Integrin alpha(v)beta1 is an adenovirus coreceptor

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.

Insights into membrane interactions and their therapeutic potential

Recent research into membrane interactions has uncovered a diverse range of therapeutic opportunities through the bioengineering of human and non-human macromolecules. Although the majority of this research is focussed on fundamental developments, emerging studies are showcasing promising new technologies to combat conditions such as cancer, Alzheimer's and inflammatory and immune-based disease, utilising the alteration of bacteriophage, adenovirus, bacterial toxins, type 6 secretion systems, annexins, mitochondrial antiviral signalling proteins and bacterial nano-syringes. To advance the field further, each of these opportunities need to be better understood, and the therapeutic models need to be further optimised. Here, we summarise the knowledge and insights into several membrane interactions and detail their current and potential uses therapeutically.

Phylogenetic and Recombination Analysis of Clinical Vitreous Humor-Derived Adenovirus Isolates Reveals Discordance Between Serotype and Phylogeny

Purpose

To sequence, identify, and perform phylogenetic and recombination analysis on three clinical adenovirus samples taken from the vitreous humor at the Bascom Palmer Eye Institute.

Methods

The PacBio Sequel II was used to sequence the genomes of the three clinical adenovirus isolates. To identify the isolates, a full genome-based multiple sequence alignment (MSA) of 722 mastadenoviruses was generated using multiple alignment using fast Fourier transform (MAFFT). MAFFT was also used to generate genome-based human adenovirus B (HAdV-B) MSAs, as well as HAdV-B fiber, hexon, and penton protein-based MSAs. To examine recombination within HAdV-B, RF-Net 2 and Bootscan software programs were used.

Results

In the course of classifying three new atypical ocular adenovirus samples, taken from the vitreous humor, we found that all three isolates were HAdV-B species. The three Bascom Palmer HAdV-B genomes were then combined with over 300 HAdV-B genome sequences, including nine ocular HAdV-B genome sequences. Attempts to categorize the penton, hexon, and fiber serotypes using phylogeny of the three Bascom Palmer samples were inconclusive due to incongruence between serotype and phylogeny in the dataset. Recombination analysis using a subset of HAdV-B strains to generate a hybridization network detected recombination between nonhuman primate and human-derived strains, recombination between one HAdV-B strain and the HAdV-E outgroup, and limited recombination between the B1 and B2 clades.

Conclusions

The discordance between serotype and phylogeny detected in this study suggests that the current classification system does not accurately describe the natural history and phylogenetic relationships among adenoviruses.

Integrin β1 is a key determinant of the expression of angiotensin-converting enzyme 2 (ACE2) in the kidney epithelial cells

The expression of the angiotensin-converting enzyme 2 (ACE2) is altered in multiple chronic kidney diseases like hypertension and renal fibrosis, where the signaling from the basal membrane proteins is critical for the development and progression of the various pathologies. Integrins are heterodimeric cell surface receptors that have important roles in the progression of these chronic kidney diseases by altering various cell signaling pathways in response to changes in the basement membrane proteins. It is unclear whether integrin or integrin-mediated signaling affects the ACE2 expression in the kidney. The current study tests the hypothesis that integrin β1 regulates the expression of ACE2 in kidney epithelial cells. The role of integrin β1 in ACE2 expression in renal epithelial cells was investigated by shRNA-mediated knockdown and pharmacological inhibition. In vivo studies were carried out using epithelial cell-specific deletion of integrin β1 in the kidneys. Deletion of integrin β1 from the mouse renal epithelial cells reduced the expression of ACE2 in the kidney. Furthermore, the downregulation of integrin β1 using shRNA decreased ACE2 expression in human renal epithelial cells. ACE2 expression levels were also decreased in renal epithelial cells and cancer cells when treated with an integrin α2β1 antagonist, BTT 3033. SARS-CoV-2 viral entry to human renal epithelial cells and cancer cells was also inhibited by BTT 3033. This study demonstrates that integrin β1 positively regulates the expression of ACE2, which is required for the entry of SARS-CoV-2 into kidney cells.

Viruses Binding to Host Receptors Interacts with Autophagy

Viruses must cross the plasma membrane to infect cells, making them eager to overcome this barrier in order to replicate in hosts. They bind to cell surface receptors as the first step of initiating entry. Viruses can use several surface molecules that allow them to evade defense mechanisms. Various mechanisms are stimulated to defend against viruses upon their entry into cells. Autophagy, one of the defense systems, degrades cellular components to maintain homeostasis. The presence of viruses in the cytosol regulates autophagy; however, the mechanisms by which viral binding to receptors regulates autophagy have not yet been fully established. This review discusses recent findings on autophagy induced by interactions between viruses and receptors. It provides novel perspectives on the mechanism of autophagy as regulated by viruses.

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.

Virus-associated disruption of mucosal epithelial tight junctions and its role in viral transmission and spread

Oropharyngeal, airway, intestinal, and genital mucosal epithelia are the main portals of entry for the majority of human pathogenic viruses. To initiate systemic infection, viruses must first be transmitted across the mucosal epithelium and then spread across the body. However, mucosal epithelia have well-developed tight junctions, which have a strong barrier function that plays a critical role in preventing the spread and dissemination of viral pathogens. Viruses can overcome these barriers by disrupting the tight junctions of mucosal epithelia, which facilitate paracellular viral penetration and initiate systemic disease. Disruption of tight and adherens junctions may also release the sequestered viral receptors within the junctional areas, and liberation of hidden receptors may facilitate viral infection of mucosal epithelia. This review focuses on possible molecular mechanisms of virus-associated disruption of mucosal epithelial junctions and its role in transmucosal viral transmission and spread.

Virus-associated disruption of mucosal epithelial tight junctions and its role in viral transmission and spread

Oropharyngeal, airway, intestinal, and genital mucosal epithelia are the main portals of entry for the majority of human pathogenic viruses. To initiate systemic infection, viruses must first be transmitted across the mucosal epithelium and then spread across the body. However, mucosal epithelia have well-developed tight junctions, which have a strong barrier function that plays a critical role in preventing the spread and dissemination of viral pathogens. Viruses can overcome these barriers by disrupting the tight junctions of mucosal epithelia, which facilitate paracellular viral penetration and initiate systemic disease. Disruption of tight and adherens junctions may also release the sequestered viral receptors within the junctional areas, and liberation of hidden receptors may facilitate viral infection of mucosal epithelia. This review focuses on possible molecular mechanisms of virus-associated disruption of mucosal epithelial junctions and its role in transmucosal viral transmission and spread.

