Human adenovirus type 9-induced rat mammary tumors

The human adenovirus PI3K-Akt activator E4orf1 is targeted by the tumor suppressor p53

Human adenoviruses (HAdV) are classified as DNA tumor viruses due to their potential to mediate oncogenic transformation in non-permissive mammalian cells and certain human stem cells. To achieve transformation, the viral early proteins of the E1 and E4 regions must block apoptosis and activate proliferation: the former predominantly through modulating the cellular tumor suppressor p53 and the latter by activating cellular pro-survival and pro-metabolism protein cascades, such as the phosphoinositide 3-kinase (PI3K-Akt) pathway, which is activated by HAdV E4orf1. Focusing on HAdV-C5, we show that E4orf1 is necessary and sufficient to stimulate Akt activation through phosphorylation in H1299 cells, which is not only hindered but repressed during HAdV-C5 infection with a loss of E4orf1 function in p53-positive A549 cells. Contrary to other research, E4orf1 localized not only in the common, cytoplasmic PI3K-Akt-containing compartment, but also in distinct nuclear aggregates. We identified a novel inhibitory mechanism, where p53 selectively targeted E4orf1 to destabilize it, also stalling E4orf1-dependent Akt phosphorylation. Co-IP and immunofluorescence studies showed that p53 and E4orf1 interact, and since p53 is bound by the HAdV-C5 E3 ubiquitin ligase complex, we also identified E4orf1 as a novel factor interacting with E1B-55K and E4orf6 during infection; overexpression of E4orf1 led to less-efficient E3 ubiquitin ligase-mediated proteasomal degradation of p53. We hypothesize that p53 specifically subverts the pro-survival function of E4orf1-mediated PI3K-Akt activation to protect the cell from metabolic hyper-activation or even transformation.IMPORTANCEHuman adenoviruses (HAdV) are nearly ubiquitous pathogens comprising numerous subtypes that infect various tissues and organs. Among many encoded proteins that facilitate viral replication and subversion of host cellular processes, the viral E4orf1 protein has emerged as an intriguing yet under-investigated player in the complex interplay between the virus and its host. Nonetheless, E4orf1 has gained attention as a metabolism activator and oncogenic agent, while recent research is showing that E4orf1 may play a more important role in modulating the cellular pathways such as phosphoinositide 3-kinase-Akt-mTOR. Our study reveals a novel and general impact of E4orf1 on host mechanisms, providing a novel basis for innovative antiviral strategies in future therapeutic settings. Ongoing investigations of the cellular pathways modulated by HAdV are of great interest, particularly since adenovirus-based vectors actually serve as vaccine or gene vectors. HAdV constitute an ideal model system to analyze the underlying molecular principles of virus-induced tumorigenesis.

E4orf1: The triple agent of adenovirus - Unraveling its roles in oncogenesis, infectious obesity and immune responses in virus replication and vector therapy

Human Adenoviruses (HAdV) are nearly ubiquitous pathogens comprising numerous sub-types that infect various tissues and organs. Among many encoded proteins that facilitate viral replication and subversion of host cellular processes, the viral E4orf1 protein has emerged as an intriguing yet under-investigated player in the complex interplay between the virus and its host. E4orf1 has gained attention as a metabolism activator and oncogenic agent, while recent research is showing that E4orf1 may play a more important role in modulating cellular pathways such as PI3K-Akt-mTOR, Ras, the immune response and further HAdV replication stages than previously anticipated. In this review, we aim to explore the structure, molecular mechanisms, and biological functions of E4orf1, shedding light on its potentially multifaceted roles during HAdV infection, including metabolic diseases and oncogenesis. Furthermore, we discuss the role of functional E4orf1 in biotechnological applications such as Adenovirus (AdV) vaccine vectors and oncolytic AdV. By dissecting the intricate relationships between HAdV types and E4orf1 proteins, this review provides valuable insights into viral pathogenesis and points to promising areas of future research.

The human adenovirus E1B-55K oncoprotein coordinates cell transformation through regulation of DNA-bound host transcription factors

The multifunctional adenovirus E1B-55K oncoprotein can induce cell transformation in conjunction with adenovirus E1A gene products. Previous data from transient expression studies and in vitro experiments suggest that these growth-promoting activities correlate with E1B-55K-mediated transcriptional repression of p53-targeted genes. Here, we analyzed genome-wide occupancies and transcriptional consequences of species C5 and A12 E1B-55Ks in transformed mammalian cells by combinatory ChIP and RNA-seq analyses. E1B-55K-mediated repression correlates with tethering of the viral oncoprotein to p53-dependent promoters via DNA-bound p53. Moreover, we found that E1B-55K also interacts with and represses transcription of numerous p53-independent genes through interactions with transcription factors that play central roles in cancer and stress signaling. Our results demonstrate that E1B-55K oncoproteins function as promiscuous transcriptional repressors of both p53-dependent and -independent genes and further support the model that manipulation of cellular transcription is central to adenovirus-induced cell transformation and oncogenesis.

Viral manipulation of cell polarity signalling

Cell polarity refers to the asymmetric distribution of biomacromolecules that enable the correct orientation of a cell in a particular direction. It is thus an essential component for appropriate tissue development and function. Viral infections can lead to dysregulation of polarity. This is associated with a poor prognosis due to viral interference with core cell polarity regulatory scaffolding proteins that often feature PDZ (PSD-95, DLG, and ZO-1) domains including Scrib, Dlg, Pals1, PatJ, Par3 and Par6. PDZ domains are also promiscuous, binding to several different partners through their C-terminal region which contain PDZ-binding motifs (PBM). Numerous viruses encode viral effector proteins that target cell polarity regulators for their benefit and include papillomaviruses, flaviviruses and coronaviruses. A better understanding of the mechanisms of action utilised by viral effector proteins to subvert host cell polarity sigalling will provide avenues for future therapeutic intervention, while at the same time enhance our understanding of cell polarity regulation and its role tissue homeostasis.

Small DNA tumor viruses and human cancer: Preclinical models of virus infection and disease

Human tumor viruses cause various human cancers that account for at least 15% of the global cancer burden. Among the currently identified human tumor viruses, two are small DNA tumor viruses: human papillomaviruses (HPVs) and Merkel cell polyomavirus (MCPyV). The study of small DNA tumor viruses (adenoviruses, polyomaviruses, and papillomaviruses) has facilitated several significant biological discoveries and established some of the first animal models of virus-associated cancers. The development and use of preclinical in vivo models to study HPVs and MCPyV and their role in human cancer is the focus of this review. Important considerations in the design of animal models of small DNA tumor virus infection and disease, including host range, cell tropism, choice of virus isolates, and the ability to recapitulate human disease, are presented. The types of infection-based and transgenic model strategies that are used to study HPVs and MCPyV, including their strengths and limitations, are also discussed. An overview of the current models that exist to study HPV and MCPyV infection and neoplastic disease are highlighted. These comparative models provide valuable platforms to study various aspects of virus-associated human disease and will continue to expand knowledge of human tumor viruses and their relationship with their hosts.

Animal Models in Human Adenovirus Research

Simple Summary

Animal models are widely used to study various aspects of human diseases and disorders. Likewise, they are indispensable for preclinical testing of medicals and vaccines. Human adenovirus infections are usually self-limiting, and can cause mild respiratory symptoms with fever, eye infection or gastrointestinal symptoms, but occasional local outbreaks with severe disease courses have been reported. In addition, adenovirus infections pose a serious risk for children and patients with a weakened immune system. Human adenovirus research in animal models to study adenovirus-induced disease and tumor development started in the 1950s. Various animal species have been tested for their susceptibility to human adenovirus infection since then, and some have been shown to mimic key characteristics of the infection in humans, including persistent infection. Furthermore, some rodent species have been found to develop tumors upon human adenovirus infection. Our review summarizes the current knowledge on animal models in human adenovirus research, describing the pros and cons along with important findings and future perspectives.

