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Results for “Integrin alphaVbeta3”

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At least 127 records · Page 7Linked to original sources

PubMed2000

Tissue factor, osteopontin, alphavbeta3 integrin expression in microvasculature of gliomas associated with vascular endothelial growth factor expression.

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor in human gliomas. VEGF-induced proteins in endothelial cells, tissue factor (TF), osteopontin (OPN) and alphavbeta3 integrin have been implicated as important molecules by which VEGF promotes angiogenesis in vivo. Sixty-eight gliomas were immunohistochemically stained with TF, VEGF, OPN and alphavbeta3 integrin antibody. Twenty-three tumours, six normal brains and nine glioma cell lines were evaluated for their mRNA expression of VEGF and TF by reverse transcription polymerase chain reaction analysis. The data indicated that TF as well as VEGF was a strong regulator of human glioma angiogenesis. First, TF expression in endothelial cells which was observed in 74% of glioblastomas, 54% of anaplastic astrocytomas and none of low-grade astrocytomas, correlated with the microvascular density of the tumours. Double staining for VEGF and TF demonstrated co-localization of these two proteins in the glioblastoma tissues. Second, there was a correlation between TF and VEGF mRNA expression in the glioma tissues. Third, glioma cell conditioned medium containing a large amount of VEGF up-regulated the TF mRNA expression in human umbilical vein endothelial cells. OPN and alphavbeta3 integrin, were also predominantly observed in the microvasculature of glioblastomas associated with VEGF expression. Microvascular expression of these molecules could be an effective antiangiogenesis target for human gliomas.

Brain Neoplasms↗

PubMed2005

Herpes simplex virus type 1 glycoprotein H binds to alphavbeta3 integrins.

Glycoprotein H (gH) homologues are found in all members of the herpes virus family, and gH is one of the virion envelope glycoproteins that is essential for virus entry. In this study, a recombinant soluble form of Herpes simplex virus type 1 (HSV-1) gH, in which the ectodomain is fused to the Fc-binding region of IgG, has been generated. This was expressed in mammalian cells together with gL and the resulting gHFc-gL heterodimer was purified using Protein A Sepharose. Low-affinity cell binding assays showed that gHFc-gL bound specifically to Vero cells and mutation of a potential integrin-binding motif, Arg-Gly-Asp (RGD), in gH abolished binding. CHO cells failed to bind in this assay. However, CHO cells expressing the human alphavbeta3 integrin bound efficiently to gHFc-gL, suggesting that HSV-1 gH can bind to cells using alphavbeta3 integrins and that this binding is mediated by the RGD motif in the gH ectodomain.

Animals↗

PubMed1996

Suppression of p53 activity and p21WAF1/CIP1 expression by vascular cell integrin alphaVbeta3 during angiogenesis.

Induction of p53 activity in cells undergoing DNA synthesis represents a molecular conflict that can lead to apoptosis. During angiogenesis, proliferative endothelial cells become apoptotic in response to antagonists of integrin alphavbeta3 and this leads to the regression of angiogenic blood vessels, thereby blocking the growth of various human tumors. Evidence is presented that administration of alphavbeta3 antagonists during angiogenesis in vivo selectively caused activation of endothelial cell p53 and increased expression of the p53-inducible cell cycle inhibitor p21WAF1/CIP1. In vitro studies revealed that the ligation state of human endothelial cell alphavbeta3 directly influenced p53 activity and the bax cell death pathway. Specifically, agonists of endothelial cell alphavbeta3, but not other integrins, suppressed p53 activity, blocked p21WAF1/CIP1 expression, and increased the bcl-2/bax ratio, thereby promoting cell survival. Thus, ligation of vascular cell integrin alphavbeta3 promotes a critical and specific adhesion-dependent cell survival signal during angiogenesis leading to inhibition of p53 activity, decreased expression of p21WAF1/CIP1, and suppression of the bax cell death pathway.

Allantois↗

PubMed1998

Blocking ligand occupancy of the alphaVbeta3 integrin inhibits insulin-like growth factor I signaling in vascular smooth muscle cells.

