Molecular and physiological roles of Pellino E3 ubiquitin ligases in immunity

A plant virus attenuates the Toll immune pathway by degradation of Pellino to facilitate viral infection in insect vectors

Many plant viruses are persistently transmitted by insect vectors. The viral antagonism of insect innate immune responses is a critical step in ensuring persistent viral infection. Recent studies have shown that the Toll immune pathway mediates the persistent and propagative transmission of rice stripe virus (RSV) in its insect vector (Laodelphax striatellus). However, whether other host factors are involved in the Toll pathway and how RSV counteracts the Toll immune response in L. striatellus remain unclear. Here, we reported that LsPellino also inhibited RSV infection in L. striatellus by interacting with LsTube and participating in the Toll immune pathway. In contrast, the viral nonstructural protein NS3 hijacked the suppressor of cytokine signaling 5 (LsSOCS5) to promote the degradation of LsPellino via the 26S proteasome pathway, thereby suppressing the Toll immune response. In summary, these findings demonstrate that RSV attenuates the Toll immune pathway by degradation of LsPellino to facilitate viral infection in insect vectors. Our research provides new insights into controlling the transmission of vector-borne viruses.

IMPORTANCE

Plant virus diseases pose a serious threat to global crop production. Nearly half of the known plant viruses are persistently transmitted by insect vectors, and these plant viruses must counteract various innate immune responses to maintain persistent infection. Here, we uncover a novel counter-defense mechanism against Toll antiviral defense. Our research showed that LsPellino exerts antiviral function by interacting with LsTube and participating in the Toll immune pathway. To counteract this immunity, a plant virus, rice stripe virus, attenuates the Toll immune pathway and promotes viral infection by using viral nonstructural protein NS3 to mediate the degradation of LsPellino in its insect vector, Laodelphax striatellus. This study not only contributes to a better understanding of the arms race between viruses and insect vectors but also provides a new perspective for controlling the transmission of plant viruses.

Tumoural Pellino-1 expression and Pellino-1-expressive cytotoxic T-cells are associated with poor prognosis in diffuse large B-cell lymphoma

Pellino-1 plays a role in regulating inflammation and immune responses, and its effects on tumours are complex, with different outcomes reported in various studies. Additionally, the role of Pellino-1 in diffuse large B-cell lymphoma (DLBCL) has not been thoroughly investigated. We aimed to examine the expression of Pellino-1 in tumour cells and tumour-infiltrating lymphocytes (TILs) separately and identify the clinicopathological significance of Pellino-1 expression in DLBCL. We evaluated Pellino-1 expression in 104 patients with DLBCL. The density of specific cell types was quantitatively analysed using digital image analysis after a multiplex immunofluorescence staining with Pellino-1, CD20, CD8, FOXP3, and PD-1. Pellino-1 expression was mostly observed in CD20+ tumour cells and CD8+ TILs. The high CD8+/Pellino-1+ group was significantly associated with the non-GCB subtype and higher numbers of Foxp3+ T-cells. Patients with high CD20+/Pellino-1+ and high CD8+/Pellino-1+ cell densities had significantly shorter event-free survival (EFS) rates. The multivariate Cox-regression analysis showed that CD20+/Pellino-1+ cell density and CD8+/Pellino-1+ cell density were independent poor prognostic factors for EFS. Furthermore, patients with low densities of both CD20+/Pellino-1+ and CD8+/Pellino-1+ cells demonstrated a prognosis superior to that of patients with high Pellino-1+ cell densities, either alone or in combination. Additionally, the multivariate analysis demonstrated that the combination of CD20+/Pellino-1+ and CD8+/Pellino-1+ cell densities was an independent prognostic factor for EFS and overall survival. Pellino-1 expression was observed in both tumour cells and TILs, particularly in cytotoxic T-cells, and was correlated with poor outcomes in DLBCL. Thus, Pellino-1 might have an oncogenic effect on DLBCL and might be a potential target for improving cytotoxic T-cell activity.

