Chicken anemia virus induced apoptosis: underlying molecular mechanisms

Molecular characterization of chicken infectious anaemia virus (CIAV) in China during 2020-2021

Chicken infectious anaemia virus (CIAV) has been identified as the causative agent of chicken infectious anaemia (CIA), causing huge economic losses to the poultry industry globally. In this study, a total of 573 clinical samples were collected from 197 broiler farms in 17 provinces of China during 2020-2021. Among them, 375 samples (375/573, 65.4%) were positive for CIAV by real-time PCR. The positive rate of CIAV detection between different regions of China ranged from 46.67% (North China) to 81.25% (Central China). The nucleotide sequences of the VP1 gene were obtained for 91 CIAV strains, whole genome sequencing was successful for 72 out of 91 strains. Phylogenetic analysis based on the VP1 gene revealed that 91 CIAV strains currently circulating in China belong to three genotypes (II, IIIa and IIIb), and most of the CIAV strains belong to genotype IIIa. Phylogenetic analysis of the whole genome showed that 71 CIAV strains belong to genotype IIIa, and one strain belongs to genotype II. Sequence analysis showed several amino acid substitutions in both the VP1, VP2 and VP3 proteins. Our results enhance the understanding of the molecular characterization of CIAV infection in China.RESEARCH HIGHLIGHTS A molecular systematic survey of CIAV in China during 2020-2021.CIAV genotype IIIa is the predominant genotype in China.

Genomic Characterization of CIAV Detected in Contaminated Attenuated NDV Vaccine: Epidemiological Evidence of Source and Vertical Transmission From SPF Chicken Embryos in China

Live attenuated vaccines have been extensively used to prevent infectious disease in poultry flocks. Freedom from exogenous virus is a high priority for any veterinary vaccines. Recently, attenuated Newcastle disease virus (NDV) vaccines were detected to be contaminated with chicken infectious anemia virus (CIAV) in a routine screening for exogenous viruses. To investigate the possible source of the contamination, we conducted virological tests on a specific-pathogen-free (SPF) layer breeder flock that provide the raw materials for vaccines in this manufacturer. Firstly, CIAV antibodies in serum and egg yolks samples of the SPF laying hens were detected by ELISA assays. The results showed that CIAV antibodies in serum and egg yolks were 62% positive and 57% positive, respectively. Then, DNA was extracted from the NDV vaccines and SPF chicken embryonated eggs, and detected by molecular virology assays. The results showed that three assays for pathogens in embryonated eggs had similar positive rates (35.8%). And the sequences of CIAV from SPF embryos and NDV vaccines consisted of 2,298 nucleotides (nt) with 100% homology. The new full-length genome of CIAV was designated SDSPF2020 (Genbank accession number: MW660821). Data showed SDSPF2020 had the sequence similarities of 95.8–99.6% with reference strains, and shared the highest homology with the Chinese strain HLJ15125. These results strongly suggested that exogenous CIAV contamination is most likely caused by wild virus infection in SPF flocks and vertical transmission to chicken embryos. Collectively, this study illustrated that vertical transmission of CIAV from a SPF layer breeder flock to embryos was a non-neglible way for exogenous virus contamination in vaccine production.

Canine Parvovirus and Its Non-Structural Gene 1 as Oncolytic Agents: Mechanism of Action and Induction of Anti-Tumor Immune Response

The exploration into the strategies for the prevention and treatment of cancer is far from complete. Apart from humans, cancer has gained considerable importance in animals because of increased awareness towards animal health and welfare. Current cancer treatment regimens are less specific towards tumor cells and end up harming normal healthy cells. Thus, a highly specific therapeutic strategy with minimal side effects is the need of the hour. Oncolytic viral gene therapy is one such specific approach to target cancer cells without affecting the normal cells of the body. Canine parvovirus (CPV) is an oncolytic virus that specifically targets and kills cancer cells by causing DNA damage, caspase activation, and mitochondrial damage. Non-structural gene 1 (NS1) of CPV, involved in viral DNA replication is a key mediator of cytotoxicity of CPV and can selectively cause tumor cell lysis. In this review, we discuss the oncolytic properties of Canine Parvovirus (CPV or CPV2), the structure of the NS1 protein, the mechanism of oncolytic action as well as role in inducing an antitumor immune response in different tumor models.

Genetic Heterogeneity among Chicken Infectious Anemia Viruses Detected in Italian Fowl

Chicken infectious anemia virus (CIAV) is a pathogen of chickens associated with immunosuppression and with a disease named chicken infectious anemia. The present survey reports an epidemiological study on CIAV distribution in Italian broiler, broiler breeder and backyard chicken flocks. Twenty-five strains were detected by a specifically developed nested PCR protocol, and molecularly characterized by partial VP1 gene or complete genome sequencing. Viral DNA amplification was successfully obtained from non-invasive samples such as feathers and environmental dust. Sequence and phylogenetic analysis showed the circulation of field or potentially vaccine-derived strains with heterogeneous sequences clustered into genogroups II, IIIa, and IIIb. Marker genome positions, reported to be correlated with CIAV virulence, were evaluated in field strains. In conclusion, this is the first survey focused on the molecular characteristics of Italian CIAVs, which have proved to be highly heterogeneous, implementing at the same time a distribution map of field viruses worldwide.

Apoptosis Triggered by ORF3 Proteins of the Circoviridae Family

Apoptosis, a form of the programmed cell death, is an indispensable defense mechanism regulating cellular homeostasis and is triggered by multiple stimuli. Because of the regulation of apoptosis in cellular homeostasis, viral proteins with apoptotic activity are particular foci of on antitumor therapy. One representative viral protein is the open reading frame 3 (ORF3) protein, also named as apoptin in the Circoviridae chicken anemia virus (CAV), and has the ability to induce tumor-specific apoptosis. Proteins encoded by ORF3 in other circovirus species, such as porcine circovirus (PCV) and duck circovirus (DuCV), have also been reported to induce apoptosis, with subtle differences in apoptotic activity based on cell types. This article is aimed at reviewing the latest research advancements in understanding ORF3 protein-mediated apoptosis mechanisms of Circoviridae from three perspectives: subcellular localization, interactions with host proteins, and participation in multiple apoptotic signaling pathways, providing a scientific basis for circovirus pathogenesis and a reference on its potential anticancer function.

