of lymphocytes to gut-associated lymphoid tissue, and the proposed retention of intraepithelial lymphocytes (IEL), respectively. Here we show that the gut mucosal cytokine TGF- beta1 increases the expression of beta7 and alphaE subunit mRNA transcripts and the cell-surface expression of M290 on T cells, and that it decreases the level of alpha4 integrin transcripts. Induced beta7 integrin gene expression was inhibited by the protein tyrosine kinase inhibitor genistein, implicating a role for tyrosine phosphorylation. An analysis of the beta7 integrin gene promoter revealed three DNAse I hypersensitivity sites, two of which mapped to the 5' and 3' ends of a promoter fragment (nucleotides +690 to +63) that directed both the basal and the TGF-beta1-induced expression of a heterologous reporter gene. Deletion analysis identified two TGF-beta1 response regions encompassing nucleotides -509 to -398 (TGFBRR1), and -122 to +32 (TGFBRR2). TGFBRR1 interacted with at least five protein complexes, whose binding could be induced with TGF-beta1 stimulation and could be antagonized by TGFBRR2 which harbored both similar and distinctive cis-elements. TGFBRR2 interacted specifically with at least two major nuclear protein complexes, whose binding was phosphorylation dependent. These data provide new insights into the mechanism by which TGF-beta may switch LPAM-1(+ve) migrating T cells to express M290, facilitating their retention in the gut.

Animals↗

PubMed1998

alphadbeta2 integrin is expressed on human eosinophils and functions as an alternative ligand for vascular cell adhesion molecule 1 (VCAM-1).

The beta2 family of integrins, CD11a, CD11b, CD11c, and alphad, are expressed on most leukocytes. We show that the newest member of this family, alphad, is expressed on human eosinophils in peripheral blood, and surface expression can be upregulated within minutes by phorbol ester or calcium ionophore A23187. Culture of eosinophils with interleukin 5 (IL-5) leads to a two- to fourfold increase in alphad levels by 3-7 d without a change in alpha4 integrin expression. Eosinophils isolated from late phase bronchoalveolar lavage fluids express alphad at levels similar to that seen after 3 d of IL-5 culture. Regarding alphadbeta2 ligands, in both freshly isolated and IL-5-cultured eosinophils, as well as alphadbeta2-transfected Chinese hamster ovary cells, alphadbeta2 can function as a ligand for vascular cell adhesion molecule 1 (VCAM-1). This conclusion is based on the ability of monoclonal antibodies to alphad, beta2, or VCAM-1 to block cell attachment in static adhesion assays. In experiments with eosinophils, the relative contribution of alphadbeta2 integrin- mediated adhesion is enhanced after IL-5 culture. These experiments demonstrate that alphadbeta2 is an alternative ligand for VCAM-1, and this integrin may play a role in eosinophil adhesion to VCAM-1 in states of chronic inflammation.

Animals↗

PubMed2003

Alpha4beta1 integrin affinity changes govern cell adhesion.

Integrin alpha4beta1 is a receptor for vascular cell adhesion molecule-1 and fibronectin. It is important in lymphopoiesis, inflammatory recruitment of leukocytes, and other situations that require cell adhesion to the vascular endothelium. The avidity of the cells expressing alpha4beta1 integrin can be rapidly changed by chemokines and chemoattractants. Different mechanisms, including changes in the number of interacting molecules due to the alteration of the receptor topology or changes in the affinity of the individual bonds, have been proposed to explain the nature of these fast changes in avidity. Recently, we described a fluorescent LDV-containing small molecule, which we used to monitor the affinity changes on live cells in real time (Chigaev, A., Blenc, A. M., Braaten, J. V., Kumaraswamy, N., Kepley, C. L., Andrews, R. P., Oliver, J. M., Edwards, B. S., Prossnitz, E. R., Larson, R. S. et al. (2001) J. Biol. Chem. 276, 48670-48678). Here we show that the affinity of the small molecule probe as well as the native ligand vascular cell adhesion molecule-1 varies in parallel when the integrin is modulated with divalent cations and that the affinity modulation leads to the changes in cell avidity. Using formyl peptide receptor-transfected U937 cells, we further show that the time course of avidity changes in response to the receptor activation coincides with the time course of the affinity changes. Taken together, these data are consistent with the idea that affinity regulation is a major factor that governs the avidity of cell adhesion mediated by the alpha4 integrin.

