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Background: Apoptin can specifically kill cancer cells but has no toxicity to normal cells. Human telomerase reverse transcriptase (hTERT) acts as a tumor-specific promoter, triggering certain genes to replicate or express only in tumor cells, conferring specific replication and killing abilities. This study aimed at investigating the anticancer potential of the recombinant adenovirus Ad-apoptin-hTERTp-E1a (Ad-VT) in ovarian cancer treatment., Methods: Crystal Violet staining and WST-1 assays were used to analyze the inhibitory effect of Ad-VT on ovarian cancer SKOV3 and OVCAR-3 cells. Ad-VT-induced apoptosis of ovarian cancer cells, was detected using Hoechst, Annexin V-FITC/PI, JC-1 staining. Cell migration and invasion of ovarian cancer cells were detected using cell-scratch and Transwell assays. The pGL4.51 plasmid was used to transfect and to generate SKOV3-LUC cells, that stably express luciferase. The in vivo tumor inhibition effect of Ad-VT was subsequently confirmed using a tumor-bearing nude mouse model., Results: Ad-VT had a strong apoptosis-inducing effect on SKOV3 and OVCAR-3 cells, that was mainly mediated through the mitochondrial apoptotic pathway. The Ad-VT could significantly increase the inhibition of ovarian cancer cell migration and invasion. The Ad-VT also can inhibit tumor growth and reduce toxicity in vivo., Conclusions: The recombinant adenovirus, comprising the apoptin protein and the hTERTp promoter, was able to inhibit the growth of ovarian cancer cells and promote their apoptosis., (Copyright © 2020. Published by Elsevier Inc.)

Background: Selective therapy has always been the main challenge in cancer treatments. Various non-replicative oncolytic viral systems have revealed the safety and efficacy of using viruses and these products. The aim of this paper is to examine the impact of recombinant apoptin on the proliferation of lung cancer and breast cancer cell lines., Methods: The present study consisted of two steps of expression of recombinant apoptin and its anti-proliferative effects on normal and cancer cells. In the first step, following bioinformatics and optimizing apoptin gene sequencing and synthesis, it was expressed using vector PET28a and E. coli BL21 (DE3). The expressed recombinant apoptin was confirmed by analytical SDSPAGE and then purified using Ni affinity chromatography. In the second step, the antiproliferative effects of recombinant apoptin on lung cancer, breast cancer and primary cell lines were determined using MTT assay., Results: According to the results of SDS-PAGE gel assay, recombinant apoptin was visible in the 14 kDa band. Also, the MTT assay results indicated that the antiproliferative effects of recombinant apoptin in cancer cell lines was different compared with the primary cell line, and followed a dose-dependent manner in both cell lines. The highest cytotoxicity (lowest cell viability) groups were 0.2 mg/mL in lung cancer (0.32 ± 0.015) ( P <0.001), and in breast cancer (0.33 ± 0.031) ( P <0.001) and 0.032 mg/mL in primary cells (0.17 ± 0.004) ( P <0.01), as compared to the control groups., Conclusion: Our results confirmed that recombinant apoptin can induce antiproliferative effects in lung cancer and breast cancer cell lines, but not in normal monkey kidney cell line Vero; thus, it can be introduced as a promising novel specific antitumor agent after further evaluation in clinical trials., (© 2020 The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.)

Background: Chicken anaemia virus (CAV) is commonly found in poultry. VP1 is the sole structural protein of CAV, which is the major component responsible for capsid assembly. The CAV virion consists of the VP1 protein and a viral genome. However, there is currently no information on the protein-nucleic acid interactions between VP1 and DNA molecules., Results: In this study, the recombinant VP1 protein of CAV was expressed and purified to characterize its DNA binding activity. When VP1 protein was incubated with a DNA molecule, the DNA molecule exhibited retarded migration on an agarose gel. Regardless of whether the sequence of the viral genome was involved in the DNA molecule, DNA retardation was not significantly influenced. This outcome indicated VP1 is a DNA binding protein with no sequence specificity. Various DNA molecules with different conformations, such as circular dsDNA, linear dsDNA, linear ssDNA and circular ssDNA, interacted with VP1 proteins according to the results of a DNA retardation assay. Further quantification of the amount of VP1 protein required for DNA binding, the circular ssDNA demonstrated a high affinity for the VP1 protein. The preferences arranged in the order of affinity for the VP1 protein with DNA are circular ssDNA, linear ssDNA, supercoiled circular dsDNA, open circular DNA and linear dsDNA., Conclusions: The results of this study demonstrated that the interaction between VP1 and DNA molecules exhibited various binding preferences that were dependent on the structural conformation of DNA. Taken together, the results of this report are the first to demonstrate that VP1 has no sequence-specific DNA binding activity. The particular binding preferences of VP1 might play multiple roles in DNA replication or encapsidation during the viral life cycle.