Abstract

Human adenovirus (HAdV) infections cause a wide variety of clinical symptoms, ranging from mild upper respiratory tract disease to lethal outcomes, particularly in immunocompromised individuals. To date, neither widely available vaccines nor approved antiadenoviral compounds are available to efficiently deal with HAdV infections. Thus, there is a need to thoroughly understand HAdV-induced disease, and for the development and preclinical evaluation of HAdV therapeutics and/or vaccines, and consequently for suitable standardizable in vitro systems and animal models. Current animal models to study HAdV pathogenesis, persistence, and tumorigenesis include rodents such as Syrian hamsters, mice, and cotton rats, as well as rabbits. In addition, a few recent studies on other species, such as pigs and tree shrews, reported promising data. These models mimic (aspects of) HAdV-induced pathological changes in humans and, although they are relevant, an ideal HAdV animal model has yet to be developed. This review summarizes the available animal models of HAdV infection with comprehensive descriptions of virus-induced pathogenesis in different animal species. We also elaborate on rodent HAdV animal models and how they contributed to insights into adenovirus-induced cell transformation and cancer.

Viral PDZ Binding Motifs Influence Cell Behavior Through the Interaction with Cellular Proteins Containing PDZ Domains

Viruses have evolved to interact with their hosts. Some viruses such as human papilloma virus, dengue virus, SARS-CoV, or influenza virus encode proteins including a PBM that interact with cellular proteins containing PDZ domains. There are more than 400 cellular protein isoforms with these domains in the human genome, indicating that viral PBMs have a high potential to influence the behavior of the cell. In this review we analyze the most relevant cellular processes known to be affected by viral PBM-cellular PDZ interactions including the establishment of cell-cell interactions and cell polarity, the regulation of cell survival and apoptosis and the activation of the immune system. Special attention has been provided to coronavirus PBM conservation throughout evolution and to the role of the PBMs of human coronaviruses SARS-CoV and MERS-CoV in pathogenesis.

Structural Determinants within the Adenovirus Early Region 1A Protein Spacer Region Necessary for Tumorigenesis

It has long been established that group A human adenoviruses (HAdV-A12, -A18, and -A31) can cause tumors in newborn rodents, with tumorigenicity related to the presence of a unique spacer region located between conserved regions 2 and 3 within the HAdV-A12 early region 1A (E1A) protein. Group B adenoviruses are weakly oncogenic, whereas most of the remaining human adenoviruses are nononcogenic. In an attempt to understand better the relationship between the structure of the AdE1A spacer region and oncogenicity of HAdVs, the structures of synthetic peptides identical or very similar to the adenovirus 12 E1A spacer region were determined and found to be α-helical using nuclear magnetic resonance (NMR) spectroscopy. This contrasts significantly with some previous suggestions that this region is unstructured. Using available predictive algorithms, the structures of spacer regions from other E1As were also examined, and the extent of the predicted α-helix was found to correlate reasonably well with the tumorigenicity of the respective virus. We suggest that this may represent an as-yet-unknown binding site for a partner protein required for tumorigenesis.IMPORTANCE This research analyzed small peptides equivalent to a region within the human adenovirus early region 1A protein that confers, in part, tumor-inducing properties to various degrees on several viral strains in rats and mice. The oncogenic spacer region is α-helical, which contrasts with previous suggestions that this region is unstructured. The helix is characterized by a stretch of amino acids rich in alanine residues that are organized into a hydrophobic, or "water-hating," surface that is considered to form a major site of interaction with cellular protein targets that mediate tumor formation. The extent of α-helix in E1A from other adenovirus species can be correlated to a limited degree to the tumorigenicity of that virus. Some serotypes show significant differences in predicted structural propensity, suggesting that the amino acid type and physicochemical properties are also of importance.

Viral Disease

This chapter discusses infections of rats with viruses in the following 14 virus families: Adenoviridae, Arenaviridae, Coronaviridae, Flaviviridae, Hantaviridae, Hepeviridae, Herpesviridae, Paramyxoviridae, Parvoviridae, Picornaviridae, Pneumoviridae, Polyomaviridae, Poxviridae, and Reoviridae . Serological surveys indicate that parvoviruses, coronaviruses, cardioviruses, and pneumoviruses are the most prevalent in laboratory rats. A new polyomavirus and a new cardiovirus that cause disease in laboratory rats are described. Metagenomic analyses of feces or intestinal contents from wild rats have detected viruses from an additional nine virus families that could potentially cause infections in laboratory rats.

Emerging Themes in PDZ Domain Signaling: Structure, Function, and Inhibition

Post-synaptic density-95, disks-large and zonula occludens-1 (PDZ) domains are small globular protein-protein interaction domains widely conserved from yeast to humans. They are composed of ∼90 amino acids and form a classical two α-helical/six β-strand structure. The prototypical ligand is the C-terminus of partner proteins; however, they also bind internal peptide sequences. Recent findings indicate that PDZ domains also bind phosphatidylinositides and cholesterol. Through their ligand interactions, PDZ domain proteins are critical for cellular trafficking and the surface retention of various ion channels. In addition, PDZ proteins are essential for neuronal signaling, memory, and learning. PDZ proteins also contribute to cytoskeletal dynamics by mediating interactions critical for maintaining cell-cell junctions, cell polarity, and cell migration. Given their important biological roles, it is not surprising that their dysfunction can lead to multiple disease states. As such, PDZ domain-containing proteins have emerged as potential targets for the development of small molecular inhibitors as therapeutic agents. Recent data suggest that the critical binding function of PDZ domains in cell signaling is more than just glue, and their binding function can be regulated by phosphorylation or allosterically by other binding partners. These studies also provide a wealth of structural and biophysical data that are beginning to reveal the physical features that endow this small modular domain with a central role in cell signaling.

Viral Interactions with PDZ Domain-Containing Proteins-An Oncogenic Trait?

Many of the human viruses with oncogenic capabilities, either in their natural host or in experimental systems (hepatitis B and C, human T cell leukaemia virus type 1, Kaposi sarcoma herpesvirus, human immunodeficiency virus, high-risk human papillomaviruses and adenovirus type 9), encode in their limited genome the ability to target cellular proteins containing PSD95/ DLG/ZO-1 (PDZ) interaction modules. In many cases (but not always), the viruses have evolved to bind the PDZ domains using the same short linear peptide motifs found in host protein-PDZ interactions, and in some cases regulate the interactions in a similar fashion by phosphorylation. What is striking is that the diverse viruses target a common subset of PDZ proteins that are intimately involved in controlling cell polarity and the structure and function of intercellular junctions, including tight junctions. Cell polarity is fundamental to the control of cell proliferation and cell survival and disruption of polarity and the signal transduction pathways involved is a key event in tumourigenesis. This review focuses on the oncogenic viruses and the role of targeting PDZ proteins in the virus life cycle and the contribution of virus-PDZ protein interactions to virus-mediated oncogenesis. We highlight how many of the viral associations with PDZ proteins lead to deregulation of PI3K/AKT signalling, benefitting virus replication but as a consequence also contributing to oncogenesis.

Adenovirus E4-ORF1 Dysregulates Epidermal Growth Factor and Insulin/Insulin-Like Growth Factor Receptors To Mediate Constitutive Myc Expression

The E4-ORF1 protein encoded by human adenovirus stimulates viral replication in human epithelial cells by binding and activating cellular phosphatidylinositol 3-kinase (PI3K) at the plasma membrane and cellular Myc in the nucleus. In this study, we showed that E4-ORF1 hijacks the tyrosine kinase activities of cellular epidermal growth factor receptor (EGFR) and insulin receptor (InsR)/insulin-like growth factor receptor 1 (IGF1R), as well as the lipid kinase activity of PI3K, to mediate constitutive Myc protein expression. We additionally demonstrated that EGFR contributes to constitutive Myc expression through the capacity of E4-ORF1 to induce ligand-independent EGFR activation and stimulation of the Ras/Mek/Erk pathway, the latter activity of which was conserved by human adenoviruses. Results further suggested that EGFR normally forms a complex with the cellular PDZ protein Discs Large 1 (Dlg1), a component of the Dlg1:E4-ORF1:PI3K ternary complex that mediates E4-ORF1-induced PI3K activation, and that E4-ORF1 binds the Dlg1:EGFR complex and promotes the association of EGFR with InsR and IGF1R. In addition to its role in constitutive Myc expression, InsR/IGF1R also negatively regulates EGFR autophosphorylation and EGFR-mediated Ras/Mek/Erk signaling, and data suggested that E4-ORF1 binding to Dlg1 antagonizes these activities. Collectively, our findings suggest that in human epithelial cells, E4-ORF1 targets EGFR, InsR/IGF1R, and PI3K at the plasma membrane to activate cytosolic signaling pathways that sustain Myc protein levels in the nucleus. We postulate that E4-ORF1-induced constitutive Myc expression functions to ensure the formation of nuclear E4-ORF1:Myc complexes, which have been shown to activate Myc and to enhance adenovirus replication.

