Interactions of soluble recombinant integrin alphav beta5 with human adenoviruses

Integrin-Targeting Strategies for Adenovirus Gene Therapy

Numerous human adenovirus (AdV) types are endowed with arginine-glycine-aspartic acid (RGD) sequences that enable them to recognize vitronectin-binding (αv) integrins. These RGD-binding cell receptors mediate AdV entry into host cells, a crucial early step in virus infection. Integrin interactions with adenoviruses not only initiate receptor-mediated endocytosis but also facilitate AdV capsid disassembly, a prerequisite for membrane penetration by AdV protein VI. This review discusses fundamental aspects of AdV-host interactions mediated by integrins. Recent efforts to re-engineer AdV vectors and non-viral nanoparticles to target αv integrins for bioimaging and the eradication of cancer cells will also be discussed.

Adenovirus receptors on antigen-presenting cells of the skin

Skin, the largest human organ, is part of the first line of physical and immunological defense against many pathogens. Understanding how skin antigen-presenting cells (APCs) respond to viruses or virus-based vaccines is crucial to develop antiviral pharmaceutics, and efficient and safe vaccines. Here, we discuss the way resident and recruited skin APCs engage adenoviruses and the impact on innate immune responses. This article is protected by copyright. All rights reserved.

Visualization of integrin molecules by fluorescence imaging and techniques

Integrin molecules are transmembrane αβ heterodimers involved in cell adhesion, trafficking, and signaling. Upon activation, integrins undergo dynamic conformational changes that regulate their affinity to ligands. The physiological functions and activation mechanisms of integrins have been heavily discussed in previous studies and reviews, but the fluorescence imaging techniques -which are powerful tools for biological studies- have not. Here we review the fluorescence labeling methods, imaging techniques, as well as Förster resonance energy transfer assays used to study integrin expression, localization, activation, and functions.

HIV-1 Tat Protein Enters Dysfunctional Endothelial Cells via Integrins and Renders Them Permissive to Virus Replication

Previous work has shown that the Tat protein of Human Immunodeficiency Virus (HIV)-1 is released by acutely infected cells in a biologically active form and enters dendritic cells upon the binding of its arginine-glycine-aspartic acid (RGD) domain to the α5β1, αvβ3, and αvβ5 integrins. The up-regulation/activation of these integrins occurs in endothelial cells exposed to inflammatory cytokines that are increased in HIV-infected individuals, leading to endothelial cell dysfunction. Here, we show that inflammatory cytokine-activated endothelial cells selectively bind and rapidly take up nano-micromolar concentrations of Tat, as determined by flow cytometry. Protein oxidation and low temperatures reduce Tat entry, suggesting a conformation- and energy-dependent process. Consistently, Tat entry is competed out by RGD-Tat peptides or integrin natural ligands, and it is blocked by anti-α5β1, -αvβ3, and -αvβ5 antibodies. Moreover, modelling–docking calculations identify a low-energy Tat-αvβ3 integrin complex in which Tat makes contacts with both the αv and β3 chains. It is noteworthy that internalized Tat induces HIV replication in inflammatory cytokine-treated, but not untreated, endothelial cells. Thus, endothelial cell dysfunction driven by inflammatory cytokines renders the vascular system a target of Tat, which makes endothelial cells permissive to HIV replication, adding a further layer of complexity to functionally cure and/or eradicate HIV infection.

Glycomics and Proteomics Approaches to Investigate Early Adenovirus-Host Cell Interactions

Adenoviruses as most viruses rely on glycan and protein interactions to attach to and enter susceptible host cells. The Adenoviridae family comprises more than 80 human types and they differ in their attachment factor and receptor usage, which likely contributes to the diverse tropism of the different types. In the past years, methods to systematically identify glycan and protein interactions have advanced. In particular sensitivity, speed and coverage of mass spectrometric analyses allow for high-throughput identification of glycans and peptides separated by liquid chromatography. Also, developments in glycan microarray technologies have led to targeted, high-throughput screening and identification of glycan-based receptors. The mapping of cell surface interactions of the diverse adenovirus types has implications for cell, tissue, and species tropism as well as drug development. Here we review known adenovirus interactions with glycan- and protein-based receptors, as well as glycomics and proteomics strategies to identify yet elusive virus receptors and attachment factors. We finally discuss challenges, bottlenecks, and future research directions in the field of non-enveloped virus entry into host cells.

Interaction of Human Enterochromaffin Cells with Human Enteric Adenovirus 41 Leads to Serotonin Release and Subsequent Activation of Enteric Glia Cells

Human adenovirus 41 (HAdV-41) causes acute gastroenteritis in young children. The main characteristics of HAdV-41 infection are diarrhea and vomiting. Nevertheless, the precise mechanism of HAdV-41-induced diarrhea is unknown, as a suitable small-animal model has not been described. In this study, we used the human midgut carcinoid cell line GOT1 to investigate the effect of HAdV-41 infection and the individual HAdV-41 capsid proteins on serotonin release by enterochromaffin cells and on enteric glia cell (EGC) activation. We first determined that HAdV-41 could infect the enterochromaffin cells. Immunofluorescence staining revealed that the cells expressed HAdV-41-specific coxsackievirus and adenovirus receptor (CAR); flow cytometry analysis supported these findings. HAdV-41 infection of the enterochromaffin cells induced serotonin secretion dose dependently. In contrast, control infection with HAdV-5 did not induce serotonin secretion in the cells. Confocal microscopy studies of enterochromaffin cells infected with HAdV-41 revealed decreased serotonin immunofluorescence compared to that in uninfected cells. Incubation of the enterochromaffin cells with purified HAdV-41 short fiber knob and hexon proteins increased the serotonin levels in the harvested cell supernatant significantly. HAdV-41 infection could also activate EGCs, as shown in the significantly altered expression of glia fibrillary acidic protein (GFAP) in EGCs incubated with HAdV-41. The EGCs were also activated by serotonin alone, as shown in the significantly increased GFAP staining intensity. Likewise, EGCs were activated by the cell supernatant of HAdV-41-infected enterochromaffin cells.IMPORTANCE The nonenveloped human adenovirus 41 causes diarrhea, vomiting, dehydration, and low-grade fever mainly in children under 2 years of age. Even though acute gastroenteritis is well described, how human adenovirus 41 causes diarrhea is unknown. In our study, we analyzed the effect of human adenovirus 41 infection on human enterochromaffin cells and found it stimulates serotonin secretion in the cells, which is involved in regulation of intestinal secretion and gut motility and can also activate enteric glia cells, which are found in close proximity to enterochromaffin cells in vivo This disruption of gut barrier homeostasis as maintained by these cells following human adenovirus 41 infection might be a mechanism in enteric adenovirus pathogenesis in humans and could indicate a possible serotonin-dependent cross talk between human adenovirus 41, enterochromaffin cells, and enteric glia cells.

Human Adenovirus Type 37 Uses αVβ1 and α3β1 Integrins for Infection of Human Corneal Cells

Epidemic keratoconjunctivitis (EKC) is a severe, contagious ocular disease that affects 20 to 40 million individuals worldwide every year. EKC is mainly caused by six types of human adenovirus (HAdV): HAdV-8, -19, -37, -53, -54, and -56. Of these, HAdV-8, -19, and -37 use sialic acid-containing glycans as cellular receptors. αVβ3, αVβ5, and a few additional integrins facilitate entry and endosomal release of other HAdVs. With the exception of a few biochemical analyses indicating that HAdV-37 can interact physically with αVβ5, little is known about the integrins used by EKC-causing HAdVs. Here, we investigated the overall integrin expression on human corneal cells and found expression of α2, α3, α6, αV, β1, and β4 subunits in human corneal in situ epithelium and/or in a human corneal epithelial (HCE) cell line but no or less accessible expression of α4, α5, β3, or β5. We also identified the integrins used by HAdV-37 through a series of binding and infection competition experiments and different biochemical approaches. Together, our data suggest that HAdV-37 uses αVβ1 and α3β1 integrins for infection of human corneal epithelial cells. Furthermore, to confirm the relevance of these integrins in the HAdV-37 life cycle, we developed a corneal multilayer tissue system and found that HAdV-37 infection correlated well with the patterns of αV, α3, and β1 integrin expression. These results provide further insight into the tropism and pathogenesis of EKC-causing HAdVs and may be of importance for future development of new antiviral drugs.

