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

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 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.

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.

E4orf1 Suppresses E1B-Deleted Adenovirus Vaccine-Induced Immune Responses

As demonstrated by the recent COVID pandemic, vaccines can reduce the burden arising from infectious agents. Adenoviruses (Ads) with deletion of the early region 1B55K (ΔE1B Ad) are currently being explored for use in vaccine delivery. ΔE1B Ads are different from Ads with deletions in early region 1 and early region 3 (ΔE1/E3) used in most Ad vaccine vectors in that they contain the Ad early region 1A (E1A), and therefore the ability to replicate. Common to almost all Ads that are being explored for clinical use is the Ad early region 4 (E4). Among the E4 genes is open reading frame 1 (E4orf1), which mediates signals through the PI3-kinase/Akt pathway that is known to modulate immune responses. This suggests that E4orf1 might also modulate immune responses, although it has remained unexplored in ΔE1B Ad. Here, we show that cells infected with an E1B55K and E4orf1-deleted (ΔE41) Ad exhibited reduced levels of phosphorylated Akt (Ser473 and Thr308)) and expressed different intrinsic innate immune cytokines from those induced in cells infected with an E4orf1-containing, ΔE1B parental Ad that exhibited elevated levels of phosphorylated Akt. Rhesus macaques immunized with a ΔE41 Ad that expressed rhFLSC (HIV-1BaL gp120 linked to rhesus CD4 D1 and D2), exhibited higher levels of rhFLSC-specific interferon γ-producing memory T-cells, higher titers of rhFLSC-specific IgG1 binding antibody in serum, and antibodies able to mediate antibody-dependent cellular cytotoxicity (ADCC) with greater killing capacity than the ΔE1B Ad. Therefore, E4orf1, perhaps by acting through the PI3-kinase/Akt pathway, limits intrinsic innate and system-wide adaptive immune responses that are important for improved ΔE1B Ad-based vaccines.

Intracellular trafficking of adeno-associated virus (AAV) vectors: challenges and future directions

In the last two decades, recombinant adeno-associated virus has emerged as the most popular gene therapy vector. Recently AAV gene therapy has been approved by the FDA for the treatment of two rare genetic disorders, namely the early childhood blindness disease Leber congenital amaurosis and spinal muscular atrophy (SMA). As is the case for the treatment of SMA, if the AAV vector must be administered systemically, very high vector doses are often required for therapeutic efficacy. But higher vector doses inevitably increase the risk of adverse events. The tragic death of three children in a clinical trial to treat X-linked myotubular myopathy with an AAV vector has thrown this limitation into sharp relief. Regardless of the precise cause(s) that led to the death of the two children, it is critical that we develop better AAV vectors to achieve therapeutic levels of expression with lower vector doses. To transduce successfully a target cell, AAV has to overcome both systemic as well as cellular roadblocks. In this review, we discuss some of the most prominent cellular roadblocks that AAV must get past to deliver successfully its therapeutic payload. We also highlight recent advancements in our knowledge of AAV biology that can potentially be harnessed to improve AAV vector performance and thereby make AAV gene therapy safer.

A New Story of the Three Magi: Scaffolding Proteins and lncRNA Suppressors of Cancer

Scaffolding molecules exert a critical role in orchestrating cellular response through the spatiotemporal assembly of effector proteins as signalosomes. By increasing the efficiency and selectivity of intracellular signaling, these molecules can exert (anti/pro)oncogenic activities. As an archetype of scaffolding proteins with tumor suppressor property, the present review focuses on MAGI1, 2, and 3 (membrane-associated guanylate kinase inverted), a subgroup of the MAGUK protein family, that mediate networks involving receptors, junctional complexes, signaling molecules, and the cytoskeleton. MAGI1, 2, and 3 are comprised of 6 PDZ domains, 2 WW domains, and 1 GUK domain. These 9 protein binding modules allow selective interactions with a wide range of effectors, including the PTEN tumor suppressor, the β-catenin and YAP1 proto-oncogenes, and the regulation of the PI3K/AKT, the Wnt, and the Hippo signaling pathways. The frequent downmodulation of MAGIs in various human malignancies makes these scaffolding molecules and their ligands putative therapeutic targets. Interestingly, MAGI1 and MAGI2 genetic loci generate a series of long non-coding RNAs that act as a tumor promoter or suppressor in a tissue-dependent manner, by selectively sponging some miRNAs or by regulating epigenetic processes. Here, we discuss the different paths followed by the three MAGIs to control carcinogenesis.

