Purification of the putative coxsackievirus B receptor from HeLa cells

Receptors and Host Factors for Enterovirus Infection: Implications for Cancer Therapy

Enteroviruses, with their diverse clinical manifestations ranging from mild or asymptomatic infections to severe diseases such as poliomyelitis and viral myocarditis, present a public health threat. However, they can also be used as oncolytic agents. This review shows the intricate relationship between enteroviruses and host cell factors. Enteroviruses utilize specific receptors and coreceptors for cell entry that are critical for infection and subsequent viral replication. These receptors, many of which are glycoproteins, facilitate virus binding, capsid destabilization, and internalization into cells, and their expression defines virus tropism towards various types of cells. Since enteroviruses can exploit different receptors, they have high oncolytic potential for personalized cancer therapy, as exemplified by the antitumor activity of certain enterovirus strains including the bioselected non-pathogenic Echovirus type 7/Rigvir, approved for melanoma treatment. Dissecting the roles of individual receptors in the entry of enteroviruses can provide valuable insights into their potential in cancer therapy. This review discusses the application of gene-targeting techniques such as CRISPR/Cas9 technology to investigate the impact of the loss of a particular receptor on the attachment of the virus and its subsequent internalization. It also summarizes the data on their expression in various types of cancer. By understanding how enteroviruses interact with specific cellular receptors, researchers can develop more effective regimens of treatment, offering hope for more targeted and efficient therapeutic strategies.

Emerging Viral Infections and the Potential Impact on Hypertension, Cardiovascular Disease, and Kidney Disease

Viruses are ubiquitous in the environment and continue to have a profound impact on human health and disease. The COVID-19 pandemic has highlighted this with impressive morbidity and mortality affecting the world's population. Importantly, the link between viruses and hypertension, cardiovascular disease, and kidney disease has resulted in a renewed focus and attention on this potential relationship. The virus responsible for COVID-19, SARS-CoV-2, has a direct link to one of the major enzymatic regulatory systems connected to blood pressure control and hypertension pathogenesis, the renin-angiotensin system. This is because the entry point for SARS-CoV-2 is the ACE2 (angiotensin-converting enzyme 2) protein. ACE2 is one of the main enzymes responsible for dampening the primary effector peptide Ang II (angiotensin II), metabolizing it to Ang-(1-7). A myriad of clinical questions has since emerged and are covered in this review. Several other viruses have been linked to hypertension, cardiovascular disease, and kidney health. Importantly, patients with high-risk apolipoprotein L1 (APOL1) alleles are at risk for developing the kidney lesion of collapsing glomerulopathy after viral infection. This review will highlight several emerging viruses and their potential unique tropisms for the kidney and cardiovascular system. We focus on SARS-CoV-2 as this body of literature in regards to cardiovascular disease has advanced significantly since the COVID-19 pandemic.

Coxsackievirus B3-Its Potential as an Oncolytic Virus

Oncolytic virotherapy represents one of the most advanced strategies to treat otherwise untreatable types of cancer. Despite encouraging developments in recent years, the limited fraction of patients responding to therapy has demonstrated the need to search for new suitable viruses. Coxsackievirus B3 (CVB3) is a promising novel candidate with particularly valuable features. Its entry receptor, the coxsackievirus and adenovirus receptor (CAR), and heparan sulfate, which is used for cellular entry by some CVB3 variants, are highly expressed on various cancer types. Consequently, CVB3 has broad anti-tumor activity, as shown in various xenograft and syngeneic mouse tumor models. In addition to direct tumor cell killing the virus induces a strong immune response against the tumor, which contributes to a substantial increase in the efficiency of the treatment. The toxicity of oncolytic CVB3 in healthy tissues is variable and depends on the virus strain. It can be abrogated by genetic engineering the virus with target sites of microRNAs. In this review, we present an overview of the current status of the development of CVB3 as an oncolytic virus and outline which steps still need to be accomplished to develop CVB3 as a therapeutic agent for clinical use in cancer treatment.

Location of the Cell Adhesion Molecule "Coxsackievirus and Adenovirus Receptor" in the Adult Mouse Brain

The coxsackievirus and adenovirus receptor (CAR) is a single-pass transmembrane cell adhesion molecule (CAM). CAR is expressed in numerous mammalian tissues including the brain, heart, lung, and testes. In epithelial cells, CAR functions are typical of the quintessential roles of numerous CAMs. However, in the brain the multiple roles of CAR are poorly understood. To better understand the physiological role of CAR in the adult brain, characterizing its location is a primordial step to advance our knowledge of its functions. In addition, CAR is responsible for the attachment, internalization, and retrograde transport of canine adenovirus type 2 (CAV-2) vectors, which have found a niche in the mapping of neuronal circuits and gene transfer to treat and model neurodegenerative diseases. In this study, we used immunohistochemistry and immunofluorescence to document the global location of CAR in the healthy, young adult mouse brain. Globally, we found that CAR is expressed by maturing and mature neurons in the brain parenchyma and located on the soma and on projections. While CAR occasionally colocalizes with glial fibrillary acidic protein, this overlap was restricted to areas that are associated with adult neurogenesis.

The coxsackievirus and adenovirus receptor: virological and biological beauty

The coxsackievirus and adenovirus receptor (CAR) is an essential multifunctional cellular protein that is only beginning to be understood. CAR serves as a receptor for many adenoviruses, human group B coxsackieviruses, swine vesicular disease virus, and possibly other viruses. While named for its function as a viral receptor, CAR is also involved in cell adhesion, immune cell activation, synaptic transmission, and signaling. Knockout mouse models were first to identify some of these biological functions; however, tissue-specific model systems have shed light on the complexity of different CAR isoforms and their specific activities. Many of these functions are mediated by the large number of interacting proteins described so far, and several new putative interactions have recently been discovered. As antiviral and gene therapy strategies that target CAR continue to emerge, future work poised to understand the biological implications of manipulating CAR in vivo is critical.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.

Enteroviruses: A Gut-Wrenching Game of Entry, Detection, and Evasion

Enteroviruses are a major source of human disease, particularly in neonates and young children where infections can range from acute, self-limited febrile illness to meningitis, endocarditis, hepatitis, and acute flaccid myelitis. The enterovirus genus includes poliovirus, coxsackieviruses, echoviruses, enterovirus 71, and enterovirus D68. Enteroviruses primarily infect by the fecal-oral route and target the gastrointestinal epithelium early during their life cycles. In addition, spread via the respiratory tract is possible and some enteroviruses such as enterovirus D68 are preferentially spread via this route. Once internalized, enteroviruses are detected by intracellular proteins that recognize common viral features and trigger antiviral innate immune signaling. However, co-evolution of enteroviruses with humans has allowed them to develop strategies to evade detection or disrupt signaling. In this review, we will discuss how enteroviruses infect the gastrointestinal tract, the mechanisms by which cells detect enterovirus infections, and the strategies enteroviruses use to escape this detection.

