Adeno-associated Virus Type 2 Infection Research Articles

Adeno-associated virus type 2 (AAV2) uncoating is a stepwise process and is linked to structural reorganization of the nucleolus.

Nucleoli are membrane-less structures located within the nucleus and are known to be involved in many cellular functions, including stress response and cell cycle regulation. Besides, many viruses can employ the nucleolus or nucleolar proteins to promote different steps of their life cycle such as replication, transcription and assembly. While adeno-associated virus type 2 (AAV2) capsids have previously been reported to enter the host cell nucleus and accumulate in the nucleolus, both the role of the nucleolus in AAV2 infection, and the viral uncoating mechanism remain elusive. In all prior studies on AAV uncoating, viral capsids and viral genomes were not directly correlated on the single cell level, at least not in absence of a helper virus. To elucidate the properties of the nucleolus during AAV2 infection and to assess viral uncoating on a single cell level, we combined immunofluorescence analysis for detection of intact AAV2 capsids and capsid proteins with fluorescence in situ hybridization for detection of AAV2 genomes. The results of our experiments provide evidence that uncoating of AAV2 particles occurs in a stepwise process that is completed in the nucleolus and supported by alteration of the nucleolar structure.

Zellzyklusspezifische Genexpression des Adeno-assoziierten Virus

The adeno-associated virus type 2 (AAV2) has a biphasic life cycle. In absence of a helper virus, the AAV2 DNA can integrate into the host cell genome or persist as episome in the cell nucleus. Co-infection with a helper virus such as herpes simplex virus type 1 (HSV-1) leads to a productive AAV2 infection, particularly in cells in S/G2 phases. HSV-1 replication, which normally takes place in any phase of the cell cycle, becomes restricted to cells in G1 phase when AAV2 is present.

Adeno-associated virus type 2 infection of nude mouse human breast cancer xenograft induces necrotic death and inhibits tumor growth

We have previously reported that infection with the non-pathogenic, tumor suppressive, wild-type adeno-associated virus type 2 (AAV2) inhibited proliferation of breast cancer-derived lines representing both weakly invasive (MCF-7 and MDA-MB-468), as well as aggressive (MDA-MB-231) cancer types. AAV2-induced death occurred via targeting pathways of apoptosis and necrosis. In contrast, normal human mammary epithelial cells were unaffected upon AAV2 infection. The current study characterizes AAV2 infection and subsequent death of the highly aggressive, triple-negative (ER−/PR−/HER2−) MDA-MB-435 cell line derived from metastatic human breast carcinoma. Monolayer MDA-MB-435 cultures infected with AAV2 underwent complete apoptotic cell death characterized by activation of caspases -7, -8, and -9 and PARP cleavage. Death was further correlated with active AAV2 genome replication and differential expression of viral non-structural proteins Rep78 and Rep52. Cell death coincided with increased entry into S and G2 phases, upregulated expression of the proliferation markers Ki-67 and the monomeric form of c-Myc. Expression of the p16INK4, p27KIP1, p21WAF1, and p53 tumor suppressors was downregulated, indicating marked S phase progression, but sharply contrasted with hypo-phosphorylated pRb. In parallel, MDA-MB-435 breast tumor xenografts which received intratumoral injections of AAV2 were growth retarded, displayed extensive areas of necrosis, and stained positively for c-Myc as well as cleaved caspase-8. Therefore, AAV2 induced death of MDA-MB-435 xenografts was modulated through activation of caspase-regulated death pathways in relation to signals for cell cycle controls. Our findings provide foundational studies for development of novel AAV2 based therapeutics for treating aggressive, triple-negative breast cancer types.

