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 1,189 records · Page 66Linked to original sources
PubMed1999

Selective antibody blockade of lymphocyte migration to mucosal sites and mast cell adhesion.

The integrins alpha4beta7 and alpha4beta1 mediate adhesion to the mucosal addressin cell adhesion molecule-1 (MAdCAM-1) and the vascular cell adhesion molecule-1 (VCAM-1) and are important in T cell and allergic inflammatory reactions in the rat. The relative contributions of alpha4beta7 and alpha4beta1 in these reactions is unknown. To examine the role of alpha4beta7 in the rat a new mAb, TA-6, was developed. TA-6 inhibited adhesion to MAdCAM-1 but not to VCAM-1, a characteristic of alpha4beta7 adhesion, and immunofluorescence and immunoprecipitation studies were compatible with binding to alpha4beta7. TA-6 blocked rat lymphocyte adhesion to mesenteric lymph nodes and T cell migration to mucosal lymphoid tissues and it bound to rat mucosal mast cells. TA-6 did not inhibit lymphocyte adhesion to peripheral lymph nodes and T cell migration to peripheral lymphoid tissues or cutaneous inflammatory sites, and was not expressed on connective tissue mast cells.

Animals↗
PubMed1999

Urokinase-type plasminogen activator inhibits alpha 4 beta 1 integrin-mediated T lymphocyte adhesion to fibronectin independently of its catalytic activity.

The urokinase-type plasminogen activator (u-PA)/plasmin system plays an important role in promoting cell migration and invasion, an effect which is largely ascribed to the proteolytic activity of these enzymes. We investigated whether u-PA modulates integrin-dependent T lymphocyte migration and adhesion on fibronectin independently of its plasminogen activator function. Here we report that u-PA reduced the spontaneous and phorbol 12-myristate 13-acetate-induced migration of peripheral blood T lymphocytes on fibronectin by 20-50%, decreased the T lymphocyte and alpha4beta1(+)/alpha5beta1(+) K562 cell adhesion on fibronectin by 30-40%, and completely suppressed integrin alpha4beta1-dependent T lymphocyte and alpha4beta1(+)/alpha5beta1(+) K562 cell adhesion to the LDV-containing 40-kDa fibronectin fragment. The u-PA receptor was not essential for this effect. In contrast, adhesion of alpha4beta1(-)/alpha5beta1(+) K562 cells to an RGD-containing fibronectin fragment was unaffected. A recombinant protein comprising the N-terminal fragment of u-PA, but lacking its proteolytic domain, had the same inhibitory effect. Decreased adhesion was neither associated with a diminished cell surface expression of alpha4beta1 nor with a suppression of alpha4beta1 ligand-binding function. Our results demonstrate that u-PA inhibits alpha4beta1- but not alpha5beta1-mediated lymphocyte/leukocyte adhesion to fibronectin independently of its proteolytic activity. This finding provides additional evidence that matrix proteinases may participate in cell adhesion and migration control independently of their matrix-degrading activity.

Catalysis↗
PubMed1998

CSF-1 (M-CSF) enhances the inflammatory response of fibronectin-primed macrophages: pathways involved in activation of the cytokine network.

We have previously reported that the priming of thioglycollate-elicited peritoneal macrophages (PMphi), as a representative population of mononuclear phagocytes (MNP), by macrophage-colony-stimulating factor (M-CSF or CSF-1) rendered these cells more susceptible to secondary stimulation by extracellular matrix (ECM) proteins, in particular fibronectin (FN), and that at least two beta1 integrins, VLA 4 (alpha4beta1 or CD49d) and VLA 5 (alpha5beta1 or CD49e), regulate IL-6 gene expression when PMphi come into contact with FN. In this report, we focused our attention on resident PMphi, as a more mature/differentiated MNP subpopulation. By using granulocyte-macrophage colony-stimulating factor (GM-CSF)- and IL-6-knockout (null) mice, we demonstrated that the cooperative effect between CSF-1 and FN in IL-6 release was a result of a sequential stimulation of the GM-CSF, but not the TNF-alpha, gene via interaction with VLA 5. We also showed that regardless of the presence or absence of CSF-1 or FN, IL-6 inhibits GM-CSF and TNF-alpha gene expression in an autocrine manner. The observed effects were specific because CSF-1 enhanced VLA 5 expression and blocking FN-treated resident PMphi in vitro with VLA 5 monoclonal antibodies inhibited the IL-6 response. We found that treatment of resident PMphi with the protein kinase C inhibitor, staurosporine, and the activator, phorbol myristate acetate (PMA), resulted in marked modulation of either FN- or FN/CSF-1-induced cytokine release. An increased level of VLA 5 expression was observed in PMA-treated resident PMphi. We concluded that in inflammatory processes, CSF-1 drives a number of pathways involved in the regulation of the expression of several genes and renders MNP highly susceptible to stimulation by ECM proteins that transform the MNP into secretory inflammatory cells.

