HCAR and MCAR: the human and mouse cellular receptors for subgroup C adenoviruses and group B coxsackieviruses

Viral cell entry induced by cross-linked decay-accelerating factor

Decay-accelerating factor (DAF) mediates cellular attachment for many human picornaviruses. In most cases, viral binding to DAF is itself insufficient to permit cell infectivity, with a second, functional internalization receptor being required to facilitate this process. Previously, we postulated that the role of DAF in enterovirus cell infection is as a sequestration receptor, maintaining a reservoir of bound virus in an infectious state, awaiting interaction with functional internalization receptors. Many of these functional receptors possess the capacity to induce relatively rapid changes in capsid conformations, resulting in the formation of altered particles (A-type particles). In this report, we show that antibody-cross-linked DAF, in contrast to endogenous surface-expressed forms, can act as a functional virus receptor to mediate coxsackie A21 virus (CAV21) lytic cell infection. In contrast to the situation with ICAM-1-mediated CAV21 infection, in which high levels of A-type particles are formed, cross-linked DAF-induced CAV21 replication occurs in the absence of detectable A-particle formation.

Short consensus repeat domain 1 of decay-accelerating factor is required for enterovirus 70 binding

Enterovirus 70 (EV70), like several other human enteroviruses, can utilize decay-accelerating factor (DAF [CD55]) as an attachment protein. Using chimeric molecules composed of different combinations of the short consensus repeat domains (SCRs) of DAF and membrane cofactor protein (CD46), we show that sequences in SCR1 of DAF are essential for EV70 binding. Of the human enteroviruses that can bind to DAF, only EV70 and coxsackievirus A21 require sequences in SCR1 for this interaction.

Receptor binding sites and antigenic epitopes on the fiber knob of human adenovirus serotype 3

The adenovirus fiber knob causes the first step in the interaction of adenovirus with cell membrane receptors. To obtain information on the receptor binding site(s), the interaction of labeled cell membrane proteins to synthetic peptides covering the adenovirus type 3 (Ad3) fiber knob was studied. Peptide P6 (amino acids [aa] 187 to 200), to a lesser extent P14 (aa 281 to 294), and probably P11 (aa 244 to 256) interacted specifically with cell membrane proteins, indicating that these peptides present cell receptor binding sites. Peptides P6, P11, and P14 span the D, G, and I beta-strands of the R-sheet, respectively. The other reactive peptides, P2 (aa 142 to 156), P3 (aa 153 to 167), and P16 (aa 300 to 319), probably do not present real receptor binding sites. The binding to these six peptides was inhibited by Ad3 virion and was independent of divalent cations. We have also screened the antigenic epitopes on the knob with recombinant Ad3 fiber, recombinant Ad3 fiber knob, and Ad3 virion-specific antisera by enzyme-linked immunosorbent assay. The main antigenic epitopes were presented by P3, P6, P12 (aa 254 to 269), P14, and especially the C-terminal P16. Peptides P14 and P16 of the Ad3 fiber knob were able to inhibit Ad3 infection of cells.

Interactions of soluble recombinant integrin alphav beta5 with human adenoviruses

alphav integrins have been identified as coreceptors for adenovirus (Ad) internalization; however, direct interactions of these molecules with Ad have not been demonstrated. We report here the expression of soluble integrin alphav beta5, which retains the ability to recognize the Ad penton base as well as vitronectin, an Arg Gly Asp (RGD)-containing extracellular matrix protein. Soluble integrin alphav beta5 reacted with seven different Ad serotypes (subgroups A to E) in solid-phase binding assays. The soluble integrin exhibited different levels of binding to each Ad serotype; however, binding to multiple Ad types required the presence of divalent metal cations and was inhibited by a synthetic RGD peptide, indicating that RGD and cation-binding sequences regulate Ad interactions with alphav beta5. Incubation of Ad particles with soluble alphav beta5 integrin also inhibited subsequent Ad internalization into epithelial cells as well as virus attachment to monocytic cells. These findings suggest that soluble alphav integrins or antagonists of these coreceptors could be used to limit infection by multiple Ad types. The generation of soluble alphav integrins should also permit further detailed kinetic and structural analysis of Ad interactions with its coreceptors.

Adenoviral-mediated gene transfer in lymphocytes

Although adenovirus can infect a wide range of cell types, lymphocytes are not generally susceptible to adenovirus infection, in part because of the absence of the expression of the cellular receptor for the adenoviral fiber protein. The cellular receptor for adenovirus and coxsackievirus (CAR) recently was cloned and shown to mediate adenoviral entry by interaction with the viral fiber protein. We show that the ectopic expression of CAR in various lymphocyte cell lines, which are almost completely resistant to adenovirus infection, is sufficient to facilitate the efficient transduction of these cells by recombinant adenoviruses. Furthermore, this property of CAR does not require its cytoplasmic domain, consistent with the idea that CAR primarily serves as a high affinity binding site for the adenoviral fiber protein, and that viral entry is mediated by interaction of the viral penton base proteins with cellular integrins. As a demonstration of their functional utility, we used CAR-expressing lymphocytes transduced with an adenovirus expressing Fas ligand to efficiently kill Fas receptor-expressing tumor cells. The ability to efficiently manipulate gene expression in lymphocyte cells by using adenovirus vectors should facilitate the functional characterization of pathways affecting lymphocyte physiology.

