Herpesvirus Genome Recognition Induced Acetylation of Nuclear IFI16 Is Essential for Its Cytoplasmic Translocation, Inflammasome and IFN-β Responses

Abstract

The IL-1β and type I interferon-β (IFN-β) molecules are important inflammatory cytokines elicited by the eukaryotic host as innate immune responses against invading pathogens and danger signals. Recently, a predominantly nuclear gamma-interferon-inducible protein 16 (IFI16) involved in transcriptional regulation has emerged as an innate DNA sensor which induced IL-1β and IFN-β production through inflammasome and STING activation, respectively. Herpesvirus (KSHV, EBV, and HSV-1) episomal dsDNA genome recognition by IFI16 leads to IFI16-ASC-procaspase-1 inflammasome association, cytoplasmic translocation and IL-1β production. Independent of ASC, HSV-1 genome recognition results in IFI16 interaction with STING in the cytoplasm to induce interferon-β production. However, the mechanisms of IFI16-inflammasome formation, cytoplasmic redistribution and STING activation are not known. Our studies here demonstrate that recognition of herpesvirus genomes in the nucleus by IFI16 leads into its interaction with histone acetyltransferase p300 and IFI16 acetylation resulting in IFI16-ASC interaction, inflammasome assembly, increased interaction with Ran-GTPase, cytoplasmic redistribution, caspase-1 activation, IL-1β production, and interaction with STING which results in IRF-3 phosphorylation, nuclear pIRF-3 localization and interferon-β production. ASC and STING knockdowns did not affect IFI16 acetylation indicating that this modification is upstream of inflammasome-assembly and STING-activation. Vaccinia virus replicating in the cytoplasm did not induce nuclear IFI16 acetylation and cytoplasmic translocation. IFI16 physically associates with KSHV and HSV-1 genomes as revealed by proximity ligation microscopy and chromatin-immunoprecipitation studies which is not hampered by the inhibition of acetylation, thus suggesting that acetylation of IFI16 is not required for its innate sensing of nuclear viral genomes. Collectively, these studies identify the increased nuclear acetylation of IFI16 as a dynamic essential post-genome recognition event in the nucleus that is common to the IFI16-mediated innate responses of inflammasome induction and IFN-β production during herpesvirus (KSHV, EBV, HSV-1) infections.

Role of nucleotide-binding oligomerization domain 1 (NOD1) and its variants in human cytomegalovirus control in vitro and in vivo

“…NOD2-deficient mice had enhanced susceptibility to infection with respiratory syncytial virus (RSV), decreased IRF3 phosphorylation, and type I IFN production. Redundancy of innate immune response pathways to herpesviruses is well known, and some of the recently described pattern recognition receptors, such as IFI16 and cGMP-AMP synthase (cGAS), appear to be broad sensors of different herpesviruses (29,(36)(37)(38)(39)(40)(41). In the case of NOD1, specific HCMV suppression through NOD1 activation (but not HSV-1 suppression) suggests the possible use of specialized pathways through HCMV which could be targeted for virus control.…”

ESCRT-0 Component Hrs Promotes Macropinocytosis of Kaposi's Sarcoma-Associated Herpesvirus in Human Dermal Microvascular Endothelial Cells

“…Proximity ligation assay (PLA) was performed using the Duolink in situ detection kit (Sigma) as per the manufacturer's instructions (33,34). Briefly, uninfected and infected cells were fixed with 4% paraformaldehyde solution for 15 min, permeabilized with Triton X-100 for 5 min, washed with phosphate-buffered saline (PBS), and incubated for 1 h with the Duolink blocking buffer.…”

Nuclear Innate Immune DNA Sensor IFI16 Is Degraded during Lytic Reactivation of Kaposi's Sarcoma-Associated Herpesvirus (KSHV): Role of IFI16 in Maintenance of KSHV Latency

“…IFI16 is a multifunctional DNA binding protein and has been implicated in various cellular functions such as transcriptional regulation, apoptosis, autoimmunity, and cell cycle regulation (25)(26)(27). Studies by us and others have reported the role of IFI16 as a DNA sensor that detects nuclear replicating herpesviral genomes such as KSHV, herpes simplex virus 1 (HSV-1), EpsteinBarr virus (EBV), and bovine herpesvirus 1 (BoHV-1), leading to IFI16 -apoptosis-associated speck-like protein containing a CARD (ASC)-procaspase-1 inflammasome formation that results in the production of the inflammatory cytokine interleukin 1␤ (IL-1␤) (28)(29)(30)(31)(32)(33). We have also shown that IFI16-mediated inflammasomes are activated during prolonged KSHV latency in endothelial and B cells, leading to a constitutive state of IL-1␤ activation (34).…”

“…We have also shown that IFI16-mediated inflammasomes are activated during prolonged KSHV latency in endothelial and B cells, leading to a constitutive state of IL-1␤ activation (34). Recently, IFI16 was also shown to be involved in the induction of IFN-␤ during KSHV and HSV-1 de novo infection of target cells via the IFI16 -stimulator of interferon genes protein (STING)-TANK-binding kinase 1 (TBK)-interferon regulatory factor 3 (IRF3) axis (31,32,35,36).…”