TonEBP: A Key Transcription Factor in Microglia Following Intracerebral Hemorrhage Induced-Neuroinflammation

Transcription factors within microglia contribute to the inflammatory response following intracerebral hemorrhage (ICH). Therefore, we employed bioinformatics screening to identify the potential transcription factor tonicity-responsive enhancer-binding protein (TonEBP) within microglia. Inflammatory stimuli can provoke an elevated expression of TonEBP in microglia. Nevertheless, the expression and function of microglial TonEBP in ICH-induced neuroinflammation remain ambiguous. In our recent research, we discovered that ICH instigated an increased TonEBP in microglia in both human and mouse peri-hematoma brain tissues. Furthermore, our results indicated that TonEBP knockdown mitigates lipopolysaccharide (LPS)-induced inflammation and the activation of NF-κB signaling in microglia. In order to more deeply comprehend the underlying molecular mechanisms of how TonEBP modulates the inflammatory response, we sequenced the transcriptomes of TonEBP-deficient cells and sought potential downstream target genes of TonEBP, such as Pellino-1 (PELI1). PELI has been previously reported to mediate nuclear factor-κB (NF-κB) signaling. Through the utilization of CUT & RUN, a dual-luciferase reporter, and qPCR, we confirmed that TonEBP is the transcription factor of Peli1, binding to the Peli1 promoter. In summary, TonEBP may enhance the LPS-induced inflammation and activation of NF-κB signaling via PELI1.

Pellino-1 expression is associated with epidermal proliferation and enhanced Th17 cell infiltration in psoriatic lesions

Pellino-1 plays a crucial role in cellular proliferation and regulates inflammatory processes. This study investigated Pellino-1 expression patterns and their relationship with CD4+ T-cell subsets in psoriasis patients. Group 1 comprised primarily biopsied psoriasis lesions from 378 patients, multiplex-immunostained for Pellino-1, CD4 and representative T helper (Th) cells (T-bet [Th1], GATA3 [Th2], and RORγt [Th17] and regulatory T cell [FoxP3] markers). Ki-67 labeling was evaluated in the epidermis. Group 2 comprised 43 Pellino-1-positive cases immunostained for Pellino-1 in both lesion and non-lesion skin biopsy samples. Five normal skin biopsies served as controls. Among 378 psoriasis cases, 293 (77.5%) were positive for Pellino-1 in the epidermis. Pellino-1-positivity was higher in psoriasis lesions than in non-lesions and normal skin (52.55% vs. 40.43% vs. 3.48%, p < 0.001; H-score, 72.08 vs. 47.55 vs. 4.40, p < 0.001, respectively). Pellino-1-positive cases also had a significantly higher Ki-67 labeling index (p < 0.001). Epidermal Pellino1-positivity was significantly associated with higher RORγt+ (p = 0.001) and FoxP3+ (p < 0.001) CD4+ T cell ratios but not T-bet+ and GATA3+ CD4+ T cell ratios. Among the CD4+ Pellino-1+ T-cell subsets, the CD4+ Pellino-1+ RORγt+ ratio was significantly associated with epidermal Pellinio-1 expression (p < 0.001). Pellino-1 expression is thus increased in psoriasis lesions and associated with increased epidermal proliferation and CD4+ T-cell subset infiltration, especially Th17 cells. This suggests that Pellino-1 could be a therapeutic target that simultaneously regulates psoriasis epidermal proliferation and immune interactions.

Pellino Proteins in Viral Immunity and Pathogenesis

Pellino proteins are a family of evolutionarily conserved ubiquitin ligases involved in intracellular signaling in a wide range of cell types. They are essential for microbe detection and the initiation of innate and adaptive immune responses. Some viruses specifically target the Pellino proteins as part of their immune evasion strategies. Through studies of mouse models of viral infections in the central nervous system, heart, lungs, and skin, the Pellino proteins have been linked to both beneficial and detrimental immune responses. Only in recent years have some of the involved mechanisms been identified. The objective of this review is to highlight the many diverse aspects of viral immunity and pathogenesis that the Pellino proteins have been associated with, in order to promote further research into their functions. After a brief introduction to the cellular signaling mechanisms involving Pellino proteins, their physiological roles in the initiation of immune responses, pathogenesis through excess inflammation, immune regulation, and cell death are presented. Known viral immune evasion strategies are also described. Throughout, areas that require more in-depth investigation are identified. Future research into the functions of the Pellino protein family may reveal fundamental insights into how our immune system works. Such knowledge may be leveraged in the fight against viral infections and their sequala.