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.

Characterization of the adipogenic protein E4orf1 from adenovirus 36 through an in silico approach

Adenovirus 36 (Ad-36) is related to human obesity due to its adipogenic activity mediated by the early 4 open reading frame 1 (E4orf1) protein. Mechanisms underlying the adipogenic effect of E4orf1 are not completely understood; however, the proliferation and differentiation of fat cells are increased through the activation of the phosphatidyl inositol 3 kinase pathway by binding proteins containing PDZ domain. This study characterized E4orf1 tridimensional structure and analyzed its interactions with PDZ domain-containing proteins in order to provide new information about the behavior of this viral protein and its targets, which could provide an interesting druggable target for obesity-related cardiometabolic alterations. In silico strategies such as homology modeling, docking, and molecular dynamics (MD) were used to study the interaction of E4orf1 with five PDZ domains of disk large homolog 1 (PDZ-1 and PDZ-2), membrane-associated guanylate kinase 1 (PDZ-3), and multi-PDZ domain protein 1 (PDZ-7 and PDZ-10). Mutagenesis analysis of selected residues was performed to evaluate their effects on the stabilization of E4orf1:PDZ complexes. MD simulations showed that the E4orf1:PDZ10 complex was more stable than the others ones. The highly hydrophobic residues at the C-terminal region (114-125) of the E4orf1 are essential in the initial phase stabilization of the complexes. Moreover, the residues 80-85 in the core region contribute to longer stabilization of the E4orf1:PDZ10 complex, a result that was confirmed by in silico mutagenesis. In conclusion, E4orf1 forms a stable complex with PDZ10 domain, and the residues 80-85 are of particular importance. The characterization of E4orf1 interactions with PDZ domains provides an initial approach to discover druggable targets for Ad-36-induced obesity.

Metabolic Reprogramming of the Host Cell by Human Adenovirus Infection

Viruses are obligate intracellular parasites that alter many cellular processes to create an environment optimal for viral replication. Reprogramming of cellular metabolism is an important, yet underappreciated feature of many viral infections, as this ensures that the energy and substrates required for viral replication are available in abundance. Human adenovirus (HAdV), which is the focus of this review, is a small DNA tumor virus that reprograms cellular metabolism in a variety of ways. It is well known that HAdV infection increases glucose uptake and fermentation to lactate in a manner resembling the Warburg effect observed in many cancer cells. However, HAdV infection induces many other metabolic changes. In this review, we integrate the findings from a variety of proteomic and transcriptomic studies to understand the subtleties of metabolite and metabolic pathway control during HAdV infection. We review how the E4ORF1 protein of HAdV enacts some of these changes and summarize evidence for reprogramming of cellular metabolism by the viral E1A protein. Therapies targeting altered metabolism are emerging as cancer treatments, and similar targeting of aberrant components of virally reprogrammed metabolism could have clinical antiviral applications.

Molecular Evolution of Human Adenovirus (HAdV) Species C

Currently, 88 different Human Adenovirus (HAdV) types are grouped into seven HAdV species A to G. Most types (57) belong to species HAdV-D. Recombination between capsid genes (hexon, penton and fiber) is the main factor contributing to the diversity in species HAdV-D. Noteworthy, species HAdV-C contains so far only five types, although species HAdV-C is highly prevalent and clinically significant in immunosuppressed patients. Therefore, the evolution of species HAdV-C was studied by generating 51 complete genome sequences from circulating strains. Clustering of the whole genome HAdV-C sequences confirmed classical typing results (fifteen HAdV-C1, thirty HAdV-C2, four HAdV-C5, two HAdV-C6). However, two HAdV-C2 strains had a novel penton base sequence and thus were re-labeled as the novel type HAdV-C89. Fiber and early gene region 3 (E3) sequences clustered always with the corresponding prototype sequence but clustering of the E4 region indicated recombination events in 26 out of the 51 sequenced specimens. Recombination of the E1 gene region was detected in 16 circulating strains. As early gene region sequences are not considered in the type definition of HAdVs, evolution of HAdV-C remains on the subtype level. Nonetheless, recombination of the E1 and E4 gene regions may influence the virulence of HAdV-C strains.

