FAT10 inhibits TRIM21 to down-regulate antiviral type-I interferon secretion.

The ubiquitin-like modifier FAT10 is upregulated under pro-inflammatory conditions, targets its substrates for proteasomal degradation and functions as a negative regulator of the type-I IFN response. Influenza A virus infection upregulates the production of type-I IFN and the expression of the E3 ligase TRIM21, which regulates type-I IFN production in a positive feedback manner. In this study, we show that FAT10 becomes covalently conjugated to TRIM21 and that this targets TRIM21 for proteasomal degradation.

Corrigendum: Immunoproteasome inhibition attenuates experimental psoriasis.

[This corrects the article DOI: 10.3389/fimmu.2022.

FAT10 is phosphorylated by IKKβ to inhibit the antiviral type-I interferon response.

IFN-I secretion provides a rapid host defense against infection with RNA viruses. Within the host cell, viral RNA triggers the activation of the RIG-I signaling pathway, leading to the production of IFN-I. Because an exaggerated IFN-I response causes severe tissue damage, RIG-I signaling is tightly regulated.

Tumor necrosis factor mediates USE1-independent FAT10ylation under inflammatory conditions.

The ubiquitin-like modifier FAT10 is up-regulated in many different cell types by IFNγ and TNFα (TNF) and directly targets proteins for proteasomal degradation. FAT10 gets covalently conjugated to its conjugation substrates by the E1 activating enzyme UBA6, the E2 conjugating enzyme USE1, and E3 ligases including Parkin. To date, USE1 was supposed to be the only E2 enzyme for FAT10ylation, and we show here that a knockout of USE1 strongly diminished FAT10 conjugation.

The ubiquitin-like modifier FAT10 covalently modifies HUWE1 and strengthens the interaction of AMBRA1 and HUWE1.

The ubiquitin-like modifier FAT10 is highly upregulated under inflammatory conditions and targets its conjugation substrates to the degradation by the 26S proteasome. This process termed FAT10ylation is mediated by an enzymatic cascade and includes the E1 activating enzyme ubiquitin-like modifier activating enzyme 6 (UBA6), the E2 conjugating enzyme UBA6-specific E2 enzyme 1 (USE1) and E3 ligases, such as Parkin. In this study, the function of the HECT-type ubiquitin E3 ligase HUWE1 was investigated as a putative E3 ligase and/or conjugation substrate of FAT10.

FAT10 and NUB1L cooperate to activate the 26S proteasome.

The interaction of the 19S regulatory particle of the 26S proteasome with ubiquitylated proteins leads to gate opening of the 20S core particle and increases its proteolytic activity by binding of the ubiquitin chain to the inhibitory deubiquitylation enzyme USP14 on the 19S regulatory subunit RPN1. Covalent modification of proteins with the cytokine inducible ubiquitin-like modifier FAT10 is an alternative signal for proteasomal degradation. Here, we report that FAT10 and its interaction partner NUB1L facilitate the gate opening of the 20S proteasome in an ubiquitin- and USP14-independent manner.

The ubiquitin-like modifier FAT10 is degraded by the 20S proteasome in vitro but not in cellulo.

Ubiquitin-independent protein degradation via the 20S proteasome without the 19S regulatory particle has gained increasing attention over the last years. The degradation of the ubiquitin-like modifier FAT10 by the 20S proteasome was investigated in this study. We found that FAT10 was rapidly degraded by purified 20S proteasomes in vitro, which was attributed to the weak folding of FAT10 and the N-terminally disordered tail.

Immunoproteasome inhibition attenuates experimental psoriasis.

Introduction: Psoriasis is an autoimmune skin disease associated with multiple comorbidities. The immunoproteasome is a special form of the proteasome expressed in cells of hematopoietic origin.

Methods: The therapeutic use of ONX 0914, a selective inhibitor of the immunoproteasome, was investigated in mice, which spontaneously develop psoriasis-like symptoms, and in the imiquimod murine model.

