Zika Virus Targets Glioblastoma Stem Cells through a SOX2-Integrin αvβ5 Axis

Zika virus (ZIKV) causes microcephaly by killing neural precursor cells (NPCs) and other brain cells. ZIKV also displays therapeutic oncolytic activity against glioblastoma (GBM) stem cells (GSCs). Here we demonstrate that ZIKV preferentially infected and killed GSCs and stem-like cells in medulloblastoma and ependymoma in a SOX2-dependent manner. Targeting SOX2 severely attenuated ZIKV infection, in contrast to AXL. As mechanisms of SOX2-mediated ZIKV infection, we identified inverse expression of antiviral interferon response genes (ISGs) and positive correlation with integrin α_v (ITGAV). ZIKV infection was disrupted by genetic targeting of ITGAV or its binding partner ITGB5 and by an antibody specific for integrin α_vβ₅. ZIKV selectively eliminated GSCs from species-matched human mature cerebral organoids and GBM surgical specimens, which was reversed by integrin α_vβ₅ inhibition. Collectively, our studies identify integrin α_vβ₅ as a functional cancer stem cell marker essential for GBM maintenance and ZIKV infection, providing potential brain tumor therapy.

Insulin-like growth factor binding protein-1 (IGFBP-1) inhibits breast cancer cell motility

The breast cancer malignant phenotype is regulated by steroid hormones and peptide growth factors. We have shown previously that insulin-like growth factor-I (IGF-I) stimulates cell motility in a metastatic cell line, MDA-231BO. In this study, we show that neutralization of IGF action by a type I IGF receptor (IGFR1) blocking antibody or neutralization of IGF-I by IGFBP-1 reduced cell motility. However, in addition to inhibiting IGF effects, IGFBP-1 also diminished basal motility. Because IGFBP-1 contains a RGD motif important in binding of fibronectin to its alpha 5 beta 1 integrin receptor, we examined the effect of inhibiting integrin function on cell motility. As expected, disruption of fibronectin-integrin interactions interrupted basal motility in MDA-231BO cells. In addition, disruption of integrin function by an alpha 5 beta 1 blocking peptide also inhibited IGF stimulation of cell motility. To determine whether integrin function could interfere with IGF signaling, we used an alpha 5 beta 1 blocking peptide to show that in MDA-231BO cells integrin occupancy appeared necessary for phosphorylation of insulin receptor substrate-2 but not for IGFR1 activation. We conclude that IGFR1 and integrin action are linked in these breast cancer cells as disruption of integrin binding to its receptor influences IGF signaling pathways. Moreover, IGFBP-1 could have dual effects on cancer cell motility by disrupting both receptor systems.

The selective regulation of alpha Vbeta 1 integrin expression is based on the hierarchical formation of alpha V-containing heterodimers

The integrin beta1 subunit can form a heterodimer with 12 different alpha subunits. According to the present model, the expression level of any alphabeta complex is regulated by the availability of the specific alpha subunit, whereas beta1 subunit is constantly present in a large excess. The expression of several heterodimers containing the alphaV subunit seems to be regulated by an identical mechanism. The fact that many cells express alphaVbeta1 heterodimer, and that this fibronectin/vitronectin receptor may be selectively regulated, compromises the present model of the regulation of beta1 and alphaV integrins. We have tried to solve this problem by assuming that distinct alphabeta heterodimers are formed with different tendency. To test the hypothesis, we analyzed WM-266-4 melanoma cells transfected with a cDNA construct coding for an intracellular single-chain anti-alphaV integrin antibody. We could see 70-80% reduction in the cell surface expression of alphaV subunit. However, the only one of the alphaV integrins reduced on the cell surface was alphaVbeta1. This suggests that the cell surface expression level of alphaVbeta1 is dependent on the number of alphaV subunits available after the formation of other alphaV-containing heterodimers. Thus, there seems to be a hierarchy in the complex formation between alphaV and its different beta-partners. These observations explain how alphaVbeta1 can be specifically regulated without concomitant changes in the expression of other alphaV or beta1 integrins.

Developmentally regulated interactions of human thymocytes with different laminin isoforms

The gene family of heterotrimeric laminin molecules consists of at least 15 naturally occurring isoforms which are formed by five different alpha, three beta and three gamma subunits. The expression pattern of the individual laminin chains in the human thymus was comprehensively analysed in the present study. Whereas laminin isoforms containing the laminin alpha1 chain (e.g. LN-1) were not present in the human thymus, laminin isoforms containing the alpha2 chain (LN-2/4) or the alpha5 chain (LN-10/11) were expressed in the subcapsular epithelium and in thymic blood vessels. Expression of the laminin alpha4 chain seemed to be restricted to endothelial cells of the thymus, whereas the LN-5 isoform containing the alpha3 chain could be detected on medullary thymic epithelial cells and weakly in the subcapsular epithelium. As revealed by cell attachment assays, early CD4- CD8- thymocytes which are localized in the thymus beneath the subcapsular epithelium adhered strongly to LN-10/11, but not to LN-1, LN-2/4 or LN-5. Adhesion of these thymocytes to LN-10/11 was mediated by the integrin alpha6beta1. During further development, the cortically localized CD4+ CD8+ thymocytes have lost the capacity to adhere to laminin-10/11. Neither do these cells adhere to any other laminin isoform tested. However, the more differentiated single positive CD8+ thymocytes which were mainly found in the medulla were able to bind to LN-5 which is expressed by medullary epithelial cells. Interactions of CD8+ thymocytes with LN-5 were integrin alpha6beta4-dependent. These results show that interactions of developing human thymocytes with different laminin isoforms are spatially and developmentally regulated.

Src-mediated coupling of focal adhesion kinase to integrin alpha(v)beta5 in vascular endothelial growth factor signaling

Vascular endothelial growth factor (VEGF) promotes vascular permeability (VP) and neovascularization, and is required for development. We find that VEGF-stimulated Src activity in chick embryo blood vessels induces the coupling of focal adhesion kinase (FAK) to integrin alpha(v)beta5, a critical event in VEGF-mediated signaling and biological responsiveness. In contrast, FAK is constitutively associated with beta1 and beta3 integrins in the presence or absence of growth factors. In cultured endothelial cells, VEGF, but not basic fibroblast growth factor, promotes the Src-mediated phosphorylation of FAK on tyrosine 861, which contributes to the formation of a FAK/alpha(v)beta5 signaling complex. Moreover, formation of this FAK/alpha(v)beta5 complex is significantly reduced in pp60c-src-deficient mice. Supporting these results, mice deficient in either pp60c-src or integrin beta5, but not integrin beta3, have a reduced VP response to VEGF. This FAK/alpha(v)beta5 complex was also detected in epidermal growth factor-stimulated epithelial cells, suggesting a function for this complex outside the endothelium. Our findings indicate that Src can coordinate specific growth factor and extracellular matrix inputs by recruiting integrin alpha(v)beta5 into a FAK-containing signaling complex during growth factor-mediated biological responses.

Patients with Glanzmann thrombasthenia lacking platelet glycoprotein alpha(IIb)beta(3) (GPIIb/IIIa) and alpha(v)beta(3) receptors are not protected from atherosclerosis

BACKGROUND

Platelets have been suggested to play a role in the early development of atherosclerosis. As one test of this hypothesis, we assessed whether patients with Glanzmann thrombasthenia who lack platelet glycoprotein alpha(IIb)beta(3) (GPIIb/IIIa) complexes or both alpha(IIb)beta(3) and the more ubiquitous alpha(v)beta(3) cell membrane complexes are protected from development of atherosclerosis.

METHODS AND RESULTS

Seven patients with Glanzmann thrombasthenia, 45 to 66 years of age, underwent bilateral carotid artery ultrasonography and screening for risk factors of atherosclerosis. Findings consistent with early atherosclerosis evaluated by measurement of intima-media thickness and presence of atherosclerotic plaques were observed in 6 of the 7 patients. Intima-media thickness values higher than the 75th and 90th percentiles of age- and sex-matched white control subjects of the Atherosclerosis Risk in Communities (ARIC) study were observed in 30 and 8 of 56 carotid artery measurements, respectively. Five of the 6 patients with signs consistent with early atherosclerosis lacked both alpha(IIb)beta(3) and alpha(v)beta(3) complexes and 1 only lacked alpha(IIb)beta(3).

CONCLUSIONS

Glanzmann thrombasthenia does not protect affected individuals from development of atherosclerosis.

