Tschopp Jürg

The Director, Professors and all members of the Department of Biochemistry have profound regret in announcing the sudden and tragic loss of our colleague, Professor Jürg Tschopp, who passed away on Tuesday March 22.

Jürg was an enlightening scientist who's ground-breaking ideas, coupled with his drive for excellence, had an enormous impact in the field of innate immunity. His passing is a great personal loss to us, and a huge loss to the scientific community.

We will miss him as a colleague and as a friend.

PATHOGEN AND DANGER-SENSING PLATFORMS THAT TRIGGER INFLAMMATION AND INNATE IMMUNITY

Traditionally innate immunity has been viewed as the first line of defense discriminating ‘‘self’’ (e.g., host proteins) from ‘‘nonself’’ (e.g., microorganisms). However, emerging literature suggests that innate immunity actually serves as a sophisticated system for sensing signals of ‘‘danger,’’ such as pathogenic microbes or host-derived signals of cellular stress, while remaining unresponsive to nondangerous motifs, such as normal host molecules, dietary antigens, or commensal gut flora.

The innate immune system engages an array of germline encoded pattern-recognition receptors (PRRs) to detect invariant microbial motifs. PRRs include the membrane-bound Toll-like receptors (TLRs), which scan the extracellular milieu and endosomal compartments for pathogen-associated molecular patterns (PAMPs). Intracellular nucleic-acid sensing PRRs cooperate to provide cytosolic surveillance, including the RNA-sensing RIG- like helicases (RLHs) and the DNA sensors, DAI and AIM2. The outcome of PAMP recognition by PRRs depends upon the nature of both the responding cell and the invading microbe. A further set of intracellular PRRs, distinct from those described above, are the NOD-like receptors (NLRs) that recognize pathogen-associated patterns (PAMPs), as well as host-derived danger signals (danger- associated molecular patterns, DAMPs).

Our laboratory mainly focuses on the study of PRRs that assemble into high-molecular weight, caspase-1-activating platforms called ‘‘inflammasomes’’. Inflammasomes control maturation and secretion of interleukins such as IL-1β and IL-18, whose potent proinflammatory activities direct host responses to infection and injury.

Our group also investigates the function of a complex, called the PIDDosome, which detects DNA damage and orchestrates DNA replication and repair under stress conditions. A further research focus is, the role of RIG-I and MAVS (Cardif), which sense the presence of viral RNA and trigger an innate anti-viral response including the synthesis of type I interferons.

Our overall goal is to understand signaling networks that control the inflammatory responses to pathogens and danger signals. We believe that this will provide important insights into the genesis of various human diseases and will allow the development of new and more effective drugs.

1. The inflammasome: A molecular platform sensing PAMPs and DAMPs triggering inflammation

The inflammasome is a multiprotein complex responsible for the activation of caspase-1 and -5, thereby leading to the processing and activation of the pro-inflammatory cytokines IL-1β and IL-18. Our group previously identified two types of inflammasomes; the NALP1 inflammasome, which is composed of NALP1/ASC/Caspase-1/Caspase-5 and the NALP3 inflammasomes that contains, in addition to NALP3, CARDINAL/ASC/Caspase-1 (Fig. 1). An alternative inflammasome is formed by IPAF that directly recruits caspase-1 without the need of an adaptor protein (Fig. 1) and AIM-2.

Fig. 1: The Nalp3 and IPAF inflammasomes
Structural organization of the typical NALP3 and IPAF inflammasomes. The core structure of the NALP3 inflammasome is formed by NALP3, the adaptor ASC, and caspase-1 (left panel). IPAF recruits caspase-1 directly via CARD–CARD interactions (right panel). The LRR of NALP3 or IPAF sense the activating signals leading to the oligomerization of the NACHT region and initiating the formation of the donut-shaped inflammasome. Based on the structure of the apoptosome, the caspases and IL-1β-processing activity most likely face the inside of the donut (lower panel).

The NALPs and IPAF are central proteins in the inflammasome complex. Fourteen NALP proteins have been identified in humans. The role of several of these proteins remains to be determined and are currently studied in our laboratory.

