Transcriptional Activation of the Adenoviral Genome Is Mediated by Capsid Protein VI

Gene expression of DNA viruses requires nuclear import of the viral genome. Human Adenoviruses (Ads), like most DNA viruses, encode factors within early transcription units promoting their own gene expression and counteracting cellular antiviral defense mechanisms. The cellular transcriptional repressor Daxx prevents viral gene expression through the assembly of repressive chromatin remodeling complexes targeting incoming viral genomes. However, it has remained unclear how initial transcriptional activation of the adenoviral genome is achieved. Here we show that Daxx mediated repression of the immediate early Ad E1A promoter is efficiently counteracted by the capsid protein VI. This requires a conserved PPxY motif in protein VI. Capsid proteins from other DNA viruses were also shown to activate the Ad E1A promoter independent of Ad gene expression and support virus replication. Our results show how Ad entry is connected to transcriptional activation of their genome in the nucleus. Our data further suggest a common principle for genome activation of DNA viruses by counteracting Daxx related repressive mechanisms through virion proteins

The whole genome sequence of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), reveals insights into the biology and adaptive evolution of a highly invasive pest species

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a major destructive insect pest due to its broad host range, which includes hundreds of fruits and vegetables. It exhibits a unique ability to invade and adapt to ecological niches throughout tropical and subtropical regions of the world, though medfly infestations have been prevented and controlled by the sterile insect technique (SIT) as part of integrated pest management programs (IPMs). The genetic analysis and manipulation of medfly has been subject to intensive study in an effort to improve SIT efficacy and other aspects of IPM control

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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Sp100A is a tumor suppressor that activates p53-dependent transcription and counteracts E1A/E1B-55K-mediated transformation.

Human adenoviruses (HAdV) are used as a model system to investigate tumorigenic processes in mammalian cells where the viral oncoproteins E1A and E1B-55K are absolutely required for oncogenic transformation, because they simultaneously accelerate cell cycle progression and inhibit tumor suppressor proteins such as p53, although the underlying mechanism is still not understood in detail. In our present study, we provide evidence that E1B-55K binding to the PML-NB component Sp100A apparently has an essential role in regulating adenovirus-mediated transformation processes. Specifically, when this E1B-55K/Sp100A complex recruits p53, Sp100A-induced activation of p53 transcriptional activity is effectively abolished. Hence, Sp100A exhibits tumor-suppressive activity, not only by stabilizing p53 transactivation but also by depressing E1A/E1B-55K-mediated transformation. E1B-55K counteracts this suppressive activity, inducing Sp100A SUMOylation and sequestering the modified cellular factor into the insoluble matrix of the nucleus or into cytoplasmic inclusions. These observations provide novel insights into how E1B-55K modulates cellular determinants to maintain growth-promoting activity during oncogenic processes and lytic infection

Sp100 isoform-specific regulation of human adenovirus 5 gene expression

Promyelocytic leukemia nuclear bodies (PML-NBs) are nuclear structures that accumulate intrinsic host factors to restrict viral infections. To ensure viral replication, these must be limited by expression of viral early regulatory proteins that functionally inhibit PML-NB-associated antiviral effects. To benefit from the activating capabilities of Sp100A and simultaneously limit repression by Sp100B, -C, and -HMG, adenoviruses (Ads) employ several features to selectively and individually target these isoforms. Ads induce relocalization of Sp100B, -C, and -HMG from PML-NBs prior to association with viral replication centers. In contrast, Sp100A is kept at the PML tracks that surround the newly formed viral replication centers as designated sites of active transcription. We concluded that the host restriction factors Sp100B, -C, and -HMG are potentially inactivated by active displacement from these sites, whereas Sp100A is retained to amplify Ad gene expression. Ad-dependent loss of Sp100 SUMOylation is another crucial part of the virus repertoire to counteract intrinsic immunity by circumventing Sp100 association with HP1, therefore limiting chromatin condensation. We provide evidence that Ad selectively counteracts antiviral responses and, at the same time, benefits from PML-NB-associated components which support viral gene expression by actively recruiting them to PML track-like structures. Our findings provide insights into novel strategies for manipulating transcriptional regulation to either inactivate or amplify viral gene expression. IMPORTANCE We describe an adenoviral evasion strategy that involves isoform-specific and active manipulation of the PML-associated restriction factor Sp100. Recently, we reported that the adenoviral transactivator E1A targets PML-II to efficiently activate viral transcription. In contrast, the PML-associated proteins Daxx and ATRX are inhibited by early viral factors. We show that this concept is more intricate and significant than originally believed, since adenoviruses apparently take advantage of specific PML-NB-associated proteins and simultaneously inhibit antiviral measures to maintain the viral infectious program. Specifically, we observed Ad-induced relocalization of the Sp100 isoforms B, C, and HMG from PML-NBs juxtaposed with viral replication centers. In contrast, Sp100A is retained at Ad-induced PML tracks that surround the newly formed viral replication centers, acting as designated sites of active transcription. The host restriction factors Sp100B, -C, and -HMG are potentially inactivated by active displacement from these sites, whereas Sp100A is retained to amplify Ad gene expression