Pellino1 Restricts Herpes Simplex Virus Infections in the Epidermis and Dissemination to Sebaceous Glands

Nearly all adults are infected with one or more herpes viruses. The most common are herpes simplex virus (HSV)-1 and HSV-2, which upon reactivation can cause painful skin and mucosal erosions. Patients who are immune compromised often experience frequent, atypical, or chronic lesions and thus a greatly diminished QOL. Pellino1 is a ubiquitin ligase involved in IL-1 and toll-like receptor signaling; however, the role of Pellino1 in skin immunity against HSV is unknown. In this study, using the mouse-flank HSV-1 skin infection model, we show that Pellino1 has several critical functions during active viral replication. Peli1‒/‒ mice succumb more than wild-type mice to systemic disease and develop larger zosteriform skin lesions along affected dermatomes. In Pellino1-deficient mice, the virus spread extensively through the epidermis and follicular infundibulum into sebaceous glands where sebocytes were found positive for the virus. The latter did not appear to involve a shift in how the virus migrated through the nervous system. Immunohistochemistry revealed delayed recruitment of myeloid and T cells to the infected epidermis in Peli1‒/‒ mice. This was associated with decreased expression of the cytokine mRNAs Il1a, Il36b and 2610528A11Rik; the latter also known as Gpr15l. In conclusion, Pellino1 plays important roles in restricting viral dissemination, and the involved pathways may represent novel therapeutic targets in patients with frequent or chronic HSV infections.

Regulatory T Cells Overexpressing Peli1 Show Better Efficacy in Repairing Ovarian Endocrine Function in Autoimmune Premature Ovarian Insufficiency

Regulatory T (Treg) cell dysfunction is involved in the pathogenesis of autoimmune premature ovarian insufficiency (POI). Adoptive transfer of Treg cells has been shown to be effective in the treatment of autoimmune POI in mice. However, the therapeutic effect of Treg cell therapy is limited because the phenotype and function of Treg cells is not properly maintained when they are reinfused in an inflammatory environment. Therefore, enhancing the function of Treg cells using genetic engineering is of great significance for improving the efficacy of Treg cells in the treatment of immune diseases. In this study, we investigated the role of the E3 ubiquitinated ligase Pellino 1 (Peli1) in the proliferation and immunosuppressive function of Treg cells and the therapeutic effect of Treg cells overexpressing Peli1 on autoimmune POI. The results showed that the overexpression of Peli1 promoted cell proliferation and enhanced the immunosuppressive function of Treg cells in vitro. After the adoptive transfer of Treg cells overexpressing Peli1 in autoimmune POI mice, the apoptosis rate of ovarian granulosa cells declined. The levels of the inflammatory inhibitors interleukin 10 and transforming growth factor-β as well as the ovarian hormone estradiol were elevated. The number of primordial, primary, secondary, and mature follicles was restored to a certain extent compared with those in control subjects. These results revealed that the adoptive transfer of Treg cells overexpressing Peli1 promoted its efficacy against zona pellucida protein 3 peptide-induced POI, which provides new insights into the treatment of autoimmune POI.

Tril dampens Nodal signaling through Pellino2- and Traf6-mediated activation of Nedd4l

Toll-like receptor 4 (Tlr) interactor with leucine-rich repeats (Tril) functions as a Tlr coreceptor to mediate innate immunity in adults. In Xenopus embryos, Tril triggers degradation of the transforming growth factor β (Tgf-ß) family inhibitor, Smad7. This enhances bone morphogenetic protein (Bmp) signaling to enable ventral mesoderm to commit to a blood fate. Here, we show that Tril simultaneously dampens Nodal signaling by catalytically activating the ubiquitin ligase NEDD4 Like (Nedd4l). Nedd4l then targets Nodal receptors for degradation. How Tril signals are transduced in a nonimmune context is unknown. We identify the ubiquitin ligase Pellino2 as a protein that binds to the cytoplasmic tail of Tril and subsequently forms a complex with Nedd4l and another E3 ligase, TNF-receptor associated factor 6 (Traf6). Pellino2 and Traf6 are essential for catalytic activation of Nedd4l, both in Xenopus and in mammalian cells. Traf6 ubiquitinates Nedd4l, which is then recruited to membrane compartments where activation occurs. Collectively, our findings reveal that Tril initiates a noncanonical Tlr-like signaling cascade to activate Nedd4l, thereby coordinately regulating the Bmp and Nodal arms of the Tgf-ß superfamily during vertebrate development.