Tissue-specific endothelial cells: a promising approach for augmentation of soft tissue repair in orthopedics

Biologics are playing an increasingly significant role in the practice of modern medicine and surgery in general and orthopedics in particular. Cell-based approaches are among the most important and widely used modalities in orthopedic biologics, with mesenchymal stem cells and other multi/pluripotent cells undergoing evaluation in numerous preclinical and clinical studies. On the other hand, fully differentiated endothelial cells (ECs) have been found to perform critical roles in homeostasis of visceral tissues through production of an adaptive panel of so-called "angiocrine factors." This newly discovered function of ECs renders them excellent candidates for novel approaches in cell-based biologics. Here, we present a review of the role of ECs and angiocrine factors in some visceral tissues, followed by an overview of current cell-based approaches and a discussion of the potential applications of ECs in soft tissue repair.

Adenovirus Protein E4-ORF1 Activation of PI3 Kinase Reveals Differential Regulation of Downstream Effector Pathways in Adipocytes

Insulin activation of phosphatidylinositol 3-kinase (PI3K) regulates metabolism, including the translocation of the Glut4 glucose transporter to the plasma membrane and inactivation of the FoxO1 transcription factor. Adenoviral protein E4-ORF1 stimulates cellular glucose metabolism by mimicking growth-factor activation of PI3K. We have used E4-ORF1 as a tool to dissect PI3K-mediated signaling in adipocytes. E4-ORF1 activation of PI3K in adipocytes recapitulates insulin regulation of FoxO1 but not regulation of Glut4. This uncoupling of PI3K effects occurs despite E4-ORF1 activating PI3K and downstream signaling to levels achieved by insulin. Although E4-ORF1 does not fully recapitulate insulin's effects on Glut4, it enhances insulin-stimulated insertion of Glut4-containing vesicles to the plasma membrane independent of Rab10, a key regulator of Glut4 trafficking. E4-ORF1 also stimulates plasma membrane translocation of ubiquitously expressed Glut1 glucose transporter, an effect that is likely essential for E4-ORF1 to promote an anabolic metabolism in a broad range of cell types.

Hepatic Expression of Adenovirus 36 E4ORF1 Improves Glycemic Control and Promotes Glucose Metabolism Through AKT Activation

Considering that impaired proximal insulin signaling is linked with diabetes, approaches that enhance glucose disposal independent of insulin signaling are attractive. In vitro data indicate that the E4ORF1 peptide derived from human adenovirus 36 (Ad36) interacts with cells from adipose tissue, skeletal muscle, and liver to enhance glucose disposal, independent of proximal insulin signaling. Adipocyte-specific expression of Ad36E4ORF1 improves hyperglycemia in mice. To determine the hepatic interaction of Ad36E4ORF1 in enhancing glycemic control, we expressed E4ORF1 of Ad36 or Ad5 or fluorescent tag alone by using recombinant adeno-associated viral vector in the liver of three mouse models. In db/db or diet-induced obesity (DIO) mice, hepatic expression of Ad36E4ORF1 but not Ad5E4ORF1 robustly improved glycemic control. In normoglycemic wild-type mice, hepatic expression of Ad36E4ORF1 lowered nonfasting blood glucose at a high dose of expression. Of note, Ad36E4ORF1 significantly reduced insulin levels in db/db and DIO mice. The improvement in glycemic control was observed without stimulation of the proximal insulin signaling pathway. Collectively, these data indicate that Ad36E4ORF1 is not a typical sensitizer, mimetic, or secretagogue of insulin. Instead, it may have insulin-sparing action, which seems to reduce the need for insulin and, hence, to reduce insulin levels.