Co-inhibition of immunoproteasome subunits LMP2 and LMP7 enables prevention of transplant arteriosclerosis.

Aims: The loss of vascular wall cells in allotransplanted arteries is the initial event leading to transplant arteriosclerosis (TA) and ensuing loss of allograft function. Pharmacological agents able to prevent TA are currently lacking. We previously showed that selective inhibition of the immunoproteasome prevented the chronic rejection of renal allografts.

Valosin-containing protein (VCP/p97) inhibition reduces viral clearance and induces toxicity associated with muscular damage.

Valosin-containing protein (VCP)/p97 has emerged as a central regulator of the ubiquitin-proteasome system by connecting ubiquitylation and degradation. The development of CB-5083, an ATPase D2-domain-selective and orally bioavailable inhibitor of VCP/p97, allows targeting of the ubiquitin-proteasome system in human diseases. In this study, we evaluated the effect of CB-5083 on the immune response in mice by using the lymphocytic choriomeningitis virus (LCMV) as an infection model.

Immunoproteasome Inhibition Reduces the T Helper 2 Response in Mouse Models of Allergic Airway Inflammation.

Background: Allergic asthma is a chronic disease and medical treatment often fails to fully control the disease in the long term, leading to a great need for new therapeutic approaches. Immunoproteasome inhibition impairs T helper cell function and is effective in many (auto-) inflammatory settings but its effect on allergic airway inflammation is unknown.

Methods: Immunoproteasome expression was analyzed in polarized T helper cell subsets.

PLGA-particle vaccine carrying TLR3/RIG-I ligand Riboxxim synergizes with immune checkpoint blockade for effective anti-cancer immunotherapy.

With emerging supremacy, cancer immunotherapy has evolved as a promising therapeutic modality compared to conventional antitumor therapies. Cancer immunotherapy composed of biodegradable poly(lactic-co-glycolic acid) (PLGA) particles containing antigens and toll-like receptor ligands induces vigorous antitumor immune responses in vivo. Here, we demonstrate the supreme adjuvant effect of the recently developed and pharmaceutically defined double-stranded (ds)RNA adjuvant Riboxxim especially when incorporated into PLGA particles.

Silencing of the proteasome and oxidative stress impair endoplasmic reticulum targeting and signal cleavage of a prostate carcinoma antigen.

The endoplasmic reticulum (ER) is an organelle with high protein density and therefore prone to be damaged by protein aggregates. One proposed preventive measure is a pre-emptive quality control pathway that attenuates ER import during protein folding stress. ER resident proteins are targeted into the ER via signal peptides cleaved rapidly upon ER insertion by the ER signal peptidase.

Immunoproteasome Upregulation Is Not Required to Control Protein Homeostasis during Viral Infection.

The prime function of proteasomes is the control of protein homeostasis in cells (i.e., the removal of proteins that are not properly folded, damaged by stress conditions like reactive oxygen species formation, or degraded on the basis of regular protein turnover).

Parkin is an E3 ligase for the ubiquitin-like modifier FAT10, which inhibits Parkin activation and mitophagy.

Parkin is an E3 ubiquitin ligase belonging to the RING-between-RING family. Mutations in the Parkin-encoding gene PARK2 are associated with familial Parkinson's disease. Here, we investigate the interplay between Parkin and the inflammatory cytokine-induced ubiquitin-like modifier FAT10.

Recent insights how combined inhibition of immuno/proteasome subunits enables therapeutic efficacy.

The proteasome is a multicatalytic protease in the cytosol and nucleus of all eukaryotic cells that controls numerous cellular processes through regulated protein degradation. Proteasome inhibitors have significantly improved the survival of multiple myeloma patients. However, clinically approved proteasome inhibitors have failed to show efficacy against solid tumors, neither alone nor in combination with other therapies.