MAGI-1 PDZ2 Domain Blockade Averts Adenovirus Infection via Enhanced Proteolysis of the Apical Coxsackievirus and Adenovirus Receptor

Adenoviruses (AdVs) are etiological agents of gastrointestinal, heart, eye, and respiratory tract infections that can be lethal for immunosuppressed people. Many AdVs use the coxsackievirus and adenovirus receptor (CAR) as a primary receptor. The CAR isoform resulting from alternative splicing that includes the eighth exon, CAREx8, localizes to the apical surface of polarized epithelial cells and is responsible for the initiation of AdV infection. We have shown that the membrane level of CAREx8 is tightly regulated by two MAGI-1 PDZ domains, PDZ2 and PDZ4, resulting in increased or decreased AdV transduction, respectively. We hypothesized that targeting the interactions between the MAGI-1 PDZ2 domain and CAREx8 would decrease the apical CAREx8 expression level and prevent AdV infection. Decoy peptides that target MAGI-1 PDZ2 were synthesized (TAT-E6 and TAT-NET1). PDZ2 binding peptides decreased CAREx8 expression and reduced AdV transduction. CAREx8 degradation was triggered by the activation of the regulated intramembrane proteolysis (RIP) pathway through a disintegrin and metalloproteinase (ADAM17) and γ-secretase. Further analysis revealed that ADAM17 interacts directly with the MAGI-1 PDZ3 domain, and blocking the PDZ2 domain enhanced the accessibility of ADAM17 to the substrate (CAREx8). Finally, we validated the efficacy of TAT-PDZ2 peptides in protecting the epithelia from AdV transduction in vivo using a novel transgenic animal model. Our data suggest that TAT-PDZ2 binding peptides are novel anti-AdV molecules that act by enhanced RIP of CAREx8 and decreased AdV entry. This strategy has additional translational potential for targeting other viral receptors that have PDZ binding domains, such as the angiotensin-converting enzyme 2 receptor. IMPORTANCE Adenovirus is a common threat in immunosuppressed populations and military recruits. There are no currently approved treatments/prophylactic agents that protect from most AdV infections. Here, we developed peptide-based small molecules that can suppress AdV infection of polarized epithelia by targeting the AdV receptor, coxsackievirus and adenovirus receptor (CAREx8). The newly discovered peptides target a specific PDZ domain of the CAREx8-interacting protein MAGI-1 and decrease AdV transduction in multiple polarized epithelial models. Peptide-induced CAREx8 degradation is triggered by extracellular domain (ECD) shedding through ADAM17 followed by γ-secretase-mediated nuclear translocation of the C-terminal domain. The enhanced shedding of the CAREx8 ECD further protected the epithelium from AdV infection. Taken together, these novel molecules protect the epithelium from AdV infection. This approach may be applicable to the development of novel antiviral molecules against other viruses that use a receptor with a PDZ binding domain.

Apigenin-Loaded PLGA-DMSA Nanoparticles: A Novel Strategy to Treat Melanoma Lung Metastasis

The flavone apigenin (APG), alone as well as in combination with other chemotherapeutic agents, is known to exhibit potential anticancer effects in various tumors and inhibit growth and metastasis of melanoma. However, the potential of apigenin nanoparticles (APG-NPs) to prevent lung colonization of malignant melanoma has not been well investigated. APG-loaded PLGA-NPs were surface-functionalized with meso-2,3-dimercaptosuccinic acid (DMSA) for the treatment of melanoma lung metastasis. DMSA-conjugated APG-loaded NPs (DMSA-APG-NPs) administered by an oral route exhibited sustained APG release and showed considerable enhancement of plasma half-life, C_max value, and bioavailability compared to APG-NPs both in plasma and the lungs. DMSA-conjugated APG-NPs showed comparably higher cellular internalization in B16F10 and A549 cell lines compared to that of plain NPs. Increased cytotoxicity was observed for DMSA-APG-NPs compared to APG-NPs in A549 cells. This difference between the two formulations was lower in B16F10 cells. Significant depolarization of mitochondrial transmembrane potential and an enhanced level of caspase activity were observed in B16F10 cells treated with DMSA-APG-NPs compared to APG-NPs as well. Western blot analysis of various proteins was performed to understand the mechanism of apoptosis as well as prevention of melanoma cell migration and invasion. DMSA conjugation substantially increased accumulation of DMSA-APG-NPs given by an intravenous route in the lungs compared to APG-NPs at 6 and 8 h. This was also corroborated by scintigraphic imaging studies with radiolabeled formulations administered by an intravenous route. Conjugation also allowed comparatively higher penetration as evident from an in vitro three-dimensional tumor spheroid model study. Finally, the potential therapeutic efficacy of the formulation was established in experimental B16F10 lung metastases, which suggested an improved bioavailability with enhanced antitumor and antimetastasis efficacy of DMSA-conjugated APG-NPs following oral administration.

Bmintegrin β1: A broadly expressed molecule modulates the innate immune response of Bombyx mori

Integrins are transmembrane glycoproteins that are broadly distributed in living organisms. As a heterodimer, they contain an α and a β subunit, which are reported to be associated with various physiological and pathological processes. In the present study, a 2502 bp full-length cDNA sequence of Bmintegrin β1 was obtained from the silkworm, Bombyx mori. Bmintegrin β1 belongs to the β subunit of the integrin family and contains several typical structures of integrins. Gene expression profile analysis demonstrated that Bmintegrin β1 was ubiquitously expressed in all tested tissues and organs, with the maximum expression levels in fat body and hemocytes. The immunofluorescence results showed that Bmintegrin β1 was located in the cell membrane and widely distributed in fat bodies and different types of hemocytes. Bmintegrin β1 expression was remarkably increased after challenging with different kinds of bacteria and pathogen-associated molecular patterns (PAMPs). Further investigation revealed that Bmintegrin β1 could participate in the agglutination of pathogenic bacteria possibly through direct binding with the relative bacteria and PAMPs. Altogether, this study provides a novel insight into the immune functional features of Bmintegrin β1.

The V2 loop of HIV gp120 delivers costimulatory signals to CD4+ T cells through Integrin α4β7 and promotes cellular activation and infection

Acute HIV infection is characterized by rapid viral seeding of immunologic inductive sites in the gut followed by the severe depletion of gut CD4⁺ T cells. Trafficking of α₄β₇-expressing lymphocytes to the gut is mediated by MAdCAM, the natural ligand of α₄β₇ that is expressed on gut endothelial cells. MAdCAM signaling through α₄β₇ costimulates CD4⁺ T cells and promotes HIV replication. Similar to MAdCAM, the V2 domain of the gp120 HIV envelope protein binds to α₄β₇ In this study, we report that gp120 V2 shares with MAdCAM the capacity to signal through α₄β₇ resulting in CD4⁺ T cell activation and proliferation. As with MAdCAM-mediated costimulation, cellular activation induced by gp120 V2 is inhibited by anti-α₄β₇ monoclonal antibodies (mAbs). It is also inhibited by anti-V2 domain antibodies including nonneutralizing mAbs that recognize an epitope in V2 that has been linked to reduced risk of acquisition in the RV144 vaccine trial. The capacity of the V2 domain of gp120 to mediate signaling through α₄β₇ likely impacts early events in HIV infection. The capacity of nonneutralizing V2 antibodies to block this activity reveals a previously unrecognized mechanism whereby such antibodies might impact HIV transmission and pathogenesis.