The coxsackievirus-adenovirus receptor protein can function as a cellular attachment protein for adenovirus serotypes from subgroups A, C, D, E, and F

Attachment of an adenovirus (Ad) to a cell is mediated by the capsid fiber protein. To date, only the cellular fiber receptor for subgroup C serotypes 2 and 5, the so-called coxsackievirus-adenovirus receptor (CAR) protein, has been identified and cloned. Previous data suggested that the fiber of the subgroup D serotype Ad9 also recognizes CAR, since Ad9 and Ad2 fiber knobs cross-blocked each other's cellular binding. Recombinant fiber knobs and 3H-labeled Ad virions from serotypes representing all six subgroups (A to F) were used to determine whether the knobs cross-blocked the binding of virions from different subgroups. With the exception of subgroup B, all subgroup representatives cross-competed, suggesting that they use CAR as a cellular fiber receptor as well. This result was confirmed by showing that CAR, produced in a soluble recombinant form (sCAR), bound to nitrocellulose-immobilized virions from the different subgroups except subgroup B. Similar results were found for blotted fiber knob proteins. The subgroup F virus Ad41 has both short and long fibers, but only the long fiber bound sCAR. The sCAR protein blocked the attachment of all virus serotypes that bound CAR. Moreover, CHO cells expressing human CAR, in contrast to untransformed CHO cells, all specifically bound the sCAR-binding serotypes. We conclude therefore that Ad serotypes from subgroups A, C, D, E, and F all use CAR as a cellular fiber receptor.

Virus assembly and disassembly: the adenovirus cysteine protease as a trigger factor

Viruses are efficient carriers of genetic material between cells. They specifically recognise a target cell and utilise host functions for genome delivery to the replication site. A mature viral capsid emerging from an infected cell serves at least three distinct functions. It enables virus egress from the infected cell, protects the extracellular genome against chemical and physical stress and mediates virus entry into a non-infected cell. How can a virus particle be stably assembled in an infected cell and moments later-after passing through the extracellular milieu-be disintegrated by a non-infected cell? In this review I discuss how adenovirus, a DNA virus, recruits cellular and viral factors and makes use of its own cysteine protease to regulate capsid assembly and disassembly. Copyright 1998 John Wiley & Sons, Ltd.

Caspase activation and specific cleavage of substrates after coxsackievirus B3-induced cytopathic effect in HeLa cells

Coxsackievirus B3 (CVB3), an enterovirus in the family Picornaviridae, induces cytopathic changes in cell culture systems and directly injures multiple susceptible organs and tissues in vivo, including the myocardium, early after infection. Biochemical analysis of the cell death pathway in CVB3-infected HeLa cells demonstrated that the 32-kDa proform of caspase 3 is cleaved subsequent to the degenerative morphological changes seen in infected HeLa cells. Caspase activation assays confirm that the cleaved caspase 3 is proteolytically active. The caspase 3 substrates poly(ADP-ribose) polymerase, a DNA repair enzyme, and DNA fragmentation factor, a cytoplasmic inhibitor of an endonuclease responsible for DNA fragmentation, were degraded at 9 h following infection, yielding their characteristic cleavage fragments. Inhibition of caspase activation by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) did not inhibit the virus-induced cytopathic effect, while inhibition of caspase activation by ZVAD.fmk in control apoptotic cells induced by treatment with the porphyrin photosensitizer benzoporphyrin derivative monoacid ring A and visible light inhibited the apoptotic phenotype. Caspase activation and cleavage of substrates may not be responsible for the characteristic cytopathic effect produced by picornavirus infection yet may be related to late-stage alterations of cellular homeostatic processes and structural integrity.

Altered tropism of an ovine adenovirus carrying the fiber protein cell binding domain of human adenovirus type 5

Ovine adenovirus OAV287 (OAV) is phylogenetically and serotypically distinct from human Ad5. OAV grows productively in CSL503 foetal ovine lung cells and abortively infects several human cell lines. OAV has a unique fiber and a penton protein that lacks a recognisable integrin-binding motif. It is not known whether a secondary receptor is required for infection. A hybrid virus was constructed in which the cell binding domain on the OAV fiber protein was exchanged for the equivalent region from human adenovirus type 5. The hybrid OAV grew to titres that were 1 to 2 log10 lower than wild-type OAV in permissive ovine cells. Human Ad5 also infected CSL503 cells but failed to compete with OAV for receptor binding sites on those cells. However, the hybrid virus did compete with Ad5, consistent with its use of the Ad primary receptor. The hybrid virus was also neutralised by Ad5 antiserum whereas OAV was not. Human 293 kidney and LNCaP prostate cell lines that were not detectably infected by OAV were infected by the hybrid virus and other human prostate and breast cancer cell lines showed greatly enhanced infectivity. Thus, modification of the fiber cell binding domain was sufficient to profoundly alter the tropism of OAV, suggesting that the interaction between the primary receptor and the virus particle is the major factor controlling virus entry during infection.