ECSIT is a critical limiting factor for cardiac function

Evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) is a protein with roles in early development, activation of the transcription factor NF-κB, and production of mitochondrial reactive oxygen species (mROS) that facilitates clearance of intracellular bacteria like Salmonella. ECSIT is also an important assembly factor for mitochondrial complex I. Unlike the murine form of Ecsit (mEcsit), we demonstrate here that human ECSIT (hECSIT) is highly labile. To explore whether the instability of hECSIT affects functions previously ascribed to its murine counterpart, we created a potentially novel transgenic mouse in which the murine Ecsit gene is replaced by the human ECSIT gene. The humanized mouse has low levels of hECSIT protein, in keeping with its intrinsic instability. Whereas low-level expression of hECSIT was capable of fully compensating for mEcsit in its roles in early development and activation of the NF-κB pathway, macrophages from humanized mice showed impaired clearance of Salmonella that was associated with reduced production of mROS. Notably, severe cardiac hypertrophy was manifested in aging humanized mice, leading to premature death. The cellular and molecular basis of this phenotype was delineated by showing that low levels of human ECSIT protein led to a marked reduction in assembly and activity of mitochondrial complex I with impaired oxidative phosphorylation and reduced production of ATP. Cardiac tissue from humanized hECSIT mice also showed reduced mitochondrial fusion and more fission but impaired clearance of fragmented mitochondria. A cardiomyocyte-intrinsic role for Ecsit in mitochondrial function and cardioprotection is also demonstrated. We also show that cardiac fibrosis and damage in humans correlated with low expression of human ECSIT. In summary, our findings identify a role for ECSIT in cardioprotection, while generating a valuable experimental model to study mitochondrial dysfunction and cardiac pathophysiology.

Identification of MTHFD2 as a novel prognosis biomarker in esophageal carcinoma patients based on transcriptomic data and methylation profiling

DNA methylation is an important epigenetic regulatory mechanism in esophageal carcinoma (EC) and is associated with genomic instability and carcinogenesis. In the present study, we aimed to identify tumor biomarkers for predicting prognosis of EC patients.We downloaded mRNA expression profiles and DNA methylation profiles associated with EC from the Gene Expression Omnibus database. Differentially expressed and differentially methylated genes between tumor tissues and adjacent normal tissue samples were identified. Functional enrichment analyses were performed, followed by the construction of protein-protein interaction networks. Data were validated based on methylation profiles from The Cancer Genome Atlas. Candidate genes were further verified according to survival analysis and Cox regression analysis.We uncovered multiple genes with differential expression or methylation in tumor samples compared with normal samples. After taking the intersection of 3 differential gene sets, we obtained a total of 232 overlapping genes. Functional enrichment analysis revealed that these genes are related to pathways such as "glutathione metabolism," "p53 signaling pathway," and "focal adhesion." Furthermore, 8 hub genes with inversed expression and methylation correlation were identified as candidate genes. The abnormal expression levels of MSN, PELI1, and MTHFD2 were correlated with overall survival times in EC patients (P < .05). Only MTHFD2 was significantly associated with a pathologic stage according to univariate analysis (P = .037) and multivariate analysis (P = .043).Our study identified several novel EC biomarkers with prognostic value by integrated analysis of transcriptomic data and methylation profiles. MTHFD2 could serve as an independent biomarker for predicting prognosis and pathological stages of EC.

