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PubMed2000

In vitro and in vivo effects of a cyclic peptide with affinity for the alpha(nu)beta3 integrin in human melanoma cells.

Expression of the integrin alpha(nu)beta3 has been shown to be associated with increasing metastatic potential in malignant melanoma. It also has a functional role on vascular endothelial cells during angiogenesis. The cyclic oligopeptide cRGDfV is known to bind with high affinity to alpha(nu)beta3. We have investigated the cellular effects of cRGDfV on a panel of human melanoma cell lines in vitro and also on the A375 melanoma cell line growing as xenografts in nude mice. cRGDfV is a potent inhibitor of alpha(nu)beta3-mediated cell adhesion, however, we have found no convincing evidence that integrin ligation by cRGDfV induces apoptosis in melanoma cell lines. However, cRGDfV when administered subcutaneously into nude mice did inhibit the growth of A375 melanoma xenografts. Histological examination of the tumours indicated that this effect was primarily one of angiogenesis inhibition. The results suggest that agents which target the alpha(nu)beta3 integrin may have a useful role as anti-angiogenesis agents in clinical oncology, but that they may not exert a direct effect on alphavbeta3-expressing tumour cells.

Animals↗
PubMed2003

Inhibition of alpha(v)beta3 integrin reduces angiogenesis, bone turnover, and tumor cell proliferation in experimental prostate cancer bone metastases.

The growth of metastatic prostate cancer cells in the bone involves an intimate interaction between the tumor cells and various elements of the bone microenvironment, resulting in increased rate of bone turnover and rapid tumor growth. The alpha(v)beta3 integrin has been shown to play an important role in tumor growth and angiogenesis, and is known to be critical to osteoclast formation and activity. This study was designed to examine the role of alpha(v)beta3 expressed by cells native to the bone in the growth and pathogenesis of prostate cancer bone metastases. Human prostate cancer cells which do not express alpha(v)beta3 or alpha(IIb)beta3 integrins were injected directly into human bone fragments previously implanted subcutaneously in SCID mice (SCID-human-bone model). At the same time treatment with anti-beta3 antibody fragment (m7E3 F(ab')2) i.p. at 300 microg/dose 3 x per week was initiated and continued for 2 weeks. In this system, m7E3 F(ab')2 only recognizes human bone-derived alpha(v)beta3. Antibody inhibition of alpha(v)beta3 integrin in vivo resulted in a specific reduction in the proportion of antigenically-human blood vessels within tumor-bearing bone implants (from 73.5% +/- 3.93 in controls to 17.74% +/- 5.64 in treated animals). Proliferation of the alpha(v)beta3-negative tumor cells was also reduced, although the overall vessel density was maintained by compensating mouse vasculature. Blockage of human bone-derived alpha(v)beta3 also significantly reduced the recruitment of osteoclasts in response to tumor cells, as well as degradation of calcified bone tissue. Together these observations confirm the importance of alpha(v)beta3 in bone metabolism and angiogenesis, and point to the role of these processes in controlling growth of metastatic prostate cancer cells in the bone.

Animals↗
PubMed1997

Cross talk between adhesion molecules: control of N-cadherin activity by intracellular signals elicited by beta1 and beta3 integrins in migrating neural crest cells.

During embryonic development, cell migration and cell differentiation are associated with dynamic modulations both in time and space of the repertoire and function of adhesion receptors, but the nature of the mechanisms responsible for their coordinated occurrence remains to be elucidated. Thus, migrating neural crest cells adhere to fibronectin in an integrin-dependent manner while maintaining reduced N-cadherin-mediated intercellular contacts. In the present study we provide evidence that, in these cells, the control of N-cadherin may rely directly on the activity of integrins involved in the process of cell motion. Prevention of neural crest cell migration using RGD peptides or antibodies to fibronectin and to beta1 and beta3 integrins caused rapid N-cadherin-mediated cell clustering. Restoration of stable intercellular contacts resulted essentially from the recruitment of an intracellular pool of N-cadherin molecules that accumulated into adherens junctions in tight association with the cytoskeleton and not from the redistribution of a preexisting pool of surface N-cadherin molecules. In addition, agents that cause elevation of intracellular Ca2+ after entry across the plasma membrane were potent inhibitors of cell aggregation and reduced the N-cadherin- mediated junctions in the cells. Finally, elevated serine/ threonine phosphorylation of catenins associated with N-cadherin accompanied the restoration of intercellular contacts. These results indicate that, in migrating neural crest cells, beta1 and beta3 integrins are at the origin of a cascade of signaling events that involve transmembrane Ca2+ fluxes, followed by activation of phosphatases and kinases, and that ultimately control the surface distribution and activity of N-cadherin. Such a direct coupling between adhesion receptors by means of intracellular signals may be significant for the coordinated interplay between cell-cell and cell-substratum adhesion that occurs during embryonic development, in wound healing, and during tumor invasion and metastasis.

