Herpes Simplex Virus ICP0 Promotes both Histone Removal and Acetylation on Viral DNA during Lytic Infection

152

209

Whether host DNA receptors have any capacity to distinguish self from nonself at the molecular level is an outstanding question in the innate immunity of mammals. Here, by using quantitative assays and electron microscopy, we show that cooperatively assembling into filaments on dsDNA may serve as an integral mechanism by which human IFN-inducible protein-16 (IFI16) engages foreign DNA. IFI16 is essential for defense against a number of different pathogens, and its aberrant activity is also implicated in several autoimmune disorders, such as Sjögren syndrome. IFI16 cooperatively binds dsDNA in a length-dependent manner and clusters into distinct protein filaments even in the presence of excess dsDNA. Consequently, the assembled IFI16·dsDNA oligomers are clearly different from the conventional noninteracting entities resembling beads on a string. The isolated DNA-binding domains of IFI16 engage dsDNA without forming filaments and with weak affinity, and it is the non-DNA-binding pyrin domain of IFI16 that drives the cooperative filament assembly. The surface residues on the pyrin domain that mediate the cooperative DNA binding are conserved, suggesting that related receptors use a common mechanism. These results suggest that IFI16 clusters into signaling foci in a switch-like manner and that it is capable of using the size of naked dsDNA as a molecular ruler to distinguish self from nonself.cooperative filament formation | inflammasome R ecognition of foreign intracellular DNA is a widely conserved defense mechanism by which the innate immune system of mammals detects and responds to invading pathogens (1, 2). Using such a universal molecule as a major danger signal for detecting pathogens must be regulated in a stringent yet efficient manner. However, only a few deciding factors are known for the host innate immune system to selectively engage foreign DNA (i.e., nonself-DNA) while minimizing interactions with self-DNA, which include the compartmentalization of mammalian cells and the size of foreign DNA. These features, however, only raise more questions than provide answers. For example, the footprints of intracellular DNA receptors usually fall below 20 bp, and yet a long foreign DNA fragment [e.g., poly(dA:dT); ≥1,000 bp] is required to induce a robust innate immune response even in a normally DNA-free environment like the cytoplasm (1, 2). On the other hand, foreign DNA-sensing pathways also exist in the host nucleus in which DNA receptors must not respond to abundant self-DNA to prevent spurious activities (1, 2). Indeed, one of the major unresolved questions in understanding the DNA-sensing pathways of mammals is whether the host intracellular DNA receptors have any capacity to distinguish self-from nonself-DNA at the molecular level (2).Human IFN inducible protein-16 (IFI16) is an intracellular DNA receptor of innate immunity that belongs to the family of absent-in-melanoma-2 (AIM2)-like receptors (ALRs) (1-4). IFI16 senses DNA from invading pathogens in both the nucleus and cytoplasm [e.g., vaccinia virus...

Section: Discussionmentioning

confidence: 56%

Section: Discussionmentioning

confidence: 99%

Cooperative assembly of IFI16 filaments on dsDNA provides insights into host defense strategy

Morrone

Wang²,

Constantoulakis³

et al. 2013

152

209

“…Histones are rapidly deposited, likely via a cellular response to infection. Whereas the chromatin structure does not appear to be that of canonically spaced nucleosomes, the levels of genomeassociated nucleosomes are similar to that observed on cellular DNA (36). The role of chromatin in regulating HSV-1 gene expression is supported by (i) the presence of nucleosomes exhibiting repressive or activating modifications that correlate with repression or activation of viral gene expression (5,10,11,(36)(37)(38) and (ii) deposition of the histone variant H3.3 on the viral genome and the requirement for the H3.3 histone chaperone HIRA for efficient viral gene expression (39).…”

mentioning

confidence: 69%

“…Although the levels of nucleosomes on the genome appear to be reduced relative to cellular DNA at later times in infection (36,40), the absolute amount of viral DNA associated with histones increases during replication (36). Additionally, it has also been observed that histone H3.1 is incorporated in a replication dependent manner (39), indicating that some level of histone assembly occurs on replicated viral DNA.…”

mentioning

confidence: 96%

Transcriptional coactivator HCF-1 couples the histone chaperone Asf1b to HSV-1 DNA replication components

