Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Integrin alpha4beta1”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 73 records · Page 4Linked to original sources
PubMed2003

Alpha4beta1 integrin mediates selective endothelial cell responses to thrombospondins 1 and 2 in vitro and modulates angiogenesis in vivo.

We examined the function of alpha4beta1 integrin in angiogenesis and in mediating endothelial cell responses to the angiogenesis modulators, thrombospondin-1 and thrombospondin-2. Alpha4beta1 supports adhesion of venous endothelial cells but not of microvascular endothelial cells on immobilized thrombospondin-1, vascular cell adhesion molecule-1, or recombinant N-terminal regions of thrombospondin-1 and thrombospondin-2. Chemotactic activities of this region of thrombospondin-1 and thrombospondin-2 are also mediated by alpha4beta1, whereas antagonism of fibroblast growth factor-2-stimulated chemotaxis is not mediated by this region. Immobilized N-terminal regions of thrombospondin-1 and thrombospondin-2 promote endothelial cell survival and proliferation in an alpha4beta1-dependent manner. Soluble alpha4beta1 antagonists inhibit angiogenesis in the chick chorioallantoic membrane and neovascularization of mouse muscle explants. The latter inhibition is thrombospondin-1-dependent and not observed in explants from thrombospondin-1-/- mice. Antagonizing alpha4beta1 may in part block proangiogenic activities of thrombospondin-1 and thrombospondin-2, because N-terminal regions of thrombospondin-1 and thrombospondin-2 containing the alpha4beta1 binding sequence stimulate angiogenesis in vivo. Therefore, alpha4beta1 is an important endothelial cell receptor for mediating motility and proliferative responses to thrombospondins and for modulation of angiogenesis.

Animals↗
PubMed2002

CD4+CD3- cells induce Peyer's patch development: role of alpha4beta1 integrin activation by CXCR5.

CD4+CD3- cells are the predominant hematopoietic cells found in mouse fetal intestine. We prove their role as Peyer's patch (PP)-inducing cells by transfer into neonatal PP-deficient mice. To test the requirement of chemokines and adhesion molecules in induction of PP, we studied mice deficient in CXCR5 and/or alpha4beta1 integrin-mediated adhesion. CXCR5-/- mice have CD4+CD3- cells, which are inefficient in inducing PP formation. We show here that CXCR5/CXCL13 signaling activates alpha4beta1 integrin on CD4+CD3- cells. Blocking of beta1 integrin or VCAM-1, the ligand of alpha4beta1 integrin, inhibits PP formation. This study demonstrates the link between chemokine receptors and adhesion molecules that regulates stromal/hematopoietic cell interaction leading to PP formation.

Adoptive Transfer↗
PubMed2004

Mechanism of CD47-induced alpha4beta1 integrin activation and adhesion in sickle reticulocytes.

We recently reported that CD47 (integrin-associated protein) on sickle red blood cells (SS RBCs) activates G-protein-dependent signaling, which promotes cell adhesion to immobilized thrombospondin (TSP) under relevant shear stress. These data suggested that signal transduction in SS RBCs may contribute to the vaso-occlusive pathology observed in sickle cell disease. However, the CD47-activated SS RBC adhesion receptor(s) that mediated adhesion to immobilized TSP remained unknown. Here we demonstrate that the alpha4beta1 integrin (VLA-4) is the receptor that mediates CD47-stimulated SS RBC adhesion to immobilized TSP. This adhesion requires both the N-terminal heparin-binding domain and the RGD site of TSP. CD47 signaling induces an "inside-out" activation of alpha4beta1 on SS RBCs as indicated by an RGD-dependent interaction of this integrin with soluble, plasma fibronectin. However, CD47 engagement also induces an alpha4beta1-mediated, RGD-independent adhesion of SS RBCs to immobilized vascular cell adhesion molecule-1 (VCAM-1). CD47 signaling in SS RBCs appears to be independent of large scale changes in cAMP formation but nonetheless promotes alpha4beta1-mediated adhesion via a protein kinase A-dependent, serine phosphorylation of the alpha4 cytoplasmic domain. CD47-activated SS RBC adhesion absolutely requires the Src family tyrosine kinases and is also enhanced by treatment of SS RBCs with low concentrations of cytochalasin D, which may release alpha4beta1 from cytoskeletal restraints. In addition, CD47 co-immunoprecipitates with alpha4beta1 in a sickle reticulocyte-enriched fraction of SS RBCs. These studies therefore identify the alpha4beta1 integrin on SS RBCs as a CD47-activated receptor for TSP, VCAM-1, and plasma fibronectin, revealing novel binding characteristics of this integrin.