Animals↗
PubMed2002

Pathogenic hantaviruses selectively inhibit beta3 integrin directed endothelial cell migration.

Hantaviruses cause two diseases of man, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Pathogenic and non-pathogenic hantaviruses use beta3 and beta1 integrins, respectively, to enter endothelial cells. Beta3 integrins were recently reported to bind receptors that regulate vascular permeability suggesting that hantavirus beta3 integrin interactions may regulate endothelial cell function and contribute to viral pathogenesis. In this study we investigated the ability of pathogenic and non-pathogenic hantaviruses to regulate beta3 and beta1 integrin directed endothelial cell functions. We found that pathogenic NY-1, SNV, HTN, SEO and PUU viruses blocked endothelial cell migration on beta3, but not beta1, integrin ligands. Migration is similarly inhibited by antibodies to beta3 integrins which selectively block vitronectin directed endothelial cell migration. As a result, the ability of endothelial cells to migrate on integrin ligands was selectively inhibited by only pathogenic hantaviruses. Infection by NY-1 virus inhibited endothelial cell migration as early as 24-48 h post-infection. In contrast, non-pathogenic PH and TUL viruses had no effect on the ability of endothelial cells to migrate on either beta3 or beta1 integrin ligands from 1 to 5 days post-infection. These findings indicate that only hantaviruses which use beta3 integrins, and are associated with HPS and HFRS diseases, functionally dysregulate endothelial cell migration. These findings further demonstrate that hantaviruses regulate only beta3 integrin directed endothelial cell functions and have no effect on beta1 integrin functions. Since beta3 integrins are linked to changes in vascular permeability and the maintenance of vascular integrity, these findings suggest a means by which hantavirus usage and regulation of beta3 integrins may contribute to hantavirus pathogenesis.

Cell Movement↗
PubMedDate not supplied

In vitro angiogenesis is modulated by the mechanical properties of fibrin gels and is related to alpha(v)beta3 integrin localization.

This study deals with the role of the mechanical properties of matrices in in vitro angiogenesis. The ability of rigid fibrinogen matrices with fibrin gels to promote capillarylike structures was compared. The role of the mechanical properties of the fibrin gels was assessed by varying concentration of the fibrin gels. When the concentration of fibrin gels was decreased from 2 mg/ml to 0.5 mg/ml, the capillarylike network increased. On rigid fibrinogen matrices, capillarylike structures were not formed. The extent of the capillarylike network formed on fibrin gels having the lowest concentration depended on the number of cells seeded. The dynamic analysis of capillarylike network formation permitted a direct visualization of a progressive stretching of the 0.5 mg/ml fibrin gels. This stretching was not observed when fibrin concentration increases. This analysis shows that 10 h after seeding, a prearrangement of cells into ringlike structures was observed. These ringlike structures grew in size. Between 16 and 24 h after seeding, the capillarylike structures were formed at the junction of two ringlike structures. Analysis of the alpha(v)beta3 integrin localization demonstrates that cell adhesion to fibrinogen is mediated through the alpha(v)beta3 integrin localized into adhesion plaques. Conversely, cell adhesion to fibrin shows a diffuse and dot-contact distribution. We suggest that the balance of the stresses between the tractions exerted by the cells and the resistance of the fibrin gels triggers an angiogenic signal into the intracellular compartment. This signal could be associated with modification in the alpha(v)beta3 integrin distribution.