IMPORTANCE

While human adenoviruses primarily produce self-limited acute infections in humans, these agents are associated with life-threatening diseases in immunocompromised patients and in otherwise healthy individuals infected with certain virulent serotypes. The adenovirus E4-ORF1 protein enhances viral replication by activating the cellular lipid kinase PI3K and the cellular transcription factor Myc. Here we report that E4-ORF1 usurps the functions of the cellular tyrosine kinase receptors EGFR and InsR /: IGF1R, as well as PI3K, to sustain Myc protein expression in cells. Furthermore, sustained Myc expression depended on E4-ORF1-induced ligand-independent EGFR activation that stimulated Ras/Mek/Erk signaling, a function found to be conserved by human adenoviruses. Given the established roles of PI3K, the Ras/Mek/Erk pathway, and Myc in the adenovirus life cycle, our findings may aid in the development of safer, more effective therapeutic strategies to treat severe adenovirus infections as well as improved adenovirus vectors for use in vaccination and gene and cancer therapy.

Hijacking Dlg1 for oncogenic phosphatidylinositol 3-kinase activation in human epithelial cells is a conserved mechanism of human adenovirus E4-ORF1 proteins

The E4-ORF1 gene of human adenoviruses encodes a 14-kDa protein that promotes viral replication as well as cellular metabolic reprogramming, survival, and transformation by constitutively activating cellular phosphatidylinositol 3-kinase (PI3K). We recently reported that the E4-ORF1 protein from subgroup D human adenovirus type 9 upregulates and oncogenically activates PI3K by a novel mechanism involving separate interactions of E4-ORF1 with cellular discs large 1 (Dlg1) and PI3K to form a ternary complex that translocates to the plasma membrane (K. Kong, M. Kumar, M. Taruishi, and R. T. Javier, PLoS Pathog. 10:e1004102, 2014, doi:10.1371/journal.ppat.1004102). The current study was carried out to investigate whether other human adenovirus E4-ORF1 proteins share this mechanism of action. The results showed that in human MCF10A epithelial cells, stable expression of E4-ORF1 proteins encoded by representative human adenovirus serotypes from subgroups A to D induce ternary complex formation, Dlg1-dependent PI3K activation, PI3K protein elevation, Dlg1 and PI3K membrane recruitment, and PI3K-dependent cellular transformation. The first three of these E4-ORF1 activities were also observed in MCF10A cells infected with each wild-type human adenovirus from subgroups A to D. Our findings indicate that most, if not all, human adenovirus E4-ORF1 proteins share a conserved molecular mechanism of PI3K activation, which confers a common capacity to promote oncogenic transformation in human epithelial cells.

IMPORTANCE

PI3K activation by the adenovirus E4-ORF1 protein mediates oncogenic cellular transformation by human adenovirus type 9, augments viral protein expression and replication by human adenovirus type 5, and dysregulates cellular glucose and lipid metabolism by human adenovirus type 36. For the first time, we report that E4-ORF1 proteins from human adenoviruses in subgroups A to D evolved a conserved molecular mechanism to mediate constitutive PI3K activation that can provoke oncogenic transformation in human epithelial cells. The results raise potential safety concerns about the use of vectors encoding the E4-ORF1 gene in human gene therapy and vaccination. Our findings further suggest that the conserved mechanism revealed here may be targeted for development of therapeutic drugs to treat and prevent adenovirus-associated human diseases.

The human adenovirus E4-ORF1 protein subverts discs large 1 to mediate membrane recruitment and dysregulation of phosphatidylinositol 3-kinase

Adenoviruses infect epithelial cells lining mucous membranes to cause acute diseases in people. They are also utilized as vectors for vaccination and for gene and cancer therapy, as well as tools to discover mechanisms of cancer due to their tumorigenic potential in experimental animals. The adenovirus E4-ORF1 gene encodes an oncoprotein that promotes viral replication, cell survival, and transformation by activating phosphatidylinositol 3-kinase (PI3K). While the mechanism of activation is not understood, this function depends on a complex formed between E4-ORF1 and the membrane-associated cellular PDZ protein Discs Large 1 (Dlg1), a common viral target having both tumor suppressor and oncogenic functions. Here, we report that in human epithelial cells, E4-ORF1 interacts with the regulatory and catalytic subunits of PI3K and elevates their levels. Like PI3K activation, PI3K protein elevation by E4-ORF1 requires Dlg1. We further show that Dlg1, E4-ORF1, and PI3K form a ternary complex at the plasma membrane. At this site, Dlg1 also co-localizes with the activated PI3K effector protein Akt, indicating that the ternary complex mediates PI3K signaling. Signifying the functional importance of the ternary complex, the capacity of E4-ORF1 to induce soft agar growth and focus formation in cells is ablated either by a mutation that prevents E4-ORF1 binding to Dlg1 or by a PI3K inhibitor drug. These results demonstrate that E4-ORF1 interacts with Dlg1 and PI3K to assemble a ternary complex where E4-ORF1 hijacks the Dlg1 oncogenic function to relocate cytoplasmic PI3K to the membrane for constitutive activation. This novel mechanism of Dlg1 subversion by adenovirus to dysregulate PI3K could be used by other pathogenic viruses, such as human papillomavirus, human T-cell leukemia virus type 1, and influenza A virus, which also target Dlg1 and activate PI3K in cells.

Adenoviruses cause acute illnesses in people, and are additionally utilized both as vehicles to cure genetic diseases, fight cancer, and deliver vaccines, and as tools to discover how cancers develop due to a capacity to generate tumors in experimental animals. The adenovirus E4-ORF1 protein reprograms cell metabolism to enhance virus production in infected cells and promotes cell survival and tumors by activating the important cellular protein phosphatidylinositol 3-kinase (PI3K). How E4-ORF1 activates PI3K is not known, though this function depends on E4-ORF1 binding to the membrane-associated cellular protein Discs Large 1 (Dlg1), which many different viruses evolved to target. In this study, we identify PI3K as a new direct target of E4-ORF1. Results further show that E4-ORF1 binds to PI3K in the cytoplasm and delivers it to Dlg1 at the membrane where the three proteins form a complex that activates PI3K and induces oncogenic growth in cells. This novel molecular mechanism in which adenovirus subverts Dlg1 to dysregulate PI3K may serve as a paradigm to understand PI3K activation mediated by other important pathogenic viruses, such as human papillomavirus, human T-cell leukemia virus type 1, and influenza A virus, which also target Dlg1 in infected cells.

Presence of adenovirus species C in infiltrating lymphocytes of human sarcoma

Human adenoviruses are known to persist in T-lymphocytes of tonsils, adenoids and intestinal tract. The oncogenic potential of different adenovirus types has been widely studied in rodents, in which adenovirus inoculation can induce multiple tumors such as undifferentiated sarcomas, adenocarcinomas and neuroectodermal tumors. However, the oncogenic potential of this virus has never been proven in human subjects. Using a highly sensitive broad-spectrum qRT-PCR, we have screened a set of different human sarcomas including leiomyosarcoma, liposarcoma and gastro intestinal stroma tumors. Primers binding the viral oncogene E1A and the capsid-coding gene Hexon were used to detect the presence of adenovirus DNA in tumor samples. We found that 18% of the tested leiomyosarcomas and 35% of the liposarcomas were positive for the presence of adenovirus DNA, being species C types the most frequently detected adenoviruses. However, only in one sample of the gastro intestinal stroma tumors the virus DNA could be detected. The occurrence of adenovirus in the tumor sections was confirmed by subsequent fluorescence in-situ-hybridization analysis and co-staining with the transcription factor Bcl11b gives evidence for the presence of the virus in infiltrating T-lymphocytes within the tumors. Together these data underline, for the first time, the persistence of adenovirus in T-lymphocytes infiltrated in muscular and fatty tissue tumor samples. If an impaired immune system leads to the viral persistence and reactivation of the virus is involved in additional diseases needs further investigation.