Apoptin Regulates Apoptosis and Autophagy by Modulating Reactive Oxygen Species (ROS) Levels in Human Liver Cancer Cells

Apoptin is a protein that specifically induces apoptosis in tumor cells. The anti-tumorigenic functions of Apoptin, including autophagy activation and its interaction with apoptosis, have not been precisely elucidated. Here we investigate the main pathways of apoptin-mediated killing of human liver cancer cells, as well as its putative role in autophagy and apoptosis. The anti-proliferative effect of apoptin in liver cancer cells was analyzed in vitro by crystal violet staining and MTS detection, and also in vivo using a tumor-based model. The main pathway related to apoptin-induced growth inhibition in vitro was evaluated by flow cytometry and fluorescence staining. The relationship between apoptosis and autophagy on apoptin-treating cells was analyzed using apoptosis and autophagy inhibitors, mitochondrial staining, Annexin V-FITC/PI flow detection, LC3 staining, and western blotting. The effect of ROS toward the apoptosis and autophagy of apoptin-treating cells was also evaluated by ROS detection, Annexin V-FITC/PI flow detection, LC3 staining, and western blotting. Inhibition of apoptosis in apoptin-treating liver cancer cells significantly reduced the autophagy levels in vitro. The overall inhibition increased from 12 h and the effect was most obvious at 48 h. Inhibition of autophagy could increase apoptin-induced apoptosis of cells in a time-dependent manner, reaching its peak at 24 h. Apoptin significantly alters ROS levels in liver cancer cells, and this effect is directly related to apoptosis and autophagy. ROS appears to be the key factor linking apoptin-induced autophagy and apoptosis through the mitochondria in liver cancer cells. Therefore, evaluating the interaction between apoptin-induced apoptosis and autophagy is a promising step for the development of alternate tumor therapies.

Neuroprotective potential of ketamine prevents developing brain structure impairment and alteration of neurocognitive function induced via isoflurane through the PI3K/AKT/GSK-3β pathway

Background

The aim of the current experimental study was to scrutinize the neuroprotective effect of ketamine on the isoflurane (iso)-induced cognitive dysfunction in rats via phosphoinositide 3 kinase (PI3K)/protein kinase B (AKT)/glycogen synthase kinase 3β (GSK-3β) pathway.

Materials and methods

Sprague-Dawley rats were used for the current experimental study. The rats were divided into six groups and rats were treated with ketamine and memantine. For the estimation of cognitive function study, we used the Morris water test. Pro-inflammatory cytokines such as IL-1β, IL-6, tumor necrosis factor-α (TNF-α), and caspase-6; the antioxidant parameters malondialdehyde, glutathione, superoxide dismutase, catalase, and protein carbonyl; acetylcholinesterase, amyloid β, and brain-derived neurotrophic factor were estimated, respectively. The protein expression of AKT, GSK-3β, p21WAF1/CIP1, and p53 was also estimated, respectively.

Results

Ketamine significantly enhanced cognitive function and showed anti-inflammatory and antioxidant effects, and exhibited the neuroprotective effect of ketamine against the isoflurane-induced cognitive impairment. Additionally, ketamine significantly (P<0.005) suppressed IL-1β, TNF-α, IL-6, caspase-6 and p21WAF1/CIP1, p53 expression and up-regulated the PI3K/AKT/GSK-3β expression in the group of iso-induced rats.

Conclusion

We can conclude that ketamine prevented the cognitive impairment induced by isoflurane anesthesia through anti-apoptotic, anti-inflammatory, and antioxidant effects via the PI3K/AKT/GSK-3β pathway.

Tissue Tropism of Chicken Anaemia Virus in Naturally Infected Broiler Chickens

Chicken anaemia virus (CAV) causes chicken infectious anaemia, a severe disease characterized by anaemia and immunosuppression and leading to serious economic losses in the poultry industry worldwide. Although CAV infection has been investigated under experimental conditions, information regarding natural infection is scarce. This report describes an outbreak of CAV infection in 18-day-old broiler chickens and investigates virus tropism in affected birds. Thymic atrophy, pale bone marrow, swelling of the legs and foot ulcers (gangrenous dermatitis) were the most common gross lesions. Severe lymphoid cell depletion in the thymic cortex and presence of intranuclear acidophilic inclusion bodies, depletion of haemopoietic cells in bone marrow and presence of lymphoid infiltrates in several organs were also observed. Immunohistochemical labelling demonstrated the CAV antigens VP1 and VP3 in several organs. The expression of both proteins was similar in the thymic cortex and in the bone marrow, the main target organs of CAV; however, VP3 expression was more abundant in the other organs. Labelling of serial sections showed that CD3⁺ T lymphocytes might be responsible for the dissemination of the virus from the thymus and bone marrow to other organs and that virus-induced apoptosis, mediated through caspase-3, occurred mainly in the thymus and bone marrow.

The Anaphase Promoting Complex/Cyclosome (APC/C): A Versatile E3 Ubiquitin Ligase

In the present chapter we discuss the essential roles of the human E3 ubiquitin ligase Anaphase Promoting Complex/Cyclosome (APC/C) in mitosis as well as the emerging evidence of important APC/C roles in cellular processes beyond cell division control such as regulation of genomic integrity and cell differentiation of the nervous system. We consider the potential incipient role of APC/C dysregulation in the pathophysiology of the neurological disorder Alzheimer's disease (AD). We also discuss how certain Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) viruses take control of the host's cell division regulatory system through harnessing APC/C ubiquitin ligase activity and hypothesise the plausible molecular mechanisms underpinning virus manipulation of the APC/C. We also examine how defects in the function of this multisubunit protein assembly drive abnormal cell proliferation and lastly argue the potential of APC/C as a promising therapeutic target for the development of innovative therapies for the treatment of chronic malignancies such as cancer.

Development of real-time PCR assays for single and simultaneous detection of infectious bursal disease virus and chicken anemia virus

Infectious bursal disease virus (IBDV) and chicken anemia virus (CAV) cause relevant immunosuppressive diseases in poultry. Clinical diagnosis of these viruses is challenging given the different disease presentations and the frequent occurrence of co-infections with other pathogens. Here, we standardized and validated simplex and duplex RT-qPCR assays for the straightforward detection of IBDV and CAV. The qPCR assays are based on primers and hydrolysis probes that target highly conserved regions of IBDV and CAV genomes. Analytical sensitivity tests on 10-fold serial dilutions containing 10⁰-10⁸ viral genomes indicated that the simplex assays have good determination coefficients and efficiency and detect a wide range of virus doses (10² to 10⁸ molecules copies/reactions). The relatively small values of intra- and inter-assay variability ensure the repeatability and support its reproducibility in different diagnostic and research facilities. The assays are also efficient tools for absolute quantification as indicated by the analytical performance analysis. The assays have an excellent specificity and absence of cross-reactivity with negative samples, or with other common avian viruses. The simplex IBDV and CAV assays use probes labelled with different dyes (FAM and HEX) and can be multiplexed for the simultaneous detection of both viruses. The determination coefficients, PCR efficiencies, and relatively small intra- and inter-assay variability were comparable to the simplex assays. This duplex assay is the first to simultaneously detect IBDV and CAV using the same RNA extraction from the bursa of Fabricius in a single and straightforward step. Therefore, this method is time saving, provides quantitative results for both targets without any cross-reaction, and reduces the risk of carrying-over contaminations. The qPCR assays here developed can be used in simplex and duplex formats for detection and quantification of large number of samples with reliable sensitivity and specificity. These tools are expected to improve surveillance and control of these ubiquitous viruses.