The cell adhesion protein CAR is a negative regulator of synaptic transmission

The Coxsackievirus and adenovirus receptor (CAR) is essential for normal electrical conductance in the heart, but its role in the postnatal brain is largely unknown. Using brain specific CAR knockout mice (KO), we discovered an unexpected role of CAR in neuronal communication. This includes increased basic synaptic transmission at hippocampal Schaffer collaterals, resistance to fatigue, and enhanced long-term potentiation. Spontaneous neurotransmitter release and speed of endocytosis are increased in KOs, accompanied by increased expression of the exocytosis associated calcium sensor synaptotagmin 2. Using proximity proteomics and binding studies, we link CAR to the exocytosis machinery as it associates with syntenin and synaptobrevin/VAMP2 at the synapse. Increased synaptic function does not cause adverse effects in KO mice, as behavior and learning are unaffected. Thus, unlike the connexin-dependent suppression of atrioventricular conduction in the cardiac knockout, communication in the CAR deficient brain is improved, suggesting a role for CAR in presynaptic processes.

Adenovirus transduction: More complicated than receptor expression

The abundance and accessibility of a primary virus receptor are critical factors that impact the susceptibility of a host cell to virus infection. The Coxsackievirus and adenovirus receptor (CAR) has two transmembrane isoforms that occur due to alternative splicing and differ in localization and function in polarized epithelia. To determine the relevance of isoform-specific expression across cell types, the abundance and localization of both isoforms were determined in ten common cell lines, and correlated with susceptibility to adenovirus transduction relative to polarized primary human airway epithelia. Data show that the gene and protein expression for each isoform of CAR varies significantly between cell lines and polarization, as indicated by high transepithelial resistance, is inversely related to adenovirus transduction. In summary, the variability of polarity and isoform-specific expression among model cells are critical parameters that must be considered when evaluating the clinical relevance of potential adenovirus-mediated gene therapy and anti-adenovirus strategies.

Membrane Dynamics and Signaling of the Coxsackievirus and Adenovirus Receptor

The coxsackievirus and adenovirus receptor (CAR) belongs to the immunoglobulin superfamily and acts as a receptor for some adenovirus types and group B coxsackieviruses. Its role is best described in epithelia where CAR participates to tight junction integrity and maintenance. Recently, several studies aimed to characterize its potential interaction with intracellular signaling pathways and highlighted several features linking CAR to gene expression. In addition, the molecular mechanisms leading to CAR-specific membrane targeting via the secretory pathway in polarized cells and its internalization are starting to be unraveled. This chapter discusses the interaction between membrane dynamics, intracellular trafficking, and signaling of CAR.

Podocyte-Specific Deletion of Murine CXADR Does Not Impair Podocyte Development, Function or Stress Response

The coxsackie- and adenovirus receptor (CXADR) is a member of the immunoglobulin protein superfamily, present in various epithelial cells including glomerular epithelial cells. Beside its known function as a virus receptor, it also constitutes an integral part of cell-junctions. Previous studies in the zebrafish pronephros postulated a potential role of CXADR for the terminal differentiation of glomerular podocytes and correct patterning of the elaborated foot process architecture. However, due to early embryonic lethality of constitutive Cxadr knockout mice, mammalian data on kidney epithelial cells have been lacking. Interestingly, Cxadr is robustly expressed during podocyte development and in adulthood in response to glomerular injury. We therefore used a conditional transgenic approach to elucidate the function of Cxadr for podocyte development and stress response. Surprisingly, we could not discern a developmental phenotype in podocyte specific Cxadr knock-out mice. In addition, despite a significant up regulation of CXADR during toxic, genetic and immunologic podocyte injury, we could not detect any impact of Cxadr on these injury models. Thus these data indicate that in contrast to lower vertebrate models, mammalian podocytes have acquired molecular programs to compensate for the loss of Cxadr.

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.

Deep sequencing analysis of viral infection and evolution allows rapid and detailed characterization of viral mutant spectrum

Motivation: The study of RNA virus populations is a challenging task. Each population of RNA virus is composed of a collection of different, yet related genomes often referred to as mutant spectra or quasispecies. Virologists using deep sequencing technologies face major obstacles when studying virus population dynamics, both experimentally and in natural settings due to the relatively high error rates of these technologies and the lack of high performance pipelines. In order to overcome these hurdles we developed a computational pipeline, termed ViVan (Viral Variance Analysis). ViVan is a complete pipeline facilitating the identification, characterization and comparison of sequence variance in deep sequenced virus populations.

Results: Applying ViVan on deep sequenced data obtained from samples that were previously characterized by more classical approaches, we uncovered novel and potentially crucial aspects of virus populations. With our experimental work, we illustrate how ViVan can be used for studies ranging from the more practical, detection of resistant mutations and effects of antiviral treatments, to the more theoretical temporal characterization of the population in evolutionary studies.

Availability and implementation: Freely available on the web at http://www.vivanbioinfo.org

Contact: nshomron@post.tau.ac.il

Supplementary information:Supplementary data are available at Bioinformatics online.

The PDZ3 domain of the cellular scaffolding protein MAGI-1 interacts with the Coxsackievirus and adenovirus receptor (CAR)

The Coxsackievirus and adenovirus receptor (CAR) is an essential cellular protein that is involved in cell-cell adhesion, protein trafficking, and viral infection. The major isoform of CAR is selectively sorted to the basolateral membrane of polarized epithelial cells where it co-localizes with the cellular scaffolding protein membrane-associated guanylate kinase with inverted domain structure-1 (MAGI-1). Previously, we demonstrated CAR interacts with MAGI-1 through a PDZ-domain dependent interaction. Here, we show that the PDZ3 domain of MAGI-1 is exclusively responsible for the high affinity interaction between the seven exon isoform of CAR and MAGI-1 using yeast-two-hybrid analysis and confirming this interaction biochemically and in cellular lysates by in vitro pull down assay and co-immunoprecipitation. The high affinity interaction between the PDZ3 domain and CAR C-terminus was measured by fluorescence resonance energy transfer. Further, we investigated the biological relevance of this high affinity interaction between CAR and the PDZ3 domain of MAGI-1 and found that it does not alter CAR-mediated adenovirus infection. By contrast, interruption of this high affinity interaction altered the localization of MAGI-1 indicating that CAR is able to traffic MAGI-1 to cell junctions. These data deepen the molecular understanding of the interaction between CAR and MAGI-1 and indicate that although CAR plays a role in trafficking PDZ-based scaffolding proteins to cellular junctions, association with a high affinity intracellular binding partner does not significantly alter adenovirus binding and entry via CAR.