Infectivity period of mice inoculated with human adenoviruses

Due to non-productive infections, mice are not a good model to study some human adenoviruses. However, mice provide an excellent model to study the metabolic effects of human adenovirus, Ad36. Research interest in Ad36 is increasing rapidly, and consequently an increase in the use of mice as a model is anticipated. However, little is known about the transmission potential of Ad36 from infected mice to other laboratory animals or personnel. While underestimating the infectivity could promote inadvertent spread of Ad36, overstating it could drain valuable laboratory resources and animals. Therefore, we determined the duration of infectivity in female C57BL/6J mice that were experimentally infected with human adenoviruses Ad36 or Ad2. Other uninfected mice were co-housed for one week with the experimentally-infected animals, four or eight weeks postinfection. Additionally, uninfected mice were housed in the cages of mice that were infected with Ad36, 12 weeks earlier. The presence of viral DNA in tissues was used to indicate infection of mice. Although experimentally-infected mice harboured viral DNA at least up to 12 weeks, the horizontal transmission of infection was observed in co-housed mice only up to four weeks postinfection. Thus, Ad36-infected mice should be considered potentially infective for eight weeks and appropriate handling and barrier containment should be used. After eight week postinfection, horizontal transmission appears unlikely. This information may provide guidelines for animal handling, and experimental design using Ad36, which may increase safety for laboratory personnel and reduce the number of mice required for experiments.

Computational analysis and identification of an emergent human adenovirus pathogen implicated in a respiratory fatality

Adenoviral infections are typically acute, self-limiting, and not associated with death. However, we present the genomic and bioinformatics analysis of a novel recombinant human adenovirus (HAdV-D56) isolated in France that caused a rare neonatal fatality, and keratoconjunctivitis in three health care workers who cared for the neonate. Whole genome alignments revealed the expected diversity in the penton base, hexon, E3, and fiber coding regions, and provided evidence for extensive recombination. Bootscan analysis confirmed recombination between HAdV-D9, HAdV-D26, HAdV-D15, and HAdV-D29 in the penton base and hexon proteins, centered around hypervariable loops within the putative proteins. Protein structure analysis of the fiber coding region revealed similarity with HAdV-D8, HAdV-D9, and HAdV-D53, possibly accounting for the ocular tropism of the virus. Based on these data, this virus appears to be a new HAdV-D type (HAdV-D56), underscoring the importance of recombination events in human adenovirus evolution and the emergence of new adenovirus pathogens.

Cell polarity proteins: common targets for tumorigenic human viruses

Loss of polarity and disruption of cell junctions are common features of epithelial-derived cancer cells, and mounting evidence indicates that such defects have a direct function in the pathology of cancer. Supporting this idea, results with several different human tumor viruses indicate that their oncogenic potential depends in part on a common ability to inactivate key cell polarity proteins. For example, adenovirus (Ad) type 9 is unique among human Ads by causing exclusively estrogen-dependent mammary tumors in experimental animals and in having E4 region-encoded open reading frame 1 (E4-ORF1) as its primary oncogenic determinant. The 125-residue E4-ORF1 protein consists of two separate protein-interaction elements, one of which defines a PDZ domain-binding motif (PBM) required for E4-ORF1 to induce both cellular transformation in vitro and tumorigenesis in vivo. Most notably, the E4-ORF1 PBM mediates interactions with a selected group of cellular PDZ proteins, three of which include the cell polarity proteins Dlg1, PATJ and ZO-2. Data further indicate that these interactions promote disruption of cell junctions and a loss of cell polarity. In addition, one or more of the E4-ORF1-interacting cell polarity proteins, as well as the cell polarity protein Scribble, are common targets for the high-risk human papillomavirus (HPV) E6 or human T-cell leukemia virus type 1 (HTLV-1) Tax oncoproteins. Underscoring the significance of these observations, in humans, high-risk HPV and HTLV-1 are causative agents for cervical cancer and adult T-cell leukemia, respectively. Consequently, human tumor viruses should serve as powerful tools for deciphering mechanisms whereby disruption of cell junctions and loss of cell polarity contribute to the development of many human cancers. This review article discusses evidence supporting this hypothesis, with an emphasis on the human Ad E4-ORF1 oncoprotein.

A new crucial protein interaction element that targets the adenovirus E4-ORF1 oncoprotein to membrane vesicles

Human adenovirus type 9 exclusively elicits mammary tumors in experimental animals, and the primary oncogenic determinant of this virus is the E4-ORF1 oncogene, as opposed to the well-known E1A and E1B oncogenes. The tumorigenic potential of E4-ORF1, as well as its ability to oncogenically stimulate phosphatidylinositol 3-kinase (PI3K), depends on a carboxyl-terminal PDZ domain-binding motif (PBM) that mediates interactions with several different membrane-associated cellular PDZ proteins, including MUPP1, PATJ, MAGI-1, ZO-2, and Dlg1. Nevertheless, because certain E4-ORF1 mutations that alter neither the sequence nor the function of the PBM abolish E4-ORF1-induced PI3K activation and cellular transformation, we reasoned that E4-ORF1 must possess an additional crucial protein element. In the present study, we identified seven E4-ORF1 amino acid residues that define this new element, designated domain 2, and showed that it mediates binding to a 70-kDa cellular phosphoprotein. We also discovered that domain 2 or the PBM independently promotes E4-ORF1 localization to cytoplasmic membrane vesicles and that this activity of domain 2 depends on E4-ORF1 trimerization. Consistent with the latter observation, molecular-modeling analyses predicted that E4-ORF1 trimerization brings together six out of seven domain 2 residues at each of the three subunit interfaces. These findings importantly demonstrate that PI3K activation and cellular transformation induced by E4-ORF1 require two separate protein interaction elements, domain 2 and the PBM, each of which targets E4-ORF1 to vesicle membranes in cells.

The stardust family protein MPP7 forms a tripartite complex with LIN7 and DLG1 that regulates the stability and localization of DLG1 to cell junctions

MPP7, a previously uncharacterized member of the p55 Stardust family of membrane-associated guanylate kinase (MAGUK) proteins, was found in a tripartite complex with DLG1 and LIN7A or LIN7C. MPP7 dimerizes with all three LIN7 family members (LIN7A, -B, and -C) through interaction of the single L27 domain of LIN7 with the carboxyl-terminal L27 domain of MPP7, thereby stabilizing both proteins. The dimer of MPP7 with LIN7A or LIN7C associates with DLG1 through an interaction requiring the amino-terminal L27 domain of MPP7. The amino-terminal L27 domain of MPP7 is not sufficient for interaction with DLG1 but interacts efficiently only if MPP7 is in a complex with LIN7A or -C. Thus the specificity of interaction of DLG1 with the LIN7-MPP7 complex is determined by L27 interactions with both MPP7 and LIN7. The tripartite complex forms in a ratio of 1:1:1 and localizes to epithelial adherens junctions in a manner dependent upon MPP7. Expression of MPP7 stabilizes DLG1 in an insoluble compartment. Expression of MPP7 deleted of the PDZ or Src homology 3 domain redistributes MPP7, DLG1, and LIN7 out of adherens junctions and into the soluble cytoplasmic fraction without changing the localization of E-cadherin. Thus, the stability and localization of DLG1 to cell-cell junctions are complex functions determined by the expression and association of particular Stardust family members together with particular LIN7 family members.

Oncogenic function for the Dlg1 mammalian homolog of the Drosophila discs-large tumor suppressor

The fact that several different human virus oncoproteins, including adenovirus type 9 E4-ORF1, evolved to target the Dlg1 mammalian homolog of the membrane-associated Drosophila discs-large tumor suppressor has implicated this cellular factor in human cancer. Despite a general belief that such interactions function solely to inactivate this suspected human tumor suppressor protein, we demonstrate here that E4-ORF1 specifically requires endogenous Dlg1 to provoke oncogenic activation of phosphatidylinositol 3-kinase (PI3K) in cells. Based on our results, we propose a model wherein E4-ORF1 binding to Dlg1 triggers the resulting complex to translocate to the plasma membrane and, at this site, to promote Ras-mediated PI3K activation. These findings establish the first known function for Dlg1 in virus-mediated cellular transformation and also surprisingly expose a previously unrecognized oncogenic activity encoded by this suspected cellular tumor suppressor gene.