Blocking alphaVbeta3 integrin occupancy results in attenuation of the cellular migration response to insulin-like growth factor I (IGF-I). To determine whether integrin antagonists alter other IGF-I-stimulated biologic actions, quiescent smooth muscle cells (SMCs) were exposed to echistatin and their ability to respond to IGF-I was determined. Echistatin (10(-7) M) inhibited IGF-I-stimulated DNA synthesis by 80%, and the protein synthesis response also was inhibited. Therefore blocking occupancy of alphaVbeta3 inhibited multiple target cell actions of IGF-I. To determine whether blocking alphaVbeta3 occupancy could alter IGF-I receptor-mediated signal transduction, the ability of IGF-I to stimulate phosphorylation of insulin receptor substrate-1 (IRS-1) was analyzed. A 10-min exposure to 100 ng/ml of IGF-I resulted in a substantial increase in phosphorylated IRS-1, and echistatin (10(-7) M) blocked the IGF-I-induced IRS-1 phosphorylation response. Echistatin also attenuated downstream signaling because the capacity of the p85 subunit of phosphatidylinositol-3 kinase (PI-3 kinase) to bind to IRS-1 was blocked. In contrast, exposure of SMCs to vitronectin (1.0 micrograms/cm2) or thrombospondin (0.25 micrograms/cm2), two known ligands for alphaVbeta3, resulted in enhancement of the IGF-I-stimulated IRS-1 response. To determine whether these effects were caused by alterations in receptor kinase activity, the IGF-I receptor was immunoprecipitated and then analyzed for phosphotyrosine. Echistatin (10(-7) M) significantly reduced IGF-I-stimulated tyrosine phosphorylation of the IGF-I receptor beta subunit. We conclude that occupancy of the alphaVbeta3 integrin is necessary for IGF-I to fully activate the kinase activity of the IGF-I receptor and phosphorylate IRS-1. Activation of the alphaVbeta3 receptor results in an interaction with the IGF-I signal transduction pathway, which modulates SMCs responsiveness to IGF-I.

Animals↗

PubMed1996

Integrin alphavbeta3 is expressed in selected microvessels after focal cerebral ischemia.

The endothelial and smooth muscle integrin alphaVbeta3, a receptor for vitronectin and fibrinogen, participates in angiogenesis associated with wound healing and tumorigenicity. The microvascular expression of alphavbeta3 and fibrin during experimental middle cerebral artery occlusion and reperfusion in a nonhuman primate model was examined by computer-assisted video imaging microscopy. No microvascular expression of alphavbeta3 was seen in the control subjects (n = 3) or the non-ischemic basal ganglia of subjects undergoing 2-hour MCA:O (middle cerebral artery occlusion) or 3-hour occlusion with 1-hour (n = 3), 4-hour (n = 3), and 24-hour (n = 3) reperfusion. In the ischemic territory, alphavbeta3 appeared initially at 2 hours of middle cerebral artery occlusion. Up-regulation of alphavbeta3 was confined to the media of 30.0- to 50.0-micron-diameter arterioles in the ischemic core and correlated significantly with fibrin deposition in those vessels (P < 0.0005). Integrin alphavbeta3 and its ligand fibrinogen appear in a subpopulation of microvessels after focal cerebral ischemia.

Animals↗

PubMedDate not supplied

Adenovirus-mediated thymidine kinase gene therapy for recurrent ovarian cancer: expression of coxsackie-adenovirus receptor and integrins alphavbeta3 and alphavbeta5.