IMPORTANCE Keratitis is a hallmark of EKC, which is caused by six HAdV types (HAdV-8, -19, -37, -53, -54, and -56). HAdV-37 and some other HAdV types interact with integrin αVβ5 in order to enter nonocular human cells. In this study, we found that αVβ5 is not expressed on human corneal epithelial cells, thus proposing other host factors mediate corneal infection. Here, we first characterized integrin expression patterns on corneal tissue and corneal cells. Among the integrins identified, competition binding and infection experiments and biochemical assays pointed out αVβ1 and α3β1 to be of importance for HAdV-37 infection of corneal tissue. In the absence of a good animal model for EKC-causing HAdVs, we also developed an in vitro system with multilayer HCE cells and confirmed the relevance of the suggested integrins during HAdV-37 infection.

Controlling cell adhesion using layer-by-layer approaches for biomedical applications

Controlling the adhesion of mammalian and bacterial cells at the interfaces between synthetic materials and biological environments is a real challenge in the biomedical fields such as tissue engineering, antibacterial coating, implantable biomaterials and biosensors. The surface properties of materials are known to profoundly influence the adhesion processes. To mediate the adhesion processes, polymeric coatings have been used to functionalize surfaces to introduce diverse physicochemical properties. The polyelectrolyte multilayer films built via the layer-by-layer (LbL) method, introduced by Moehwald, Decher, and Lvov 20years ago, has led to significant developments ranging from the fundamental understanding of cellular processes to controlling cell adhesion for biomedical applications. In this review, we focus our attention on the modification of surface physicochemical properties, using the LbL approach, to construct films which can either promote or inhibit mammalian/bacterial cell adhesion. We also discuss the emerging field of multifunctional surfaces capable of responding to specific cellular activity but being inert to the others.

The cleaved N-terminus of pVI binds peripentonal hexons in mature adenovirus

Mature human adenovirus particles contain four minor capsid proteins, in addition to the three major capsid proteins (penton base, hexon and fiber) and several proteins associated with the genomic core of the virion. Of the minor capsid proteins, VI plays several crucial roles in the infection cycle of the virus, including hexon nuclear targeting during assembly, activation of the adenovirus proteinase (AVP) during maturation and endosome escape following cell entry. VI is translated as a precursor (pVI) that is cleaved at both N- and C-termini by AVP. Whereas the role of the C-terminal fragment of pVI, pVIc, is well established as an important co-factor of AVP, the role of the N-terminal fragment, pVIn, is currently elusive. In fact, the fate of pVIn following proteolytic cleavage is completely unknown. Here, we use a combination of proteomics-based peptide identification, native mass spectrometry and hydrogen-deuterium exchange mass spectrometry to show that pVIn is associated with mature human adenovirus, where it binds at the base of peripentonal hexons in a pH-dependent manner. Our findings suggest a possible role for pVIn in targeting pVI to hexons for proper assembly of the virion and timely release of the membrane lytic mature VI molecule.

αvβ6- and αvβ8-integrins serve as interchangeable receptors for HSV gH/gL to promote endocytosis and activation of membrane fusion

Herpes simplex virus (HSV) - and herpesviruses in general - encode for a multipartite entry/fusion apparatus. In HSV it consists of the HSV-specific glycoprotein D (gD), and three additional glycoproteins, gH/gL and gB, conserved across the Herpesviridae family and responsible for the execution of fusion. According to the current model, upon receptor binding, gD propagates the activation to gH/gL and to gB in a cascade fashion. Questions remain about how the cascade of activation is controlled and how it is synchronized with virion endocytosis, to avoid premature activation and exhaustion of the glycoproteins. We considered the possibility that such control might be carried out by as yet unknown receptors. Indeed, receptors for HSV gB, but not for gH/gL, have been described. In other members of the Herpesviridae family, such as Epstein-Barr virus, integrin receptors bind gH/gL and trigger conformational changes in the glycoproteins. We report that αvβ6- and αvβ8-integrins serve as receptors for HSV entry into experimental models of keratinocytes and other epithelial and neuronal cells. Evidence rests on loss of function experiments, in which integrins were blocked by antibodies or silenced, and gain of function experiments in which αvβ6-integrin was expressed in integrin-negative cells. αvβ6- and αvβ8-integrins acted independently and are thus interchangeable. Both bind gH/gL with high affinity. The interaction profoundly affects the route of HSV entry and directs the virus to acidic endosomes. In the case of αvβ8, but not αvβ6-integrin, the portal of entry is located at lipid microdomains and requires dynamin 2. Thus, a major role of αvβ6- or αvβ8-integrin in HSV infection appears to be to function as gH/gL receptors and to promote virus endocytosis. We propose that placing the gH/gL activation under the integrin trigger point enables HSV to synchronize virion endocytosis with the cascade of glycoprotein activation that culminates in execution of fusion.

In order to infect their hosts and cause disease, viruses must enter their host cells. The human pathogen herpes simplex virus (HSV) - and herpesviruses in general - are equipped with a complex, multipartite entry apparatus, made of four glycoproteins – gD, gH/gL, gB. These glycoproteins must be activated in a timely, coordinated manner. According to the current model, the flux of activation goes from receptor-bound gD, to gH/gL and gB. The premature activation, and hence exhaustion of the glycoproteins must also be prevented. We report on a checkpoint at the gH/gL level. Specifically, αvβ6- and αvβ8-integrins serve as receptors for HSV entry into keratinocytes and other epithelial and neuronal cells. Both bind gH/gL with high affinity. The interaction profoundly affects the pathway of HSV entry, promoting HSV endocytosis into acidic endosomes. For αvβ8-integrin, the portal of entry is at lipid microdomains and requires dynamin 2. We propose that, by placing the activation of gH/gL under control of an integrin trigger point, HSV can synchronize virion endocytosis with the cascade of activation that culminates in the execution of fusion between the virion envelope and cellular membranes.

Construction, expression, and purification of recombinant αVβ5 integrin

A recombinant integrin expression system has been created for the large-scale production of αVβ5 integrin extracellular domains that take advantage of Fos and Jun dimerization for expression in bacterial, insect, and mammalian cells. This utilizes an all-in-one vector, pQE-TriSystem, with molecular machinery for parallel expression without the need of additional subcloning. Optimal expression in HEK293 cells was determined by a time course analysis. The heterodimer was purified in a one-step nickel column purification scheme, and the sequence and functional state were confirmed by mass spectrometry and inhibition assays, respectively. The yields of αVβ5 integrin obtained are in quantities suitable for multiple applications including structural biology and functional assays.

Integrin and defensin modulate the mechanical properties of adenovirus

The propensity for capsid disassembly and uncoating of human adenovirus is modulated by interactions with host cell molecules like integrins and alpha defensins. Here, we use atomic force microscopy (AFM) nanoindentation to elucidate, at the single-particle level, the mechanism by which binding of these host molecules affects virus particle elasticity. Our results demonstrate the direct link between integrin or defensin binding and the mechanical properties of the virus. We show that the structure and geometry of adenovirus result in an anisotropic elastic response that relates to icosahedral symmetry. This elastic response changes upon binding host molecules. Whereas integrin binding softens the vertex regions, binding of a human alpha defensin has exactly the opposite effect. Our results reveal that the ability of these host molecules to influence adenovirus disassembly correlates with a direct effect on the elastic strength of the penton region. Host factors that influence adenovirus infectivity thus modulate the elastic properties of the capsid. Our findings reveal a direct link between virus-host interactions and capsid mechanics.