Transfer and expression of recombinant nitric oxide synthase genes in the cardiovascular system

Gene therapy involves the transfer of a functional gene into host cells to correct the malfunction of a specific gene or to alleviate the symptoms of a disease. For gene transfer to the cardiovascular system, adenoviral vectors are the most efficient means of transfer. Recently, transfer and functional expression of recombinant nitrio oxide synthase (NOS) genes to cerebral and cardiovascular beds have been demonstrated both ex vivo and in vivo. Here, Alex Chen and colleagues review current progress in the field of vascular NOS gene transfer and the potential use of NOS gene therapy for a number of cardiovascular diseases. Although the feasibility of the NOS gene transfer approach has been demonstrated in animal models, currently available vectors have a number of technical and safety limitations that have to be solved before human NOS gene therapy for cardiovascular disease can be attempted.

Limited entry of adenovirus vectors into well-differentiated airway epithelium is responsible for inefficient gene transfer

Investigations of the efficiency and safety of human adenovirus vector (AdV)-mediated gene transfer in the airways of patients with cystic fibrosis (CF) in vivo have demonstrated little success in correcting the CF bioelectrical functional defect, reflecting the inefficiency of AdV-mediated gene transfer to the epithelial cells that line the airway luminal surface. In this study, we demonstrate that low AdV-mediated gene transfer efficiency to well-differentiated (WD) cultured airway epithelial cells is due to three distinct steps in the apical membrane of the airway epithelial cells: (i) the absence of specific adenovirus fiber-knob protein attachment receptors; (ii) the absence of alphavbeta3/5 integrins, reported to partially mediate the internalization of AdV into the cell cytoplasm; and (iii) the low rate of apical plasma membrane uptake pathways of WD airway epithelial cells. Attempts to increase gene transfer efficiency by increasing nonspecific attachment of AdV were unsuccessful, reflecting the inability of the attached vector to enter (penetrate) WD cells via nonspecific entry paths. Strategies to improve the efficiency of AdV for the treatment of CF lung disease will require methods to increase the attachment of AdV to and promote its internalization into the WD respiratory epithelium.

Cardiovirulent coxsackieviruses and the decay-accelerating factor (CD55) receptor

Group B coxsackieviruses are etiologically linked with many human diseases including acute myocarditis and associated chronic dilated cardiomyopathy. Well-established CVB3 cardiovirulent strains (CVB3c(s)) with known phenotypic difference have been used to study the pathogenesis of virus-induced heart disease. The receptor-binding characteristics of cardiovirulent CVB3 are not known, but may represent one mechanism accounting for differences in disease virulence. In this study, interactions between CVB3c(s) and the decay-accelerating factor (DAF or CD55) cell surface receptor were examined. Anti-DAF monoclonal antibodies (MAbs) blocked virus binding and infection of susceptible HeLa cells. Virus binding was significantly reduced by treatment of these cells with phosphatidylinositol phospholipase C enzyme, which rendered them DAF-deficient CVB3c(s) exhibited a differential propensity for the DAF receptor, as several cardiovirulent strains interacted more strongly than others. However, virus binding and infection was always most effectively blocked by MAbs directed against the SCR 2 and 3 domains of DAF, suggesting that binding occurs at a similar site(s) on the molecule for all strains. Virus binding and internalization were associated with DAF down-regulation at the cell surface, as monitored by flow cytometry analysis. Cardiovirulent CVB3 did not interact with molecules functionally and/or structurally related to DAF, including CD35, CD46, Factor H, or C4-binding protein. Adenovirus type 2 (Ad2) does not use the DAF receptor. However, competitive binding assays between Ad2 and CVB1-6, CVB3c(s), anti-DAF MAbs, or DAF-reduced cells indicated that DAF is associated with Ad2 receptors on the HeLa cell membrane. In summary, this study indicates that DAF is an attachment receptor for cardiovirulent CVB3 and that DAF interaction may be important in the pathogenesis of CVB-mediated heart disease.

Foot-and-mouth disease virus virulent for cattle utilizes the integrin alpha(v)beta3 as its receptor