Enhanced antitumor effect and reduced vector dissemination with fiber-modified adenovirus vectors expressing herpes simplex virus thymidine kinase

There are at least two hurdles confronting the use of the adenovirus (Ad)-mediated herpes simplex virus thymidine kinase (HSVtk)/ganciclovir (GCV) system for the treatment of cancer. One is inefficient Ad vector-mediated gene transfer into tumor cells lacking the primary receptor, i.e., the coxsackievirus and adenovirus receptor (CAR). The other is hepatotoxicity due to unwanted vector spread into the liver, even when Ad vectors are injected intratumorally. Herein, we present an attractive strategy for overcoming such limitations based on use of a fiber-modified Ad vector containing an RGD peptide motif in the fiber knob. HSVtk-expressing Ad vectors containing mutant fiber (AdRGD-tk) or wild-type fiber (Ad-tk) were injected intratumorally into CAR-negative B16 melanoma cells inoculated into mice, after which GCV was injected intraperitoneally for 10 days. AdRGD-tk showed approximately 25 times more antitumor activity than Ad-tk. Histopathological studies suggested that liver damage in mice injected with AdRGD-tk was significantly lower than that in mice injected with Ad-tk. Intratumoral administration of luciferase-expressing Ad vectors containing the mutant fiber (AdRGD-L2) resulted in nearly 40 times more luciferase production in the tumor, but 8 times less production in the liver than the conventional Ad vectors (Ad-L2). These results indicate that combination of fiber-modified vectors and a HSVtk/GCV system is a potentially useful and safe approach for the treatment of tumors lacking CAR expression, and that fiber-modified vectors could be of great utility for gene therapy and gene transfer experiments.

Reduced transduction efficiency of adenoviral vectors expressing human p53 gene by repeated transduction into glioma cells in vitro

PURPOSE

Recombinant adenoviral vectors are widely used in clinical and experimental studies to treat malignant tumors. Recently, host immune responses have been proposed as a major limitation in using adenoviral vectors for repeated gene delivery. We demonstrate another limitation unrelated to host immunity.

EXPERIMENTAL DESIGN

We repeatedly transduced an adenoviral vector expressing the human p53 gene (AxCIhp53) into U373MG, a p53-susceptible cell line, and established the AxCIhp53-resistant cell line U373R. Most U373R cells survived even after AxCIhp53 treatment due to reduced transduction efficiency. Expression levels of adenovirus receptors were estimated to investigate the cause of reduced transduction efficiency. The mutant vector was used to overcome the resistance.

RESULTS

The transduction efficiency of an adenoviral vector possessing the reporter LacZ gene (AxCAZ2-F/wt) for U373R cells was 25.4-fold less than that for parent cells. The expression levels of integrins alpha(v)beta(3) and alpha(v)beta(5) were found to be decreased in U373R cells without affecting the expression levels of Coxsackievirus and adenovirus receptor. The mutant vector AxCAZ2-F/K20, with a linker and a stretch of 20 lysine residues at the COOH-terminal of the fiber protein, improved the transduction efficiency of U373R cells to 12.6-fold of that of AxCAZ2-F/wt. A mutant vector carrying the p53 gene, AxCAhp53-F/K20, dramatically induced apoptosis in U373R cells.

CONCLUSIONS

Glioma cells expressing low levels of adenovirus receptors might survive and proliferate to recur after repeated adenoviral transduction, even if the adenoviral transduction is effective at first. Changing the tropism of vectors is a potent method to overcome resistance.

Integrin alphavbeta1 is a receptor for foot-and-mouth disease virus

Infection by field strains of Foot-and-mouth disease virus (FMDV) is initiated by binding to certain species of arginine-glycine-aspartic acid (RGD)-dependent integrin including alphavbeta3 and the epithelial integrin alphavbeta6. In this report we show that the integrin alphavbeta1, when expressed as a human/hamster heterodimer on transfected CHOB2 cells, is a receptor for FMDV. Virus binding and infection mediated by alphavbeta1 was inefficient in the presence of physiological concentrations of calcium and magnesium but were significantly enhanced by reagents that activate the integrin and promote ligand binding. The ability of chimeric alpha5/alphav integrin subunits, in association with the beta1 chain, to bind FMDV and mediate infection matched the ligand binding specificity of alphavbeta1, not alpha5beta1, thus providing further evidence for the receptor role of alphavbeta1. In addition, data are presented suggesting that amino acid residues near the RGD motif may be important for differentiating between the binding specificities of alphavbeta1 and alphavbeta6.

Basal keratinocytes from uninvolved psoriatic skin exhibit accelerated spreading and focal adhesion kinase responsiveness to fibronectin

We previously proposed that the keratinocyte hyperproliferative state in psoriatic skin results from a combination of T cell cytokine interaction with basal keratinocytes that exist in a primed state. We now provide evidence that basal keratinocytes from psoriatic uninvolved skin are in a preactivated state with regard to their interaction with fibronectin. Freshly isolated basal keratinocytes (K(1)/K(10)(-)) from non-lesional psoriatic skin demonstrated a significantly higher percentage of spreading cells 1 h after plating on fibronectin-coated plates than keratinocytes isolated from normal skin (p =0.0002). No differences were observed on collagen-laminin-coated plates, however. The keratinocyte spreading on fibronectin-coated plates involved alpha 5 beta 1 and alpha V beta 1 integrins. To address the potential signaling cascades that may respond to integrin changes in psoriatic keratinocytes, focal adhesion kinase changes were assessed. The percentage of keratinocytes from psoriatic uninvolved skin that exhibit positive focal adhesion kinase staining was significantly greater than the percentage from healthy volunteers after 1 h incubation on fibronectin (p =0.006). Additionally, focal adhesion kinase isolated from uninvolved psoriatic keratinocytes had a greater degree of tyrosine phosphorylation. Thus, the proliferative effect of fibronectin in combination with T cell lymphokines on psoriatic uninvolved basal keratinocyte progenitors may be due to abnormal in vivo integrin-driven focal adhesion kinase activity and downstream signaling.

Ectodomain shedding of L1 adhesion molecule promotes cell migration by autocrine binding to integrins

The L1 adhesion molecule plays an important role in axon guidance and cell migration in the nervous system. L1 is also expressed by many human carcinomas. In addition to cell surface expression, the L1 ectodomain can be released by a metalloproteinase, but the biological function of this process is unknown. Here we demonstrate that membrane-proximal cleavage of L1 can be detected in tumors and in the developing mouse brain. The shedding of L1 involved a disintegrin and metalloproteinase (ADAM)10, as transfection with dominant-negative ADAM10 completely abolishes L1 release. L1-transfected CHO cells (L1-CHO) showed enhanced haptotactic migration on fibronectin and laminin, which was blocked by antibodies to alpha v beta 5 and L1. Migration of L1-CHO cells, but not the basal migration of CHO cells, was blocked by a metalloproteinase inhibitor, indicating a role for L1 shedding in the migration process. CHO and metalloproteinase-inhibited L1-CHO cells were stimulated to migrate by soluble L1-Fc protein. The induction of migration was blocked by alpha v beta 5-specific antibodies and required Arg-Gly-Asp sites in L1. A 150-kD L1 fragment released by plasmin could also stimulate CHO cell migration. We propose that ectodomain-released L1 promotes migration by autocrine/paracrine stimulation via alpha v beta 5. This regulatory loop could be relevant for migratory processes under physiological and pathophysiological conditions.

Differential roles of CD36 and alphavbeta5 integrin in photoreceptor phagocytosis by the retinal pigment epithelium

Retinal pigment epithelial (RPE) cells employ alphavbeta5 integrin and CD36 receptors to phagocytose photoreceptor outer segment fragments (OS). We explored special properties of RPE phagocytosis to identify the contribution of CD36 to RPE phagocytosis measuring effects of CD36 antibodies on OS binding and internalization kinetics. Early, CD36 antibodies had no effect on OS binding or internalization. Both control and CD36 antibody treated RPE initiated internalization approximately 2 hours after OS challenge. Later, bivalent CD36 IgG accelerated OS engulfment while monovalent Fab fragments inhibited engulfment. Cross-linking Fab fragments restored the accelerating activity of intact IgG. Strikingly, antibodies were effective even if added to OS already bound by RPE. alphavbeta5 blocking antibody reduced OS binding equally well in the presence of CD36 antibodies but CD36 antibodies accelerated internalization of remaining bound OS. Furthermore, CD36 ligation at either apical or basal RPE surface partially substituted for soluble factors that are required for internalization but not for binding of OS at the RPE apical surface. Our results demonstrate that CD36 ligation is necessary and sufficient to activate the OS internalization mechanism of RPE. They suggest that CD36 acts as a signaling molecule in postbinding steps of RPE phagocytosis independently of the OS binding receptor alphavbeta5 integrin.

Adenovirus type 5 uptake by lung adenocarcinoma cells in culture correlates with Ad5 fibre binding is mediated by alpha(v)beta1 integrin and can be modulated by changes in beta1 integrin function

BACKGROUND

Recombinant adenoviruses (Ad) have been employed as vectors for a wide variety of gene therapy applications, but their use has been hindered by problems relating to efficacy and safety. The efficiency of Ad-mediated gene transfer depends on the interaction of the fibre and penton base proteins with their corresponding cell receptors. Ad infection is initiated by the formation of a high affinity complex between the fibre protein and a host cell protein that for most Ad serotypes is CAR (the coxsackie B virus and Ad receptor). A second molecule, the MHC class I, may also be involved in Ad type 2 and Ad type 5 uptake. Ad internalization results from the interaction of the penton base protein with cell surface integrins alpha(v)beta3 and alpha(v)beta5. In this study, we addressed the interaction between Ad type 5 (Ad5) and its receptors on lung derived adenocarcinoma cells in culture.