Coagulation factor IX mediates serotype-specific binding of species A adenoviruses to host cells

Human species A adenoviruses (HAdVs) comprise three serotypes: HAdV-12, -18, and -31. These viruses are common pathogens and cause systemic infections that usually involve the airways and/or intestine. In immunocompromised individuals, species A adenoviruses in general, and HAdV-31 in particular, cause life-threatening infections. By combining binding and infection experiments, we demonstrate that coagulation factor IX (FIX) efficiently enhances binding and infection by HAdV-18 and HAdV-31, but not by HAdV-12, in epithelial cells originating from the airways or intestine. This is markedly different from the mechanism for HAdV-5 and other human adenoviruses, which utilize coagulation factor X (FX) for infection of host cells. Surface plasmon resonance experiments revealed that the affinity of the HAdV-31 hexon-FIX interaction is higher than that of the HAdV-5 hexon-FX interaction and that the half-lives of these interactions are profoundly different. Moreover, both HAdV-31-FIX and HAdV-5-FX complexes bind to heparan sulfate-containing glycosaminoglycans (GAGs) on target cells, but binding studies utilizing cells expressing specific GAGs and GAG-cleaving enzymes revealed differences in GAG dependence and specificity between these two complexes. These findings add to our understanding of the intricate infection pathways used by human adenoviruses, and they may contribute to better design of HAdV-based vectors for gene and cancer therapy. Furthermore, the interaction between the HAdV-31 hexon and FIX may also serve as a target for antiviral treatment.

Fusion of Epstein-Barr virus with epithelial cells can be triggered by αvβ5 in addition to αvβ6 and αvβ8, and integrin binding triggers a conformational change in glycoproteins gHgL

Fusion of herpesviruses with their target cells requires a minimum of three glycoproteins, namely, gB and a complex of gH and gL. Epstein-Barr virus (EBV) fusion with an epithelial cell requires no additional virus glycoproteins, and we have shown previously that it can be initiated by an interaction between integrin αvβ6 or αvβ8 and gHgL. We now report that integrin αvβ5 can also bind to gHgL and trigger fusion. Binding of gHgL to integrins is a two-step reaction. The first step, analyzed by surface plasmon resonance, was fast, with high association and low dissociation rate constants. The second step, detected by fluorescence spectroscopy of gHgL labeled at cysteine 153 at the domain I-domain II interface with the environmentally sensitive probes acrylodan and IANBD, involved a slower conformational change. Interaction of gHgL with neutralizing monoclonal antibodies or Fab' fragments was also consistent with a two-step reaction involving fast high-affinity binding and a subsequent slower conformational change. None of the antibodies bound to the same epitope, and none completely inhibited integrin binding. However, binding of each decreased the rate of conformational change induced by integrin binding, suggesting that neutralization might involve a conformational change that precludes fusion. Overall, the data are consistent with the interaction of gHgL with an integrin inducing a functionally important rearrangement at the domain I-domain II interface.

An adenovirus traffic update: from receptor engagement to the nuclear pore

Adenoviruses have a bipolar nature: they are ubiquitous pathogens that occasionally cause life-threatening diseases or they can be engineered into powerful gene transfer vectors. The goal of this article is to summarize the most recent advances in adenovirus receptor engagement, internalization, endosomal maturation, endosomal escape and trafficking to the nuclear pore. A better understanding of this initial part of the adenovirus lifecycle may identify new mechanistic-based treatments for adenovirus-induced diseases and help in the engineering of more efficient vectors.

Retargeted adenoviral cancer gene therapy for tumour cells overexpressing epidermal growth factor receptor or urokinase-type plasminogen activator receptor

We have assessed the ability of bispecific fusion proteins to improve adenovirus-mediated transfer of therapeutic and marker transgenes. We constructed an expression vector that can be easily modified to synthesize a variety of fusion proteins for retargeting adenoviral gene therapy vectors to cell surface markers, which are differentially expressed between normal and cancer cells. Adenoviral transduction can be improved in a number of tumour cell lines which overexpress EGFR (epidermal growth factor receptor) or uPAR (urokinase-type plasminogen activator receptor), but which have only low levels of endogenous hCAR (human coxsackie B and adenovirus receptor) expression. Up to 40-fold improvement in beta-galactosidase transgene expression was seen using an EGFR retargeting protein, and up to 16-fold using a second fusion protein targeting uPAR. In vitro, our uPAR retargeting fusion protein improved the sensitivity to adenoviral herpes simplex virus thymidine kinase/ganciclovir by an order of magnitude, whereas in vivo, our EGFR retargeting protein is able to significantly delay tumour growth in rodent animal models in a dose-dependent manner. The 'cassette' design of our fusion protein constructs offers a flexible method for the straightforward synthesis of multiple adenoviral retargeting proteins, directed against a variety of tumour-associated antigens, for use in clinical trials.

Adenovirus vectors targeting distinct cell types in the retina

Purpose. Gene therapy for a number of retinal diseases necessitates efficient transduction of photoreceptor cells. Whereas adenovirus (Ad) serotype 5 (Ad5) does not transduce photoreceptors efficiently, previous studies have demonstrated improved photoreceptor transduction by Ad5 pseudotyped with Ad35 (Ad5/F35) or Ad37 (Ad5/F37) fiber or by the deletion of the RGD domain in the Ad5 penton base (Ad5DeltaRGD). However, each of these constructs contained a different transgene cassette, preventing the evaluation of the relative performance of these vectors, an important consideration before the use of these vectors in the clinic. The aim of this study was to evaluate these vectors in the retina and to attempt photoreceptor-specific transgene expression. Methods. Three Ad5-based vectors containing the same expression cassette were generated and injected into the subretinal space of adult mice. Eyes were analyzed for green fluorescence protein expression in flat-mounts, cross-sections, quantitative RT-PCR, and a modified stereological technique. A 257-bp fragment derived from the mouse opsin promoter was analyzed in the context of photoreceptor-specific transgene expression. Results. Each virus tested efficiently transduced the retinal pigment epithelium. The authors found no evidence that Ad5/F35 or Ad5/F37 transduced photoreceptors. Instead, they found that Ad5/F37 transduced Müller cells. Robust photoreceptor transduction by Ad5DeltaRGD was detected. Photoreceptor-specific transgene expression from the 257-bp mouse opsin promoter in the context of Ad5DeltaRGD vectors was found. Conclusions. Adenovirus vectors may be designed with tropism to distinct cell populations. Robust photoreceptor-specific transgene expression can be achieved in the context of Ad5DeltaRGD vectors.

Cryo-electron microscopy structure of an adenovirus-integrin complex indicates conformational changes in both penton base and integrin

A structure of adenovirus type 12 (HAdV12) complexed with a soluble form of integrin alphavbeta5 was determined by cryo-electron microscopy (cryoEM) image reconstruction. Subnanometer resolution (8 A) was achieved for the icosahedral capsid with moderate resolution (27 A) for integrin density above each penton base. Modeling with alphavbeta3 and alpha(IIb)beta3 crystal structures indicates that a maximum of four integrins fit over the pentameric penton base. The close spacing (approximately 60 A) of the RGD protrusions on penton base precludes integrin binding in the same orientation to neighboring RGD sites. Flexible penton-base RGD loops and incoherent averaging of bound integrin molecules explain the moderate resolution observed for the integrin density. A model with four integrins bound to a penton base suggests that integrin might extend one RGD-loop in the direction that could induce a conformational change in the penton base involving clockwise untwisting of the pentamer. A global conformational change in penton base could be one step on the way to the release of Ad vertex proteins during cell entry. Comparison of the cryoEM structure with bent and extended models for the integrin ectodomain reveals that integrin adopts an extended conformation when bound to the Ad penton base, a multivalent viral ligand. These findings shed further light on the structural basis of integrin binding to biologically relevant ligands, as well as on the molecular events leading to HAdV cell entry.

