Heparan sulfates and coxsackievirus-adenovirus receptor: each one mediates coxsackievirus B3 PD infection

Identification of individual structural fragments of N,N'-(bis-5-nitropyrimidyl)dispirotripiperazine derivatives for cytotoxicity and antiherpetic activity allows the prediction of new highly active compounds

OBJECTIVES

The objectives of this study were (i) to apply computer-based technologies to evaluate the structure of 48 N,N'-(bis-5-nitropyrimidyl)dispirotripiperazines which belong to a new class of highly active antiviral compounds binding to cell surface heparan sulphates, (ii) to understand the chemical- biological interactions governing their activities, and (iii) to design new compounds with strong antiviral activity.

METHODS

The logarithm of 50% cytotoxic concentration (CC(50)) in GMK cells, of 50% inhibitory concentration (IC(50)) against herpes simplex virus type 1, and of selectivity index (SI = CC(50)/IC(50)) was used to develop quantitative structure-activity relationships (QSARs) based on simplex representation of molecular structure. The QSAR model was applied to design new compounds. Two of these compounds were synthesized, physico-chemically characterized and tested for cytotoxicity and antiviral activity.

RESULTS

Statistic characteristics for partial least squares models allow the prediction of CC(50), IC(50) and SI values. The QSAR results demonstrate a high impact of individual structural fragments for antiviral activity. Molecular fragments that promote and interfere with antiviral activity were defined on the basis of the obtained models. Electrostatic factors (38%) and hydrophobicity (34%) were the most important determinants of antiherpetic activity. Using the established method, new potential dispirotripiperazine derivatives were computationally designed. Two of these computationally designed compounds were synthesized. The biological test results confirm the computationally predicted values of these compounds.

CONCLUSIONS

The established QSAR model is suitable for the design of new antiherpetic compounds and prediction of their activity.

Human rhinovirus type 54 infection via heparan sulfate is less efficient and strictly dependent on low endosomal pH

K-type major-group human rhinoviruses (HRVs) (including HRV54) share a prominent lysine residue in the HI surface loop of VP1 with all minor-group HRVs. Despite the presence of this residue, they cannot use members of the low-density lipoprotein receptor family for productive infection. Reexamining all K-type viruses for receptor usage, we noticed that HRV54 is able to replicate in RD cells that lack the major-group receptor intercellular adhesion molecule 1 (ICAM-1). By using receptor blocking assays, inhibition of sulfation, enzymatic digestion, and proteoglycan-deficient cell lines, we show here that wild-type HRV54, without any adaptation, uses heparan sulfate (HS) proteoglycan as an alternate receptor. However, infection via HS is less efficient than infection via ICAM-1. Moreover, HRV54 has an acid lability profile similar to that of the minor-group virus HRV2. In ICAM-1-deficient cells its replication is completely blocked by the H(+)-ATPase inhibitor bafilomycin A1, whereas in ICAM-1-expressing cells it replicates in the presence of the drug. Thus, use of a "noncatalytic" receptor requires the virus to be highly unstable at low pH.

Differential usage of carbohydrate co-receptors influences cellular tropism of Theiler's murine encephalomyelitis virus infection of the central nervous system

Theiler's murine encephalomyelitis viruses (TMEV) are ubiquitous pathogens of mice, producing either rapidly fatal encephalitis (high-neurovirulence strains) or persistent central nervous system infection and inflammatory demyelination (low-neurovirulence strains). Although a protein entry receptor has not yet been identified, carbohydrate co-receptors that effect docking and concentration of the virus on the cell surface are known for both TMEV neurovirulence groups. Low-neurovirulence TMEV use alpha2,3-linked N-acetylneuramic acid (sialic acid) on an N-linked glycoprotein, whereas high-neurovirulence TMEV use the proteoglycan heparan sulfate (HS) as a co-receptor. While the binding of low-neurovirulence TMEV to sialic acid can be inhibited completely, only a third of the binding of high-neurovirulence TMEV to HS is inhibitable, suggesting that high-neurovirulence strains use another co-receptor or bind directly to the putative protein entry receptor. Four amino acids on the surface (VP2 puff B) of low-neurovirulence strains make contact with sialic acid through non-covalent hydrogen bonds. Since these virus residues are conserved in all TMEV strains, the capsid conformation of this region is probably responsible for sialic acid binding. A persistence determinant that maps within the virus coat using recombinant TMEV is also conformational in nature. Low-neurovirulence virus variants that do not bind to sialic acid fail to persist in the central nervous system of mice, indicating a role for sialic acid binding in TMEV persistence. Analysis of high-neurovirulence variants that do not bind HS demonstrates that HS co-receptor usage influences neuronal tropism in brain, whereas, the HS co-receptor use is not required for the infection of spinal cord anterior horn cells associated with poliomyelitis.