Herpesviruses dUTPases: A New Family of Pathogen-Associated Molecular Pattern (PAMP) Proteins with Implications for Human Disease

The human herpesviruses are ubiquitous viruses and have a prevalence of over 90% in the adult population. Following a primary infection they establish latency and can be reactivated over a person's lifetime. While it is well accepted that human herpesviruses are implicated in numerous diseases ranging from dermatological and autoimmune disease to cancer, the role of lytic proteins in the pathophysiology of herpesvirus-associated diseases remains largely understudies. Only recently have we begun to appreciate the importance of lytic proteins produced during reactivation of the virus, in particular the deoxyuridine triphosphate nucleotidohydrolases (dUTPase), as key modulators of the host innate and adaptive immune responses. In this review, we provide evidence from animal and human studies of the Epstein-Barr virus as a prototype, supporting the notion that herpesviruses dUTPases are a family of proteins with unique immunoregulatory functions that can alter the inflammatory microenvironment and thus exacerbate the immune pathology of herpesvirus-related diseases including myalgic encephalomyelitis/chronic fatigue syndrome, autoimmune diseases, and cancer.

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.

Targeted Gene Resequencing (Astrochip) to Explore the Tripartite Synapse in Autism-Epilepsy Phenotype with Macrocephaly

The frequent co-occurrence of autism spectrum disorders (ASD) and epilepsy, or paroxysmal EEG abnormalities, defines a condition termed autism-epilepsy phenotype (AEP). This condition results, in some cases , from dysfunctions of glial inwardly rectifying potassium channels (Kir), which are mainly expressed in astrocytes where they mediate neuron-glia communication. Macrocephaly is also often comorbid with autism-epilepsy (autism-epilepsy phenotype with macrocephaly, MAEP), and it is tempting to hypothesize that shared pathogenic mechanisms might explain concurrence of these conditions. In the present study, we assessed whether protein pathways involved, along with Kir channels, in astrocyte-neuron interaction at the tripartite synapse play a role in the etiopathogenesis of MAEP. Using a targeted resequencing methodology, we investigated the coding regions of 35 genes in 61 patients and correlated genetic results with clinical features. Variants were subdivided into 12 classes and clustered into four groups. We detected rare or previously unknown predicted deleterious missense changes in GJA1, SLC12A2, SNTA1, EFNA3, CNTNAP2, EPHA4, and STXBP1 in seven patients and two high-frequency variants in DLG1 in six individuals. We also found that a group of variants (predicted deleterious and non-coding), segregating with the comorbid MAEP/AEP subgroups, belong to proteins specifically involved in glutamate transport and metabolism (namely, SLC17A6, GRM8, and GLUL), as well as in potassium conductance (KCNN3). This "endophenotype-oriented" study, performed using a targeted strategy, helped to further delineate part of the complex genetic background of ASD, particularly in the presence of coexisting macrocephaly and/or epilepsy/paroxysmal EEG, and suggests that use of stringent clinical clustering might be an approach worth adopting in order to unravel the complex genomic data in neurodevelopmental disorders.

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.

Human herpesviruses-encoded dUTPases: a family of proteins that modulate dendritic cell function and innate immunity

We have previously shown that Epstein-Barr virus (EBV)-encoded dUTPase can modulate innate immune responses through the activation of TLR2 and NF-κB signaling. However, whether this novel immune function of the dUTPase is specific for EBV or a common property of the Herpesviridae family is not known. In this study, we demonstrate that the purified viral dUTPases encoded by herpes simplex virus type 2 (HSV-2), human herpesvirus-6A (HHV-6A), human herpesvirus-8 (HHV-8) and varicella-zoster virus (VZV) differentially activate NF-κB through ligation of TLR2/TLR1 heterodimers. Furthermore, activation of NF-κB by the viral dUTPases was inhibited by anti-TLR2 blocking antibodies (Abs) and the over-expression of dominant-negative constructs of TLR2, lacking the TIR domain, and MyD88 in human embryonic kidney 293 cells expressing TLR2/TLR1. In addition, treatment of human dendritic cells and PBMCs with the herpesviruses-encoded dUTPases from HSV-2, HHV-6A, HHV-8, and VZV resulted in the secretion of the inflammatory cytokines IL-1β, IL-6, IL-8, IL-12, TNF-α, IL-10, and IFN-γ. Interestingly, blocking experiments revealed that the anti-TLR2 Ab significantly reduced the secretion of cytokines by the various herpesviruses-encoded dUTPases (p < 0.05). To our knowledge, this is the first report demonstrating that a non-structural protein encoded by herpesviruses HHV-6A, HHV-8, VZV and to a lesser extent HSV-2 is a pathogen-associated molecular pattern. Our results reveal a novel function of the virus-encoded dUTPases, which may be important to the pathophysiology of diseases caused by these viruses. More importantly, this study demonstrates that the immunomodulatory functions of dUTPases are a common property of the Herpesviridae family and thus, the dUTPase could be a potential target for the development of novel therapeutic agents against infections caused by these herpesviruses.