Flow cytometry analysis of coxsackievirus B receptors expression in human CaCo-2 cells

A subset of coxsackieviruses B (CV-B) is able to initiate intestinal infection via the attachment to two cell surface proteins, decayaccelerating factor (DAF) and coxsackie adenovirus receptor (CAR). The aim of the present study was to investigate the expression pattern of these receptors in the polarized CaCo-2 cell line using flow cytometry. The expression of CAR-specific mRNA and proteins was analyzed by reverse transcriptase polymerase chain reaction and western blotting, respectively. Flow cytometry analysis was used to study the surface expression patterns of CAR and DAF. CAR and DAF were well detected at the surface of CaCo-2 cells by flow cytometry. Despite the fact that CAR was susceptible to the action of trypsin, a few amounts of the latter enzyme and a precise dilution did not impair its correct detection by flow cytometry. This technique was used to demonstrate that the density of cells did not influence the expression of CAR at the cell surface. CaCo-2 cells express high levels of CAR and DAF at their surface. Flow cytometry, if used adequately, represents a helpful tool for the study of the interactions between these cells and various viral targets.

The Coxsackievirus and Adenovirus Receptor (CAR) undergoes ectodomain shedding and regulated intramembrane proteolysis (RIP)

The Coxsackievirus and Adenovirus Receptor (CAR) is a cell adhesion molecule originally characterized as a virus receptor but subsequently shown to be involved in physiological processes such as neuronal and heart development, epithelial tight junction integrity, and tumour suppression. Proteolysis of cell adhesion molecules and a wide variety of other cell surface proteins serves as a mechanism for protein turnover and, in some cases, cell signaling. Metalloproteases such as A Disintegrin and Metalloprotease (ADAM) family members cleave cell surface receptors to release their substrates' ectodomains, while the presenilin/ɣ-secretase complex mediates regulated intramembrane proteolysis (RIP), releasing intracellular domain fragments from the plasma membrane. In the case of some substrates such as Notch and amyloid precursor protein (APP), the released intracellular domains enter the nucleus to modulate gene expression. We report that CAR ectodomain is constitutively shed from glioma cells and developing neurons, and is also shed when cells are treated with the phorbol ester phorbol 12-myristate 13-acetate (PMA) and the calcium ionophore ionomycin. We identified ADAM10 as a sheddase of CAR using assays involving shRNA knockdown and rescue, overexpression of wild-type ADAM10 and inhibition of ADAM10 activity by addition of its prodomain. In vitro peptide cleavage, mass spectrometry and mutagenesis revealed the amino acids M224 to L227 of CAR as the site of ADAM10-mediated ectodomain cleavage. CAR also undergoes RIP by the presenilin/γ-secretase complex, and the intracellular domain of CAR enters the nucleus. Ectodomain shedding is a prerequisite for RIP of CAR. Thus, CAR belongs to the increasing list of cell surface molecules that undergo ectodomain shedding and that are substrates for ɣ-secretase-mediated RIP.

[Early steps of picornavirus infection]

Picornaviridae is a large family of viruses that cause a variety of infectious diseases in humans and animals. It includes important viruses such as poliovirus, hepatisis A virus and foot and mouth disease virus. Early steps of infection play important roles in determining the host range and the target organs for each virus. Here, I review the recent advances in the studies of cellular receptors for picornaviruses, mechanisms of cell entry and viral uncoating.

The PDZ1 and PDZ3 domains of MAGI-1 regulate the eight-exon isoform of the coxsackievirus and adenovirus receptor

Epithelial integrity is essential for homeostasis and poses a formidable barrier to pathogen entry. Major factors for viral entry into epithelial cells are the localization and abundance of the primary receptor. The coxsackievirus and adenovirus receptor (CAR) is a primary receptor for these two pathogenic groups of viruses. In polarized epithelia, a low-abundance, alternatively spliced eight-exon isoform of CAR, CAR(Ex8), is localized apically where it can support viral infection from the air-exposed surface. Using biochemical, cell biology, genetic, and spectroscopic approaches, we show that the levels of apical CAR(Ex8) are negatively regulated by the PDZ domain-containing protein MAGI-1 (membrane-associated guanylate kinase with inverted orientation protein-1) and that two MAGI-1 PDZ domains, PDZ1 and PDZ3, regulate CAR(Ex8) levels in opposing ways. Similar to full-length MAGI-1, expression of the isolated PDZ3 domain significantly reduces cell surface CAR(Ex8) abundance and adenovirus infection. In contrast, the PDZ1 domain is able to rescue CAR(Ex8) and adenovirus infection from MAGI-1-mediated suppression. These data suggest a novel cell-based strategy to either suppress viral infection or augment adenovirus-based gene therapy.

Cell-surface nucleolin is involved in lipopolysaccharide internalization and signalling in alveolar macrophages

C23 (nucleolin) shuttling between the nucleus, cytoplasm and cell surface has been implicated in controlling regulatory processes and may play a role in pathogen infection and autoimmune diseases. It has been reported that cell surface-expressed C23 on THP-1 monocytes is involved in the inflammatory response induced by LPS (lipopolysaccharide). This study investigates whether C23 is a membrane receptor for LPS during LPS-induced AMs (alveolar macrophages) activation. First, using immunofluorescence and microscopy, we detected the expression of C23 on the surface of AMs. Second, using LPS affinity columns, we demonstrated that C23 directly binds to LPS. Third, we found that LPS colocalized with C23 on both the cell surface and in the cytoplasm. Finally, knockdown of C23 expression on the cell surface using siRNA (small interfering RNA) led to significant reductions in the internalization of LPS, in LPS-induced NF-κB (nuclear factor κB)-DNA binding and in the protein expression of TNF (tumour necrosis factor)-α and IL-6 (interleukin-6). These findings provide evidence that cell-surface C23 on AMs may serve as a receptor for LPS and are essential for internalization and transport of LPS. Furthermore, C23 participates in the regulation of LPS-induced inflammation of AMs, which indicates that cell-surface C23 is a new and promising therapeutic target for the treatment of bacterial infections.

Variations of coxsackievirus B3 capsid primary structure, ligands, and stability are selected for in a coxsackievirus and adenovirus receptor-limited environment

While group B coxsackieviruses (CVB) use the coxsackievirus and adenovirus receptor (CAR) as the receptor through which they infect susceptible cells, some CVB strains are known for their acquired capacity to bind other molecules. The CVB3/RD strain that emerged from a CVB3/Nancy population sequentially passaged in the CAR-poor RD cell line binds decay-accelerating factor (DAF) (CD55) and CAR. A new strain, CVB3/RDVa, has been isolated from RD cells chronically infected with CVB3/RD and binds multiple molecules in addition to DAF and CAR. The capsid proteins of CVB3/RD differ from those of CVB3/28, a cloned strain that binds only CAR, by only four amino acids, including a glutamate/glutamine dimorphism in the DAF-binding region of the capsid. The capsid proteins of CVB3/RD and CVB3/RDVa differ by seven amino acids. The ability of CVB3/RDVa to bind ligands in addition to CAR and DAF may be attributed to lysine residues near the icosahedral 5-fold axes of symmetry. Considered with differences in the stability of the CVB3 strains, these traits suggest that in vitro selection in a CAR-limited environment selects for virus populations that can associate with molecules on the cell surface and survive until CAR becomes available to support infection.