Animals↗

PubMed2004

Specific amino acid restriction inhibits attachment and spreading of human melanoma via modulation of the integrin/focal adhesion kinase pathway and actin cytoskeleton remodeling.

We had previously found that selective restriction of amino acids inhibits invasion of human A375 melanoma. Integrins, cell surface receptors for the components of extracellular matrix (ECM), are activated during cell adhesion and spreading, and initiate signaling pathways that control growth and invasion of tumor cells. We examined the effect of tyrosine (Tyr) and phenylalanine (Phe), methionine (Met) or glutamine (Gln) restriction on attachment and spreading of A375 and MeWo melanoma cell lines on fibronectin and laminin. In A375 cells, restriction of Tyr/Phe or Met inhibited attachment to and spreading on laminin and fibronectin, inhibited alpha3 and alpha4 integrin expression, and inhibited accumulation of FAK-Tyr397 and F-actin at leading edges of cell protrusions. Tyr/Phe restriction also inhibited attachment-induced autophosporylation of FAK-Tyr397. In MeWo cells, the order of inhibition by amino acid restriction on cell attachment and spreading was as follows: Gln > Tyr/Phe > Met. Restriction of Gln reduced alpha5 integrin expression. All amino acid restrictions similarly inhibited phosphorylation of FAK-Tyr397, FAK-Tyr577, FAK-Tyr861 and paxillin-Tyr31. Gln restriction exhibited the strongest inhibition of actin cytoskeleton remodeling during the cell spreading. The present study reveals that specific amino acid restriction inhibits attachment and spreading of melanoma via inhibition of specific integrin expression, inhibition of integrin-mediated FAK phosphorylation, and modulation of actin cytoskeleton remodeling. These data provide additional understanding of the mechanism by which specific amino acid restriction controls invasion and migration of melanoma.

Amino Acids↗

PubMed2006

Phospholipase C, calcium, and calmodulin are critical for alpha4beta1 integrin affinity up-regulation and monocyte arrest triggered by chemoattractants.

During inflammation, monocytes roll on activated endothelium and arrest after stimulation by proteoglycan-bound chemokines and other chemoattractants. We investigated signaling pathways downstream of G protein-coupled receptors (GPCRs) that are relevant to alpha4beta1 integrin affinity up-regulation using formyl peptide receptor-transfected U937 cells stimulated with fMLP or stromal-derived factor-1alpha and human peripheral blood monocytes stimulated with multiple chemokines or chemoattractants. The up-regulation of soluble LDV peptide or vascular cell adhesion molecule-1 (VCAM-1) binding by these stimuli was critically dependent on activation of phospholipase C (PLC), inositol 1,4,5-triphosphate receptors, increased intracellular calcium, influx of extracellular calcium, and calmodulin, suggesting that this signaling pathway is required for alpha4 integrins to assume a high-affinity conformation. In fact, a rise in intracellular calcium following treatment with thapsigargin or ionomycin was sufficient to induce binding of ligand. Blockade of p44/42 and p38 mitogen-activated protein (MAP) kinases, phosphoinositide 3-kinase, or protein kinase C (PKC) signaling did not inhibit chemoattractant-induced LDV or VCAM-1 binding. However, activation of PKC by phorbol ester up-regulated alpha4beta1 affinity with kinetics distinct from those of GPCR signaling. A critical role for PLC and calmodulin was also established for leukocyte arrest and adhesion strengthening.

Calcium↗

PubMed2000

A regulated interaction between alpha5beta1 integrin and osteopontin.