Anemia, Sickle Cell↗
PubMed2000

A novel RGD-independent fibronectin assembly pathway initiated by alpha4beta1 integrin binding to the alternatively spliced V region.

Fibronectin (FN) matrix assembly is a multi-step process that involves binding to integrin receptors, FN-FN interactions and connections to the actin cytoskeleton. Ultimately, FN is converted into stable matrix fibrils that are detergent-insoluble. RGD-binding integrins such as alpha5beta1 play a major role in the assembly of fibrillar FN. Here we show that alpha4beta1 binding to the alternatively spliced V (IIICS) region of FN initiates an alternative assembly pathway. Activation of alpha4beta1 with exogenous agents such as Mn(2+) or a beta1-stimulatory antibody TS2/16 was sufficient to induce initiation of FN fibrillogenesis by Ramos B lymphoma cells and by CHO(B2)alpha4 cells. Using recombinant FNs lacking specific sequences, we show that assembly is independent of the RGD sequence but requires the V25/CS-1 segment. Previously, we have characterized an activated recombinant FN (FN III(1-7)) that rapidly forms detergent-insoluble multimers upon binding to alpha5beta1 integrin. Alpha4beta1 also formed FNdeltaIII(1-7) multimers without the aid of exogenous stimulants, suggesting that an activated form of FN can override the need for activation of the integrin. In contrast to assembly by alpha5beta1, actin filaments remained largely cortical and no change in cell growth rate was observed with alpha4beta1-mediated assembly. These results show that binding sites on FN other than the RGD sequence/synergy site and distant from the cell binding domain can promote FN assembly. Thus, there appear to be multiple, integrin-specific mechanisms for assembly of FN matrix.

Alternative Splicing↗
PubMed2002

Engagement of alpha4beta1 integrin by fibronectin induces in vitro resistance of B chronic lymphocytic leukemia cells to fludarabine.

B-cell chronic lymphocytic leukemia is characterized by the accumulation of malignant B lymphocytes as a result of abnormal survival signals operating in vivo. Previously, we showed that adhesion of B-CLL cells to the fibronectin fragment H89, a ligand for alpha4beta1 integrin, prevents their spontaneous apoptosis in vitro. We have now studied whether alpha4beta1/H89 interaction affected the response of B-CLL cells to the therapeutic drug fludarabine. B-CLL cells cultured on H89 during treatment with fludarabine showed significantly higher mean viability (P<0.05) than cells cultured on the control polylysine for all doses of drug tested. Similar results were obtained with the EHEB cell line. Analysis of the expression of Bcl-2-family proteins after 48 h of fludarabine treatment revealed that Bcl-xL levels were significantly higher (P<0.05) for cells cultured on H89 than on polylysine and correlated (r=0.56, P<0.05) with the increased cell viability observed on H89 cultures. These results indicate that Bcl-xL is involved in the survival signals induced by alpha4beta1 ligation and may contribute to the progressive drug resistance observed in B-CLL.

Aged↗
PubMed2005

Engagement of integrin alpha4beta1 enhances thrombopoietin-induced megakaryopoiesis.

OBJECTIVE: Studies in numerous adherent cell systems have indicated that engagement of integrins is required for cell survival and proliferation. Although not classically thought of as an adherent cell type, megakaryocytes in the marrow develop in juxtaposition to endothelial cells which display a number of integrin counter-receptors. Moreover, a number of other hematopoietic cell types, including stem cells and erythroid progenitors, have been shown to engage and be affected by integrin ligands. METHODS: The role of beta1 integrins in thrombopoietin-mediated megakaryopoiesis was studied using both gain-of-function and loss-of-function strategies. RESULTS: We found that pan-blockade of integrins with a relatively nonspecific disintegrin blocked TPO-induced MK growth, but that an alpha5beta1 disintegrin, and a function-blocking monoclonal antibody, failed to affect megakaryopoiesis in vitro. In contrast, a neutralizing alpha4beta1 monoclonal antibody blocked TPO-induced MK growth, and an integrin alpha4beta1 ligand, the H296 fragment of fibronectin, enhanced MK growth at all concentrations of TPO. CONCLUSIONS: These findings have important implications for thrombopoiesis in general, and potentially for the enhanced platelet production found in states of systemic inflammation and following the use of therapeutic strategies designed to block alpha4beta1 integrin engagement in states of chronic inflammation and autoimmunity.