The integrin facilitated internalization of fibronectin-functionalized camptothecin-loaded DNA-nanofibers for high-efficiency anticancer effects

Camptothecin (CMPT) in a free form is extremely cytotoxic as well as hydrophobic drug, and is considered to be highly contagious for systemic administration. The fibronectin (FN)-functionalized DNA-based nanocarrier has been designed to load CMPT and target integrin (αvβ3) receptors which are highly expressed on the A549 cancer cells. Here, we report DNA nanocarrier in the form of DNA-nanofibers (DNA-NFs) capable of loading CMPT via strand intercalation in the GC (base pairs)-rich regions of the DNA duplex. Hence, our keen purpose was to explore the potential of DNA-NFs to load CMPT and assess the improvements of the outcomes in terms of enhanced therapeutic effects to integrin-rich A549 cancer cells with reduced cytotoxic effects to integrin-lacking HEK293 cells. DNA-NFs were formulated as a polymer of DNA triangles. DNA triangles arranged in a programmed way through the complementary overhangs present at the vertices. DNA triangles were primarily obtained through the annealing of the freshly circularized scaffold strands with the three distinct staple strands of specific sequences. The polymerized triangular tiles instead of forming two-dimensional nanosheets underwent self-coiling to give rise to DNA-NF-shaped structures. Flow cytometry and MTT assays were performed to observe cytotoxic and apoptotic effects on integrin-rich A549 cancer cells compared with the integrin-deficient HEK293 cells. AFM, native-page, and confocal experiments confirmed the polymerization of DNA triangles and the morphology of the resulting nanostructures. AFM and confocal images revealed the length of DNA-NFs to be 3-6 μm and the width from 70 to 110 nm. CMPT loading (via strands intercalation) in GC-rich regions of DNA-NFs and the FN functionalization (TAMRA tagged; red fluorescence) via amide chemistry using amino-modified strands of DNA-NFs were confirmed through the UV-shift analysis (> 10 nm shift) and confocal imaging. Blank DNA-NFs were found to be highly biocompatible in 2-640 μM concentrations. MTT assay and flow cytometry experiments revealed that CMPT-loaded DNA-NFs showed a dose-dependent decrease in the cell viability to integrin-rich A549 cancer cells compared with the integrin-deficient HEK293 cells. Conclusively, FN-functionalized, CMPT-loaded DNA-NFs effectively destroyed integrin-rich A549 cancer cells in a targeted manner compared with integrin-deficient HEK293 cells. Grapical abstract.

Mystery eye: Human adenovirus and the enigma of epidemic keratoconjunctivitis

Known to occur in widespread outbreaks, epidemic keratoconjunctivitis (EKC) is a severe ocular surface infection with a strong historical association with human adenovirus (HAdV). While the conjunctival manifestations can vary from mild follicular conjunctivitis to hyper-acute, exudative conjunctivitis with formation of conjunctival membranes, EKC is distinct as the only form of adenovirus conjunctivitis in which the cornea is also involved, likely due to the specific corneal epithelial tropism of its causative viral agents. The initial development of a punctate or geographic epithelial keratitis may herald the later formation of stromal keratitis, and manifest as subepithelial infiltrates which often persist or recur for months to years after the acute infection has resolved. The chronic keratitis in EKC is associated with foreign body sensation, photophobia, glare, and reduced vision. However, over a century since the first clinical descriptions of EKC, and over 60 years since the first causative agent, human adenovirus type 8, was identified, our understanding of this disorder remains limited. This is underscored by a current lack of effective diagnostic tools and treatments. In part, stasis in our knowledge base has been encouraged by the continued acceptance, and indeed propagation of, inaccurate paradigms pertaining to disease etiology and pathogenesis, particularly with regard to mechanisms of innate and adaptive immunity within the cornea. Owing to its often persistent and medically refractory visual sequelae, reconsideration of key aspects of EKC disease biology is warranted to identify new treatment targets to curb its worldwide socioeconomic burden.

Genomic foundations of evolution and ocular pathogenesis in human adenovirus species D

Human adenovirus commonly causes infections of respiratory, gastrointestinal, genitourinary, and ocular surface mucosae. Although most adenovirus eye infections are mild and self-limited, specific viruses within human adenovirus species D are associated with epidemic keratoconjunctivitis (EKC), a severe and highly contagious ocular surface infection, which can lead to chronic and/or recurrent, visually disabling keratitis. In this review, we discuss the links between adenovirus ontogeny, genomics, immune responses, and corneal pathogenesis, for those viruses that cause EKC.

ITGB1b-Deficient Rare Minnows Delay Grass Carp Reovirus (GCRV) Entry and Attenuate GCRV-Triggered Apoptosis

Integrin β-1 (ITGB1) is a transmembrane protein belonging to the integrin family and it plays an important role in viral entry. In this study, the itgb1b gene of the rare minnow, Gobiocypris rarus, was cloned and analyzed. To investigate the possible role of itgb1b on grass carp reovirus (GCRV) infection, we generated an ITGB1b-deficient rare minnow (ITGB1b^-/-) using the CRISPR/Cas9 system. Following stimulation with GCRV, the survival time of the -ITGB1b^-/- rare minnows was extended in comparison to the wild-type minnows. Moreover, the relative copy number of GCRV and the level of clathrin-mediated endocytosis-associated and apoptosis-related gene expression in the ITGB1b^-/- rare minnows was significantly lower than that of the wild-type minnows. These results suggested that the absence of itgb1b reduced viral entry efficiency and the expression of apoptosis-related genes. Moreover, the data suggested that itgb1b played an important role in mediating the entry of viruses into the cells via clathrin. Therefore, these findings provide novel insight into the function of itgb1b in the process of GCRV infection.

Enteric Species F Human Adenoviruses use Laminin-Binding Integrins as Co-Receptors for Infection of Ht-29 Cells

The enteric species F human adenovirus types 40 and 41 (HAdV-40 and -41) are the third most common cause of infantile gastroenteritis in the world. Knowledge about HAdV-40 and -41 cellular infection is assumed to be fundamentally different from that of other HAdVs since HAdV-40 and -41 penton bases lack the αV-integrin-interacting RGD motif. This motif is used by other HAdVs mainly for internalization and endosomal escape. We hypothesised that the penton bases of HAdV-40 and -41 interact with integrins independently of the RGD motif. HAdV-41 transduction of a library of rodent cells expressing specific human integrin subunits pointed to the use of laminin-binding α2-, α3- and α6-containing integrins as well as other integrins as candidate co-receptors. Specific laminins prevented internalisation and infection, and recombinant, soluble HAdV-41 penton base proteins prevented infection of human intestinal HT-29 cells. Surface plasmon resonance analysis demonstrated that HAdV-40 and -41 penton base proteins bind to α6-containing integrins with an affinity similar to that of previously characterised penton base:integrin interactions. With these results, we propose that laminin-binding integrins are co-receptors for HAdV-40 and -41.