Interactions between multiple genetic determinants in the 5' UTR and VP1 capsid control pathogenesis of chronic post-viral myopathy caused by coxsackievirus B1

Mice infected with coxsackievirus B1 Tucson (CVB1(T)) develop chronic, post-viral myopathy (PVM) with clinical manifestations of hind limb muscle weakness and myositis. The objective of the current study was to establish the genetic basis of myopathogenicity in CVB1(T). Using a reverse genetics approach, full attenuation of PVM could only be achieved by simultaneously mutating four sites located at C706U in the 5' untranslated region (5' UTR) and at Y87F, V136A, and T276A in the VP1 capsid. Engineering these four myopathic determinants into an amyopathic CVB1(T) variant restored the ability to cause PVM. Moreover, these same four determinants controlled PVM expression in a second strain of mice, indicating that the underlying mechanism is operational in mice of different genetic backgrounds. Modeling studies predict that C706U alters both local and long range pairing in the 5' UTR, and that VP1 determinants are located on the capsid surface. However, these differences did not affect viral titers, temperature stability, pH stability, or the antibody response to virus. These studies demonstrate that PVM develops from a complex interplay between viral determinants in the 5' UTR and VP1 capsid and have uncovered intriguing similarities between genetic determinants that cause PVM and those involved in pathogenesis of other enteroviruses.

Coxsackievirus and adenovirus receptor is up-regulated in migratory germ cells during passage of the blood-testis barrier

The coxsackievirus and adenovirus receptor (CAR) is a cell adhesion molecule expressed in epithelial tight junctions and other cell-cell contacts. Using indirect immunofluorescence, quantitative RT-PCR, and Western blots, the expression and distribution of CAR in developing and adult testis are examined. CAR is highly expressed in both Sertoli and germ cells during perinatal and postnatal development, followed by a rapid down-regulation of both mRNA and protein levels. Interestingly, we find that CAR is a previously unknown downstream target for FSH because CAR mRNA levels were induced in primary cultures of FSH-stimulated Sertoli cells. In contrast to other epithelia, CAR is not a general component of tight junctions in the seminiferous epithelium, and Sertoli cells in the adult testis do not express CAR. Instead, CAR expression is stage dependent and specifically found in migratory germ cells. RT-PCR also demonstrated the presence of junctional adhesion molecule-like (JAML) in the testis. JAML was previously reported by others to form a functional complex with CAR regulating transepithelial migration of leukocytes. The expression of JAML in the testis suggests that a similar functional complex might be present during germ cell migration across the blood-testis barrier. Finally, an intermediate compartment occupied by CAR-positive, migrating germ cells and flanked by two occludin-containing junctions is identified. Together, these results implicate a function for CAR in testis morphogenesis and in migration of germ cells across the blood-testis barrier during spermatogenesis.

Adenovirus fiber shaft contains a trimerization element that supports peptide fusion for targeted gene delivery

Adenoviral (Ad) vectors have been widely used in human gene therapy clinical trials. However, their application has frequently been restricted by the unfavorable expression of cell surface receptors critical for Ad infection. Infections by Ad2 and Ad5 are largely regulated by the elongated fiber protein that mediates its attachment to a cell surface receptor, coxsackie and adenovirus receptor (CAR). The fiber protein is a homotrimer consisting of an N-terminal tail, a long shaft, and a C-terminal knob region that is responsible for high-affinity receptor binding and Ad tropism. Consequently, the modification of the knob region, including peptide insertion and C-terminal fusion of ligands for cell surface receptors, has become a major research focus for targeting gene delivery. Such manipulation tends to disrupt fiber assembly since the knob region contains a stabilization element for fiber trimerization. We report here the identification of a novel trimerization element in the Ad fiber shaft. We demonstrate that fiber fragments containing the N-terminal tail and shaft repeats formed stable trimers that assembled onto Ad virions independently of the knob region. This fiber shaft trimerization element (FSTE) exhibited a capacity to support peptide fusion. We showed that Ad, modified with a chimeric protein by direct fusion of the FSTE with a growth factor ligand or a single-chain antibody, delivered a reporter gene selectively. Together, these results indicate that the shaft region of Ad fiber protein contains a trimerization element that allows ligand fusion, which potentially broadens the basis for Ad vector development.

Coxsackievirus myocarditis: interplay between virus and host in the pathogenesis of heart disease

Coxsackievirus (CVB) infection is a significant cause of myocarditis and dilated cardiomyopathy (DCM). Heart disease may be caused by direct cytopathic effects of the virus, a pathologic immune response to persistent virus, or autoimmunity triggered by the viral infection. CVB interacts with its host at multiple stages during disease development. Signaling through viral receptors may alter the intracellular environment in addition to facilitating virus entry. Viral genetic determinants that encode cardiovirulence have been mapped and may change depending on the nutritional status of the host. Virus persistence is directly associated with pathology, and recent work demonstrates that CVB evolves into a slowly replicating form capable of establishing a low-grade infection in the heart. The innate immune response to CVB has taken on increasing importance because of its role in shaping the development of the adaptive immune response that is responsible for cardiac pathology. Studies of T cell responsiveness and the development of autoimmunity at the molecular level are beginning to clarify the mechanisms through which CVB infection causes inflammatory heart disease.

Specific interactions of mouse organ proteins with the 5'untranslated region of coxsackievirus B3: potential determinants of viral tissue tropism

Coxsackievirus B3 (CVB3) infects multiple organs of humans and causes different diseases such as myocarditis, pancreatitis, and meningitis. However, the mechanisms of organ-specific tropism are poorly understood. Coxsackievirus and adenovirus receptor (CAR) have been known to be important determinants for tissue tropism. However, current data on CAR mRNA expression in certain organs of mouse did not correlate well with the susceptibility of the respective tissues, suggesting that intracellular proteins may also play important roles in the regulation of viral infectivity through interaction with viral RNA. To search for such proteins and their interacting sites, we performed in situ hybridization to detect viral RNA in the organs of 4-week- and 10-week-old CVB3-infected mice and then correlated the data to patterns of host protein-viral RNA interactions. We found that heart and pancreas are the most heavily infected organs while the kidney remains highly resistant to the virus. The brain exhibited localized foci of viral replication, while the heart and liver showed random distribution of CVB3 RNA. The exocrine pancreas is highly susceptible to CVB3 infection but the endocrine cell type is resistant. In contrast to infections in other organs, mouse heart appears more resistant to CVB3 infection with increasing age. This resistance to infection in the kidney and older heart correlates well with the interaction of a 28 kDa mouse protein with the antisense sequence of nucleotides 210-529 of CVB3 5UTR. In addition, more intensified protein interactions were found within the nucleotides 530-630, a region that contains the internal ribosome entry site, which supports the previous findings that this segment plays critical roles in regulation of viral replication.