Enhancing gene delivery of adeno-associated viruses by cell-permeable peptides

Adeno-associated virus type 2 (AAV2) is considered a promising gene delivery vector and has been extensively applied in several disease models; however, inefficient transduction in various cells and tissues has limited its widespread application in many areas of gene therapy. In this study, we have developed a general, but efficient, strategy to enhance viral transduction, both in vitro and in vivo, by incubating viral particles with cell-permeable peptides (CPPs). We show that CPPs increase internalization of viral particles into cells by facilitating both energy-independent and energy-dependent endocytosis. Moreover, CPPs can significantly enhance the endosomal escape process of viral particles, thus enhancing viral transduction to those cells that have exhibited very low permissiveness to AAV2 infection as a result of impaired intracellular viral processing. We also demonstrated that this approach could be applicable to other AAV serotypes. Thus, the membrane-penetrating ability of CPPs enables us to generate an efficient method for enhanced gene delivery of AAV vectors, potentially facilitating its applicability to human gene therapy.

Adeno-associated virus type 2 infection activates caspase dependent and independent apoptosis in multiple breast cancer lines but not in normal mammary epithelial cells

BackgroundIn normal cells proliferation and apoptosis are tightly regulated, whereas in tumor cells the balance is shifted in favor of increased proliferation and reduced apoptosis. Anticancer agents mediate tumor cell death via targeting multiple pathways of programmed cell death. We have reported that the non-pathogenic, tumor suppressive Adeno-Associated Virus Type 2 (AAV2) induces apoptosis in Human Papillomavirus (HPV) positive cervical cancer cells, but not in normal keratinocytes. In the current study, we examined the potential of AAV2 to inhibit proliferation of MCF-7 and MDA-MB-468 (both weakly invasive), as well as MDA-MB-231 (highly invasive) human breast cancer derived cell lines. As controls, we used normal human mammary epithelial cells (nHMECs) isolated from tissue biopsies of patients undergoing breast reduction surgery.ResultsAAV2 infected MCF-7 line underwent caspase-independent, and MDA-MB-468 and MDA-MB-231 cell lines underwent caspase-dependent apoptosis. Death of MDA-MB-468 cells was marked by caspase-9 activation, whereas death of MDA-MB-231 cells was marked by activation of both caspase-8 and caspase-9, and resembled a mixture of apoptotic and necrotic cell death. Cellular demise was correlated with the ability of AAV2 to productively infect and differentially express AAV2 non-structural proteins: Rep78, Rep68 and Rep40, dependent on the cell line. Cell death in the MCF-7 and MDA-MB-231 lines coincided with increased S phase entry, whereas the MDA-MB-468 cells increasingly entered into G2. AAV2 infection led to decreased cell viability which correlated with increased expression of proliferation markers c-Myc and Ki-67. In contrast, nHMECs that were infected with AAV2 failed to establish productive infection or undergo apoptosis.ConclusionAAV2 regulated enrichment of cell cycle check-point functions in G1/S, S and G2 phases could create a favorable environment for Rep protein expression. Inherent Rep associated endonuclease activity and AAV2 genomic hair-pin ends have the potential to induce a cellular DNA damage response, which could act in tandem with c-Myc regulated/sensitized apoptosis induction. In contrast, failure of AAV2 to productively infect nHMECs could be clinically advantageous. Identifying the molecular mechanisms of AAV2 targeted cell cycle regulation of death inducing signals could be harnessed for developing novel therapeutics for weakly invasive as well as aggressive breast cancer types.

Adeno-Associated Virus Type 2 Capsids with Externalized VP1/VP2 Trafficking Domains Are Generated prior to Passage through the Cytoplasm and Are Maintained until Uncoating Occurs in the Nucleus