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.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Oral Administration and Detection of a Near-Infrared Molecular Imaging Agent in an Orthotopic Mouse Model for Breast Cancer Screening

Molecular imaging is advantageous for screening diseases such as breast cancer by providing precise spatial information on disease-associated biomarkers, something neither blood tests nor anatomical imaging can achieve. However, the high cost and risks of ionizing radiation for several molecular imaging modalities have prevented a feasible and scalable approach for screening. Clinical studies have demonstrated the ability to detect breast tumors using nonspecific probes such as indocyanine green, but the lack of molecular information and required intravenous contrast agent does not provide a significant benefit over current noninvasive imaging techniques. Here we demonstrate that negatively charged sulfate groups, commonly used to improve solubility of near-infrared fluorophores, enable sufficient oral absorption and targeting of fluorescent molecular imaging agents for completely noninvasive detection of diseased tissue such as breast cancer. These functional groups improve the pharmacokinetic properties of affinity ligands to achieve targeting efficiencies compatible with clinical imaging devices using safe, nonionizing radiation (near-infrared light). Together, this enables development of a “disease screening pill” capable of oral absorption and systemic availability, target binding, background clearance, and imaging at clinically relevant depths for breast cancer screening. This approach should be adaptable to other molecular targets and diseases for use as a new class of screening agents.

Beyond the Matrix: The Many Non-ECM Ligands for Integrins

The traditional view of integrins portrays these highly conserved cell surface receptors as mediators of cellular attachment to the extracellular matrix (ECM), and to a lesser degree, as coordinators of leukocyte adhesion to the endothelium. These canonical activities are indispensable; however, there is also a wide variety of integrin functions mediated by non-ECM ligands that transcend the traditional roles of integrins. Some of these unorthodox roles involve cell-cell interactions and are engaged to support immune functions such as leukocyte transmigration, recognition of opsonization factors, and stimulation of neutrophil extracellular traps. Other cell-cell interactions mediated by integrins include hematopoietic stem cell and tumor cell homing to target tissues. Integrins also serve as cell-surface receptors for various growth factors, hormones, and small molecules. Interestingly, integrins have also been exploited by a wide variety of organisms including viruses and bacteria to support infectious activities such as cellular adhesion and/or cellular internalization. Additionally, the disruption of integrin function through the use of soluble integrin ligands is a common strategy adopted by several parasites in order to inhibit blood clotting during hematophagy, or by venomous snakes to kill prey. In this review, we strive to go beyond the matrix and summarize non-ECM ligands that interact with integrins in order to highlight these non-traditional functions of integrins.

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.

Integrin beta and receptor for activated protein kinase C are involved in the cell entry of Bombyx mori cypovirus

Receptor-mediated endocytosis using a β1 integrin-dependent internalization was considered as the primary mechanism for the initiation of mammalian reovirus infection. Bombyx mori cypovirus (BmCPV) is a member of Reoviridae family which mainly infects the midgut epithelium of silkworm; the cell entry of BmCPV is poorly explored. In this study, co-immunoprecipitation (Co-IP), virus overlay protein binding assay (VOPBA), and BmCPV-protein interaction on the polyvinylidene difluoride membrane (BmCPV-PI-PVDF) methods were employed to screen the interacting proteins of BmCPV, and several proteins including integrin beta and receptor for activated protein kinase C (RACK1) were identified as the candidate interacting proteins for establishing the infection of BmCPV. The infectivity of BmCPV was investigated in vivo and in vitro by RNA interference (RNAi) and antibody blocking methods, and the results showed that the infectivity of BmCPV was significantly reduced by either small interfering RNA-mediated silencing of integrin beta and RACK1 or antibody blocking of integrin beta and RACK1. The expression level of integrin beta or RACK1 is not the highest in the silkworm midgut which is a principal target tissue of BmCPV, suggesting that the molecules other than integrin beta or RACK1 might play a key role in determining the tissue tropism of BmCPV infection. The establishment of BmCPV infection depends on other factors, and these factors interacted with integrin beta and RACK1 to form receptor complex for the cell entry of BmCPV.

Cell-cell communication mediated by the CAR subgroup of immunoglobulin cell adhesion molecules in health and disease

The immunoglobulin superfamily represents a diverse set of cell-cell contact proteins and includes well-studied members such as NCAM1, DSCAM, L1 or the contactins which are strongly expressed in the nervous system. In this review we put our focus on the biological function of a less understood subgroup of Ig-like proteins composed of CAR (coxsackievirus and adenovirus receptor), CLMP (CAR-like membrane protein) and BT-IgSF (brain and testis specific immunoglobulin superfamily). The CAR-related proteins are type I transmembrane proteins containing an N-terminal variable (V-type) and a membrane proximal constant (C2-type) Ig domain in their extracellular region which are implicated in homotypic adhesion. They are highly expressed during embryonic development in a variety of tissues including the nervous system whereby in adult stages the protein level of CAR and CLMP decreases, only BT-IgSF expression increases within age. CAR-related proteins are concentrated at specialized cell-cell communication sites such as gap or tight junctions and are present at the plasma membrane in larger protein complexes. Considerable progress has been made on the molecular structure and interactions of CAR while research on CLMP and BT-IgSF is at an early stage. Studies on mouse mutants revealed biological functions of CAR in the heart and for CLMP in the gastrointestinal and urogenital systems. Furthermore, CAR and BT-IgSF appear to regulate synaptic function in the hippocampus.

Role of MyD88 in adenovirus keratitis

Pattern recognition receptors (PRRs) are critical to the early detection and innate immune responses to pathogens. In particular, the TLR system and its associated adaptor proteins play essential roles in early host responses to infection. Epidemic keratoconjunctivitis, caused by the human adenovirus, is a severe ocular surface infection associated with corneal inflammation (stromal keratitis). We previously showed that adenovirus capsid was a key molecular pattern in adenovirus keratitis, with viral DNA playing a lesser role. We have now investigated the role of the adaptor molecule MyD88 in a mouse model of adenovirus keratitis in which there is no viral replication. In MyD88^−/− mice infected with human adenovirus type 37, clinical keratitis was markedly reduced, along with infiltration of CD45⁺ cells, and expression of inflammatory cytokines. Reduction of inflammatory cytokines was also observed in infected primary human corneal fibroblasts pretreated with a MyD88 inhibitory peptide. Keratitis similar to wild type mice was observed in TLR2, TLR9, and IL-1R knockout mice, but was reduced in TLR2/9 double knockout mice, consistent with synergy of TLR2 and TLR9 in the response to adenovirus infection. MyD88 co-immunoprecipitated with Src kinase in mice corneas and in human corneal fibroblasts infected with adenovirus, and MyD88 inhibitory peptide reduced Src phosphorylation, linking MyD88 activation to inflammatory gene expression through a signaling cascade previously shown to be directed by Src. Our findings reveal a critical role for the PRRs TLR2 and 9, and their adaptor protein MyD88, in corneal inflammation upon adenovirus infection.