Peng

Nogueira

Vogel

et al. 2010

The cellular transcriptional coactivator HCF-1 interacts with numerous transcription factors as well as other coactivators and is a component of multiple chromatin modulation complexes. The protein is essential for the expression of the immediate early genes of both herpes simplex virus (HSV) and varicella zoster virus and functions, in part, by coupling chromatin modification components including the Set1 or MLL1 histone methyltransferases and the histone demethylase LSD1 to promote the installation of positive chromatin marks and the activation of viral immediately early gene transcription. Although studies have investigated the role of HCF-1 in both cellular and viral transcription, little is known about other processes that the protein may be involved in. Here we demonstrate that HCF-1 localizes to sites of HSV replication late in infection. HCF-1 interacts directly and simultaneously with both HSV DNA replication proteins and the cellular histone chaperone Asf1b, a protein that regulates the progression of cellular DNA replication forks via chromatin reorganization. Asf1b localizes with HCF-1 in viral replication foci and depletion of Asf1b results in significantly reduced viral DNA accumulation. The results support a model in which the transcriptional coactivator HCF-1 is a component of the HSV DNA replication assembly and promotes viral DNA replication by coupling Asf1b to DNA replication components. This coupling provides a novel function for HCF-1 and insights into the mechanisms of modulating chromatin during DNA replication.

“…Because ICP0 does not bind DNA, its most likely function is to recruit to the ND10 bodies at which the DNA is aggregated host proteins that derepress and enable expression of the genes encoded by the DNAs (17,18). Second, ICP0 does not discriminate between viral and irrelevant DNA deposited at the ND10 nuclear bodies.…”

Section: Dna Binding Proteins | Gene Derepressionmentioning

confidence: 99%

Use of biotinylated plasmid DNA as a surrogate for HSV DNA to identify proteins that repress or activate viral gene expression

Mallon¹,

Wakim²,

Roizman³

2012

ICP0, a key herpes simplex virus regulatory protein, functions first in the nucleus and then in the cytoplasm. The duration of its nuclear sojourn in cells transfected with DNA and then infected is related to the quantity of transfected DNA. Furthermore, ICP0 transactivates both viral genes and genes encoded by the transfected DNA. The data support the hypothesis that ICP0 is retained in the nucleus until it completes the replacement of repressive chromatin with effector proteins that enable transcription of both DNA templates. To identify the effector proteins, we transfected cells with biotinylated DNA encoding a nonviral gene and then infected the cells with wild-type virus. Proteins bound to transfected biotinylated plasmid recovered from mock-treated and infected cells were identified using mass spectrometry followed by appropriate database search. The transfected DNA from mock-infected cells yielded proteins associated with repression, whereas DNA recovered from infected cells included proteins known to enable transcription and proteins that have not been previously associated with that role. To test the hypothesis that the proteins hitherto not known to associate with viral gene expression are nevertheless essential, we tested the role of the DEAD-box helicase Ddx17. We report that Ddx17 plays a critical role in the expression of early and late viral genes. Thus, biotinylated DNA recovered from transfected infected cells can function as a surrogate for viral DNA and is a rich source of proteins that play a role in viral gene expression but which have not been previously identified in that role. DNA binding proteins | gene derepressionU pon entry into the nucleus, the DNA of HSV-1 is immediately coated by repressive cellular proteins and bound to a dynamic nuclear body known as ND10 (1). Expression of viral genes requires sequential derepression at least at two checkpoints (2). In the first VP16, a viral tegument protein introduced into the cell during infection, recruits to the promoters of the α (immediate early) genes numerous host proteins that include the Octamer binding protein 1, Host cell factor 1, and Lysine Specific Demethylase 1 (LSD1) (1, 2). The consequence of derepression of the α genes is the synthesis of the six α proteins. One of these proteins, ICP0, plays a key role in the transition through the second checkpoint. Briefly, newly synthesized ICP0 colocalizes with ND10, recruits the ubiquitin-conjugating enzyme UbcH5a, and mediates the degradation of PML and SP100, key components of the ND10 nuclear bodies (3-5). In addition, it interacts with a repressor complex whose key components are HDAC-1/2, CoREST, LSD1, and REST. In this instance ICP0 binds to CoREST and dislodges HDAC-1/2 from the repressor complex (6-8). Last, ICP0 either recruits or enhances the recruitment of numerous host proteins to the viral replication compartment erected in the space formerly occupied by the ND10 nuclear bodies. These include cyclin D3, cdc34, CoREST, USP7, Bmal1, and the histone acetyl transferase CLOCK (...