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.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

N- and 6-O-sulfated heparan sulfates mediate internalization of coxsackievirus B3 variant PD into CHO-K1 cells

Recently, it was demonstrated that the coxsackievirus B3 variant PD (CVB3 PD) is able to infect coxsackievirus-adenovirus receptor (CAR)-lacking cells by using heparan sulfates (HS) as additional receptors (A. E. Zautner, U. Korner, A. Henke, C. Badorff, and M. Schmidtke, J. Virol. 77:10071-10077, 2003). For this study, competition experiments with growth factors binding to known HS sequences as well as with specifically desulfated heparins were performed with Chinese hamster ovary cells (CHO-K1) to determine the structural requirements of HS for interaction with CVB3. Hepatocyte growth factor interacting with HS sequences containing [IdUA-GlcNSO(3)(6OSO(3))](n), but not basic fibroblast growth factor binding to [HexUA-GlcNSO(3)-HexUA-GlcNSO(3)-IdUA(2OSO(3))](n), was shown to compete effectively with CVB3 PD for cell surface HS. Whereas unmodified heparin and 2-O-desulfated heparin strongly inhibited the CVB3 PD-induced cytopathic effect, the antiviral activity was markedly reduced after N-, O- and 6-O-desulfation of heparin. Taken together, these results indicate that 6-O- and N-sulfation of GlcNAc of HS is crucial for HS interaction with CVB3 PD and that the disaccharide [IdUA-GlcNSO(3)(6OSO(3))](n) is involved in viral binding. Results from experiments with various inhibitors of endocytic pathways suggest that HS-mediated virus internalization is pH dependent. Despite the fact that CVB3 PD initiates infection about four times slower by making use of HS as a receptor than by using CAR, the time required for a complete viral life cycle in Chinese hamster ovary cells was independent of the utilized receptor.

Susceptibility of coxsackievirus B3 laboratory strains and clinical isolates to the capsid function inhibitor pleconaril: antiviral studies with virus chimeras demonstrate the crucial role of amino acid 1092 in treatment

OBJECTIVES

At present, most promising compounds to treat enterovirus-induced diseases are broad-spectrum capsid function inhibitors which bind into a hydrophobic pocket in viral capsid protein 1 (VP1). Coxsackievirus B3 (CVB3) Nancy was the only prototypic enterovirus strain shown to be pleconaril-resistant. This study was designed to better understand the polymorphism of the hydrophobic pocket in CVB3 laboratory strains and clinical isolates and its implications for treatment with the capsid function inhibitor pleconaril.

METHODS

Pleconaril susceptibility was determined in cytopathic effect-inhibitory, plaque reduction or virus yield assays. Sequence analysis of the genome region coding for VP1 and/or subsequent alignment of amino acids lining the hydrophobic pocket of five CVB3 laboratory strains and 20 clinical isolates were carried out. Virus chimeras and computational analysis were used to prove the role of amino acid 1092.

RESULTS AND CONCLUSIONS

Despite high conservation of pocket amino acids, polymorphism was detected at positions 1092, 1094 and 1180. Neither Pro-1094-->Thr nor Val-1180-->Ile altered efficacy of pleconaril treatment. But the amino acid at position 1092 was strongly associated with susceptibility of CVB3 to the capsid inhibitor. Whereas leucine was involved in resistance, isoleucine and valine were detected in pleconaril-susceptible CVB3. Results from antiviral assays with hybrid viruses demonstrate the crucial role of amino acid 1092 in pleconaril susceptibility. A resistant cDNA-generated CVB3 became pleconaril-susceptible after accepting parts from the genome region encoding Ile-1092 into its capsid. Computational analysis suggests that conformational changes in the hydrophobic pocket occur when leucine is substituted for isoleucine or valine and that this change leads to susceptibility to pleconaril.