Viral oncoprotein-induced mislocalization of select PDZ proteins disrupts tight junctions and causes polarity defects in epithelial cells

The development of human cancers is frequently associated with a failure of epithelial cells to form tight junctions and to establish proper apicobasal polarity. Interestingly, the oncogenic potential of the adenovirus E4-ORF1 protein correlates with its binding to the cellular PDZ proteins MUPP1, MAGI-1, ZO-2 and SAP97, the first three of which assemble protein complexes at tight junctions. Given that E4-ORF1 sequesters these three PDZ proteins in the cytoplasm of fibroblasts, we postulated that E4-ORF1 would inhibit tight junction formation in epithelial cells. Providing further support for this idea, we identified MUPP1-related PATJ, a key component of the tight junction-associated CRB3-PALS1-PATJ polarity complex, as a new PDZ-protein target for both the E4-ORF1 and high-risk human papillomavirus type 18 E6 oncoproteins. Moreover, in epithelial cells, E4-ORF1 blocked the tight junction localization of PATJ and ZO-2, as well as their interacting partners, and disrupted both the tight junction barrier and apicobasal polarity. These significant findings expose a direct link between the tumorigenic potential of E4-ORF1 and inactivation of cellular PDZ proteins involved in tight junction assembly and polarity establishment.

Cell transformation by human adenoviruses

The last 40 years of molecular biological investigations into human adenoviruses have contributed enormously to our understanding of the basic principles of normal and malignant cell growth. Much of this knowledge stems from analyses of their productive infection cycle in permissive host cells. Also, initial observations concerning the carcinogenic potential of human adenoviruses subsequently revealed decisive insights into the molecular mechanisms of the origins of cancer, and established adenoviruses as a model system for explaining virus-mediated transformation processes. Today it is well established that cell transformation by human adenoviruses is a multistep process involving several gene products encoded in early transcription units 1A (E1A) and 1B (E1B). Moreover, a large body of evidence now indicates that alternative or additional mechanisms are engaged in adenovirus-mediated oncogenic transformation involving gene products encoded in early region 4 (E4) as well as epigenetic changes resulting from viral DNA integration. In particular, detailed studies on the tumorigenic potential of subgroup D adenovirus type 9 (Ad9) E4 have now revealed a new pathway that points to a novel, general mechanism of virus-mediated oncogenesis. In this chapter, we summarize the current state of knowledge about the oncogenes and oncogene products of human adenoviruses, focusing particularly on recent findings concerning the transforming and oncogenic properties of viral proteins encoded in the E1B and E4 transcription units.

Selective PDZ protein-dependent stimulation of phosphatidylinositol 3-kinase by the adenovirus E4-ORF1 oncoprotein

While PDZ domain-containing proteins represent cellular targets for several different viral oncoproteins, including human papillomavirus E6, human T-cell leukemia virus type 1 Tax, and human adenovirus E4-ORF1, the functional consequences for such interactions have not been elucidated. Here we report that, at the plasma membrane of cells, the adenovirus E4-ORF1 oncoprotein selectively and potently stimulates phosphatidylinositol 3-kinase (PI3K), triggering a downstream cascade of events that includes activation of both protein kinase B and p70S6-kinase. This activity of E4-ORF1 could be abrogated by overexpression of its PDZ-protein targets or by disruption of its PDZ domain-binding motif, which was shown to mediate complex formation between E4-ORF1 and PDZ proteins at the plasma membrane of cells. Furthermore, E4-ORF1 mutants unable to activate the PI3K pathway failed to transform cells in culture or to promote tumors in animals, and drugs that block either PI3K or p70S6-kinase inhibited E4-ORF1-induced transformation of cells. From these results, we propose that the transforming and tumorigenic potentials of the adenovirus E4-ORF1 oncoprotein depend on its capacity to activate PI3K through a novel PDZ protein-dependent mechanism of action.

Adenovirus early E4 genes in viral oncogenesis

Previous investigations into potential transforming activities of adenovirus (Ad) early genes were largely overshadowed by the more obvious roles of E1A and E1B products. One exception was an Ad9 E4 protein (ORF1) shown to enhance transformation of cultured cells and promote mammary tumors in female rats. Recently, significant advances in understanding Ad E4 gene products at the molecular level have revealed that these proteins possess an unexpectedly diverse collection of functions, which not only orchestrate many viral processes, but overlap with oncogenic transformation of primary mammalian cells. Operating through a complex network of protein interactions with key viral and cellular regulatory components, Ad E4 products are apparently involved in transcription, apoptosis, cell cycle control, DNA repair, cell signaling, posttranslational modifications and the integrity of nuclear multiprotein complexes known as PML oncogenic domains (PODs). Some of these functions directly relate to known transforming and oncogenic processes, or implicate mechanisms such as modulating the function and subcellular localization of cellular PDZ domain-containing proteins, POD reorganization, targeted proteolytic degradation, inhibition of DNA double-strand break repair and 'hit-and-run' mutagenesis. Here, we summarize the recent data and discuss how E4 gene product interactions may contribute to viral oncogenesis.

Molecular regulation and biological function of adenovirus early genes: the E4 ORFs

Over the past few years there have been a number of interesting advances in our understanding of the functions encoded by the adenovirus early transcription unit 4 (Ad E4). A large body of recent data demonstrates that E4 proteins encompass an unexpectedly diverse collection of functions required for efficient viral replication. E4 gene products operate through a complex network of protein interactions with key viral and cellular regulatory components involved in transcription, apoptosis, cell cycle control and DNA repair, as well as host cell factors that regulate cell signaling, posttranslational modifications and the integrity of nuclear multiprotein complexes known as nuclear bodies (NBs) or PML oncogenic domains (PODs). As understood at present, some of the lytic functions overlap with roles in oncogenic transformation of primary mammalian cells. These observations, together with findings that E4 proteins substantially affect cell toxicity and the immune response of the host have profound implications for the development of Ad vectors for gene therapy. In this article we will summarize recent findings regarding the diverse functions of E4 gene products in the context of earlier work. We will emphasize the interaction of E4 proteins with cellular and viral interaction partners, the role of these interactions for lytic virus growth and how these interactions may contribute to viral oncogenesis. Finally, we will discuss their role in Ad vector and adeno-associated virus infections.

Link of the unique oncogenic properties of adenovirus type 9 E4-ORF1 to a select interaction with the candidate tumor suppressor protein ZO-2

Adenovirus type 9 (Ad9) is distinct among human adenoviruses because it elicits solely mammary tumors in animals and its primary oncogenic determinant is the E4 region-encoded ORF1 (E4-ORF1) protein. We report here that the PDZ domain-containing protein ZO-2, which is a candidate tumor suppressor protein, is a cellular target for tumorigenic Ad9 E4-ORF1 but not for non-tumorigenic wild-type E4-ORF1 proteins encoded by adenovirus types 5 and 12. Complex formation was mediated by the C-terminal PDZ domain-binding motif of Ad9 E4- ORF1 and the first PDZ domain of ZO-2, and in cells this interaction resulted in aberrant sequestration of ZO-2 within the cytoplasm. Furthermore, transformation-defective Ad9 E4-ORF1 mutants exhibited impaired binding to and sequestration of ZO-2 in cells, and overexpression of wild-type ZO-2, but not mutant ZO-2 lacking the second and third PDZ domains, interfered with Ad9 E4-ORF1-induced focus formation. Our results suggest that the select capacity to complex with the candidate tumor suppressor protein ZO-2 is key to defining the unique transforming and tumorigenic properties of the Ad9 E4-ORF1 oncoprotein.

Several E4 region functions influence mammary tumorigenesis by human adenovirus type 9

Among oncogenic adenoviruses, human adenovirus type 9 (Ad9) is unique in eliciting exclusively estrogen-dependent mammary tumors in rats and in not requiring viral E1 region transforming genes for tumorigenicity. Instead, studies with hybrid viruses generated between Ad9 and the closely related nontumorigenic virus Ad26 have roughly localized an Ad9 oncogenic determinant(s) to a segment of the viral E4 region containing open reading frame 1 (E4-ORF1), E4-ORF2, and part of E4-ORF3. Although subsequent findings have shown that E4-ORF1 codes for an oncoprotein essential for tumorigenesis by Ad9, it is not known whether other E4 region functions may similarly play a role in this process. We report here that new results with Ad9/Ad26 hybrid viruses demonstrated that the minimal essential Ad9 E4-region DNA sequences include portions of both E4-ORF1 and E4-ORF2. Investigations with Ad9 mutant viruses additionally showed that the E4-ORF1 protein and certain E4-ORF2 DNA sequences are necessary for Ad9-induced tumorigenesis, whereas the E4-ORF2 and E4-ORF3 proteins are not. In fact, the E4-ORF3 protein was found to antagonize this process. Also pertinent was that certain crucial nucleotide differences between Ad9 and Ad26 within E4-ORF1 and E4-ORF2 were found to be silent with respect to the amino acid sequences of the corresponding proteins. Furthermore, supporting a prominent role for the E4-ORF1 oncoprotein in Ad9-induced tumorigenesis, an E1 region-deficient Ad5 vector that expresses the Ad9 but not the Ad26 E4-ORF1 protein was tumorigenic in rats and, like Ad9, promoted solely mammary tumors. These findings argue that the E4-ORF1 oncoprotein is the major oncogenic determinant of Ad9 and that an undefined regulatory element(s) within the E4 region represents a previously unidentified second function likewise necessary for tumorigenesis by this virus.