How are the inflammasomes activated?

Little is also known about the natural stimuli that lead to the assembly and activation of the inflammasomes. Our group provided a model in which NALP3 is a more general sensor of cellular stress through its activation by ROS generated in spatial and proximity to the inflammasome. All NALP3 activators that have been examined, including ATP and particulate activators such as asbestos and uric acid crystals, trigger the generation of short-lived ROS, and treatment with various ROS scavengers blocks NALP3 activation in response to a range of agonists. We recently found some insight into the molecular events potentially driving ROS-dependent inflammasome activation. Treatment with NALP3 agonists triggers the association of NALP3 with thioredoxin-interacting protein (TXNIP) in a ROS-dependent manner. In unstimulated cells, TXNIP is constitutively bound to and inhibited by the oxidoreductase thio- redoxin. Following an increase in cellular ROS concentration, this complex dissociates and TXNIP binds to NALP3. In support of such an activation mechanism, knockdown of thioredoxin potentiates inflammasome activation. Furthermore, TXNIP knockout impairs caspase-1 activation and IL-1β secretion in β-cells following stimulation by various NALP33 agonists. However, capase-1 activation is not blocked completely in the absence of TXNIP in macrophages, which indicates that other regulators of inflammasome activity exist and that other pathways might function together with the ROS pathway to initiate a complete inflammatory response.

The NALP3 Inflammasome and diseases

Mutations in the gene coding for NALP3 have been associated with several autoinflammatory disorders such as Muckle-Wells syndrome, familial cold urticaria and CINCA (Chronic Infantile Neurological Cutaneous and Articular autoinflammatory disease). These disorders are characterized by recurrent episodes of fever and serosal inflammation, due to increased production of IL-1β. Based on the discovery of the function of the inflammasome, patients are now successfully treated with the natural IL-1 inhibitor IL-1ra (Anakinra) or neutralizing antibodies to IL-1β.

Development of the acute and chronic inflammatory response known as gout is associated with the deposition of monosodium urate crystals (MSU) in joints and periarticular tissues (Fig. 2).

Although MSU crystals were first identified as the etiologic agent of gout in the 18th century and more recently as a "danger signal" released from dying cells, little was known concerning the molecular mechanisms underlying MSU-induced inflammation. We found that MSU engage the NALP3 inflammasome, resulting in the production of active IL-1β. Macrophages from mice deficient in various components of the inflammasome such as caspase-1, ASC and NALP3 are defective in crystal-induced IL-1β activation. Moreover, an impaired neutrophil influx is found in an in vivo model of crystal-induced peritonitis in inflammasome-deficient mice or mice deficient in the IL-1β receptor (IL-1R). Excitingly, acute pain attacks occurring in gout are considerably shortened when patients are treated with antibodies to IL-1β. In addition to gout, several other inflammatory diseases including Type 2 diabetes and artheroscleoris appear to be based on a deregulated inflammasome and may therefore be potentially treated with IL-1 antagonists.

2. The RIG-I/CARDIF platform: Sensing viruses and activating type I interferons

Innate immunity against a pathogen is mounted upon recognition by the host of, for example, viral products. One of these viral 'signatures', double-stranded (ds) RNA, is a replication product of most viruses within infected cells and is sensed by Toll-like receptor 3 (TLR3) and the recently identified cytosolic RNA helicases RIG-I and MDA5. Both helicases detect dsRNA, and through their protein-interacting CARD domains, relay a poorly defined signal resulting in the activation of the transcription factors interferon regulatory factor 3 (IRF3) and NF-κB. We have identified Cardif (also known as IPS-1, MAVS or VISA), a new CARD-containing adaptor protein that interacts with RIG-I and recruits IKKα, IKKβ and IKKε kinases by means of its C-terminal region, leading to the activation of NF-κB and IRF3. Activation of Cardif results in interferon-β and NF-κB promoter activation, and the absence of Cardif inhibits RIG-I-dependent antiviral responses. Cardif is localized to mitochondria and is targeted and inactivated by NS3-4A, a serine protease from hepatitis C virus known to block interferon-β production. Cardif thus functions as an adaptor, linking the cytoplasmic dsRNA receptor RIG-I to the initiation of antiviral programmes.