METHODS

Using flow cytometry, we determined the level of expression of attachment and internalization receptors that are expressed on the cell surface of A549, H322 and H441 lung-derived adenocarcinoma cells in culture. The level of alpha(v)beta1 cell surface integrin was assessed by immunoprecipitation. Measuring the level of luciferase gene expression at different viral titres quantitated Ad5 uptake by these cells. The kinetics of binding of Ad5 fibre knobs to A549, H322 and H441 cells was assessed in direct binding studies using 125I labelling of purified recombinant Ad5 fibre-knob domains. In order to assess the functionality of integrins, adhesion assays were performed in the presence or absence of activators of integrin function. In competition experiments, prior to exposure to the virus, the cells were pre-incubated with purified recombinant Ad5 fibre-knob domains, function blocking anti-integrin antibodies, or integrin activating agents, prior to the introduction of luciferase expressing Ad5.

RESULTS

We found that Ad5-mediated gene transfer in A549, H322 and H441 adenocarcinoma cells in culture is highly variable and that this variation correlates with specific binding of Ad5 fibre-knob domain binding to the cell surface. We also found, for the first time, that Ad5 infection is mediated by integrin alpha(v)beta1 and that functional activation of beta1 integrin by means of the specific anti-beta1 monoclonal antibody, TS2/16, induced increased A549 cell adhesion to fibronectin and vitronectin and also enhanced Ad5 uptake by these cells.

CONCLUSIONS

Our studies demonstrate that the Ad5 fibre-knob domain interaction with CAR represents a major determinant of Ad5-mediated gene transfer to lung-derived adenocarcinoma cells in culture. The finding that integrin alpha(v)beta1 is involved in Ad5 infection has implications for the use of recombinant Ad5 vectors for cancer gene therapy, since alpha(v)beta1 is expressed at high levels and acts as an alternative vitronectin receptor in many epithelial and some melanoma tumours which express no alpha(v)beta3 and constant low levels of alpha(v)beta5. The fact that the beta1 integrin-activating antibody TS2/16 can enhance alpha(v)beta1-mediated Ad5 infection suggests that the efficacy of Ad5-mediated gene transfer might be influenced not only by the level of cell surface expression of integrins but also by their state of activation.

Variable protection of beta 3-integrin--deficient mice from thrombosis initiated by different mechanisms

Platelet integrin alpha IIb beta 3 (GPIIb/IIIa) plays a central role in the initiation of arterial thrombosis, but its contribution to disseminated microvascular thrombosis is less well defined. Therefore, wild-type mice (beta 3(+/+)), beta 3-integrin-deficient mice (beta 3(-/-)), and wild-type mice treated with a hamster monoclonal antibody (1B5) that blocks murine alpha IIb beta 3 function were tested in models of large-vessel and microvascular thrombosis. In the large-vessel model, ferric chloride was used to injure the carotid artery, and the time to thrombosis was measured. In beta 3(+/+) mice, the median time to occlusion was 6.7 minutes, whereas occlusion did not occur in any of the beta 3(-/-) mice tested (P <.001). Fab and F(ab')(2) fragments of 1B5 increased the median time to occlusion. To initiate systemic intravascular thrombosis, prothrombotic agents were administered intravenously, and platelet thrombus formation was monitored by the decrease in circulating platelet count. Three minutes after the injection of adenosine diphosphate (ADP), collagen + epinephrine, or tissue factor, the platelet counts in beta 3(+/+) mice decreased by 289, 424, and 429 x 10(3)/microL, respectively. beta 3(-/-) mice and wild-type mice pretreated with 1B5 Fab (1 mg/kg, IP) were nearly completely protected from the effects of ADP. In contrast, beta 3(-/-) mice were only partially protected from the effects of collagen + epinephrine and minimally protected from the effects of tissue factor. In all cases, less fibrin became deposited in the lungs of beta 3(-/-) mice than in wild-type mice. These results suggest that though alpha IIb beta 3 plays a dominant role in large-vessel thrombosis, it plays a variable role in systemic intravascular thrombosis. (Blood. 2001;98:1055-1062)

Intercellular adhesion molecule-4 binds alpha(4)beta(1) and alpha(V)-family integrins through novel integrin-binding mechanisms

The LW blood group glycoprotein, ICAM-4, is a member of the intercellular adhesion molecule (ICAM) family expressed in erythroid cells. To begin to address the function of this molecule, ligands for ICAM-4 on hemopoietic and nonhemopoietic cell lines were identified. Peptide inhibition studies suggest that adhesion of cell lines to an ICAM-4-Fc construct is mediated by an LDV-inhibitable integrin on hemopoietic cells and an RGD-inhibitable integrin on nonhemopoietic cells. Antibody inhibition studies identified the hemopoietic integrin as alpha(4)beta(1.) Antibody inhibition studies on alpha(4)beta(1)-negative, nonhemopoietic cell lines suggested that adhesion of these cells is mediated by alpha(V) integrins (notably alpha(V)beta(1) and alpha(V)beta(5)). The structure of ICAM-4 modeled on the crystal structure of ICAM-2 was used to identify surface-exposed amino acid residues for site-directed mutagenesis. Neither an unusual LETS nor an LDV motif in the first domain of ICAM-4 was critical for integrin binding. ICAM-4 is the first ICAM family member shown to be a ligand for integrins other than those of the beta(2) family, and the data suggest that ICAM-4 has a novel integrin-binding site(s). These findings suggest a role for ICAM-4 in normal erythropoiesis and may also be relevant to the adhesive interactions of sickle cells.

CYR61 stimulates human skin fibroblast migration through Integrin alpha vbeta 5 and enhances mitogenesis through integrin alpha vbeta 3, independent of its carboxyl-terminal domain

CYR61, an angiogenic factor and a member of the CCN protein family, is an extracellular matrix-associated, heparin-binding protein that mediates cell adhesion, promotes cell migration, and enhances growth factor-stimulated cell proliferation. CYR61 induces angiogenesis and promotes tumor growth in vivo and is expressed in dermal fibroblasts during cutaneous wound healing. It has been demonstrated recently that adhesion of primary skin fibroblasts to CYR61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans, resulting in adhesive signaling and up-regulation of matrix metalloproteinases 1 and 3. CYR61 is composed of four discrete structural domains that bear sequence similarities to the insulin-like growth factor-binding proteins, von Willebrand factor type C repeat, thrombospondin type 1 repeat, and a carboxyl-terminal (CT) domain that resembles cysteine knots found in some growth factors. In this study, we show that a CYR61 mutant (CYR61DeltaCT) that has the CT domain deleted is unable to support adhesion of primary human skin fibroblasts but is still able to stimulate chemotaxis and enhance basic fibroblast growth factor-induced mitogenesis similar to wild type. In addition, fibroblast migration to CYR61 is mediated through integrin alpha(v)beta(5) but not integrins alpha(6)beta(1) or alpha(v)beta(3). Furthermore, we show that CYR61 binds directly to purified integrin alpha(v)beta(5) in vitro. By contrast, CYR61 enhancement of basic fibroblast growth factor-induced DNA synthesis is mediated through integrin alpha(v)beta(3), a known receptor for CYR61 that mediates CYR61-dependent cell adhesion and chemotaxis in vascular endothelial cells. Thus, CYR61 promotes primary human fibroblast adhesion, migration, and mitogenesis through integrins alpha(6)beta(1), alpha(v)beta(5), and alpha(v)beta(3), respectively. Together, these findings establish CYR61 as a novel ligand for integrin alpha(v)beta(5) and show that CYR61 interacts with distinct integrins to mediate disparate activities in a cell type-specific manner.

Integrin alpha(v)beta1 is an adenovirus coreceptor

The human embryonic kidney (HEK293) cell line, commonly used for recombinant adenovirus (Ad) propagation, does not express the Ad coreceptor alpha(v)beta3 or alpha(v)beta5 integrins, yet these cells are efficiently infected by Ad vectors. Here we demonstrate that Ad binds to HEK293 cells via the fiber receptor CAR and is subsequently internalized via interaction with integrin alpha(v)beta1. Function-blocking antibodies directed against alpha(v) or beta1, but not beta3, beta5, or alpha5, integrin subunits block Ad infection and viral endocytosis. Therefore, alpha(v)beta1 serves as a coreceptor for Ad infection, and the lack of beta3 and/or beta5 but the relatively high expression of alpha(v)beta1 integrins on certain tumor cell types may explain why these cells are readily transduced by Ad vectors.

alpha v beta 6 Integrin upregulates matrix metalloproteinase 9 and promotes migration of normal oral keratinocytes

The integrin alpha v beta 6 is a fibronectin receptor that is undetectable on normal keratinocytes in situ, but is increased significantly in wound healing and in culture-established keratinocytes, suggesting that it may promote changes associated with cell motility. Using normal human oral keratinocytes we have shown that cultured cells express relatively high levels of alpha v beta 6 and this integrin has a functional role in both cell adhesion and migration towards fibronectin. We provide experimental evidence that the increased expression of alpha v beta 6 by normal human oral keratinocytes results in coordinate changes, which promote a more migratory phenotype. Thus increased expression of alpha v beta 6 results in a fibronectin-dependent increase in pro-matrix metalloproteinase 9, matrix metalloproteinase 9 activity increases normal human oral keratinocyte migration, and this may be further dependent on plasmin activation. The results suggest a key role for alpha v beta 6 in these processes and indicate a coordinated link between alpha v beta 6 expression and upregulation of matrix metalloproteinase 9. It appears that alpha v beta 6 may function in normal human oral keratinocyte migration through matrix-metalloproteinase-9-dependent and -independent mechanisms.