OBJECTIVE: Ten patients with recurrent ovarian cancer received a combined treatment of optimal tumor debulking, adenovirus-mediated herpes simplex virus thymidine kinase gene therapy (GT), and systemic application of acyclovir or valacyclovir and topotecan. Biopsies were taken at the time of secondary debulking about 1 month after the application of GT and chemotherapy and were analyzed for expression of coxsackie-adenovirus receptor (CAR) and integrins alphavbeta3 and alphavbeta5 with respect to treatment response. METHODS: Treatment modalities and study design have been described recently. Immunohistochemistry was used to visualize expression of CAR and integrins alphavbeta3 and alphavbeta5 in tumor samples taken before and after application of GT. RESULTS: Before GT six of ten patients presented with CAR-positive and four with CAR-negative tumors. After GT all tumors showed CAR expression. Integrin alphavbeta3 was found in all tumors before and after GT. Expression of integrin alphavbeta5 was seen in eight of ten tumor samples before GT and in all samples after GT. CONCLUSION: Despite the importance of CAR and integrin expression for successful adenovirus internalization, other cell surface receptors might be involved in this process. It is too early to decide whether expressions of CAR and integrin alphavbeta3/alphavbeta5 on tumor cells are appropriate additional inclusion criteria for the enrollment of patients in GT trials. Further research is necessary to evaluate the effect of GT plus chemotherapy on CAR and integrin expression.

Adult↗

PubMed1997

Alphavbeta3 integrin associates with activated insulin and PDGFbeta receptors and potentiates the biological activity of PDGF.

Integrin-mediated cell attachment modulates growth responses and growth factors regulate cell attachment. Moreover, both cell attachment to extracellular matrix and mitogenic signaling by growth factors are necessary for the proliferation of most types of normal cells, suggesting that integrin and growth factor receptor signaling pathways meet at some downstream point. We report here that a small, highly tyrosine-phosphorylated fraction of PDGFbeta and insulin receptors co-immunoprecipitates with the alphavbeta3 integrin from cells. The integrin association requires growth factor stimulation of the receptors. Several signaling molecules that are known to be associated with activated growth factor receptors were present in the alphavbeta3 integrin complexes. Mitogenicity and chemotaxis induced by PDGF-BB were enhanced in cells plated on the alphavbeta3 ligand vitronectin compared with cells plated on the beta1 integrin ligand collagen. Thus, the engagement of the alphavbeta3 integrin in cell-matrix interactions appears to coordinate an intense response to growth factors, helping to explain the importance of this integrin for tissue regeneration, angiogenesis and tumor metastasis.

3T3 Cells↗

PubMed1998

Transmembrane-truncated alphavbeta3 integrin retains high affinity for ligand binding: evidence for an 'inside-out' suppressor?

The molecular mechanisms of alphavbeta3 integrin affinity regulation have important biological implications in tumour development, wound repair and angiogenesis. We expressed, purified and characterized recombinant forms of human alphavbeta3 (r-alphavbeta3) and compared the activation state of these with alphavbeta3 in its cellular environment. The ligand specificity and selectivity of recombinant full-length and double transmembrane truncations of r-alphavbeta3 cloned in BacPAK6 vectors and expressed in Sf9 and High Five insect cells were compared with those of native placental alphavbeta3 and the receptor in situ on the cell surface. r-alphavbeta3 integrins were purified by affinity chromatography from detergent extracts of cells (full-length), and from the culture medium of cells expressing double-truncated r-alphavbeta3. r-alphavbeta3 had the same epitopes, ligand-binding specificities, bivalent cation requirements and susceptibility to RGD-containing peptides as native alphavbeta3. On M21-L4 melanoma cells, alphavbeta3 mediated binding to vitronectin, but not to fibrinogen unless activated with Mn2+. Non-activated alphaIIbbeta3 integrin as control in M21-L-IIb cells had the opposite profile, mediating binding to fibrinogen, but not to vitronectin unless activated with Mn2+. Thus these receptors had moderate to low ligand affinity. In marked contrast, purified alphavbeta3 receptors, with or without transmembrane and cytoplasmic domains, were constitutively of high affinity and able to bind strongly to vitronectin, fibronectin and fibrinogen under physiological conditions. Our data suggest that, in contrast with the positive regulation of alphaIIbbeta3 in situ, intracellular controls lower the affinity of alphavbeta3, and the cytoplasmic domains may act as a target for negative regulators of alphavbeta3 activity.

Amino Acid Sequence↗

PubMed1999

Neutrophils sense flow-generated stress and direct their migration through alphaVbeta3-integrin.