Emerging treatments for viral myocarditis

Although viral myocarditis has been mostly attributed to enterovirus and adenovirus infection, the importance of hepatitis C virus has recently been noted. Clinical trials of antiviral agents, such as interferons, are in progress, while new therapies such as viral vaccines, recombinant virus and virus receptors, are in preclinical development. Whereas immunosuppression with corticosteroids or cyclosporin is ineffective, immunosuppressors that do not promote viral replication, such as FTY720, and immunomodulation by interleukin-10, are promising new approaches. Inhibition of nuclear factor-κB, angiotensin II and endothelin effectively suppresses inflammation in experimental viral myocarditis. Embryonic stem cell therapy has been demonstrated to be beneficial; however, this requires further investigation.

Human rhinovirus type 89 variants use heparan sulfate proteoglycan for cell attachment

We have previously isolated mutants of the major-group human rhinovirus type 89 that grow in cells deficient in intercellular adhesion molecule 1 (ICAM-1), the receptor used by the wild-type virus for cell entry [A. Reischl, M. Reithmayer, G. Winsauer, R. Moser, I. Goesler, and D. Blaas., J. Virol. 75:9312-9319, 2001]. We now demonstrate that one of these variants utilizes heparan sulfate proteoglycan (HSPG) as a cellular receptor. Adaptation to ICAM-1-deficient cells not only resulted in the newly acquired receptor specificity but also rendered the virus less stable at low pH and at elevated temperatures. This instability might compensate for the absence of the uncoating activity of ICAM-1. Whereas wild-type virus infection via ICAM-1 proceeded in the presence of the vesicular H(+)-ATPase inhibitor bafilomycin A1, infection by the mutant via HSPG was prevented by the drug. This suggests that the low pH prevailing in endosomal compartments is required for uncoating in the absence of the catalytic activity of ICAM-1.

Simultaneous type 1 diabetes onset in mother and son coincident with an enteroviral infection

Enterovirus (EV) infections have been implicated in the development of type 1 diabetes. (T1D). They may cause beta-cell destruction either by cytolytic infection of the cells or indirectly by triggering the autoimmune response. Virus was isolated from a woman at diagnosis of T1D (Tuvemo 1) and in addition, virus was isolated from her son at diagnosis of T1D at the same day (Tuvemo 2). None of the isolates could initially be serotyped by conventional methods. The Tuvemo 1 virus was genotyped and after sub-cultivation it was also serotyped as Coxsackievirus B5. The mother revealed antibodies against GAD65. The boy and the father both revealed a significant increase in neutralization antibody titre against two strains of CBV-4, clearly indicating a recent or ongoing EV infection. In addition, the brother showed such a titre rise against another CBV-4 strain (E2) and against a CBV-5 strain (4429). These results show that the whole family had a proven EV infection at the time of T1D diagnosis of the mother and the 10-years-old boy, indicating that the infection might cause or accelerate the T1D.

Interaction with coxsackievirus and adenovirus receptor, but not with decay-accelerating factor (DAF), induces A-particle formation in a DAF-binding coxsackievirus B3 isolate

Although many coxsackie B viruses interact with decay accelerating factor (DAF), attachment to DAF by itself is not sufficient to initiate infection. We examined the early events in infection that follow virus interaction with DAF, and with the coxsackievirus and adenovirus receptor (CAR). Interaction with soluble CAR in a cell-free system, or with CAR on the surfaces of transfected cells, induced the formation of A particles; interaction with soluble or cell surface DAF did not. The results suggest that CAR, but not DAF, is capable of initiating the conformational changes in the viral capsid that lead to release of viral nucleic acid.

Prevalent human coxsackie B-5 virus infects porcine islet cells primarily using the coxsackie-adenovirus receptor

BACKGROUND

We have previously demonstrated that transplanting porcine encephalomyocarditis virus (EMCV)-infected porcine islet cells (PICs) results in transmission of the virus to recipient mice, which is manifested by acute fatal infection within 5 to 8 days. Here, we determined PIC susceptibility to a related and highly prevalent human picornavirus, coxsackie B-5 virus (CVB-5).

METHODS

PICs were inoculated with CVB-5 in vitro for up to 96 hours and infectivity, level of virus replication, and cellular function determined. Subsequently, monoclonal and polyclonal antibody blocking experiments were used to investigate the receptor CVB-5 uses to enter PICs, and the ability of CVB-5-infected islets to reverse diabetes analyzed in mice.