Interactions of the PDZ-protein MAGI-1 with adenovirus E4-ORF1 and high-risk papillomavirus E6 oncoproteins

The oncoproteins of small DNA tumor viruses promote tumorigenesis by complexing with cellular factors intimately involved in the control of cell proliferation. The major oncogenic determinants for human adenovirus type 9 (Ad9) and high-risk human papillomaviruses (HPV) are the E4-ORF1 and E6 proteins, respectively. These seemingly unrelated viral oncoproteins are similar in that their transforming activities in cells depend, in part, on a carboxyl-terminal PDZ domain-binding motif which mediates interactions with the cellular PDZ-protein DLG. Here we demonstrated that both Ad9 E4-ORF1 and high-risk HPV E6 proteins also bind to the DLG-related PDZ-protein MAGI-1. These interactions resulted in MAGI-1 being aberrantly sequestered in the cytoplasm by the Ad9 E4-ORF1 protein or being targeted for degradation by high-risk HPV E6 proteins. Transformation-defective mutant viral proteins, however, were deficient for these activities. Our findings indicate that MAGI-1 is a member of a select group of cellular PDZ proteins targeted by both adenovirus E4-ORF1 and high-risk HPV E6 proteins and, in addition, suggest that the tumorigenic potentials of these viral oncoproteins depend, in part, on an ability to inhibit the function of MAGI-1 in cells.

Rat models of premalignant breast disease

While a number of agents have been shown to induce mammary carcinogenesis in the rat, premalignant stages of the disease have been best characterized in chemically-induced models, specifically those initiated by either 7,12 dimethylbenz[alpha]anthracene (DMBA) or 1-methyl-1-nitrosourea (MNU). In general, it appears that epithelial cells in mammary terminal end buds or terminal ductules are the targets of carcinogenic initiation, and that a series of morphologically identifiable steps are involved in the development of mammary carcinoma. The premalignant steps include ductal hyperplasia of the usual type and carcinoma in situ of the cribriform or comedo type; atypical ductal hyperplasia has not been reported. Thus the histogenesis of lesions occurring in chemically induced mammary carcinogenesis in the rat is similar to that observed in the human; although, the spectrum of lesions observed in the rat is limited. Opportunities to investigate the biological and molecular characteristics of premalignant breast disease in the rat are presented.

Induction of transformation and p53-dependent apoptosis by adenovirus type 5 E4orf6/7 cDNA

Adenovirus (Ad) E4orf6/7, one of the early gene products of human Ads, forms a stable complex with the cellular transcription factor E2F to activate transcription from the Ad E2 promoter. E2F cDNAs have growth-promoting and apoptosis-inducing activities when overexpressed in cells. We cloned Ad5 E4orf6/7 cDNA in both simian virus 40- and human cytomegalovirus-based expression vectors to examine its transforming and apoptotic activities. The cloned E4orf6/7 collaborated with a retinoblastoma protein (RB)-nonbinding and therefore E2F-nonreleasing mutant of Ad5 E1A (dl922/947) to morphologically transform primary rat cells, suggesting that E2F is an important cellular protein functioning downstream of E1A for transformation. In a G418 colony formation assay, E4orf6/7 was shown to suppress growth of untransformed rat cells. Moreover, a recombinant Ad expressing Ad5 E4orf6/7 induced apoptosis in rat cells when coinfected with wild-type p53-expressing Ad. Mutational analysis of E4orf6/7 revealed that both of the domains required for growth inhibition and transformation by E4orf6/7 lay in the C-terminal region, which is essential for transactivation from the upstream sequence of an E2a promoter containing E2F-binding sites. However, the smallest mutant of E4orf6/7, encoding the C-terminal 59 amino acids, failed to complement the RB-nonbinding dl922/947 mutant despite showing growth inhibition and E2F transactivation activities. Thus, it is suggested that a subregion of E4orf6/7 which is required for growth inhibition and transformation in collaboration with dl922/947 overlaps the transactivation domain of E4orf6/7.

Early region 1 transforming functions are dispensable for mammary tumorigenesis by human adenovirus type 9

Some human adenoviruses are tumorigenic in rodents. Subgroup A and B human adenoviruses generally induce sarcomas in both male and female animals, and the gene products encoded within viral early region 1 (E1 region) are both necessary and sufficient for this tumorigenicity. In contrast, subgroup D human adenovirus type 9 (Ad9) induces estrogen-dependent mammary tumors in female rats and requires the E4 region-encoded ORF1 oncoprotein for its tumorigenicity. Considering the established importance of the viral E1 region for tumorigenesis by adenoviruses, we investigated whether this viral transcription unit is also necessary for Ad9 to generate mammary tumors. The nucleotide sequence of the Ad9 E1 region indicated that the gene organization and predicted E1A and E1B polypeptides of Ad9 are closely related to those of other human adenovirus E1 regions. In addition, an Ad9 E1 region plasmid demonstrated focus-forming activity in both low-passage-number and established rat embryo fibroblasts, whereas a large deletion within either the E1A or E1B gene of this plasmid diminished transforming activity. Surprisingly, we found that introducing the same transformation-inactivating E1A and E1B deletions into Ad9 results in mutant viruses that retain the ability to elicit mammary tumors in rats. These results are novel in showing that Ad9 represents a unique oncogenic adenovirus in which the E4 region, rather than the E1 region, encodes the major oncogenic determinant in the rat.

Activation of transgene expression by early region 4 is responsible for a high level of persistent transgene expression from adenovirus vectors in vivo

The persistence of transgene expression has become a hallmark for adenovirus vector evaluation in vivo. Although not all therapeutic benefit in gene therapy is reliant on long-term transgene expression, it is assumed that the treatment of chronic diseases will require significant persistence of expression. To understand the mechanisms involved in transgene persistence, a number of adenovirus vectors were evaluated in vivo in different strains of mice. Interestingly, the rate of vector genome clearance was not altered by the complete deletion of early region 4 (E4) in our vectors. The GV11 (E1- E4-) vector genome cleared with a similar kinetic profile as the GV10 (E1-) vector genome in immunocompetent and immunocompromised mice. These results suggest that the majority of adenovirus vector genomes are eliminated from transduced tissue via a mechanism(s) independent of T-cell, B-cell, and NK cell immune mechanisms. While the levels of persistence of transgene expression in liver or lung transduced with GV10 and GV11 vectors expressing beta-galactosidase, cystic fibrosis transmembrane conductance regulator, or secretory alkaline phosphatase were similar in immunocompetent mice, a marked difference was observed in immunocompromised animals. Levels of transgene expression initially from both GV10 and GV11 vectors were the same. However, GV11 transgene expression correlated with loss of vector genome, while GV10 transgene expression persisted at a high level. Coadministration and readministration of GV10 vectors showed that E4 provided in trans could activate transgene expression from the GV11 vector genome. While transgene expression activity per genome from the GV10 vector is clearly activated, expression from a cytomegalovirus promoter expression cassette in a GV11 vector appeared to be further inactivated as a function of time. Understanding the molecular mechanisms underlying these expression effects will be important for developing persistent adenovirus vectors for chronic applications.