Epidemiology and molecular characterization of chicken anaemia virus from commercial and native chickens in Taiwan

Chicken infectious anaemia (CIA) is a disease with a highly economic impact in the poultry industry. The infected chickens are characterized by aplastic anaemia and extreme immunosuppression, followed by the increased susceptibility to secondary infectious pathogens and suboptimal immune responses for vaccination. Commercially available CIA vaccines are routinely used in the breeders in Taiwan to protect their progeny with maternal-derived antibodies. However, CIA cases still occur in the field and little is known about the genetic characteristics of Taiwanese chicken anaemia viruses (CAVs). In this study, CAV DNA was detected in 72 of 137 flocks collected during 2010-2015. Among the PCR-positive samples, the coding regions of 51 CAVs were sequenced. Phylogenetic analysis of the VP1 gene revealed that, although most of Taiwanese CAVs belonged to genotypes II and III, some isolates were clustered into a novel genotype (genotype IV). Moreover, a Taiwanese isolate in this novel genotype IV appeared to be derived from a recombination event between genotypes II and III viruses. Five Taiwanese CAV isolates were highly similar to the vaccine strains, 26P4 or Del-Ros. Taken together, these results indicate that the sequences of CAVs in Taiwan are variable, and inter-genotypic recombination had occurred between viruses of different genotypes. Moreover, vaccine-like strains might induce clinical signs of CIA in chickens. Our findings could be useful for understanding the evolution of CAVs and development of a better control strategy for CIA.

A novel anti-CD22 scFv-apoptin fusion protein induces apoptosis in malignant B-cells

CD22 marker is a highly internalizing antigen which is located on the surface of B-cells and is being used as a promising target for treatment of B cell malignancies. Monoclonal antibodies targeting CD22 have been introduced and some are currently under investigation in clinical trials. Building on the success of antibody drug conjugates, we developed a fusion protein consisting of a novel anti-CD22 scFv and apoptin and tested binding and therapeutic effects in lymphoma cells. The recombinant protein was expressed in E. coli and successfully purified and refolded. In vitro binding analysis by immunofluorescence and flow cytometry demonstrated that the recombinant protein specifically binds to CD22 positive Raji cells but not to CD22 negative Jurkat cells. The cytotoxic properties of scFv–apoptin were assessed by an MTT assay and Annexin V/PI flow cytometry analysis and showed that the recombinant protein induced apoptosis preferentially in Raji cells with no detectable effects in Jurkat cells. Our findings indicated that the recombinant anti-CD22 scFv–apoptin fusion protein could successfully cross the cell membrane and induce apoptosis with high specificity, make it as a promising molecule for immunotherapy of B-cell malignancies.

Review: Oncolytic virotherapy, updates and future directions

Oncolytic viruses (OVs) are viral strains that can infect and kill malignant cells while spare their normal counterparts. OVs can access cells through binding to receptors on their surface or through fusion with the plasma membrane and establish a lytic cycle in tumors, while leaving normal tissue essentially unharmed. Multiple viruses have been investigated in humans for the past century. IMLYGIC™ (T-VEC/Talimogene Laherparepvec), a genetically engineered Herpes Simplex Virus, is the first OV approved for use in the United States and the European Union for patients with locally advanced or non-resectable melanoma. Although OVs have a favorable toxicity profile and are impressively active anticancer agents in vitro and in vivo the majority of OVs have limited clinical efficacy as a single agent. While a virus-induced antitumor immune response can enhance oncolysis, when OVs are used systemically, the antiviral immune response can prevent the virus reaching the tumor tissue and having a therapeutic effect. Intratumoral administration can provide direct access to tumor tissue and be beneficial in reducing side effects. Immune checkpoint stimulation in tumor tissue has been noted after OV therapy and can be a natural response to viral-induced oncolysis. Also for immune checkpoint inhibition to be effective in treating cancer, an immune response to tumor neoantigens and an inflamed tumor microenvironment are required, both of which treatment with an OV may provide. Therefore, direct and indirect mechanisms of tumor killing provide rationale for clinical trials investigating the combination of OVs other forms of cancer therapy, including immune checkpoint inhibition.

Identification of the interaction and interaction domains of chicken anemia virus VP2 and VP3 proteins

Chicken anemia virus (CAV) is a small, single-stranded DNA virus of Anelloviridae family. Its genome segments encode three proteins, VP1, VP2, and VP3. This study identified an interaction between VP2 and VP3 and mapped the interaction domains. Through the yeast two-hybrid (Y2H) system, VP2 was found to interact with VP3. The presence of the VP2-VP3 complex in CAV-infected chicken cells was confirmed by co-immunoprecipitation. Confocal microscopy showed that VP2 and VP3 were expressed in the cytoplasm in cotransfected Vero cells. In the Y2H system, the interaction domains were identified as being within the N-terminal aa 1-30 and C-terminal aa 17-60 for VP2 and the N-terminal aa 46-60 and C-terminal aa 1-7 for VP3. This study showed the interaction between VP2 and VP3 of CAV and identified multiple independent interactive domains within the two proteins. This provides novel information for investigating the biological functions of these proteins.

Genomic and pathogenic analysis of a Muscovy duck parvovirus strain causing short beak and dwarfism syndrome without tongue protrusion

In 2008, clinical cases of short beak and dwarfism syndrome (SBDS) caused by Muscovy duck parvovirus (MDPV) infection were found in mule duck and Taiwan white duck farms in Fujian, China. A MDPV LH strain causing duck SBDS without tongue protrusion was isolated in this study. Phylogenetic analysis show that the MDPV LH strain was clustered together with other MDPV strains, but divergent from GPV isolates. Two major fragment deletions were found in the inverted terminal repeats (ITR) of MDPV LH similar to the ones in the ITR of MDPV GX5, YY and SAAS-SHNH strains. To investigate the pathogenicity of the MDPV LH strain, virus infection of young mule ducks was performed. The infected ducks showed SBDS symptoms including retard growth and shorten beaks without tongue protrusion. Atrophy of thymus, spleen and bursa of Fabricius was identified in the infected ducks. The results show that MDPV LH strain is moderately pathogenic to mule duck, leading to occurrence of SBDS. As far as we know, it is the first study showing that SBDS without tongue protrusion, and atrophy of thymus, spleen and bursa of Fabricius possibly associated with immunosuppression were found in the MDPV-infected ducks. The established duck-MDPV-SBDS system will help us to further work on the virus pathogenesis and develop efficacious vaccine against MDPV infection.