Pellino1 promotes chronic inflammatory skin disease via keratinocyte hyperproliferation and induction of the T helper 17 response

Psoriasis is one of the most common immune-mediated chronic inflammatory skin diseases. However, little is known about the molecular mechanism underlying the immunological circuits that maintain innate and adaptive immune responses in established psoriasis. In this study, we found that the Pellino1 (Peli1) ubiquitin E3 ligase is activated by innate pattern-recognition receptors (PRRs), such as Toll-like receptors (TLRs), and is highly upregulated in human psoriatic skin lesions and murine psoriasis-like models. Increased Peli1 expression is strongly correlated with the immunopathogenesis of psoriasis by activating hyperproliferation of keratinocytes in the S and G2/M phases of the cell cycle and promoting chronic skin inflammation. Furthermore, Peli1-induced psoriasis-like lesions showed significant changes in the expression levels of several T helper 17 (Th17)-related cytokines, such as IL-17a, IL-21, IL-22, IL-23, and IL-24, indicating that overexpression of Peli1 resulted in the sequential engagement of the Th17 cell response. However, the overexpression of Peli1 in T cells was insufficient to trigger psoriasis, while T cells were indispensable for disease manifestation. In summary, our findings demonstrate that Peli1 is a critical cell cycle activator of innate immunity, which subsequently links Th17 cell immune responses to the psoriatic microenvironment.

An immune-regulating protein that mediates chronic inflammation in the skin offers a new therapeutic target for the autoimmune disorder psoriasis. A research team from South Korea led by Chang-Woo Lee from Sungkyunkwan University School of Medicine in Suwon and Heounjeong Go from the University of Ulsan College of Medicine in Seoul have discovered that Pellino1, a protein known to modulate immune responses to pathogens, is also found in abundance in the skin lesions of people with psoriasis. Using mouse models, the researchers showed how Pellino1 induces the proliferation of certain skin cells and triggers an inflammatory state through the activation of small proteins and immune cells normally involved in defense against infection. Targeting strategy that inactivate Pellino1 could help blunt the inflammatory signaling in the skin that drives the development of psoriatic lesions.

Identification and Molecular Characterization of a Pellino Protein in Kuruma Prawn (Marsupenaeus Japonicus) in Response to White Spot Syndrome Virus and Vibrio Parahaemolyticus Infection

Kuruma prawn, Marsupenaeus japonicus, has the third largest annual yield among shrimp species with vital economic significance in China. White spot syndrome virus (WSSV) is a great threat to the global shrimp farming industry and results in high mortality. Pellino, a highly conserved E3 ubiquitin ligase, has been found to be an important modulator of the Toll-like receptor (TLR) signaling pathways that participate in the innate immune response and ubiquitination. In the present study, the Pellino gene from Marsupenaeus japonicus was identified. A qRT-PCR assay showed the presence of MjPellino in all the tested tissues and revealed that the transcript level of this gene was significantly upregulated in both the gills and hemocytes after challenge with WSSV and Vibrio parahaemolyticus. The function of MjPellino was further verified at the protein level. The results of the three-dimensional modeling and protein-protein docking analyses and a GST pull-down assay revealed that the MjPellino protein was able to bind to the WSSV envelope protein VP26. In addition, the knockdown of MjPellino in vivo significantly decreased the expression of MjAMPs. These results suggest that MjPellino might play an important role in the immune response of kuruma prawn.

Pellino-1 Regulates Immune Responses to Haemophilus influenzae in Models of Inflammatory Lung Disease

Non-typeable Haemophilus influenzae (NTHi) is a frequent cause of lower respiratory tract infection in people with chronic obstructive pulmonary disease (COPD). Pellino proteins are a family of E3 ubiquitin ligases that are critical regulators of TLR signaling and inflammation. The aim of this study was to identify a role for Pellino-1 in airway defense against NTHi in the context of COPD. Pellino-1 is rapidly upregulated by LPS and NTHi in monocyte-derived macrophages (MDMs) isolated from individuals with COPD and healthy control subjects, in a TLR4 dependent manner. C57BL/6 Peli1^−/− and wild-type (WT) mice were subjected to acute (single LPS challenge) or chronic (repeated LPS and elastase challenge) airway inflammation followed by NTHi infection. Both WT and Peli1^−/− mice develop airway inflammation in acute and chronic airway inflammation models. Peli1^−/− animals recruit significantly more neutrophils to the airway following NTHi infection which is associated with an increase in the neutrophil chemokine, KC, in bronchoalveolar lavage fluid as well as enhanced clearance of NTHi from the lung. These data suggest that therapeutic inhibition of Pellino-1 may augment immune responses in the airway and enhance bacterial clearance in individuals with COPD.