Adenovirus receptors: implications for tropism, treatment and targeting

Adenoviruses (Ads) are the most frequently used viral vectors in gene therapy and cancer therapy. Obstacles to successful clinical application include accumulation of vector and transduction in liver cells, coupled with poor transduction of target cells and tissues such as tumours. Many host molecules, including coagulation factor X, have been identified and suggested to serve as mediators of Ad liver tropism. This review summarises current knowledge concerning these molecules and the mechanisms used by Ads to bind to target cells, and considers the prospects of designing vectors that have been detargeted from the liver and retargeted to cells and tissues of interest in the context of gene therapy and cancer therapy.

Adenovirus receptors and their implications in gene delivery

Adenoviruses (Ads) have gained popularity as gene delivery vectors for therapeutic and prophylactic applications. Ad entry into host cells involves specific interactions between cell surface receptors and viral capsid proteins. Several cell surface molecules have been identified as receptors for Ad attachment and entry. Tissue tropism of Ad vectors is greatly influenced by their receptor usage. A variety of strategies have been investigated to modify Ad vector tropism by manipulating the receptor-interacting moieties. Many such strategies are aimed at targeting and/or detargeting of Ad vectors. In this review, we discuss the various cell surface molecules that are implicated as receptors for virus attachment and internalization. Special emphasis is given to Ad types that are utilized as gene delivery vectors. Various strategies to modify Ad tropism using the knowledge of Ad receptors are also discussed.

Adenovirus dodecahedron cell attachment and entry are mediated by heparan sulfate and integrins and vary along the cell cycle

The adenovirus penton base is a strategic protein involved in the virus internalisation pathway through interaction between its RGD sequences and integrin. In some human adenovirus serotypes, this pentameric protein features the ability of interacting together by twelve, leading to the formation of a symmetric nanoparticle called dodecahedron (Dd). This non-infectious adenovirus-like particle exhibiting sixty RGD sequences interacts with integrin but also with heparan sulfate proteoglycans (HSPGs) expressed at the cell surface. In this study, we discriminate the respective importance of HSPGs and integrin on human adenovirus serotype 3 dodecahedron attachment and entry. Using different cell lines and a specific integrin inhibitor, we have determined that HSPGs are mainly responsible for particle attachment to the cell surface, favouring a strictly required interaction with integrin that triggers internalisation. No other receptors are involved in Dd entry and integrins on their own can mediate the particle entry in HSPGs-deficient cells. Moreover, integrin recognition by Dd is highly susceptible to cations and particularly to manganese that enhances particle binding by 4- to 7-fold compared to calcium. Interestingly, investigations on Dd receptors along the cell cycle revealed an enhanced particle targeting to mitotic cells and a loss of internalisation at this stage. This phenomenon observed with both HeLa- and HSPGs-deficient cells, depends on integrin remodelling during mitosis. This provides new clues for the use of this adenovirus nanoparticle as a delivery vector and sheds light on the integrin and HSPGs relationship in both resting and dividing cells.

Adenoviral Receptor Expression of Normal Bladder and Transitional Cell Carcinoma of the Bladder

OBJECTIVE

The insertion of absent or underexpressed genes into cancer cells to alter their malignant phenotype is an important potential application of available gene therapy technology. One of the more common viral vector systems that has been extensively studied for this purpose are the replication-deficient adenoviruses (Ad). Adenoviral infection of cells is mediated through a complex pathway, initiated following viral-cell attachment. Adenoviral-cell attachment occurs following interactions with a 46-kDa transmembrane protein with high affinity for both the Coxsackie and adenovirus, designated the CAR (Coxsackie and adenoviral receptor). Additional important cell-viral interactions that occur involve the alpha(v)-based integrins, specifically alpha(v)beta3 and alpha(v)beta5. The purpose of the present study was to determine the extent of expression and localization of the known Ad receptor proteins (CAR, alpha(v)beta3, and alpha(v)beta5) in normal and cancerous human bladders.

MATERIAL AND METHODS

Frozen tissue samples of normal bladder and invasive transitional cell cancers of the bladder were evaluated. Tissue blocks containing muscle-invasive transitional cell carcinoma (TCC) were obtained following radical cystectomy, which were performed at our institution. Thirty-two invasive transitional cell bladder tumors were evaluated, each with a matched sample of histologically normal-appearing bladder used as a control. Four additional samples of normal bladder were obtained from patients with no evidence of disease of the bladder and served as further controls. Three additional cases of invasive bladder cancer with no matching normal tissue were also evaluated. Identification of the CAR receptor was performed using the anti-CAR mouse monoclonal antibody designated RmBC. The integrins alpha(v)beta3 and alpha(v)beta5 were identified using the mouse monoclonal antibodies designated LM609 and P1F6 respectively. All slides were evaluated by two of the authors (M.B., B.B.) without knowledge of the clinical and pathological data.

RESULTS

Normal bladder: Normal bladder mucosa demonstrated a marked positivity for CAR in 29/35 (82.8%) cases. In contrast, normal transitional epithelial cells were uniformly negative when tested for the integrins alpha(v)beta3 and alpha(v)beta5. Subepithelial tissues, specifically the connective tissue components of the lamina propria and deep muscle wall of the bladder, were positive for alpha(v)beta3 and for alpha(v)beta5 in 61 and 75% of samples, respectively. Endothelial cells associated with the various layers throughout the bladder uniformly expressed both integrins and served as a consistent internal control for both antibodies. An almost identical staining pattern of the endothelium was observed using LM609 and P1F6 in all samples tested. Bladder transitional cell carcinoma: CAR immunoreactivity against TCC cells was uniformly decreased compared to normal transitional cells. Nine tumors exhibited a weak positivity for CAR while the remaining samples were negative. In some cases, the absence of CAR positivity was associated with histological evidence of carcinoma in situ. In 6 cases, it led to the identification of small regions of carcinoma in situ that were not noted on primary pathological evaluation. Peritumoral connective tissue expressed both integrins in the majority of cases, similar to the pattern described above for normal bladder. Transitional cell cancers demonstrated a similar pattern of expression of alpha(v)beta5, in which all tumor cells exhibited minimal or no staining.

CONCLUSIONS

The success of all viral-mediated gene therapy strategies relies on the ability of the vector to efficiently deliver its genetic material to a target cell population. In the current study, we demonstrate that the bladder epithelial layer consistently expresses high levels of CAR. Deeper layers of the epithelium also express CAR, including the basal layer cells. A decrease in the expression of CAR appears as an early event in bladder carcinogenesis. We observed that both alpha(v)beta3 and alpha(v)beta5 are strongly expressed in muscle cells surrounding the neoplastic cells, as well as within the peritumoral connective tissue. In cases of invasive bladder cancer that have lost CAR expression, an adenoviral vector may still be utilized through the less efficient interactions with the integrins. Bladder tumor tissue may be less susceptible to an adenoviral-mediated gene therapy approach in which a significant percentage of tumor cells require transduction. Adenoviral uptake by tumor or peritumoral cells with subsequent gene transfer could be predicted by the level of CAR and alpha(v)-based integrin expression. This would enhance our ability to identify those patients whose tumors would be more susceptible to Ad-mediated gene delivery as part of an antitumor treatment.

Protein transduction into human cells by adenovirus dodecahedron using WW domains as universal adaptors

BACKGROUND

Direct protein transduction is a recent technique that involves use of peptide vectors. In this study, we demonstrate that adenovirus dodecahedron (Dd), a virus-like particle devoid of DNA and able to penetrate cells with high efficiency, can be used as a vector for protein delivery.

METHODS

Taking advantage of Dd interaction with structural domains called WW, we have elaborated a universal adaptor to attach a protein of interest to this vector.