MDA7 combined with targeted attenuated Salmonella vector SL7207/pBud-VP3 inhibited growth of gastric cancer cells

BACKGROUND/AIM

To investigate the therapeutic effect of MDA7 combined with apoptin targeted attenuated Salmonella typhimurium vector SL7207/pBud-VP3 on gastric cancer cells.

MATERIALS AND METHODS

MDA7 was inserted into pBud-VP3 using molecular cloning technology to obtain the eukaryotic expression plasmid pBud-VP3-MDA7 and it was transformed into attenuated Salmonella typhimurium SL7207 by high voltage electroporation to obtain SL7207/pBud-VP3-MDA7. Mice bearing a sarcoma of gastric cancer cells were treated with SL7207/pBud-VP3-MDA7 and the growth-suppressing effect was assessed by measurement of tumor volume. Western blot was used to identify the MDA7 expression products. IL-6, INF-γ, TNF-α and caspase-3, VEGF in tumor tissue were detected by RT-PCR and immunohistochemistry.

RESULTS

SL7207/pBud-VP3-MDA7 was successfully constructed and expression of the protein MDA7 was identified in tumor tissue. SL7207/pBud-VP3-MDA7 significantly caused tumor inhibition and regression (p<0.05). The level of expression of cytokines IL-6, INF-γ, TNF-α in tumor tissue was significantly higher than in the other groups (p<0.05). The expression of caspase-3 was up-regulated and VEGF was down-regulated (p<0.05).

CONCLUSION

This study shows that SL7207/pBud-VP3-MDA7 has inhibitory effect on the growth of gastric cancer cells. The mechanism involved is related to the promotion of tumor apoptosis, immunity regulation and inhibition of tumor blood vessels.

Impact of virus load on immunocytological and histopathological parameters during clinical chicken anemia virus (CAV) infection in poultry

Chicken anemia virus (CAV) is one the important pathogen affecting commercial poultry sector globally by causing mortality, production losses, immunosuppression, aggravating co-infections and vaccination failures. Here, we describe the effects of CAV load on hematological, histopathological and immunocytochemical alterations in 1-day old infected chicks. The effects of CAV on cytokine expression profiles and generation of virus specific antibody titer were also studied and compared with viral clearance in various tissues. The results clearly confirmed that peak viral load was achieved mainly in lymphoid tissues between 10 and 20 days post infection (dpi), being highest in the blood (log1010.63 ±0.87/ml) and thymus (log1010.29 ±0.94/g) followed by spleen, liver, bone marrow and bursa. The histopathology and immunoflowcytometric analysis indicated specific degeneration of T lymphoid cells in the thymus, spleen and blood at 15 dpi. While the transcript levels of interleukin (IL)-1, IL-2, IL-12 decreased at all dpi, interferon (IFN)-γ increased (3-15 fold) during early stages of infection and the appearance of virus specific antibodies were found to be strongly associated with virus clearance in all the tissues. Our findings support the immunosuppressive nature of CAV and provide the relation between the virus load in the various body tissues and the immunopathological changes during clinical CAV infections.

Evidence of apoptosis induced by viral protein 2 of chicken anaemia virus

Although viral protein 3 (VP3) of chicken anaemia virus (CAV) has been well recognised as an inducer of apoptosis, viral protein 2 (VP2) of the virus has only been speculated to have apoptotic activity. This has not been verified because the open reading frame (ORF) encoding VP2 completely encompasses that encoding VP3, and thus the possibility of expression of VP3 cannot be excluded. The aim of this study was to elucidate the potential role of VP2 as an inducer of apoptosis. Site-directed mutagenesis was used to generate a point mutation that knocked out VP3 by early termination of its translation with a stop codon without imposing any change in the amino acid sequence of VP2. The mutated sequence was inserted into the pCAT plasmid preceded by a favorable Kozak's consensus sequence to create pCAT-VP2(+)VP3(-). The absence of VP3 expression in MSB1 cells transfected with this plasmid was confirmed using Western blotting, and DNA strand breaks and nuclear morphological changes were assessed to detect apoptosis. There was an increased level of apoptotic death in cells transfected with pCAT-VP2(+)VP3(-) compared to those transfected with the vector alone. This provides evidence that CAV VP2 can induce apoptosis.

Viral genes as oncolytic agents for cancer therapy

Many viruses have the ability to modulate the apoptosis, and to accomplish it; viruses encode proteins which specifically interact with the cellular signaling pathways. While some viruses encode proteins, which inhibit the apoptosis or death of the infected cells, there are viruses whose encoded proteins can kill the infected cells by multiple mechanisms, including apoptosis. A particular class of these viruses has specific gene(s) in their genomes which, upon ectopic expression, can kill the tumor cells selectively without affecting the normal cells. These genes and their encoded products have demonstrated great potential to be developed as novel anticancer therapeutic agents which can specifically target and kill the cancer cells leaving the normal cells unharmed. In this review, we will discuss about the viral genes having specific cancer cell killing properties, what is known about their functioning, signaling pathways and their therapeutic applications as anticancer agents.

Avian Immunosuppressive Diseases and Immunoevasion

Subclinical immunosuppression in chickens is an important but often underestimated factor in the subsequent development of clinical disease. Immunosuppression can be caused by pathogens such as chicken infectious anemia virus, infectious bursal disease virus, reovirus, and some retroviruses (e.g., reticuloendotheliosis virus). Mycotoxins and stress, often caused by poor management practices, can also cause immunosuppression. The effects on the innate and acquired immune responses and the mechanisms by which mycotoxins, stress and infectious agents cause immunosuppression are discussed. Immunoevasion is a common ploy by which viruses neutralize or evade immune responses. DNA viruses such as herpesvirus and poxvirus have multiple genes, some of them host-derived, which interfere with effective innate or acquired immune responses. RNA viruses may escape acquired humoral and cellular immune responses by mutations in protective antigenic epitopes (e.g., avian influenza viruses), while accessory non-structural proteins or multi-functional structural proteins interfere with the interferon system (e.g., Newcastle disease virus).

Expression and characterization of highly antigenic domains of chicken anemia virus viral VP2 and VP3 subunit proteins in a recombinant E. coli for sero-diagnostic applications

Background

Chicken anemia virus (CAV) is an important viral pathogen that causes anemia and severe immunodeficiency syndrome in chickens worldwide. Generally, CAV infection occurs via vertical transmission in young chicks that are less than two weeks old, which are very susceptible to the disease. Therefore, epidemiological investigations of CAV infection and/or the evaluation of the immunization status of chickens is necessary for disease control. Up to the present, systematically assessing viral protein antigenicity and/or determining the immunorelevant domain(s) of viral proteins during serological testing for CAV infection has never been performed. The expression, production and antigenic characterization of CAV viral proteins such as VP1, VP2 and VP3, and their use in the development of diagnostic kit would be useful for CAV infection prevention.

