Receptor Binding And Early Steps Of Cellular Infection By Parvoviruses

Parvoviruses are small, non-enveloped, single stranded DNA viruses. The specific attributes of the capsid and genome dictate how the virus interacts with the environment and the host cell in terms of transmission, tissue tropism, anti-viral immunity, and disease states. A major focus of these studies is viral entry into host cells. During infection, the parvovirus capsid hijacks cellular pathways to reach the nucleus for genome replication. Receptor binding is critical for determining host range and tissue tropism, and various receptors are utilized by different parvoviruses. However, the intracellular trafficking pathways followed by viruses after endocytosis are poorly understood. Chapter 2 examines the dynamic nature of parvoviral uptake and entry by wild type viruses, while chapter 3 examines the ability of these viruses to use variant receptors for uptake and infection. In addition to successfully navigating entry into host cells, parvoviruses must survive in the environment and evade host defenses. Humoral immunity plays a particularly important role in the control of these viruses. This is a benefit as vaccination is generally successful in controlling parvoviral disease, but is a challenge that must be overcome in the development of adeno-associated viruses as gene therapy vectors. The studies that follow expand our knowledge about the interaction of antibodies with a newly described variant of CPV in raccoons, RPV-2 (Chapter 4) and the adenoassociated virus capsid (Chapter 5). One final aspect of parvoviral biology addressed in this work is how changes in host range, antigenicity, and receptor interactions have evolved with small numbers of capsid changes in these closely related viruses. The trafficking studies in chapters 2 and 3 were performed within this contextual framework to examine the differences in the interactions of FPV and CPV with host cells. Chapter 4 describes the phylogenetic origin, host range, and receptor binding properties of several recently characterized parvovirus strains isolated from raccoons, and places this animal as an important intermediate host in the evolution of CPV. Finally, two of the more dissimilar serotypes of AAV were examined in Chapter 5 to look at the interaction of antibodies with capsids displaying somewhat different surface features

Mucosal transmissibility, disease induction and coreceptor switching of R5 SHIVSF162P3N molecular clones in rhesus macaques

Background: Mucosally transmissible and pathogenic CCR5 (R5)-tropic simian-human immunodeficiency virus (SHIV) molecular clones are useful reagents to identity neutralization escape in HIV-1 vaccine experiments and to study the envelope evolutionary process and mechanistic basis for coreceptor switch during the course of natural infection. Results: We observed progression to AIDS in rhesus macaques infected intrarectally with molecular clones of the pathogenic R5 SHIVSF162P3N isolate. Expansion to CXCR4 usage was documented in one diseased macaque that mounted a neutralizing antibody response and in another that failed to do so, with the latter displaying a rapid progressor phenotype. V3 loop envelop glycoprotein gp120 sequence changes that are predictive of a CXCR4 (X4)-using phenotype in HIV-1 subtype B primary isolates, specifically basic amino acid substations at positions 11 (S11R), 24 (G24R) and 25 (D25K) of the loop were detected in the two infected macaques. Functional assays showed that envelopes with V3 S11R or D25K mutation were dual-tropic, infecting CD4+ target cells that expressed either the CCR5 or CXCR4 coreceptor. And, consistent with findings of coreceptor switching in macaques infected with the pathogenic isolate, CXCR4-using variant was first detected in the lymph node of the chronically infected rhesus monkey several weeks prior to its presence in peripheral blood. Moreover, X4 emergence in this macaque coincided with persistent peripheral CD4+ T cell loss and a decline in neutralizing antibody titer that are suggestive of immune deterioration, with macrophages as the major virus-producing cells at the end-stage of disease. Conclusions: The data showed that molecular clones derived from the R5 SHIVSF162P3N isolate are mucosally transmissible and induced disease in a manner similar to that observed in HIV-1 infected individuals, providing a relevant and useful animal infection model for in-depth analyses of host selection pressures and the env evolutionary changes that influence disease outcome, coreceptor switching and vaccine escape

Feline aminopeptidase N is not a functional receptor for avian infectious bronchitis virus