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.

Metabolism goes viral

Viral and cellular oncogenes converge in targeting critical protein interaction networks to reprogram the cellular DNA and protein replication machinery for pathological replication. In this issue, Thai et al. (2014) show that adenovirus E4ORF1 activates MYC glycolytic targets to induce a Warburg-like effect that converts glucose into nucleotides for viral replication.

Adenovirus E4ORF1-induced MYC activation promotes host cell anabolic glucose metabolism and virus replication

Virus infections trigger metabolic changes in host cells that support the bioenergetic and biosynthetic demands of viral replication. Although recent studies have characterized virus-induced changes in host cell metabolism (Munger et al., 2008; Terry et al., 2012), the molecular mechanisms by which viruses reprogram cellular metabolism have remained elusive. Here, we show that the gene product of adenovirus E4ORF1 is necessary for adenovirus-induced upregulation of host cell glucose metabolism and sufficient to promote enhanced glycolysis in cultured epithelial cells by activation of MYC. E4ORF1 localizes to the nucleus, binds to MYC, and enhances MYC binding to glycolytic target genes, resulting in elevated expression of specific glycolytic enzymes. E4ORF1 activation of MYC promotes increased nucleotide biosynthesis from glucose intermediates and enables optimal adenovirus replication in primary lung epithelial cells. Our findings show how a viral protein exploits host cell machinery to reprogram cellular metabolism and promote optimal progeny virion generation.

Epstein-Barr virus encoded dUTPase containing exosomes modulate innate and adaptive immune responses in human dendritic cells and peripheral blood mononuclear cells

We have recently demonstrated that Epstein-Barr virus (EBV)-encoded deoxyuridine triphosphate nucleotidohydrolase (dUTPase) modulates innate immunity in human primary monocyte-derived macrophages through toll-like receptor (TLR) 2 leading to NF-κB activation and the production of pro-inflammatory cytokines. Our previous depletion studies indicated that dendritic cells (DCs) may also be a target of the EBV-encoded dUTPase. However, the role of EBV-encoded dUTPase in DC activation/function and its potential contribution to the inflammatory cellular milieu characteristic of EBV-associated diseases remains poorly understood. In the present study, we demonstrate that EBV-encoded dUTPase significantly altered the expression of genes involved in oncogenesis, inflammation and viral defense mechanisms in human primary DCs by microarray analysis. Proteome array studies revealed that EBV-encoded dUTPase modulates DC immune responses by inducing the secretion of pro-inflammatory T_H1/T_H17 cytokines. More importantly, we demonstrate that EBV-encoded dUTPase is secreted in exosomes from chemically induced Raji cells at sufficient levels to induce NF-κB activation and cytokine secretion in primary DCs and peripheral blood mononuclear cells (PBMCs). Interestingly, the production of pro-inflammatory cytokines in DCs and PBMCs was TLR2-dependent. Together these findings suggest that the EBV-encoded dUTPase may act as an intercellular signaling molecule capable of modulating the cellular microenvironment and thus, it may be important in the pathophysiology of EBV related diseases.