Coxsackievirus B3 replication is related to activation of the late extracellular signal-regulated kinase (ERK) signal

MAP kinase signaling has been implicated in coxsackievirus B3 (CVB3) pathogenesis and as necessary in the virus lifecycle. We studied the correlation with extracellular signal-regulated kinase 1/2 (ERK1/2) signaling and virus replication in the presence of coxsackievirus and adenovirus receptor (CAR). In CHO cells that do not expressed CAR, specific ERK1/2 phosphorylation (pERK1/2) was not detected, and progeny virus was not produced after infection. By contrast, in HeLa and CHO-CAR cells, which expressed CAR, the specific early and late pERK1/2 at 0.5 and 8 h were induced, and progeny viruses were produced progressively through 24 h after infection. However, when CHO-CAR cells were infected with replication-defective CVB3, specific pERK1/2 was not detected. In addition, when late pERK1/2 is inhibited by the MEK1 inhibitor PD98059, at 4 h after infection, virus replication significantly decreased. Therefore, our findings suggest that early pERK1/2 is a response to virus binding to CAR, whereas late pERK1/2 is related to the viral replication.

The erythrocyte viral trap: transgenic expression of viral receptor on erythrocytes attenuates coxsackievirus B infection

Viruses rely on attachment to specific cell surface receptors to infect host cells. Selective expression of viral receptors has the potential to attenuate infection of susceptible tissues by redirecting virus to cells that cannot support viral replication. We propose that erythrocytes are an ideal instrument for this strategy, because they are present in vast numbers, permeate every organ, and cannot serve as hosts for viral propagation. To test this hypothesis, we generated a transgenic mouse, termed globin transcription factor 1 (GATA1)-coxsackie and adenovirus receptor (CAR), that expressed the CAR on erythrocytes. Coxsackievirus group B (CVB) adhered to the surface of CAR-expressing erythrocytes and was rendered noninfectious. Upon infection with CVB, GATA1-CAR mice had diminished viremia and reduced viral replication in heart, brain, and liver. Furthermore, when faced with a CVB challenge that was lethal to WT littermates, the survival of GATA1-CAR mice was prolonged, and their ultimate mortality was reduced. The GATA1-CAR mouse model presented here demonstrates that erythrocyte expression of CAR limits CVB pathogenesis. Erythrocytes also may be coated with a variety of receptors by nontransgenic methods, making this a very flexible model for the treatment of infectious diseases in humans.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

Neutrophil migration across tight junctions is mediated by adhesive interactions between epithelial coxsackie and adenovirus receptor and a junctional adhesion molecule-like protein on neutrophils

Neutrophil (polymorphonuclear leukocytes [PMN]) transepithelial migration during inflammatory episodes involves a complex series of adhesive interactions and signaling events. Previous studies have shown that key adhesive interactions between leukocyte CD11b/CD18 and basally expressed fucosylated glycoproteins followed by binding to desmosomal-associated JAM-C are key elements of the transmigration response. Here we provide the first evidence that PMN-expressed junctional adhesion molecule-like protein (JAML) regulates transmigration via binding interactions with epithelial coxsackie and adenovirus receptor (CAR). Experiments with a JAML fusion protein revealed specific binding of JAML to epithelial CAR expressed at tight junctions in T84 cell monolayers and normal human colonic mucosa. Furthermore, JAML-CAR binding is mediated via the membrane distal immunoglobulin (Ig) loop of CAR and the membrane proximal Ig loop of JAML. PMN bound to immobilized CAR but not JAML in a divalent cation-independent manner. Lastly, in assays of PMN transepithelial migration, JAML/CAR fusion proteins and their antibodies significantly inhibited transmigration in a specific manner. Taken together, these results indicate that JAML and CAR are a novel pair of adhesion molecules that play an important role in modulating PMN migration cross epithelial tight junctions. These findings add a new element to a multistep model of PMN transepithelial migration and may provide new targets for anti-inflammatory therapies.

Enteroviruses as agents of emerging infectious diseases

Although the enteroviruses as a group are ubiquitous and not normally considered as "emerging pathogens," the many different serotypes circulate at different frequencies in any given year and the prevalence of a given serotype may fluctuate wildly from year to year. As a result, several enterovirus serotypes have been associated with the emergence of specific diseases (for example, pandemic acute hemorrhagic conjunctivitis) and specific serotypes have emerged to cause outbreaks of major public health concern. Enterovirus 71 is a recognized cause of epidemic severe central nervous system disease in Southeast Asia. Acute hemorrhagic conjunctivitis was a newly described disease in the 1970s associated with emergence of enterovirus 70 and coxsackievirus A24 variant. In addition, the impending eradication of poliovirus and some of the challenges currently faced by the eradication program present the possibility that poliomyelitis could emerge in the posteradication era. These links between enterovirus infections and emerging diseases are reviewed.

Coxsackievirus and adenovirus receptor is essential for cardiomyocyte development

The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein that is known to be a site of viral attachment and entry, but its physiologic functions are undefined. CAR expression is maximal in neonates and wanes rapidly after birth in organs such as heart, muscle, and brain, suggesting that CAR plays a role in the development of these tissues. Here, we show that CAR deficiency resulted in an embryonic lethal condition associated with cardiac defects. Specifically, commencing approximately 10.5 days postconception (dpc), CAR-/- cardiomyocytes exhibited regional apoptosis evidenced by both histopathologic features of cell death and positive staining for the apoptotic marker cleaved caspase 3. CAR-/- fetuses invariably suffered from degeneration of the myocardial wall and thoracic hemorrhaging, leading to death by 11.5 dpc. These findings are consistent with the view that CAR provides positive survival signals to cardiomyocytes that are essential for normal heart development.

The Coxsackievirus and Adenovirus Receptor Interacts with the Multi-PDZ Domain Protein-1 (MUPP-1) within the Tight Junction

The coxsackievirus and adenovirus receptor (CAR) is a component of the epithelial cell tight junction. In a yeast two-hybrid screen we identified the multi-PDZ domain protein MUPP1 as an interaction partner for the CAR cytoplasmic domain. CAR and MUPP1 were found to colocalize at the tight junction, to coprecipitate from epithelial cells, and to interact in vitro. The interaction was found to specifically involve the PDZ-binding motif within the CAR C terminus and MUPP1 PDZ domain 13. In transfected cells, CAR recruited MUPP1 to cell-cell contacts. The inhibition of CAR expression with small interfering RNA inhibited MUPP1 localization to the tight junction. The results indicated that CAR interacts with MUPP1 and is involved in MUPP1 recruitment to the tight junction.