BACKGROUND: Coronaviruses are an important cause of infectious diseases in humans, including severe acute respiratory syndrome (SARS), and have the continued potential for emergence from animal species. A major factor in the host range of a coronavirus is its receptor utilization on host cells. In many cases, coronavirus-receptor interactions are well understood. However, a notable exception is the receptor utilization by group 3 coronaviruses, including avian infectious bronchitis virus (IBV). Feline aminopeptidase N (fAPN) serves as a functional receptor for most group 1 coronaviruses including feline infectious peritonitis virus (FIPV), canine coronavirus, transmissible gastroenteritis virus (TGEV), and human coronavirus 229E (HCoV-229E). A recent report has also suggested a role for fAPN during IBV entry (Miguel B, Pharr GT, Wang C: The role of feline aminopeptidase N as a receptor for infectious bronchitis virus. Brief review. Arch Virol 2002, 147:2047–2056. RESULTS: Here we show that, whereas both transient transfection and constitutive expression of fAPN on BHK-21 cells can rescue FIPV and TGEV infection in non-permissive BHK cells, fAPN expression does not rescue infection by the prototype IBV strain Mass41. To account for the previous suggestion that fAPN could serve as an IBV receptor, we show that feline cells can be infected with the prototype strain of IBV (Mass 41), but with low susceptibility compared to primary chick kidney cells. We also show that BHK-21 cells are slightly susceptible to certain IBV strains, including Ark99, Ark_DPI, CA99, and Iowa97 (<0.01% efficiency), but this level of infection is not increased by fAPN expression. CONCLUSION: We conclude that fAPN is not a functional receptor for IBV, the identity of which is currently under investigation

Tye7 regulates yeast Ty1 retrotransposon sense and antisense transcription in response to adenylic nucleotides stress

Transposable elements play a fundamental role in genome evolution. It is proposed that their mobility, activated under stress, induces mutations that could confer advantages to the host organism. Transcription of the Ty1 LTR-retrotransposon of Saccharomyces cerevisiae is activated in response to a severe deficiency in adenylic nucleotides. Here, we show that Ty2 and Ty3 are also stimulated under these stress conditions, revealing the simultaneous activation of three active Ty retrotransposon families. We demonstrate that Ty1 activation in response to adenylic nucleotide depletion requires the DNA-binding transcription factor Tye7. Ty1 is transcribed in both sense and antisense directions. We identify three Tye7 potential binding sites in the region of Ty1 DNA sequence where antisense transcription starts. We show that Tye7 binds to Ty1 DNA and regulates Ty1 antisense transcription. Altogether, our data suggest that, in response to adenylic nucleotide reduction, TYE7 is induced and activates Ty1 mRNA transcription, possibly by controlling Ty1 antisense transcription. We also provide the first evidence that Ty1 antisense transcription can be regulated by environmental stress conditions, pointing to a new level of control of Ty1 activity by stress, as Ty1 antisense RNAs play an important role in regulating Ty1 mobility at both the transcriptional and post-transcriptional stages

Evolutionary Reconstructions of the Transferrin Receptor of Caniforms Supports Canine Parvovirus Being a Re-emerged and Not a Novel Pathogen in Dogs

Parvoviruses exploit transferrin receptor type-1 (TfR) for cellular entry in carnivores, and specific interactions are key to control of host range. We show that several key mutations acquired by TfR during the evolution of Caniforms (dogs and related species) modified the interactions with parvovirus capsids by reducing the level of binding. These data, along with signatures of positive selection in the TFRC gene, are consistent with an evolutionary arms race between the TfR of the Caniform clade and parvoviruses. As well as the modifications of amino acid sequence which modify binding, we found that a glycosylation site mutation in the TfR of dogs which provided resistance to the carnivore parvoviruses which were in circulation prior to about 1975 predates the speciation of coyotes and dogs. Because the closely-related black-backed jackal has a TfR similar to their common ancestor and lacks the glycosylation site, reconstructing this mutation into the jackal TfR shows the potency of that site in blocking binding and infection and explains the resistance of dogs until recent times. This alters our understanding of this well-known example of viral emergence by indicating that canine parvovirus emergence likely resulted from the re-adaptation of a parvovirus to the resistant receptor of a former host

