Mammals defend against infection by detecting foreign and/or danger signals to mount both cell-autonomous as well as paracrine immune responses. Among the microbial signatures sensed by mammalian hosts are a new class of signaling intermediates termed cyclic di-nucleotides (CDNs). CDNs are recognized by the host protein, STING (STimulator of INterferon Genes), to elicit type I IFN production. In this application we will characterize a new CDN recognition system that mobilizes protective immunity independently of STING or type I IFN release. This new circuit enlists four members of an immune GTPase family ? the 65-73kDa Guanylate Binding Proteins (GBPs) ? to activate distinct host defense programs in both humans and mice. Preliminary evidence implicates GBP1 as the proximal CDN sensor which recruits GBP2, GBP3 and GBP5 as adaptors that link the antimicrobial machinery further downstream.
In Aim 1, we will test the importance of GBP1 to act as a broad-spectrum CDN sensor capable of binding c-diGMP, c-diAMP and cGAMPs under physiological conditions to elicit either inflammasome assembly, pyroptosis or autophagy in a STING-independent manner. This will be examined using a powerful host-pathogen genetic strategy where mice and cells lacking GBP1 or expressing GBP1 CDN-binding mutants will be infected with important bacterial pathogens (M. tuberculosis, S. typhimurium and L. monocytogenes) engineered to secrete a specific CDN moiety to define this relationship in vitro and in vivo.
In Aim 2, we expand this CDN sensor circuit to include GBP2, GBP3 and GBP5 as heterotypic partners that direct core components of the inflammasome, pyroptotic or autophagy cascade to restrict bacterial replication.
This aim will enlist newly-created Gbp2-/-, Gbp3-/- and Gbp5-/- mice as well as mixed sensor-adaptor chimeras as a novel binary approach to dissect how the GBP relay mobilizes different types of CDN-dependent immunity to bacterial pathogens. Collectively, our proposal examines a new set of host proteins that define a novel CDN sensor-adaptor circuit with important implications for developing host- directed therapies as an adjunct to standard antibiotic treatment.
. Our ability to fight intracellular infections relies on immune proteins capable of sensing different microbial products to mobilize antimicrobial defense programs. This proposal focuses on a new family of host defense factors - the Guanylate Binding Proteins (GBPs) ? that recognize bacterial second messengers termed cyclic dinucleotides (CDNs) to co-ordinate antibacterial immunity within infected target cells. This new GBP-mediated defense circuit operates against CDN-producing bacteria that are responsible for tuberculosis as well as food- borne gastroenteritis and blood-borne sepsis, the latter a common cause of death in U.S. intensive care units. Here we will identify how GBPs detect and integrate CDN-based signals from bacteria to co-ordinate an effective immune response against these globally important pathogens. Understanding the molecular basis of GBP-mediated immunity to secreted CDNs has serious implications for host-directed therapies against these human diseases and as well as for our understanding of mammalian host defense.
| Kim, Bae-Hoon; Chee, Jonathan D; Bradfield, Clinton J et al. (2016) Interferon-induced guanylate-binding proteins in inflammasome activation and host defense. Nat Immunol 17:481-9 |
| Gaudet, Ryan G; Bradfield, Clinton J; MacMicking, John D (2016) Evolution of Cell-Autonomous Effector Mechanisms in Macrophages versus Non-Immune Cells. Microbiol Spectr 4: |
| MacMicking, John D (2014) Cell-autonomous effector mechanisms against mycobacterium tuberculosis. Cold Spring Harb Perspect Med 4: |
| Das, Rituparna; Koo, Mi-Sun; Kim, Bae Hoon et al. (2013) Macrophage migration inhibitory factor (MIF) is a critical mediator of the innate immune response to Mycobacterium tuberculosis. Proc Natl Acad Sci U S A 110:E2997-3006 |
| Randow, Felix; MacMicking, John D; James, Leo C (2013) Cellular self-defense: how cell-autonomous immunity protects against pathogens. Science 340:701-6 |
| Selleck, Elizabeth M; Fentress, Sarah J; Beatty, Wandy L et al. (2013) Guanylate-binding protein 1 (Gbp1) contributes to cell-autonomous immunity against Toxoplasma gondii. PLoS Pathog 9:e1003320 |
| MacMicking, John D (2012) Interferon-inducible effector mechanisms in cell-autonomous immunity. Nat Rev Immunol 12:367-82 |
| Shenoy, Avinash R; Wellington, David A; Kumar, Pradeep et al. (2012) GBP5 promotes NLRP3 inflammasome assembly and immunity in mammals. Science 336:481-5 |
| Bradfield, Clinton J; Kim, Bae-Hoon; MacMicking, John D (2012) Crossing the Rubicon: new roads lead to host defense. Cell Host Microbe 11:221-3 |
| Kim, Bae-Hoon; Shenoy, Avinash R; Kumar, Pradeep et al. (2012) IFN-inducible GTPases in host cell defense. Cell Host Microbe 12:432-44 |
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