Coxsackievirus B3 infection and type 1 diabetes development in NOD mice: insulitis determines susceptibility of pancreatic islets to virus infection

Group B coxsackieviruses (CVB) are believed to trigger some cases of human type 1 diabetes (T1D), although the mechanism by which this may occur has not been shown. We demonstrated previously that inoculation of young nonobese diabetic (NOD) mice with any of several different CVB strains reduced T1D incidence. We also observed no evidence of CVB replication within islets of young NOD mice, suggesting no role for CVB in T1D induction in the NOD mouse model. The failure to observe CVB replication within islets of young NOD mice has been proposed to be due to interferon expression by insulin-producing beta cells or lack of expression of the CVB receptor CAR. We found that CAR protein is detectable within islets of young and older NOD mice and that a CVB3 strain, which expresses murine IL-4, can replicate in islets. Mice inoculated with the IL-4 expressing CVB3 chimeric strain were better protected from T1D onset than were mock-infected control mice despite intraislet viral replication. Having demonstrated that CVB can replicate in healthy islets of young NOD mice when the intraislet environment is suitably altered, we asked whether islets in old prediabetic mice were resistant to CVB infection. Unlike young mice in which insulitis is not yet apparent, older NOD mice demonstrate severe insulitis in all islets. Inoculating older prediabetic mice with different pathogenic CVB strains caused accelerated T1D onset relative to control mice, a phenomenon that was preceded by detection of virus within islets. Together, the results suggest a model for resolving conflicting data regarding the role of CVB in human T1D etiology.

The coxsackie adenovirus receptor inhibits cancer cell migration

The coxsackie and adenovirus receptor (CAR) is a key factor in adenoviral cancer gene therapy. Reduced expression of CAR during progression of prostate and bladder cancer has been reported. In embryonic development and tissue differentiation, CAR is also differentially expressed. This study suggests a role of CAR expression in cell adhesion and cell motility of human cancer cells. Stable CAR-expressing clones from E-cadherin-deficient A2780 ovarian and CaSki cervical cancer cells with originally low and high CAR expression levels, respectively, were established. CAR reexpression in otherwise singularly growing A2780 parental cells resulted in formation of cell-cell contacts and aggregation in cell clusters. CAR overexpression in cell adhesion-forming CaSki cells did not result in morphological changes. Migration of the A2780 CAR clones was strongly reduced as characterized by using spread-off assays. Using migration chambers, formation of satellite colonies was reduced by 97% in CAR-expressing A2780 cell clones and by 23% in CAR-expressing CaSki cell clones. Parental A2780 and CaSki cells selected for high migratory ability by using migration chambers expressed endogenous CAR on lower levels associated with lower adenoviral transduction efficiency. Our data suggest CAR as a new inhibitory factor for cancer cell migration.

Coxsackievirus and adenovirus receptor (CAR) is modified and shed in membrane vesicles

Vesicles shed by U87-MG cells contain coxsackievirus and adenovirus receptor (CAR) protein that has been posttranslationally modified. Relative to full-length CAR, migration of the vesicle-associated soluble CAR antigen (CARd6) on SDS-polyacrylamide gels indicated a loss of approximately 6 kDa. HeLa and END-HHV6 cells also shed a similar vesicle-associated CAR protein. Vesicles shed by U87-MG cells following stimulation with calcium and A23187 contained CARd6 similar to that present in vesicles shed constitutively. RD cells transfected to express full-length CAR produced CARd6, but cells that expressed CAR with a truncated cytoplasmic domain produced no equivalent to CARd6. In U87-MG cells, calpain activity was required for release of CARd6 with shed vesicles, and accumulation of CARd6 in cells that rounded up and released from the plastic substrate in response to A23187 treatment was blocked by N-ethylmaleimide. These experiments show that CAR, posttranslationally modified in the cytoplasmic domain, can be released with vesicles shed by cells. Posttranslational modification of the CAR cytoplasmic domain occurs during cell rounding and release from the culture substrate. This modified, vesicle-associated CAR was the principal form of soluble CAR released by the cells.

Solution Structure of the Coxsackievirus and Adenovirus Receptor Domain 1,

The coxsackievirus and adenovirus receptor (CAR) mediates entry of coxsackievirus B (CVB) and adenovirus (Ad). The normal cellular function of CAR, which is expressed in a wide variety of tissue types, is thought to involve homophilic cell adhesion in the developing brain. The extracellular domain of CAR consists of two immunoglobulin (Ig) domains termed CAR-D1 and CAR-D2. CAR-D1 is shown by sedimentation velocity to be monomeric at pH 3.0. The solution structure and the dynamic properties of monomeric CAR-D1 have been determined by NMR spectroscopy at pH 3.0. The determinants of the CAR-D1 monomer-dimer equilibrium, as well as the binding site of CVB and Ad on CAR, are discussed in light of the monomer structure.

CLMP, a novel member of the CTX family and a new component of epithelial tight junctions

The CTX family is a growing group of type I transmembrane proteins within the immunoglobulin superfamily (IgSF). They localize to junctional complexes between endothelial and epithelial cells and seem to participate in cell-cell adhesion and transmigration of leukocytes. Here, we report the identification of a new member of the CTX family. This protein, which was designated CLMP (coxsackie- and adenovirus receptor-like membrane protein), is composed of 373 amino acids including an extracellular part containing a V- and a C2-type domain, a transmembrane region and a cytoplasmic tail. CLMP mRNA was detected in a variety of both human and mouse tissues and cell lines. The protein migrated with an Mr of around 48 on SDS-PAGE and was predominantly expressed in epithelial cells within different tissues. In cultured epithelial cells, CLMP was detected in areas of cell-cell contacts. When exogenously expressed in polarized MDCK cells, CLMP was restricted to the subapical area of the lateral cell surface, where it co-localized with the tight junction markers ZO-1 and occludin. Also endogenous CLMP showed association with tight junctions, as analyzed in polarized human CACO-2 cells. This suggested a role for CLMP in cell-cell adhesion and indeed, overexpressed CLMP induced aggregation of non-polarized CHO cells. Furthermore, CLMP-expressing MDCK cells showed significantly increased transepithelial resistance, indicating a role for CLMP in junctional barrier function. Thus, we conclude that CLMP is a novel cell-cell adhesion molecule and a new component of epithelial tight junctions. We also suggest, based on phylogenetic studies, that CLMP, CAR, ESAM, and BT-IgSF form a new group of proteins within the CTX family.

Developmental distribution of coxsackie virus and adenovirus receptor localized in the nervous system

Mouse coxsackie virus and adenovirus receptor (mCAR), which was isolated from the nerve growth cone-enriched fraction of newborn mouse brains, is a member of immunoglobulin-super family, and functions as a homophilic adhesion molecule. We observed the expression of mCAR in embryos to adult tissues by means of immunohistochemical analysis with a peptide antibody. mCAR expression was first detected in the embryonic ectoderm in the uterus on embryonic day 6.5 (E6.5). Then it was strongly expressed in the neuroepithelium of the neural tube, the developing brain and the spinal cord from E8.5 to postnatal day 7 (P7), in the cranial motor nerves from E9.5 to E11.5, and in the optic nerve from E13.5 to P7, which agrees with periods of their respective morphogenetic peaks. This expression of mCAR decreased postnatally and was absent in adult tissues. We found that mCAR occurred in a few proliferating cells of the hippocampal dentate gyrus, the subventricular zone (SVZ) of the lateral ventricles, and the rostral migratory stream (RMS) over P21. These observations demonstrate that mCAR was expressed characteristically in the immature neuroepithelium including progenitor cells or radial cells derived from the neural tube and in immature cells in a selected germinal zone of the mature brain. Based on our findings, we propose that mCAR is involved in migration and fasciculation during a restricted period as an adhesion molecule.