Adsorption and plaque formation of foot-and-mouth disease virus (FMDV) serotype A12 are inhibited by antibodies to the integrin alpha(v)beta3 (A. Berinstein et al., J. Virol. 69:2664-2666, 1995). A human cell line, K562, which does not normally express alpha(v)beta3 cannot replicate this serotype unless cells are transfected with cDNAs encoding this integrin (K562-alpha(v)beta3 cells). In contrast, we found that a tissue culture-propagated FMDV, type O1BFS, was able to replicate in nontransfected K562 cells, and replication was not inhibited by antibodies to the endogenously expressed integrin alpha5beta1. A recent report indicating that cell surface heparan sulfate (HS) was required for efficient infection of type O1 (T. Jackson et al., J. Virol. 70:5282-5287, 1996) led us to examine the role of HS and alpha(v)beta3 in FMDV infection. We transfected normal CHO cells, which express HS but not alpha(v)beta3, and two HS-deficient CHO cell lines with cDNAs encoding human alpha(v)beta3, producing a panel of cells that expressed one or both receptors. In these cells, type A12 replication was dependent on expression of alpha(v)beta3, whereas type O1BFS replicated to high titer in normal CHO cells but could not replicate in HS-deficient cells even when they expressed alpha(v)beta3. We have also analyzed two genetically engineered variants of type O1Campos, vCRM4, which has greatly reduced virulence in cattle and can bind to heparin-Sepharose columns, and vCRM8, which is highly virulent in cattle and cannot bind to heparin-Sepharose. vCRM4 replicated in wild-type K562 cells and normal, nontransfected CHO (HS+ alpha(v)beta3-) cells, whereas vCRM8 replicated only in K562 and CHO cells transfected with alpha(v)beta3 cDNAs. A similar result was also obtained in assays using a vCRM4 virus with an engineered RGD-->KGE mutation. These results indicate that virulent FMDV utilizes the alpha(v)beta3 integrin as a primary receptor for infection and that adaptation of type O1 virus to cell culture results in the ability of the virus to utilize HS as a receptor and a concomitant loss of virulence.

[Enteroviral myocarditis and dilated cardiomyopathy]

In situ hybridization and PCR studies have demonstrated that enteroviruses of the human picornavividae, and in particular coxsackieviruses of group B (CVB), are detectable in endomyocardial biopsies of patients with acute and chronic myocarditis, indicating the possibility of enterovirus persistence in the human heart. As well, such infections are observed in patients with end-stage dilated cardiomyopathy, suggesting an etiologic link between myocarditis and dilated cardiomyopathy. The molecular diagnosis of persistent heart muscle infection allows to differentiate myocarditis and dilated cardiomyopathy, sustained by virus persistence, from postviral immune-mediated cardiac disease. Apart from providing an etiologic diagnosis, there are therapeutic implications from in situ demonstration of myocardial enterovirus infection. As to whether antiviral therapy with interferon is capable of providing protection against enterovirus myocarditis must be determined by controlled prospective clinical studies. Immunosuppressive therapy of myocarditis appears to be justified only after exclusion of persistent heart muscle infection. Experimental studies indicate that altered viral replication strategies, the incompetence of effector mediators of local immunity to eliminate persistently infected myocardial cells as well as infection of cellular constituents of the immune system itself, are major pathogenic determinants for development and maintenance of chronic myocarditis and cardiomyopathy.

Coxsackie B virus and its interaction with permissive host cells

BACKGROUND

Observations in humans and the results of experiments on laboratory animals have provided evidence that coxsackieviruses of group B (CVB) are major etiologic agents of acute and chronic enterovirus myocarditis and various other virus-induced diseases.

OBJECTIVE

This minireview briefly summarizes the investigations to elucidate various molecular mechanisms for the induction and maintenance of persistent CVB infections. With regard to the recent findings that CVB may use several different receptor proteins, this article focuses on virus-host cell interactions and the potential impact of these interactions for enteroviral replication.

STUDY DESIGN

The interaction of CVB with specific cell surface proteins was analyzed in cultured cell lines and murine tissues at the level of virus attachment and virus internalization. As example for the interaction of CVB with intracellular proteins, the state of p21rasGTPase-activating protein (RasGAP) was investigated in mock-infected and CVB3-infected HeLa cells.

RESULTS AND CONCLUSIONS

The experiments to elucidate the virus receptor interactions revealed the necessity to differentiate between CVB attachment proteins and proteins involved in virus internalization. Since more than one protein may be required to initiate the uptake of CVB into permissive host cells, a model of the putative interaction of these proteins within a multimeric receptor complex is proposed. It is further tempting to speculate that the presence of multiple attachment proteins may influence the tissue tropism of CVB as well as pathogenicity.

Adenovirus internalization and infection require dynamin

The cell receptors that facilitate adenovirus internalization into cells have been identified; however, the infectious pathway of virus entry has not been established. Adenovirus entry and infection were examined in HeLa cells lacking or overexpressing mutant dynamin, a protein that specifically regulates clathrin-mediated endocytosis. Expression of mutant dynamin significantly reduced adenovirus internalization and gene delivery, indicating a functional requirement for this molecule. These findings are consistent with virus entry via the clathrin-coated pit pathway.

Role of integrin expression in adenovirus-mediated gene delivery to the intestinal epithelium

Adenoviral vectors are being developed for oral delivery of therapeutic genes to the intestine. Initial studies in the rat using mucolytics and direct application of adenovirus encoded with the interleukin-1 receptor antagonist gene to the jejunum produced limited gene expression. The goal of this study was to determine the role of integrins in adenovirus-mediated gene delivery to the intestinal epithelium. Integrins are involved in cellular differentiation and tight junction formation and mediate adenoviral internalization. Results from Caco-2 and IEC-18 cells suggest that, as enterocytes differentiate, cell-surface integrin expression decreases. Pretreatment of Caco-2 cells with RGD peptides reduced adenoviral transduction efficiency by 80% in undifferentiated cells and 20% in differentiated cells. Both differentiated and undifferentiated IEC-18 cells showed a 70% drop in transduction when pretreated with the peptide. Infection inhibition studies with monoclonal antibodies further suggest that alpha(v)beta3 and alpha6beta1 integrins play significant roles in adenoviral internalization in the intestine. Expression of integrins in cell culture models of the intestine correlated with in vivo expression in intestinal segments. These results indicate that the ileum is a prime target for efficient adenovirus-mediated gene transfer in the rat. To enhance transduction in differentiated enterocytes (probable targets for oral gene delivery), Caco-2 cells were treated with interleukin-1beta (a cytokine known to increase integrin expression) prior to administration of the virus. Transduction efficiency increased four-fold.