Fig. 3: Overview of TLR- and RIG-I-dependent antiviral pathways (Left) Upon ssRNA or dsRNA binding within endosomes, TLR7/8 and TLR3, respectively, recruit the adaptors MyD88 or Trif through a TIR-TIR interaction. MyD88 recruits IRAKs through DD-DD interactions, and also TRAF3 and TRAF6, to activate IRF and NF-kB. Trif recruits RIP1 through a RHIM-RHIM interaction to activate NF-kB. To activate IRF, Trif recruits TBK1 and possibly TRAF3. (Right) Upon dsRNA binding, RIG-I (and also MDA5) recruits the mitochondrial-bound adaptor Cardif, which in turn recruits appropriate IKKs to activate NF-kB and IRF. During an infection with HCV, both Trif and Cardif are cleaved by the HCV NS3-4A protease. As a consequence, Trif cannot recruit TBK1, which prevents IRF activation and type-I interferon production.

3. The PIDDosome: Detecting DNA damage and activating caspase-2 

Activation of initiatior caspases is a key event in apoptosis execution. Prototypically, activation is triggered upon complex-mediated clustering of the inactive zymogen such as in the caspase-9-activating apoptosome complex. Likewise, caspase-2, which is involved in stress-induced cell death, is recruited into a large protein complex that contains the death-domain containing protein PIDD. Increased amounts of PIDD expression result in spontaneous activation of caspase-2 and sensitization to apoptosis by genotoxic stimuli. Because PIDD functions in p53-mediated apoptosis, the complex assembled by PIDD and caspase-2 is likely to have a crucial role in the regulation of apoptosis induced by genotoxins. We found that PIDD also plays a critical role in DNA damage-induced NF-κB activation. Upon genotoxic stress, a complex between PIDD, RIP1 and NEMO is formed. Cells stably expressing PIDD show enhanced genotoxic stress-induced NF-κB activation, through augmented sumoylation and ubiquitination of NEMO. Knock-down of PIDD and RIP1 expression abrogates DNA damage-induced NEMO-modification and hence NF-κB activation.

PIDD is constitutively processed giving rise to a 48-kDa N-terminal fragment and a 51-kDa C-terminal fragment (PIDD-C). The latter undergoes further cleavage resulting in a 37-kDa fragment (PIDD-CC). Processing occurs at S446 (generating PIDD-C) and S588 (generating PIDD-CC) by an auto-processing mechanism. Auto-cleavage of PIDD determines the outcome of the downstream signaling events. Whereas initially formed PIDD-C mediates the activation of NF-κB via the recruitment of RIP1 and NEMO, subsequent formation of PIDD-CC causes caspase-2 activation and thus cell death. In this way, auto-proteolysis of PIDD might participate in the orchestration of the DNA damage-induced life and death signaling pathways (Fig. 4).

Fig. 4: PIDD acts as a molecular switch, controlling the balance
between life and death upon DNA damage.