Receptor Binding And Early Steps Of Cellular Infection By Parvoviruses

Parvoviruses are small, non-enveloped, single stranded DNA viruses. The specific attributes of the capsid and genome dictate how the virus interacts with the environment and the host cell in terms of transmission, tissue tropism, anti-viral immunity, and disease states. A major focus of these studies is viral entry into host cells. During infection, the parvovirus capsid hijacks cellular pathways to reach the nucleus for genome replication. Receptor binding is critical for determining host range and tissue tropism, and various receptors are utilized by different parvoviruses. However, the intracellular trafficking pathways followed by viruses after endocytosis are poorly understood. Chapter 2 examines the dynamic nature of parvoviral uptake and entry by wild type viruses, while chapter 3 examines the ability of these viruses to use variant receptors for uptake and infection. In addition to successfully navigating entry into host cells, parvoviruses must survive in the environment and evade host defenses. Humoral immunity plays a particularly important role in the control of these viruses. This is a benefit as vaccination is generally successful in controlling parvoviral disease, but is a challenge that must be overcome in the development of adeno-associated viruses as gene therapy vectors. The studies that follow expand our knowledge about the interaction of antibodies with a newly described variant of CPV in raccoons, RPV-2 (Chapter 4) and the adenoassociated virus capsid (Chapter 5). One final aspect of parvoviral biology addressed in this work is how changes in host range, antigenicity, and receptor interactions have evolved with small numbers of capsid changes in these closely related viruses. The trafficking studies in chapters 2 and 3 were performed within this contextual framework to examine the differences in the interactions of FPV and CPV with host cells. Chapter 4 describes the phylogenetic origin, host range, and receptor binding properties of several recently characterized parvovirus strains isolated from raccoons, and places this animal as an important intermediate host in the evolution of CPV. Finally, two of the more dissimilar serotypes of AAV were examined in Chapter 5 to look at the interaction of antibodies with capsids displaying somewhat different surface features

Presumptive acute polyradiculoneuritis in an 11 year old mixed breed dog

Abstract: This report summarizes the diagnosis and treatment of presumptive acute canine polyradiculoneuritis (ACP), also known as coonhound paralysis, in a mixed breed dog. ACP is characterized by acute onset, rapidly progressive ascending tetraparesis to tetraplegia with hyporeflexia and occasional facial weakness and hyperesthesia. Exposure to raccoons is a common but not universal antecedent event. The presumptive diagnosis is made by ruling out other causes of neuromuscular disease; no specific confirmatory test is available. Treatment is primarily supportive, and most dogs regain the ability to walk after weeks to months. Complications include respiratory paralysis resulting in death, pneumonia, urinary tract infections, and permanent neurologic or musculoskeletal deficits

Early Steps in Cell Infection by Parvoviruses: Host-Specific Differences in Cell Receptor Binding but Similar Endosomal Trafficking ▿ †

Canine parvovirus (CPV) and feline panleukopenia virus (FPV) are closely related parvoviruses that differ in their host ranges for cats and dogs. Both viruses bind their host transferrin receptor (TfR), enter cells by clathrin-mediated endocytosis, and traffic with that receptor through endosomal pathways. Infection by these viruses appears to be inefficient and slow, with low numbers of virions infecting the cell after a number of hours. Species-specific binding to TfR controls viral host range, and in this study FPV and strains of CPV differed in the levels of cell attachment, uptake, and infection in canine and feline cells. During infection, CPV particles initially bound and trafficked passively on the filopodia of canine cells while they bound to the cell body of feline cells. That binding was associated with the TfR as it was disrupted by anti-TfR antibodies. Capsids were taken up from the cell surface with different kinetics in canine and feline cells but, unlike transferrin, most did not recycle. Capsids labeled with fluorescent markers were seen in Rab5-, Rab7-, or Rab11-positive endosomal compartments within minutes of uptake, but reached the nucleus. Constitutively active or dominant negative Rab mutants changed the intracellular distribution of capsids and affected the infectivity of virus in cells