RESULTS

A tandem of three WW structural domains derived from the Nedd4 protein enables the formation of stable complexes with Dd, without impairing its endocytosis efficiency. Our protein of interest fused to the triple WW linker is delivered by the dodecahedron in 100% of cells in culture with on average more than ten million molecules per cell.

CONCLUSION

These data demonstrate the great potential of adenovirus dodecahedron in combination with WW domains as a protein transduction vector.

Human adenovirus type 37 and the BALB/c mouse: progress toward a restricted adenovirus keratitis model (an American Ophthalmological Society thesis)

PURPOSE

To establish a mouse model of adenovirus keratitis in order to study innate immune mechanisms in the adenovirus-infected cornea.

METHODS

Balb/c 3T3 fibroblasts were inoculated with human adenovirus (HAdV) serotypes 8, 19, or 37 and observed for cytopathic effect. Viral growth titers were performed, and apoptosis was measured by TUNEL assay. Viral and host cytokine gene expression was assessed by RT-PCR in cultured Balb/c 3T3 fibroblasts and in the corneas of virus-injected Balb/c mice. Western blot analysis was performed to detect cell signaling in the virus-infected cornea.

RESULTS

Only HAdV37 induced cytopathic effect in mouse cells. Viral gene expression was limited, and viral replication was not detected. Apoptotic cell death in HAdV37-infected Balb/c cells was evident 48 and 72 hours postinfection (P < .01). MCP-1, IL-6, KC, and IP-10 mRNA levels were increased maximally by 8.4, 9.6, 10.5, and 20.0-fold, respectively, at 30 to 90 minutes after HAdV37 infection. Similar cytokine elevations were observed in the corneas of Balb/c mice 4 hours after stromal injection of HAdV37, when viral gene expression for the viral capsid protein IIIa was not detected. Western blot showed increased phosphorylation of ERK1/2 at 4 and 24 hours after corneal infection.

CONCLUSIONS

Despite limited viral gene expression, HAdV37 infection of Balb/c 3T3 fibroblasts results in increased proinflammatory gene expression. A similar pattern of cytokine expression in the corneas of HAdV37-infected Balb/c mice suggests the mouse adenoviral keratitis model may be useful for the study of early innate immune responses in the adenovirus-infected corneal stroma.

What Does It Take to Bind CAR?

Recombinant adenoviruses (Ads) have been used as reagents for biological studies and therapeutic protocols for the treatment of human patients. The two most commonly used Ads, Ad2 and Ad5, infect a broad range of tissues through interaction with the coxsackie and adenovirus receptor CAR. Both mutational analyses and crystal structure data have established residues in the fiber knob and shaft critical for Ad-CAR binding. In this report we review the contributions of various residues to Ad-CAR binding, taking into consideration the documented cellular tropism of other Ad serotypes.

Adenovirus type 5 pseudotyped with adenovirus type 37 fiber uses sialic acid as a cellular receptor

For purposes of gene therapy, the tropism of adenovirus (Ad) serotype 5 vectors can be altered with fibers derived from alternative serotypes. However, there is currently limited information available on the cellular receptors used by the approximately 51 known Ad serotypes. Recently, alpha(2-->3)-linked sialic acid (2,3-SA) has been implicated as the cellular receptor for wild-type Ad37. However, some studies have demonstrated that wild-type Ad37 uses a 50-kDa protein and not sialic acid as its primary receptor for binding of human conjunctival cells. The sialic acid receptor has also been shown not to play a major role in the infection of these cells by an Ad5 virion pseudotyped with Ad37 fiber (Ad5.GFP.DeltaF/37F). In this study, we demonstrate that a similar virus (Ad5F37) can indeed use alpha(2-->3)-linked sialic acid as a cellular receptor. We also find that the receptor used by Ad5F37 is sensitive to proteases and that Ad5F37 can use integrin more efficiently than sialic acid for cell entry. Unlike Ad5 vectors, Ad5F37 does not efficiently employ the coxsackie and adenovirus receptor (CAR) to infect cells. Similar to Ad5, Ad5F37 infection of cells that form tight junctions can be enhanced by ethylenediaminetetraacetic acid (EDTA). These results have implications in the design of pseudotyped adenovirus vectors for gene therapy and may have particular use in the treatment of diseases involving breakdown of the blood-retinal barrier.

Membrane cofactor protein is a receptor for adenoviruses associated with epidemic keratoconjunctivitis

Subgroup D adenovirus (Ad) types 8, 19, and 37 (Ad8, -19, and -37, respectively) are causative agents of epidemic keratoconjunctivitis and genital tract infections. Previous studies showed that Ad37 binds to a 50-kDa membrane glycoprotein expressed on human ocular (conjunctival) cells. To identify and characterize the role of the 50-kDa glycoprotein in Ad37 infection, we partially purified this molecule from solubilized Chang C conjunctival cell membranes by using lentil lectin chromatography and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Liquid chromatography coupled to nano-electrospray ionization-tandem mass spectrometry was subsequently used to identify four Ad37 receptor candidates: CD46, CD87, CD98, and CD147. Immunodepletion analyses demonstrated that the 50-kDa protein is identical to CD46 (also known as membrane cofactor protein). The Ad37, but not Ad5, fiber knob bound to the extracellular domain of CD46, demonstrating a direct interaction of an Ad37 capsid protein with CD46. An antibody specific for the N-terminal 19 amino acids of CD46 also blocked Ad37 infection of human cervical carcinoma and conjunctival cells, indicating a requirement for CD46 in infection. Finally, expression of a 50-kDa isoform of human CD46 in a CD46-null cell line increased cell binding by wild-type Ad37 and gene delivery by an Ad vector pseudotyped with the Ad37 fiber, but not by a vector bearing the Ad5 fiber. Together, these studies demonstrate that CD46 serves as an attachment receptor for Ad37 and shed further light on the cell entry pathway of subgroup D Ads.

Evolution of cell recognition by viruses: a source of biological novelty with medical implications

The picture beginning to form from genome analyses of viruses, unicellular organisms, and multicellular organisms is that viruses have shared functional modules with cells. A process of coevolution has probably involved exchanges of genetic information between cells and viruses for long evolutionary periods. From this point of view present-day viruses show flexibility in receptor usage and a capacity to alter through mutation their receptor recognition specificity. It is possible that for the complex DNA viruses, due to a likely limited tolerance to generalized high mutation rates, modifications in receptor specificity will be less frequent than for RNA viruses, albeit with similar biological consequences once they occur. It is found that different receptors, or allelic forms of one receptor, may be used with different efficiency and receptor affinities are probably modified by mutation and selection. Receptor abundance and its affinity for a virus may modulate not only the efficiency of infection, but also the capacity of the virus to diffuse toward other sites of the organism. The chapter concludes that receptors may be shared by different, unrelated viruses and that one virus may use several receptors and may expand its receptor specificity in ways that, at present, are largely unpredictable.

Integrin alpha3beta1 is an alternative cellular receptor for adenovirus serotype 5

Many adenovirus serotypes enter cells by high-affinity binding to the coxsackievirus-adenovirus receptor (CAR) and integrin-mediated internalization. In the present study, we analyzed the possible receptor function of alpha3beta1 for adenovirus serotype 5 (Ad5). We found that penton base and integrin alpha3beta1 could interact in vitro. In vivo, both Ad5-cell binding and virus-mediated transduction were inhibited in the presence of anti-alpha3 and anti-beta1 function-blocking antibodies, and this occurred in both CAR-positive and CAR-negative cell lines. Peptide library screenings and data from binding experiments with wild-type and mutant penton base proteins suggest that the Arg-Gly-Asp (RGD) in the penton base protein, the best known integrin binding motif, is only part of the binding interface with alpha3beta1, which involved multiple additional contact sites.