Induction of beta3-integrin gene expression by sustained activation of the Ras-regulated Raf-MEK-extracellular signal-regulated kinase signaling pathway

Alterations in the expression of integrin receptors for extracellular matrix (ECM) proteins are strongly associated with the acquisition of invasive and/or metastatic properties by human cancer cells. Despite this, comparatively little is known of the biochemical mechanisms that regulate the expression of integrin genes in cells. Here we demonstrate that the Ras-activated Raf-MEK-extracellular signal-regulated kinase (ERK) signaling pathway can specifically control the expression of individual integrin subunits in a variety of human and mouse cell lines. Pharmacological inhibition of MEK1 in a number of human melanoma and pancreatic carcinoma cell lines led to reduced cell surface expression of alpha6- and beta3-integrin. Consistent with this, conditional activation of the Raf-MEK-ERK pathway in NIH 3T3 cells led to a 5 to 20-fold induction of cell surface alpha6- and beta3-integrin expression. Induced beta3-integrin was expressed on the cell surface as a heterodimer with alphav-integrin; however, the overall level of alphav-integrin expression was not altered by Ras or Raf. Raf-induced beta3-integrin was observed in primary and established mouse fibroblast lines and in mouse and human endothelial cells. Consistent with previous reports of the ability of the Raf-MEK-ERK signaling pathway to induce beta3-integrin gene transcription in human K-562 erythroleukemia cells, Raf activation in NIH 3T3 cells led to elevated beta3-integrin mRNA. However, unlike immediate-early Raf targets such as heparin binding epidermal growth factor and Mdm2, beta3-integrin mRNA was induced by Raf in a manner that was cycloheximide sensitive. Surprisingly, activation of the Raf-MEK-ERK signaling pathway by growth factors and mitogens had little or no effect on beta3-integrin expression, suggesting that the expression of this gene requires sustained activation of this signaling pathway. In addition, despite the robust induction of cell surface alphavbeta3-integrin expression by Raf in NIH 3T3 cells, such cells display decreased spreading and adhesion, with a loss of focal adhesions and actin stress fibers. These data suggest that oncogene-induced alterations in integrin gene expression may participate in the changes in cell adhesion and migration that accompany the process of oncogenic transformation.

Tumor cell invasion is promoted by activation of protease activated receptor-1 in cooperation with the alpha vbeta 5 integrin

The first prototype of the protease activated receptor (PAR) family, the thrombin receptor PAR1, plays a central role both in the malignant invasion process of breast carcinoma metastasis and in the physiological process of placental implantation. The molecular mechanism underlying PAR1 involvement in tumor invasion and metastasis, however, is poorly defined. Here we show that PAR1 increases the invasive properties of tumor cells primarily by increased adhesion to extracellular matrix components. This preferential adhesion is accompanied by the cytoskeletal reorganization of F-actin toward migration-favoring morphology as detected by phalloidin staining. Activation of PAR1 increased the phosphorylation of focal adhesion kinase and paxillin, and the induced formation of focal contact complexes. PAR1 activation affected integrin cell-surface distribution without altering their level of expression. The specific recruitment of alpha(v)beta(5) to focal contact sites, but not of alpha(v)beta(3) or alpha(5)beta(1), was observed by immunofluorescent microscopy. PAR1 overexpressing cells showed selective reciprocal co-precipitation with alpha(v)beta(5) and paxillin but not with alpha(v)beta(3) that remained evenly distributed under these conditions. This co-immunoprecipitation failed to occur in cells containing the truncated form of PAR1 that lacked the entire cytoplasmic portion of the receptor. Thus, the PAR1 cytoplasmic tail is essential for conveying the cross-talk and recruiting the alpha(v)beta(5) integrin. While PAR1 overexpressing cells were invasive in vitro, as reflected by their migration through a Matrigel barrier, invasion was further enhanced by ligand activation of PAR1. Moreover, the application of anti-alpha(v)beta(5) antibodies specifically attenuated this PAR1 induced invasion. We propose that the activation of PAR1 may lead to a novel cooperation with the alpha(v)beta(5) integrin that supports tumor cell invasion.

Adenoviral gene delivery can inactivate Kupffer cells: role of oxidants in NF-kappaB activation and cytokine production

Kupffer cells play a significant role in the pathogenesis of several liver diseases; therefore, a potential therapeutic strategy would be to inactivate the Kupffer cell with a gene-delivery system. Although recombinant adenovirus provides robust, transgene expression in parenchymal cells, whether adenovirus transduces Kupffer cells is unclear. Thus, the purpose of this study was to evaluate this possibility. In animals infected with adenovirus, Kupffer cells were identified positively to express adenoviral transgenes by immunohistochemical techniques and Western blot analysis, indicating that Kupffer cells are transduced in vivo. Indeed, isolated Kupffer cells were transduced in vitro with recombinant adenovirus in a dose-dependent manner. Moreover, adenoviral transduction of Kupffer cells was blocked by inhibitors of alphaVbeta5 integrin, the co-receptor for adenovirus binding, supporting the hypothesis that adenovirus transduces Kupffer cells via an alphaVbeta5 integrin-dependent mechanism. Indeed, it is shown here that Kupffer cells express alphaVbeta5 integrins. In a functional assay, infection of isolated Kupffer cells with adenovirus containing superoxide dismutase or IkappaB alpha super-repressor blunted LPS-induced nuclear transcription factor kappa B (NF-kappaB) activation and tumor necrosis factor alpha (TNF-alpha) production but not IL-10 production. Moreover, superoxide production was blocked by expression of superoxide dismutase. These data support the hypothesis that LPS-induced NF-kappaB activation and TNF-alpha production in Kupffer cells are oxidant-dependent. These findings suggest that Kupffer cell-targeted approaches may be a potential therapeutic strategy against many inflammatory diseases including early alcohol-induced liver injury.

Integrin-mediated adhesion regulates cell polarity and membrane protrusion through the Rho family of GTPases

Integrin-mediated adhesion is a critical regulator of cell migration. Here we demonstrate that integrin-mediated adhesion to high fibronectin concentrations induces a stop signal for cell migration by inhibiting cell polarization and protrusion. On fibronectin, the stop signal is generated through alpha 5 beta 1 integrin-mediated signaling to the Rho family of GTPases. Specifically, Cdc42 and Rac1 activation exhibits a biphasic dependence on fibronectin concentration that parallels optimum cell polarization and protrusion. In contrast, RhoA activity increases with increasing substratum concentration. We find that cross talk between Cdc42 and Rac1 is required for substratum-stimulated protrusion, whereas RhoA activity is inhibitory. We also show that Cdc42 activity is inhibited by Rac1 activation, suggesting that Rac1 activity may down-regulate Cdc42 activity and promote the formation of stabilized rather than transient protrusion. Furthermore, expression of RhoA down-regulates Cdc42 and Rac1 activity, providing a mechanism whereby RhoA may inhibit cell polarization and protrusion. These findings implicate adhesion-dependent signaling as a mechanism to stop cell migration by regulating cell polarity and protrusion via the Rho family of GTPases.

MDC-9 (ADAM-9/Meltrin gamma) functions as an adhesion molecule by binding the alpha(v)beta(5) integrin

MDC-9 is a widely expressed member of the metalloproteinase/disintegrin/cysteine-rich protein family. The disintegrin domain of MDC-9 lacks an RGD motif but has recently been reported to bind the alpha(6)beta(1) integrin; however, it is unclear whether MDC-9 can bind other integrins. In the present study myeloma cells, but not lymphoblastoid cells, were shown to bind to immobilised, recombinantly expressed MDC-9 disintegrin domain (A9dis). Binding was divalent cation-dependent, being supported by Mn(2+) and Ca(2+). Adhesion of myeloma cells to A9dis was completely inhibited by an antibody to the alpha(v)beta(5) integrin but not by antibodies to other subunits. RGD-containing peptides had no effect on binding, suggesting that MDC-9 interacts with alpha(v)beta(5) in an RGD-independent manner. Flow cytometric analyses demonstrated that myeloma cells, but not lymphoblastoid cells, expressed alpha(v)beta(5) on the cell membrane. These data indicated that the disintegrin domain of MDC-9 can function as an adhesion molecule by interacting with an alpha(v)beta(5) integrin.

alphavbeta5 integrin recruits the CrkII-Dock180-rac1 complex for phagocytosis of apoptotic cells

Integrin receptors are important for the phagocytosis of apoptotic cells. However, little is known about their function in mediating internalization, as previous studies used blocking antibodies for the inhibition of binding. Here we show that the alphavbeta5 receptor mediates both binding and internalization of apoptotic cells. Internalization is dependent upon signalling through the beta5 cytoplasmic tail, and engagement of the alphavbeta5 heterodimer results in recruitment of the p130cas-CrkII-Dock180 molecular complex, which in turn triggers Rac1 activation and phagosome formation. In addition to defining integrin-receptor signalling as critical for the internalization of apoptotic material, our results also constitute the first evidence in human cells that the CED-2-CED-5-CED-10 complex defined in Caenorhabditis elegans is functionally analagous to the CrkII-Dock180-Rac1 molecular complex in mammalian cells. By linking the alphavbeta 5 receptor to this molecular switch, we reveal an evolutionarily conserved signalling pathway that is responsible for the recognition and internalization of apoptotic cells by both professional and non-professional phagocytes.