Animals↗
PubMed2000

Exosomes released during reticulocyte maturation bind to fibronectin via integrin alpha4beta1.

Exosomes are vesicles formed in the endosomal compartment and released in the extracellular medium during reticulocyte maturation into erythrocytes. They have a clearing function because of their enrichment with some proteins known to decrease or disappear from the cell surface during maturation, e.g. acetylcholinesterase and transferrin receptor. We show here that integrin alpha4beta1, present on the surface of erythroid precursors but absent from the mature red cell membrane, is at least partly cleared from the reticulocyte plasma membrane by the exosomal pathway. Using flow cytometry, we found that the alpha4 subunit disappears from the reticulocyte surface during in vitro maturation. Two different monoclonal antibodies (B-5G10 and HP 2/1) were used to demonstrate the presence of the alpha4 chain on the exosome surface. Moreover, membrane acetylcholinesterase and lumenal peroxidase-like (i.e. hemoglobin) enzymatic activities were assayed to demonstrate exosome binding to plates coated with increasing fibronectin (FN) concentrations. This interaction was dependent on divalent cations (MnCl2 > MgCl2 > CaCl2). Similarly, vesicles bound to plates coated with the chymotryptic 40 K fragment (FN-40) containing the heparin-binding region of FN. This binding was inhibited by exosome preincubation with fibronectin CS1 peptide and with a monoclonal antibody (HP 2/1) against the integrin alpha4-chain, confirming an alpha4beta1-induced interaction. The importance of the exosome clearance function is highlighted here, since the presence of VLA-4 on reticulocytes often leads to blood circulation complications in some diseases. Moreover, the presence of alpha4beta1 on the exosome surface, by allowing binding to endothelial cells through vascular cell adhesion molecule 1 (VCAM-1), might confer another physiological function to the secreted vesicles.

Animals↗
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↗
PubMed1998

Co-ligation of alpha4beta1 integrin and TCR rescues human thymocytes from steroid-induced apoptosis.

Maturation of thymocytes represents a sequence of events during which thymocytes expressing TCR with moderate avidity for self antigen/MHC are positively selected, whereas those with high or insufficient TCR avidity die. Glucocorticoids are produced intrathymically and can contribute to apoptosis of unselected thymocytes. Thymocytes differentiate in a close contact with epithelial cells, expressing vascular adhesion molecule-1 (VCAM-1) and secreting glucocorticoids, with bone marrow-derived macrophages, and with extracellular matrix containing fibronectin (FN) and collagen. Their contact with FN is mediated by alpha4beta1 and alpha5beta1 integrins. We examined the contribution of TCR and integrin signaling to the survival of thymocytes from dexamethasone (Dex)-induced apoptosis. We demonstrate that FN and VCAM-1 (both of which bind alpha4beta1 integrin), but not collagen, considerably augment TCR-mediated protection of thymocytes from Dex-induced apoptosis. This 'survival' signal is transduced through the alphabeta1, but not through the alpha5beta1 integrin. The observed protection from Dex-induced apoptosis correlated with an increase in bcl-2 protein levels. FN-alpha4beta1 and VCAM-1-alpha4beta1 engagement induced up-regulation bcl-2 protein, while alpha5beta1 binding to FN induced a negative signal that was blocked by anti-alpha5beta1 antibody. These data suggest that alpha4beta1 integrin may contribute to protection of thymocytes with moderate avidity TCR from glucocorticoid-induced death during intrathymic maturation.

Antibodies, Monoclonal↗
PubMed2006

Combinatorial chemistry identifies high-affinity peptidomimetics against alpha4beta1 integrin for in vivo tumor imaging.

Small peptide-based agents have attracted wide interest as cancer-targeting agents for diagnostic imaging and targeted therapy. There is a need to develop new high-affinity and high-specificity peptidomimetic or small-molecule ligands against cancer cell surface receptors. Here we report on the identification of a high-affinity peptidomimetic ligand (LLP2A; IC50 = 2 pM) against alpha4beta1 integrin using both diverse and highly focused one-bead-one-compound combinatorial peptidomimetic libraries in conjunction with high-stringency screening. We further demonstrate that LLP2A can be used to image alpha4beta1-expressing lymphomas with high sensitivity and specificity when conjugated to a near infrared fluorescent dye in a mouse xenograft model. Thus, LLP2A provides an important tool for noninvasive monitoring of alpha4beta1 expression and activity during tumor progression, and it shows great potential as an imaging and therapeutic agent for alpha4beta1-positive tumors.