Human Parechovirus 1 Infection Occurs via αVβ1 Integrin

Human parechovirus 1 (HPeV-1) (family Picornaviridae) is a global cause of pediatric respiratory and CNS infections for which there is no treatment. Although biochemical and in vitro studies have suggested that HPeV-1 binds to αVβ1, αVβ3 and αVβ6 integrin receptor(s), the actual cellular receptors required for infectious entry of HPeV-1 remain unknown. In this paper we analyzed the expression profiles of αVβ1, αVβ3, αVβ6 and α5β1 in susceptible cell lines (A549, HeLa and SW480) to identify which integrin receptors support HPeV-1 internalization and/or replication cycle. We demonstrate by antibody blocking assay, immunofluorescence microscopy and RT-qPCR that HPeV-1 internalizes and replicates in cell lines that express αVβ1 integrin but not αVβ3 or αVβ6 integrins. To further study the role of β1 integrin, we used a mouse cell line, GE11-KO, which is deficient in β1 expression, and its derivate GE11-β1 in which human integrin β1 subunit is overexpressed. HPeV-1 (Harris strain) and three clinical HPeV-1 isolates did not internalize into GE11-KO whereas GE11-β1 supported the internalization process. An integrin β1-activating antibody, TS2/16, enhanced HPeV-1 infectivity, but infection occurred in the absence of visible receptor clustering. HPeV-1 also co-localized with β1 integrin on the cell surface, and HPeV-1 and β1 integrin co-endocytosed into the cells. In conclusion, our results demonstrate that in some cell lines the cellular entry of HPeV-1 is primarily mediated by the active form of αVβ1 integrin without visible receptor clustering.

The αvβ1 integrin plays a critical in vivo role in tissue fibrosis

Integrins are transmembrane heterodimeric receptors that contribute to diverse biological functions and play critical roles in many human diseases. Studies using integrin subunit knockout mice and inhibitory antibodies have identified important roles for nearly every integrin heterodimer and led to the development of a number of potentially useful therapeutics. One notable exception is the αvβ1 integrin. αv and β1 subunits are individually present in numerous dimer pairs, making it challenging to infer specific roles for αvβ1 by genetic inactivation of individual subunits, and αvβ1 complex-specific blocking antibodies do not yet exist. We therefore developed a potent and highly specific small-molecule inhibitor of αvβ1 to probe the function of this understudied integrin. We found that αvβ1, which is highly expressed on activated fibroblasts, directly binds to the latency-associated peptide of transforming growth factor-β1 (TGFβ1) and mediates TGFβ1 activation. Therapeutic delivery of this αvβ1 inhibitor attenuated bleomycin-induced pulmonary fibrosis and carbon tetrachloride-induced liver fibrosis, suggesting that drugs based on this lead compound could be broadly useful for treatment of diseases characterized by excessive tissue fibrosis.

Tenascin-C and integrins in cancer

Tenascin-C (TNC) is highly expressed in cancer tissues. Its cellular sources are cancer and stromal cells, including fibroblasts/myofibroblasts, and also vascular cells. TNC expressed in cancer tissues dominantly contains large splice variants. Deposition of the stroma promotes the epithelial-mesenchymal transition, proliferation, and migration of cancer cells. It also facilitates the formation of cancer stroma including desmoplasia and angiogenesis. Integrin receptors that mediate the signals of TNC have also been discussed.

Tight Junctions Go Viral!

Tight junctions (TJs) are highly specialized membrane domains involved in many important cellular processes such as the regulation of the passage of ions and macromolecules across the paracellular space and the establishment of cell polarity in epithelial cells. Over the past few years there has been increasing evidence that different components of the TJs can be hijacked by viruses in order to complete their infectious cycle. Viruses from at least nine different families of DNA and RNA viruses have been reported to use TJ proteins in their benefit. For example, TJ proteins such as JAM-A or some members of the claudin family of proteins are used by members of the Reoviridae family and hepatitis C virus as receptors or co-receptors during their entry into their host cells. Reovirus, in addition, takes advantage of the TJ protein Junction Adhesion Molecule-A (JAM-A) to achieve its hematogenous dissemination. Some other viruses are capable of regulating the expression or the localization of TJ proteins to induce cell transformation or to improve the efficiency of their exit process. This review encompasses the importance of TJs for viral entry, replication, dissemination, and egress, and makes a clear statement of the importance of studying these proteins to gain a better understanding of the replication strategies used by viruses that infect epithelial and/or endothelial cells.

Beyond RGD: virus interactions with integrins

Viruses successfully infect host cells by initially binding to the surfaces of the cells, followed by an intricate entry process. As multifunctional heterodimeric cell-surface receptor molecules, integrins have been shown to usefully serve as entry receptors for a plethora of viruses. However, the exact role(s) of integrins in viral pathogen internalization has yet to be elaborately described. Notably, several viruses harbor integrin-recognition motifs displayed on viral envelope/capsid-associated proteins. The most common of these motifs is the minimal peptide sequence for binding integrins, RGD (Arg-Gly-Asp), which is known for its role in virus infection via its ability to interact with over half of the more than 20 known integrins. Not all virus-integrin interactions are RGD-dependent, however. Non-RGD-binding integrins have also been shown to effectively promote virus entry and infection as well. Such virus-integrin binding is shown to facilitate adhesion, cytoskeleton rearrangement, integrin activation, and increased intracellular signaling. Also, we have attempted to discuss the role of carbohydrate moieties in virus interactions with receptor-like host cell surface integrins that drive the process of internalization. As much as possible, this article examines the published literature regarding the role of integrins in terms of virus infection and virus-encoded glycosylated proteins that mediate interactions with integrins, and it explores the idea of targeting these receptors as a therapeutic treatment option.

Early Events in Chikungunya Virus Infection-From Virus Cell Binding to Membrane Fusion

Chikungunya virus (CHIKV) is a rapidly emerging mosquito-borne alphavirus causing millions of infections in the tropical and subtropical regions of the world. CHIKV infection often leads to an acute self-limited febrile illness with debilitating myalgia and arthralgia. A potential long-term complication of CHIKV infection is severe joint pain, which can last for months to years. There are no vaccines or specific therapeutics available to prevent or treat infection. This review describes the critical steps in CHIKV cell entry. We summarize the latest studies on the virus-cell tropism, virus-receptor binding, internalization, membrane fusion and review the molecules and compounds that have been described to interfere with virus cell entry. The aim of the review is to give the reader a state-of-the-art overview on CHIKV cell entry and to provide an outlook on potential new avenues in CHIKV research.

