Tumor Necrosis Factor-mediated survival of CD169⁺ cells promotes immune activation during vesicular stomatitis virus infection

Innate immune activation is essential to mount an effective antiviral response and to prime adaptive immunity. Although a crucial role of CD169+ cells during vesicular stomatitis virus (VSV) infections is increasingly recognized, factors regulating CD169+ cells during viral infections remain unclear. Here, we show that tumor necrosis factor is produced by CD11b+ Ly6C+ Ly6G+ cells following infection with VSV. The absence of TNF or TNF receptor 1 (TNFR1) resulted in reduced numbers of CD169+ cells and in reduced type I interferon (IFN-I) production during VSV infection, with a severe disease outcome. Specifically, TNF triggered RelA translocation into the nuclei of CD169+ cells; this translocation was inhibited when the paracaspase MALT-1 was absent. Consequently, MALT1 deficiency resulted in reduced VSV replication, defective innate immune activation, and development of severe disease. These findings indicate that TNF mediates the maintenance of CD169+ cells and innate and adaptive immune activation during VSV infection

Transcriptome-wide analysis uncovers the targets of the RNA-binding protein MSI2 and effects of MSI2's RNA-binding activity on IL-6 signaling

The RNA-binding protein Musashi 2 (MSI2) has emerged as an important regulator in cancer initiation, progression, and drug resistance. Translocations and deregulation of the MSI2 gene are diagnostic of certain cancers, including chronic myeloid leukemia (CML) with translocation t(7;17), acute myeloid leukemia (AML) with translocation t(10;17), and some cases of B-precursor acute lymphoblastic leukemia (pB-ALL). To better understand the function of MSI2 in leukemia, the mRNA targets that are bound and regulated by MSI2 and their MSI2-binding motifs need to be identified. To this end, using photoactivatable ribonucleoside cross-linking and immunoprecipitation (PAR-CLIP) and the Multiple EM for Motif Elicitation (MEME) analysis tool, here we identified MSI2’s mRNA targets and the consensus RNA-recognition element (RRE) motif recognized by MSI2 (UUAG). Of note, MSI2 knockdown altered the expression of several genes with roles in eukaryotic initiation factor 2 (eIF2), hepatocyte growth factor (HGF), and epidermal growth factor (EGF) signaling pathways. We also show that MSI2 regulates classic interleukin-6 (IL-6) signaling by promoting the degradation of the mRNA of IL-6 signal transducer (IL6ST or GP130), which, in turn, affected the phosphorylation statuses of signal transducer and activator of transcription 3 (STAT3) and the mitogen-activated protein kinase ERK. In summary, we have identified multiple MSI2-regulated mRNAs and provided evidence that MSI2 controls IL6ST activity that control oncogenic signaling networks. Our findings may help inform strategies for unraveling the role of MSI2 in leukemia to pave the way for the development of targeted therapies

RAIDD Mediates TLR3 and IRF7 Driven Type I Interferon Production

Background/Aims: Viral infections represent a global health problem with the need for new viral therapies and better understanding of the immune response during infection. The most immediate and potent anti-viral defense mechanism is the production of type I interferon (IFN-I) which are activated rapidly following recognition of viral infection by host pathogen recognition receptors (PRR). The mechanisms of innate cellular signaling downstream of PRR activation remain to be fully understood. In the present study, we demonstrate that CASP2 and RIPK1 domain-containing adaptor with death domain (CRADD/RAIDD) is a critical component in type I IFN production. Methods: The role of RAIDD during IFN-I production was investigated using western blot, shRNA mediated lentiviral knockdown, immunoprecipitation and IFN-I driven dual luciferase assay. Results: Immunoprecipitation analysis revealed the molecular interaction of RAIDD with interferon regulatory factor 7 (IRF7) and its phosphorylating kinase IKKε. Using an IFN-4α driven dual luciferase analysis in RAIDD deficient cells, type I IFN activation by IKKε and IRF7 was dramatically reduced. Furthermore, deletion of either the caspase recruitment domain (CARD) or death domain (DD) of RAIDD inhibited IKKε and IRF7 mediated interferon-4α activation. Conclusion: We have identified that the adaptor molecule RAIDD coordinates IKKε and IRF7 interaction to ensure efficient expression of type I interferon

Deficiency of the B cell-activating factor receptor results in limited CD169+ macrophage function during viral infection

The B cell-activating factor (BAFF) is critical for B cell development and humoral immunity in mice and humans. While the role of BAFF in B cells has been widely described, its role in innate immunity remains unknown. Using BAFF receptor (BAFFR)-deficient mice, we characterized BAFFR-related innate and adaptive immune functions following infection with vesicular stomatitis virus (VSV) and lymphocytic choriomeningitis virus (LCMV).Weidentified a critical role for BAFFR signaling in the generation and maintenance of the CD169+ macrophage compartment. Consequently, Baffr-/- mice exhibited limited induction of innate type I interferon production after viral infection. Lack of BAFFR signaling reduced virus amplification and presentation following viral infection, resulting in highly reduced antiviral adaptive immune responses. As a consequence, BAFFR-deficient mice showed exacerbated and fatal disease after viral infection. Mechanistically, transient lack of B cells in Baffr-/- animals resulted in limited lymphotoxin expression, which is critical for maintenance of CD169+ cells. In conclusion, BAFFR signaling affects both innate and adaptive immune activation during viral infections. © 2015, American Society for Microbiology