The extracellular matrix protein osteopontin (OPN) interacts with a number of integrins, namely alphavbeta1, alphavbeta3, alphavbeta5, alpha9beta1, alpha8beta1, and alpha4beta1. We have investigated the interaction of alpha5beta1 integrin with OPN using K562 cells, which only express alpha5beta1. alpha5beta1 is in a low activation state in this cell line, but can be stimulated to a higher activation state by the phorbol ester TPA. Treating K562 wild-type cells (K562-WT) with TPA stimulated an interaction between alpha5beta1 and OPN. No interaction was seen in the absence of TPA. alpha5beta1 selectively interacted with a GST fusion protein of the N-terminal fragment of OPN (aa17-168), which is generated in vivo by thrombin cleavage of OPN. Expression of the alpha4 integrin in K562 cells (K562-alpha4beta1) stimulated alpha5beta1-dependent binding to aa17-168 in the absence of TPA, suggesting that alpha4beta1 activates alpha5beta1 in K562 cells. Adhesion via alpha5beta1 is mediated by the Arg-Gly-Asp (RGD) motif of OPN, as mutating this sequence to Arg-Ala-Asp (RAD) blocked binding of both cell types. These data demonstrate that thrombin cleavage regulates the adhesive properties of OPN and that alpha5beta1 integrin can interact with thrombin-cleaved osteopontin when in a high activation state.

Amino Acid Sequence↗

PubMed1999

Anti-inflammatory activity of c(ILDV-NH(CH2)5CO), a novel, selective, cyclic peptide inhibitor of VLA-4-mediated cell adhesion.

1. Small, N- to C-terminal cyclized peptides containing the leucyl-aspartyl-valine (LDV) motif from fibronectin connecting segment-1 (CS-1) have been investigated for their effects on the adhesion of human T-lymphoblastic leukaemia cells (MOLT-4) to human plasma fibronectin in vitro mediated by the integrin Very Late Antigen (VLA)-4 (alpha4beta1, CD49d/CD29). 2. Cyclo(-isoleucyl-leucyl-aspartyl-valyl-aminohexanoyl-) (c(ILDV-NH(CH2)5CO)) was approximately 5 fold more potent (IC50 3.6+/-0.44 microM) than the 25-amino acid linear CS-1 peptide. Cyclic peptides containing two more or one less methylene groups had similar potency to c(ILDV-NH(CH2)5CO) while a compound containing three less methylene groups, c(ILDV-NH(CH2)2CO), was inactive at 100 microM. 3. c(ILDV-NH(CH2)5CO) had little effect on cell adhesion mediated by two other integrins, VLA-5 (alpha5,beta1, CD49e/CD29) (K562 cell adhesion to fibronectin) or Leukocyte Function Associated molecule-1 (LFA-1, alphabeta2, CD11a/CD18) (U937 cell adhesion to Chinese hamster ovary cells transfected with intercellular adhesion molecule-1) at concentrations up to 300 microM. 4. c(ILDV-NH(CH2)5CO) inhibited ovalbumin delayed-type hypersensitivity or oxazolone contact hypersensitivity in Balb/c mice when dosed continuously from subcutaneous osmotic mini-pumps (0.1-10 mg kg(-1) day(-1)). Maximum inhibition (approximately 40%) was similar to that caused by the monoclonal antibody PS/2 (7.5 mg kg(-1) i.v.) directed against the alpha4 integrin subunit. 5. c(ILDV-NH(CH2)5CO) also inhibited oxazolone contact hypersensitivity when dosed intravenously 20 h after oxazolone challenge (1-10 mg kg(-1)). Ear swelling was reduced at 3 h and 4 h but not at 1 h and 2 h post-dose (10 mg kg(-1)). 6. Small molecule VLA-4 inhibitors derived from c(ILDV-NH(CH2)5CO) may be useful as anti-inflammatory agents.

Amino Acid Sequence↗

PubMed1999

Lymphocyte function-associated antigen-1 binding residues in intercellular adhesion molecule-2 (ICAM-2) and the integrin binding surface in the ICAM subfamily.