• Gross, O. Measuring the inflammasome. In: Methods in Molecular Biology (Springer), in press.
• Gross, O., Thomas, C.J., Layland, L.E. (2011). Inflammasome activation in response to eukaryotic pathogens. In: The Inflammasomes (I. Couillin, V. Pétrilli, F. Martinon, Eds) Springer.
• Menu, P., Mayor, A., Zhou, R., Tardivel, A., Ichijo, I., Mori, K., Tschopp, J. ER stress activates the NLRP3 inflammasome via an UPR-independent pathway. Cell Death Dis., in press.
• Heinz, L.X., Rebsamen, M., Rossi, D.C., Staehli, F., Schroder, K., Quadroni, M., Gross, O., Schneider, P., Tschopp, J. The death domain-containing protein Unc5CL is a novel MyD88-independent activator of the pro-inflammatory IRAK signaling cascade. Cell Death Differ., in press.
• Gross, O., Thomas, C.J., Guarda, G., Tschopp, J. (2011). The inflammasome: an integrated view. Immunol. Rev., 243, 136-151. PubMed
• Witzenrath, M., Pache, F., Lorenz, D., Koppe, U., Gutbier, B., Tabeling, C., Reppe, K., Meixenberger, K., Dorhoi, A., Ma, J., Holmes, A., Trendelenburg, G., Heimesaat, M.M., Bereswill, S., van der Linden, M., Tschopp, J., Mitchell, T.J. Suttorp, N., Opitz, B. (2011). The NLRP3 inflammasome is differentially activated by pneumolysin variants and contributes to host defense in pneumococcal pneumonia. J. Immunol., 187, 434-440. PubMed
• Rebsamen, M., Vazquez, J., Tardivel, A., Guarda, G., Curran, J., Tschopp, J. (2011). NLRX1/NOD5 deficiency does not affect MAVS signalling. Cell Death Differ., 18, 1387. PubMed
• Tschopp, J. (2011). Mitochondria: Sovereign of inflammation? Eur. J. Immunol., 41,1196-202. PubMed
• Mankan, A.K., Canli, O., Schwitalla, S., Ziegler, P., Tschopp, J., Korn, T., Greten, F.R. (2011). TNF-alpha-dependent loss of IKKbeta-deficient myeloid progenitors triggers a cytokine loop culminating in granulocytosis. Proc. Natl Acad. Sci. U.S.A. 108, 6567-6572. PubMed
• Menu, P., Pellegrin, M., Aubert, J.F., Bouzourene, K., Tardivel, A., Mazzolai, L., Tschopp, J. (2011). Atherosclerosis in ApoE-deficient mice progresses independently of the NLRP3 inflammasome. Cell Death Dis., 2, e137. PubMed
• Besnard, A.G., Guillou, N., Tschopp, J., Erard, F., Couillin, I., Iwakura, Y., Quesniaux, V., Ryffel, B., Togbe, D. (2011). NLRP3 inflammasome is required in murine asthma in the absence of aluminum adjuvant. Allergy, 66, 1047-1057. PubMed
• Logette, E., Schuepbach-Mallepell, S., Eckert, M.J., Leo, X.H., Jaccard, B., Manzl, C., Tardivel, A., Villunger, A., Quadroni, M., Gaide, O., Tschopp, J. (2011). PIDD orchestrates translesion DNA synthesis in response to UV irradiation. Cell Death Differ. 18, 1036-1045. PubMed
• Flach, T.L., Ng, G., Hari, A., Desrosiers, M.D., Zhang, P., Ward, S.M., Seamone, M.E., Vilaysane, A., Mucsi, A.D., Fong, Y., Prenner, E., Ling, C.C., Tschopp, J., Muruve, D.A., Amrein, M.W., Shi, Y. (2011). Alum interaction with dendritic cell membrane lipids is essential for its adjuvanticity. Nat. Med. 17, 479-87. PubMed
• Guarda, G., Braun, M., Staehli, F., Tardivel, A., Mattmann, C., Förster, I., Farlik, M., Decker, T., Du Pasquier, R.A., Romero, P., Tschopp, J. (2011). Type I interferon inhibits interleukin-1 production and inflammasome activation. Immunity, 34, 213-23. PubMed
• Allam, R., Darisipudi, M.N., Rupanagudi, K.V., Lichtnekert, J., Tschopp, J., Anders, H.J. (2011). Cyclic polypeptide and aminoglycoside antibiotics trigger IL-1β secretion by activating the NLRP3 inflammasome. J. Immunol., 186, 2714-2718. PubMed
