PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-7 (7)
 

Clipboard (0)
None

Select a Filter Below

Journals
Year of Publication
Document Types
1.  Mouse, but not human STING, binds and signals in response to the vascular disrupting agent DMXAA 
Vascular disrupting agents (VDAs) such as DMXAA (5,6-dimethylxanthenone-4-acetic acid) represent a novel approach for cancer treatment. DMXAA has potent anti-tumor activity in mice and, despite significant pre-clinical promise, failed human clinical trials. The anti-tumor activity of DMXAA has been linked to its ability to induce type I interferons in macrophages although the molecular mechanisms involved are poorly understood. Here we identify STING as a direct receptor for DMXAA leading to TBK1 and IRF3 signaling. Remarkably, the ability to sense DMXAA was restricted to murine STING. Human STING failed to bind to or signal in response to DMXAA. Human STING also failed to signal in response to cyclic-dinucleotides, conserved bacterial second messengers known to bind and activate murine STING signaling. Collectively, these findings detail an unexpected species-specific role for STING as a receptor for an anti-cancer drug and uncover important insights that may explain the failure of DMXAA in clinical trials for human cancer.
doi:10.4049/jimmunol.1300097
PMCID: PMC3647383  PMID: 23585680
2.  Structures of The HIN Domain:DNA Complexes Reveal Ligand Binding and Activation Mechanisms of The AIM2 Inflammasome and IFI16 Receptor 
Immunity  2012;36(4):561-571.
SUMMARY
Recognition of DNA by the innate immune system is central to anti-viral and anti-bacterial defenses, as well as an important contributor to autoimmune diseases involving self DNA. AIM2 (absent in melanoma 2) and IFI16 (interferon-inducible protein 16) have been identified as DNA receptors that induce inflammasome formation and interferon production, respectively. Here we present the crystal structures of their HIN domains in complex with double-stranded (ds) DNA. Non-sequence specific DNA recognition is accomplished through electrostatic attraction between the positively charged HIN domain residues and the dsDNA sugar-phosphate backbone. An intramolecular complex of the AIM2 Pyrin and HIN domains in an autoinhibited state is liberated by DNA binding, which may facilitate the assembly of inflammasomes along the DNA staircase. These findings provide novel mechanistic insights into dsDNA as the activation trigger and oligomerization platform for the assembly of large innate signaling complexes such as the inflammasomes.
doi:10.1016/j.immuni.2012.02.014
PMCID: PMC3334467  PMID: 22483801
3.  Innate immune recognition of an AT-rich stem-loop DNA motif in the Plasmodium falciparum genome 
Immunity  2011;35(2):194-207.
SUMMARY
Although Toll-like receptor 9 (TLR9) has been implicated in regulating cytokine and type I interferon (IFN) production during malaria in humans and mice, the high AT content of the Plasmodium falciparum genome prompted us to examine the possibility that malarial DNA triggered TLR9-independent DNA sensing pathways. Over 6000 ATTTTTAC (“AT-rich”) motifs are present in the genome of P. falciparum, which we show here potently induce type I IFNs. Parasite DNA, parasitized erythrocytes and oligonucleotides containing the AT-r motif induce type I IFNs via a pathway that did not involve previously described sensors including TLR9, DAI, RNA polymerase-III or IFI16/p204. Rather, AT-rich DNA sensing involved an unknown receptor that coupled to STING, TBK1 and IRF3-IRF7 signaling pathway. Mice lacking both IRF3 and IRF7, the kinase TBK1 or the type I IFN receptor were resistant to otherwise lethal cerebral malaria. Collectively, these observations implicate AT-rich DNA sensing via STING, TBK1 and IRF3-IRF7 in P. falciparum malaria.
doi:10.1016/j.immuni.2011.05.016
PMCID: PMC3162998  PMID: 21820332
4.  The AIM2 inflammasome is essential for host-defense against cytosolic bacteria and DNA viruses 
Nature immunology  2010;11(5):395-402.
Inflammasomes regulate the activity of capase-1 and maturation of interleukin-1β and interleukin-18. Recently, AIM2 was shown to bind DNA and engage ASC to form a caspase-1 activating inflammasome. Using Aim2-deficient mice, we reveal a central role for AIM2 in regulating caspase-1-dependent maturation of IL-1β and IL-18, as well as pyroptosis in response to synthetic dsDNA. AIM2 is essential for inflammasome activation in response to Fransicella tularensis, vaccinia virus, mouse cytomegalovirus and plays a partial role in sensing Listeria monocytogenes. Moreover, production of IL-18 and NK cell-dependent IFN-γ production, events critical in early control of virus replication were dependent on AIM2 during mCMV infection in vivo. Collectively, these observations reveal the importance of AIM2 in sensing both bacterial and viral pathogens and triggering innate immunity.
doi:10.1038/ni.1864
PMCID: PMC2887480  PMID: 20351692
5.  Cell-type specific recognition of human Metapneumoviruses by RIG-I and TLR7 and viral interference of RIG-I ligand recognition by HMPVB1 Phosphoprotein 