Caspase-3 activation and ERK phosphorylation during CVB3 infection of cells: influence of the coxsackievirus and adenovirus receptor and engineered variants

Caspase activation and MAP kinase signaling have been implicated in coxsackievirus B3 (CVB3) pathogenesis, and both have been demonstrated late in the virus life cycle. We studied activation of caspase-3, an effector protease of apoptosis, and ERK phosphorylation, indicative of MAPK signaling pathway activation, following CVB3 infection of cells that express the coxsackievirus and adenovirus receptor (CAR) or CAR constructs lacking the cytoplasmic domain, and cells which express no detectable CAR. These experiments showed that a burst of caspase-3 activity preceded lysis of CVB3-infected cells expressing CAR, irrespective of the CAR cytoplasmic domain. In RD cells, which were infected in the absence of detectable CAR, caspase-3 activity increased progressively over 52 h with no apparent burst. ERK phosphorylation also occurred late in the virus life cycle, preceding caspase-3 activation, and occurred in cells expressing full-length CAR but not in RD. These results show that ERK phosphorylation precedes caspase-3 activation, both occur late in the infection, and both are influenced by the presence of CAR.

CAR is a cell-cell adhesion protein in human cancer cells and is expressionally modulated by dexamethasone, TNFalpha, and TGFbeta

The coxsackie adenovirus receptor (CAR) has become of interest for gene therapy due to its crucial function in adenoviral cell entry. In clinical trials with adenoviral vectors, dexamethasone is applied to reduce side effects such as inflammatory reactions or emesis. By using a beta-galactosidase-expressing adenovirus (AdGal), we observed that dexamethasone treatment resulted in decreased adenoviral gene transfer into human cancer cells. Expression of CAR and integrin alpha5beta1 was transcriptionally downregulated by dexamethasone as shown for HeLa cervical cancer cells and U87MG glioblastoma cells. TNFalpha increased CAR expression in HeLa and ovarian cancer cells but decreased CAR expression in U87MG cells. In all tested cancer cell lines, TNFalpha induced a significant increase in the expression of adenovirus-binding integrins alpha5beta1, alphavbeta3 and alphavbeta5. Pretreatment with TNFalpha increased AdGal gene transfer into cancer cells and enhanced the cytotoxic effect of a p53-expressing adenovirus. In contrast, TGFbeta reduced CAR expression level and adenoviral gene transfer into OV-UL-2 ovarian cancer cells. Confocal immunofluorescence analysis revealed localization of CAR at cell-cell adhesions in several human cancer cell lines and disruption of cell-cell contacts increased adenoviral gene transfer into human cancer cells. In clinical cancer gene therapy, efficiency of adenoviral gene delivery could be altered by cell adhesion, TNFalpha, TGFbeta, and dexamethasone.

Toward testing the hypothesis that group B coxsackieviruses (CVB) trigger insulin-dependent diabetes: inoculating nonobese diabetic mice with CVB markedly lowers diabetes incidence

Insulin-dependent (type 1) diabetes mellitus (T1D) onset is mediated by individual human genetics as well as undefined environmental influences such as viral infections. The group B coxsackieviruses (CVB) are commonly named as putative T1D-inducing agents. We studied CVB replication in nonobese diabetic (NOD) mice to assess how infection by diverse CVB strains affected T1D incidence in a model of human T1D. Inoculation of 4- or 8-week-old NOD mice with any of nine different CVB strains significantly reduced the incidence of T1D by 2- to 10-fold over a 10-month period relative to T1D incidences in mock-infected control mice. Greater protection was conferred by more-pathogenic CVB strains relative to less-virulent or avirulent strains. Two CVB3 strains were employed to further explore the relationship of CVB virulence phenotypes to T1D onset and incidence: a pathogenic strain (CVB3/M) and a nonvirulent strain (CVB3/GA). CVB3/M replicated to four- to fivefold-higher titers than CVB3/GA in the pancreas and induced widespread pancreatitis, whereas CVB3/GA induced no pancreatitis. Apoptotic nuclei were detected by TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay in CVB3/M-infected pancreata but not in CVB3/GA-infected pancreata. In situ hybridization detected CVB3 RNA in acinar tissue but not in pancreatic islets. Although islets demonstrated inflammatory infiltrates in CVB3-protected mice, insulin remained detectable by immunohistochemistry in these islets but not in those from diabetic mice. Enzyme-linked immunosorbent assay-based examination of murine sera for immunoglobulin G1 (IgG1) and IgG2a immunoreactivity against diabetic autoantigens insulin and HSP60 revealed no statistically significant relationship between CVB3-protected mice or diabetic mice and specific autoimmunity. However, when pooled sera from CVB3/M-protected mice were used to probe a Western blot of pancreatic proteins, numerous proteins were detected, whereas only one band was detected by sera from CVB3/GA-protected mice. No proteins were detected by sera from diabetic or normal mice. Cumulatively, these data do not support the hypothesis that CVB are causative agents of T1D. To the contrary, CVB infections provide significant protection from T1D onset in NOD mice. Possible mechanisms by which this virus-induced protection may occur are discussed.

Comparative analysis of two coxsackievirus B3 strains: putative influence of virus-receptor interactions on pathogenesis

Strain-specific differences in the interaction of coxsackievirus B3 (CVB3) with the coxsackievirus-adenovirus receptor (CAR) and the decay-accelerating factor (DAF) co-receptor proteins were investigated using a non-haemagglutinating (CVB3) and a haemagglutinating (CVB3-HA) strain of CVB3. A panel of receptor-transfected hamster CHO cells, expressing either CAR (CHOCAR cells), DAF (CHODAF cells), or both receptor proteins (CHODC cells) were used to study the interplay of CAR and DAF receptor molecules with regard to binding and infection with CVB3 and CVB3-HA. Despite clear differences in their binding phenotypes, both virus strains were found to primarily depend on the CAR receptor protein for initialization of productive infections. Cytopathic effects induced by CVB3-HA were influenced by co-expression of DAF receptor proteins. The cardiotropic potential of both virus strains was investigated in A.BY/SnJ mice. Despite comparable virus replication of both CVB3 strains in individual myocytes, the number of infected heart muscle cells was significantly lower in CVB3-HA infected mice. Infections of pancreata correlated with myocardial infections. Together these data suggest that even small differences in virus-receptor interactions, influencing virus binding and virus spread, may have an impact on the pathogenesis of CVB-induced diseases.