Characterization of an adenovirus vector containing a heterologous peptide epitope in the HI loop of the fiber knob

The utility of the present generation of recombinant adenovirus vectors for gene therapy applications could potentially be improved by designing targeted vectors capable of gene delivery to selected cell types in vivo. In order to achieve such targeting, we are investigating the possibilities of incorporation of ligands in the adenovirus fiber protein, which mediates primary binding of adenovirus to its cell surface receptor. Based on the proposed structure of the cell-binding domain of the fiber, we hypothesized that the HI loop of the fiber knob can be utilized as a convenient locale for incorporation of heterologous ligands. In this study, we utilized recombinant fiber proteins expressed in baculovirus-infected insect cells to demonstrate that the incorporation of the FLAG octapeptide into the HI loop does not ablate fiber trimerization and does not disturb formation of the cell-binding site localized in the knob. We then generated a recombinant adenovirus containing this modified fiber and showed that the short peptide sequence engineered in the knob is compatible with the biological functions of the fiber. In addition, by using a ligand-specific antibody, we have shown that the peptide incorporated into the knob remains available for binding in the context of mature virions containing modified fibers. These findings suggest that heterologous ligands can be incorporated into the HI loop of the fiber knob and that this locale possesses properties consistent with its employment in adenovirus retargeting strategies.

Immune response to recombinant capsid proteins of adenovirus in humans: antifiber and anti-penton base antibodies have a synergistic effect on neutralizing activity

Replication-deficient adenovirus used in humans for gene therapy induces a strong immune response to the vector, resulting in transient recombinant protein expression and the blocking of gene transfer upon a second administration. Therefore, in this study we examined in detail the capsid-specific humoral immune response in sera of patients with lung cancer who had been given one dose of a replication-defective adenovirus. We analyzed the immune response to the three major components of the viral capsid, hexon (Hx), penton base (Pb), and fiber (Fi). A longitudinal study of the humoral response assayed on adenovirus particle-coated enzyme-linked immunosorbent assay plates showed that patients had preexisting immunity to adenovirus prior to the administration of adenovirus-beta-gal. The level of the response increased in three patients after adenovirus administration and remained at a maximum after three months. One patient had a strong immune response to adenovirus prior to treatment, and this response was unaffected by adenovirus administration. Sera collected from the patients were assayed for recognition of each individual viral capsid protein to determine more precisely the molecular basis of the humoral immune response. Clear differences existed in the humoral response to the three major components of the viral capsid in serum from humans. Sequential appearance of these antibodies was observed: anti-Fi antibodies appeared first, followed by anti-Pb antibodies and then by anti-Hx antibodies. Moreover, anti-Fi antibodies preferentially recognized the native trimeric form of Fi protein, suggesting that they recognized conformational epitopes. Our results showed that sera with no neutralizing activity contained only anti-Fi antibodies. In contrast, neutralizing activity was only obtained with sera containing anti-Fi and anti-Pb antibodies. More importantly, we showed that anti-native Fi and anti-Pb antibodies had a synergistic effect on neutralization. The application of these conclusions to human gene therapy with recombinant adenovirus should lead to the development of strategies to overcome the formation of such neutralization antibodies, which have been shown to limit the efficacy of gene transfer in humans.

Fluorescent virions: dynamic tracking of the pathway of adenoviral gene transfer vectors in living cells

The pathogenic agent, adenovirus (Ad), has taken on a new role as a vector for gene transfer in both laboratory and clinical settings. To help understand the intracellular pathways and fate of Ad gene transfer vectors, we covalently conjugated fluorophores to E1-, E3- Ad vectors and used quantitative fluorescence microscopy to assess essential steps of Ad vector gene transfer to the A549 human epithelial lung cell line including binding, internalization, escape from endosomes, translocation to the nucleus, dissociation of capsids and gene expression. The data demonstrate that Ad internalizes with a t1/2 2.5 min, breaks out of endosomes early, likely prior to endosome-endosome fusion, exhibits sustained, intracellular velocities averaging 0.58 microm/sec, and translocates to the nucleus with >80% of internalized fluorophore demonstrating nuclear localization within 60 min of infection. Interestingly, 24 hr after infection, half of the initially internalized fluorescence was detected but lacked nuclear localization, suggesting that the capsid is released from the nucleus and is likely degraded. Fluorescent labeling of virions provides a novel quantitative, morphological strategy to characterize the interaction of gene transfer vectors with the intracellular environment.