Transforming growth factor-beta up-regulates the beta 5 integrin subunit expression via Sp1 and Smad signaling

Integrin-mediated cell-matrix interactions play important roles in regulating cell function. Since transforming growth factor-beta (TGF-beta) modulates many osteoblast activities, we hypothesized that the growth factor acts in part by modulating integrin expression. TGF-beta increased cell adhesion to vitronectin and up-regulated the surface level of alpha(v)beta(5) via increasing beta(5) protein synthesis by a transcriptional mechanism. Promoter activity analysis demonstrated that a TGF-beta-responsive element resides between nucleotides -63 and -44. Electrophoretic mobility shift assay and immunoprecipitation/Western studies indicated that the nuclear complex formed using the -66/-42 oligonucleotide contained both Sp1/Sp3 and Smad proteins. Since nuclear Sp1/Sp3 levels were not altered, whereas Smad levels were increased by TGF-beta, we investigated the roles of Smad proteins in the up-regulation of beta(5) gene activation. Co-transfection of cells with beta(5) promoter reporter construct and expression vectors for Smad3, Smad4, and Sp1 increased the stimulatory effect of TGF-beta. Furthermore, expression of dominant negative Smad3 or Smad4 in cells decreased or abolished the stimulation of beta(5) promoter activity by TGF-beta. Smad4 mutant also inhibited the up-regulation of surface beta(5) level by TGF-beta. Thus, TGF-beta increases expression of the integrin beta(5) gene by mechanisms involving Sp1/Sp3 and Smad transcription factors.

Suppression of integrin alpha(v) expression by endothelin-1 in vascular smooth muscle cells

Both integrins and endothelins (ETs) are known to play important roles in vascular remodeling via proliferation, apoptosis, and migration of vascular smooth muscle cells (VSMCs), whose dysfunctions have been implicated in the pathogenesis of end-organ damage associated with hypertension and arteriosclerosis. However, whether there is any interaction between endothelin-1 (ET-1) and integrins remains unknown. Therefore, the aim of the present study was to elucidate whether ET-1 regulates the expression of integrin alpha(v) in rat VSMCs. ET-1 dose- and time-dependently suppressed the integrin alpha(v) messenger RNA (mRNA) transcripts, as quantified by a real-time quantitative polymerase chain reaction (PCR) method, and decreased the transcriptional activity of integrin alpha(v) gene, as demonstrated by integrin alpha(v)-luciferase assay. The inhibitory effect of ET-1 on integrin alpha(v) gene expression was abrogated by an ETA receptor antagonist (BQ123) but not by an ET(B) receptor antagonist (BQ788). ET-1 also suppressed the cell surface expression of integrin alpha(v)beta5 and the adhesion to vitronectin, but not to fibronectin. These results demonstrate that the adhesion of vitronectin to rat VSMCs is inhibited by ET-1 via the ET(A) receptors by suppressing integrin alpha(v) gene transcription, suggesting that ET-1 is involved in regulation of vascular integrin alpha(v) gene expression.

Role of endoproteolytic processing in the adhesive and signaling functions of alphavbeta5 integrin

Some integrin alpha subunits undergo a post-translational cleavage in their extracellular domain. However, the role of this cleavage in integrin function is unclear. Enzymes involved in this maturation belong to the subtilisin-like endoprotease family (convertases). To understand the role of the alpha subunit cleavage in integrin function, we have designed stable transfectants (PDX39P cells) expressing alpha(1)-PDX, a convertase inhibitor. Immunoprecipitation of cell surface proteins from PDX39P showed that alpha(3), alpha(6) and alpha(v) integrins lack endoproteolytic cleavage. We have compared adhesion between PDX39P cells and mock-transfected cells on different extracellular matrix proteins. No difference in adhesion could be observed on laminin-1 and type I collagen, while attachment of PDX39P cells to vitronectin (ligand of the alpha(v)beta(5) integrin) was dramatically reduced. The reduced adhesion of PDX39P cells was not due to changes in integrin affinity as determined by solid-phase receptor assay in a cell-free environment. Intracellular signaling pathways activated by alpha(v) integrin ligation were also affected in PDX39P cells. It thus seems that the absence of endoproteolytic cleavage of alpha(v) integrins has important consequences on signal transduction pathways leading to alterations in integrin function such as cell adhesion.

Stable integration of large (>100 kb) PAC constructs in HaCaT keratinocytes using an integrin-targeting peptide delivery system

Transfer of large DNA constructs in gene therapy studies is being recognised for its importance in maintaining the natural genomic environment of the gene of interest and providing tissue-specific regulation and control. However, methods used to deliver such constructs have been poorly studied. We used a receptor-mediated, integrin-targeting transfection system enhanced by liposomes, to deliver a 110 kb PAC (P1-based artificial chromosome) to HaCaT keratinocytes. The PAC contained the collagen VII locus, an EGFP (enhanced green fluorescent protein) reporter gene and the puromycin resistance gene (pac) to allow selection of stably transfected cells. Analysis of puromycin resistant and EGFP-expressing colonies by Western blot showed that collagen VII production increased dramatically after transfection, indicating successful transfer of a large fully functional genomic locus. Fluorescent in situ hybridisation (FISH) and Southern blot analysis revealed that the PAC had integrated as at least one copy per cell. EGFP expression has persisted for 35 weeks, suggesting stable transgene expression. We conclude that the integrin-targeting peptide method of gene delivery is an effective means of stably delivering large DNA constructs to human keratinocytes and could be of benefit for genomic gene therapy approaches.

Molecular basis of ligand recognition by integrin alpha 5beta 1. I. Specificity of ligand binding is determined by amino acid sequences in the second and third NH2-terminal repeats of the alpha subunit

The NH(2)-terminal portion (putative ligand-binding domain) of alpha subunits contains 7 homologous repeats, the last 3 or 4 of which possess divalent cation binding sequences. These repeats are predicted to form a seven-bladed beta-propeller structure. To map ligand recognition sites on the alpha(5) subunit we have taken the approach of constructing and expressing alpha(V)/alpha(5) chimeras. Although the NH(2)-terminal repeats of alpha(5) and alpha(V) are >50% identical at the amino acid level, alpha(5)beta(1) and alpha(V)beta(1) show marked differences in their ligand binding specificities. Thus: (i) although both integrins recognize the Arg-Gly-Asp (RGD) sequence in fibronectin, the interaction of alpha(5)beta(1) but not of alpha(V)beta(1) with fibronectin is strongly dependent on the "synergy" sequence Pro-His-Ser-Arg-Asn; (ii) alpha(5)beta(1) binds preferentially to RGD peptides in which RGD is followed by Gly-Trp (GW) whereas alpha(V)beta(1) has a broader specificity; (iii) only alpha(5)beta(1) recognizes peptides containing the sequence Arg-Arg-Glu-Thr-Ala-Trp-Ala (RRETAWA). Therefore, amino acid residues involved in ligand recognition by alpha(5)beta(1) can potentially be identified in gain-of-function experiments by their ability to switch the ligand binding properties of alpha(V)beta(1) to those of alpha(5)beta(1). By introducing appropriate restriction enzyme sites, or using site-directed mutagenesis, parts of the NH(2)-terminal repeats of alpha(V) were replaced with the corresponding regions of the alpha(5) subunit. Chimeric subunits were expressed on the surface of Chinese hamster ovary-B2 cells (which lack endogenous alpha(5)) as heterodimers with hamster beta(1). Stable cell lines were generated and tested for their ability to attach to alpha(5)beta(1)-selective ligands. Our results demonstrate that: (a) the first three NH(2)-terminal repeats contain the amino acid sequences that determine ligand binding specificity and the same repeats include the epitopes of function blocking anti-alpha subunit mAbs; (b) the divalent cation-binding sites (in repeats 4-7) do not confer alpha(5)beta(1)- or alpha(V)beta(1)-specific ligand recognition; (c) amino acid residues Ala(107)-Tyr(226) of alpha(5) (corresponding approximately to repeats 2 and 3) are sufficient to change all the ligand binding properties of alpha(V)beta(1) to those of alpha(5)beta(1); (d) swapping a small part of a predicted loop region of alpha(V) with the corresponding region of alpha(5) (Asp(154)-Ala(159)) is sufficient to confer selectivity for RGDGW and the ability to recognize RRETAWA.