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.

The use of viruses for treatment of cancer overcomes the bottlenecks of chemotherapy and radiotherapy. Several viruses and their proteins have been evaluated for oncolytic effect. The VP3 protein (apoptin) of chicken anemia virus is one such protein with an inherent ability to lyse cancer and transformed cells while leaving normal cells unharmed. In the present study, the apoptosis inducing potential of VP3 protein of CAV was evaluated in human cervical cancer cell line (HeLa). It was found that in VP3-induced apoptosis, caspase-dependent intrinsic pathway plays an important role with the cleavage of poly (ADP-ribose) polymerase (PARP) and there was no evidence of involvement of death receptor-mediated extrinsic pathway. The results of this study provide intuitive information and strengthen the candidacy of apoptin as a viral oncotherapeutic agent.

Three chicken anemia viruses (CAV) were detected by PCR during screening of field samples from village chickens collected in Cambodia in 2011/2012. Nearly full-length VP1 viral structural protein genes (nt 1-1,293) from the 3 CAV were sequenced and characterized. Phylogenetic analysis revealed that all 3 of the Cambodian CAV were clustered with CAV strains belonging to genotype II and were most closely related to CAV strains from Guangdong province, China. On the amino acid level, major substitutions were observed at 12 residues in the VP1 protein (positions 22, 75, 97, 125, 139, 144, 254, 287, 290, 370, 376, and 413) when compared with published reference CAV strains. In motifs associated with virulence, all Cambodian CAV had virulence-associated motifs composed of 75I, 89T, 125I, 139Q, 141Q, 144Q, and 394Q, which are commonly found in highly virulent genotype II viruses and some genotype III viruses. This is the first report of CAV isolated from village chickens in Southeast Asia as well as Cambodia.

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.

The worldwide distribution of chicken anemia virus (CAV) and Marek's disease virus (MDV) is well documented. In addition to their economic significance in single- or dual-virus infections, the two viruses can often accompany various other pathogens and affect poultry health either directly, by causing tumors, anemia, and delayed growth, or indirectly, by aggravating other diseases, as a result of their immunosuppressive effects. After a decade of employing the molecular diagnosis of those viruses, which replaced conventional virus isolation, we present the development of a real-time multiplex PCR for the simultaneous detection of both viruses. The real-time PCRs for MDV and for CAV alone are more sensitive than the respective end-point PCRs. In addition, the multiplex real-time shows a similar sensitivity when compared to the single real-time PCR for each virus. The newly developed real-time multiplex PCR is of importance in terms of the diagnosis and detection of low copies of each virus, MDV and CAV in single- and in multiple-virus infections, and its applicability will be further evaluated.

Apoptin is a chicken anemia virus-derived, p53-independent, bcl-2-insensitive apoptotic protein with the ability to specifically induce apoptosis in various human tumor cells, but not in normal cells. To explore the use of apoptin in tumor gene therapy, we assessed a recombinant adenovirus expressing the apoptin protein (Ad-hTERTp-E1a-Apoptin) in order to determine its lethal and growth-inhibitory effects on PC-3 and RM-1 cells in vitro and its antitumor effect on solid tumors in vivo. 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), acridine orange (AO)/ethidium bromide (EB), 4'-6-diamidino-2-phenylindole (DAPI), and Annexin V assays showed that Ad-hTERTp-E1a-Apoptin inhibited the proliferation of PC-3 and RM-1 cells in vitro by inducing apoptosis of prostate cancer cells, and that this inhibitory effect was dose and time-dependent. In the animal models, Ad-hTERTp-E1a-Apoptin significantly inhibited tumor growth and extended the lifespan of animals. Experimental results indicate that Ad-hTERTp-E1a-Apoptin has a potential application in tumor gene therapy.