A carboxy-terminal region required by the adenovirus type 9 E4 ORF1 oncoprotein for transformation mediates direct binding to cellular polypeptides

Human adenovirus type 9 (Ad9) is unique among oncogenic adenoviruses in that it elicits exclusively mammary tumors in rats and requires the viral E4 region open reading frame 1 (9ORF1) gene for tumorigenicity. The 9ORF1 oncogenic determinant codes for a 14-kDa transforming protein, and three separate regions of this polypeptide, including one at the extreme C terminus, are necessary for transforming activity. In this study, we investigated whether the 9ORF1 transforming protein interacts with cellular factors. Following incubation with cell extracts, a glutathione S-transferase (GST)-9ORF1 fusion protein associated with several cellular phosphoproteins (p220, p180, p160, p155), whereas GST fusion proteins of transformation-defective 9ORF1 C-terminal mutants did not. Similar interactions requiring the 9ORF1 C terminus were revealed with protein-blotting assays, in which a GST-9ORF1 protein probe reacted specifically with cellular polypeptides having gel mobilities resembling those of the 9ORF1-associated cellular phosphoproteins, as well as with additional cellular polypeptides designated p140/p130. In addition, GST fusion proteins containing 9ORF1 C-terminal fragments associated with some of the 9ORF1-associated cellular polypeptides, as did GST fusion proteins of full-length wild-type Ad5 and Ad12 E4 ORF1 transforming proteins. Significantly, the results of coimmunoprecipitation analyses suggested that the same cellular polypeptides also associate with wild-type but not C-terminal-mutant 9ORF1 proteins in vivo. Together, these findings suggest that the 9ORF1 C terminus, which is essential for transformation, participates in specific and direct binding of the 9ORF1 oncoprotein to multiple cellular polypeptides. We propose that interactions with these cellular factors may be responsible, at least in part, for the transforming activity of the 9ORF1 viral oncoprotein.

Binding of human virus oncoproteins to hDlg/SAP97, a mammalian homolog of the Drosophila discs large tumor suppressor protein

The 9ORF1 gene encodes an adenovirus E4 region oncoprotein that requires a C-terminal region for transforming activity. Screening a lambdagt11 cDNA expression library with a 9ORF1 protein probe yielded a novel cellular PDZ domain-containing protein, 9BP-1, which binds to wild-type, but not a transformation-defective, C-terminal, mutant 9ORF1 protein. The fact that PDZ domains complex with specific sequences at the free C-terminal end of some proteins led to the recognition that the 9ORF1 C-terminal region contained such a consensus-binding motif. This discovery prompted investigations into whether the 9ORF1 protein associates with additional cellular proteins having PDZ domains. It was found that the 9ORF1 protein interacts directly, in vitro and in vivo, with the PDZ domain-containing protein hDlg/SAP97 (DLG), which is a mammalian homolog of the Drosophila discs large tumor suppressor protein and which also binds the adenomatous polyposis coli tumor suppressor protein. Of interest, in forming complexes, the 9ORF1 protein preferentially associated with the second PDZ domain of DLG, similar to adenomatous polyposis coli protein. Human T cell leukemia virus type 1 Tax and most oncogenic human papillomavirus E6 oncoproteins also possessed PDZ domain-binding motifs at their C termini and, significantly, human T cell leukemia virus type 1 Tax and human papillomavirus 18 E6 proteins bound DLG in vitro. Considering the requirement of the 9ORF1 C-terminal region in transformation, these findings suggest that interactions with the cellular factor DLG may contribute to the tumorigenic potentials of several different human virus oncoproteins.

Mutant adenovirus type 9 E4 ORF1 genes define three protein regions required for transformation of CREF cells

Human adenovirus type 9 (Ad9) elicits exclusively estrogen-dependent mammary tumors in rats, and an essential oncogenic determinant for this virus is Ad9 E4 open reading frame 1 (9ORF1), which encodes a 125-residue cytoplasmic protein with cellular growth-transforming activity in vitro. In this study, we engineered 48 different mutant 9ORF1 genes in an attempt to identify regions of this viral protein essential for transformation of the established rat embryo fibroblast cell line CREF. In initial assays with CREF cells, 17 of the 48 mutant 9ORF1 genes proved to be severely defective for generating transformed foci but only 7 of these defective genes expressed detectable amounts of protein. To further examine the defects of the seven mutant proteins, we selected individual cell pools of stable CREF transformants for the wild-type and mutant 9ORF1 genes. Compared to cell pools expressing the wild-type 9ORF1 protein, most cell pools expressing mutant proteins displayed decreased growth in soft agar, and all generated significantly smaller tumors in syngeneic animals. The altered amino acid residues of the seven mutant 9ORF1 polypeptides clustered within three separate regions referred to as region I (residues 34 to 41), region II (residues 89 to 91), and C-terminal region III (residues 122 to 125). By using indirect immunofluorescence, we also assessed whether the mutant proteins localized properly to the cytoplasm of cells. The region I and region II mutants displayed approximately wild-type subcellular localizations, whereas most region III mutants aberrantly accumulated within the nucleus of cells. In summary, we have identified three 9ORF1 protein regions necessary for cellular transformation and have demonstrated that C-terminal region III sequences significantly influence the proper localization of the 9ORF1 polypeptide in cells.

Human adenovirus early region 4 open reading frame 1 genes encode growth-transforming proteins that may be distantly related to dUTP pyrophosphatase enzymes

An essential oncogenic determinant of subgroup D human adenovirus type 9 (Ad9), which uniquely elicits estrogen-dependent mammary tumors in rats, is encoded by early region 4 open reading frame 1 (E4 ORF1). Whereas Ad9 E4 ORF1 efficiently induces transformed foci on the established rat embryo fibroblast cell line CREF, the related subgroup A Ad12 and subgroup C Ad5 E4 ORF1s do not (R. T. Javier, J. Virol. 68:3917-3924, 1994). In this study, we found that the lack of transforming activity associated with non-subgroup D adenovirus E4 ORF1s in CREF cells correlated with significantly reduced protein levels compared to Ad9 E4 ORF1 in these cells. In the human cell line TE85, however, the non-subgroup D adenovirus E4 ORF1s produced protein levels higher than those seen in CREF cells as well as transforming activities similar to that of Ad9 E4 ORF1, suggesting that all adenovirus E4 ORF1 polypeptides possess comparable cellular growth-transforming activities. In addition, searches for known proteins related to these novel viral transforming proteins revealed that the E4 ORF1 proteins had weak sequence similarity, over the entire length of the E4 ORF1 polypeptides, with a variety of organismal and viral dUTP pyrophosphatase (dUTPase) enzymes. Even though adenovirus E4 ORF1 proteins lacked conserved protein motifs of dUTPase enzymes or detectable enzymatic activity, E4 ORF1 and dUTPase proteins were predicted to possess strikingly similar secondary structure arrangements. It was also established that an avian adenovirus protein, encoded within a genomic location analogous to that of the human adenovirus E4 ORF1s, was a genuine dUTPase enzyme. Although no functional similarity was found for the E4 ORF1 and dUTPase proteins, we propose that human adenovirus E4 ORF1 genes have evolved from an ancestral adenovirus dUTPase and, from this structural framework, developed novel transforming properties.

A gene transfer vector-cell line system for complete functional complementation of adenovirus early regions E1 and E4

The improvements to adenovirus necessary for an optimal gene transfer vector include the removal of virus gene expression in transduced cells, increased transgene capacity, complete replication incompetence, and elimination of replication-competent virus that can be produced during the growth of first-generation adenovirus vectors. To achieve these aims, we have developed a vector-cell line system for complete functional complementation of both adenovirus early region 1 (E1) and E4. A library of cell lines that efficiently complement both E1 and E4 was constructed by transforming 293 cells with an inducible E4-ORF6 expression cassette. These 293-ORF6 cell lines were used to construct and propagate viruses with E1 and E4 deleted. While the construction and propagation of AdRSV beta gal.11 (an E1-/E4- vector engineered to contain a deletion of the entire E4 coding region) were possible in 293-ORF6 cells, the yield of purified virus was depressed approximately 30-fold compared with that of E1- vectors. The debilitation in AdRSV beta gal.11 vector growth was found to correlate with reduced fiber protein and mRNA accumulation. AdCFTR.11A, a modified E1-/E4- vector with a spacer sequence placed between late region 5 and the right inverted terminal repeat, efficiently expressed fiber and grew with the same kinetic profile and virus yield as did E1- vectors. Moreover, purified AdCFTR.11A yields were equivalent to E1- vector levels. Since no overlapping sequences exist in the E4 regions of E1-/E4- vectors and 293-ORF6 cell lines, replication-competent virus cannot be generated by homologous recombination. In addition, these second-generation E1-/E4- vectors have increased transgene capacity and have been rendered virus replication incompetent outside of the new complementing cell lines.