Common features of parvovirus capsids are open pores at the fivefold symmetry axes that traverse the virion shell. Upon limited heat treatment in vitro, the pores can function as portals to externalize VP1/VP2 protein N-terminal sequences which harbor infection-relevant functional domains, such as a phospholipase A(2) catalytic domain. Here we show that adeno-associated virus type 2 (AAV2) also exposes its VP1/VP2 N termini in vivo during infection, presumably in the endosomal compartment. This conformational change is influenced by treatment with lysosomotropic reagents. While incubation of cells with bafilomycin A1 reduced exposure of VP1/VP2 N termini, incubation with chloroquine stimulated externalization transiently. N-terminally located basic amino acid clusters with nuclear localization activity also become exposed in this process and are accessible on the virus capsid when it enters the cytoplasm. This is an obligatory step in AAV2 infection. However, a direct role of these sequences in nuclear translocation of viral capsids could not be determined by microinjection of wild-type or mutant viruses. This suggests that further modifications of the capsid have to take place in a precytoplasmic entry step that prepares the virus for nuclear entry. Microinjection of several capsid-specific antibodies into the cell nucleus blocked AAV2 infection completely, supporting the conclusion that AAV2 capsids bring the infectious genome into the nucleus.

Adeno-Associated Virus Type 2 Contains an Integrin α5β1 Binding Domain Essential for Viral Cell Entry

Integrins have been implicated as coreceptors in the infectious pathways of several nonenveloped viruses. For example, adenoviruses are known to interact with alphaV integrins by virtue of a high-affinity arginine-glycine-aspartate (RGD) domain present in the penton bases of the capsids. In the case of adeno-associated virus type 2 (AAV2), which lacks this RGD motif, integrin alphaVbeta5 has been identified as a coreceptor for cellular entry. However, the molecular determinants of AAV2 capsid-integrin interactions and the potential exploitation of alternative integrins as coreceptors by AAV2 have not been established thus far. In this report, we demonstrate that integrin alpha5beta1 serves as an alternative coreceptor for AAV2 infection in human embryonic kidney 293 cells. Such interactions appear to be mediated by a highly conserved domain that contains an asparagine-glycine-arginine (NGR) motif known to bind alpha5beta1 integrin with moderate affinity. The mutation of this domain reduces transduction efficiency by an order of magnitude relative to that of wild-type AAV2 vectors in vitro and in vivo. Further characterization of mutant and wild-type AAV2 capsids through transduction assays in cell lines lacking specific integrins, cell adhesion studies, and cell surface/solid-phase binding assays confirmed the role of the NGR domain in promoting AAV2-integrin interactions. Molecular modeling studies suggest that NGR residues form a surface loop close to the threefold axis of symmetry adjacent to residues previously implicated in binding heparan sulfate, the primary receptor for AAV2. The aforementioned results suggest that the internalization of AAV2 in 293 cells might follow a "click-to-fit" mechanism that involves the cooperative binding of heparan sulfate and alpha5beta1 integrin by the AAV2 capsids.

7. Adeno-Associated Virus Type 2 (AAV2) Contains an Integrin alpha5beta1 Recognition Sequence Essential for Viral Cell Entry

Integrins have been implicated as co-receptors in the infectious pathways of several non-enveloped viruses. For example, adenoviruses are known to interact with several alphaV integrins by virtue of a high affinity arginine-glycine-aspartate (RGD) domain present in the penton base of the capsid. In case of adeno-associated virus type 2 (AAV2), which lacks this RGD motif, integrin alpha Vbeta5 has been identified as a co-receptor for cellular entry. However, the molecular determinants of AAV2 capsid-integrin interactions and the potential exploitation of alternative integrins as co-receptors by AAV2 have not been determined thus far. In this report, we demonstrate that integrin alpha5beta1 serves as an alternative co-receptor for AAV2 infection in human embryonic kidney 293 cells. Such interactions are mediated by a highly conserved asparagine-glycine-arginine (NGR) motif known to bind alpha5beta1 integrin with moderate affinity. Mutation of this domain reduces transduction efficiency by 10-fold ompared with wild type AAV2 in vitro and in vivo. Further characterization of mutant and wild type AAV2 capsids using cell surface and solid phase binding assays, peptide inhibition studies, and transduction assays in cell lines lacking specific integrins confirmed the role of the NGR motif in promoting AAV2-integrin interactions. Molecular modeling studies suggest that the NGR domain forms a surface loop located at the three-fold axis of symmetry adjacent to residues previously implicated in binding heparan sulfate, the primary receptor for AAV2. Based on the aforementioned results, we propose that cellular internalization of AAV2 follows a |[ldquo]|click-to-fit|[rdquo]| mechanism that involves co-operative binding of heparan sulfate and alpha5beta1 integrin receptors by the AAV2 capsid.