Animals↗
PubMed1999

The adhesion of anti-CD3-activated mouse T cells to syngeneic colon adenocarcinoma cells is differentially regulated by protein tyrosine kinase-, protein kinase C-, and cAMP-dependent pathways in the effector cell.

The adhesion of anti-CD3-activated mouse T cells (AK-T cells) to syngeneic colon adenocarcinoma (MCA-38) cells is mediated principally through the integrin VLA-4 (alpha4beta1). We investigated the signalling pathways through which this adhesive interaction might be regulated. The protein tyrosine kinase inhibitors genistein and methyl 2,5-dihydroxycinnamate (MDHC) markedly inhibited the adhesion of AK-T cells to MCA-38 cells. Furthermore, pretreatment of the AK-T cells alone (but not the MCA-38 targets) with MDHC inhibited adhesion to a comparable extent as when MDHC was present during the assay. Calphostin C, an inhibitor of protein kinase C, also inhibited the adhesion of AK-T cells to MCA-38 monolayers. However, the phosphatidylinositol 3-kinase inhibitor wortmannin failed to alter AK-T cell adhesion to MCA-38 tumour cells. Inhibition of protein kinase A with the Rp diastereomer of adenosine cyclic 3',5'-phosphorothioate had no effect on adhesion, but the adenylyl cyclase activator forskolin and the cell-permeable cAMP analogues 8-Br-cAMP and dibutyryl-cAMP significantly suppressed adhesion. Pretreatment of AK-T cells alone with forskolin also inhibited adhesion. The adhesion of AK-T cells to MCA-38 tumour targets is therefore promoted by protein tyrosine kinases and protein kinase C, but inhibited by cAMP-dependent pathways, and the predominant location of the regulatory pathways is within the effector cell.

Adenocarcinoma↗
PubMed2004

Human CD(4+)CD(25+) regulatory T cells and infectious tolerance.

Control of autoaggressive T cells by regulatory T cells (Treg) is essential to ensuring peripheral tolerance. Several subsets of CD(4+) T cells with suppressive properties have been described, including induced T helper (Th) type 3 and T regulatory (Tr) type 1 cells and naturally occurring CD(4+)CD(25+) Treg. CD(4+)CD(25+) Treg suppress the response of conventional T cells in a cell contact-dependent manner, whereas Th3 and Tr1 cells produce immunosuppressive cytokines. Two subsets of human CD(4+)CD(25+) Treg, characterized by expression of the integrins alpha4beta7 or alpha4beta1, are able to convey suppressive capacity to conventional CD(4+) T cells, thereby generating Th suppressor cells (Th(sup)). One outstanding feature is the generation of Th(sup) with distinct properties. alpha4beta7 Treg induce Tr1-like interleukin (IL)-10-producing Th(sup), whereas alpha4beta1 Treg induce Th3-like Th(sup), which produce transforming growth factor (TGF)-beta. Thus, our findings reconcile contradictory results clearly demonstrating that suppression is contact dependent in vitro but mediated by soluble factors (IL-10 and TGF-beta) in vivo.

CD4-Positive T-Lymphocytes↗
PubMed1999

Mechanisms of eosinophil cationic protein release in the serum: role of adhesion molecules.