During inflammation neutrophils are recruited from the blood onto the surface of microvascular endothelial cells. In this milieu the presence of soluble chemotactic gradients is disallowed by blood flow. However, directional cues are still required for neutrophils to migrate to the junctions of endothelial cells where extravasation occurs. Shear forces generated by flowing blood provide a potential alternative guide. In our flow-based adhesion assay neutrophils preferentially migrated in the direction of flow when activated after attachment to platelet monolayers. Neutralizing alphaVbeta3-integrin with monoclonal antibodies or turning the flow off randomized the direction of migration without affecting migration velocity. Purified, immobilized alphaVbeta3-integrin ligands, CD31 and fibronectin, could both support flow-directed neutrophil migration in a concentration-dependent manner. Migration could be randomized by neutralizing alphaVbeta3-integrin interactions with the substrate using antibodies or Arg-Gly-Asp-containing peptide. These results exemplify mechanical signal transduction through integrin-ligand interactions and reveal a guidance system that was hitherto unknown in neutrophils. In more general terms, it demonstrates that cells can use integrin molecules to "sample" their physical microenvironment through adhesion and use this information to modulate their behavior.

Blood Circulation↗

PubMed1998

Integrin alphavbeta3 requirement for sustained mitogen-activated protein kinase activity during angiogenesis.

Angiogenesis depends on growth factors and vascular cell adhesion events. Integrins and growth factors are capable of activating the ras/MAP kinase pathway in vitro, yet how these signals influence endothelial cells during angiogenesis is unknown. Upon initiation of angiogenesis with basic fibroblast growth factor (bFGF) on the chick chorioallantoic membrane (CAM), endothelial cell mitogen-activated protein (MAP) kinase (ERK) activity was detected as early as 5 min yet was sustained for at least 20 h. The initial wave of ERK activity (5-120 min) was refractory to integrin antagonists, whereas the sustained activity (4-20 h) depended on integrin alphavbeta3, but not beta1 integrins. Inhibition of MAP kinase kinase (MEK) during this sustained alphavbeta3-dependent ERK signal blocked the formation of new blood vessels while not influencing preexisting blood vessels on the CAM. Inhibition of MEK also blocked growth factor induced migration but not adhesion of endothelial cells in vitro. Therefore, angiogenesis depends on sustained ERK activity regulated by the ligation state of both a growth factor receptor and integrin alphavbeta3.

Animals↗

PubMed2003

Tyrosine phosphorylation of the beta3-subunit of the alphaVbeta3 integrin is required for embrane association of the tyrosine phosphatase SHP-2 and its further recruitment to the insulin-like growth factor I receptor.

Ligand occupancy of the alphaVbeta3 integrin is required for IGF-I receptor (IGF-IR) phosphorylation of an appropriate duration and for stimulation of IGF-I actions. In vascular smooth muscle cells (SMCs), the tyrosine phosphatase SHP-2 regulates the duration of IGF-IR phosphorylation and biological actions. We determined the role of ligand occupancy of the alphaVbeta3 integrin on beta3 phosphorylation and studied the role of beta3 phosphorylation in regulating both SHP-2 recruitment to the cell membrane and IGF-I-dependent biological responses. Vitronectin binding to alphaVbeta3 induced tyrosine phosphorylation of the beta3-subunit in subconfluent SMCs and was accompanied by increased association of SHP-2 with beta3. In confluent SMCs, the beta3-subunit was constitutively phosphorylated leading to basal binding of SHP-2. The Src kinase inhibitor PP2 caused a concentration-dependent decrease in beta3 phosphorylation and resulted in decreased SHP-2 association with beta3 and with the cell membrane. In contrast to control cells, SMCs expressing a mutant beta3 that had two tyrosines changed to phenylalanines showed a 89.9 +/- 1.2% decrease in beta3 phosphorylation. This decrease was associated with reduced SHP-2 binding to nonphosphorylated beta3 and a corresponding decrease in the membrane association of SHP-2. When IGF-I was added to cells expressing mutant beta3, SHP-2 was not recruited to the Src homology 2 domain-containing tyrosine phosphatase substrate-1 or to IGF-IR. This was associated with prolonged IGF-IR phosphorylation and an impaired cellular DNA synthesis response to IGF-I. These results define a mechanism by which ligand occupancy of alphaVbeta3 regulates the SMC response to IGF-I.

