Tripartite motif (TRIM) proteins make up a large family of coiledcoil-containing RING E3 ligases that function in many cellular processes, particularly innate antiviral response pathways. Both dimerization and higher-order assembly are important elements of TRIM protein function, but the atomic details of TRIM tertiary and quaternary structure have not been fully understood. Here, we present crystallographic and biochemical analyses of the TRIM coiled-coil and show that TRIM proteins dimerize by forming interdigitating antiparallel helical hairpins that position the Nterminal catalytic RING domains at opposite ends of the dimer and the C-terminal substrate-binding domains at the center. The dimer core comprises an antiparallel coiled-coil with a distinctive, symmetric pattern of flanking heptad and central hendecad repeats that appear to be conserved across the entire TRIM family. Our studies reveal how the coiled-coil organizes TRIM25 to polyubiquitylate the RIG-I/viral RNA recognition complex and how dimers of the TRIM5α protein are arranged within hexagonal arrays that recognize the HIV-1 capsid lattice and restrict retroviral replication.antiparallel dimer | disulfide crosslinking | X-ray crystallography T ripartite motif (TRIM) proteins make up the largest superfamily of RING E3 ubiquitin ligases, with more than 100 members in the human proteome (1, 2). TRIM proteins function in a variety of cellular pathways, and many regulate innate immunity and/or mediate antiviral responses. Antiviral TRIMs include TRIM25, which regulates the IFN response to RNA viruses (3, 4), and TRIM5α, which senses and inhibits early stages of retroviral replication (5, 6).TRIM proteins share a common N-terminal domain organization, termed the tripartite or RBCC (RING, B-box, coiled-coil) motif, followed by variable C-terminal protein recognition domains ( Fig. 1 A and B). "Linker" segments of unknown structure typically separate both the RING and B-box domains (L1) and the coiledcoil and terminal effector domains (L2). The coiled-coil region mediates oligomerization, and both homooligomeric and heterooligomeric TRIMs have been described (7-13). Furthermore, many TRIM proteins form higher-order assemblies in vitro and form punctate or fibrous structures in cells (14-16). For example, TRIM5α assembly allows the protein to function as a cytosolic patternrecognition receptor that can intercept the incoming capsids of diverse retroviruses, including HIV-1 (6). This results in species-specific "restriction" of viral replication (5), capsid dissociation (5, 6), and induction of innate immune responses (17). Retroviral capsids are recognized through a remarkable mechanism of multivalent pattern recognition. TRIM5α forms a homodimer (10, 11, 18), which can further assemble into a 2D lattice of linked hexagons (18). The hexagonal TRIM5α net matches the symmetry and spacing of the retroviral capsid surface lattice, thereby positioning multiple C-terminal B30.2/SPRY domains to interact with their repeating binding epitopes on the capsid.Struct...

Nobs et al. show that PPARγ drives pathogenic type-2 effector responses in the lung in both T cells and DCs by controlling IL-33–driven Th2 effector function and lung DC migration and Th2 priming capacity.

Generation of chimeric mice with Gpx4-proficient and Gpx4-deficient hematopoietic cells and analysis of blood parametersFemale wild-type (wt) recipient mice of 10 to 12 weeks (Taconic Biosciences, Köln) were lethally irradiated with 850 cGy and reconstituted with 10 6 BM cells from Gpx4 fl/fl ;CreERT2 or Gpx4 wt/wt ;CreERT2 donor mice. BM cells had been collected by flushing the leg bones and crushing the pelvic bone.

Tissue-resident macrophages play a crucial role in maintaining homeostasis. Macrophage progenitors migrate to tissues perinatally, where environmental cues shape their identity and unique functions. Here, we show that the absence of PPARγ affects neonatal development and VCAM-1 expression of splenic iron-recycling red pulp macrophages (RPMs) and bone marrow erythroblastic island macrophages (EIMs). Transcriptome analysis of the few remaining Pparg-deficient RPM-like and EIM-like cells suggests that PPARγ is required for RPM and EIM identity, cell cycling, migration, and localization, but not function in mature RPMs. Notably, Spi-C, another transcription factor implicated in RPM development, was not essential for neonatal expansion of RPMs, even though the transcriptome of Spic-deficient RPMs was strongly affected and indicated a loss of identity. Similarities shared by Pparg- and Spic-deficient RPM-like cells allowed us to identify pathways that rely on both factors. PPARγ and Spi-C collaborate in inducing transcriptional changes, including VCAM-1 and integrin αD expression, which could be required for progenitor retention in the tissue, allowing access to niche-related signals that finalize differentiation.

Tissue-resident macrophages (MΦ TR ) originate from at least two distinct waves of erythro-myeloid progenitors (EMP) arising in the yolk sac (YS) at E7.5 and E8.5 with the latter going through a liver monocyte intermediate. The relative potential of these precursors in determining development and functional capacity of MΦ TR remains unclear. Here, we studied development of alveolar macrophages (AM) after single and competitive transplantation of different precursors from YS, fetal liver, and fetal lung into neonatal Csf2ra À/À mice, which lack endogenous AM. Fetal monocytes, promoted by Myb, outcompeted primitive MΦ (pMΦ) in empty AM niches and preferentially developed to mature AM, which is associated with enhanced mitochondrial respiratory and glycolytic capacity and repression of the transcription factors c-Maf and MafB. Interestingly, AM derived from pMΦ failed to efficiently clear alveolar proteinosis and protect from fatal lung failure following influenza virus infection. Thus, our data demonstrate superior developmental and functional capacity of fetal monocytes over pMΦ in AM development and underlying mechanisms explaining replacement of pMΦ in fetal tissues.

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Growth arrest and DNA damage-inducible (GADD) 45 proteins are regulators of cell death and survival. The proinflammatory cytokine IL-1β strongly increases the level of the transcript encoding GADD45α in rat insulinproducing INS-1E cells. The activation of Gadd45α gene is clearly dependent on JNK and NF-κB activation and the synthesis of the secondary mediator nitric oxide (NO). Interestingly, the observed twelve-fold increase in the GADD45α-coding transcript level is not followed by increased expression of GADD45α at the protein level. An analysis of IL-1β toxicity in INS-1E cells overexpressing GADD45α revealed no correlation between theGADD45α protein level and the sensitivity to IL-1β toxicity. These findings suggest that the potential engagement of GADD45α in IL-1β toxicity towards beta cells is limited to the effects induced by the basal expression level of this protein.