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Systematic profiling of protein complex dynamics reveals DNA-PK phosphorylation of IFI16 en route to herpesvirus immunity.

ABSTRACT: Dynamically shifting protein-protein interactions (PPIs) regulate cellular responses to viruses and the resulting immune signaling. Here, we use thermal proximity coaggregation (TPCA) mass spectrometry to characterize the on-off behavior of PPIs during infection with herpes simplex virus 1 (HSV-1), a virus with an ancient history of coevolution with hosts. Advancing the TPCA analysis to infer associations de novo, we build a time-resolved portrait of thousands of host-host, virus-host, and virus-virus PPIs. We demonstrate that, early in infection, the DNA sensor IFI16 recruits the active DNA damage response kinase, DNA-dependent protein kinase (DNA-PK), to incoming viral DNA at the nuclear periphery. We establish IFI16 T149 as a substrate of DNA-PK upon viral infection or DNA damage. This phosphorylation promotes IFI16-driven cytokine responses. Together, we characterize the global dynamics of PPIs during HSV-1 infection, uncovering the co-regulation of IFI16 and DNA-PK functions as a missing link in immunity to herpesvirus infection.

SUBMITTER: Justice JL

PROVIDER: S-EPMC8213230 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Rapid and dynamically shifting protein-protein interactions (PPIs) underlie the capacity of cells to recognize viral infections and ignite the downstream cascades that constitute the innate-immune response. Herpesviruses share an ancient history of coevolution with their hosts and have developed reciprocal methods to suppress or hijack immune response proteins — underscoring the biological complexity of host-pathogen interactions during the immune response. Accordingly, conventional approaches to studying PPIs downstream of innate immune sensing fail to capture both the global scope and the dynamic on-off behavior of protein complexes as they are altered throughout cellular space and time. To overcome this barrier, we have applied Thermal Proteome Profiling Mass Spectrometry (TPP-MS) to systemically characterize PPIs that coordinate the innate-immune response to Herpes Simplex Virus 1 (HSV-1) infection in primary human fibroblasts. Further, by advancing the power of thermal protein co ggregation analysis (TPCA) to infer associations de novo and to globally track these PPIs, we developed a time-resolved portrait of cellular and viral protein associations with IFI16, a nuclear DNA sensor that serves as a central platform for HSV-1 immune responses. Our TPCA analysis, along with high-resolution microscopy and molecular virological techniques, linked IFI16 sensing of viral DNA in the nuclear periphery to the master DNA damage response (DDR) regulatory kinase, DNA-PK — the activation of which we show to be necessary for the antiviral and inflammatory responses to infection. Finally, phospho-peptide enrichment and MS analysis of DNA-PK substrates revealed IFI16 to be targeted by DNA-PK after both DNA damage and viral infection. Functional analysis of this DDR-dependent IFI16 phosphorylation revealed the specific modified residue required for IFI16-driven cytokine responses. Altogether, our study represents the first systems-wide characterization of the global dynamics of PPIs during HSV-1 infection and uncovers a missing link in the immune signaling pathway that places IFI16 and DNA-PK at the center of herpesvirus innate immunity.

Project description:The formation of multimerized protein assemblies has emerged as a core component of immune signal amplification, yet the biochemical basis of this phenomenon remains unclear for many mammalian proteins within host defense pathways. The interferon-inducible protein 16 (IFI16) is a viral DNA sensor that oligomerizes upon binding to nuclear viral DNA and induces downstream antiviral responses. Here, we identify the pyrin domain (PYD) residues that mediate IFI16 oligomerization in a charge-dependent manner. Based on structure modeling, these residues are predicted to be surface exposed within distinct α-helices. By generating oligomerization-deficient mutants, we demonstrate that IFI16 homotypic clustering is necessary for its assembly onto parental viral genomes at the nuclear periphery upon herpes simplex virus 1 (HSV-1) infection. Preventing oligomerization severely hampered the capacity of IFI16 to induce antiviral cytokine expression, suppress viral protein levels, and restrict viral progeny production. Restoring oligomerization via residue-specific charge mimics partially rescued IFI16 antiviral roles. We show that pyrin domains from PYHIN proteins are functionally interchangeable, facilitating cooperative assembly with the IFI16 HINs, highlighting an inherent role for pyrin domains in antiviral response. Using immunoaffinity purification and targeted mass spectrometry, we establish that oligomerization promotes IFI16 interactions with proteins involved in transcriptional regulation, including PAF1C, UBTF, and ND10 bodies. We further discover PAF1C as an HSV-1 restriction factor. Altogether, our study uncovers intrinsic properties that govern IFI16 oligomerization, which serves as a signal amplification platform to activate innate immune responses and to recruit transcriptional regulatory proteins that suppress HSV-1 replication.IMPORTANCE The ability of mammalian cells to detect the genomes of nuclear-replicating viruses via cellular DNA sensors is fundamental to innate immunity. Recently, mounting evidence is supporting the universal role of polymerization in these host defense factors as a signal amplification strategy. Yet, what has remained unclear are the intrinsic properties that govern their immune signal transmission. Here, we uncover the biochemical basis for oligomerization of the nuclear DNA sensor, IFI16. Upon infection with herpes simplex virus 1 (HSV-1) in human fibroblasts, we characterize the contribution of IFI16 oligomerization to downstream protein interactions and antiviral functions, including cytokine induction and suppression of HSV-1 replication. Until now, the global characterization of oligomerization-dependent protein interactions for an immune receptor has never been explored. Our integrative quantitative proteomics, molecular CRISPR/Cas9-based assays, mutational analyses, and confocal microscopy shed light on the dynamics of immune signaling cascades activated against pathogens.

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Systematic profiling of protein complex dynamics reveals DNA-PK phosphorylation of IFI16 en route to herpesvirus immunity.

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