The adaptor protein STING mediates the production of type III interferon in response to cytosolic DNA and DNA viruses.

Human Ku70 is a well-known endogenous nuclear protein involved in the non-homologous end joining pathway to repair double-stranded breaks in DNA. However, Ku70 has been studied in multiple contexts and grown into a multifunctional protein. In addition to the extensive functional study of Ku70 in DNA repair process, many studies have emphasized the role of Ku70 in various other cellular processes, including apoptosis, aging, and HIV replication. In this review, we focus on discussing the role of Ku70 in inducing interferons and proinflammatory cytokines as a cytosolic DNA sensor. We explored the unique structure of Ku70 binding with DNA; illustrated, with evidence, how Ku70, as a nuclear protein, responds to extracellular DNA stimulation; and summarized the mechanisms of the Ku70-involved innate immune response pathway. Finally, we discussed several new strategies to modulate Ku70-mediated innate immune response and highlighted some potential physiological insights based on the role of Ku70 in innate immunity.

Summary: We have previously identified that human Ku70, a nuclear protein, serves as a cytosolic DNA sensor. Upon transfection with DNA or infection with DNA virus, Ku70 translocates from the nucleus into the cytoplasm and then predominately induces interferon lambda1 (IFN‐λ1) rather than IFN‐alpha or IFN‐beta, through a STING‐dependent signalling pathway. However, a detailed mechanism for Ku70 cytoplasmic translocation and its correlation with IFN‐λ1 induction have not been fully elucidated. Here, we observed that cytoplasmic translocation of Ku70 only occurred in DNA‐triggered IFN‐λ1‐inducible cells. Additionally, infection by Herpes simplex virus type‐1 (HSV‐1), a DNA virus, induces cytoplasmic translocation of Ku70 and IFN‐λ1 induction in a strain‐dependent manner: the translocation and IFN‐λ1 induction were detected upon infection by HSV‐1 McKrae, but not MacIntyre, strain. A kinetic analysis indicated that cytoplasmic translocation of Ku70 was initiated right after DNA transfection and was peaked at 6 hr after DNA stimulation. Furthermore, treatment with leptomycin B, a nuclear export inhibitor, inhibited both Ku70 translocation and IFN‐λ1 induction, suggesting that Ku70 translocation is an essential and early event for its cytosolic DNA sensing. We further confirmed that enhancing the acetylation status of the cells promotes Ku70’s cytoplasmic accumulation, and therefore increases DNA‐mediated IFN‐λ1 induction. These findings provide insights into the molecular mechanism by which the versatile sensor detects pathogenic DNA in a localization‐dependent manner.

Trace metals are essential for various physiological processes, but their roles in innate immunity have not been fully explored. Here, we found that manganese (Mn) significantly enhanced DNA-mediated IFN-α, IFN-β, and IFN-λ1 production. Microarray analysis demonstrated Mn highly upregulated 351 genes, which were involved in multiple biological functions related to innate immune response. Moreover, we found that Mn²⁺ alone activates phosphorylation of TANK-binding kinase 1 (TBK1). Inhibiting ataxia telangiectasia mutated (ATM) kinase using ATM inhibitor or siRNA suppressed Mn-enhanced DNA-mediated immune response with decreasing phosphorylation of TBK-1, suggesting that ATM involves in Mn-dependent phosphorylation of TBK1. Given that TBK1 is an essential mediator in DNA- or RNA-mediated signaling pathways, we further demonstrated that Mn²⁺ suppressed infection of HSV-1 (DNA virus) or Sendai virus (RNA virus) into human macrophages by enhancing antiviral immunity. Our finding highlights a beneficial role of Mn in nucleic-acid-based preventive or therapeutic reagents against infectious diseases.

Herpes simplex virus 1 (HSV-1) strain McKrae is highly virulent and relatively neuroinvasive in animal models compared with other wild-type HSV-1 strains. To identify the genetic determinants that lead to the unique phenotypes of the McKrae strain, we sequenced its genome with PacBio single-molecule real-time (SMRT) technology and resolved the complete sequence.

Herpes simplex virus type 2 (HSV-2) is a common causative agent of genital tract infections. Moreover, HSV-2 and HIV infection can mutually increase the risk of acquiring another virus infection. Due to the high GC content and highly repetitive regions in HSV-2 genomes, only the genomes of four strains have been completely sequenced (HG52, 333, SD90e, and MS). Strain G is commonly used for HSV-2 research, but only a partial genome sequence has been assembled with Illumina sequencing reads. In the current study, we de novo assembled and annotated the complete genome of strain G using PacBio long sequencing reads, which can span the repetitive regions, analyzed the ‘α’ sequence, which plays key roles in HSV-2 genome circulation, replication, cleavage, and packaging of progeny viral DNA, identified the packaging signals homologous to HSV-1 within the ‘α’ sequence, and determined both termini of the linear genome and cleavage site for the process of concatemeric HSV-2 DNA produced via rolling-circle replication. In addition, using Oxford Nanopore Technology sequencing reads, we visualized four HSV-2 genome isomers at the nucleotide level for the first time. Furthermore, the coding sequences of HSV-2 strain G have been compared with those of HG52, 333, and MS. Moreover, phylogenetic analysis of strain G and other diverse HSV-2 strains has been conducted to determine their evolutionary relationship. The results will aid clinical research and treatment development of HSV-2.