BACKGROUND: Measurement of eosinophil cationic protein (ECP) in serum has been utilized as a marker for allergic inflammation. The serum level of ECP represents the level found in vivo plus additional proteins released in vitro from peripheral blood eosinophils during the coagulation period. The mechanisms of release, however, are unclear. We investigated a possible involvement of adhesion molecules in the ECP release. MATERIALS AND METHODS: Venous blood was drawn in the presence of EDTA from allergic donors. The blood was incubated with neutralizing monoclonal antibodies to CD18, CD11a, CD11b, CD29, CD49d, CD54, alpha4beta7, or isotype-matched control antibodies, respectively, at 4 degrees C for 30 min. Calcium gluconate (calcium) was then added to induce coagulation. The blood was further incubated for 90 min and centrifuged to obtain the serum. ECP in the serum was measured with RIA. In some experiments, purified eosinophils were incubated with plasma and calcium, then ECP in the supernatants was assayed. RESULTS: ECP in the samples with calcium was significantly higher than in those without calcium. Purified eosinophils released ECP upon plasma coagulation. Anti-CD18, CD49d, and alpha4beta7 antibodies significantly suppressed ECP levels in the serum. CONCLUSIONS: These results suggest that ECP release in the serum is calcium and plasma coagulation-dependent and that cell adhesion through alphaLbeta2, alphaMbeta2, alpha4beta1 and alpha4beta7 integrins is at least in part responsible for ECP release.

Antigens, CD↗
PubMed2004

Ultraviolet radiation induces release of MIA: a new mechanism for UVR-induced progression of melanoma.

MIA is a potent melanoma detachment factor that interferes with cellular adherence by binding to fibronectin and laminin, blocking their interaction with alpha4beta1 and alpha5beta1 integrins. The direct correlation between serum MIA levels of patients with progressing melanomas and tumor load supports a role for MIA as a melanoma progression factor. The goal of this study was to determine the effect of ultraviolet radiation (UVR), activating ras mutation, or loss of p53 function on MIA expression and release from melanoma cells. We previously showed that transfection of a mutant constitutively active ras into the melanoma cell line, WM35, induces a phenotypic change from radial to vertical growth, exhibiting increased proliferation and migration. Here, we report that MIA release was elevated in a ras-transfected cell line. In addition, loss of functional p53, using a dominant negative construct, substantially lowered the level of MIA release compared to control. UVR stimulated release of MIA into the extracellular compartment in both the control and ras-transfected cell lines. In addition, MIA mRNA was increased following UVR in all cell lines tested. By inducing either apoptosis or necrosis, we were able to confirm that MIA protein is not released from cells due to cell death alone. We have identified a transcriptional effect of UVR on MIA expression and have shown that release of MIA protein is dependent upon functional p53. We propose that UVR-induced production and release of MIA may promote the detachment of radial and vertical growth phase melanomas from basement membrane or matrix proteins, serving as a unique progression mechanism for melanoma.

Cell Line, Tumor↗
PubMed1999

CrkL activates integrin-mediated hematopoietic cell adhesion through the guanine nucleotide exchange factor C3G.

CrkL is a member of the Crk family of adapter proteins consisting mostly of SH2 and SH3 domains. CrkL is most abundantly expressed in hematopoietic cells and has been implicated in pathogenesis of chronic myelogenous leukemia. However, its function has not been precisely defined. Here, we show that overexpression of CrkL enhances the adhesion of hematopoietic 32D cells to fibronectin. The CrkL-induced increase in cell adhesion was blocked by antibodies against VLA-4 (alpha4beta1) and VLA-5 (alpha5beta1) but was observed without changes in surface expression levels of these integrins. Studies using CrkL mutants demonstrated that the SH2 domain is partially required for enhancing cell adhesion, whereas the C-terminal SH3 domain as well as the tyrosine phosphorylation site (Y207) is dispensable. In contrast, the N-terminal SH3 domain, involved in binding C3G and other signaling molecules, was showed to play a crucial role, because a mutant defective of this domain showed an inhibitory effect on the cell adhesion to fibronectin. Furthermore, overexpression of C3G also increased the adhesion of hematopoietic cells to fibronectin, whereas a C3G mutant lacking the guanine nucleotide exchange domain abrogated the CrkL-induced increase in cell adhesion. On the other hand, a dominant negative mutant of H-Ras or that of Raf-1 enhanced the basal and CrkL-induced cell adhesion and that of R-Ras modestly decreased the adhesion. Taken together, these results indicate that the CrkL-C3G complex activates VLA-4 and VLA-5 in hematopoietic cells, possibly by activating the small GTP binding proteins, including R-Ras, through the guanine nucleotide exchange activity of C3G.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Defining extracellular integrin alpha-chain sites that affect cell adhesion and adhesion strengthening without altering soluble ligand binding.