Association of p130CAS with phosphatidylinositol-3-OH kinase mediates adenovirus cell entry

The Crk-associated substrate, p130(CAS), has been implicated in the regulation of the actin cytoskeleton following ligation of cell integrins with the extracellular matrix. Integrin-mediated cell adhesion involves p130(CAS) association with focal adhesion kinase (p125(FAK)). Internalization/cell entry of type 2 and type 5 adenoviruses (Ad) is also mediated by alpha(v) integrins. However, expression of dominant negative forms of p125(FAK) does not alter virus entry, and Ad entry occurs normally in p125(FAK)-deficient fibroblasts. We now provide evidence that Ad internalization, a process which is mediated by alpha(v) integrins, also requires p130(CAS) and phosphatidylinositol-3-OH kinase (PI 3-kinase). Ad induces p130(CAS) phosphorylation and inhibition of p130(CAS) phosphorylation by tyrphostin and genistein, or expression of the substrate domain deleted p130(CAS) blocks Ad internalization. p130(CAS) was also found to associate with the p85 subunit of PI 3-kinase through its proline-rich domain during virus internalization and expression of p130(CAS) containing a deleted proline-rich domain (PRD) inhibited adenovirus cell entry. We showed further that the RPLPSPP motif in the proline-rich region of p130(CAS) interacts with the SH3 domain of p85/PI 3-kinase. These studies reveal the molecular basis by which p130(CAS) coordinates the signaling pathways involved in integrin-mediated Ad endocytosis.

Foot-and-mouth disease virus is a ligand for the high-affinity binding conformation of integrin alpha5beta1: influence of the leucine residue within the RGDL motif on selectivity of integrin binding

Field isolates of foot-and-mouth disease virus (FMDV) use RGD-dependent integrins as receptors for internalization, whereas strains that are adapted for growth in cultured cell lines appear to be able to use alternative receptors like heparan sulphate proteoglycans (HSPG). The ligand-binding potential of integrins is regulated by changes in the conformation of their ectodomains and the ligand-binding state would be expected to be an important determinant of tropism for viruses that use integrins as cellular receptors. Currently, alphavbeta3 is the only integrin that has been shown to act as a receptor for FMDV. In this study, a solid-phase receptor-binding assay has been used to characterize the binding of FMDV to purified preparations of the human integrin alpha5beta1, in the absence of HSPG and other RGD-binding integrins. In this assay, binding of FMDV resembled authentic ligand binding to alpha5beta1 in its dependence on divalent cations and specific inhibition by RGD peptides. Most importantly, binding was found to be critically dependent on the conformation of the integrin, as virus bound only after induction of the high-affinity ligand-binding state. In addition, the identity of the amino acid residue immediately following the RGD motif is shown to influence differentially the ability of FMDV to bind integrins alpha5beta1 and alphavbeta3 and evidence is provided that alpha5beta1 might be an important FMDV receptor in vivo.

Adenoviral-mediated gene transfer into ex vivo expanded human bone marrow mesenchymal progenitor cells

OBJECTIVE

Based on their differentiation properties and facilely of ex vivo expansion, human bone marrow mesenchymal progenitor cells (MPC), are considered as attractive targets to deliver foreign genes to the bone marrow or other mesenchymal tissues. In this study we investigated the feasibility of transduce MPC with adenoviral vectors (Adv).

METHODS

MPC were expanded ex vivo and transduced with replication-defective Adv-containing reporter genes (lacZ or GFP) under the control of CMV promoter. Transfection efficiency was assessed by microscopical scoring or by flow cytometry. Expression and involvement of Adv-attachment (CAR) and Adv-internalization (integrins alphav) receptors were evaluated by flow cytometric studies.

RESULTS

Transgene expression analysis showed that only 19%+/-3% of cells expressed the transgenes at high levels. MPC express the attachment and internalization receptors required for Adv infection. While integrins alphavbeta3 and alphavbeta5 are expressed by all MPC, CAR is solely expressed by a fraction of low size cells. Antibodies against CAR and alphavbeta5, but not against alphavbeta3, blocked Adv-mediated gene transfer into MPC, showing that CAR and alphavbeta5 are required for infection. Because alphavbeta5, as compared with CAR, is overexpressed in MPC, the results suggest that the efficiency of Adv-mediated gene transfer into MPC depends on the level of CAR expression.

CONCLUSION

These findings demonstrate that Adv may be useful to engineer a subpopulation of ex vivo expanded human mesenchymal progenitors, with a high level of transgene expression.

Empirical advantages of adeno associated viral vectors in vivo gene therapy for arthritis

OBJECTIVE

To evaluate the utility of the adeno associated viral (AAV) vector for gene delivery to joint cells in vivo and in vitro, and to assess its potential as a vector for arthritis gene therapy.

METHODS

A recombinant AAV (rAAV) vector expressing the bacterial beta-galactosidase (beta-gal) gene (rAAV-CMV-LacZ) was directly introduced into healthy-normal mouse knees, or arthritic knees in mice overexpressing tumor necrosis factor-alpha (hTNFalpha-Tg). Beta-gal expression levels were determined by immunohistochemistry and chemiluminescence. The transduction efficiency of this vector on primary fibroblast-like synoviocytes (FLS) in vitro was determined by FACS. The effects of UV and gamma-irradiation as well as TNF-alpha on transduction efficiency were determined using the same methods.

RESULTS

We found little evidence of rAAV transduction in the joint cells of healthy mice. Target gene expression was detected in all animals at Day 3, and peaked at Day 7 before returning to baseline levels 21 days after injection. In contrast, synoviocytes, articular chondrocytes, and meniscal cells of diseased mice were transduced by rAAV-CMV-LacZ in hTNFalpha-Tg animals. Transduction efficiencies correlated with joint damage, and target gene expression was up to 10-fold greater than that seen in the normal mice. In vitro, we found that rAAV transduction of FLS can be enhanced by pretreatment with UV or gamma-irradiation and TNF-alpha stimulation.

CONCLUSION

We find that rAAV vectors have several empirical advantages for in vivo gene therapy for arthritis: (1) rAAV preferentially transduces arthritic joint cells in vivo. (2) rAAV can transduce both FLS and chondrocytes in vivo. (3) rAAV transduction of FLS can be augmented by pretreatment with agents that induce DNA repair enzymes.

Regulation of adenovirus membrane penetration by the cytoplasmic tail of integrin beta5

Adenovirus (Ad) cell entry involves sequential interactions with host cell receptors that mediate attachment (CAR), internalization (alphavbeta3 and alphavbeta5), and penetration (alphavbeta5) of the endosomal membrane. These events allow the virus to deliver its genome to the nucleus. While integrins alphavbeta3 and alphavbeta5 both promote Ad internalization into cells, integrin alphavbeta5 selectively facilitates Ad-mediated membrane permeabilization and endosome rupture. In the experiments reported herein, we demonstrate that the intracellular domain of the integrin beta5 subunit specifically regulates Ad-mediated membrane permeabilization and gene delivery. CS-1 melanoma cells expressing a truncated integrin beta5 or a chimeric (beta5-beta3) cytoplasmic tail (CT) supported normal levels of Ad endocytosis but had reduced Ad-mediated gene delivery and membrane permeabilization relative to cells expressing a wild-type integrin beta5. Thin-section electron microscopy revealed that virion particles were capable of being endocytosed into cells expressing a truncated beta5CT, but they failed to escape cytoplasmic vesicles and translocate to the nucleus. Site-specific mutagenesis studies suggest that a C-terminal TVD motif in the beta5CT plays a major role in Ad membrane penetration.

Opposing role of mitogen-activated protein kinase subtypes, erk-1/2 and p38, in the regulation of chondrogenesis of mesenchymes

The present studies were performed to determine subtype-specific roles of mitogen-activated protein kinase in chondrogenesis. Erk-1/2 activities, downstream of protein kinase C, decreased as chondrogenesis proceeded, whereas p38 activities, independent of protein kinase C, continuously increased during chondrogenesis. Inhibition of Erk-1/2 with PD98059 enhanced chondrogenesis up to 1. 7-fold, whereas inhibition of p38 with SB203580 reduced it to about 30% of the control level. Inhibition of Erk-1/2 or p38 did not affect precartilage condensation. However, cartilage nodule formation was significantly blocked by the inhibition of p38, whereas Erk-1/2 inhibition did not affect it. Modulation of chondrogenesis by the inhibition of Erk-1/2 and p38 was accompanied by altered expression of adhesion molecules in an opposite way. Expression of N-cadherin was reduced as chondrogenesis proceeded. Inhibition of p38 caused sustained expression of N-cadherin, whereas Erk-1/2 inhibition accelerated the reduction of N-cadherin expression. Expression of integrin alpha5beta1 and fibronectin were found to transiently increase during chondrogenesis. Inhibition of p38 caused continuous increase of expression of these molecules, whereas Erk-1/2 inhibition accelerated the decrease of expression of these molecules at a later period of chondrogenesis. Because temporal expression of these adhesion molecules regulates chondrogenesis, the above results indicate that Erk-1/2 and p38 conversely regulate chondrogenesis at post-precartilage condensation stages by modulating expression of adhesion molecules.