Biomechanical Phenomena↗
PubMed2006

Dexamethasone inhibits the formation of multinucleated osteoclasts via down-regulation of beta3 integrin expression.

Although glucocorticoids are known to affect osteoclast differentiation and function, there have been conflicting reports about the effect of glucocorticoids on osteoclast formation, leading to the assumption that microenvironment and cell type influence their action. We explored the effect of the synthetic glucocorticoid analog dexamethasone on the formation of osteoclasts. Dexamethasone inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts without affecting the formation of TRAP-positive mononuclear cells in a coculture of mouse osteoblasts and bone marrow cells. Dexamethasone did not inhibit mRNA expression levels of the receptor activator of nuclear factor-kappaB ligand and osteoprotegerin, the essential regulators of osteoclastogenesis. Dexamethasone down-regulated the expression of beta3 integrin mRNA and protein but did not alter expression of other osteoclast differentiation marker genes. Both dexamethasone and echistatin, a beta3 integrin function blocker, inhibited TRAP-positive multinucleated osteoclast formation but not TRAP-positive mononuclear cell formation. These results suggest that dexamethasone inhibits the formation of multinucleated osteoclasts, at least in part, through the down-regulation of beta3 integrin, which plays an important role in the formation of multinucleated osteoclasts.

Animals↗
PubMed2003

In vitro regulation of beta1 and beta3 integrin subunits in endometrial epithelial cells from normal endometrium.

OBJECTIVE: To evaluate the effect of prostaglandin E2 (PGE2) and interleukin-1beta (IL-1beta) on integrin expression. DESIGN Cultures of endometrial epithelial cells from normal endometrium. SETTING: All endometrial specimens were obtained from the Obstetrics and gynecology Department of the Catholic University, Rome, Italy. PATIENTS: Four patients were normal menstrual cycles undergoing operative laparoscopy for non-endometrial problems. INTERVENTION: Endometrial samples were collected by uterine courettings. MAIN OUTCOME MEASURE: Immunocytochemistry for beta1 and beta3 integrin subunits. RESULTS: PGE2 clearly enhances both beta1 and beta3 integrin subunit expression. IL-1beta seem to slightly increase only beta3 subunit expression. CONCLUSIONS: In light of the critical role played by eicosanoids in endometrial differentiation, we suggest that PGE2 is also involved in local paracrine regulation of integrin expression.

Cells, Cultured↗
PubMed2007

Integrin beta3 Leu33Pro polymorphism increases BRCA1-associated ovarian cancer risk.

Integrins are heterodimeric transmembrane glycoproteins that function as key adhesion and cell signalling receptors. A functional polymorphism in the integrin beta3 subunit encoded by the ITGB3 gene, Leu33Pro, has been shown to modify a variety of traits of beta3-expressing cells. To analyse the role of this functional polymorphism in modifying BRCA1-associated ovarian and breast cancer risks, a case-control study was performed among Polish BRCA1 mutation carriers including 319 breast cancer cases, 146 ovarian cancer cases and 290 controls unaffected by breast and ovarian cancer, in situ breast cancer or any other kind of cancer. Genotyping analysis was performed using PCR-based restriction fragment length polymorphism analysis. Odds ratios were calculated using univariate and multivariate logistic regression, taking into account a series of confounding variables, including the presence of related study subjects, that potentially could have biased any association. The results revealed that the ITGB3_Leu33Pro polymorphism was associated with a 2.5-fold increased risk of ovarian cancer, whereas no association with breast cancer risk was found. Thus, it appears that the ITGB3_Leu33Pro polymorphism may potentially increase the risk of ovarian cancer in Polish women with an inherited BRCA1 mutation.

Adult↗
PubMed2001

Noninvasive imaging of alpha(v)beta3 integrin expression using 18F-labeled RGD-containing glycopeptide and positron emission tomography.