Mitotic catastrophe is an oncosuppressive mechanism that senses mitotic failure leading to cell death or senescence. As such, it protects against aneuploidy and genetic instability, and its induction in cancer cells by exogenous agents is currently seen as a promising therapeutic end point. Apoptin, a small protein from Chicken Anemia Virus (CAV), is known for its ability to selectively induce cell death in human tumor cells. Here, we show that apoptin triggers p53-independent abnormal spindle formation in osteosarcoma cells. Approximately 50% of apoptin-positive cells displayed non-bipolar spindles, a 10-fold increase as compared to control cells. Besides, tumor cells expressing apoptin are greatly limited in their progress through anaphase and telophase, and a significant drop in mitotic cells past the meta-to-anaphase transition is observed. Time-lapse microscopy showed that mitotic osteosarcoma cells expressing apoptin displayed aberrant mitotic figures and/or had a prolonged cycling time during mitosis. Importantly, all dividing cells expressing apoptin eventually underwent cell death either during mitosis or during the following interphase. We infer that apoptin can efficiently trigger cell death in dividing human tumor cells through induction of mitotic catastrophe. However, the killing activity of apoptin is not only confined to dividing cells, as the CAV-derived protein is also able to trigger caspase-3 activation and apoptosis in non-mitotic cancer cells.

The pathogenesis of the co-infection of CAV to MDV is complicated. In order to investigate the impact of CAV on the transformation phase of MD, MDV and, subsequently, CAV, were inoculated at 1day and 4weeks of age, respectively. Chickens were divided into six groups; vvMDV, vvMDV-CAV, vMDV, vMDV-CAV, CAV and a control group. The CAV inclusions and antigens were continuously detected in MD lymphomas in the vMDV-CAV and vvMDV-CAV groups in large bizarre-shape (presumably CD4+ T cells) and small MD lymphoid cells (presumably CD8+ T cells). The MD lymphomas were composed primarily of CD4+ T cells, but CD8+ T cells were infiltrated singly or in clusters. CAV enhanced the MDV-induced brain lesions in the vMDV-CAV group. The lymphoproliferative lesion (LP) in the vvMDV-CAV and vMDV-CAV groups was non-significantly higher than those in vvMDV and vMDV groups, respectively. CAV significantly increased the LP lesion in sciatic nerves. In conclusion, MD lymphomas enabled CAV replication and dissemination. The depletion of CTLs by CAV did not significantly affect progression of MD lymphoma, although they are essential for possible transition of lymphomatous to inflammatory lesion., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Apoptin, a nonstructural protein encoded by the VP3 gene of chicken anemia virus (CAV), has been shown to not only induce apoptosis when introduced into the precursors of chicken thymocytes, but has been found to specifically kill human cancer cells, tumor cell and transformed cells without affecting the proliferation of normal cells. This tumor-specific apoptotic characteristic of the protein potentially may allow the development of a protein drug that has applications in tumor therapy. However, several major problems, which include poor expression and poor protein solubility, have hampered the production of apoptin in bacteria., Results: Significantly increased expression of recombinant full-length apoptin that originated from chicken anemia virus was demonstrated using an E. coli expression system. The CAV VP3 gene was fused with a synthetic sequence containing a trans-acting activator of transcription (TAT) protein transduction domain (PTD). The resulting construct was cloned into various different expression vectors and these were then expressed in various E. coli strains. The expression of the TAT-Apoptin in E. coli was significantly increased when TAT-Apoptin was fused with GST-tag rather than a His-tag. When the various rare amino acid codons of apoptin were optimized, the expression level of the GST-TAT-Apoptin(opt) in E. coli BL21(DE3) was significantly further increased. The highest protein expression level obtained was 8.33 g/L per liter of bacterial culture after induction with 0.1 mM IPTG for 4 h at 25 °C. Moreover, approximately 90% of the expressed GST-TAT-Apoptin(opt) under these conditions was soluble. After purification by GST affinity chromatography, the purified recombinant TAT-Apoptin(opt) protein was used to evaluate the recombinant protein's apoptotic activity on tumor cells. The results demonstrated that the E. coli-expressed GST-TAT-apoptin(opt) showed apoptotic activity and was able to induce human premyelocytic leukemia HL-60 cells to enter apoptosis., Conclusions: On expression in E. coli, purified recombinant TAT-Apoptin(opt) that has been fused to a GST tag and had its codons optimized, was found to have great potential. This protein may in the future allow the development of a therapeutic protein that is able to specifically kill tumor cells.