The ubiquitin-like modifier FAT10 - much more than a proteasome-targeting signal.

Human leukocyte antigen (HLA)-F adjacent transcript 10 (FAT10) also called ubiquitin D (UBD) is a member of the ubiquitin-like modifier (ULM) family. The gene is localized in the MHC class I locus and FAT10 protein expression is mainly restricted to cells and organs of the immune system. In all other cell types and tissues, FAT10 expression is highly inducible by the pro-inflammatory cytokines interferon (IFN)-γ and tumor necrosis factor (TNF).

Evidence for an involvement of the ubiquitin-like modifier ISG15 in MHC class I antigen presentation.

The IFN stimulated gene 15 (ISG15) encodes a 15-kDa ubiquitin-like protein, that is induced by type I IFNs and is conjugated to the bulk of newly synthesized polypeptides at the ribosome. ISG15 functions as an antiviral molecule possibly by being covalently conjugated to viral proteins and disturbing virus particle assembly. Here, we have investigated the effect of ISGylation on degradation and antigen presentation of viral and cellular proteins.

Regulation of Interferon Induction by the Ubiquitin-Like Modifier FAT10.

The revelation that the human major histocompatibility complex (MHC) class I locus encodes a ubiquitin-like protein designated HLA-F adjacent transcript 10 (FAT10) or ubiquitin D (UBD) has attracted increasing attention to the function of this protein. Interestingly, the pro-inflammatory cytokines interferon (IFN)-γ and tumor necrosis factor (TNF) α synergize to strongly induce FAT10 expression, thereby suggesting a role of FAT10 in the immune response. Recent reports that FAT10 downregulates type I interferon production while it upregulates IFN-γ pose mechanistic questions on how FAT10 differentially regulates interferon induction.

FAT10 localises in dendritic cell aggresome-like induced structures and contributes to their disassembly.

Dendritic cell (DC) aggresome-like induced structures (DALIS) are protein aggregates of polyubiquitylated proteins that form transiently during DC maturation. DALIS scatter randomly throughout the cytosol and serve as antigen storage sites synchronising DC maturation and antigen presentation. Maturation of DCs is accompanied by the induction of the ubiquitin-like modifier FAT10 (also known as UBD), which localises to aggresomes, structures that are similar to DALIS.

Membrane Compartmentalization and Scaffold Proteins in Leukocyte Migration.

Leukocyte migration across vessels into and within peripheral and lymphoid tissues is essential for host defense against invading pathogens. Leukocytes are specialized in sensing a variety of guidance cues and to integrate environmental stimuli to navigate in a timely and spatially controlled manner. These extracellular signals must be transmitted across the leukocyte's plasma membrane in a way that intracellular signaling cascades enable directional cell movement.

The ubiquitin-like modifier FAT10 interferes with SUMO activation.

The covalent attachment of the cytokine-inducible ubiquitin-like modifier HLA-F adjacent transcript 10 (FAT10) to hundreds of substrate proteins leads to their rapid degradation by the 26 S proteasome independently of ubiquitylation. Here, we identify another function of FAT10, showing that it interferes with the activation of SUMO1/2/3 in vitro and down-regulates SUMO conjugation and the SUMO-dependent formation of promyelocytic leukemia protein (PML) bodies in cells. Mechanistically, we show that FAT10 directly binds to and impedes the activity of the heterodimeric SUMO E1 activating enzyme AOS1/UBA2 by competing very efficiently with SUMO for activation and thioester formation.

Flotillins promote T cell receptor sorting through a fast Rab5-Rab11 endocytic recycling axis.

The targeted endocytic recycling of the T cell receptor (TCR) to the immunological synapse is essential for T cell activation. Despite this, the mechanisms that underlie the sorting of internalised receptors into recycling endosomes remain poorly understood. To build a comprehensive picture of TCR recycling during T cell activation, we developed a suite of new imaging and quantification tools centred on photoactivation of fluorescent proteins.