Integrins alpha5beta1, alphavbeta1, and alphavbeta6 collaborate in squamous carcinoma cell spreading and migration on fibronectin

The expression of alphavbeta6 fibronectin/tenascin receptor integrin is induced in malignant transformation of oral epithelium. In this study, we demonstrate the contribution of alphavbeta6 as well as other fibronectin receptor integrins in squamous cell carcinoma (SCC) cell adhesion and migration. Of 11 SCC cell lines isolated from the head and neck area, 8 (73%) expressed alphavbeta6 integrin on the cell surface. Three cell lines were chosen for further functional experiments: 1 with relatively high, 1 with moderate, and 1 with minimal surface expression of alphavbeta6 integrin. In addition to alphavbeta6, all 3 cell lines expressed alpha5beta1 and alphavbeta1 fibronectin receptor integrins. Function-blocking experiments with inhibitory anti-integrin antibodies showed that all these three integrins were functional in SCC cell spreading on fibronectin. Integrin alphavbeta6, however, was not used as a primary but as an alternative fibronectin receptor by SCC cells, as the inhibitory anti-beta6 integrin antibody alone had no effect on spreading. In migration, however, alphavbeta6, alpha5beta1, and alphavbeta1 integrins were all used in cooperation. The presence of alphavbeta1 integrin in SCC cells is a novel finding as is its contribution to SCC cell migration. When one or two of these three receptors were blocked, the cells demonstrated an adaptive ability to remain migratory using integrins that were not targeted by antibodies. Utilization of a combination of receptors of different affinities may be beneficial for SCC cell migration versatility.

Normal development, wound healing, and adenovirus susceptibility in beta5-deficient mice

Integrins have been shown to play important roles in embryonic development, wound healing, metastasis, and other biological processes. alphavbeta5 is a receptor for RGD-containing extracellular matrix proteins that has been suggested to be important in cutaneous wound healing and adenovirus infection. To examine the in vivo function of this receptor, we have generated mice lacking beta5 expression, using homologous recombination in embryonic stem cells. Mice homozygous for a null mutation of the beta5 subunit gene develop, grow, and reproduce normally. Keratinocytes harvested from beta5(-/-) mice demonstrate impaired migration on and adhesion to the alphavbeta5 ligand, vitronectin. However, the rate of healing of cutaneous wounds is not different in beta5(-/-) and beta5(+/+) mice. Furthermore, keratinocytes and airway epithelial cells obtained from null mice show adenovirus infection efficiency equal to that from wild-type mice. These data suggest that alphavbeta5 is not essential for normal development, reproduction, adenovirus infection, or the healing of cutaneous wounds.

Different integrins mediate cell spreading, haptotaxis and lateral migration of HaCaT keratinocytes on fibronectin

Collaborative role of various fibronectin-binding integrins (alpha5beta1, alphavbeta1 and alphavbeta6) as mediators of cell adhesion and migration on fibronectin was studied using cultured HaCaT keratinocytes. This cell line spontaneously expressed all three fibronectin-binding integrins. In addition, the expression of alphavbeta6 integrin was strongly and specifically upregulated by transforming growth factor-beta1 (TGFbeta1) whereas the amount of other integrins remained practically unchanged on the cell surface. Adhesion, spreading and motility of HaCaT keratinocytes on fibronectin were promoted by TGFbeta1. Based on antibody blocking experiments, both untreated and TGFbeta1-treated HaCaT cells used alphavbeta6 integrin as their main fibronectin receptor for cell spreading. In contrast to TGFbeta1-treated cells, the untreated cells also needed alpha5beta1 integrin for maximal cell spreading on fibronectin. Combinations of antibodies blocking both of these receptors totally prevented spreading of both untreated and TGFbeta1-treated cells. Haptotactic motility of individual HaCaT cells through fibronectin-coated membranes was again mainly dependent on alphavbeta6 integrin, while alphavbeta1 and alpha5beta1 integrins played a lesser role both in untreated and TGFbeta1-treated HaCaT cells. However, unlike haptotaxis, lateral migration of HaCaT cell sheet was mainly mediated by beta1 integrins, and alphavbeta6 integrin showed a minor role. The migration process appeared to involve a number of beta1 integrins that could adaptively replace each other when blocking antibodies were present. Thus, keratinocytes appear to use different fibronectin receptors for different functions, such as cell spreading, haptotaxis and lateral migration. The cells can also adapt to a situation where one receptor is unfunctional by switching to another receptor of the same ligand.

Tumor necrosis factor alpha regulates alpha(v)beta5 integrin expression by osteoclast precursors in vitro and in vivo

Early osteoclast precursors, in the form of murine bone marrow macrophages (BMMs), while expressing no detectable alpha(v)beta3 integrin, contain abundant alpha(v)beta5 and attach to matrix in an alpha(v) integrin-dependent manner. Furthermore, alpha(v)beta5 expression by osteoclast precursors progressively falls as they assume the resorptive phenotype. We find the osteoclastogenic agent, tumor necrosis factor-alpha, (TNF) down-regulates alpha(v)beta5 expression by BMMS via attenuation of beta5 messenger RNA (mRNA) t1/2. Using BMMs from TNF receptor knockout mice we establish the p55 receptor transmits the beta5 suppressive effect. The functional implications of TNF-mediated alpha(v)beta5 down-regulation are underscored by the capacity of an alpha(v) inhibitory peptide mimetic to prevent spreading by BMMs expressing abundant alpha(v)beta5 while failing to impact those in which the integrin has been diminished by TNF. Finally, beta5 mRNA in BMMs of wild-type mice administered lipopolysaccharide (LPS) progressively falls with time of in vivo treatment. Alternatively, beta5 mRNA does not decline in BMMs of LPS-treated mice lacking both TNF receptors, documenting down-regulation of the beta5 integrin subunit, in vivo, is mediated by TNF. Thus, matrix attachment of osteoclast precursors and mature osteoclasts are governed by distinct alpha(v) integrins which are differentially regulated by specific cytokines.

In vitro adenoviral vector p53-mediated transduction and killing correlates with expression of coxsackie-adenovirus receptor and alpha(nu)beta5 integrin in SUDHL-1 cells derived from anaplastic large-cell lymphoma

Adenoviral vector-mediated p53 expression induced apoptosis is a well established gene therapy approach that has been evaluated extensively in epithelial tumors but only recently in lymphoid malignancies mainly due to the known resistance of the lymphoid lineage to adenovirus infection. Recently, it was shown that this resistance is not absolute and that cell lines derived from anaplastic large cell lymphoma (ALCL) and some other lymphoid malignancies are efficiently transduced by adenoviral vectors. Normal circulating T lymphocytes do not express coxsackie-adenovirus receptor (CAR) and alpha(nu)beta integrins and are relatively resistant to infection by adenovirus. These molecules serve as receptors for adenovirus entry into the cells. ALCL-derived SUDHL-1 cells were evaluated for transduction efficiency and expression of p53 after infection with an adenoviral vector containing wild-type p53 (AdWTp53). Cells derived from ALCL and circulating mononucleated cells (MNCs) were also evaluated for expression of CAR and alpha(nu)beta integrins. AdWTp53-mediated expression of p53 resulted in p21/WAF1 induction, G1 arrest, and apoptosis in SUDHL-1 cells. The expression of CAR and alpha(nu)beta5 integrin was high in SUDHL-1 cells and comparable to levels observed with epithelial tumor cells, but it was absent in MNCs. The susceptibility to adenoviral vector transduction of the tumor-derived cells implies an important biological difference between them and circulating MNCs, possibly underlying the malignant transformation that ALCL cells undergo. Further studies will be required to evaluate this initial observation in more cell lines and tissue derived from ALCL.

Review: resolution issues in single-particle reconstruction

Specific factors that affect the resolution of single-particle reconstructions are discussed. We present reconstructions of six particles (DNA-dependent protein kinase catalytic subunit, alphaB-crystallin, the ribonucleoprotein vault, hepatitis A virus, adenovirus type 2, and the adenovirus type 12/alpha(v)beta5 integrin complex), which have a variety of symmetries (asymmetric to 60-fold) and a wide range of molecular masses (470 kDa to 150 MDa). In the case of icosahedral viruses, we have found that applying a "soft" mask to remove regions of disordered density improves the resolution given by the Fourier shell correlation 0.5 criterion. This masking procedure is also useful during refinement to improve the quality of the reference model and thus aid in precise alignment of the particle images. For asymmetric particles, we note that image classification, although often a necessary step to generate a first reconstruction, can limit the achievable resolution. The diameter of the particle and the available computational power can also affect the resolution, as can structural variability within the particle.