The alpha(v)beta3 integrin is an important cell adhesion receptor involved in tumor-induced angiogenesis and tumor metastasis. Here we describe the 18F-labeling of the RGD-containing glycopeptide cyclo(-Arg-Gly-Asp-D-Phe-Lys(sugar amino acid)-) with 4-nitrophenyl 2-[18F]fluoropropionate and the evaluation of this compound in vitro and in tumor mouse models. Binding assays with isolated immobilized alpha(v)beta3, alpha(v)beta5, and alpha(IIb)beta3 as well as in vivo studies using alpha(v)beta3-positive and -negative murine and xenotransplanted human tumors demonstrated receptor-specific binding of the radiolabeled glycopeptide yielding high tumor:background ratios (e.g., 120 min postinjection: tumor:blood, 27.5; tumor:muscle, 10.2). First imaging results using a small animal positron emission tomograph suggest that this compound is suitable for noninvasive determination of the alpha(v)beta3 integrin status and therapy monitoring.

Animals↗
PubMed2006

Adenoviral-encoded antigens are presented efficiently by a subset of dendritic cells expressing high levels of alpha(v)beta3 integrins.

Dendritic cells (DC) play a central role in antigen presentation and are often targeted by adenoviral (Ad)-based gene therapy. However, DC lack the coxsackie-Ad receptor, and little is known about the process by which they acquire and present Ad-encoded antigens. We examined the expression of alpha(v)beta3 integrins (CD51/CD61) on mouse bone marrow-derived DC (BM-DC) and their susceptibility to transduction by Ad vectors. Less than 10% of BM-DC precursors expressed CD51, but expression increased over time in culture with granulocyte macrophage-colony stimulating factor (GM-CSF)/interleukin (IL)-4. After 7 days, 28 +/- 1.7% of CD11c+ DC expressed high levels of CD51 (CD51(hi)), and the remaining DC expressed low levels of CD51 (CD51(lo)). CD51(hi) CD express higher major histocompatibility complex type 1 (MHC I); however, both of the DC subsets expressed similar levels of MHC II and costimulatory molecules. When exposed to a first-generation Ad vector, transgene expression was restricted to the CD51(hi) DC subset and blocked by soluble peptides expressing an arginine, glycine, aspartic acid (RGD) sequence, confirming the role of integrins in viral entry. Consistent with this, a modified Ad expressing an RGD-binding sequence in its fiber knob (Ad-RGD) transduced the CD51(hi) DC subset with significantly higher efficiency. When BM-DC were transduced with an Ad-expressing ovalbumin (Ad-OVA), the CD51(hi) subset proved superior in activating OT-I (T cell receptor-OVA) T cells. Similar to in vitro effects, systemic administration of GM-CSF/IL-4 increased the expression of CD51 on splenic DC and rendered these cells susceptible to Ad transduction. These results suggest that a limited subset of DC expressing high levels of alpha(v)beta3 integrins is preferentially transduced by Ad vectors and activates CD8+ T cell responses against Ad-encoded antigens.

Adenoviridae↗
PubMed1998

Effects of beta3-integrin blockade (c7E3) on the response to angioplasty and intra-arterial stenting in atherosclerotic nonhuman primates.

Because the beta3-antagonist abciximab (c7E3 Fab) has significantly improved late outcomes after coronary angioplasty, the beta3 integrins have been implicated in the arterial response to injury. However, the mechanisms underlying this benefit are unknown. The observation that c7E3 binds beta3 integrins on vascular cells (alphavbeta3) with affinity equal to that for the platelet glycoprotein IIb/IIIa integrin has led to the hypothesis that c7E3 may act directly on the artery wall to prevent restenosis after angioplasty. To test this hypothesis, we studied the effects of c7E3 on structural changes within the artery wall after angioplasty or stent angioplasty in 23 male cynomolgus monkeys with established atherosclerosis. Animals were randomly assigned to receive either a bolus of c7E3 (0.4 mg/kg IV, n=11) followed by a 48-hour infusion (0. 2 microg. kg-1. min-1) or an equal volume of vehicle (n=12). Animals received weight-adjusted aspirin and heparin and then underwent unilateral iliac artery experimental angioplasty and subclavian artery stent angioplasty (Palmaz). Iliac artery lumen diameter (LD) was determined by angiography at baseline (LDPre), after angioplasty (LDPost), and 35 days later (LDDay35). Arteries were then fixed by perfusion and removed for analysis. Lumen, intima, media, and external elastic lamina (EEL) areas were measured in iliac artery cross sections. Values from each injured iliac artery were normalized to the contralateral uninjured iliac artery to control for interanimal variability in baseline artery size and atherosclerosis extent. Intimal area was also measured in subclavian stent cross sections. c7E3 blocked platelet aggregation and prolonged the bleeding time from 2.8+/-1.1 to 19.8+/-2.5 minutes, P<0.001. Experimental angioplasty increased LDPost an average of 28%, and the initial gain was similar in both groups (P=NS). Despite an anti-platelet effect, c7E3 did not inhibit iliac lumen narrowing (LDDay35-LDPost: c7E3, -0.69+/-0.17 versus vehicle, -0.99+/-.17 mm, P=0.35); intimal hyperplasia (neointima area: c7E3, 1.12+/-.28 versus vehicle, 1.22+/-.20 mm2, P=0.77); or decrease in artery wall size (EEL area [percent of uninjured control]: c7E3, 101+/-7% versus vehicle, 121+/-7%). Stent intimal hyperplasia was also unaltered by c7E3 treatment (neointimal area: c7E3, 1.09+/-0.16 versus vehicle, 1. 28+/-0.11 mm2, P=0.36). These results suggest that the benefits of c7E3 treatment in coronary angioplasty were not from inhibition of intimal hyperplasia or improved artery wall remodeling. Alternative mechanisms should be explored to explain improved late outcomes after angioplasty in patients treated with c7E3.