Simultaneous CAR- and alpha V integrin-binding ablation fails to reduce Ad5 liver tropism

Targeting adenovirus encoding therapeutic genes to specific cell types has become a major goal in gene therapy. Coxsackievirus and adenovirus receptor (CAR) and alpha(V) integrins have been identified as the primary cell surface components that interact with adenovirus type 5 (Ad5)-based vectors during in vitro transduction. Redirecting Ad5-based vectors requires abrogation of the natural interaction between the viral capsid and its cellular receptors and simultaneous introduction of a new binding specificity into the viral capsid. To abrogate native Ad5 tropism, fiber knob mutations Pro409Glu and Lys417Ala were each incorporated into adenoviral vectors, while the RGD motif was deleted from the penton base. In vitro transduction experiments showed that these capsid mutations eliminated Ad5 interactions with CAR and alpha(V) integrins. Moreover, incorporation in the fiber HI loop of a vitronectin-derived ligand (VN4) specific for the uPAR/CD87 receptor provided the Lys417Ala virus with an alternative entry pathway specific for uPAR-expressing cells, indicating a successful in vitro retargeting of the vector. Unexpectedly, however, simultaneous disruption of Ad5 binding to CAR and alpha(V) integrins had no effect on liver gene transfer following systemic administration in mice. This study highlights the need to understand better the molecular determinants involved in adenovirus uptake by the liver to control the fate of adenoviral vectors in vivo.

Flexibility of the adenovirus fiber is required for efficient receptor interaction

The adenovirus (Ad) fiber protein mediates Ad binding to the coxsackievirus and Ad receptor (CAR) and is thus a major determinant of viral tropism. The fiber contains three domains: an N-terminal tail that anchors the fiber to the viral capsid, a central shaft region of variable length and flexibility, and a C-terminal knob domain that binds to cell receptors. Ad type 37 (Ad37), a subgroup D virus associated with severe ocular infections, is unable to use CAR efficiently to infect host cells, despite containing a CAR binding site in its fiber knob. We hypothesized that the relatively short, inflexible Ad37 fiber protein restricts interactions with CAR at the cell surface. To test this hypothesis, we analyzed the infectivity and binding of recombinant Ad particles containing modified Ad37 or Ad5 fiber proteins. Ad5 particles equipped with a truncated Ad5 fiber or with a chimeric fiber protein comprised of the Ad5 knob fused to the short, rigid Ad37 shaft domain had significantly reduced infectivity and attachment. In contrast, placing the Ad37 knob onto the long, flexible Ad5 shaft allowed CAR-dependent virus infection and cell attachment, demonstrating the importance of the shaft domain in receptor usage. Increasing fiber rigidity by substituting the predicted flexibility modules in the Ad5 shaft with the corresponding regions of the rigid Ad37 fiber dramatically reduced both virus infection and cell attachment. Cryoelectron microscopy (cryo-EM) single-particle analysis demonstrated the increased rigidity of this chimeric fiber. These studies demonstrate that both length and flexibility of the fiber shaft regulate CAR interaction and provide a molecular explanation for the use of alternative receptors by subgroup D Ad with ocular tropism. We present a molecular model for Ad-CAR interactions at the cell surface that explains the significance of fiber flexibility in cell attachment.

Integrin-nucleated Toll-like receptor (TLR) dimerization reveals subcellular targeting of TLRs and distinct mechanisms of TLR4 activation and signaling

Toll-like receptors (TLRs) are activated by microbial structures. To investigate the mechanisms of TLR activation, the 10 human TLRs were expressed as chimeras with the integrin alphav and beta5 subunits. Co-expression of the alphav-TLR and beta5-TLR chimeras in 293T cells generated 10 TLR homodimers, but only TLR4/4 could effectively activate NF-kappaB. TLR4 monomers also activated NF-kappaB but it was enhanced upon homodimerization. The TLR homodimers showed differential surface/intracellular expression. In TLR heterodimers, only TLR2/1 and TLR2/6 were potent in NF-kappaB activation. NF-kappaB activation by TLR2/1, TLR2/6 and the TLR4 monomer, but not TLR4/4, was completely inhibited by dominant negative MyD88, suggesting that TLR4 homodimers and monomers could activate NF-kappaB through different mechanisms.

Adenovirus mediated gene transfer to skeletal muscle

Transfer of therapeutic genes into muscle tissue has promise for the treatment of a variety of muscular dystrophies. Various vectors have been used to deliver genes to skeletal muscle but their application has faced several major limitations including: (1) the lack of transgene persistence caused by the immune rejection of transduced myofibers and/or vector toxicity, and (2) the maturation dependence of viral transduction. While the immunorejection and/or cytotoxic problems are being overcome with the development of new vectors, maturation-dependent viral transduction is still a major hurdle in gene transfer to skeletal muscle. Poor adenoviral transduction in mature myofibers has been attributed to: (1) the extracellular matrix of mature myofibers may form a physical barrier and prevent the passage of large viral particles; (2) viral receptors are down-regulated with muscle maturation; and (3) loss of myoblasts with muscle maturation, which serve as intermediaries in the viral transduction. In this review, we will focus on recent developments in overcoming those hurdles of gene therapy in skeletal muscle, especially to adenovirus (Ad), including: (1) new mutant vectors lacking all viral genes to decrease immunogenicity, and hence, improve persistence of transgene expression in muscle in vivo; (2) using tissue specific promoters to evade immunorejection; (3) permeabilization of the extracellular matrix; (4) modifying the viral receptors in mature myofibers; and (5) myoblast or muscle stem cell mediated ex vivo gene transfer.

Adenovirus inhibition by peptidomimetic integrin antagonists

Many viruses and bacterial pathogens are capable of exploiting host cell surface integrins during their replication cycles. The ligands for many integrins contain an arginine-glycine-aspartic acid (RGD) amino acid sequence that is essential for protein-protein interaction. Human adenovirus particles contain this sequence in the penton base protein, and previous studies support a role for this RGD in integrin-dependent internalization of the virus by the cell. As synthetic peptidomimetics of RGD have been shown in other experimental systems to be antagonists of the activities of specific integrins both in vitro and in vivo, we sought to determine whether these small molecules are antagonists of adenovirus infection. Such compounds inhibited viral infection of cultured cells with similar rank order potency to that determined in assays utilizing purified extracellular matrix proteins as integrin ligands. The maximal level of inhibition achieved with the peptidomimetics was comparable to that of RGD-containing peptides, whereas no significant effects were apparent with an RGE-containing peptide. An engineered adenovirus having a mutated RGD sequence in the penton base was not susceptible to the inhibition. The results obtained with these synthetic antagonists, which have varied structures and potencies, suggest that integrins interact with adenoviral RGD in a manner similar to that of other protein ligands such as vitronectin. Furthermore, the results confirm the role of RGD in the replication cycle, and suggest peptidomimetic compounds may be useful antimicrobial agents in the treatment of a variety of diseases.