Animals↗
PubMed2004

Integrin alpha4beta1 involvement in stromal cell-derived factor-1alpha-promoted myeloma cell transendothelial migration and adhesion: role of cAMP and the actin cytoskeleton in adhesion.

The chemokine stromal cell-derived factor-1alpha (SDF-1alpha) is expressed by bone marrow (BM) stromal cells and plays key roles in cell homing to and retention into the bone marrow. In multiple myeloma, blood-borne malignant plasma cells home to the BM and accumulate in contact with stromal cells, implicating myeloma cell migration across endothelium. Myeloma cells express the SDF-1alpha receptor CXCR4, as well as the integrin alpha4beta1, which mediates their attachment to BM stroma. We show here that SDF-1alpha promotes transendothelial migration of purified BM myeloma cells and myeloma-derived NCI-H929 cells, involving a transient upregulation of alpha4beta1-dependent cell adhesion to the endothelium. Characterization of intracellular signaling pathways involved in the modulation by SDF-1alpha of alpha4beta1-mediated myeloma cell adhesion revealed that intracellular cAMP amounts associated with the activation of protein kinase A play key roles in this modulation. Furthermore, a functional link between cAMP actions on the dynamics of actin cytoskeleton, RhoA activation, and alpha4beta1-dependent cell adhesion in response to SDF-1alpha has been found. The regulation of alpha4beta1-mediated myeloma cell adhesion by SDF-1alpha could play key roles during myeloma cell homing into and trafficking inside the BM, and characterization of the molecular events involved in SDF-1alpha-activated modulation of this adhesion will contribute to a better understanding of mechanisms participating in cell migration.

Actin Cytoskeleton↗
PubMed2001

The lymphocyte metalloprotease MDC-L (ADAM 28) is a ligand for the integrin alpha4beta1.

The interaction of lymphocytes with other cells is critical for normal immune surveillance and response. MDC-L (ADAM 28), a member of the ADAM (a disintegrin and metalloprotease) protein family, is expressed on the surface of human lymphocytes. ADAMs possess a disintegrin-like domain similar in sequence to small non-enzymatic snake venom peptides that act as integrin antagonists. We report here that the disintegrin domain of MDC-L is recognized by the leukocyte integrin alpha(4)beta(1). Recombinant Fc fusion proteins possessing the disintegrin domain of MDC-L supported adhesion of the T-lymphoma cell line, Jurkat, in a concentration- and divalent cation-dependent manner. Adhesion of Jurkat cells to the disintegrin domain of MDC-L was inhibited by an anti-MDC-L monoclonal antibody (mAb), Dis1-1. The epitope for mAb Dis1-1 was localized within 59 residues of the disintegrin domain. Recombinant expression of this 59-residue fragment of the disintegrin domain also supported cell adhesion. Adhesion of Jurkat cells to the MDC-L disintegrin domain was specifically inhibited by anti-alpha(4) and anti-beta(1) function-blocking mAbs. Furthermore, adhesion of various cell lines to MDC-L correlated with expression of the integrin alpha(4)-subunit. Transfected K562 cells expressing alpha(4)beta(1) adhered to the disintegrin domain in contrast to non-transfected K562 cells. We further investigated the binding of recombinant MDC-L disintegrin domain (rDis-Fc) in solution. The rDis-Fc was found to bind to Jurkat cells in solution in a concentration-dependent and saturable manner. Both adhesion and solution binding of rDis-Fc was inhibited by the alpha(4)beta(1) ligand mimetic CS-1 peptide. Additionally, recognition of the MDC-L disintegrin domain required "activation" of lymphocyte beta(1) integrins. The interaction of MDC-L with alpha(4)beta(1) may potentially regulate metalloprotease function by targeting or sequestering the active protease on the cell surface. These results suggest a potential role for the lymphocyte ADAM, MDC-L, in the interaction of lymphocytes with alpha(4)beta(1)-expressing leukocytes.

ADAM Proteins↗
PubMed2005

Integrin alpha4beta1 promotes focal adhesion kinase-independent cell motility via alpha4 cytoplasmic domain-specific activation of c-Src.