Cell Membrane↗

PubMed2006

Regulation of protein L-isoaspartyl methyltransferase by cell-matrix interactions: involvement of integrin alphavbeta3, PI 3-kinase, and the proteasome.

The enzyme L-isoaspartyl methyltransferase (PIMT) is known to repair damaged proteins that have accumulated abnormal aspartyl residues during cell aging. However, little is known about the mechanisms involved in the regulation of PIMT expression. Here we report that PIMT expression in bovine aortic endothelial cells is regulated by cell detachment and readhesion to a substratum. During cell detachment, the PIMT level was rapidly and strongly increased and correlated with a stimulation of protein synthesis. Aside from endothelial cells, PIMT levels were also regulated by cell adhesion in various cancer cell lines. The upregulation of PIMT expression could be prevented by an anti-alphavbeta3 antibody (LM609) or by a cyclic RGD peptide (XJ735) specific to integrin alphavbeta3, indicating that this integrin was likely involved in PIMT regulation. Moreover, we found that PIMT expression returned to the basal level when cells were replated on a substratum after detachment, though downregulation of PIMT expression could be partly prevented by the PI3K inhibitors LY294002 and wortmannin, as well as by the proteasome inhibitors MG-132, lactacystin, and beta-lactone. These findings support the assumption that the PIMT level was downregulated by proteasomal degradation, involving the PI3K pathway, during cell attachment. This study reports new insights on the molecular mechanisms responsible for the regulation of PIMT expression in cells. The regulation of PIMT level upon cell-substratum contact suggests a potential role for PIMT in biological processes such as wound healing, cell migration, and tumor metastasis dissemination.

Animals↗

PubMed1999

Microfibril-associated glycoprotein-2 specifically interacts with a range of bovine and human cell types via alphaVbeta3 integrin.

Microfibril-associated glycoprotein (MAGP)-1 and MAGP-2 are small structurally related glycoproteins that are specifically associated with fibrillin-containing microfibrils. MAGP-2, unlike MAGP-1, contains an RGD motif with potential for integrin binding. To determine if the RGD sequence is active, a series of cell binding assays was performed. MAGP-2 was shown to promote the attachment and spreading of bovine nuchal ligament fibroblasts when coated onto plastic wells in molar quantities similar to those of fibronectin. In contrast, approximately 10-fold more MAGP-1 was required to support comparable levels of cell adhesion. The fibroblast binding to MAGP-2 was completely inhibited if the peptide GRGDSP or the MAGP-2-specific peptide GVSGQRGDDVTTVTSET was added to the reaction medium at a 10 microM final concentration. The control peptide GRGESP had no effect on the interaction. These findings indicate that the cell interaction with MAGP-2 is an RGD-mediated event. A monoclonal antibody to human alphaVbeta3 integrin (LM609) almost completely blocked cell attachment to MAGP-2 when added to the medium at 0.5 microgram/ml, whereas two monoclonal antibodies specific for the human beta1 integrin subunit, 4B4 (blocking) and QE2.E5 (activating), had no effect even at 10 microgram/ml. Fetal bovine aortic smooth muscle cells, ear cartilage chondrocytes, and arterial endothelial cells and human skin fibroblasts and osteoblasts were also observed to adhere strongly to MAGP-2. In addition, each cell type was able to spread on MAGP-2 substrate, with the exception of the endothelial cells, which remained spherical after 2 h of incubation. The binding of each cell type was blocked when the anti-alphaVbeta3 integrin antibody was included in the assay, indicating that alphaVbeta3 integrin is the major receptor for MAGP-2 on several cell types. Thus, MAGP-2 may mediate interactions between fibrillin-containing microfibrils and cell surfaces during the development of a variety of tissues.