Establishment and characterization of a bovine mammary myoepithelial cell line

The thermolabile large T-antigen, encoded by the simian virus 40 early region mutant tsA58, was used to establish clonal cell lines (BMM-UV) from primary bovine myoepithelial cells. The BMM-UV cells have undergone more than 300 population doublings without any signs of senescence, and they contain the intranuclear large T antigen. At low confluency, they grow in a spindlelike manner and develop very long projections that most likely allow for communication of cells at a distance from each other. Establishment results in a decrease in the number of cells that contract in response to oxytocin compared with the parental nontransfected cells (20% versus 45%). Oxytocin responsiveness of BMM-UV cells increases when the cells are cultured in a medium supplemented with staphylococcal proteases. Proliferation of BMM-UV cells increases when they are cultured in the presence of epidermal growth factor (10 ng/ml) or insulinlike growth factor I (50 ng/ml). The BMM-UV cells may become a useful model to study growth properties, cell-to-cell communication, and the function of bovine mammary myoepithelial cells.

Human adenovirus type 9 E4 open reading frame 1 encodes a cytoplasmic transforming protein capable of increasing the oncogenicity of CREF cells

The induction of estrogen-dependent rat mammary tumors by human adenovirus type 9 (Ad9) requires the Ad9 E4 open reading frame 1 (9ORF1) protein, which alone can transform that rat embryo fibroblast cell line CREF in vitro. In the present study, independent pools of both 9ORF1-expressing and control CREF cells were generated by selection with G418 and compared with respect to transformed properties. Indirect immunofluorescence analyses revealed that more than 99% of the cells that made up the 9ORF1-transfected pools expressed 9ORF1 protein and, together with confocal laser scanning microscopy, indicated that this E4 protein was located predominantly within the cytoplasm of cells. With regard to transformation, cells of the 9ORF1-expressing pools differed from those of control pools by forming foci, displaying morphological alterations, growing more efficiently in soft agar, and reaching higher saturation densities. Following injection into immunocompetent syngeneic rats, the 9ORF1-expressing pool cells exhibited greatly enhanced oncogenicity compared with control pool cells. These results show that 9ORF1 protein (i) localizes predominantly within the cytoplasm, (ii) confers multiple general transformed characteristics to CREF cells in vitro, and (iii) increases the tumorigenic properties of these cells in vivo.

Mammary tumors induced by human adenovirus type 9: a role for the viral early region 4 gene

Human adenovirus type 9 (Ad9) elicits exclusively estrogen-dependent mammary tumors when injected into female rats. Three different histological types of mammary tumor (benign fibroadenomas, phyllodes tumors, and malignant solid sarcomas) have been described in Ad9-infected animals, with benign fibroadenomas being seen most frequently. Interestingly, in contrast to other adenoviruses, in which oncogenic viral functions are entirely encoded within the E1 region, Ad9 requires an E4 region transforming protein (ORF1) for its unique mammary oncogenicity. Studies of Ad9-induced rat mammary tumors may lead to a detailed molecular understanding for the development of fibroadenoma, a common human breast tumor.

Integration of viral sequences into the c-myc gene in two mammary adenocarcinomas induced by polyomavirus in athymic nude mice

We report the analysis of polyomavirus (Py) DNA integration into chromosomal DNA of two Py-induced mammary adenocarcinomas of athymic nude mice. Prior observations had established that these tumors had high levels of episomal Py DNA, making analysis of integration sites difficult. Propagation of tumor cells in culture allows the isolation of lines which have lost episomal Py DNA but are still tumorigenic and thus can be used for in situ and Southern analysis of Py sequences. The data reported here support the conclusion that Py DNA integrated into and next to the c-myc gene, adding further importance to this tumor system which, in its modifications of c-myc expression, appears to be similar to some human mammary cancers. In situ hybridization experiments on metaphase chromosomes of tumor cells showed that (i) in both cases, there was a single integration site at the same position on the same chromosome in all cells of a given tumor, and (ii) integration sites were different in the two tumors; in one, it was located on chromosome 15, near the c-myc proto-oncogene, and in the other, it was situated in the distal part of chromosome 1. We have demonstrated a probable rearrangement between chromosome 1 and chromosome 15, in the region of Py insertion, thus suggesting that a specific site on chromosome 15 is involved in tumorigenesis. The discovery that Py DNA was integrated at specific sites in host chromosomes raised the questions of whether such integrations were correlated with the activation of specific oncogenes. The rearrangements of the c-myc proto-oncogene observed on Southern blot analysis for both tumors, along with similar integration patterns of Py sequences, the overexpression of the c-myc gene, and the synthesis of abnormal oversized hybrid transcripts between c-myc and Py genes, favor this hypothesis. Finally, the analysis of episomal Py DNA in various tumors shows viral populations presenting a specific deletion in a part of the Py late region. This deleted region in the episomal virus genome was systematically found integrated in chromosomal DNA, thus arguing for the importance of Py integration in the induction of mammary tumor.

Adenovirus type 9 E4 open reading frame 1 encodes a transforming protein required for the production of mammary tumors in rats

The E4 region of human adenovirus type 9 (Ad9) transforms established rat embryo fibroblasts and encodes an essential determinant for the production of estrogen-dependent mammary tumors in rats. Testing of the seven Ad9 E4 open reading frames (ORFs) individually for transformation of the established rat embryo fibroblast cell line CREF indicated that only Ad9 E4 ORF1 possessed a significant ability to generate transformed foci on these cells. In contrast, the E4 ORF1 sequences from human Ad5 and Ad12 lacked the transforming potential exhibited by Ad9 E4 ORF1. Cell lines derived from Ad9 E4 ORF1-transformed foci expressed the 14-kDa Ad9 E4 ORF1 protein and formed colonies in soft agar. In addition, the Ad9 E4 ORF1 protein was required for initiation of mammary oncogenesis in vivo, as E4 ORF1 mutant viruses failed while E4 ORF2 and ORF3 mutant viruses succeeded in eliciting mammary tumors in animals. A role for Ad9 E4 ORF1 in tumor maintenance was suggested by the fact that 100% of virus-induced mammary tumors expressed the E4 ORF1 protein. Taken together, the facts that the Ad9 E4 ORF1 protein exhibits transforming potential in culture and is required by Ad9 to produce mammary tumors in animals suggest that Ad9 E4 ORF1 is a new viral oncoprotein.

Bovine mammary myoepithelial cells. 1. Isolation, culture, and characterization

The objective of this study was to isolate, purify, culture, and characterize myoepithelial cells from bovine mammary glands. Myoepithelial cells were separated from other mammary and blood cells after collagenase digestion and centrifugation using metrizoate-ficoll gradients. Myoepithelial cells were identified by their characteristic morphology and cloned using selective detachment. They contained many densely packed myofilaments, very few cytoplasmic organelles, elongated surface projections, and a dense, irregularly shaped nuclei. Some cells were as large as 1.2 mm in culture. Myoepithelial cells contained an extensive network of cytoskeletal proteins, including alpha-smooth muscle actin, alpha-actinin, and vimentin. When cultured, they tended to repel one another and never grew as closely associated cells. The myoepithelial nature of these cells was verified by showing that they contracted in response to oxytocin, bound oxytocin, and did not produce casein. Myoepithelial cells from fetal and lactating glands grew very well in culture. Active division of myoepithelial cells could be maintained for at least 3 mo, and cells could be serially subcultured at least seven times. The successful isolation and culture of bovine mammary myoepithelial cells make utilization of these cells possible in order to study their role in mammary growth and differentiation and milk ejection.

Requirement for the adenovirus type 9 E4 region in production of mammary tumors

Oncogenic viruses demonstrating a strict tropism for the mammary gland provide special opportunities to study the susceptibility of this tissue to neoplasia. In rats, human adenovirus type 9 (Ad9) elicits mammary fibroadenomas that are similar to common breast tumors in women, as well as phyllodes-like tumors and mammary sarcomas. By constructing recombinant adenoviruses between Ad9 and Ad26 (a related nontumorigenic virus), it was shown that the Ad9 E4 region was absolutely required to produce these mammary tumors. This indicates that an adenovirus gene located outside the classic transforming region (E1) can significantly influence the in vivo oncogenicity of an adenovirus. Consistent with a direct role in mammary gland oncogenesis, the Ad9 E4 region also exhibited transforming properties in vitro. Therefore, the Ad9 E4 region is a viral oncogene specifically involved in mammary gland tumorigenesis.