RESULTS

Adult pig islets inoculated with CVB-5 in vitro showed a typical picornaviral replication cycle with a 2-h lag phase followed by a 4-h exponential phase during which the virus titer increased by 4 logs. However, CVB-5 was less cytolytic to PICs than EMCV, resulting in a persistent productive infection lasting for up to 96 h, with minimal evidence of cell lysis. Double immunostaining confirmed the presence of CVB-5 antigens in insulin-producing islets. Infection of PICs in the presence of antibodies against human coxsackie-adenovirus receptor (CAR) resulted in near complete blockage in production of infectious virus particles whereas blocking with anti-porcine decay-accelerating factor (DAF, also called CD55) or anti-porcine membrane cofactor protein (MCP, also called CD46) only slightly decreased the number of infectious CVB-5 particles produced. Immunofluoresence staining showed CAR and MCP expression on the islet surface, but not DAF. Transplanting CVB-5-infected PICs into diabetic C57BL/6 mice resulted in reversal of diabetes.

CONCLUSION

Although PICs are susceptible to human CVB-5, the infection does not appear to affect xenograft function in vitro or in vivo in the short term.

The hypervariable region 1 of the E2 glycoprotein of hepatitis C virus binds to glycosaminoglycans, but this binding does not lead to infection in a pseudotype system

The hypervariable region 1 (HVR1) of hepatitis C virus (HCV) E2 envelope glycoprotein is a 27-amino-acid sequence located at its N terminus. In this study, we investigated the functional role of HVR1 for interaction with the mammalian cell surface. The C-terminal truncated E2 glycoprotein was appended to a transmembrane domain and cytoplasmic tail of vesicular stomatitis virus (VSV) G protein for generation of the chimeric E2-G gene construct. A deletion of the HVR1 sequence from E2 was created for the construction of E2DeltaHVR1-G. Pseudotype virus, generated separately by infection of a stable cell line expressing E2-G or E2DeltaHVR1-G with a temperature-sensitive mutant of VSV (VSVts045), displayed unique functional properties compared to VSVts045 as a negative control. Virus generated from E2DeltaHVR1-G had a reduced plaquing efficiency ( approximately 50%) in HepG2 cells compared to that for the E2-G virus. Cells prior treated with pronase (0.5 U/ml) displayed a complete inhibition of infectivity of the E2DeltaHVR1-G or E2-G pseudotypes, whereas heparinase I treatment (8 U/ml) of cells reduced 40% E2-G pseudotype virus titer only. E2DeltaHVR1-G pseudotypes were not sensitive to heparin (6 to 50 micro g/ml) as an inhibitor of plaque formation compared to the E2-G pseudotype virus. Although the HVR1 sequence itself does not match with the known heparin-binding domain, a synthetic peptide representing 27 amino acids of the E2 HVR1 displayed a strong affinity for heparin in an enzyme-linked immunosorbent assay. This binding was competitively inhibited by a peptide from the V3 loop of a human immunodeficiency virus glycoprotein subunit (gp120) known to bind with cell surface heparin. Taken together, our results suggest that the HVR1 of E2 glycoprotein binds to the cell surface proteoglycans and may facilitate virus-host interaction for replication cycle of HCV.

Heparan sulphate mediates swine vesicular disease virus attachment to the host cell

Heparan sulphate (HS) has been found to serve as receptor for initial cell binding of numerous viruses. Different glycosaminoglycans (GAGs), including heparin and HS, were analysed for their ability to bind swine vesicular disease virus (SVDV), a picornavirus with close homology to human coxsackie B5 virus. Binding of SVDV was established by heparin-affinity chromatography. In addition, infection of IB-RS-2 epithelial porcine cells was inhibited by treating the virus with soluble HS, heparin, and chondroitin sulphate B (CS-B), as well as by enzymic digestion of cell surface GAGs. Analysis of the infection course showed that SVDV uses cellular HS for its binding to the cell surface and that this interaction occurs during attachment of the virus, prior to its internalization into the cell. Sequence analysis of SVDV variants selected for their lack of sensitivity to heparin inhibition in vitro led to the identification of two residues (A2135V and I1266K) potentially involved in heparin/HS interaction. The location of these residues in a three-dimensional model shows that they are clustered in a well-exposed region of the capsid, providing a physical mechanism that could account for the heparin-binding phenotype.