TANK-binding kinase 1 (TBK1) is of central importance for the induction of type-I interferon (IFN) in response to pathogens. We identified the DEAD-box helicase DDX3X as an interaction partner of TBK1. TBK1 and DDX3X acted synergistically in their ability to stimulate the IFN promoter, whereas RNAi-mediated reduction of DDX3X expression led to an impairment of IFN production. Chromatin immunoprecipitation indicated that DDX3X is recruited to the IFN promoter upon infection with Listeria monocytogenes, suggesting a transcriptional mechanism of action. DDX3X was found to be a TBK1 substrate in vitro and in vivo. Phosphorylation-deficient mutants of DDX3X failed to synergize with TBK1 in their ability to stimulate the IFN promoter. Overall, our data imply that DDX3X is a critical effector of TBK1 that is necessary for type I IFN induction.

Viruses must enter host cells to replicate, assemble and propagate. Because of the restricted size of their genomes, viruses have had to evolve efficient ways of exploiting host cell processes to promote their own life cycles and also to escape host immune defence mechanisms. Many viral open reading frames (viORFs) with immune-modulating functions essential for productive viral growth have been identified across a range of viral classes. However, there has been no comprehensive study to identify the host factors with which these viORFs interact for a global perspective of viral perturbation strategies. Here we show that different viral perturbation patterns of the host molecular defence network can be deduced from a mass-spectrometry-based host-factor survey in a defined human cellular system by using 70 innate immune-modulating viORFs from 30 viral species. The 579 host proteins targeted by the viORFs mapped to an unexpectedly large number of signalling pathways and cellular processes, suggesting yet unknown mechanisms of antiviral immunity. We further experimentally verified the targets heterogeneous nuclear ribonucleoprotein U, phosphatidylinositol-3-OH kinase, the WNK (with-no-lysine) kinase family and USP19 (ubiquitin-specific peptidase 19) as vulnerable nodes in the host cellular defence system. Evaluation of the impact of viral immune modulators on the host molecular network revealed perturbation strategies used by individual viruses and by viral classes. Our data are also valuable for the design of broad and specific antiviral therapies.

It has been suggested that transthyretin (TTR) is involved in preventing A-Beta fibrillization in AlzheimerÕs disease (AD). Here, we characterized the TTR/A-Beta interaction by competition binding assays. TTR binds to different A-Beta peptide species: soluble (Kd, 28 nM), oligomers and fibrils; diverse TTR variants bind differentially to A-Beta. Transmission electron microscopy (TEM) analysis demonstrated that TTR is capable of interfering with A-Beta fibrillization by both inhibiting and disrupting fibril formation. Co-incubation of the two molecules resulted in the abolishment of A-Beta toxicity. Our results confirmed TTR as an A-Beta ligand and indicated the inhibition/disruption of A-Beta fibrils as a possible mechanism underlying the protective role of TTR in AD.

Aicardi-Goutières syndrome (AGS) is a rare inherited autoimmune disease caused by mutations in genes encoding the RNase H2 subunits A, B, and C; the DNase three prime repair exonuclease 1 (TREX1); and sterile alpha motif (SAM) domain and HD domain-containing protein 1 (SAMHD1). Using unbiased affinity purification coupled to protein mass spectrometry, we identify SAMHD1 as a nucleic-acid-binding protein displaying a preference for RNA over DNA. In contrast to TREX1 and the RNase H2 complex, SAMHD1 has no obvious nuclease activity. In addition, interrogating truncation mutants of SAMHD1 observed in AGS patients, we map the nucleic-acid-binding domain to residues 164-442, thus overlapping with the HD domain. Furthermore, we show that although wild-type SAMHD1 displays almost exclusive nuclear localization, 11 of 12 SAMHD1 mutants show at least partial mislocalization to the cytosol. Overall, these data suggest that SAMHD1 has a role in the nucleus that, if disrupted by mutation, leads to cytosolic accumulation of SAMHD1 and autoimmune disease.