• Guarda, G., Zenger, M., Yazdi, A.S., Schroder, K., Ferrero, I., Menu, P., Tardivel, A., Mattmann, C., Tschopp, J. (2011). Differential expression of NLRP3 among hematopoietic cells. J. Immunol., 186, 2529-2534. PubMed
• Harris, J., Hartman, M., Roche, C., Zeng, S.G., O'Shea, A., Sharp, F.A., Lambe, E.M., Creagh, E.M., Golenbock, D.T., Tschopp, J., Kornfeld, H., Fitzgerald, K.A., Lavelle, E.C. (2011). Autophagy controls IL-1beta secretion by targeting pro-IL-1beta for degradation. J. Biol. Chem. 286, 9587-9597. PubMed
• Zhou, R., Yazdi, A.S., Menu, P., Tschopp, J. (2011). A role for mitochondria in NLRP3 inflammasome activation. Nature, 469, 221-225. Erratum in: Nature, 475, 122, 2011. PubMed
• Tinel, A., Eckert, M.J., Logette, E., Lippens, S., Janssens, S., Jaccard, B., Quadroni, M., Tschopp, J. (2011). Regulation of PIDD auto-proteolysis and activity by the molecular chaperone Hsp90. Cell Death Differ., 18, 506-515. PubMed
• Hirota, S.A., Ng, J., Lueng, A., Khajah, M., Parhar, K., Li, Y., Lam, V., Potentier, M.S., Ng, K., Bawa, M., McCafferty, D.M., Rioux, K.P., Ghosh, S., Xavier, R.J., Colgan, S.P., Tschopp, J., Muruve, D., MacDonald, J.A., Beck, P.L. (2011). NLRP3 inflammasome plays a key role in the regulation of intestinal homeostasis. Inflamm. Bowel Dis., 17, 1359-1372. PubMed
• Yazdi, A.S., Guarda, G., Riteau, N., Drexler, S.K., Tardivel, A., Couillin, I., Tschopp, J. (2010). Nanoparticles activate the NLR pyrin domain containing 3 (Nlrp3) inflammasome and cause pulmonary inflammation through release of IL-1α and IL-1β. Proc. Natl Acad. Sci. U.S.A. 107, 19449-19454. PubMed
• Schroder, K., Tschopp, J. (2010). The inflammasomes. Cell 140, 821-832. PubMed
• Schroder, K., Zhou, R., Tschopp, J. (2010). The NLRP3 inflammasome: a sensor for metabolic danger? Science 327, 296-300. PubMed
• Zhou, R., Tardivel, A., Thorens, B., Choi, I., Tschopp, J. (2010). Thioredoxin-interacting protein links oxidative stress to inflammasome activation. Nat. Immunol. 11, 136-140. PubMed
• Guarda, G., Dostert, C., Staehli, F., Cabalzar, K., Castillo, R., Tardivel, A., Schneider, P., Tschopp, J. (2009). T cells dampen innate immune responses through inhibition of NLRP1 and NLRP3 inflammasomes. Nature 460, 269-273. PubMed
• Rebsamen, M., Heinz, L.X., Meylan, E., Michallet, M.C., Schroder, K., Hofmann, K., Vazquez, J., Benedict, C.A., Tschopp, J. (2009). DAI/ZBP1 recruits RIP1 and RIP3 through RIP homotypic interaction motifs to activate NF-kappaB. EMBO Rep. 10, 916-922. PubMed
• Rebsamen, M., Meylan, E., Curran J., Tschopp, J. (2008b). The antiviral adaptor proteins Cardif and Trif are processed and inactivated by caspases. Cell Death Differ. 15, 1804-11. PubMed
• Dostert, C., Pétrilli, V., Van Bruggen, R., Steele, C., Mossman, B., Tschopp, J. (2008c). Innate immune activation through Nalp3 inflammasome sensing of asbestos and silica. Science 320, 674-7. PubMed
• Dostert, C., Meylan, E., Tschopp, J. (2008a). Intracellular pattern-recognition receptors. Adv. Drug Deliv. Rev. 60, 830-40. PubMed
• Cuenin, S., Tinel, A., Janssens, S., Tschopp, J. (2008a). p53-induced protein with a death domain (PIDD) isoforms differentially activate nuclear factor-kappaB and caspase-2 in response to genotoxic stress. Oncogene 27, 387-96. PubMed