Results

Three CAV viral proteins VP1, VP2 and VP3 was separately cloned and expressed in recombinant E. coli. The purified recombinant CAV VP1, VP2 and VP3 proteins were then used as antigens in order to evaluate their reactivity against chicken sera using indirect ELISA. The results indicated that VP2 and VP3 show good immunoreactivity with CAV-positive chicken sera, whereas VP1 was found to show less immunoreactivity than VP2 and VP3. To carry out the further antigenic characterization of the immunorelevant domains of the VP2 and VP3 proteins, five recombinant VP2 subunit proteins (VP2-435N, VP2-396N, VP2-345N, VP2-171C and VP2-318C) and three recombinant VP3 subunit proteins (VP3-123N, VP3-246M, VP3-366C), spanning the defined regions of VP2 and VP3 were separately produced by an E. coli expression system. These peptides were then used as antigens in indirect ELISAs against chicken sera. The results of these ELISAs using truncated recombinant VP2 and VP3 subunit proteins as coating antigen showed that VP2-345N, VP2-396N and VP3-246M gave good immunoreactivity with CAV-positive chicken sera compared to the other subunit proteins. Moreover, the VP2-396N and VP2-345 based ELISAs had better sensitivity (97.5%) and excellent specificity (100%) during serodiagnosis testing using a mean plus three standard deviations cut-off. The VP3-246M based ELISA showed a sensitivity of 85% and a specificity of 100% at the same cut-off value.

Conclusions

This is the first report to systematically assess the antigenic characteristics of CAV viral proteins for sero-diagnosis purposes. Purified recombinant VP2-396N and VP2-345N subunit proteins, which span defined regions of VP2, were demonstrated to have good antigenicity and higher sensitivities than VP3-246M and were able to recognize CAV-positive chicken serum using an ELISA assay. The defined antigenicity potential of these chimeric subunit proteins produced by expression in E. coli seem to have potential and could be useful in the future for the development of the CAV diagnostic tests based on a subunit protein ELISA system.

Human gyrovirus DNA in human blood, Italy

HGyV in blood suggests the infection might be systemic.

Human gyrovirus (HGyV) is a recent addition to the list of agents found in humans. Prevalence, biologic properties, and clinical associations of this novel virus are still incompletely understood. We used qualitative PCRs to detect HGyV in blood samples of 301 persons from Italy. HGyV genome was detected in 3 of 100 solid organ transplant recipients and in 1 HIV-infected person. The virus was not detected in plasma samples from healthy persons. Furthermore, during observation, persons for whom longitudinal plasma samples were obtained had transient and scattered presence of circulating HGyV. Sequencing of a 138-bp fragment showed nucleotide identity among all the HGyV isolates. These results show that HGyV can be present in the blood of infected persons. Additional studies are needed to investigate possible clinical implications.

Apoptin induces apoptosis in human bladder cancer EJ and BIU-87 cells

OBJECTIVE

To investigate whether apoptin is a apoptosis-inducing protein with a potential for bladder cancer therapy.

METHODS

We constructed a PCDNA3/Apoptin eukaryotic expression vector, and transfected this vector into bladder cancer cell lines BIU-87 and EJ, then observed the results by RT-PCR, transmission electron microscopy, MTT assay and the flow cytometry (TUNEL method).

RESULTS

PCDNA3/Apoptin successfully induced a high level apoptosis in both bladder cancer cell lines, compared with the controls (p<0.05).

CONCLUSIONS

Apoptin can induce high level apoptosis in human bladder cancer EJ and BIU-87 cells, which suggests a potential for human bladder cancer therapy.

How viruses affect the cell cycle through manipulation of the APC/C

Viruses frequently exploit host cell cycle machineries for their own benefit, often by targeting 'master switches' of cell cycle regulation. By doing so, they achieve maximum effect from minimal input. One such master switch is the anaphase promoting complex or cyclosome (APC/C), a multicomponent ubiquitin ligase and a dominant regulator of the cell cycle. A growing number of viruses have been shown to target the APC/C. Although differing strategies are employed, viral manipulation of the APC/C seems to serve a common purpose, namely, to create an environment supportive of viral replication. Here, the molecular mechanisms employed by these viruses are summarized and discussed.

Identification of the NLS and NES motifs of VP2 from chicken anemia virus and the interaction of VP2 with mini-chromosome maintenance protein 3

Background

VP2 of chicken anemia virus (CAV) is a dual-specificity phosphatase required for virus infection, assembly and replication. The functions of the nuclear localization signal (NLS) and nuclear export signal (NES) of VP2 in the cell, however, are poorly understood. Our study identified the presence of a NLS in VP2 and showed that the protein interacted significantly with mini-chromosome maintenance protein 3 (MCM3) in the cell.

Results

An arginine-lysine rich NLS could be predicted by software and spanned from amino acids 133 to 138 of VP2. The critical amino acids residues between positions 136 and 138, and either residue 133 or 134 are important for nuclear import in mammalian cells based on systematic mutagenesis. A NES is also predicted in VP2; however the results suggest that no functional NES is present and that this protein is CRM1 independent. It was also shown that VP2 is a chromatin binding protein and, notably, using a co-immunoprecipitation assay, it was found that VP2 association with MCM3 and that this interaction does not require DSP activity.

Conclusions

VP2 contains a NLS that span from amino acids 133 to 138. VP2 is a CRM1 independent protein during nuclear export and associates with MCM3 in cells.

Gallus Heat shock cognate protein 70, a novel binding partner of Apoptin

Background

Chicken anemia virus (CAV) infection of newly hatched chickens induces generalized lymphoid atrophy and causes immunosuppressive. VP3, also known as Apoptin, is non-structural protein of CAV. Apoptin specifically induces apoptosis in transformed or tumor cells but not in normal cells. In particular, there are no known cellular homologues of Apoptin hindering genetic approaches to elucidate its cellular function. Although a number of Apoptin-interacting molecules have been identified, the molecular mechanism underlying Apoptin's action is still poorly understood. To learn more about the molecular mechanism of Apoptin's action, we searched for Apoptin associated proteins.

