Tumor necrosis factor (TNF) can induce apoptosis and activate NF-kappa B through signaling cascades emanating from TNF receptor 1 (TNFR1). TRADD is a TNFR1-associated signal transducer that is involved in activating both pathways. Here we show that TRADD directly interacts with TRAF2 and FADD, signal transducers that activate NF-kappa B and induce apoptosis, respectively. A TRAF2 mutant lacking its N-terminal RING finger domain is a dominant-negative inhibitor of TNF-mediated NF-kappa B activation, but does not affect TNF-induced apoptosis. Conversely, a FADD mutant lacking its N-terminal 79 amino acids is a dominant-negative inhibitor of TNF-induced apoptosis, but does not inhibit NF-kappa B activation. Thus, these two TNFR1-TRADD signaling cascades appear to bifurcate at TRADD.

Viral infection triggers activation of transcription factors such as NF-kappaB and IRF3, which collaborate to induce type I interferons (IFNs) and elicit innate antiviral response. Here, we identified MITA as a critical mediator of virus-triggered type I IFN signaling by expression cloning. Overexpression of MITA activated IRF3, whereas knockdown of MITA inhibited virus-triggered activation of IRF3, expression of type I IFNs, and cellular antiviral response. MITA was found to localize to the outer membrane of mitochondria and to be associated with VISA, a mitochondrial protein that acts as an adaptor in virus-triggered signaling. MITA also interacted with IRF3 and recruited the kinase TBK1 to the VISA-associated complex. MITA was phosphorylated by TBK1, which is required for MITA-mediated activation of IRF3. Our results suggest that MITA is a critical mediator of virus-triggered IRF3 activation and IFN expression and further demonstrate the importance of certain mitochondrial proteins in innate antiviral immunity.

The tumor necrosis factor receptor 2 signal transducers TRAF2 and c-IAP1 are components of the tumor necrosis factor receptor 1 signaling complex (tumor necrosis factor signaling) HONG-BING SHU, MASAHIRO TAKEUCHI, AND DAVID V. GOEDDEL Tularik, Inc., Two Corporate Drive, South San Francisco, CA 94080 Contributed by David V. Goeddel, September 19, 1996 ABSTRACTThe two cell surface receptors for tumor necrosis factor (TNF) interact with a number of intracellular signal transducing proteins. The association of TRADD, a 34-kDa cytoplasmic protein containing a C-terminal death domain, with aggregated TNF receptor 1 (TNF-R1) through their respective death domains leads to NF-B activation and programmed cell death. In contrast, TNF receptor 2 (TNF-R2) interacts with the TNF receptor associated factors 2͞1 (TRAF2͞TRAF1) heterocomplex, which mediates the recruitment of two cellular inhibitor of apoptosis proteins (c-IAP1 and c-IAP2) to TNF-R2. Here we show that the TNF-R2 signal transducers TRAF2 and c-IAP1 are a part of the TNF-R1 signaling complex. The recruitment of TRAF2 and c-IAP1 to TNF-R1 is TNF-dependent, is mediated by TRADD, and is independent of TNF-R2. These data establish the physiological involvement of TRAF2 and c-IAP1 in TNF-R1 signaling and help provide a molecular explanation for both the overlapping and distinct signals generated by the two TNF receptors.

SUMMARY Stimulator of interferon genes (STING, also named MITA, MYPS or ERIS) is an intracellular DNA sensor that induces type I interferon through its interaction with TANK-binding kinase 1 (TBK1). Here we found that the nucleotide-binding, leucine-rich repeat containing protein, NLRC3, reduced STING-dependent innate immune activation in response to cytosolic DNA, cyclic di-GMP (c-di-GMP) and DNA viruses. NLRC3 associated with both STING and TBK1, and impeded STING-TBK1 interaction and downstream type I interferon production. Using purified recombinant proteins NLRC3 was found to interact directly with STING. Furthermore, NLRC3 prevented proper trafficking of STING to perinuclear and punctated region, known to be important for its activation. In animals, herpes simplex virus 1 (HSV-1)-infected Nlrc3−/− mice exhibited enhanced innate immunity, reduced morbidity and viral load. This demonstrates the intersection of two key pathways of innate immune regulation, NLR and STING, to fine tune host response to intracellular DNA, DNA virus and c-di-GMP

The arterial wail responds to thrombosis or mechanical I jury through the induction of specific gene products that increase cellular proliferation and connective tissue formation. These changes result in intimal hyperplasia that is observed in restenosis and the early phases of atherosclerosis. gene: procoUlagen synthesis induced by TGF-131 was greater, and celular proliferation was less prominent. These rmdings show that TGF-8l1 differentially modulates extracellular matrix production and cellular proliferation in the arterial wall in vivo and could play a reparative role in the response to arterial inJury.