β-Arrestin-1 inhibits glucocorticoid receptor turnover and alters glucocorticoid signaling

Glucocorticoids are among the most widely used drugs to treat many autoimmune and inflammatory diseases. Although much research has been focused on investigating glucocorticoid activity, it remains unclear how glucocorticoids regulate distinct processes in different cells. Glucocorticoids exert their effects through the glucocorticoid receptor (GR), which, upon glucocorticoid binding, interacts with regulatory proteins, affecting its activity and function. These protein-protein interactions are necessary for the resolution of glucocorticoid-dependent physiological and pharmacological processes. In this study, we discovered a novel protein interaction between the glucocorticoid receptor and β-arrestin-1, a scaffold protein with a well-established role in G protein-coupled receptor signaling. Using co-immunoprecipitation and in situ proximity ligation assays in A549 cells, we observed that β-arrestin-1 and unliganded GR interact in the cytoplasm and that, following glucocorticoid binding, the protein complex is found in the nucleus. We show that siRNA-mediated β-arrestin-1 knockdown alters GR protein turnover by up-regulating the E3 ubiquitin ligase Pellino-1, which catalyzes GR ubiquitination and thereby marks the receptor for proteasomal degradation. The enhanced GR turnover observed in β-arrestin-1-deficient cells limits the duration of the glucocorticoid response on GR target genes. These results demonstrate that β-arrestin-1 is a crucial player for the stability of the glucocorticoid receptor. The GR/β-arrestin-1 interaction uncovered here may help unravel mechanisms that contribute to the cell type-specific activities of glucocorticoids.

Pellino1 regulates reversible ATM activation via NBS1 ubiquitination at DNA double-strand breaks

DNA double-strand break (DSB) signaling and repair are critical for genome integrity. They rely on highly coordinated processes including posttranslational modifications of proteins. Here we show that Pellino1 (Peli1) is a DSB-responsive ubiquitin ligase required for the accumulation of DNA damage response proteins and efficient homologous recombination (HR) repair. Peli1 is activated by ATM-mediated phosphorylation. It is recruited to DSB sites in ATM- and γH2AX-dependent manners. Interaction of Peli1 with phosphorylated histone H2AX enables it to bind to and mediate the formation of K63-linked ubiquitination of NBS1, which subsequently results in feedback activation of ATM and promotes HR repair. Collectively, these results provide a DSB-responsive factor underlying the connection between ATM kinase and DSB-induced ubiquitination.

Occurrence of DNA double-strand break (DSB) repair is important for genome integrity. Here, the authors reveal that Pellino1 is a DSB-responsive ubiquitin ligase required for promoting the accumulation of ATM and MRN complex at DSB sites via NBS1 ubiquitination.

Peli1 Modulates the Subcellular Localization and Activity of Mdmx

Mdm2 and Mdmx, both major repressors of p53 in human cancers, are predominantly localized to the nucleus and cytoplasm, respectively. The mechanism by which subcellular localization of Mdmx is regulated remains unclear. In this study, we identify the E3 ligase Peli1 as a major binding partner and regulator of Mdmx in human cells. Peli1 bound Mdmx in vitro and in vivo and promoted high levels of ubiquitination of Mdmx. Peli1-mediated ubiquitination was degradation-independent, promoting cytoplasmic localization of Mdmx, which in turn resulted in p53 activation. Consistent with this, knockdown or knockout Peli1 in human cancer cells induced nuclear localization of Mdmx and suppressed p53 activity. Myc-induced tumorigenesis was accelerated in Peli1-null mice and associated with downregulation of p53 function. Clinical samples of human cutaneous melanoma had decreased Peli1 expression, which was associated with poor overall survival. Together, these results demonstrate that Peli1 acts as a critical factor for the Mdmx-p53 axis by modulating the subcellular localization and activity of Mdmx, thus revealing a novel mechanism of Mdmx deregulation in human cancers.Significance: Peli1-mediated regulation of Mdmx, a major inhibitor of p53, provides critical insight into activation of p53 function in human cancers. Cancer Res; 78(11); 2897-910. ©2018 AACR.