Results

Using yeast two-hybrid and colony-life filter approaches we got five positive yeast clones. Through sequencing and BLASTed against NCBI, one of the clones was confirmed containing Gallus heat shock cognate protein 70 (Hsc70). Hsc70 gene was clone into pRK5-Flag plasmid, coimmunoprecipitation assay show both exogenous Hsc70 and endogenous Hsc70 can interact with Apoptin. Truncated Apoptin expression plasmids were made and coimmunoprecipitation were performed, the results show the binding domain of Apoptin with Hsc70 is located between amino acids 30-60. Truncated expression plasmids of Hsc70 were also constructed and coimmunoprecipitation were performed, the results show the peptide-binding and variable domains of Hsc70 are responsible for the binding to Apoptin. Confocal assays were performed and results show that under physiological condition Hsc70 is predominantly distributed in cytoplasm, whereas Hsc70 is translocated into the nuclei and colocalized with Apoptin in the presence of Apoptin in DF-1 cell. Functional studies show that Apoptin markedly down-regulate the mRNA level of RelA/p65 in DF-1 cell. To explore the effect of Hsc70 on Apoptin-mediated RelA/p65 gene expression, we have searched two Hsc70 RNAi sequences, and found that all of them dramatically inhibited the expression of endogenous Hsc70, with the #2 Hsc70 RNAi sequence being the most effective. Knockdown of Hsc70 show Apoptin-inhibited RelA/p65 expression was abolished. Our data demonstrate that Hsc70 is responsible for the down-regulation of Apoptin induced RelA/p65 gene expression.

Conclusion

We identified Gallus Hsc70 as an Apoptin binding protein and showed the translocation of Hsc70 into the nuclei of DF-1 cells treated with Apoptin. Hsc70 regulates RelA/p65 gene expression induced by Apoptin.

Chicken anemia virus: an understanding of the in-vitro host response over time

Chicken anemia virus (CAV) is an economically important virus affecting the chicken meat and egg industry. CAV is characterized by anemia, lymphoid depletion, and immunosuppression. Microarrays were used to investigate the response of MDCC-MSB1 cells (MSB1) to infection with CAV at 24 and 48 h post-infection (hpi). The major genes responding to CAV infection include genes involved in inflammation, apoptosis, and antiviral activity. Several cytokines were differentially regulated at either 24 or 48 hpi, including interleukin 2 (IL-2), interleukin receptors IL-1R, IL-22R, IL-18R, and IL-7R, and interferon-α (IFN-α). While there were many genes differentially regulated in this experiment, only two genes were common to both time points, suggesting a dramatic change in gene expression over the two time points studied. The present study is the first microarray experiment to investigate CAV, and we identified a number of key pathways involved in viral infection. Overall, there were more genes upregulated at 24 hpi than at 48 hpi, including genes involved in cytokine signaling, apoptosis, and antiviral activity. The two time points were vastly different in their gene expression patterns, in that at 24 hpi there were many genes involved in the response to infection, whereas at 48 hpi there were many genes associated with apoptosis and immunosuppression.

Naturally occurring, tumor-specific, therapeutic proteins

The emerging approach to cancer treatment known as targeted therapies offers hope in improving the treatment of therapy-resistant cancers. Recent understanding of the molecular pathogenesis of cancer has led to the development of targeted novel drugs such as monoclonal antibodies, small molecule inhibitors, mimetics, antisense and small interference RNA-based strategies, among others. These compounds act on specific targets that are believed to contribute to the development and progression of cancers and resistance of tumors to conventional therapies. Delivered individually or combined with chemo- and/or radiotherapy, such novel drugs have produced significant responses in certain types of cancer. Among the most successful novel compounds are those which target tyrosine kinases (imatinib, trastuzumab, sinutinib, cetuximab). However, these compounds can cause severe side-effects as they inhibit pathways such as epidermal growth factor receptor (EGFR) or platelet-derived growth factor receptor, which are also important for normal functions in non-transformed cells. Recently, a number of proteins have been identified which show a remarkable tumor-specific cytotoxic activity. This toxicity is independent of tumor type or specific genetic changes such as p53, pRB or EGFR aberrations. These tumor-specific killer proteins are either derived from common human and animal viruses such as E1A, E4ORF4 and VP3 (apoptin) or of cellular origin, such as TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) and MDA-7 (melanoma differentiation associated-7). This review aims to present a current overview of a selection of these proteins with preferential toxicity among cancer cells and will provide an insight into the possible mechanism of action, tumor specificity and their potential as novel tumor-specific cancer therapeutics.

Apoptin, a tumor-selective killer

Apoptin, a small protein from chicken anemia virus, has attracted great attention, because it specifically kills tumor cells while leaving normal cells unharmed. The subcellular localization of apoptin appears to be crucial for this tumor-selective activity. In normal cells, apoptin resides in the cytoplasm, whereas in cancerous cells it translocates into the nucleus. The nuclear translocation of apoptin is largely controlled by its phosphorylation. In tumor cells, apoptin causes the nuclear accumulation of survival kinases including Akt and is phosphorylated by CDK2. Thereby, apoptin redirects survival signals into cell death responses. Apoptin also binds as a multimeric complex to DNA and interacts with several nuclear targets, such as the anaphase-promoting complex, resulting in a G2/M phase arrest. The proapoptotic signal of apoptin is then transduced from the nucleus to cytoplasm by Nur77, which triggers a p53-independent mitochondrial death pathway. In this review, we summarize recent discoveries of apoptin's mechanism of action that might provide intriguing insights for the development of novel tumor-selective anticancer drugs.

Apoptosis-inducing proteins in chicken anemia virus and TT virus

Torque teno viruses (TTVs) share several genomic similarities with the chicken anemia virus (CAV). CAV encodes the protein apoptin that specifically induces apoptosis in (human) tumor cells. Functional studies reveal that apoptin induces apoptosis in a very broad range of (human) tumor cells. A putative TTV open reading frame (ORF) in TTV genotype 1, named TTV apoptosis inducing protein (TAIP), it induces, like apoptin, p53-independent apoptosis in various human hepatocarcinoma cell lines to a similar level as apoptin. In comparison to apoptin, TAIP action is less pronounced in several analyzed human non-hepatocarcinoma-derived cell lines. Detailed sequence analysis has revealed that the TAIP ORF is conserved within a limited group of the heterogeneous TTV population. However, its N-terminal half, N-TAIP, is rather well conserved in a much broader set of TTV isolates. The similarities between apoptin and TAIP, and their relevance for the development and treatment of diseases is discussed.