Hepatocyte Growth Factor Receptor Is a Coreceptor for Adeno-Associated Virus Type 2 Infection

After the first attachment of virus to the cell surface through a primary receptor, efficient entry of virus requires the presence of a coreceptor. For adeno-associated virus type 2 (AAV2) infection, heparan sulfate proteoglycan is supposed as the primary receptor, and alphavbeta5 integrin and FGFR1 are reported to act as coreceptors. In this study, we were able to demonstrate that hepatocyte growth factor receptor, c-Met, is also a coreceptor for AAV2 infection. AAV2-mediated transgene analyses revealed that c-Met expression significantly up-regulated transgene expression without increasing AAV2 cell binding. Moreover, a viral overlay assay elucidated the physical interaction between AAV2 and the beta subunit of c-Met. These data suggest that c-Met plays the role of coreceptor for AAV2 infection by facilitating AAV2 internalization into the cytoplasm.

A1-6 Conséquences des expositions aux pesticides sur la fertilité des ouvriers agricoles en Guadeloupe

Adeno-associated virus type 2 (AAV2) is considered a promising gene delivery vector and has been extensively applied in several disease models; however, inefficient transduction in various cells and tissues has limited its widespread application in many areas of gene therapy. In this study, we have developed a general, but efficient, strategy to enhance viral transduction, both in vitro and in vivo, by incubating viral particles with cell-permeable peptides (CPPs). We show that CPPs increase internalization of viral particles into cells by facilitating both energy-independent and energy-dependent endocytosis. Moreover, CPPs can significantly enhance the endosomal escape process of viral particles, thus enhancing viral transduction to those cells that have exhibited very low permissiveness to AAV2 infection as a result of impaired intracellular viral processing. We also demonstrated that this approach could be applicable to other AAV serotypes. Thus, the membrane-penetrating ability of CPPs enables us to generate an efficient method for enhanced gene delivery of AAV vectors, potentially facilitating its applicability to human gene therapy.

Prevention of chemotherapy-related toxic side effects by infection with adeno-associated virus type 2.

Drug resistance and toxic side effects are major limiting factors in the clinical use of antineoplastic chemotherapy. Patients with pancreatic cancer generally do not benefit from chemotherapy. The nonpathogenic adeno-associated virus type 2 (AAV-2) has been shown to sensitize human tumor cells to gamma irradiation and chemotherapeutic drugs. In the present study, we characterized the therapeutic role of AAV-2 infection in combination with 5-fluorouracil (5-FU)-based chemotherapy on pancreatic cancer cells in an animal model. In Lewis rats bearing s.c. implants of syngeneic DSL6A pancreatic cancer cells, intratumoral infection with AAV-2 (MOI 10E8 i.u.) in combination with 5-FU (5 or 50 mg/kg body weight) resulted in significantly reduced tumor growth and prolonged survival time compared with 5-FU single therapy. Most surprisingly, AAV-2-infected rats remained in a much better physical condition compared to their noninfected counterparts. While rats treated with 5-FU single therapy lost weight, were sluggish and died within 4 months after tumor implantation, animals infected with AAV showed much better vigilance, with body weight, leukocyte number and hemoglobin levels similar to healthy rats. In particular, 5-FU-related side effects like thrombocytopenia and leukopenia were significantly reduced in animals treated with the combination regimen. By in vitro analysis, human (Capan-1 and DANG) pancreatic cancer cell lines were shown to be sensitized to 5-FU chemotherapy to an extent similar to DSL6A cells. AAV-2 infection enhanced 5-FU-induced apoptosis by a factor of 8 to 14 in both human and rat pancreatic cancer cell lines. The data suggest that infection with the nonpathogenic AAV-2 significantly improves both chemotherapy efficacy and physical appearance and offers a novel strategy in cancer treatment.