Abciximab↗
PubMed1998

Cleavage of the cytoplasmic domain of the integrin beta3 subunit during endothelial cell apoptosis.

In this study, we report that the cytoplasmic domain of the integrin beta3 subunit is a target for limited proteolysis during apoptosis of human umbilical vein endothelial cells. Calpain inhibitors inhibited the cleavage of the beta3 cytoplasmic domain, indicating that calpain is required. Calpain-mediated proteolysis of fodrin was also detected, indicating that calpain is activated during endothelial cell apoptosis. A phosphatase inhibitor, sodium orthovanadate, inhibited endothelial cell apoptosis and cleavage beta3, suggesting that protein dephosphorylation preceded integrin cleavage in the apoptosis signaling pathway. beta3 cleavage was observed in cells that were viable, suggesting that it is an early event and not the consequence of post-death proteolysis. The extent of beta3 cleavage correlated with a loss in the capacity of cells to reattach to matrix proteins. Loss of reattachment capacity during apoptosis was significantly retarded by a calpain inhibitor. As the beta3 cytoplasmic domain is required for integrin signaling and interaction with the cytoskeleton, our results suggest that cleavage in the beta3 cytoplasmic domain by calpain or a calpain-like protease negatively regulates integrin-mediated adhesion, signaling, and cytoskeleton association.

Antigens, CD↗
PubMed2004

Antitumor activity of bacteriophages in murine experimental cancer models caused possibly by inhibition of beta3 integrin signaling pathway.

Bacteriophages (phages) as bacterial viruses are generally believed to have no intrinsic tropism for mammalian cells. In this study the interactions between phages and various eukaryotic cells were investigated. Binding of phages to the membranes of cancer and normal blood cells was observed. Moreover, it was shown that the wild-type phage T4 (wtT4) and its substrain HAP1 with enhanced affinity for melanoma cells inhibit markedly and significantly experimental lung metastasis of murine B16 melanoma cells by 47% and 80%, respectively. A possible molecular mechanism of these effects, namely a specific interaction between the Lys-Gly-Asp motif of the phage protein 24 and beta3-integrin receptors on target cells is proposed. It was also shown that anti-beta3 antibodies and synthetic peptides mimicking natural beta3 ligands inhibit the phage binding to cancer cells. This is in line with the well-described beta3 integrin-dependent mechanism of tumor metastasis. It is concluded that the blocking of beta3 integrins by phage preparations results in a significant decrease in tumor invasiveness.

Animals↗
PubMed1998

Ser752 mutation to Pro or Ala in the beta3 integrin subunit differentially affects the kinetics of cell spreading to von Willebrand factor and fibrinogen.

