Sp100 Isoform-Specific Regulation of Human Adenovirus 5 Gene Expression

Abstract

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. IMPORTANCEWe 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-NBassociated 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.

Adenovirus E1A Targets the DREF Nuclear Factor To Regulate Virus Gene Expression, DNA Replication, and Growth

“…As expected, in cells treated with a control siRNA, the 72k DBP localized to distinct subnuclear domains (Fig. 6B, top row), which constitute the viral replication centers reported by others (34,35). DREF colocalized with the 72k DBP.…”

Multifaceted Histone H3 Methylation and Phosphorylation Readout by the Plant Homeodomain Finger of Human Nuclear Antigen Sp100C

“…In human fibroblasts, IFN-␤ treatment changes the differential splicing of the Sp100 transcripts in favor of the Sp100C isoform, which blocks the transcription of the herpes simplex virus type 1 (HSV-1) immediate early genes ICP0 and ICP4 (7,8). Adenovirus infection induces relocalization of Sp100C from promyelocytic leukemia nuclear bodies to viral replication centers, probably in order to repress viral factor transcription at the chromatin level in a manner similar to epigenetic reader SPOC1 (survival time-associated PHD protein in ovarian cancer 1/PHF13) (6).…”

“…Sp100 is a constitutive component of promyelocytic leukemia nuclear bodies and serves as an intrinsic immune response factor along with PML, DAXX, and ATRX in a small ubiquitin-like modifier (SUMO) 2 -dependent manner (5). Human Sp100 proteins are transcribed from a single gene and alternatively spliced into four isoforms designated Sp100A, Sp100B, Sp100C, and Sp100-HMG, all of which harbor a heterochromatin protein 1 (HP1)-interacting region at the N terminus (6). The longer isoforms B, C, and HMG share one additional C-terminal SAND domain (named after Sp100, AIRE-1, NucP41/75, DEAF-1) that is preferable for unmethylated CpG DNA binding.…”

Promyelocytic leukemia protein isoform II inhibits infection by human adenovirus type 5 through effects on HSP70 and the interferon response

“…Human adenovirus type 5 (HAdV-C5, Ad5) infection also targets PML, rearranging it from PML-NB into track-like structures (Carvalho et al, 1995;Doucas et al, 1996); other PML-NB components are also redistributed, including some into virus replication centres (Berscheminski et al, 2014;Doucas et al, 1996). The Ad5 E4 Orf3 protein, which forms nuclear tracks by self-association (Ou et al, 2012;Patsalo et al, 2012), acts directly on PML-II, binding to its unique C-terminal domain to cause the redistribution of all PML isoforms (Hoppe et al, 2006;Leppard et al, 2009).…”

“…These findings fit a model in which PML-NBs or their components are broadly antiviral and hence viruses have evolved functions to disrupt these activities in order to favour virus replication. Alternatively, and not mutually exclusively, the interaction of viruses with PML-NB may have been selected to favour the virus, with disruption of PML-NBs liberating proteins that act to increase virus production (Berscheminski et al, 2014).…”