The adaptor and signaling proteins TRAF2, TRAF3 and cIAP1 and cIAP2 were suggested to inhibit alternative nuclear factor kappa B (NF-κB) signaling in resting cells by targeting NF-κB inducing kinase (NIK) to ubiquitin-dependent degradation, thus preventing processing of the NF-κB2 precursor protein p100 to release p52. However, the respective functions of TRAF2 and TRAF3 in NIK degradation and activation of alternative NF-κB signaling has remained elusive. We now show that CD40 or BAFF receptor activation resulted in TRAF3 degradation in a cIAP1-cIAP2-and TRAF2-dependent way due to enhanced cIAP1, cIAP2 TRAF3-directed ubiquitin ligase activity. Receptor-induced activation of cIAP1 and cIAP2 correlated with their K63-linked ubiquitination by TRAF2. Degradation of TRAF3 prevented association of NIK with the cIAP1-cIAP2-TRAF2 ubiquitin ligase complex, which resulted in NIK stabilization and NF-κB2-p100 processing. Constitutive activation of this pathway causes perinatal lethality and lymphoid defects.

INTRODUCTION Parkinson’s disease (PD) is the second most common neurodegenerative disorder that leads to slowness of movement, tremor, rigidity and in the later stages of PD, cognitive impairment. Pathologically PD is characterized by the accumulation of α-synuclein in Lewy bodies and neurites. There is degeneration of neurons throughout the nervous system with the degeneration of dopamine neurons in the substantia nigra pars compacta leading to the major symptoms of PD. RATIONALE In the brains of PD patients, pathologic α-synuclein seems to spread from cell-to-cell via self-amplification, propagation, and transmission in a stereotypical and topographical pattern among neighboring cells and/or anatomically connected brain regions. The spread or transmission of pathologic α-synuclein is emerging as potentially important driver of PD pathogenesis. The underlying mechanisms and molecular entities responsible for the transmission of pathologic α-synuclein from cell-to-to cell are not known, but the entry of pathologic α-synuclein into neurons is thought to occur, in part through an active clathrin-dependent endocytic process. RESULTS Using recombinant α-synuclein pre-formed fibrils (PFF) as a model system to study the transmission of misfolded α-synuclein from neuron to neuron, we screened a library encoding transmembrane proteins for α-synuclein-biotin PFF binding candidates via detection by streptavidin-AP (alkaline phosphatase) staining. Three positive clones were identified that bind α-synuclein PFF and include lymphocyte-activation gene 3 (LAG3), neurexin 1β and amyloid beta precursor-like protein 1 (APLP1). Of these three transmembrane proteins, LAG3 demonstrated the highest ratio of selectivity for α-synuclein PFF over the α-synuclein monomer. α-Synuclein PFF binds to LAG3 in a saturable manner (Kd = 77 nM), while the α-synuclein monomer does not bind to LAG3. Co-immunoprecipitation also suggests that pathological α-synuclein PFF specifically binds to LAG3. Tau PFF, β-amyloid oligomer and β-amyloid PFF do not bind LAG3 indicating that LAG3 is specific for α-synuclein PFF. The internalization of α-synuclein PFF involves LAG3 since deletion of LAG3 reduces the endocytosis of α-synuclein PFF. LAG3 colocalizes with the endosomal GTPases, Rab5 and Rab7 and co-endocytoses with pathologic α-synuclein. Neuron-to-neuron transmission of pathologic α-synuclein and the accompanying pathology and neurotoxicity is substantially attenuated by deletion of LAG3 or by LAG3 antibodies. The lack of LAG3 also substantially delayed α-synuclein PFF induced loss of dopamine neurons, as well as biochemical and behavioral deficits in vivo. CONCLUSION We discovered that pathologic α-synuclein transmission and toxicity is initiated by binding to LAG3 and that neuron-to-neuron transmission of pathological α-synuclein involves the endocytosis of exogenous α-synuclein PFF by the engagement of LAG3 on neurons. Depletion of LAG3 or antibodies to LAG3 substantially reduce the pathology set in motion by the transmission of pathologic α-...

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Thymus-derived T reg cell (tT reg cell)' should be used instead of 'natural T reg cell (nT reg cell)'. 2. 'Peripherally derived T reg cell (pT reg cell)' should be used instead of 'induced or adaptive T reg cell (iT reg cell or aT reg cell)'. 3. 'In vitro-induced T reg cell (iT reg cell)' should be used to clearly distinguish between those T reg cell populations generated in vivo versus those generated in vitro. 4. T reg cell terms should be used only when there is definitive evidence justifying their use. 5. The development and use of new T reg cell terminology should be limited, especially for subpopulations.

Balanced production of type I interferons (IFN) and proinflammatory cytokines upon engagement of Toll-like receptors (TLRs), which signal via adaptors containing a Toll-IL-1-Receptor (TIR) domain, such as MyD88 and TRIF, has been proposed to control the pathogenesis of autoimmune disease and tumor responses to inflammation. Here we show that TRAF3, a ubiquitin ligase that interacts with both MyD88 and TRIF, differentially regulated production of IFN and proinflammatory cytokines. Degradative TRAF3 ubiquitination during MyD88-dependent TLR signaling was essential for activation of mitogen-activated protein kinases (MAPKs) and inflammatory cytokine production. By contrast, TRIF-dependent signaling triggered non-canonical TRAF3 self-ubiquitination that activated the IFN response. Inhibition of degradative TRAF3 ubiquitination prevented expression of all proinflammatory cytokines without impacting the IFN response.