The crystal structure of intercellular adhesion molecule-2 (ICAM-2) revealed significant differences in the presentation of the critical acidic residue important for integrin binding between I and non-I-domain integrin ligands. Based on this crystal structure, we mutagenized ICAM-2 to localize the binding site for the integrin lymphocyte function-associated antigen-1 (LFA-1). The integrin binding site runs diagonally across the GFC beta-sheet and includes residues on the CD edge of the beta-sandwich. The site is oblong and runs along a flat ridge on the upper half of domain 1, which is proposed to dock to a groove in the I domain of LFA-1, with the critical Glu-37 residue ligating the Mg2+ in the I domain. Previous mutagenesis of ICAM-1 and ICAM-3, interpreted in light of the recently determined ICAM-1 and ICAM-2 structures, suggests similar binding sites. By contrast, major differences are seen with vascular cell adhesion molecule-1 (VCAM-1), which binds alpha4 integrins that lack an I domain. The binding site on VCAM-1 includes the lower portion of domain 1 and the upper part of domain 2, whereas the LFA-1 binding site on ICAM is confined to the upper part of domain 1.

Amino Acid Sequence↗

PubMedDate not supplied

Fibronectin receptor defects in NOD mouse leucocytes: possible consequences for type 1 diabetes.

Integrins of the very late antigen (VLA) family mediate leucocyte traffic to lymphoid organs under physiological conditions and in chronic inflammatory situations such as autoimmunity. Accordingly, the current thinking is of a positive correlation between VLA expression and capability of the generation of autoimmunity. Herein we discuss recent findings on the defective expression of integrin-type fibronectin receptors alpha4beta1 (VLA-4) and alpha5beta1 (VLA-5) in the non-obese diabetic (NOD) mouse, a murine model of autoimmune insulin-dependent diabetes mellitus. As compared with normal animals, NOD thymocytes (including the CD4+CD25+ regulatory T cells) exhibit a decrease in the membrane expression of alpha5beta1, resulting in a functional impairment of fibronectin-mediated interactions, including cell migration. Interestingly, thymocytes that are trapped within the giant perivascular spaces seen in NOD thymus are consistently alpha5beta1 negative, suggesting that the progressive arrest of mature cells can be related to the alpha5beta1 defect. Peripheral T cells also exhibit decreased alpha5beta1 membrane expression and impaired fibronectin-driven migration. Additionally, we observed a defect in alpha4beta1 fibronectin receptor expression in NOD macrophages. Peritoneal, bone marrow-derived-precursor, as well as thymic macrophages of NOD mice showed an impaired upregulation of alpha4-integrin chain expression, dependent on the level of macrophage maturation. Overall these data lead to the notion that NOD leucocytes bear distinct fibronectin receptor-mediated cell migration defects, which may be involved in the pathogenesis and/or pathophysiology of the autoimmune events seen in NOD mice. Further studies will be helpful to define whether or not this concept can be applied for other autoimmune diseases.

Animals↗

PubMed2000

Bidirectional induction of the cognate receptor-ligand alpha4/VCAM-1 pair defines a novel mechanism of tumor intravasation.

Engagement of cell surface adhesion receptors with extracellular constituents and with cellular counter-receptors is crucial for the extravasation of blood-borne neoplastic cells and their seeding at distant sites; however, the early events of tumor dissemination-ie, the intravasation step(s)-have been largely neglected. A role for the alpha4beta7 integrin was hypothesized to explain the high leukemogenicity exhibited by one (NQ22) among several T-cell lymphomas studied. To clarify the mechanisms of early aggressivity, the behavior of highly and poorly leukemogenic cell lines were compared in vitro. Cocultivation of physically separated leukemic cells with resting endothelial cells resulted in the up-regulation of VCAM-1 expression. NQ22 cells expressed mRNA of different cytokines that up-regulate VCAM-1 and at higher levels than cells of a nonaggressive lymphoma, and they migrated more efficiently through an activated endothelial cell layer. With the use of neutralizing antibodies against interferon-gamma, granulocyte macrophage colony-stimulating factor, and tumor necrosis factor (TNF)-alpha, it was determined that TNF-alpha is one of the soluble factors released by NQ22 cells involved in the up-regulation of VCAM-1. The finding that vascular cells within the early local growth were strongly positive for VCAM-1 indicated that NQ22 cells could activate endothelial cells also in vivo. Finally, cocultivation of preleukemic alpha4(-)NQ22 cells with TNF-alpha-activated endothelial cells induced the expression of alpha4 integrins on the former cells. Reciprocal up-regulation and engagement of alpha4/VCAM-1 pairs determined the sequential transmigration and intravasation steps, and similar mechanisms might affect the aggressivity of human T lymphoblastic lymphomas.