Insulin sparing action of adenovirus 36 and its E4orf1 protein

Additional drugs are required to effectively manage diabetes and its complications. Recent studies have revealed protective effects of Ad36, a human adenovirus, and its E4orf1 protein on glucose disposal, which may be creatively harnessed to develop novel anti-diabetic agents. Experimental Ad36 infection improves hyperglycemia in animal models and natural Ad36 infection in humans is associated with better glycemic control. Available data indicate distinctive advantages for a drug that may mimic the action of Ad36/E4orf1. The key features of such a potential drug include the ability to increase glucose uptake by adipose tissue and skeletal muscle, to reduce hepatic glucose output independent of proximal insulin signaling, and to up-regulate adiponectin and its hepatic action. The effect of Ad36/E4orf1 on hepatocyte metabolism suggests a role for treating hepatic steatosis. Despite these potential advantages, considerable research is required before such a drug is developed. The in vivo efficacy and safety of E4orf1 in improving hyperglycemia remain unknown, and an appropriate drug delivery system is required. Nonetheless, Ad36 E4orf1 offers a research opportunity to develop a new anti-diabetic agent with multiple potential advantages and conceptually advances the use of a rather unconventional source, microbial proteins, for anti-diabetic drug development.

Intracellular transport of recombinant adeno-associated virus vectors

Recombinant adeno-associated viral vectors (rAAVs) have been widely used for gene delivery in animal models, and are currently evaluated for human gene therapy after successful clinical trials in the treatment of inherited, degenerative or acquired diseases, such as Leber congenital amaurosis, Parkinson disease or heart failure. However, limitations in vector tropism, such as limited tissue specificity and insufficient transduction efficiencies of particular tissues and cell types, still preclude therapeutic applications in certain tissues. Wild-type adeno-associated viruses (AAVs) are defective viruses that require the presence of a helper virus to complete their life cycle. On the one hand, this unique property makes AAV vectors one of the safest available viral vectors for gene delivery. On the other, it also represents a potential obstacle because rAAV vectors have to overcome several biological barriers in the absence of a helper virus to transduce successfully a cell. Consequently, a better understanding of the cellular roadblocks that limit rAAV gene delivery is crucial and, during the last 15 years, numerous studies resulted in an expanding body of knowledge of the intracellular trafficking pathways of rAAV vectors. This review describes our current understanding of the mechanisms involved in rAAV attachment to target cells, endocytosis, intracellular trafficking, capsid processing, nuclear import and genome release with an emphasis on the most recent discoveries in the field and the emerging strategies used to improve the efficiency of AAV-derived vectors.

Genomic characterization of human adenovirus 36, a putative obesity agent

Increased levels of serum antibody titers against human adenovirus 36 (HAdV-D36) are associated with human obesity and experimental obesity in laboratory animals. While HAdV-D36 has been studied as an infectious agent implicated in obesity for over a decade, the complete genome sequence and its analysis have yet to be reported. A detailed analysis of the genome sequence of HAdV-D36 may be important to understand its role in obesity. Genomic and bioinformatic comparisons with other HAdVs identified differences that suggested unique functions. Global pairwise genome alignment with all sequenced human adenovirus D (HAdV-D) genomes revealed areas of nonconserved sequences in the hexon, E3 CR1 beta, E3 CR1 gamma, and fiber genes. Phylogenetic analysis of all HAdV-D36 proteins confirmed that this virus belongs to species Human adenovirus D. This genomic analysis of HAdV-D36 provides an important tool for comprehending the role that this unique adenovirus may play in human obesity. Low amino acid sequence identity in the E3 CR1 beta and CR1 gamma genes may suggest distinctive roles for these proteins. Furthermore, the predicted molecular models of the HAdV-D36 fiber protein seem to implicate a unique tissue tropism for HAdV-D36.