Two closely related adenovirus genome types with kidney or respiratory tract tropism differ in their binding to epithelial cells of various origins

The host cell interactions of the genome types Ad11p and Ad11a of human adenovirus serotype 11, displaying kidney or respiratory tropism, were compared using FACS analysis. Kinetic experiments indicated that the virus binding stated immediately and reached a plateau after 30 min. The binding of biotinylated virions to seven continuous cell lines. A549, A498, J82, HeLa, CHO, MDCK, and human diploid fibroblasts (HEDF), was quantitated by FACS analysis. The binding capacities of the two viruses to all human cell lines but A549 cells appeared to differ. Ad11p virions manifested high affinities, whereas Ad11a virions presented low affinities. Neither of the two viruses bound to CHO or MDCK cells. Reciprocal competition experiments showed that the Ad11a virions could be weakly blocked by the Ad11p virions, whereas the Ad11p virions could not be competed at all by the Ad11a virions. The binding of the Ad11p virions to cells could be blocked by the rfiber antiserum of Ad11p, but not by the corresponding antiserum against Ad11a or Ad35p. A comparison of the cytopathogenicity of the seven cell lines infected by Ad11p and Ad11a demonstrated that the efficiency of the initial event of an adenovirus infection directly affects the outcome of the viral infection. The Ad11a in the A498, J82, HeLa, or HEDF cells that presented lower affinity and receptor concentration showed 100 times less infectivity than that in A549 cells displaying high affinity and receptor concentration. These results indicate that the cell susceptibility to Ad11p and Ad11a infection strongly depends on both the number of fiber receptors on the host cells and the receptor affinity for ligands on the fiber knob. Our findings also suggest that the receptors for Ad11p and Ad11a on the surface of different cell types may be different or on different sites.

The murine CAR homolog is a receptor for coxsackie B viruses and adenoviruses

Complementary DNA clones encoding the murine homolog (mCAR) of the human coxsackievirus and adenovirus receptor (CAR) were isolated. Nonpermissive CHO cells transfected with mCAR cDNA became susceptible to infection by coxsackieviruses B3 and B4 and showed increased susceptibility to adenovirus-mediated gene transfer. These results indicate that the same receptor is responsible for virus interactions with both murine and human cells. Analysis of receptor expression in human and murine tissues should be useful in defining factors governing virus tropism in vivo.

Integrin alpha v beta 6 enhances coxsackievirus B1 lytic infection of human colon cancer cells

Viral entry into host cells depends upon specific interactions between virus attachment proteins and cell surface receptors that enable virus binding and internalization of virus and/or the virus-receptor complex. We have recently reported that the ubiquitous cell surface molecule, decay-accelerating factor (DAF), is a major cell attachment receptor for Coxsackieviruses B1, B3, and B5. However, DAF permits only virus binding and not virus internalization, invoking the presence of secondary or accessory receptors. Among the known receptors for enteroviruses are members of the cell adhesion molecule family known as integrins. In the present study, we found that expression of the epithelial-restricted integrin, alpha v beta 6, on colonic epithelial cells significantly enhanced Coxsackievirus B1-mediated cell lysis. Importantly, the viral-mediated cell killing required the presence of the 11-amino-acid C-terminal cytoplasmic extension unique to the beta 6 subunit, providing the first evidence of regulation of viral infectivity by integrin cytoplasmic domains. These results indicate that alpha v beta 6 expression on intestinal epithelial cells critically affects Coxsackievirus B1 infectivity. This may be essential in the conversion of asymptomatic enterovirus infection into clinically apparent disease.

Distinct pathogenic effects of group B coxsackieviruses on human glomerular and tubular kidney cells

The six group B coxsackieviruses (CVBs) are highly prevalent human pathogens that cause viremia followed by involvement of different organs. Clinical and experimental evidence suggests that CVBs can induce kidney injury, but the susceptibility of human renal cells to these viruses is unknown. By using pure cultures of human glomerular and tubular cells, we demonstrated that all CVBs are capable of productively infecting renal cells of three different histotypes. Distinct pathogenic effects were observed. Proximal tubular epithelial cells and, to a lesser extent, glomerular podocytes were highly susceptible to CVBs; in both cases, infection led to cytolysis. In contrast, glomerular mesangial cells supported the replication of the six CVBs but failed to develop overt cytopathologic changes. Mesangial cells continued to produce infectious progeny for numerous serial subcultures (i.e., more than 50 days), especially with type 1, 3, 4, and 5 viruses. In the above cells, persistent infection induced the de novo synthesis of platelet-derived growth factor A/B and enhanced the release of transforming growth factor beta1/2. These two factors are important mediators of progression from glomerular inflammation to glomerulosclerosis. CVB replication appeared also to impair the phagocytic and contractile activity of mesangial cells. Loss of these properties--which are important in glomerular physiopathology--may contribute to the development of progressive nephropathy. The results show that CVBs induce distinct effects in different types of cultured renal cells and suggest that CVB infections may be associated with both acute and progressive renal injury.

