Interaction of parvoviruses with the nuclear envelope.

Parvoviruses are serious pathogens but also serve as platforms for gene therapy or for using their lytic activity in experimental cancer treatment. Despite of their growing importance during the last decade little is known on how the viral genome is transported into the nucleus of the infected cell, which is crucial for replication. As nucleic acids are not karyophilic per se nuclear import must be driven by proteins attached to the viral genome. In turn, presence and conformation of these proteins depend upon the entry pathway of the virus into the cell. This review focuses on the trafficking of the parvoviral genome from the cellular periphery to nucleus. Despite of the uncertainties in knowledge about the entry pathway we show that parvoviruses developed a unique strategy to pass the nuclear envelope by hijacking enzymes involved in mitosis.

Parvoviruses cause nuclear envelope breakdown by activating key enzymes of mitosis.

Disassembly of the nuclear lamina is essential in mitosis and apoptosis requiring multiple coordinated enzymatic activities in nucleus and cytoplasm. Activation and coordination of the different activities is poorly understood and moreover complicated as some factors translocate between cytoplasm and nucleus in preparatory phases. Here we used the ability of parvoviruses to induce nuclear membrane breakdown to understand the triggers of key mitotic enzymes. Nuclear envelope disintegration was shown upon infection, microinjection but also upon their application to permeabilized cells. The latter technique also showed that nuclear envelope disintegration was independent upon soluble cytoplasmic factors. Using time-lapse microscopy, we observed that nuclear disassembly exhibited mitosis-like kinetics and occurred suddenly, implying a catastrophic event irrespective of cell- or type of parvovirus used. Analyzing the order of the processes allowed us to propose a model starting with direct binding of parvoviruses to distinct proteins of the nuclear pore causing structural rearrangement of the parvoviruses. The resulting exposure of domains comprising amphipathic helices was required for nuclear envelope disintegration, which comprised disruption of inner and outer nuclear membrane as shown by electron microscopy. Consistent with Ca⁺⁺ efflux from the lumen between inner and outer nuclear membrane we found that Ca⁺⁺ was essential for nuclear disassembly by activating PKC. PKC activation then triggered activation of cdk-2, which became further activated by caspase-3. Collectively our study shows a unique interaction of a virus with the nuclear envelope, provides evidence that a nuclear pool of executing enzymes is sufficient for nuclear disassembly in quiescent cells, and demonstrates that nuclear disassembly can be uncoupled from initial phases of mitosis.

Mechanistic insights into the enhancement of adeno-associated virus transduction by proteasome inhibitors.

Proteasome inhibitors (e.g., bortezomib, MG132) are known to enhance adeno-associated virus (AAV) transduction; however, whether this results from pleotropic proteasome inhibition or off-target serine and/or cysteine protease inhibition remains unresolved. Here, we examined recombinant AAV (rAAV) effects of a new proteasome inhibitor, carfilzomib, which specifically inhibits chymotrypsin-like proteasome activity and no other proteases. We determined that proteasome inhibitors act on rAAV through proteasome inhibition and not serine or cysteine protease inhibition, likely through positive changes late in transduction.

[Non-structural protein NS1 of canine parvovirus induces the apoptosis of cells].

OBJECTIVE: To investigate the effects of canine parvovirus (CPV) non-structural protein-1 (NS1) on the cell apoptosis induced by CPV and preliminarily explore the mechanism of CPV-induced apoptosis. METHODS: First, the NS1 gene was amplified by PCR from CPV genomic DNA and subcloned into pcDNA3. 1A vector to generate NS1 eukaryotic expression vector pcDNA-NS1. To verify whether pcDNA-NS1 vector can mediate NS1 expression in eukaryotic cells, the human embryo kideny (HEK) 293FT cells were used to transiently express the recombinant NS1. The effects of NS1 on CPV-induced apoptosis were investigated by infecting the F81 host cells with CPV and transfecting the cells with NS1 vector. The apoptosis of the cells was detected by AnnexinV/PI double staining for phosphatidylserine externalization on membrane and by luminescence method for caspase-3/7 activities. RESULTS: The results show that the sequence of NS1 gene amplified was consistent with the GenBank. The NS1 expression vector was shown to be correct and could mediate NS1 expression in eukaryotic cells. The phosphatidylserine on outside of membrane was detected and the caspase-3/7 activities were increased in both CPV-infected cells and NS1-transfected cells. These results indicate that both CPV and NS1 protein can induce the apoptosis of the cells. CONCLUSION: CPV-induced apoptosis was closely related to its non-structural protein NS1.

Adeno-associated virus type 2 modulates the host DNA damage response induced by herpes simplex virus 1 during coinfection.

Adeno-associated virus type 2 (AAV2) is a human parvovirus that relies on a helper virus for efficient replication. Herpes simplex virus 1 (HSV-1) supplies helper functions and changes the environment of the cell to promote AAV2 replication. In this study, we examined the accumulation of cellular replication and repair proteins at viral replication compartments (RCs) and the influence of replicating AAV2 on HSV-1-induced DNA damage responses (DDR). We observed that the ATM kinase was activated in cells coinfected with AAV2 and HSV-1. We also found that phosphorylated ATR kinase and its cofactor ATR-interacting protein were recruited into AAV2 RCs, but ATR signaling was not activated. DNA-PKcs, another main kinase in the DDR, was degraded during HSV-1 infection in an ICP0-dependent manner, and this degradation was markedly delayed during AAV2 coinfection. Furthermore, we detected phosphorylation of DNA-PKcs during AAV2 but not HSV-1 replication. The AAV2-mediated delay in DNA-PKcs degradation affected signaling through downstream substrates. Overall, our results demonstrate that coinfection with HSV-1 and AAV2 provokes a cellular DDR which is distinct from that induced by HSV-1 alone.