MUPP1 complexes renal K+ channels to alter cell surface expression and whole cell currents

We previously found that the Ca(2+)-sensing receptor (CaR) interacts with and inactivates the inwardly rectifying K(+) channel Kir4.2 that is expressed in the kidney cortex and that has a COOH-terminal PDZ domain. To identify potential scaffolding proteins that could organize a macromolecular signaling complex involving the CaR and Kir4.2, we used yeast two-hybrid cloning with the COOH-terminal 125 amino acids (AA) of Kir4.2 as bait to screen a human kidney cDNA library. We identified two independent partial cDNAs corresponding to the COOH-terminal 900 AA of MUPP1, a protein containing 13 PDZ binding domains that is expressed in the kidney in tight junctions and lateral borders of epithelial cells. When expressed in human embryonic kidney (HEK)-293 cells, Kir4.2 coimmunoprecipitates reciprocally with MUPP1 but not with a Kir4.2 construct lacking the four COOH-terminal amino acids, Kir5.1, or the CaR. MUPP1 and Kir4.2 coimmunoprecipitate reciprocally from rat kidney cortex extracts. Coexpression of MUPP1 with Kir4.2 in HEK-293 cells leads to reduced cell surface expression of Kir4.2 as assessed by cell surface biotinylation. Coexpression of MUPP1 and Kir4.2 in Xenopus oocytes results in reduced whole cell currents compared with expression of Kir4.2 alone, whereas expression of Kir4.2DeltaPDZ results in minimal currents and is not affected by coexpression with MUPP1. Immunofluorescence studies of oocytes demonstrate that MUPP1 reduces Kir4.2 membrane localization. These results indicate that Kir4.2 interacts selectively with MUPP1 to affect its cell surface expression. Thus MUPP1 and Kir4.2 may participate in a protein complex in the nephron that could regulate transport of K(+) as well as other ions.

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.

Generation of a functional and durable vascular niche by the adenoviral E4ORF1 gene

Vascular cells contribute to organogenesis and tumorigenesis by producing unknown factors. Primary endothelial cells (PECs) provide an instructive platform for identifying factors that support stem cell and tumor homeostasis. However, long-term maintenance of PECs requires stimulation with cytokines and serum, resulting in loss of their angiogenic properties. To circumvent this hurdle, we have discovered that the adenoviral E4ORF1 gene product maintains long-term survival and facilitates organ-specific purification of PECs, while preserving their vascular repertoire for months, in serum/cytokine-free cultures. Lentiviral introduction of E4ORF1 into human PECs (E4ORF1(+) ECs) increased the long-term survival of these cells in serum/cytokine-free conditions, while preserving their in vivo angiogenic potential for tubulogenesis and sprouting. Although E4ORF1, in the absence of mitogenic signals, does not induce proliferation of ECs, stimulation with VEGF-A and/or FGF-2 induced expansion of E4ORF1(+) ECs in a contact-inhibited manner. Indeed, VEGF-A-induced phospho MAPK activation of E4ORF1(+) ECs is comparable with that of naive PECs, suggesting that the VEGF receptors remain functional upon E4ORF1 introduction. E4ORF1(+) ECs inoculated in implanted Matrigel plugs formed functional, patent, humanized microvessels that connected to the murine circulation. E4ORF1(+) ECs also incorporated into neo-vessels of human tumor xenotransplants and supported serum/cytokine-free expansion of leukemic and embryonal carcinoma cells. E4ORF1 augments survival of PECs in part by maintaining FGF-2/FGF-R1 signaling and through tonic Ser-473 phosphorylation of Akt, thereby activating the mTOR and NF-kappaB pathways. Therefore, E4ORF1(+) ECs establish an Akt-dependent durable vascular niche not only for expanding stem and tumor cells but also for interrogating the roles of vascular cells in regulating organ-specific vascularization and tumor neo-angiogenesis.

Functionally distinct monomers and trimers produced by a viral oncoprotein

While the process of homo-oligomer formation and disassembly into subunits represents a common strategy to regulate protein activity, reports of proteins in which the subunit and homo-oligomer perform independent functions are scarce. Tumorigenesis induced by the adenovirus E4-ORF1 oncoprotein depends on its binding to a select group of cellular PDZ proteins, including MUPP1, MAGI-1, ZO-2 and Dlg1. We report here that in cells E4-ORF1 exists as both a monomer and trimer and that monomers specifically bind and sequester MUPP1, MAGI-1 and ZO-2 within insoluble complexes whereas trimers specifically bind Dlg1 and promote its translocation to the plasma membrane. This work exposes a novel strategy wherein the oligomerization state of a protein not only determines the capacity to bind separate related targets but also couples the interactions to different functional consequences.