A decay-accelerating factor-binding strain of coxsackievirus B3 requires the coxsackievirus-adenovirus receptor protein to mediate lytic infection of rhabdomyosarcoma cells

The composition of the cellular receptor complex for coxsackievirus B3 (CVB3) has been an area of much contention for the last 30 years. Recently, two individual components of a putative CVB3 cellular receptor complex have been identified as (i) decay-accelerating factor (DAF) and (ii) the coxsackievirus-adenovirus receptor protein (CAR). The present study elucidates the individual roles of DAF and CAR in cell entry of CVB3 Nancy. First, we confirm that the DAF-binding phenotype of CVB3 correlates to the presence of key amino acids located in the viral capsid protein, VP2. Second, using antibody blockade, we show that complete protection of permissive cells from infection by high input multiplicities of CVB3 requires a combination of both anti-DAF and anti-CAR antibodies. Finally, it is shown that expression of the CAR protein on the surface of nonpermissive DAF-expressing RD cells renders them highly susceptible to CVB3-mediated lytic infection. Therefore, although the majority of CVB3 Nancy attaches to the cell via DAF, only virus directly interacting with the CAR protein mediates lytic infection. The role of DAF in CVB3 cell infection may be analogous to that recently described for coxsackievirus A21 (D. R. Shafren, D. J. Dorahy, R. A. Ingham, G. F. Burns, and R. D. Barry, J. Virol. 71:4736-4743, 1997), in that DAF may act as a CVB3 sequestration site, enhancing viral presentation to the functional CAR protein.

Myocarditis as systemic disease: new perspectives on pathogenesis

1. Myocarditis may be an early indicator of or may subsequently lead to dilated cardiomyopathy in humans. This hypothesis has evolved from research on viruses that induce myocarditis, wherein the coxsackie B group viruses (CVB) in the family Picornaviridae are the most common known viral infectants of heart muscle. 2. Many competing hypotheses exist as to the pathogenesis of CVB3-induced myocarditis, including direct virus-induced myocyte damage and immunopathological disease with autoimmune sequelae. Evidence to support the direct-damage and viral RNA-persistence hypothesis is derived from in situ hybridization and gene amplification studies. 3. Recent use of terminal deoxynucleotidyl transferase-mediated nick-end labelling indicates that this injury in target organs is largely non-apoptotic in nature. Most apoptotic bodies in cardiac tissue are derived from immune cells. 4. Beyond infection of heart muscle, CVB3 can also associate with, infect and persist in cells of immune origin. The CVB3 localizes to follicles in spleens and lymph nodes of the murine host and this particular localization may continue in mice susceptible to more aggressive myocarditis. Whether virus-immune cell association in these compartments is advantageous (or essential) to the host in the evolution of anti-viral immune responses or whether it is more advantageous to the virus in immunosuppression of the host is not known. 5. We suggest that CVB3 can directly perturb or alter the immune response, thereby delaying viral clearance from vulnerable systemic organs. Both host and viral genetic factors can influence susceptibility, persistence and disease progression. 6. Picornaviruses use a unique method for the initiation of translation, involving the internal binding of the ribosome on a sequence element of the 5' untranslated region, termed an internal ribosome entry site (IRES). 7. The IRES of CVB3 is located at approximately stem loops G, H and I, spanning nucloetides 530 and 630. Arrest of host translation is also a feature of picornavirus infection. Such regulation of host cell translation machinery no doubt fosters viral replication at the expense of the host cell. 8. Differences between cell types in the mechanisms, along with those at other key steps in the viral life cycle and in signalling via kinase pathways, may determine viral tropism and cellular destruction and the physiological outcome of neighbouring cells.

Structural and functional determinants in adenovirus type 2 penton base recombinant protein

Discrete domains involved in structural and functional properties of adenovirus type 2 (Ad2) penton base were investigated with site-directed mutagenesis of the recombinant protein expressed in baculovirus-infected cells. Seventeen substitution mutants were generated and phenotyped for various functions in insect and human cells as follows. (i) Pentamerization of the penton base protein was found to be dependent on three amino acid side chains, the indole ring of Trp119, the hydroxylic group of Tyr553, and the basic group of Lys556. (ii) Arg254, Cys432, and Trp439, the stretch of basic residues at positions 547 to 556, and Arg340 of the RGD motif played a critical role in stable fiber-penton base interactions in vivo. (iii) Nuclear localization of penton base in Sf9 cells was negatively affected in mutants W119H or W165H, and, to a lesser extent, by substitutions in the consensus polybasic signal at positions 547 to 549. (iv) Penton base mutants were also assayed for HeLa cell binding, cell detachment, plasmid DNA internalization, and Ad-mediated gene delivery. The results obtained suggested that the previously identified integrin-binding motifs RGD340 and LDV287 were functionally and/or topologically related to other discrete regions which include Trp119, Trp165, Cys246, Cys432, and Trp439, all of which were involved in penton base-cell surface recognition, endocytosis, and postendocytotic steps of the virus life cycle.