Alteration of aortic function from streptozotocin-diabetic rats with Kilham's virus is associated with inducible nitric oxide synthase.

Kilham's rat virus (KRV) is a parvovirus commonly known to affect laboratory rats. Qualitative immunohistochemical analysis revealed that aorta isolated from KRV-infected streptozotocin (STZ)-induced diabetic adult rats expressed markedly greater levels of inducible nitric oxide synthase (iNOS) than aorta from KRV-infected controls. In contrast with the prevailing literature, nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was not blunted by STZ-diabetes, but was comparable to relaxations of aorta from controls. However, with increasing ex vivo duration, a decreased response to acetylcholine was observed in the STZ-diabetic aorta. In addition, whereas contraction responses to phenylephrine were not significantly altered over time in control tissue, aorta from STZ-diabetic rats developed increased tensions. The data suggest that increased iNOS-derived nitric oxide masks expected acetylcholine-mediated relaxation deficits as a result of KRV-infection, and that the deficit is unmasked by iNOS turnover ex vivo.

[Parvovirus B19 as a cause of acute liver symptoms in adults]. / Parvovirus B19 som årsag til akut leverpåvirkning hos voksne.

Parvovirus B19 (B19), also known as "erythema infectiosum", is a disease that occurs in smaller outbreaks during late winter and early summer; and in Denmark an epidemic occurs every three years. The symptoms vary from fever, fatigue and the characteristic maculopapoulous erythema to asymptomatic cases in 50% of the infected patients. Two-thirds of the Danish population have been infected. The virus has a broad spectrum of clinical manifestations ranging from erythema nodosum in children, arthralgia/arthritis (especially in adults), aplastic crisis in patients with haemolytic anaemia, chronic anaemia in immunocompromised patients, to hydrops foetalis following acute infection during pregnancy. In two adult females aged 41 and 35 years with persisting fatigue, malaise, transitory swelling and arthralgia we found elevated ALT and alkaline phosphatase (pt. 1), despite no serological evidence of hepatitis, cytomegalovirus (CMV), or Epstein-Barrvirus and no story of alcohol consumption or recent travelling outside Denmark. Ongoing B19 infection was diagnosed by ELISA and confirmed by B19 DNA PCR in case 2 and IgG avidity and epitope-type specificity in case 1, who was B19 DNA negative in three different samples. The concentrations of alkaline phosphatase and ALT returned to normal as the antibody response shifted from acute B19 infection to IgG positivity. In conclusion we suggest that a serological test and/or B19 DNA for B19 infection is a relevant test to undertake when screening patients for viral hepatitis especially during B19 epidemics and in exposed individuals.

Human parvovirus infection: rheumatic manifestations, angioedema, C1 esterase inhibitor deficiency, ANA positivity, and possible onset of systemic lupus erythematosus.

OBJECTIVE: To investigate the clinical and serological characteristics of parvovirus infection. CASE SERIES: during 1993-4, 9 adult patients presented with polyarthralgias/polyarthritis. Clinical evaluation and serological studies of antinuclear antibodies, rheumatoid factor (RF), IgM and IgG antibodies to human parvovirus were done in all patients. Other serologies including anti-DNA, serum complement, and C1 esterase inhibitor levels were obtained in some patients. RESULTS: All 9 patients had polyarthralgias/polyarthritis, serological evidence of parvovirus B19 IgM and IgG antibodies, and normal sedimentation rate. All patients were seronegative for RF. Four women had positive ANA titers. In 2 of them the ANA positivity was transient. One developed systemic lupus erythematosus (SLE). Three women had angioedema of the face and tongue; one had transient C1 esterase inhibitor deficiency and another a transient decrease in C4 levels. CONCLUSION: Parvovirus may be implicated in the development of SLE as well as other chronic arthropathies. This is the first reported case of angioedema and decreased C1 esterase inhibitor levels associated with parvovirus infection.

A novel primase-free form of murine DNA polymerase alpha induced by infection with minute virus of mice.

Two species of DNA polymerase alpha free of primase activity were identified in extracts of Ehrlich mouse cells that had been infected with minute virus of mice. Primase-free forms of DNA polymerase alpha eluted with 150 and 180 mM NaCl during ion-exchange chromatography on DEAE-cellulose columns, exhibited sedimentation coefficients of 11 S and 8.2 S, respectively, and were inhibited by aphidicolin, N2-(p-n-butylphenyl)-9-(2-deoxy-beta-D-ribofuranosyl)guanine 5'-triphosphate, and 2-(p-n-butylanilino)-9-(2-deoxy-beta-D-ribofuranosyl)adenine 5'-triphosphate. The ratio of primase-free DNA polymerase alpha to the DNA polymerase alpha-primase complex increased from 1.5 to greater than 100 during the course of infection, and free primase was produced during the MVM replicative cycle.

Aplastic crisis due to human B19 parvovirus infection in red cell pyrimidine-5'-nucleotidase deficiency.

Two siblings with chronic hemolytic anemia due to red cell pyrimidine-5'-nucleotidase (P-5'-N) deficiency, presented within a few days of each other with a febrile illness and pancytopenia. The cause of the aplastic crisis was an acute infection with human B19 parvovirus (B19 HPV) as proven by immunoelectron microscopy and DNA hybridization. This is the first report on the association of B19-HPV-related aplastic crisis with P-5'-N deficiency.