Sensitization of sarcoma cells to doxorubicin treatment by concomitant wild-type adeno-associated virus type 2 (AAV-2) infection

Doxorubicin-based chemotherapy is used in the treatment of sarcomas. Toxic side effects and poor response rates underline the demand for an improvement in current chemotherapeutic protocols. Recently, it has been reported that parvoviruses confer various antineoplastic properties to infected cells, and that adeno-associated virus type 2 (AAV-2) infection sensitizes malignant epithelial cells to radiation- or chemotherapy-based genotoxic treatment. Thus, we analyzed whether AAV-2 infection leads to an improved efficacy of doxorubicin chemotherapy in malignant mesenchymal cells, using 13 human sarcoma cell lines. Therapeutic effects were analyzed by measuring cell viability and proliferation (WST-1, colony forming, and propidium iodide assays). Additionally, permissivity for AAV-2 infection was determined by Southern dot blot analysis. AAV-2 infection strongly increased the efficacy of doxorubicin treatment in rhabdomyo-, fibro-, osteo- and chondrosarcoma cells in a dose-dependent manner. This effect was not observed in liposarcoma and synovial sarcoma cells, although a susceptability to AAV-2 infection was documented. Our results indicate that the sensitization effects towards genotoxic treatment exerted by non-pathogenic AAV-2 infection are not restricted to epithelial malignancies but may also be exploited for the improvement of chemotherapy in patients suffering from rhabdomyo-, fibro-, osteo-, or chondrosarcomas.

Monoclonal antibodies against the adeno-associated virus type 2 (AAV-2) capsid: epitope mapping and identification of capsid domains involved in AAV-2-cell interaction and neutralization of AAV-2 infection.

The previously characterized monoclonal antibodies (MAbs) A1, A69, B1, and A20 are directed against assembled or nonassembled adeno-associated virus type 2 (AAV-2) capsid proteins (A. Wistuba, A. Kern, S. Weger, D. Grimm, and J. A. Kleinschmidt, J. Virol. 71:1341-1352, 1997). Here we describe the linear epitopes of A1, A69, and B1 which reside in VP1, VP2, and VP3, respectively, using gene fragment phage display library, peptide scan, and peptide competition experiments. In addition, MAbs A20, C24-B, C37-B, and D3 directed against conformational epitopes on AAV-2 capsids were characterized. Epitope sequences on the capsid surface were identified by enzyme-linked immunoabsorbent assay using AAV-2 mutants and AAV serotypes, peptide scan, and peptide competition experiments. A20 neutralizes infection following receptor attachment by binding an epitope formed during AAV-2 capsid assembly. The newly isolated antibodies C24-B and C37-B inhibit AAV-2 binding to cells, probably by recognizing a loop region involved in binding of AAV-2 to the cellular receptor. In contrast, binding of D3 to a loop near the predicted threefold spike does not neutralize AAV-2 infection. The identified antigenic regions on the AAV-2 capsid surface are discussed with respect to their possible roles in different steps of the viral life cycle.