Animals↗

PubMed2001

MAdCAM-1 expressed in chronic inflammatory liver disease supports mucosal lymphocyte adhesion to hepatic endothelium (MAdCAM-1 in chronic inflammatory liver disease).

Mucosal addressin cell adhesion molecule (MAdCAM-1) plays a pivotal role in T-lymphocyte homing to the gut. Given the strong association between the autoimmune liver diseases primary sclerosing cholangitis and autoimmune hepatitis and inflammatory bowel disease, we investigated the role of MAdCAM-1 in recruiting mucosal lymphocytes to the liver. MAdCAM-1 was strongly expressed on inflamed portal vein/sinusoidal endothelium in autoimmune mediated liver disease. In modified Stamper-Woodruff assays, MAdCAM-1 on hepatic vessels supported adhesion of alpha4beta7+ lymphocytes (i.e., gut-derived T cells) from patients with inflammatory bowel disease and primary sclerosing cholangitis. This adhesion was inhibited by pretreatment with blocking antibodies to MAdCAM-1, alpha4beta7, or the integrin alpha4 chain indicating that MAdCAM-1 in inflamed liver is functionally active. Circulating lymphocytes from patients with primary sclerosing cholangitis showed rolling adhesion on MAdCAM-1 transfectants in a flow-based adhesion assay that could be blocked by anti-MAdCAM-1 or anti-alpha4beta7 mAbs. These findings indicate that, under certain circumstances, vessels in the human liver support adhesion of alpha4beta7+ mucosal lymphocytes via binding to aberrantly expressed MAdCAM-1 on liver endothelium. This provides a mechanism to explain the hepatic recruitment of mucosal lymphocytes in inflammatory liver disease complicating inflammatory bowel disease.

Blood Cells↗

PubMed2004

CCN2 (connective tissue growth factor) promotes fibroblast adhesion to fibronectin.

In vivo, CCN2 (connective tissue growth factor) promotes angiogenesis, osteogenesis, tissue repair, and fibrosis, through largely unknown mechanisms. In vitro, CCN2 promotes cell adhesion in a variety of systems via integrins and heparin sulfate proteoglycans (HSPGs). However, the physiological relevance of CCN2-mediated cell adhesion is unknown. Here, we find that HSPGs and the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase cascade are required for adult human dermal fibroblasts to adhere to CCN2. Endogenous CCN2 directly binds fibronectin and the fibronectin receptors integrins alpha4 beta1 and alpha5 and syndecan 4. Using Ccn2-/- mouse embryonic fibroblasts, we show that loss of endogenous CCN2 results in impaired spreading on fibronectin, delayed alpha-smooth muscle actin stress fiber formation, and reduced ERK and focal adhesion kinase phosphorylation. These results suggest that a physiological role of CCN2 is to potentiate the ability of fibroblasts to spread on fibronectin, which may be important in modulating fibroblast adhesion to the provisional matrix during tissue development and wound healing. These results are consistent with the notion that a principal function of CCN2 is to modulate receptor/ligand interactions in vivo.

Animals↗

PubMed1999

Melanoma chondroitin sulphate proteoglycan regulates cell spreading through Cdc42, Ack-1 and p130cas.