It was previously shown that mutations of integrin alpha4 chain sites, within putative EF-hand-type divalent cation-binding domains, each caused a marked reduction in alpha4beta1-dependent cell adhesion. Some reports have suggested that alpha-chain "EF-hand" sites may interact directly with ligands. However, we show here that mutations of three different alpha4 "EF-hand" sites each had no effect on binding of soluble monovalent or bivalent vascular cell adhesion molecule 1 whether measured indirectly or directly. Furthermore, these mutations had minimal effect on alpha4beta1-dependent cell tethering to vascular cell adhesion molecule 1 under shear. However, EF-hand mutants did show severe impairments in cellular resistance to detachment under shear flow. Thus, mutation of integrin alpha4 "EF-hand-like" sites may impair 1) static cell adhesion and 2) adhesion strengthening under shear flow by a mechanism that does not involve alterations of initial ligand binding.

Amino Acid Sequence↗
PubMed1998

Oral antiplatelet efficacy and specificity of a novel nonpeptide platelet GPIIb/IIIa receptor antagonist, DMP 802.

This study was undertaken to define the platelet glycoprotein alphaIIb beta3 integrin (GPII/IIIa) affinity, specificity, and oral antiplatelet efficacy of DMP 802, a small-molecule nonpeptide antiplatelet agent. Platelet GPIIb/IIIa integrin binding affinity and specificity for DMP 802 were determined by using binding and adhesion assays with cells from various species, including human. DMP 802 demonstrated a potent antiplatelet efficacy [median inhibitory concentration (IC50), 0.029 +/- 0.0042 microM] in inhibiting human platelet aggregation induced by 10 microM adenosine diphosphate (ADP), as assessed by light-transmittance aggregometry. DMP 802 inhibited 125I-fibrinogen binding to activated (ADP, epinephrine, and arachidonic acid at 100 microM each) gel purified human platelets with an IC50 of 0.012 +/- 0.003 microM. DMP 802 demonstrated tight association with unactivated human, baboon, or canine platelets (t(1/2) of dissociation, 32 +/- 2, 32 +/- 13, and 11 +/- 1 min, respectively). DMP 802 binds with high affinity to both unactivated and activated human platelets (Kd = 0.61 +/- 0.17, 0.57 +/- 0.21 nM, respectively). DMP 802 demonstrated species specificity in inhibiting platelet aggregation with IC50 values ranging from 0.025 to 0.092 microM (human, guinea pig, dog, swine, hamster) and 0.88-1.0 microM (rabbit and rat) in platelets obtained from these various species. DMP 802 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alphaIIb/beta3) as compared with other integrins including alpha(v)beta3 (IC50, >10 microM), alpha(v)beta5 (IC50, >100 microM), alpha4beta1 (IC50, >100 microM), and alpha5beta1 (IC50, >10 microM). Oral antiplatelet efficacy of DMP 802 was examined after single oral (0.05-0.20 mg/kg) and after repeated oral dosing at 0.05 mg/kg daily for 5 days in mongrel dogs. Dose-dependent antiplatelet efficacy with an extended duration of antiplatelet efficacy was demonstrated based on ex vivo inhibition of platelet aggregation induced by 100 microM ADP. DMP 802 has an oral bioavailability of 14.9% in dogs. In conclusion, the alpha sulfonamide isoxazoline analog, DMP 802, is a novel oral antiplatelet agent with high affinity, relatively slow dissociation rate and specificity for human platelet GPIIb/IIIa receptors.

Administration, Oral↗
PubMed2001

Fibronectin regulates the activation of THP-1 cells by TGF-beta1.

OBJECTIVE AND DESIGN: To determine how fibronectin regulates the immunomodulatory effects of transforming growth factor (TGF)-beta on THP-1 cells. MATERIAL OR SUBJECTS: THP-1 monocytic cell line. TREATMENT: THP-1 cells were primed for 48 h in the presence or absence of 250 pM TGF-beta1. METHODS: Assays or assessments carried out, together with statistical test applied. RESULTS: We found that adherence to fibronectin dramatically modulates the effects of TGF-beta1 on the human monocytic cell line THP-1. TGF-beta did not significantly affect constitutive interleukin (IL)-8 secretion or IL-1beta-induced IL-8 secretion from suspended cells. In contrast, TGF-beta stimulated IL-8 secretion as well as augmented IL-1beta-induced IL-8 secretion from adherent cells. The differential effects of TGF-beta1 on IL-8 secretion from suspended and adherent cells could not be explained by differences in IL-1 receptor antagonist production. The effects of fibronectin on TGF-beta1 induced IL-8 secretion from THP-1 cells were mimicked by adhesion to immobilized anti-a4beta1 integrin antibody and to a fibronectin fragment containing the CS-1 domain. CONCLUSIONS: These results indicate that alpha4beta1-mediated adhesion to fibronectin may play a key role during inflammation by profoundly influencing the effects of TGF-beta1 on monocytes.