Tenascin-C and integrins in cancer

Tenascin-C (TNC) is highly expressed in cancer tissues. Its cellular sources are cancer and stromal cells, including fibroblasts/myofibroblasts, and also vascular cells. TNC expressed in cancer tissues dominantly contains large splice variants. Deposition of the stroma promotes the epithelial-mesenchymal transition, proliferation, and migration of cancer cells. It also facilitates the formation of cancer stroma including desmoplasia and angiogenesis. Integrin receptors that mediate the signals of TNC have also been discussed.

Adenovirus entry from the apical surface of polarized epithelia is facilitated by the host innate immune response

Prevention of viral-induced respiratory disease begins with an understanding of the factors that increase or decrease susceptibility to viral infection. The primary receptor for most adenoviruses is the coxsackievirus and adenovirus receptor (CAR), a cell-cell adhesion protein normally localized at the basolateral surface of polarized epithelia and involved in neutrophil transepithelial migration. Recently, an alternate isoform of CAR, CAREx8, has been identified at the apical surface of polarized airway epithelia and is implicated in viral infection from the apical surface. We hypothesized that the endogenous role of CAREx8 may be to facilitate host innate immunity. We show that IL-8, a proinflammatory cytokine and a neutrophil chemoattractant, stimulates the protein expression and apical localization of CAREx8 via activation of AKT/S6K and inhibition of GSK3β. Apical CAREx8 tethers infiltrating neutrophils at the apical surface of a polarized epithelium. Moreover, neutrophils present on the apical-epithelial surface enhance adenovirus entry into the epithelium. These findings suggest that adenovirus evolved to co-opt an innate immune response pathway that stimulates the expression of its primary receptor, apical CAREx8, to allow the initial infection the intact epithelium. In addition, CAREx8 is a new target for the development of novel therapeutics for both respiratory inflammatory disease and adenoviral infection.

Ultrastructure of adenovirus keratitis

PURPOSE

We determined the ultrastructure of mouse adenovirus keratitis, a model for human adenovirus keratitis.

METHODS

Adenovirus keratitis was induced in C57Bl/6j mice by intrastromal injection of human adenovirus species D type 37 (HAdV-D37) with a heat-pulled, glass, micropipette needle under compressed air. At select time points after infection, mice were euthanized and their corneas removed, fixed, and sectioned at 70-nm thickness for electron microscopy.

RESULTS

Injection of HAdV-D37 into the mouse corneal stroma placed virus predominantly in the pericellular corneal stromal matrix. Virus was seen bound to and entering stromal cells at 1 and 2 hours after infection, respectively. Cell membrane transit by virus was seen to involve two distinct structures resembling caveolae and macropinosomes. However, later during infection intracellular virus was not seen within membrane-bound organelles. By 8 hours after infection, intracellular virus had accumulated into densely packed, perinuclear arrays. Virus disassembly was not obvious at any time point after infection. Infiltrating neutrophils seen by one day after infection had engulfed degraded stromal cells by 4 days after infection.

CONCLUSIONS

By transmission electron microscopy, injected HAdV-D37 readily enters stromal cells in the C57Bl/6j mouse cornea and induces stromal inflammation, as was shown previously by light microscopy. However, electron microscopy also revealed dense, static arrays of intracytoplasmic virus, suggesting a block in viral capsid disassembly and viral DNA nuclear entry. These findings may explain why human adenoviruses do not replicate in the mouse corneal stroma.

Integrins and integrin-associated proteins in the cardiac myocyte

Integrins are heterodimeric, transmembrane receptors that are expressed in all cells, including those in the heart. They participate in multiple critical cellular processes including adhesion, extracellular matrix organization, signaling, survival, and proliferation. Particularly relevant for a contracting muscle cell, integrins are mechanotransducers, translating mechanical to biochemical information. Although it is likely that cardiovascular clinicians and scientists have the highest recognition of integrins in the cardiovascular system from drugs used to inhibit platelet aggregation, the focus of this article will be on the role of integrins specifically in the cardiac myocyte. After a general introduction to integrin biology, the article will discuss important work on integrin signaling, mechanotransduction, and lessons learned about integrin function from a range of model organisms. Then we will detail work on integrin-related proteins in the myocyte, how integrins may interact with ion channels and mediate viral uptake into cells, and also play a role in stem cell biology. Finally, we will discuss directions for future study.

Kinetic analysis of mouse brain proteome alterations following Chikungunya virus infection before and after appearance of clinical symptoms

Recent outbreaks of Chikungunya virus (CHIKV) infection have been characterized by an increasing number of severe cases with atypical manifestations including neurological complications. In parallel, the risk map of CHIKV outbreaks has expanded because of improved vector competence. These features make CHIKV infection a major public health concern that requires a better understanding of the underlying physiopathological processes for the development of antiviral strategies to protect individuals from severe disease. To decipher the mechanisms of CHIKV infection in the nervous system, a kinetic analysis on the host proteome modifications in the brain of CHIKV-infected mice sampled before and after the onset of clinical symptoms was performed. The combination of 2D-DIGE and iTRAQ proteomic approaches, followed by mass spectrometry protein identification revealed 177 significantly differentially expressed proteins. This kinetic analysis revealed a dramatic down-regulation of proteins before the appearance of the clinical symptoms followed by the increased expression of most of these proteins in the acute symptomatic phase. Bioinformatic analyses of the protein datasets enabled the identification of the major biological processes that were altered during the time course of CHIKV infection, such as integrin signaling and cytoskeleton dynamics, endosome machinery and receptor recycling related to virus transport and synapse function, regulation of gene expression, and the ubiquitin-proteasome pathway. These results reveal the putative mechanisms associated with severe CHIKV infection-mediated neurological disease and highlight the potential markers or targets that can be used to develop diagnostic and/or antiviral tools.

Transgene delivery to cultured keratinocytes via replication-deficient adenovirus vectors

Transient transgene expression can facilitate investigation of that gene-product function or effect on keratinocyte biology. Several chemical and biologic delivery systems are available, and among them adenoviruses offer particular advantages in efficiency and transgene capacity. Here we describe the advantages of bicistronic adenovirus and inclusion of the polycation hexadimethrine bromide to aid in the detection of positively transduced cells and enhance transduction efficiency.

Co-liposomes comprising a lipidated multivalent RGD-peptide and a cationic gemini cholesterol induce selective gene transfection in αvβ3 and αvβ5 integrin receptor-rich cancer cells

Palmitoylated-RGD4 mediated gene transfer and cell targeting using a cationic gemini cholesterol based liposome.