Chicken anemia virus

Chicken anemia virus (CAV), the only member of the genus Gyrovirus of the Circoviridae, is a ubiquitous pathogen of chickens and has a worldwide distribution. CAV shares some similarities with Torque teno virus (TTV) and Torque teno mini virus (TTMV) such as coding for a protein inducing apoptosis and a protein with a dual-specificity phosphatase. In contrast to TTV, the genome of CAV is highly conserved. Another important difference is that CAV can be isolated in cell culture. CAV produces a single polycistronic messenger RNA (mRNA), which is translated into three proteins. The promoter-enhancer region has four direct repeats resembling estrogen response elements. Transcription is enhanced by estrogen and repressed by at least two other transcription factors, one of which is COUP-TF1. A remarkable feature of CAV is that the virus can remain latent in gonadal tissues in the presence or absence of virus-neutralizing antibodies. In contrast to TTV, CAV can cause clinical disease and subclinical immunosuppression especially affecting CD8+ T lymphocytes. Clinical disease is associated with infection in newly hatched chicks lacking maternal antibodies or older chickens with a compromised humoral immune response.

Relationship of Torque teno virus to chicken anemia virus

This chapter examines the correlation between Torque teno virus (TTV) and chicken anemia virus (CAV). Each has a circular single-stranded (ss)DNA genome with every one of its known open reading frames (ORF) on its antigenomic strand. This structure is distinct from those of circoviruses. The genomic sizes of TTV and CAV are different, 3.8 kb and 2.3 kb, respectively. While the spectrum of the TTV genome is enormously diverse, that of the CAV genome is quite narrow. Although a 36-nt stretch near the replication origin of TA278 TTV possesses more than 80% similarity to that of CAV, the sequence of the other genomic regions does not exhibit a significant similarity. Nevertheless, the relative allocation of ORFs on each frame in these viruses mimics each other. Three or more messenger RNA (mRNAs) are generated by transcription in both of them. The structural protein with the replicase domain is coded for by frame 1 in each virus, and a nonstructural protein with a phosphatase domain is coded for by frame 2. A protein on frame 3 in each virus induces apoptosis in transformed cells. Recently, we confirmed that apoptin is necessary for the replication of CAV. TTV has been proposed to constitute a new family, Anelloviridae. Considering these similarities and dissimilarities between CAV and TTV, it seems more reasonable to place CAV, the only member of genus Gyrovirus, into Anelloviridae together with TTV, or into a new independent family.

Replication of chicken anemia virus (CAV) requires apoptin and is complemented by VP3 of human torque teno virus (TTV)

To test requirement for apoptin in the replication of chicken anemia virus (CAV), an apoptin-knockout clone, pCAV/Ap(-), was constructed. DNA replication was completely abolished in cells transfected with replicative form of CAV/Ap(-). A reverse mutant competent in apoptin production regained the full level of DNA replication. DNA replication and virus-like particle (VLP) production of CAV/Ap(-) was fully complemented by supplementation of the wild-type apoptin. The virus yield of a point mutant, CAV/ApT(108)I, was 1/40 that of the wild type, even though its DNA replication level was full. The infectious titer of CAV was fully complemented by supplementing apoptin. Progeny virus was free from reverse mutation for T(108)I. To localize the domain within apoptin molecule inevitable for CAV replication, apoptin-mutant expressing plasmids, pAp1, pAp2, pAp3, and pAp4, were constructed by deleting amino acids 10-36, 31-59, 59-88 and 80-112, respectively. While Ap1 and Ap2 were preferentially localized in nuclei, Ap3 and Ap4 were mainly present in cytoplasm. Although complementation capacity of Ap3 and Ap4 was 1/10 of the wild type, neither of them completely lost its activity. VP3 of TTV did fully complement the DNA replication and VLP of CAV/Ap(-). These data suggest that apoptin is inevitable not only for DNA replication but also VLP of CAV. The common feature of apoptin and TTV-VP3 presented another evidence for close relatedness of CAV and TTV.

Secretory Transactivating Transcription-apoptin fusion protein induces apoptosis in hepatocellular carcinoma HepG2 cells

AIM: To determine whether SP-TAT-apoptin induces apoptosis and also maintains its tumor cell specificity.

METHODS: In this study, we designed a secretory protein by adding a secretory signal peptide (SP) to the N terminus of Transactivating Transcription (TAT)-apoptin (SP-TAT-apoptin), to test the hypothesis that it gains an additive bystander effect as an anti-cancer therapy. We used an artificial human secretory SP whose amino acid sequence and corresponding cDNA sequence were generated by the SP hidden Markov model.

RESULTS: In human liver carcinoma HepG2 cells, SP-TAT-apoptin expression showed a diffuse pattern in the early phase after transfection. After 48 h, however, it translocated into the nuclear compartment and caused massive apoptotic cell death, as determined by 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and annexin-V binding assay. SP-TAT-apoptin did not, however, cause any cell death in non-malignant human umbilical vein endothelial cells (HUVECs). Most importantly, the conditioned medium from Chinese hamster ovary (CHO) cells transfected with SP-TAT-apoptin also induced significant cell death in HepG2 cells, but not in HUVECs.

CONCLUSION: The data demonstrated that SP-TAT-apoptin induces apoptosis only in malignant cells, and its secretory property might greatly increase its potency once it is delivered in vivo for cancer therapy.

Apoptin: therapeutic potential of an early sensor of carcinogenic transformation

The avian virus-derived protein apoptin induces p53-independent apoptosis in a tumor-specific way. Apoptin acts as a multimeric complex and forms superstructures upon binding to DNA. In tumor cells, apoptin is phosphorylated and mainly nuclear, whereas in normal cells it is unphosphorylated, cytoplasmic, and becomes readily neutralized. Interestingly, apoptin phosphorylation, nuclear translocation, and apoptosis can transiently be induced in normal cells by cotransfecting SV40 large T oncogene, indicating that apoptin recognizes early stages of oncogenic transformation. In cancer cells, apoptin appears to recognize survival signals, which it is able to redirect into cell death impulses. Apoptin targets include DEDAF, Nur77, Nmi, Hippi, and the potential drug target APC1. Apoptin-transgenic mice and animal tumor models have revealed apoptin as a safe and efficient antitumor agent, resulting in significant tumor regression. Future antitumor therapies could use apoptin either as a therapeutic bullet or as an early sensor of druggable tumor-specific processes.

Apoptin: specific killer of tumor cells?