The chicken anaemia virus-derived protein Apoptin/VP3 (CAV-Apoptin) has the important ability to induce tumour-selective apoptosis in a variety of human cancer cells. Recently the first human Gyrovirus (HGyV) was isolated from a human skin swab. It shows significant structural and organisational resemblance to CAV and encodes a homologue of CAV-Apoptin/VP3. Using overlapping primers we constructed a synthetic human Gyrovirus Apoptin (HGyV-Apoptin) fused to green fluorescent protein in order to compare its apoptotic function in various human cancer cell lines to CAV-Apoptin. HGyV-Apoptin displayed a similar subcellular expression pattern as observed for CAV-Apoptin, marked by translocation to the nucleus of cancer cells, although it is predominantly located in the cytosol of normal human cells. Furthermore, expression of either HGyV-Apoptin or CAV-Apoptin in several cancer cell lines triggered apoptosis at comparable levels. These findings indicate a potential anti-cancer role for HGyV-Apoptin.

Expression of enhanced green fluorescent protein (EGFP) under control of the promoter-enhancer of chicken infectious anemia virus (CAV) is increased in an oestrogen receptor-enhanced cell line when treated with oestrogen and the promoter-enhancer binds unidentified proteins that recognize a consensus oestrogen response element (ERE). Co-transfection assays with the CAV promoter and the nuclear receptor chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF1) showed that expression of EGFP was decreased by 50 to 60 % in DF-1 and LMH cells. The CAV promoter that included sequences at and downstream of the transcription start point had less expression than a short promoter construct. Mutation of a putative E box at this site restored expression levels. Electromobility shift assays showed that the transcription regulator delta-EF1 (deltaEF1) binds to this E box region. These findings indicate that the CAV promoter activity can be affected directly or indirectly by COUP-TF1 and deltaEF1.

Chicken anemia virus (CAV) is an immunosuppressive pathogen of chickens. To further examine the role of viral protein 2 (VP2), which possesses dual-specificity protein phosphatase (DSP) activity, in viral cytopathogenicity and its influence on viral growth and virulence, an infectious genomic clone of CAV was subjected to site-directed mutagenesis. Substitution mutations C87R, R101G, K102D and H103Y were introduced into the DSP catalytic motif and R129G, Q131P, R/K/K150/151/152G/A/A, D/E161/162G/G, L163P, D169G and E186G into a region predicted to have a high degree of secondary structure. All mutant constructs were infectious, but their growth curves differed. The growth curve for mutant virus R/K/K150/151/152G/A/A was similar to that for wild-type virus, a second cluster of mutant viruses had an extended latent period and a third cluster of mutant viruses had extended latent and eclipse periods. All mutants had a reduced cytopathogenic effect in infected cells and VP3 was restricted to the cytoplasm. Mutation of the second basic residue (K102D) in the atypical DSP signature motif resulted in a marked reduction in virus replication efficiency, whereas mutation of the first basic residue (R101G) attenuated cytopathogenicity, but did not reduce replication efficiency. Expression of major histocompatibility complex (MHC) class I was markedly downregulated in cells infected with wild-type CAV, but not in those infected with mutants. This study further demonstrates the significance of VP2 in CAV replication and shows that specific mutations introduced into the gene encoding this protein can reduce virus replication, cytopathogenicity and downregulation of MHC I in infected cells.

Biliary tract cancer, or cholangiocarcinoma, has a poor prognosis. Resection is the only curative treatment, but only a minority of patients are eligible. Chemotherapy and gamma-irradiation are merely palliative, as they are unable to remove the malignancy completely. The chicken anemia virus-derived protein apoptin induces apoptosis in a wide range of human tumor cells and is not hindered by mutations inactivating p53 or by overexpression of Bcl-2, changes known to frustrate chemotherapy and radiation therapy. We examined whether apoptin kills human biliary tract cancer cells. Expression of apoptin by means of plasmids caused extensive cell death in three independent cholangiocarcinoma cell lines, CC-LP, CC-SW, and Mz-ChA-1, regardless of their oncogenic mutations, which included inactivated p16 and p53 and the disruption of the transforming growth factor beta signaling pathway. In vitro delivery of apoptin by an adenoviral vector completely eradicated cholangiocarcinoma cells. Moreover, coexpression of the broad-spectrum caspase inhibitor p35 with apoptin only delayed the induced cell death. Changes in nuclear morphology still occurred early after transfection, and nuclei eventually disintegrated, suggesting that apoptin-induced cell death in these cells is not blocked by mutations in either the initiation or execution phase of apoptosis. The efficient induction of cell death by apoptin in cholangiocarcinoma cell lines makes apoptin an attractive candidate for molecular therapy of biliary tract cancer.