Caveolin-1 associated adenovirus entry into human corneal cells

The cellular entry of viruses represents a critical area of study, not only for viral tropism, but also because viral entry dictates the nature of the immune response elicited upon infection. Epidemic keratoconjunctivitis (EKC), caused by viruses within human adenovirus species D (HAdV-D), is a severe, ocular surface infection associated with corneal inflammation. Clathrin-mediated endocytosis has previously been shown to play a critical role in entry of other HAdV species into many host cell types. However, HAdV-D endocytosis into corneal cells has not been extensively studied. Herein, we show an essential role for cholesterol rich, lipid raft microdomains and caveolin-1, in the entry of HAdV-D37 into primary human corneal fibroblasts. Cholesterol depletion using methyl-β-cyclodextrin (MβCD) profoundly reduced viral infection. When replenished with soluble cholesterol, the effect of MβCD was reversed, allowing productive viral infection. HAdV-D37 DNA was identified in caveolin-1 rich endosomal fractions after infection. Src kinase activity was also increased in caveolin-1 rich endosomal fractions after infection, and Src phosphorylation and CXCL1 induction were both decreased in caveolin-1-/- mice corneas compared to wild type mice. siRNA knock down of caveolin-1 in corneal cells reduced chemokine induction upon viral infection, and caveolin-1-/- mouse corneas showed reduced cellular entry of HAdV-D37. As a control, HAdV-C2, a non-corneal pathogen, appeared to utilize the caveolar pathway for entry into A549 cells, but failed to infect corneal cells entirely, indicating virus and cell specific tropism. Immuno-electron microscopy confirmed the presence of caveolin-1 in HAdV-D37-containing vesicles during the earliest stages of viral entry. Collectively, these experiments indicate for the first time that HAdV-D37 uses a lipid raft mediated caveolin-1 associated pathway for entry into corneal cells, and connects the processes of viral entry with downstream proinflammatory cell signaling.

Amino Acid Sequences Mediating Vascular Cell Adhesion Molecule 1 Binding to Integrin Alpha 4: Homologous DSP Sequence Found for JC Polyoma VP1 Coat Protein

The JC polyoma viral coat protein VP1 was analyzed for amino acid sequences homologies to the IDSP sequence which mediates binding of VLA-4 (integrin alpha 4) to vascular cell adhesion molecule 1. Although the full sequence was not found, a DSP sequence was located near the critical arginine residue linked to infectivity of the virus and binding to sialic acid containing molecules such as integrins (3). For the JC polyoma virus, a DSP sequence was found at residues 70, 71 and 72 with homology also noted for the mouse polyoma virus and SV40 virus. Three dimensional modeling of the VP1 molecule suggests that the DSP loop has an accessible site for interaction from the external side of the assembled viral capsid pentamer.

The disulfide bond of an RGD4C motif inserted within the Hi loop of the adenovirus type 5 fiber protein is critical for retargeting to αv -integrins

BACKGROUND

The α(v) -integrin binding motif RGD4C (CDCRGDCFC) has been used extensively to circumvent inefficient adenovirus type 5 (Ad5) transduction of cells expressing low levels of the coxsackie and adenovirus receptor. However, until now, it has been unclear whether disulfide bonds in the RGD4C motif influence the retargeting potential of RGD4C-modified Ad5.

METHODS

Replication deficient Ad5 bearing wild-type fiber (Ad5wt) or RGD4G, RGD4C and RGD2C2G insertions within the HI loop of the fiber protein (Ad5RGD4G, Ad5RGD4C and Ad5RGD2C2G, respectively) were used to transduce a panel of cancer cell lines, with or without previous treatment of these Ad5s with the reducing agent dithiothreitol (DTT). In parallel, native and DTT-treated fiber proteins isolated from purified Ad5RGD4C were compared by mass spectrometry.

RESULTS

Ad5RGD4C transduced all studied cell lines much more efficiently than Ad5wt, whereas Ad5RGD4G transduced cells only slightly more efficiently than Ad5wt. DTT treatment had no effect on cell transduction by wild-type Ad5wt and Ad5RGD4G but abolished the increased transduction efficacy of Ad5RGD4C in a dose-dependent manner. The mass spectra of native and DTT-reduced tryptic digests of the Ad5RGD4C fiber protein are consistent with the presence of a C(547) -C(549) linkage in the C(547) DC(549) RGDC(553) FC(555) motif. Finally, the high transduction efficacy of Ad5RGD4C is conserved in Ad5RGD2C2G.

CONCLUSIONS

We provide genetic and biochemical data strongly suggesting that cysteines C(547) and C(549) from the C(547) DC(549) RGDC(553) FC(555) motif inserted in the HI loop of the Ad5 fiber form a single disulfide bond, with this disulfide bond being crucial for Ad5RGD4C retargeting to av-integrins.

Integrins modulate the infection efficiency of West Nile virus into cells

The underlying mechanisms allowing West Nile virus (WNV) to replicate in a large variety of different arthropod, bird and mammal species are largely unknown but are believed to rely on highly conserved proteins relevant for viral entry and replication. Consistent with this, the integrin αvβ3 has been proposed lately to function as the cellular receptor for WNV. More recently published data, however, are not in line with this concept. Integrins are highly conserved among diverse taxa and are expressed by almost every cell type at high numbers. Our study was designed to clarify the involvement of integrins in WNV infection of cells. A cell culture model, based on wild-type and specific integrin knockout cell lines lacking the integrin subunits αv, β1 or β3, was used to investigate the susceptibility to WNV, and to evaluate binding and replication efficiencies of four distinct strains (New York 1999, Uganda 1937, Sarafend and Dakar). Though all cell lines were permissive, clear differences in replication efficiencies were observed. Rescue of the β3-integrin subunit resulted in enhanced WNV yields of up to 90 %, regardless of the virus strain used. Similar results were obtained for β1-expressing and non-expressing cells. Binding, however, was not affected by the expression of the integrins in question, and integrin blocking antibodies failed to have any effect. We conclude that integrins are involved in WNV infection but not at the level of binding to target cells.

Chapter two--Adenovirus strategies for tissue-specific targeting

Cancer gene therapy approaches have benefited greatly from the utilization of molecular-based therapeutics. Of these, adenovirus-based interventions hold much promise as a platform for targeted therapeutic delivery to tumors. However, a barrier to this progression is the lack of native adenovirus receptor expression on a variety of cancer types. As such, any adenovirus-based cancer therapy must take into consideration retargeting the vector to nonnative cellular surface receptors. Predicated upon the knowledge gained in native adenovirus biology, several strategies to transductionally retarget adenovirus have emerged. Herein, we describe the biological hurdles as well as strategies utilized in adenovirus transductional targeting, covering the progress of both adapter-based and genetic manipulation-based targeting. Additionally, we discuss recent translation of these targeting strategies into a clinical setting.