Human adenoviruses of subgenera B, C, and E with various tropisms differ in both binding to and replication in the epithelial A549 and 293 cells

Adenoviruses of six subgenera, namely, adenovirus 31 (Ad31) (subgenus A), Ad3, Ad7, Ad11p, Ad11a, and Ad35 (subgenus B), Ad5v and Ad5p (subgenus C), Ad37 (subgenus D), Ad4 (subgenus E), and Ad41 (subgenus F), were studied. The relative binding properties of different adenoviruses to 293 (human kidney embryonic cells) and A549 (human lung carcinoma cells) cells were compared by flow cytometry. All analyzed adenoviruses bound to cells in a dose-dependent manner. The binding capacity showed that Ad11p, Ad35 (subgenus B:2) with kidney tropism, and Ad4 (subgenus E), which can cause adenopharyngoconjunctivitis, bound strongly to both A549 and 293 cells. The other members of subgenus B and Ad37 of subgenus D manifested an intermediate binding capacity. The analyzed adenoviruses of subgenera A, C, and F manifested a low affinity. Adenoviruses of subgenera B:2 and E manifested high binding affinity to preparations of cell membranes from the epithelial cell lines. Reciprocal competition experiments using Ad11p and Ad4 demonstrated that the two viruses did not block each other. Antibodies against alphavbeta3 and alphavbeta5 reduced the binding of Ad5v virions and slightly impaired the binding of Ad4 but did not affect Ad11p binding to the A549 cell surface. Recombinant fiber proteins of Ad11p and Ad35 reciprocally blocked the binding of both viruses to the epithelial cells but they could not block Ad4. The hexon protein expression of Ad11p and Ad4 was 100 times more efficient than that of the Ad5 vector (pFG140), whereas the infectivity of Ad11p and Ad4 was 40- to 200-fold that of the commonly used Ad5v vector. Taken together, our findings demonstrate that Ad11p and Ad4 bind different receptor molecules and that the fibers of these two viruses provide the predominant high degree of binding, which obviously is a requirement for subsequent internalization and efficacious expression.

Production of soluble integrin alpha2beta1 heterodimer complex functionally active in vitro and in vivo

Integrin alpha2beta1, which is a membrane protein consisting of noncovalently bound alpha2 and beta1 chains, mediates cell binding to collagen and plays a role in platelet functions. DNAs encoding the chimeric proteins in which the extracellular domains of each alpha2 and beta1 chain was fused to hinge and Fc regions of human IgG(1)gamma chain were cotransfected into CHO cells. Soluble integrin alpha2beta1 (salpha2beta1) in which alpha2 and beta1 chains were covalently bound by disulfide bonds was recovered from the culture supernatant. salpha2beta1 maintained functional characteristics of cell surface alpha2beta1 as indicated by cation-dependent binding to collagen and conformational changes induced by cations or ligand. Intravenously administered salpha2beta1 in rats colocalized with collagen in inflamed microvessels. Moreover, salpha2beta1-conjugated liposome administered intravenously reduced bleeding time of the thrombocytopenic mice. These results indicated that salpha2beta1 has pharmaceutical utilities as an agent for detecting injured vessels and a component of platelet substitute.

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.

Generation of a minimal alpha5beta1 integrin-Fc fragment

The tertiary structure of the integrin heterodimer is currently unknown, although several predictive models have been generated. Detailed structural studies of integrins have been consistently hampered for several reasons, including the small amounts of purified protein available, the large size and conformational flexibility of integrins, and the presence of transmembrane domains and N-linked glycosylation sites in both receptor subunits. As a first step toward obtaining crystals of an integrin receptor, we have expressed a minimized dimer. By using the Fc dimerization and mammalian cell expression system designed and optimized by Stephens et al. (Stephens, P. E., Ortlepp, S., Perkins, V. C., Robinson, M. K., and Kirby, H. (2000) Cell. Adhes. Commun. 7, 377-390), a series of recombinant soluble human alpha(5)beta(1) integrin truncations have been expressed as Fc fusion proteins. These proteins were examined for their ligand-binding properties and for their expression of anti-integrin antibody epitopes. The shortest functional alpha(5)-subunit truncation contained the N-terminal 613 residues, whereas the shortest beta(1)-subunit was a fragment containing residues 121-455. Each of these minimally truncated integrins displayed the antibody binding characteristics of alpha(5)beta(1) purified from human placenta and bound ligand with the same apparent affinity as the native receptor.

Ex vivo adenovirus mediated gene transfection of human conjunctival epithelium

AIM

To investigate the efficacy of "ex vivo" adenoviral vector mediated gene transfection of human conjunctival epithelial cell as a possible route for gene therapy for the distribution of anti-inflammatory agents for the potential treatment of immune mediated ocular inflammatory disorders.

METHODS

Human conjunctival cells (HCs) were cultured with various concentrations of recombinant adenoviral vectors carrying a reporter gene LacZ, GFP, or an immunomodulating cytokine vIL-10. vIL-10 in culture supernatant was detected by sandwich ELISA and biological activity was assessed by suppression of ConA stimulated splenocyte proliferation. X-gal and GFP expression was assessed by histochemistry.

RESULTS

The extent of adenoviral vector mediated transfer of both reporter genes and vIL-10 was dose dependent. LacZ expression could be detected for at least 50 day after infection with multiple of infection (MOI) 200. Following AdCMVvIL-10 transduction, vIL-10 protein expression occurred between 4-6 days post-transduction, and was maintained at a detectable level for at least 1 month. Secreted vIL-10 showed biological activity, significantly inhibiting Con A induced splenocyte proliferation. Additionally, transfection of HCs with two Adv vectors, one carrying LacZ and the other carrying GFP, resulted in co-expression within a single cell.

CONCLUSION

These results confirm previous successful adenoviral vector mediated gene transfer to HCs and further show that expression can be maintained. Furthermore the data show HCs can secrete biologically active vIL-10 that could be developed as a strategy to suppress immune mediated disorders. The successful co-transduction of HCs as described for other tissues, opens avenues to develop a multiple target gene therapy locally.

Structural analysis of a fiber-pseudotyped adenovirus with ocular tropism suggests differential modes of cell receptor interactions

Adenovirus (Ad) entry into cells is initiated by the binding of the fiber knob to a cell surface receptor. The coxsackie- and adenovirus receptor (CAR) functions as the attachment receptor for many, but not all, Ad serotypes. Ad type 37 (Ad37), a subgroup D virus that causes keratoconjunctivitis in humans, does not infect cells via CAR despite demonstrated binding of the Ad37 knob to CAR. We have pseudotyped a fiber deletion Ad5 vector with the Ad37 fiber (Ad37f), and this vector retains the ocular tropism of Ad37. Here we present a cryo-electron microscopy reconstruction of Ad37f that shows the entire Ad37 fiber, including the shaft and knob domains. We have previously proposed that Ad37 may not utilize CAR for cell entry because of the geometric constraints imposed by a rigid fiber (E. Wu, J. Fernandez, S. K. Fleck, D. Von Seggern, S. Huang, and G. R. Nemerow, Virology 279:78-89, 2001). Consistent with this hypothesis, our structural results show that the Ad37 fiber is straight and rigid. Modeling of the interaction between Ad37f and host cell receptors indicates that fiber flexibility or rigidity, as well as length, can affect receptor usage and cellular tropism.

Superactivation of integrin (α)v(β)3 by low antagonist concentrations

Integrins are implicated in cell adhesion, migration and homeostasis. An important feature is their ability to adopt different affinity states that can be regulated by a variety of intra- and extracellular factors. To study affinity modulation of the integrin ectodomain by extracellular factors, we produced a soluble recombinant form of mouse integrin (α)v(β)3 in a mammalian expression system and isolated it to purity. We show that the two transmembrane truncated integrin subunits stably associate to form a functional receptor, soluble recombinant (α)v(β)3. The affinity of this receptor for its ligands vitronectin, fibronectin and fibrinogen can be modulated by the divalent cations magnesium, calcium and manganese. Most importantly, we found that a cyclic RGD-peptide has a biphasic effect on rs(α)v(β)3and native purified (α)v(β)3, with an antagonistic phase at high concentrations, and an agonistic phase at low concentrations. This integrin superactivation by low antagonist concentrations is shown in binding of sr(α)v(β)3 to immobilized ligands by ELISA, and in adhesion of cells that express the chimaeric integrin ligand KISS31 to immobilized rs(α)v(β)3 and native purified (α)v(β)3. Our results indicate that low concentrations of the ligand mimetic cyclo-RGD can result in superactivation of the extracellular domain of integrin (α)v(β)3 to a comparable level as activation by manganese.