The beta3 cytoplasmic domain of the alpha v beta3 integrin is essential for intracellular signals required for cytoskeletal rearrangements. Expression of beta3Ser752Pro mutation in heterologous cells profoundly affects cell spreading and beta3 localization into focal contacts. However, the beta3Ser752Ala substitution mostly restores normal integrin functions, suggesting that the presence of Pro is responsible for the receptor's loss of function. To further assess the role of the Ser752 of the beta3 cytoplasmic domain in the cytoskeletal organization of adherent cells, we developed a computer-assisted method of image analysis allowing the automatic classification of spread cells according to the quantitative analysis of their cell morphology. We compared adhesion and spreading to von Willebrand factor (vWF) or fibrinogen (Fg) of cells expressing beta3 wild type, beta3Ser752Pro or beta3Ser752Ala mutated integrin subunit as a chimeric alpha v beta3 receptor. The beta3Ser752Ala substitution did not impair the general ability of cells to spread, but resulted in a delayed and reduced spreading on both vWF and Fg. Moreover, the beta3Ser752Ala mutation produced modifications of the morphology of spread cells, suggesting a disorganization of their cytoskeleton. Attachment studies showed that the beta3Ser752Ala mutation did not modify the capacity of cells to attach to the substrate, indicating no change in the ligand binding affinity of the alpha v beta3 integrin. Furthermore, we identified a slight defect of beta3Ser752Pro cell attachment to vWF and Fg, beside their impairment of spreading. Taken together, these results suggest a role of Ser752 of the beta3 cytoplasmic domain in the optimal cytoskeletal organization of adherent cells.

Alanine↗
PubMed1997

Molecular determinants of arg-gly-asp ligand specificity for beta3 integrins.

The Arg-Tyr-Asp (RYD) and Arg-Gly-Asp (RGD) sequences within the third complementarity-determining region of the heavy chain (H3) of murine recombinant Fab molecules OPG2 and AP7, respectively, are responsible for their specific binding to the platelet integrin alphaIIbbeta3. In this study, we evaluated the influence of divalent cation composition and single amino acid substitutions at key positions within H3 on the selectivity of these Fab molecules for integrin alphaIIbbeta3 versus the vitronectin receptor alphaVbeta3. The parent Fab molecule OPG2 (H3 sequence, HPFYRYDGGN) binds selectively to alphaIIbbeta3 and not at all to any other RGD-cognitive integrin, particularly alphaVbeta3, under any divalent cation conditions. The binding of the AP7 Fab molecule (HPFYRGDGGN) to alphaIIbbeta3 is not affected by the relative composition of calcium, magnesium or manganese. However, AP7 binding to alphaVbeta3, either expressed by M21 cells or as the purified integrin, is supported by manganese and inhibited by calcium. If the flanking asparagine 108 residue within the AP7 H3 loop is replaced by alanine (HPFYRGDGGA), the resulting Fab molecule AP7.4 binds selectively to alphaVbeta3 in a cation-dependent manner, but does not bind at all to alphaIIbbeta3 under any conditions. AP7.4 binding to alphaVbeta3 is supported by manganese, completely inhibited by calcium, and largely unaffected by magnesium. This behavior mimics that of the adhesive protein, osteopontin, another ligand that binds preferentially to alphaVbeta3. Despite these differences in specificity for alphaIIbbeta3 and alphaVbeta3, AP7 and AP7.4 remain selective for the beta3 integrins and do not bind to cell lines that express the RGD-cognitive integrins alphaVbeta5 or alpha5beta1. These results confirm that subtle changes in the amino acid composition immediately flanking the RGD or RYD motifs can have a profound effect on beta3 integrin specificity, most likely because they influence the juxtaposition of the arginine and aspartate side chains within the extended RGD loop sequence.

Amino Acid Sequence↗
PubMed1997

The role of conserved amino acid motifs within the integrin beta3 cytoplasmic domain in triggering focal adhesion kinase phosphorylation.