PML isoforms IV and V contribute to adenovirus-mediated oncogenic transformation by functionally inhibiting the tumor-suppressor p53

Although modulation of the cellular tumor-suppressor p53 is considered to have the major role in E1A/E1B-55K-mediated tumorigenesis, other promyelocytic leukemia nuclear body (PML-NB)/PML oncogenic domain (POD)-associated factors including SUMO, Mre11, Daxx, as well as the integrity of these nuclear bodies contribute to the transformation process. However, the biochemical consequences and oncogenic alterations of PML-associated E1B-55K by SUMO-dependent PML-IV and PML-V interaction have so far remained elusive. We performed mutational analysis to define a PML interaction motif within the E1B-55K polypeptide. Our results showed that E1B-55K/PML binding is not required for p53, Mre11 and Daxx interaction. We also observed that E1B-55K lacking subnuclear PML localization because of either PML-IV or PML-V-binding deficiency was no longer capable of mediating E1B-55K-dependent SUMOylation of p53, inhibition of p53-mediated transactivation or efficiently transforming primary rodent cells. These results together with the observation that E1B-55K-dependent SUMOylation of p53 is required for efficient cell transformation, provides evidence for the idea that the SUMO ligase activity of the E1B-55K viral oncoprotein is intimately linked to its growth-promoting oncogenic activities

Adenovirus Type 5 Early Region 1B 55K Oncoprotein-Dependent Degradation of Cellular Factor Daxx Is Required for Efficient Transformation of Primary Rodent Cells▿

Early region 1B 55K (E1B-55K) from adenovirus type 5 (Ad5) is a multifunctional regulator of lytic infection and contributes in vitro to complete cell transformation of primary rodent cells in combination with Ad5 E1A. Inhibition of p53 activated transcription plays a key role in processes by which E1B-55K executes its oncogenic potential. Nevertheless, additional functions of E1B-55K or further protein interactions with cellular factors of DNA repair, transcription, and apoptosis, including Mre11, PML, and Daxx, may also contribute to the transformation process. In line with previous results, we performed mutational analysis to define a Daxx interaction motif within the E1B-55K polypeptide. The results from these studies showed that E1B-55K/Daxx binding is not required for inhibition of p53-mediated transactivation or binding and degradation of cellular factors (p53/Mre11). Surprisingly, these mutants lost the ability to degrade Daxx and showed reduced transforming potential in primary rodent cells. In addition, we observed that E1B-55K lacking the SUMO-1 conjugation site (SCS/K104R) was sufficient for Daxx interaction but no longer capable of E1B-55K-dependent proteasomal degradation of the cellular factor Daxx. These results, together with the observation that E1B-55K SUMOylation is required for efficient transformation, provides evidence for the idea that SUMO-1-conjugated E1B-55K-mediated degradation of Daxx plays a key role in adenoviral oncogenic transformation. We assume that the viral protein contributes to cell transformation through the modulation of Daxx-dependent pathways. This further substantiates the assumption that further mechanisms for efficient transformation of primary cells can be separated from functions required for the inhibition of p53-stimulated transcription