The Interaction of Heparin Sulfate and Adeno-Associated Virus 2

Recently heparan sulfate was proposed as the host cell receptor for the dependovirus, adeno-associated virus type 2 (AAV2). We show that although heparan sulfate on the cell surface may contribute to the binding of AAV2 to permissive cells, the amount of heparan sulfate on the cell surface as determined by flow cytometry using four different monoclonal antibodies does not correlate with AAV2 binding to cells or recombinant AAV2 transduction efficiency. Experiments with either mutant CHO cells or cells treated with chlorate to remove sulfate groups showed that sulfation was not absolutely required for infection or binding: in the absence of cell surface sulfation, recombinant AAV2 was still able to be transduced in previously permissive cells. Heparin is commonly used as a substitute in studies of the interaction between heparan sulfate and ligand, and we demonstrate that the binding affinity of AAV2/heparin is low, with a Kd value of ∼2.0 nM. A study of the direct interaction between AAV2 and artificial glycosaminoglycans showed that a high degree of sulfation on heparin was critical for the ability to bind AAV2 and compete rAAV2 transduction and that both O- and N-sulfate groups are required. Overall, our data suggest that, as has been shown for other viruses, the presence of a high-affinity AAV2 receptor mediates AAV2 infection in addition to the low-affinity heparan sulfate binding.

Integrin αVβ5 Is Not Involved in Adeno-Associated Virus Type 2 (AAV2) Infection

αVβ5 integrin was recently proposed as a coreceptor for adeno-associated virus type 2 (AAV2) infection (Summerford et al., 1999, Nat. Med. 5, 78–82), based mainly on the direct binding of AAV2 to denatured β5 by virus overlay assay. In studies using purified natural or recombinant human integrin αVβ5 we were unable to demonstrate AAV2 binding, either by virus overlay or by liquid binding assay. Furthermore, neither purified integrin αVβ5, nor RGD peptides, nor functional blocking monoclonal antibody blocked rAAV2 transduction. These data strongly suggest that integrin αVβ5 is not involved in AAV2 infection.

Enhanced sensitivity of small cell lung cancer cell lines to cisplatin and etoposide after infection with adeno-associated virus type 2

In previous studies we have reported the sensitisation of human tumour cells to gamma irradiation and chemotherapeutic drugs upon infection with the human non-pathogenic adeno-associated virus type 2 (AAV-2) in vitro and in vivo. Treatment of small cell lung cancer (SCLC) is consistently hampered by relapses due to the selection of chemotherapy-resistant cell clones. Hence, we were interested to test whether selection of chemotherapy-resistant SCLC cells might be reduced or even prevented if chemotherapy is applied in combination with AAV-2 infection. In vitro proliferation assays indicated that the number of proliferating cells, after combined treatment with cisplatin and etoposide, can be significantly reduced by concomitant AAV-2 infection, as compared with treated but non-infected controls. H446 SCLC cells, which show resistance to etoposide/cisplatin chemotherapy (compared with a cell line which was never chemotherapeutically treated before, like NCI-H209) were significantly more sensitive after AAV-2 infection, suggesting that the therapeutic efficacy of chemotherapy in SCLC can be enhanced even if the cells are already relatively resistant to chemotherapy. Similarly, in vivo growth of tumours induced by inoculation of SCLC cells into immunocompromised nude mice was reduced more efficiently in AAV-2-infected animals compared with tumours in mice treated with chemotherapeutic drugs alone. These data extend and further support our previous reports on AAV functions which might be useful in improving the efficacy of chemotherapeutic drugs used in human cancer treatment.

Adeno-associated virus type 2 interferes with early development of mouse embryos.

The human helper-dependent adeno-associated virus type 2 (AAV-2) has been shown to induce differentiation in various cell types in culture including pluripotent embryonic cells, in the absence of helper virus. To assess whether induction of differentiation may influence developmental processes we analysed the effect of AAV-2 on developing mouse embryos. In vitro infection of fertilized eggs induced arrest of development at the two-cell stage. Moreover, micro injection of AAV-2 DNA (comprising either the complete AAV-2 genome or a fragment containing the P5 promoter region) into one-cell embryos, blocked development at the morula stage. In vivo, AAV-2 infection of pregnant mice led to fetal death and early abortion. These results demonstrate that the human adeno-associated virus, which is thought to be non-pathogenic, can perturb embryonic development in mice. This may provide a suitable animal model system to further elucidate the biological significance of the recent detection of adeno-associated virus DNA in human abortion material.