The fibronectin binding integrins alpha5beta1 and alpha4beta1 generate signals pivotal for cell migration through distinct yet undefined mechanisms. For alpha5beta1, beta1-mediated activation of focal adhesion kinase (FAK) promotes c-Src recruitment to FAK and the formation of a FAK-Src signaling complex. Herein, we show that FAK expression is essential for alpha5beta1-stimulated cell motility and that exogenous expression of human alpha4 in FAK-null fibroblasts forms a functional alpha4beta1 receptor that promotes robust cell motility equal to the alpha5beta1 stimulation of wild-type and FAK-reconstituted fibroblasts. alpha4beta1-stimulated FAK-null cell spreading and motility were dependent on the integrity of the alpha4 cytoplasmic domain, independent of direct paxillin binding to alpha4, and were not affected by PRNK expression, a dominant-negative inhibitor of Pyk2. alpha4 cytoplasmic domain-initiated signaling led to a approximately 4-fold activation of c-Src which did not require paxillin binding to alpha4. Notably, alpha4-stimulated cell motility was inhibited by catalytically inactive receptor protein-tyrosine phosphatase alpha overexpression and blocked by the p50Csk phosphorylation of c-Src at Tyr-529. alpha4beta1-stimulated cell motility of triple-null Src(-/-), c-Yes(-/-), and Fyn(-/-) fibroblasts was dependent on c-Src reexpression that resulted in p130Cas tyrosine phosphorylation and Rac GTPase loading. As p130Cas phosphorylation and Rac activation are common downstream targets for alpha5beta1-stimulated FAK activation, our results support the existence of a novel alpha4 cytoplasmic domain connection leading to c-Src activation which functions as a FAK-independent linkage to a common motility-promoting signaling pathway.

Amino Acid Sequence↗
PubMed2005

Rotaviruses interact with alpha4beta7 and alpha4beta1 integrins by binding the same integrin domains as natural ligands.

Group A rotaviruses are major intestinal pathogens that express potential alpha4beta1 and alpha4beta7 integrin ligand sequences Leu-Asp-Val and Leu-Asp-Ile in their outer capsid protein VP7, and Ile-Asp-Ala in their spike protein VP4. Monkey rotavirus SA11 can use recombinant alpha4beta1 as a cellular receptor. In this study a new potential alpha4beta1, alpha4beta7 and alpha9beta1 integrin ligand sequence, Tyr-Gly-Leu, was identified in VP4. It was shown that several human and monkey rotaviruses bound alpha4beta1 and alpha4beta7, but not alpha9beta1. Binding to alpha4beta1 mediated the infectivity and growth of monkey rotaviruses, and binding to alpha4beta7 mediated their infectivity. A porcine rotavirus interacted with alpha4 integrins at a post-binding stage to facilitate infection. Activation of alpha4beta1 increased rotavirus infectivity. Cellular treatment with peptides containing the alpha4 integrin ligand sequences Tyr-Gly-Leu and Ile-Asp-Ala eliminated virus binding to alpha4 integrins and infectivity. In contrast, rotavirus recognition of alpha4 integrins was unaffected by a peptide containing the sequence Leu-Asp-Val or by a mutation in the VP7 Leu-Asp-Val sequence. VP4 involvement in rotavirus recognition of alpha4beta1 was demonstrated with rotavirus reassortants. Swapping and point mutagenesis of alpha4 surface loops showed that rotaviruses required the same alpha4 residues and domains for binding as the natural alpha4 integrin ligands: mucosal addressin cell adhesion molecule-1, fibronectin and vascular cell adhesion molecule-1. Several rotaviruses are able to use alpha4beta7 and alpha4beta1 for cell binding or entry, through the recognition of the same alpha4-subunit domains as natural alpha4 ligands.

Animals↗
PubMed2004

Integrin alpha4beta1 function is required for cell survival in developing retina.

In the retina, integrins in the beta1 family have been shown to be important in many phases of neuronal development, particularly neuroblast migration and axon outgrowth. However, the functions of specific integrin heterodimers are not well defined. In this study, we investigated the functions of beta1 integrins in developing chicken retina by expression of a dominant-negative beta1A construct using a replication-competent retrovirus. Inhibition of integrins using this approach resulted in alteration of cell morphology and increased apoptosis, but did not preclude migration and axon elongation. In an attempt to identify which specific beta1 heterodimer was important, expression and function of the alpha4beta1 heterodimer were also investigated. At early developmental stages, alpha4 protein and mRNA were detected in undifferentiated neuroblasts throughout the retina. At later stages, expression was confined to retinal ganglion cells (RGCs) and amacrine cells. A small molecule antagonist of alpha4 integrins was shown to inhibit neurite outgrowth on recombinant soluble vascular cell adhesion molecule-1 (VCAM-1), a known ligand of alpha4beta1. Introduction of alpha4 antagonist in vivo gave rise to increased apoptosis and led to a thinning of the retina and reduced numbers of retinal ganglion cells (RGCs). We conclude that the integrin alpha4beta1 is important for survival of developing retinal neurons, including RGCs.