Cell Adhesion↗
PubMed2004

Developing neonatal rabbit appendix, a primary lymphoid organ, is seeded by immature blood-borne B cells: evidence for roles for CD62L/PNAd, CCR7/CCL21, alpha4beta1 and LFA-1.

Young rabbit appendix is a homologue of chicken bursa of Fabricius; both are crucial sites for preimmune B-cell repertoire development. We describe here some of the molecules involved in the multi-step recruitment of blood-borne B cells into neonatal rabbit developing appendix. Sialyl-Lewis-x, CD62L and integrins such as LFA-1 and alpha4beta1 were detected on B cells in peripheral blood. Peripheral lymph node addressin (PNAd), a CD62L counter-receptor was observed on appendix HEV. We also detected chemokine receptor CCR7 on peripheral blood B cells and one of the CCR7 ligands, CCL21, on appendix HEV but not in appendix follicles. Higher levels of CXCR5 expression compared to CCR7 on appendix B cells suggest that CXCR5 may be involved in recruitment of B cells into follicles. The proportions of appendix B cells expressing CD62L, sialyl-Lewis-x and alpha4beta1 declined between day 3 and 4 weeks after birth while percentages of Lewis-x+ appendix B cells increased. These changes correlate with the stage of repertoire diversification by gene conversion in both rabbits and chickens. The cross-reactivity of antibodies to mouse or human adhesion molecules described in this study indicates that some of the structures of these important molecules are conserved across species.

Animals↗
PubMed1997

Integrin cross talk: activation of lymphocyte function-associated antigen-1 on human T cells alters alpha4beta1- and alpha5beta1-mediated function.

A regulated order of adhesion events directs leukocytes from the vascular compartment into injured tissues in response to inflammatory stimuli. We show that on human T cells, the interaction of the beta2 integrin leucocyte function-associated antigen-1 (LFA-1) with its ligand intercellular adhesion molecule-1 (ICAM-1) will decrease adhesion mediated by alpha4beta1 and, to a lesser extent, alpha5beta1. Similar inhibition is also seen when T cells are exposed to mAb 24, which stabilizes LFA-1 in an active state after triggering integrin function through divalent cation Mg2+, PdBu, or T cell receptor/ CD3 complex (TCR/CD3) cross-linking. Such cross talk decreases alpha4beta1 integrin-mediated binding of T cells to fibronectin and vascular cell adhesion molecule-1 (VCAM-1). In contrast, ligand occupancy or prolonged activation of beta1 integrin has no effect on LFA-1 adhesion to ICAM-1. We also show that T cell migration across fibronectin, unlike adhesion, is mediated solely by alpha5beta1, and is increased when the alpha4beta1-mediated component of fibronectin adhesion is decreased either by cross talk or the use of alpha4-blocking mAb. The ability of mAb 24 Fab' fragments to induce cross talk without cross-linking LFA-1 suggests signal transduction through the active integrin. These data provide the first direct evidence for cross talk between LFA-1 and beta1 integrins on T cells. Together, these findings imply that activation of LFA-1 on the extravasating T cell will decrease the binding to VCAM-1 while enhancing the subsequent migration on fibronectin. This sequence of events provides a further level of complexity to the coordination of T cell integrins, whose sequential but overlapping roles are essential for transmigration.

Anti-Allergic Agents↗
PubMed1997

Mutational evidence for control of cell adhesion through integrin diffusion/clustering, independent of ligand binding.