Adult↗

PubMed2004

Enhancement of the antiangiogenic activity of interleukin-12 by peptide targeted delivery of the cytokine to alphavbeta3 integrin.

We engineered a fusion protein, mrIL-12vp [mouse recombinant interleukin (IL)-12 linked to vascular peptide], linking the vascular homing peptide CDCRGDCFC (RGD-4C), a ligand for alphavbeta3 integrin, to mrIL-12 to target IL-12 directly to tumor neovasculature. The fusion protein stimulated IFN-gamma production in vitro and in vivo, indicating its biological activity was consistent with mrIL-12. Immunofluorescence techniques showed mrIL-12vp specifically bound to alphavbeta3 integrin-positive cells but not to alphavbeta3 integrin-negative cells. In corneal angiogenesis assays using BALB/c mice treated with either 0.5 microg/mouse/d of mrIL-12vp or mrIL-12 delivered by subcutaneous continuous infusion, mrIL-12vp inhibited corneal neovascularization by 67% compared with only a slight reduction (13%) in angiogenesis in the mrIL-12-treated animals (P = 0.008). IL-12 receptor knockout mice given mrIL-12vp showed a marked decrease in the area of corneal neovascularization compared with mice treated with mrIL-12. These results indicate that mrIL-12vp inhibits angiogenesis through IL-12-dependent and IL-12-independent mechanisms, and its augmented antiangiogenic activity may be due to suppression of endothelial cell signaling pathways by the RGD-4C portion of the fusion protein. Mice injected with NXS2 neuroblastoma cells and treated with mrIL-12vp showed significant suppression of tumor growth compared with mice treated with mrIL-12 (P = 0.03). Mice did not show signs of IL-12 toxicity when treated with mrIL-12vp, although hepatic necrosis was present in mrIL-12-treated mice. Localization of IL-12 to neovasculature significantly enhances the antiangiogenic effect, augments antitumor activity, and decreases toxicity of IL-12, offering a promising strategy for expanding development of IL-12 for treatment of cancer patients.

Angiogenesis Inhibitors↗

PubMed2006

Functional inhibition of NF-kappaB signal transduction in alphavbeta3 integrin expressing endothelial cells by using RGD-PEG-modified adenovirus with a mutant IkappaB gene.

In order to selectively block nuclear factor kappaB (NF-kappaB)-dependent signal transduction in angiogenic endothelial cells, we constructed an alphavbeta3 integrin specific adenovirus encoding dominant negative IkappaB (dnIkappaB) as a therapeutic gene. By virtue of RGD modification of the PEGylated virus, the specificity of the cell entry pathway of adenovirus shifted from coxsacki-adenovirus receptor dependent to alphavbeta3 integrin dependent entry. The therapeutic outcome of delivery of the transgene into endothelial cells was determined by analysis of cellular responsiveness to tumor necrosis factor (TNF)-alpha. Using real time reverse transcription PCR, mRNA levels of the cell adhesion molecules E-selectin, vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1, the cytokines/growth factors IL-6, IL-8 and vascular endothelial growth factor (VEGF)-A, and the receptor tyrosine kinase Tie-2 were assessed. Furthermore, levels of ICAM-1 protein were determined by flow cytometric analysis. RGD-targeted adenovirus delivered the dnIkappaB via alphavbeta3 to become functionally expressed, leading to complete abolishment of TNF-alpha-induced up-regulation of E-selectin, ICAM-1, VCAM-1, IL-6, IL-8, VEGF-A and Tie-2. The approach of targeted delivery of dnIkappaB into endothelial cells presented here can be employed for diseases such as rheumatoid arthritis and inflammatory bowel disease where activation of NF-kappaB activity should be locally restored to basal levels in the endothelium.

Adenoviridae↗

PubMed1998

Aggregation of mononucleated precursors triggers cell surface expression of alphavbeta3 integrin, essential to formation of osteoclast-like multinucleated cells.