Animals↗
PubMed1997

Activation status and function of the VLA-4 (alpha4beta1) integrin expressed on human melanoma cell lines.

We have examined the functional status of the VLA-4/alpha4beta1 integrin in a panel of human melanoma cell lines, focusing on the ability of cells expressing alpha4beta1 to mediate adhesion to the alpha4-specific ligands CS-1 peptide and VCAM-1. All melanoma cells expressing alpha4pbeta1 (8 of 10 lines examined) were capable of adhering to these specific ligands in adhesion assays, whereas 2 cell lines (HMB2 and VUP) which lacked surface alpha4 were unable to do so. Adherence of different melanoma cell lines to VCAM-1 was relatively uniform and not susceptible to upregulation with known integrin-activating factors, such as manganese ions, phorbol ester and activating monoclonal antibody (mAb) TS2/16. Cell adhesion to CS-1 peptide, however, varied according to cell surface receptor density and, in some cases, could be up-regulated by integrin-activating factors. Adhesion of SK23 cells to CS-1 peptide was increased by all 3 activating stimuli, whereas for all other melanoma cells an increase was obtained only by the use of TS2/16 mAb. Our data indicate not only an unusually low activation state of alpha4beta1 in SK23 cells but also heterogeneity in the activating capacity of the various stimuli. Moreover, a protein kinase C-dependent role in alpha4beta1 activity was suggested by adhesion assays carried out in the presence of the protein kinase C inhibitor calphostin C, which considerably reduced adhesion to CS-1 peptide.

Anti-Allergic Agents↗
PubMed2006

Differential engagement of modules 1 and 4 of vascular cell adhesion molecule-1 (CD106) by integrins alpha4beta1 (CD49d/29) and alphaMbeta2 (CD11b/18) of eosinophils.

We have studied adhesion of eosinophils to various forms of vascular cell adhesion molecule 1 (VCAM-1, CD106), an integrin counter-receptor implicated in eosinophil recruitment to the airway in asthma. Full-length 7d-VCAM-1, with seven immunoglobulin-like modules, contains integrin-binding sites in modules 1 and 4. The alternatively spliced six-module protein, 6d-VCAM-1, lacks module 4. In static assays, unactivated purified human blood eosinophils adhered similarly to recombinant soluble human 6d-VCAM-1 and 7d-VCAM-1 coated onto polystyrene microtiter wells. Further experiments, however, revealed differences in recognition of modules 1 and 4. Antibody blocking indicated that eosinophil adhesion to 6d-VCAM-1 or a VCAM-1 construct containing only modules 1-3, 1-3VCAM-1, is mediated by alpha4beta1 (CD49d/29), whereas adhesion to a construct containing modules 4-7, 4-7VCAM-1, is mediated by bothalpha4beta1 andalphaMbeta2 (CD11b/18). Inhibitors of phosphoinositide 3-kinase, which block adhesion of eosinophils mediated by alphaMbeta2, blocked adhesion to 4-7VCAM-1 but had no effect on adhesion to 6d-VCAM-1. Consistent with the antibody and pharmacological blocking experiments, eosinophilic leukemic cell lines lacking alphaMbeta2 did not adhere to 4-7VCAM-1 but did adhere to 6d-VCAM-1 or 1-3VCAM-1. Activation of eosinophils by interleukin (IL)-5 enhanced static adhesion to 6d-VCAM-1, 7d-VCAM-1, or 4-7VCAM-1; IL-5-enhanced adhesion to all 3 constructs was blocked by anti-alphaMbeta2. Adhesion of unstimulated eosinophils to 7d-VCAM-1 under flow conditions was inhibited by anti-alpha4 or anti-alphaM. IL-5 treatment decreased eosinophil adhesion to 7d-VCAM-1 under flow, and anti-alphaM had the paradoxical effect of increasing adhesion. These results demonstrate that alphaMbeta2 modulatesalpha4beta1-mediated eosinophil adhesion to VCAM-1 under both static and flow conditions.

Binding Sites↗