In the early 1990s it was discovered that the VP3/Apoptin protein encoded by the Chicken Anemia virus (CAV) possesses an inherent ability to specifically kill cancer cells. Apoptin was found to be located in the cytoplasm of normal cells while in tumor cells it was localized mainly in the nucleus.(1) These differences in the localization pattern were suggested to be the main mechanism by which normal cells show resistance to Apoptin-mediated cell killing. Although the mechanism of action of Apoptin is presently unknown, it seems to function by the induction of programmed cell death (PCD) after translocation from the cytoplasm to the nucleus and arresting the cell cycle at G2/M, possibly by interfering with the cyclosome.(2) In addition, cancer specific phosphorylation of Threonine residue 108 has been suggested to be important for Apoptin's function to kill tumor cells.(3) In contrast to the large number of publications reporting that nuclear localization, induction of PCD and phosphorylation of Apoptin is restricted to cancer cells, several recent studies have shown that Apoptin has the ability to migrate to the nucleus and induce PCD in some of the normal cell lines tested. There is evidence that high protein expression levels as well as the cellular growth rate may influence Apoptin's ability to specifically kill tumor cells. Thus far both in vitro and in vivo studies indicate that Apoptin is a powerful apoptosis inducing protein with a promising prospective utility in cancer therapy. However, here we show that several recent findings contradict some of the earlier results on the tumor specificity of Apoptin, thus creating some controversy in the field. The aim of this article is to review the available data, some published and some unpublished, which either agree or contradict the reported "black and white" tumor cell specificity of Apoptin. Understanding what factors appear to influence its function should help to develop Apoptin into a potent anti-cancer agent.

Assessing the expression of chicken anemia virus proteins in plants

Chicken anemia virus (CAV) is an important pathogen of chicken worldwide, causing severe anemia and immunodeficiency. Its small single-stranded DNA genome (2.3kb) encodes three proteins: VP1, the only structural protein, VP2, a protein phosphatase, and VP3, also known as apoptin, which induces apoptosis. In this study, CAV proteins were expressed in plants as an alternative for recombinant protein production in animal cells. Additionally, the effect of VP3 expression was tested to evaluate possible involvement in programmed cell death in plants. The CAV genes were cloned in binary vectors with the Green fluorescent protein (GFP) as N terminal fusion, and into a Potato virus X (PVX) and Tobacco Mosaic Virus (TMV)-based vectors. Nicotiana benthamiana plants were inoculated with Agrobacterium tumefaciens containing the binary vector constructs or the PVX and TMV constructs. Upon transient expression GFP:VP1 and GFP:VP2 were observed throughout the nucleoplasm, whereas VP3 formed compact aggregates within the nucleus, indicating functional nuclear localization signals in all three proteins. An intense fluorescence was observed for VP2 and VP3 fusions, whereas GFP:VP1 fluorescence remained faint and was only detected in a limited number of cells. Co-expression of GFP:VP1 and VP2 had a marked alteration on the distribution of GFP:VP1, forming large VP1 aggregates throughout the nucleus, indicating an interaction of the two CAV proteins. No visible alteration on GFP pattern was detected upon co-expression of GFP:VP1 and VP3, or with GFP:VP2 and VP3. Plants infected with PVX or TMV-based vectors expressing VP3 displayed strong necrosis and wilting, however, a direct association with VP3 expression and programmed cell death in plants, could not be established. Overall, our results show that all CAV proteins can be expressed in plant cells, though expression level of VP1 needs to be further optimized before testing its potential as (edible) subunit vaccine.

Viral protein apoptin as a molecular tool and therapeutic bullet: implications for cancer control

The chicken anemia virus-derived protein apoptin induces apoptosis in human tumor cells via a p53-independent pathway, while leaving normal cells intact. Moreover, apoptin treatment in preclinical animal studies leads to reduced tumor growth or remission without a detectable effect on healthy tissues. Apoptin is activated by a still unknown tumor-specific kinase activity. The mode of action of apoptin is under intense investigation, as certain features make it a promising tool for discovering early events in tumorigenesis, identifying druggable targets for antitumor treatment and possibly serving as an antitumor therapy in itself.

Effect of the VP3 gene of chicken anemia virus on canine mammary tumor cells

OBJECTIVE

To investigate the antitumor effect of the chicken anemia virus (CAV) VP3 gene in canine mammary tumor (CMT) cells. SAMPLE POPULATIONS: Established primary canine cell lines that originated from epithelial cells of resected CMTs and nonneoplastic mammary gland epithelial (MGE) cells.

PROCEDURES

Expression vectors and lentiviral vectors encoding the VP3 gene from a Taiwan-Ilan isolate of CAV were used to deliver the VP3 gene into CMT cells and nonneoplastic MGE cells. Ectopic gene expression and the pro-apoptotic effect of the VP3 gene on CMT and nonneoplastic MGE cells by either transfection or viral infection were evaluated via immunofluorescence microscopy, western blot analysis, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling analysis.

RESULTS

Overexpression of the enhanced green fluorescent protein-VP3 fusion protein was detected predominantly in the nuclei of CMT cells. In contrast, the VP3 protein was localized to the cytoplasm of nonneoplastic MGE cells. Among the fusion protein-expressing CMT cells, most underwent characteristic changes of apoptosis, whereas apoptosis was not detected in fusion protein-expressing, nonneoplastic MGE cells. Induction of apoptosis by VP3 gene overexpression in CMT cells was associated with the caspase-9-, but not the caspase-8-, mediated apoptosis pathway.

CONCLUSIONS AND CLINICAL RELEVANCE

These data indicate that the VP3 gene of the CAV induces apoptosis in malignant CMT cells, but not in nonneoplastic canine MGE cells. On the basis of such tumor cell-specific killing, the VP3 gene may be a promising agent for the treatment of malignant mammary gland tumors in dogs.

Torque teno virus (TTV): current status

Torque teno virus (TTV), currently classified into the family Circoviridae, genus Anellovirus, was first found in a patient with non-A-E hepatitis. TTV has a single stranded circular DNA of approximately 3.8 kb. TTVs are extraordinarily diverse, spanning five groups including SANBAN and SEN viruses. Torque teno mini virus (TTMV) with approximately 2.9 kb genome also has wide variants. Recently, two related 2.2- and 2.6-kb species joined this community. Recombinations between variants are frequent. This extensive TTV diversity remains unexplained; it is unclear how TTVs could be viable, and why they require such genetic variation. An unequivocal culture system is still not available. TTVs are ubiquitous in > 90% of adults worldwide but no human pathogenicity of TTV has been fully established. Epidemiological surveys need to specify the variants being studied and clinical targets, and must calibrate the sensitivity of the assay used. Potentially interesting observations include a higher viral load in patients with severe idiopathic inflammatory myopathies, cancer and lupus. Active replication was also found in infants with acute respiratory diseases. TTV/TTMV-related viruses were found in chimpanzees, apes, African monkeys and tupaias, and also in chickens, pigs, cows, sheep and dogs. Experimentally, rhesus monkeys were persistently infected by TTV, but only 1/53 chimpanzees. TTV transcribes three species of mRNAs, 3.0-, 1.2- and 1.0-kb in the ratio of 60:5:35. Recently, at least three mRNAs were shown in chicken anaemia virus. The genomic region -154/-76 contains a critical promoter. TTV seems to have at least three proteins; however, the definite functions of these proteins await further research work.