Coxsackie B viruses that use human DAF as a receptor infect pig cells via pig CAR and do not use pig DAF

Coxsackie B viruses (CVB) are enteroviruses belonging to the family Picornaviridae. Serotypes 1, 3 and 5 of CVB bind to the human membrane complement regulator decay-accelerating factor (DAF) and the coxsackievirus/adenovirus receptor (CAR), using either or both as receptors. These viruses are known to infect pig cell lines, but the receptor(s) involved has not been identified. We have recently characterized the pig homologue of DAF and here explore the interactions of human DAF-binding CVB with pig homologues of DAF and CAR. CVB infection of three pig cell lines resulted in cytolysis, which could be not be blocked by anti-pig DAF antibodies. CVB bound to CHO cells transfected with human DAF, but not pig DAF. Modification of pig DAF by incorporation of the fourth short consensus repeat of human DAF did not confer CVB-binding capacity. CVB did bind CHO cells expressing pig or human CAR, and pre-incubation of pig cells with anti-CAR antibody blocked CVB infection.

Coxsackievirus and adenovirus receptor (CAR) binds immunoglobulins

The coxsackievirus and adenovirus receptor protein (CAR) serves as the cell surface receptor for group B coxsackieviruses and most adenoviruses, but the physiological function and ligand for this protein remain to be described. An affinity column was constructed with the recombinant extracellular domain of the CAR (rECAR) to isolate potential ligands by affinity chromatography. Immunoglobulins G and M were consistently isolated from human sera passed through the column, suggesting that the CAR may be an immunoglobulin-binding protein. Further investigation revealed that the affinity-purified immunoglobulins bound to rECAR-coated immunoassay plates, and the peroxidase-labeled rECAR bound the immunoglobulins on ligand-overlay blots. The peroxidase-labeled rECAR was incorporated into immunoprecipitates formed between the affinity-purified immunoglobulins and rabbit antibodies against human immunoglobulins, but not into immunoprecipitates formed between mouse IgG and rabbit antibodies against mouse IgG. The CAR present in HeLa cell lysates also bound to the affinity-purified immunoglobulins on Immobilon membranes, showing that the association is not limited to the recombinant protein. These results demonstrate that the CAR binds IgG and IgM present in serum, and reveal a direct interaction between the coxsackievirus and adenovirus receptor and the immune system.

The group B coxsackieviruses and myocarditis

The six serotypes of the group B coxsackieviruses (CVB) are common human enteroviruses linked etiologically to inflammatory cardiomyopathies. This has been demonstrated by molecular detection of enteroviral RNA in human heart tissue, serologic associations with disease, and virus isolation from cases of fulminant myocarditis. The murine model of CVB-associated myocarditis has demonstrated that CVB can be attenuated through mutations at different genomic sites. Human CVB3 isolates demonstrate varying degrees of cardiovirulence in the murine model; one site of virulence determination has been mapped to domain II of the 5' non-translated region. The interplay of CVB replication and the immune response to that replication in the heart is a complex interaction determining the extent to which the virus replication is limited and the degree to which a pathogenic inflammation of cardiac muscle occurs. Studies of CVB3-induced myocarditis in murine strains lacking subsets of the immune system or genes regulating the immune response have demonstrated a pivotal role of the T cell response to the generation of myocarditis. While CVB are associated with 20-25% of cases of myocarditis or cardiomyopathy, the severity of the disease and the existence of attenuated strains shown to generate protective immunity in animal models indicates that vaccination against the CVBs would be valuable.

Receptor for the group B coxsackieviruses and adenoviruses: CAR

Considerable progress towards the characterisation of the long-sought receptor, CAR (coxsackievirus and adenovirus receptor), shared by group B coxsackieviruses (CVB) and most adenoviruses (Ad) has been made since it was isolated and cloned in 1997. The primary sequence of CAR shows that it is a member of the immunoglobulin superfamily of proteins, containing two Ig superfamily domains: an amino-terminal V-like module and a C2-like module. The CAR cytoplasmic domain, representing nearly one-third of the protein, is separated from the C2-like module by a single membrane-spanning sequence. The structure of the CAR V-like module complexed with the Ad fibre knob has been determined using recombinant proteins, and reveals three CAR modules associated with a single knob. Although recombinant CAR expressed in mammalian cells confers permissivity to CVB infection, details of the interaction between CAR and CVB remain to be elucidated. The expression of CAR appears to be highly regulated with respect to both cell type and developmental age. In rodents, CAR is expressed at high levels just before birth, and declines thereafter. Expressed levels have been found to increase in regenerating muscle and in response to immunological mediators or inflammation, and in RD cells and umbilical vein endothelial cells in response to high cell density. These studies indicate that CAR expression is highly regulated, but the mechanisms and molecules that mediate the expression remain to be discovered. The physiological function of CAR and its natural ligand also remain to be discovered. In addition, while CAR expression generally correlates with viral tropism, the relationship between the physiological function of CAR and the pathologies of CVB and Ad infections remain to be described.

Kinetic analysis of adenovirus fiber binding to its receptor reveals an avidity mechanism for trimeric receptor-ligand interactions

Most adenoviruses bind to the N-terminal immunoglobulin domain D1 of the coxsackievirus and adenovirus receptor via the head part of their fiber proteins. Three receptor molecules can bind per fiber head. We expressed the D1 domain and the adenovirus type 2 fiber head in bacteria and studied binding interactions by surface plasmon resonance measurements. When receptor domains bind adenovirus fiber independently of each other, the dissociation constant is 20-25 nm. However, when adenovirus fiber binds to receptors immobilized on the sensor chip, a situation better mimicking adenovirus binding to receptors on the cell surface, the dissociation constant was around 1 nm. Kinetic analysis shows that this happens via an avidity mechanism; three identical interactions with high on and off rate constants lead to tight binding of one fiber head to three receptor molecules with a very low overall off rate. The avidity mechanism could be used by other viruses that have multimeric adhesion proteins to attach to target cells. It could also be more general to trimeric receptor-ligand interactions, including those involved in intracellular signaling.

Swine vesicular disease virus. Pathology of the disease and molecular characteristics of the virion

Swine vesicular disease is a highly contagious disease of pigs that is caused by an enterovirus of the family Picornaviridae. The virus is a relatively recent derivative of the human coxsackievirus B5, with which it has high molecular and antigenic homology. The disease is not severe, and affected animals usually show moderate general weakening and slight weight loss that is recovered in few days, as well as vesicular lesions in the mucosa of the mouth and nose and in the interdigital spaces of the feet. However, the similarity of these lesions to those caused by foot-and-mouth disease virus has led to the inclusion of this virus in list A of the Office International des Epizooties. The disease has been eradicated in the European Union except in Italy, where it is considered endemic in the south. Nevertheless, as occasional outbreaks still appear and must be eliminated rapidly, European countries are on the alert and farms are monitored routinely for the presence of the virus. This circumstance has led to a considerable effort to study the pathology of the disease and the molecular biology and antigenicity of the virus, andto the development of optimized methods for the diagnosis of the infection.