Integrin alphaVbeta5 is not involved in adeno-associated virus type 2 (AAV2) infection

alphaVbeta5 integrin was recently proposed as a coreceptor for adeno-associated virus type 2 (AAV2) infection (Summerford et al., 1999, Nat. Med. 5, 78-82), based mainly on the direct binding of AAV2 to denatured beta5 by virus overlay assay. In studies using purified natural or recombinant human integrin alphaVbeta5 we were unable to demonstrate AAV2 binding, either by virus overlay or by liquid binding assay. Furthermore, neither purified integrin alphaVbeta5, nor RGD peptides, nor functional blocking monoclonal antibody blocked rAAV2 transduction. These data strongly suggest that integrin alphaVbeta5 is not involved in AAV2 infection.

Urokinase receptor interacts with alpha(v)beta5 vitronectin receptor, promoting urokinase-dependent cell migration in breast cancer

Perturbation of adhesive interactions at cell-substratum and cell-cell contact sites is a critical event in the multistep process of cancer invasion. Recent studies indicate that the urokinase receptor (uPAR) is associated in large molecular complexes with other molecules, such as integrins. To test the possibility that uPAR may physically and functionally interact with vitronectin (Vn) receptors, we determined the expression level of uPAR, alpha(v)beta3, and alpha(v)beta5 Vn receptors in 10 human breast carcinomas. Here, we show the ability of uPAR to physically associate with alpha(v)beta5 in the breast carcinomas examined. The functional effects of this interaction were studied using HT1080 human fibrosarcoma and MCF-7 human breast carcinoma cell lines, both exhibiting a urokinase-dependent physical association between uPAR and alpha(v)beta5. Both cell lines respond to urokinase or to its noncatalytic amino-terminal fragment by exhibiting remarkable cytoskeletal rearrangements that are mediated by alpha(v)beta5 and require protein kinase C activity. On the contrary, binding of Vn to alpha(v)beta5 results in the protein kinase C-independent formation of F-actin containing microspike-type structures. Furthermore, alpha(v)beta5 is required for urokinase-directed, receptor-dependent MCF-7 and HT1080 cell migration. These data show that uPAR association with alpha(v)beta5 leads to a functional interaction of these receptors and suggest that uPAR directs cytoskeletal rearrangements and cell migration by altering alpha(v)beta5 signaling specificity.

Involvement of alpha5beta1 integrins in interleukin 8 production induced by oral viridans streptococcal protein I/IIf in cultured endothelial cells

Using human endothelial cells, we define a mechanism that accounts for the induction of interleukin 8 (IL-8) by protein I/IIf, an adhesin from Streptococcus mutans serotype f. We report that protein I/IIf interactions with endothelial cells increased the tyrosine phosphorylation of three cellular components with relative mass of 145,000, 125,000 and 70,000 in endothelial cells. These proteins were identified as phospholipase Cgamma (PLCy), focal adhesion kinase (FAK) and paxillin after immunoprecipitation with monoclonal antibodies (mAbs) and immunoblotting with antiphosphotyrosine mAbs. These results suggested that beta1 integrins could be one of the components implicated in the modulin activity of protein I/IIf. By incubating protein I/IIf with either purified alpha5beta1 integrins or with alpha5beta1 integrins overexpressing CHO cells, we demonstrated that alpha5beta1 integrins act as cell receptors for protein I/IIf. We also showed that protein I/IIf interactions with alpha5beta1 integrins lead to IL-8 secretion. Using specific inhibitors, we demonstrated that protein I/IIf-induced IL-8 release involves mitogen-activated protein kinases (MAPKs), and that PLCgamma and PKC also seem to contribute to protein I/IIf stimulation. However, PI-3K activation is not involved in IL-8 release. Altogether, these results indicate that, after binding to alpha5beta1 integrins, protein I/IIf induces IL-8 release by activating the MAPKs signalling pathways.

Role of alpha(v) integrins in adenovirus cell entry and gene delivery

Adenoviruses (Ad) are a significant cause of acute infections in humans; however, replication-defective forms of this virus are currently under investigation for human gene therapy. Approximately 20 to 25% of all the gene therapy trials (phases I to III) conducted over the past 10 years involve the use of Ad gene delivery for treatment inherited or acquired diseases. At present, the most promising applications involve the use of Ad vectors to irradicate certain nonmetastatic tumors and to promote angiogenesis in order to alleviate cardiovascular disease. While specific problems of using Ad vectors remain to be overcome (as is true for almost all viral and nonviral delivery methods), a distinct advantage of Ad is the extensive knowledge of its macromolecular structure, genome organization, sequence, and mode of replication. Moreover, significant information has also been acquired on the interaction of Ad particles with distinct host cell receptors, events which strongly affect virus tropism. This review provides an overview of the structure and function of Ad attachment (coxsackievirus and Ad receptor [CAR]) and internalization (alpha(v) integrins) receptors and discusses their precise role in virus infection and gene delivery. Recent structure studies of integrin-Ad complexes by cryoelectron microscopy are also highlighted. Finally, unanswered questions arising from the current state of knowledge of Ad-receptor interactions are presented in the context of improving Ad vectors for future human gene therapy applications.

Fibronectin-binding protein acts as Staphylococcus aureus invasin via fibronectin bridging to integrin alpha5beta1

The ability of Staphylococcus aureus to invade mammalian cells may explain its capacity to colonize mucosa and to persist in tissues after bacteraemia. To date, the underlying molecular mechanisms of cellular invasion by S. aureus are unknown, despite its high prevalence and difficulties in treatment. Here, we show cellular invasion as a novel function for an S. aureus adhesin, previously implicated solely in attachment. S. aureus, but not S. epidermidis, invaded epithelial 293 cells in a temperature- and F-actin-dependent manner. Formaldehyde-fixed and live bacteria were equally invasive, suggesting that no active bacterial process was involved. All clinical S. aureus isolates analysed, but only a subset of laboratory strains, were invasive. Fibronectin-binding proteins (FnBPs) acted as S. aureus invasins, because: (i) FnBP deletion mutants of invasive laboratory strains lost invasiveness; (ii) expression of FnBPs in noninvasive strains conferred invasiveness; and (iii) the soluble isolated fibronectin-binding domain of FnBP (D1-D4) completely blocked invasion. Integrin alpha5beta1 served as host cell receptor, which interacted with staphylococcal FnBPs through cellular or soluble fibronectin. FnBP-deficient mutants lost invasiveness for epithelial cells, endothelial cells and fibroblasts. Thus, fibronectin-dependent bridging between S. aureus FnBPs and host cell integrin alpha5beta1 is a conserved mechanism for S. aureus invasion of human cells. This may prove useful in developing new therapeutic and vaccine strategies for S. aureus infections.

Structure of adenovirus complexed with its internalization receptor, alphavbeta5 integrin

The three-dimensional structure of soluble recombinant integrin alphavbeta5 bound to human adenovirus types 2 and 12 (Ad2 and -12) has been determined at approximately 21-A resolution by cryoelectron microscopy (cryo-EM). The alphavbeta5 integrin is known to promote Ad cell entry. Cryo-EM has shown that the integrin-binding RGD (Arg-Gly-Asp) protrusion of the Ad2 penton base protein is highly mobile (P. L. Stewart, C. Y. Chiu, S. Huang, T. Muir, Y. Zhao, B. Chait, P. Mathias, and G. R. Nemerow, EMBO J. 16:1189-1198, 1997). Sequence analysis indicated that the Ad12 RGD surface loop is shorter than that of Ad2 and probably less flexible, hence more suitable for structural characterization of the Ad-integrin complex. The cryo-EM structures of the two virus-receptor complexes revealed a ring of integrin density above the penton base of each virus serotype. As expected, the integrin density in the Ad2 complex was diffuse while that in the Ad12 complex was better defined. The integrin consists of two discrete subdomains, a globular domain with an RGD-binding cleft approximately 20 A in diameter and a distal domain with extended, flexible tails. Kinetic analysis of Ad2 interactions with alphavbeta5 indicated approximately 4.2 integrin molecules bound per penton base at close to saturation. These results suggest that the precise spatial arrangement of five RGD protrusions on the penton base promotes integrin clustering and the signaling events required for virus internalization.

Role of actin stress fibres in the development of the intervertebral disc: cytoskeletal control of extracellular matrix assembly

Orientation of collagen fibrils is a key event in the development of many tissues. In the intervertebral disc, the outer annulus fibrosus comprises lamellae of parallel collagen fibres, the direction of orientation of the long axis of which alternates in angle between lamellae. In development, this organisation is preceded by the formation of sheets of oriented fibroblasts, which then deposit the oriented lamellae. Here, using fluorescent labelling, confocal and electron microscopic techniques on developmental series, we show that the orientation of cells in lamellae is associated with the formation of adherens junctions intercellularly, involving cadherins and vinculin, and longitudinal stress fibres (label for filamentous actin and tropomyosin) intracellularly. The stress fibres direct the initial elongation of cells and control the deposition of oriented extracellular matrix via junctional complexes with the matrix involving vinculin and alpha 5 beta 1 integrins, which in turn promote the formation of oriented fibronectin at the cell surface; oriented collagen is deposited between cells at the same stages. Shortly after birth, the stress fibres disappear, probably because cells now gain orientational cues from the matrix, and are undergoing differentiation-related changes to form fibrocartilage cells. Dev Dyn 1999;215:179-189.