• Muruve, D.A., Petrilli, V., Zaiss, A.K., White, L.R., Clark, S.A, Ross, J., Parks, R.A., Tschopp, J. (2008). The inflammasome recognizes cytosolic microbial and host DNA and triggers an innate immune response. Nature, 452, 103-107. PubMed
• Dostert, C., Petrilli, V., Van Bruggen, R., Steele, C., Mossman, B.T., Tschopp, J. (2008). Innate immune activation through Nalp3 inflammasome sensing of asbestos and silica. Science 320, 674-677. PubMed
• Michallet, M.C., Meylan, E., Ermolaeva, M.A., Vazquez, J., Rebsamen, M., Curran, J., Poeck, H., Bscheider, M., Hartmann, G., Konig, M., et al. (2008). TRADD protein is an essential component of the RIG-like helicase antiviral pathway. Immunity 28, 651-661. PubMed
• Park, H.H., Logette, E., Raunser, S., Cuenin, S., Walz, T., Tschopp, J., Wu, H. (2007). Death Domain Assembly Mechanism Revealed by Crystal Structure of the Oligomeric PIDDosome Core Complex. Cell 128, 533-546. PubMed
• Mayor, A., Martinon, F., De Smedt, T., Petrilli, V., Tschopp, J. (2007). A crucial function of SGT1 and HSP90 in inflammasome activity links mammalian and plant innate immune responses. Nat. Immunol. 8, 497-503. PubMed
• Papin, S., Cuenin, S., Agostini, L., Martinon, F., Werner, S., Beer, H., Grütter, C., Grütter, M., Tschopp, J. (2007). The SPRY domain of Pyrin, mutated in familial Mediterranean fever patients, interacts with inflammasome components and inhibits proIL-1beta processing. Cell Death Differ. 14, 1457-66. PubMed
• Pétrilli, V., Dostert, C., Muruve, D., Tschopp, J. (2007a). The inflammasome: a danger sensing complex triggering innate immunity. Curr Opin Immunol. 19, 615-22. PubMed
• Pétrilli, V., Papin, S., Dostert, C., Mayor, A., Martinon, F. Tschopp, J. (2007b). Activation of the NALP3 inflammasome is triggered by low intracellular potassium concentration. Cell Death Differ. 14, 1583-9. PubMed
• Rossi, D.C., Ballenegger, S., Ingold, K., Schneider, P. Tschopp, J. (2007). Kino me siRNA screen of the human Fas pathway. Swiss Medical Weekly. 137, 29S-29S.
• Schwaller, J., Schneider, P., Mhawech-Fauceglia, P., McKee, T., Myit, S., Matthes, T., Tschopp, J., Donze, O., F. A. Le Gal and B. Huard (2007) Neutrophil-derived APRIL concentrated in tumor lesions by proteoglycans correlates with human B-cell lymphoma aggressiveness. Blood. 109, 331-338. PubMed
• Tinel, A., Janssens, S., Lippens, S., Cuenin, S., Logette, E., Jaccard, B., Quadroni, M., Tschopp, J. (2007). Autoproteolysis of PIDD marks the bifurcation between pro-death caspase-2 and pro-survival NF-kappaB pathway. EMBO J. 26, 197-208. PubMed
• Martinon, F., Tschopp, J. (2007). Inflammatory caspases and inflammasomes: master switches of inflammation. Cell Death Differ. 14, 10-22. PubMed
• Pétrilli, V., Martinon, F. (2007). The inflammasome, autoinflammatory diseases, and gout. Joint Bone Spine. 74, 571-6. PubMed
• Dostert, C., Meylan, E., Tschopp, J. (2007). Intracellular pattern-recognition receptors. Adv Drug Deliv Rev. 60, 830-40. PubMed
• Kummer, J.A., Micheau, O., Schneider, P., Bovenschen, N., Broekhuizen, R., Quadir, R., Strik, M.C.M., Hack, C. E., Tschopp, J. (2007). Ectopic expression of the serine protease inhibitor PI9 modulates death receptor-mediated apoptosis. Cell Death and Differentiation. 14, 1486-1496. PubMed

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