An adenovirus vector incorporating carbohydrate binding domains utilizes glycans for gene transfer

BACKGROUND

Vectors based on human adenovirus serotype 5 (HAdV-5) continue to show promise as delivery vehicles for cancer gene therapy. Nevertheless, it has become clear that therapeutic benefit is directly linked to tumor-specific vector localization, highlighting the need for tumor-targeted gene delivery. Aberrant glycosylation of cell surface glycoproteins and glycolipids is a central feature of malignant transformation, and tumor-associated glycoforms are recognized as cancer biomarkers. On this basis, we hypothesized that cancer-specific cell-surface glycans could be the basis of a novel paradigm in HAdV-5-based vector targeting.

METHODOLOGY/PRINCIPAL FINDINGS

As a first step toward this goal, we constructed a novel HAdV-5 vector encoding a unique chimeric fiber protein that contains the tandem carbohydrate binding domains of the fiber protein of the NADC-1 strain of porcine adenovirus type 4 (PAdV-4). This glycan-targeted vector displays augmented CAR-independent gene transfer in cells with low CAR expression. Further, we show that gene transfer is markedly decreased in cells with genetic glycosylation defects and by inhibitors of glycosylation in normal cells.

CONCLUSIONS/SIGNIFICANCE

These data provide the initial proof-of-concept for HAdV-5 vector-mediated gene delivery based on the presence of cell-surface carbohydrates. Further development of this new targeting paradigm could provide targeted gene delivery based on vector recognition of disease-specific glycan biomarkers.

Reduced infectivity of adenovirus type 5 particles and degradation of entering viral genomes associated with incomplete processing of the preterminal protein

To investigate further the contribution of the adenovirus type 5 (Ad5) E1B 55-kDa protein to genome replication, viral DNA accumulation was examined in primary human fibroblasts and epithelial cells infected with Ad5 or the E1B 55-kDa-null mutant Hr6. Unexpectedly, all cell types were observed to contain a significantly higher concentration of entering Hr6 than of Ad5 DNA, as did an infectious unit of Hr6. However, the great majority of the Hr6 genomes were degraded soon after entry. As this unusual phenotype cannot be ascribed to the Hr6 E1B frameshift mutation (J. S. Chahal and S. J. Flint, J. Virol. 86:3064-3072, 2012), the sequences of the Ad5 and Hr6 genomes were compared by using high-throughput sequencing. Seven previously unrecognized mutations were identified in the Hr6 genome, two of which result in substitutions in virion proteins, G315V in the preterminal protein (preTP) and A406V in fiber protein IV. Previous observations and the visualization by immunofluorescence of greater numbers of viral genomes entering the cytosol of Hr6-infected cells than of Ad5-infected cells indicated that the fiber mutation could not be responsible for the low-infectivity phenotype of Hr6. However, comparison of the forms of terminal protein present in purified virus particles indicated that the production of mature terminal protein from a processing intermediate is impaired in Hr6 particles. We therefore propose that complete processing of preTP within virus particles is necessary for the ability of viral genomes to become localized at appropriate sites and persist in infected cells.

Guiding plant virus particles to integrin-displaying cells

Viral nanoparticles (VNPs) are structurally regular, highly stable, tunable nanomaterials that can be conveniently produced in high yields. Unmodified VNPs from plants and bacteria generally do not show tissue specificity or high selectivity in binding to or entry into mammalian cells. They are, however, malleable by both genetic and chemical means, making them useful scaffolds for the display of large numbers of cell- and tissue-targeting ligands, imaging moieties, and/or therapeutic agents in a well-defined manner. Capitalizing on this attribute, we modified the genetic sequence of the Cowpea mosaic virus (CPMV) coat protein to display an RGD oligopeptide sequence derived from human adenovirus type 2 (HAdV-2). Concurrently, wild-type CPMV was modified via NHS acylation and Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry to attach an integrin-binding cyclic RGD peptide. Both types of particles showed strong and selective affinity for several different cancer cell lines that express RGD-binding integrin receptors.

Analysis of human adenovirus type 19 associated with epidemic keratoconjunctivitis and its reclassification as adenovirus type 64

PURPOSE

Human adenovirus species D type 19 (HAdV-D19) has been associated with epidemic keratoconjunctivitis (EKC), a highly inflammatory infection of the ocular surface. Confusion exists regarding the origins of HAdV-D19. The prototype virus (HAdV-D19p) does not cause EKC, while a virus identified later with the identical serologic determinant is a significant ocular pathogen.

METHODS

High throughput genome sequencing and bioinformatics analysis were performed on HAdV-D19p and three HAdV-D19 EKC strains, and compared to the previously sequenced clinical isolate, HAdV-D19 (C) and HAdV-D37. Corneas of C57BL/6J mice were injected with HAdV-D19p, HAdV-D19 (C), or virus-free buffer, and inflammation assessed by clinical examination, flow cytometry, and cytokine ELISA. Confocal microscopy and real-time PCR of infected corneal cell cultures were used to test viral entry.

RESULTS

HAdV-D19 (C) and the other clinical EKC isolates showed nearly 100% sequence identity. EKC strains diverged from HAdV-D19p in the penton base, E3, and fiber transcription units. Simplot analysis showed recombination between EKC-associated HAdV-D19 with HAdV-D37, HAdV-D22, and HAdV-D19p, the latter contributing only the hexon gene, the principal serum neutralization determinant. HAdV-D19p induced stromal keratitis in the C57BL/6J mouse, but failed to infect productively human corneal epithelial cells. These data led to retyping of the clinical EKC isolates with a HAdV-D19 hexon gene as HAdV-D64.

CONCLUSIONS

HAdV-D19 associated with EKC (HAdV-D64) originated from a recombination between HAdV-D19p, HAdV-D37, and HAdV-D22, and was mischaracterized because of a shared hexon gene. HAdV-D19p is not infectious for corneal epithelial cells, thus explaining the lack of any association with keratitis.

Comparative proteomic analysis of a cytosolic fraction from β3 integrin-deficient cells

Integrins are heterodimeric transmembrane receptors involved in sensing and transmitting informational cues from the extracellular environment to the cell. This study explored sub-proteome changes in response to elimination of the β3 integrin using a knockout murine model. Cleavable isotope-coded affinity tagging (cICAT) in combination with sub-cellular fractionation, multiple dimensions of separation and tandem mass spectrometry (MS/MS) were used to characterize differentially expressed proteins among β3 integrin(-/-) (β3(-/-)) mouse embryonic fibroblasts and isogenic wild-type (WT) controls. From a cytosolic protein fraction, 48 proteins were identified, in which expression differed by > 1.5-fold. Predominant ontological groups included actin-binding/cytoskeletal proteins and protease/protease inhibitors. Interestingly, β3 integrin expression was inversely correlated with expression of cathepsin B, a lysosomal cysteine protease, as its expression was greater by over 3.5-fold in the β3(-/-) cells. This inverse correlation was also observed in stable heterologous cells transfected with β3 integrin, where the intracellular expression and activity of cathepsin B was lower compared to control cells. Our data suggests that the composition of the cellular proteome is influenced by integrin expression patterns and reveals a strong functional relationship between β3 integrin and cathepsin B.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.