Previous studies have shown that integrin alpha chain tails make strong positive contributions to integrin-mediated cell adhesion. We now show here that integrin alpha4 tail deletion markedly impairs static cell adhesion by a mechanism that does not involve altered binding of soluble vascular cell adhesion molecule 1 ligand. Instead, truncation of the alpha4 cytoplasmic domain caused a severe deficiency in integrin accumulation into cell surface clusters, as induced by ligand and/ or antibodies. Furthermore, alpha4 tail deletion also significantly decreased the membrane diffusivity of alpha4beta1, as determined by a single particle tracking technique. Notably, low doses of cytochalasin D partially restored the deficiency in cell adhesion seen upon alpha4 tail deletion. Together, these results suggest that alpha4 tail deletion exposes the beta1 cytoplasmic domain, leading to cytoskeletal associations that apparently restrict integrin lateral diffusion and accumulation into clusters, thus causing reduced static cell adhesion. Our demonstration of integrin adhesive activity regulated through receptor diffusion/clustering (rather than through altered ligand binding affinity) may be highly relevant towards the understanding of inside-out signaling mechanisms for beta1 integrins.

Animals↗
PubMed2005

Aza-bicyclic amino acid carboxamides as alpha4beta1/alpha4beta7 integrin receptor antagonists.

A series of N-carboxy, N-alkyl, and N-carboxamido azabicyclo[2.2.2]octane carboxamides were prepared and assayed for inhibition of alpha4beta1-VCAM-1 and alpha4beta7-MAdCAM-1 interactions. Potency and alpha4beta1/alpha4beta7 selectivity were sensitive to the substituent R1-R3 in the structures 6, 7, and 8. Several compounds demonstrated low nanomolar balanced alpha4beta1/alpha4beta7 in vitro activity. Two compounds were selected for in vivo leukocytosis studies and demonstrated increases in circulating lymphocytes up to 250% over control.

Amino Acids, Cyclic↗
PubMed1998

During human thymic development, beta 1 integrins regulate adhesion, motility, and the outcome of RHAMM/hyaluronan engagement.

During human thymic differentiation, interactions between fibronectin (Fn)/beta1 integrins and hyaluronan (HA)/RHAMM control motility and Fn/beta1 integrins mediate spontaneous Fn-dependent adhesion. Multinegative (MN, CD3-4-8-) thymocytes exhibit strong spontaneous adherence to Fn (75%) that was efficiently inhibited by anti-alpha5beta1 and only weakly inhibited by anti-alpha4beta1. The relatively weak adherence of unfractionated thymocytes to Fn required both alpha4beta1 and alpha5beta1. Video time-lapse microscopy indicates that a subset of thymocytes also undergo spontaneous Fn-dependent motility mediated by alpha5beta1, alpha4beta1, and the HA-receptor RHAMM, but not by CD44. The loss of motility after hyaluronidase treatment of thymocytes indicated that motility is strongly dependent on HA. Of motile cells, 55% were DP, 19% were DN, and 24% were CD4+SP, but only 1% were CD8+SP. Overall, for MN thymocytes, beta1 integrin mediated Fn-adhesion, but after expression of CD4/CD8, beta1 integrins mediated Fn-dependent motility. Treatment with the activating anti-beta1 mAb QE.2E5 inhibited thymic motility and converted otherwise nonadherent thymocytes to an adherent state. High-avidity interactions via integrins appear to supercede the motogenicity of RHAMM and HA, suggesting that integrin avidity may regulate RHAMM. During thymic development, changes in adhesion or motility appear to be mediated by integrin avidity modulation.

Adult↗
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↗
PubMed1998

Role of two conserved glycine residues in the beta-propeller domain of the integrin alpha4 subunit in VLA-4 conformation and function.

The N-terminal region of the alpha integrin subunits is predicted to fold into a beta-propeller domain. Using K562 alpha4 transfectants we show that mutations at alpha4 subunit residues Gly130 and Gly190 affect the conformation of this domain causing a reduction in the recognition of alpha4 by anti-alpha4 antibodies which map to the beta-propeller. The improper alpha4 conformation also led to an altered association with the beta1 subunit, and to a lack of alpha4beta1 adhesion to VCAM-1 and CS-1/fibronectin, as well as an abolishment of anti-alpha4- and anti-beta1-dependent homotypic aggregation. The total conservation of Gly130 and Gly190 among integrin alpha subunits suggests their importance in the correct folding of their respective beta-propeller domains, and thus, in the adhesive activity of the integrins.

Antigens, CD↗