Melanoma chondroitin sulphate proteoglycan (MCSP) is a cell-surface antigen that has been implicated in the growth and invasion of melanoma tumours. Although this antigen is expressed early in melanoma progression, its biological function is unknown. MCSP can stimulate the integrin-alpha4 beta1-mediated adhesion and spreading of melanoma cells. Here we show that stimulated MCSP recruits tyrosine-phosphorylated p130 cas, an adaptor protein important in tumour cell motility and invasion. MCSP stimulation also results in a pronounced activation and recruitment of the Rho-family GTPase Cdc42. MCSP-induced spreading of melanoma cells is dependent upon active Cdc42, a Cdc42-associated tyrosine kinase (Ack-1) and tyrosine phosphorylation of p130cas. Furthermore, vectors inhibiting Ack-1 or Cdc42 expression and/or function abrogate MCSP-induced tyrosine phosphorylation and recruitment of p130cas. Our findings indicate that MCSP may modify tumour growth or invasion by a unique signal-transduction pathway that links Cdc42 activation to downstream tyrosine phosphorylation and subsequent cytoskeletal reorganization.

Cell Movement↗

PubMed1997

Extracellular matrix proteins expressed by human adult astrocytes in vivo and in vitro: an astrocyte surface protein containing the CS1 domain contributes to binding of lymphoblasts.

Primary cultures of human astrocytes, expressing glial fibrillary acidic protein (GFAP), were obtained from postmortem brain tissue samples. These cultured astrocytes produced an extracellular matrix (ECM), containing laminin (Ln) and fibronectin (Fn), as shown with specific antibodies. The perinuclear staining observed in these cells indicated that these proteins were de novo synthesized. Monoclonal antibody (mAb) 90.45, which recognizes the CS1 sequence found in an alternatively spliced form of Fn, also stained cultured astrocytes. Immunohistochemical analysis of normal human brain tissue showed positive staining for the CS1 domain, both on protoplasmic and fibrous astrocytes located in the gray and white matter. In contrast to cultured astrocytes, no immunoreactivity for Ln or Fn was found on astrocytes in normal human brain tissue. These in situ data indicate that the CS1 domain expressed by astrocytes is not part of a splicing variant of Fn. Western blot analysis confirmed that the CS1 domain expressed by cultured human astrocytes is part of an astrocyte protein which is different from human Fn. The CS1 domain is a known ligand for the adhesion receptor alpha4beta1 (VLA-4). We found that the human lymphoma cell lines Jurkat and Ramos, which express alpha4beta1, bound to cultured human astrocytes, and that this interaction could be partly blocked by mAb 90.45 or a synthetic CS1 peptide. Thus, the novel CS1-containing surface protein expressed by astrocytes in vitro and in vivo, contributes to binding of lymphoblasts, and therefore may be a relevant adhesion molecule for the recruitment of alpha4-integrin expressing leukocytes into the central nervous system (CNS).

Aged↗

PubMed2002

The role of selectins and integrins in adenovirus vector-induced neutrophil recruitment to the liver.

Adenovirus vectors for human gene therapy induce early host inflammatory responses in transduced tissues that limit gene transfer efficiency and can result in significant morbidity. The present study aimed to elucidate the cellular mechanisms underlying the acute inflammation induced by adenovirus vectors in the liver. Leukocyte rolling and adhesion in response to an intravenously administered adenovirus vector was examined by intravital microscopy in mouse liver. Adenovirus vectors significantly increased leukocyte rolling and adhesion in the postsinusoidal venules within minutes of transduction. Unlike other inflammatory states in the liver, no leukocyte retention was seen in the sinusoids in response to adenovirus vector administration. Inhibition of P-selectin, alpha(4)-integrin, and E-selectin was necessary to completely block leukocyte rolling and subsequent adhesion. The administration of an anti-alpha(4)-integrin antibody alone significantly reduced leukocyte adhesion. In contrast, adenovirus vector-induced leukocyte adhesion was unchanged in CD18-knockout mice. Depletion of circulating neutrophils eliminated leukocyte rolling and adhesion in response to adenovirus vector transduction in the liver. In conclusion, adenovirus vectors induce rapid neutrophil-mediated inflammation in the post-sinusoidal venules by selectins and alpha(4)-integrin but surprisingly not by CD18.

Adenoviridae↗