The chicken anemia virus-derived Apoptin protein induces tumor-specific apoptosis. Here, we show that recombinant Apoptin protein spontaneously forms non-covalent globular aggregates comprising 30 to 40 subunits in vitro. This multimerization is robust and virtually irreversible, and the globular aggregates are also stable in cell extracts, suggesting that they remain intact within the cell. Furthermore, studies of Apoptin expressed in living cells confirm that Apoptin indeed exists in large complexes in vivo. We map the structural motifs responsible for multimerization in vitro and aggregation in vivo to the N-terminal half of the protein. Moreover, we show that covalently fixing the Apoptin monomers within the recombinant protein multimer by internal cross-linking does not affect the biological activity of Apoptin, as these fixed aggregates exhibit similar tumor-specific localization and apoptosis-inducing properties as non-cross-linked Apoptin. Taken together, our results imply that recombinant Apoptin protein is a multimer when inducing apoptosis, and we propose that this multimeric state is an essential feature of its ability to do so. Finally, we determine that Apoptin adopts little, if any, regular secondary structure within the aggregates. This surprising result would classify Apoptin as the first protein for which, rather than the formation of a well defined tertiary and quaternary structure, semi-random aggregation is sufficient for activity.

In order to testify the antitumor effect, especially its effect against liver carcinoma in vivo, of VP3 protein, one kind of protein coded by chicken anemia virus, recombinants pcDNA-vp3 containing chicken anemia virus vp3 gene, and control vector pcDNA3 were mixed with murine liver carcinoma cell lines H22 respectively. The mixture was injected subcutaneously into Balb/C mice. Some days later, the mice were killed and the solid tumor weighed. The antitumor efficiency was evaluated. The manners of VP3 protein in vivo inducing tumor cell death were identified by using TUNEL assay. All the results suggested that the injection of pcDNA-vp3 and H22 mixture resulted in a significant reduction of tumor growth in mice when compared with the results of control groups. TUNEL assay revealed that VP3 induced apoptosis in vivo. All these indicated that CAV vp3 might be a potential new gene in reducing the growth rate of tumor cells in liver carcinoma or in other kind of solid tumors in vivo.

A study was conducted to isolate and identify chicken anaemia virus (CAV) from field samples of clinically infected broiler chickens in Malaysia. A total of 125 samples were collected from chickens aged 2-6 weeks with clinically depressed and retarded growth, of which five samples were found positive to CAV directly by polymerase chain reaction (PCR). Later, five isolates of CAV from the respective five PCR positive samples were isolated in MDCC-MSB1 cells at passage 4 based on cytopathic effects, PCR and indirect immunofluorescent antibody test. The isolates were identified as BL-1, BL-2, BL-3, BL-4 and BL-5. These CAV isolates were found to resist treatment with chloroform and heat at 37 degrees C for 2 h, 56 degrees C for 30 min and 70 degrees C for 5 min. One of the isolates, BL-5 produced significant reduction (p < 0.001) of hematocrit values (9-19%), pale bone marrow, thymus atrophy and haemorrhages in skin/muscle when inoculated into 1-day old SPF chickens. Restriction enzyme digestion of 926 bp genomic fragments of all the isolates including Cux-1 isolate with HindIII exhibited a similar pattern of bands in 2% agarose gel. The present findings confirmed the presence of CAV in Malaysia.