Binding properties, cell delivery, and gene transfer of adenoviral penton base displaying bacteriophage

The penton base of adenovirus mediates viral attachment to integrin receptors and particle internalisation, properties that can be exploited to reengineer prokaryotic viruses for the infection of mammalian cells. We report that filamentous phage displaying either the full-length penton base gene or a central region of 107 amino acids on their surface were able to bind, internalise, and transduce mammalian cells expressing integrin receptors. Both phage bound alphavbeta3, alphavbeta5, alpha3beta1, and alpha5beta1 integrin subtypes. Cell-binding was shown by electron microscopy; internalisation was investigated by immunofluorescence and confirmed by micropanning. As it has been described for adenovirus, pharmacologic disruption of phosphoinositide-30H kinase, but not of myosin light-chain kinase, inhibited phage internalisation. Recombinant phage encoding an eukaryotic expression cassette was able to mediate gene expression in mammalian cells. Taken together, these data open insights for the exploit of recombinant phage for integrin-targeted gene delivery.

Pharmacological aspects of targeting cancer gene therapy to endothelial cells

Targeting cancer gene therapy to endothelial cells seems to be a rational approach, because (a) a clear correlation exists between proliferation of tumor vessels and tumor growth and malignancy, (b) differences of cell membrane structures between tumor endothelial cells and normal endothelial cells exist which could be used for targeting of vectors and (c) tumor endothelial cells are accessible to vector vehicles in spite of the peculiarities of the transvascular and interstitial blood flow in tumors. Based on the knowledge on the pharmacokinetics of macromolecules it can be concluded that vectors targeting tumor endothelial cells should own a long blood residence time after intravascular application. This precondition seems to be fulfilled best by vectors exhibiting a slight anionic charge. A long blood residence time would allow the formation of a high amount of complexes between tumor endothelial cells and vector particles. Such high amount of complexes should enable a high transfection rate of tumor endothelial cells. In view of their pharmacokinetic behavior nonviral vectors seem to be more suitable for in vivo targeting tumor endothelial cells than viral vectors. Specific binding of nonviral vectors to tumor endothelial cells should be enhanced by multifunctional ligands and the transduction efficiency should be improved by cationic carriers. Effector genes should encode proteins potent enough to induce reactions which eliminate the tumor tissue. To be effective to that degree such proteins should induce self-amplifying antitumor reactions. Examples for proteins which have the potential to induce such self-amplifying tumor reactions are proteins endowed with antiangiogenic and antiproliferative activity, enzymes which convert prodrugs into drugs and possibly also proteins which induce embolization of tumor vessels. The pharmacological data for such examples are discussed in detail.

Adenovirus serotype 7 retention in a late endosomal compartment prior to cytosol escape is modulated by fiber protein

The intracellular trafficking of adenovirus (Ad) subgroup B (e.g., Ad7) differs from that of subgroup C (e.g., Ad5) in that Ad5 rapidly escapes from endocytic compartments following infection whereas Ad7 accumulates in organelles. To assess the hypothesis that Ad7 is targeted to the lysosomal pathway, Ad7 and Ad5 were conjugated with fluorophores and their trafficking in A549 epithelial cells was analyzed by fluorescence microscopy. Within 1 h after infection, Ad7, but not Ad5, accumulated in the cytoplasm of A549 cells. The pH in the environment of Ad5 was nearly neutral (pH 7), while Ad7 occupied acidic compartments (pH 5) over the first 2 h with a gradual shift toward neutrality by 8 h. Ad7 partially colocalized with alpha(2)-macroglobulin and late endosomal and lysosomal marker proteins, including Rab7, mannose-6-phosphate receptor, and LAMP-1. The pH optimum for membrane lysis by Ad7, as well as a chimeric Ad5 capsid that expressed the Ad7 fiber (Ad5fiber7), was pH 5.5, while that for lysis by Ad5 was pH 6.0. Thus, the native trafficking pathway for Ad7 involves residence in late endosomes and lysosomes, with information encoded in the Ad7 fiber acting as a pH-dependent trigger for membrane lysis and escape to the cytosol.

A 50-kDa membrane protein mediates sialic acid-independent binding and infection of conjunctival cells by adenovirus type 37

The ocular tropism of adenovirus type 37 (Ad37) does not correlate with the wide distribution of the 46-kDa coxsackievirus and adenovirus receptor (CAR), the major receptor for most adenovirus serotypes. We previously found that Ad37 infects and binds well to conjunctival cells (Chang C), but poorly to lung epithelial (A549) cells that express CAR and hypothesized that this serotype uses a distinct receptor that is selectively expressed on conjunctival cells. To test this, we produced particles of a fiber-deleted Ad5 vector containing the Ad37 fiber protein. The "pseudotyped" vector infected Chang C cells better than A549 cells using a CAR-independent pathway. Ad37 binding was calcium-dependent and was abolished by protease digestion of cell surface proteins. Using a virus overlay protein blot assay (VOPBA), we detected calcium-dependent Ad37 binding to 50- and 60-kDa membrane proteins on permissive Chang C cells. In contrast, calcium-dependent binding was detected with only the 60-kDa protein on nonpermissive A549 cells. Ad19p, a closely related serotype that failed to bind to conjunctival cells, recognized the 60-kDa, but not the 50-kDa, protein. Ad37 has been reported to use sialic acid instead of CAR as a cell receptor on A549 cells. Pretreatment of Chang C cells with neuraminidase abolished Ad37 binding to only the 60-kDa protein, suggesting that sialic acid mediates Ad37 binding to the 60-kDa protein. The pseudotyped Ad37 vector was also able to infect neuraminidase-treated Chang C cells. Thus, subgroup D adenoviral binding to the 50-kDa protein is calcium-dependent and cell type- and serotype-specific, whereas binding to the 60-kDa protein is not necessary for infection of conjunctival cells. Together, these data suggest that the 50-kDa protein is the major receptor for Ad37 on conjunctival cells.

Selective transduction of murine myelomonocytic leukemia cells (WEHI-3B) with regular and RGD-adenoviral vectors

On the basis of the susceptibility of normal myelomonocytic cells to adenoviral vectors, we have studied the possibility of selectively transducing myelomonocytic murine leukemic cells (WEHI-3B) with regular (Reg-Ad) and genetically modified (RGD-Ad) adenoviral vectors. An 8-h incubation of WEHI-3B cells with 100 pfu of Reg-Ad vectors/cell resulted in the whole population becoming positive for transgene expression. Under identical conditions of infection, 20-30% of mouse bone marrow (BM) cells were positive for the transgene. When RGD-Ad vectors were used, a brief exposure (10 min) of WEHI-3B cells to 150 pfu of the virus/cell was enough for 100% of the leukemia cells to become positive for the marker transgene (EGFP). Under these conditions, only 15-20% of BM cells and of primitive hematopoietic progenitors (Lin(-)Sca-1(+) cells) became EGFP(+), indicating an improved selectivity of the vectors for the leukemic cells. The incubation of WEHI-3B but not normal BM cells with soluble fiber protein (FP) inhibited the infection with Reg-Ad. The use of the RGD-Ad bypassed the FP-CAR interaction required for the transduction of WEHI-3B cells with Reg-Ad, suggesting that the abrogation of this requirement accounts for the improved infectivity of these leukemic cells and for the selectivity of RGD-Ad in targeting WEHI-3B leukemia cells.

Subversion of integrins by enteropathogenic Yersinia

Enteropathogenic Yersinia are gram-negative bacterial species that translocate from the lumen of the intestine and are able to grow within deep tissue sites. During the earliest stages of disease, the organism is able to bind integrin receptors that are presented on the apical surface of M cells in the intestine, which allows its internalization and subsequent translocation into regional lymph nodes. The primary integrin substrate is the outer-membrane protein invasin, which binds with extraordinarily high affinity to at least five different integrins that have the (beta)(1) chain. Bacterial uptake into host cells is modulated by the affinity of receptor-substrate interaction, receptor concentration and the ability of the substrate to aggregate target receptors.