Integrin-mediated adhesion of cells to extracellular matrix proteins triggers a variety of intracellular signaling pathways including a cascade of tyrosine phosphorylations. In many cell types, the cytoplasmic focal adhesion tyrosine kinase, FAK, appears to be the initial protein that becomes tyrosine-phosphorylated in response to adhesion; however, the molecular mechanisms regulating integrin-triggered FAK phosphorylation are not understood. Previous studies have shown that the integrin beta1, beta3, and beta5 subunit cytoplasmic domains all contain sufficient information to trigger FAK phosphorylation when expressed in single-subunit chimeric receptors connected to an extracellular reporter. In the present study, beta3 cytoplasmic domain deletion and substitution mutants were constructed to identify amino acids within the integrin beta3 cytoplasmic domain that regulate its ability to trigger FAK phosphorylation. Cells transiently expressing chimeric receptors containing these mutant cytoplasmic domains were magnetically sorted and assayed for the tyrosine phosphorylation of FAK. Analysis of these mutants indicated that structural information in both the membrane-proximal and C-terminal segments of the beta3 cytoplasmic domain is important for triggering FAK phosphorylation. In the C-terminal segment of the beta3 cytoplasmic domain, the highly conserved NPXY motif was found to be required for the beta3 cytoplasmic domain to trigger FAK phosphorylation. However, the putative FAK binding domain within the N-terminal segment of the beta3 cytoplasmic domain was found to be neither required nor sufficient for this signaling event. We also demonstrate that the serine 752 to proline mutation, known to cause a variant of Glanzmann's thrombasthenia, inhibits the ability of the beta3 cytoplasmic domain to signal FAK phosphorylation, suggesting that a single mutation in the beta3 cytoplasmic domain can inhibit both "inside-out" and "outside-in" integrin signaling.

Amino Acid Sequence↗
PubMed2004

Integrin beta3 Leu33Pro polymorphism and breast cancer risk: a population-based case-control study in Germany.

A functional polymorphism at codon 33 (leucine-to-proline, Leu33Pro)/nucleotide 1565 (T-to-C, T1565C) of the integrin beta3 has been hypothesized to increase the risk of breast cancer and its metastasis. Three studies have been conducted up to date and the results were contradictory. We used a large population-based age-matched case-control study in German Caucasian women by the age of 50 years to assess breast cancer risk associated with this polymorphism, taking into consideration of possible interaction with other risk factors, and to examine if it affects clinical presentation. Overall, the odds ratios (OR) for breast cancer were not increased in women carrying either allele. However, we observed a differential effect of the Leu33Pro polymorphism by age group when patients were stratified by 45 years of age (p=0.055). Being a carrier of the 33proline allele was found to be associated with a 32% increased risk (95% Cl=1.0-1.8) for breast cancer compared to the wild-type leucine homozygotes among women age 45 or younger but not in older women. Furthermore, we observed significant dose effect of the 33proline allele (p=0.04), with 30% risk increase per allele (95% Cl=1.0-1.7). Significant evidence was also found for a positive association between 33proline carrier status and increasing axillary node involvement (p=0.048) but neither size nor grading of tumor in this study. Our data suggest that inheritance of the integrin beta3 Leu33Pro polymorphism may increase the breast cancer risk by age 45 in the German population.

Adult↗
PubMed2005

Microparticles from apoptotic vascular smooth muscle cells induce endothelial dysfunction, a phenomenon prevented by beta3-integrin antagonists.

Fragile atherosclerotic plaques are rich in apoptotic smooth muscle cells (SMCs) and macrophages, generating microparticules (MPs) which accumulate locally and may be released in blood in case of mechanical or spontaneous plaque disruption. Besides being highly procoagulant, this material may interact with downstream endothelium. Using a model of mouse aorta vaso-reactivity, we have investigated the effects of apoptotic MPs prepared in vitro from Fas-ligand sensitive SMCs. Short-term preincubation of aorta rings with the MPs dose-dependently reduced the vasodilatory response to acetylcholine dependent on the endothelium. This effect was prevented by the addition of abxicimab or eptifibatide, indicating a role for a beta3 integrin in this process. We further investigated its mechanism using cultured endothelial cells. The MPs were found to bind to the cells and to inhibit the production and the release of nitric oxide (NO) in response to bradykinin. This phenomenom was redox sensitive, independent of the generation of activated coagulation proteases, and was abrogated when the MPs were pretreated by trypsin. The metabolic effects of MPs were prevented by the addition of eptifibatide. Taken together, these results suggest a potential, platelet-independent, mechanism for the improvement of microvascular perfusion observed with beta3-integrin antagonists.

Abciximab↗