Alphavbeta3 is a key integrin mediating adhesion of multinucleated osteoclasts during bone resorption. 1, 25-dihydroxyvitamin D3 upregulates alphavbeta3 integrin expression in mononucleated osteoclast precursors and concomitantly stimulates their differentiation into osteoclasts. This suggests that this integrin could play a major role during osteoclast differentiation. We have developed an in vitro model, in which 1, 25-dihydroxyvitamin D3 sequentially modifies the behavior of macrophages: It first induces rounding up of these cells, then their subsequent aggregation and spreading, which finally leads to cell fusion and the formation of osteoclast-like multinucleated giant cells. We show that, while 1,25-dihydroxyvitamin D3 stimulates the de novo synthesis of alphavbeta3 in macrophages early in this process, its accumulation on the surface is triggered by cell aggregation. A high level of integrin alphavbeta3 cell surface expression correlates with macrophage spreading preceding fusion. This was confirmed by means of novel cell permeable peptides containing the C-terminal sequence of the integrin beta3 tail to specifically block (alphavbeta3 function. Although this peptide has no effect on the aggregation step, it disrupts the spreading of osteoclast precursors and consequently inhibits their fusion. These findings suggest a novel role of the integrin alphavbeta3 in a discrete step of osteoclast differentiation.

Amino Acid Sequence↗

PubMed2002

The role of the alphaVbeta3 integrin in the development of osteolytic bone metastases: a pharmacological target for alternative therapy?

Common cancers frequently develop bone metastases, which are often osteolytic in nature due to activation of osteoclast differentiation and bone resorption. This may result from direct stimulation of these cells by the metastasis, or may be due to indirect enhancement of osteoclast activity by osteoblasts. A further feature of the bone metastasis is an extensive medullary angiogenesis which supports tumor growth. The alphaVbeta3 integrin is highly expressed in bone metastatic cells, as well as in osteoclasts and in the activated endothelium, where it plays a major role in cell function. In contrast, this receptor is barely expressed in other cell types. Our hypothesis is that inhibition of this mechanism, which is not widespread in most tissues and at the same time is common to several steps of cancer-induced osteolysis (i.e., homing, growth, and survival of metastatic cells, osteoclast bone resorption, and angiogenesis), should represent a suitable target to block the development of bone spreading of metastatic tumors. We extend this hypothesis to downstream signalling molecules activated by ligation of the alphaVbeta3 integrin, some of which (i.e., Src, PYK2, and Shc) could have similar specific roles in tumor cells, activated endothelium and osteoclasts, but not in other cell types.

Antineoplastic Agents↗

PubMed2003

Activated integrin alphavbeta3 cooperates with metalloproteinase MMP-9 in regulating migration of metastatic breast cancer cells.

Expression of adhesion receptor integrin alphavbeta3 in an activated functional form strongly promotes metastasis in human breast cancer cells. Here, we report that alphavbeta3 cooperates with matrix metalloproteinase type 9 (MMP-9) in breast cancer cell migration. This cooperation is regulated by the activation state of the integrin. Expression of activated alphavbeta3 in metastatic variants of MDA-MB 435 human breast cancer cells and primary metastatic cells from breast cancer patients strongly enhanced migration toward vitronectin and fibrinogen. This enhancement was mediated by a soluble factor produced by breast cancer cells expressing activated alphavbeta3. When transferred, this factor also up-regulated alphavbeta3-dependent migration of breast cancer cells that express the nonactivated integrin. The factor was identified as metalloproteinase MMP-9. Whereas all tested breast cancer cell variants produced latent MMP-9, only those with activated alphavbeta3 produced the mature form of this metalloproteinase. Recombinant mature MMP-9, but not latent MMP-9 or either form of MMP-2, enhanced alphavbeta3-dependent breast cancer cell migration. The migratory response was inhibited by tissue inhibitors of metalloproteinase or when MMP-9 was depleted from the inducing supernatants. The results indicate a causal relationship between the expression of activated integrin alphavbeta3 and production of enzymatically active MMP-9 in metastatic breast cancer cells. These molecules cooperate to enhance breast cancer cell migration toward specific matrix proteins, and this may contribute to the strongly enhanced metastatic capacity of breast cancer cells that express activated alphavbeta3.

Breast Neoplasms↗