Unlabelled chicken anaemia virus (CAV) DNA probe, produced by PCR, was immobilized onto nitrocellulose discs that then were fitted into microtitre plate wells in order to develop a competitive, non-radioactive hybridization test for detection of CAV. The discs were hybridized with either DNA extracts of buffy coats or dilutions of CAV DNA (for standard curves), followed by hybridization with biotin-labelled CAV DNA probe in excess of the immobilized, capture probe. Thus, CAV from sample DNA extracts and standard DNA preparations competed with the biotin-labelled CAV DNA probe for the immobilized, capture probe, decreasing subsequent colour development by an avidin-biotin-alkaline phosphatase detection system. Standard curves were log linear from 5-100 ng viral DNA with r(2)> or =0.91. Tests were considered positive at 2 SD less than mean absorbence of samples from uninfected chickens, and ranged from 52 to 108 microm viral DNA or 2 to 4.2x10(10)virions microg(-1)buffy coat DNA. Blood samples from chickens infected and not infected with CAV at one day of age were tested for evidence of infection until 28 days of age by viral isolation, competitive hybridization in microtitre plates, dot-blots, enzyme-linked immunosorbent assay (ELISA), and in situ hybridization on blood smears. None of the tests was positive for uninfected chickens. Viral isolation from buffy coats, though expensive and lengthy, was the most sensitive method. It detected virus in buffy coat from each infected chicken, while competitive hybridization detected 72% of infected chickens, in situ hybridization 69%, dot-blots 67%, and ELISA 36%. Sensitivity of competitive hybridization was 0.78, and its specificity was 1.00. Three chickens must be sampled from an infected flock for a 90% chance of detecting a positive chicken at the 0.025 one-tailed level of significance, assuming 100% prevalence., (Copyright 2001 Academic Press.)

The chicken anemia virus protein Apoptin has been shown to induce apoptosis in a large number of transformed and tumor cell lines, but not in primary cells. Whereas many other apoptotic stimuli (e.g., many chemotherapeutic agents and radiation) require functional p53 and are inhibited by Bcl-2, Apoptin acts independently of p53, and its activity is enhanced by Bcl-2. Here we study the involvement of caspases, an important component of the apoptotic machinery present in mammalian cells. Using a specific antibody, active caspase-3 was detected in cells expressing Apoptin and undergoing apoptosis. Although Apoptin activity was not affected by CrmA, p35 did inhibit Apoptin-induced apoptosis, as determined by nuclear morphology. Cells expressing both Apoptin and p35 showed only a slight change in nuclear morphology. However, in most of these cells, cytochrome c is still released and the mitochondria are not stained by CMX-Ros, indicating a drop in mitochondrial membrane potential. These results imply that although the final apoptotic events are blocked by p35, parts of the upstream apoptotic pathway that affect mitochondria are already activated by Apoptin. Taken together, these data show that the viral protein Apoptin employs cellular apoptotic factors for induction of apoptosis. Although activation of upstream caspases is not required, activation of caspase-3 and possibly also other downstream caspases is essential for rapid Apoptin-induced apoptosis.

Apoptin, a small protein encoded by chicken anemia virus (CAV) was expressed in various human hematologic malignant cell lines derived from leukemias and lymphoma. Three of these cell lines contain bcl-2 or BCR-ABL proteins, known to block apoptosis induced by chemotherapeutic compounds. By immunofluorescence and propidium-iodide staining apoptin was shown to induce apoptosis in all analysed cell lines. Early after expression, apoptin exhibited a fine-granular distribution in the still intact nucleus. Later, apoptin became aggregated and the nucleus segmented. The data with truncated apoptin indicate that for optimal induction of apoptosis apoptin has to be located in the nucleus.

Antisera raised against oriented peptide conjugates were used to identify and partially characterize a 24 kDa protein product expressed by chicken anaemia virus (CAV). The peptides derived from the N and C termini of the protein were shown to react against the native protein, expressed within virus-infected cells, by immunofluorescence, immunoperoxidase and immunogold thin section electron microscopy techniques. The protein product was located by immunogold single labelling in intranuclear inclusions similar to those described previously for the 13 kDa CAV protein, which causes apoptosis. The 24 kDa protein was co-localized to the nuclear inclusions with the CAV 13 kDa protein by simultaneous dual labelling immunogold electron microscopy. Following isolation of the CAV proteins by nuclei isolation and SDS-PAGE, the antisera were used to probe for the protein by immunoblotting. The antisera recognized an expressed protein product of apparent molecular mass 30 kDa. An immunofluorescence time course study of CAV protein expression was carried out and the peptide antisera reacted against the protein at 12 h post-infection. Antisera against the 13 kDa protein reacted at similar times post-infection. This was in contrast to antisera raised against the 52 kDa capsid protein which is detectable by immunofluorescence only after 24 h. The 13 kDa and 24 kDa proteins thus appear to be early antigens produced by CAV during infection.