Human Metapneumoviruses (HMPV) are recently identified Paramyxoviridae that contribute to respiratory tract infections in children. No effective treatments or vaccines are available. Successful defense against virus infection relies on early detection by germline encoded pattern recognition receptors and activation of cytokine and type I interferon genes. Recently, the RNA helicase Retinoic acid inducible gene (RIG-I) has been shown to sense HMPV. In this study, we investigated the ability of two prototype strains of HMPV (A1 [NL\1\00] and B1 [NL\1\99]) to activate RIG-I and induce type I interferons (IFN). Despite the ability of both HMPV-A1 and B1 to infect and replicate in cell lines and primary cells, only the HMPV-A1 strain triggered RIG-I to induce IFNA/B gene transcription. The failure of the HMPV-B1 strain to elicit type I IFN production was dependent on the B1 phosphoprotein, which specifically prevented RIG-I-mediated sensing of HMPV viral 5’ triphosphate RNA. In contrast to most cell types, plasmacytoid dendritic cells (PDC) displayed a unique ability to sense both the A1 and B1 strains and in this case sensing was via Toll-like receptor (TLR)-7 rather than RIG-I. Collectively, these data reveal differential mechanisms of sensing for two closely related viruses, which operate in cell-type specific manners.
doi:10.4049/jimmunol.0902750
PMCID: PMC2834787  PMID: 20042593
Viral; Signal Transduction; Knockout mouse
6.  Insights into interferon regulatory factor activation from the crystal structure of dimeric IRF5 
Nature structural & molecular biology  2008;15(11):1213-1220.
Interferon regulatory factors (IRFs) are essential in the innate immune response and other physiological processes. Activation of these proteins in the cytoplasm is triggered by phosphorylation of Ser/Thr residues in a C-terminal autoinhibitory region, which stimulates dimerization, transport into the nucleus, assembly with the coactivator CBP/p300 and initiation of transcription. The novel crystal structure of the transactivation domain of pseudophosphorylated human IRF5 reveals a striking dimer in which the bulk of intersubunit interactions involve a highly extended C-terminal region. The corresponding region has previously been shown to block CBP/p300 binding to unphosphorylated IRF3. Mutation of key interface residues supports the observed dimer as the physiologically activated state of IRF5 and IRF3. Thus phosphorylation likely activates IRF5 and other family members by triggering remarkable conformational rearrangements that switch the C-terminal segment from an autoinihibitory to a dimerization role.
doi:10.1038/nsmb.1496
PMCID: PMC2757928  PMID: 18836453
7.  NOD2, RIP2 and IRF5 Play a Critical Role in the Type I Interferon Response to Mycobacterium tuberculosis 
PLoS Pathogens  2009;5(7):e1000500.
While the recognition of microbial infection often occurs at the cell surface via Toll-like receptors, the cytosol of the cell is also under surveillance for microbial products that breach the cell membrane. An important outcome of cytosolic recognition is the induction of IFNα and IFNβ, which are critical mediators of immunity against both bacteria and viruses. Like many intracellular pathogens, a significant fraction of the transcriptional response to Mycobacterium tuberculosis infection depends on these type I interferons, but the recognition pathways responsible remain elusive. In this work, we demonstrate that intraphagosomal M. tuberculosis stimulates the cytosolic Nod2 pathway that responds to bacterial peptidoglycan, and this event requires membrane damage that is actively inflicted by the bacterium. Unexpectedly, this recognition triggers the expression of type I interferons in a Tbk1- and Irf5-dependent manner. This response is only partially impaired by the loss of Irf3 and therefore, differs fundamentally from those stimulated by bacterial DNA, which depend entirely on this transcription factor. This difference appears to result from the unusual peptidoglycan produced by mycobacteria, which we show is a uniquely potent agonist of the Nod2/Rip2/Irf5 pathway. Thus, the Nod2 system is specialized to recognize bacteria that actively perturb host membranes and is remarkably sensitive to mycobacteria, perhaps reflecting the strong evolutionary pressure exerted by these pathogens on the mammalian immune system.
Author Summary
Bacterial and viral infection stimulates production of several cytokines and chemokines that are thought to protect the host against infection. The bacterial strain known to cause tuberculosis elicits production of type I interferons, yet it was unclear how the bacteria isolated within the cell was capable of stimulating this host response. This study reveals that the bacteria use a specialized system to cause damage to these cellular compartments and release bacterial products that activate intracellular innate immune pathways. In this work, we demonstrate that Nod2, Rip2, Tbk-1, Irf3 and Irf5 proteins cooperate to produce type I interferons. Understanding how these pathways are mediated is likely to aid in the design of more effective tuberculosis vaccines.
doi:10.1371/journal.ppat.1000500
PMCID: PMC2698121  PMID: 19578435

Results 1-7 (7)