Increased in vitro and in vivo gene transfer by adenovirus vectors containing chimeric fiber proteins

Alteration of the natural tropism of adenovirus (Ad) will permit gene transfer into specific cell types and thereby greatly broaden the scope of target diseases that can be treated by using Ad. We have constructed two Ad vectors which contain modifications to the Ad fiber coat protein that redirect virus binding to either alpha(v) integrin [AdZ.F(RGD)] or heparan sulfate [AdZ.F(pK7)] cellular receptors. These vectors were constructed by a novel method involving E4 rescue of an E4-deficient Ad with a transfer vector containing both the E4 region and the modified fiber gene. AdZ.F(RGD) increased gene delivery to endothelial and smooth muscle cells expressing alpha(v) integrins. Likewise, AdZ.F(pK7) increased transduction 5- to 500-fold in multiple cell types lacking high levels of Ad fiber receptor, including macrophage, endothelial, smooth muscle, fibroblast, and T cells. In addition, AdZ.F(pK7) significantly increased gene transfer in vivo to vascular smooth muscle cells of the porcine iliac artery following balloon angioplasty. These vectors may therefore be useful in gene therapy for vascular restenosis or for targeting endothelial cells in tumors. Although binding to the fiber receptor still occurs with these vectors, they demonstrate the feasibility of tissue-specific receptor targeting in cells which express low levels of Ad fiber receptor.

Complement component 3 interactions with coxsackievirus B3 capsid proteins: innate immunity and the rapid formation of splenic antiviral germinal centers

Innate immunity is central to the clearance of pathogens from hosts as well as to the definition of acquired immune responses (D. T. Fearon, and R. M. Locksley, Science 272:50-53, 1996). Coxsackievirus B3 (CVB3), a human cardiopathic virus, was evaluated for the ability to activate the alternative and classical pathway of complement. CVB3 proteins interact with complement component 3 (C3, a soluble protein effector of innate immunity) after either in vitro exposure to mouse serum or in vivo murine infection and activate the alternative pathway of complement. In addition, we demonstrate that viral antigen retention and localization in germinal centers is dependent on C3, while virus antigen retention in extrafollicular regions in the spleen is not. In vivo depletion of native C3 abolished the rapid formation of virus-specific germinal centers (by day 3 post-CVB3 infection) in the absence of serum anti-CVB3 antibodies. These studies demonstrate that innate immune mechanisms, such as C3 interaction with CVB3, are essential for splenic antiviral germinal center formation in naive (antigen nonsensitized) mice resistant (C57BL/6J strain) and susceptible (A/J strain) to CVB3-induced myocarditis.

The role of the nuclear pore complex in adenovirus DNA entry

Adenovirus targets its genome to the cell nucleus by a multistep process involving endocytosis, membrane penetration and cytoplasmic transport, and finally imports its DNA into the nucleus. Using an immunochemical and biochemical approach combined with inhibitors of nuclear import, we demonstrate that incoming viral DNA and DNA-associated protein VII enter the nucleus via nuclear pore complexes (NPCs). Depletion of calcium from nuclear envelope and endoplasmic reticulum cisternae by ionophores or thapsigargin blocked DNA and protein VII import into the nucleus, but had no effect on virus targeting to NPCs. Calcium-depleted cells were capable of disassembling incoming virus. In contrast, inhibitors of cytosolic O-linked glycoproteins of the NPC blocked virus attachment to the nuclear envelope, capsid disassembly and also nuclear import of protein VII. The data indicate that NPCs have multiple roles in adenovirus entry into cells: they contain a virus-binding and/or dissociation activity and provide a gateway for the incoming DNA genome into the nucleus.

Adenoviral vectors for gene transfer

Adenoviruses began to be developed into highly effective gene expression vectors in the early 1980s. Recently, the increased interest in utilizing this transfer system in vivo has posed new problems for heterologous gene-transfer, spurring a renewed effort in the field of vector development toward solving the structural, immunological and targeting problems posed by gene therapy applications.

Targeted adenovirus-mediated gene delivery to T cells via CD3

T cells are primary targets in numerous gene therapy protocols. However, the use of subgroup C adenovirus serotype 2 or 5 (Ad2 or Ad5) as a vector to transduce T cells is limited by its poor transduction efficiency for these cells. In this report we show that poor T-cell transduction results from these cells lacking both the primary Ad2-Ad5 receptor, used in attachment, and the secondary Ad receptor, which mediates entry of most adenovirus serotypes. These deficiencies were overcome by using a bispecific antibody (bsAb) with specificities for human CD3 and for a FLAG epitope genetically introduced into Ad5 (Ad.FLAG) to redirect the virus to human T cells. The anti-FLAG x anti-CD3 bsAb increased Ad.FLAG binding 30-fold, induced the efficient uptake of Ad.FLAG into the cells, and led to a 100- to 500-fold increase in the transduction of resting T cells. Moreover, fluorescence-activated cell sorter analysis showed that 25 to 90% of the T cells were transduced by the bsAb-complexed Ad.FLAG at multiplicities of infection between 20 and 100 active particles per cell. These results demonstrate that bsAbs can target Ad to non-Ad receptors on cells that are normally resistant to Ad, resulting in their efficient and specific transduction.