Cytosolic Pellino-1-Mediated K63-Linked Ubiquitination of IRF5 in M1 Macrophages Regulates Glucose Intolerance in Obesity

IRF5 is a signature transcription factor that induces M1 macrophage polarization. However, little is known regarding cytosolic proteins that induce IRF5 activation for M1 polarization. Here, we report the interaction between ubiquitin E3 ligase Pellino-1 and IRF5 in the cytoplasm, which increased nuclear translocation of IRF5 by K63-linked ubiquitination in human and mouse M1 macrophages. LPS and/or IFN-γ increased Pellino-1 expression, and M1 polarization was attenuated in Pellino-1-deficient macrophages in vitro and in vivo. Defective M1 polarization in Pellino-1-deficient macrophages improved glucose intolerance in mice fed a high-fat diet. Furthermore, macrophages in adipose tissues from obese humans exhibited increased Pellino-1 expression and IRF5 nuclear translocation compared with nonobese subjects, and these changes are associated with insulin resistance index. This study demonstrates that cytosolic Pellino-1-mediated K63-linked ubiquitination of IRF5 in M1 macrophages regulates glucose intolerance in obesity, suggesting a cytosolic mediator function of Pellino-1 in TLR4/IFN-γ receptor-IRF5 axis during M1 polarization.

The E3 ubiquitin ligase Pellino2 mediates priming of the NLRP3 inflammasome

The NLRP3 inflammasome has an important function in inflammation by promoting the processing of pro-IL-1β and pro-IL-18 to their mature bioactive forms, and by inducing cell death via pyroptosis. Here we show a critical function of the E3 ubiquitin ligase Pellino2 in facilitating activation of the NLRP3 inflammasome. Pellino2-deficient mice and myeloid cells have impaired activation of NLRP3 in response to toll-like receptor priming, NLRP3 stimuli and bacterial challenge. These functions of Pellino2 in the NLRP3 pathway are dependent on Pellino2 FHA and RING-like domains, with Pellino2 promoting the ubiquitination of NLRP3 during the priming phase of activation. We also identify a negative function of IRAK1 in the NLRP3 inflammasome, and describe a counter-regulatory relationship between IRAK1 and Pellino2. Our findings reveal a Pellino2-mediated regulatory signaling system that controls activation of the NLRP3 inflammasome.

The NLRP3 inflammasome is important for inducing IL-1β and IL-18 inflammatory responses. Here the authors show, by generating and characterizing Peli2 deficient mice and immune cells, that an E3 ubiquitin ligase Pellino2 promotes inflammasome priming by inducing NLRP3 ubiquitination and by targeting IRAK1.

Differential modulation of Helicobacter pylori lipopolysaccharide-mediated TLR2 signaling by individual Pellino proteins

BACKGROUND

Eradication rates for current H. pylori therapies have fallen in recent years, in line with the emergence of antibiotic resistant infections. The development of therapeutic alternatives to antibiotics, such as immunomodulatory therapy and vaccines, requires a more lucid understanding of host-pathogen interactions, including the relationships between the organism and the innate immune response. Pellino proteins are emerging as key regulators of immune signaling, including the Toll-like receptor pathways known to be regulated by H. pylori. The aim of this study was to characterize the role of Pellino proteins in the innate immune response to H. pylori lipopolysaccharide.

MATERIALS AND METHODS

Gain-of-function and loss-of-function approaches were utilized to elucidate the role of individual Pellino proteins in the Toll-like receptor 2-mediated response to H. pylori LPS by monitoring NF-ĸB activation and the induction of proinflammatory chemokines. Expression of Pellino family members was investigated in gastric epithelial cells and gastric tissue biopsy material.

RESULTS

Pellino1 and Pellino2 positively regulated Toll-like receptor 2-driven responses to H. pylori LPS, whereas Pellino3 exerted a negative modulatory role. Expression of Pellino1 was significantly higher than Pellino3 in gastric epithelial cells and gastric tissue. Furthermore, Pellino1 expression was further augmented in gastric epithelial cells in response to infection with H. pylori or stimulation with H. pylori LPS.

CONCLUSIONS

The combination of low Pellino3 levels together with high and inducible Pellino1 expression may be an important determinant of the degree of inflammation triggered upon Toll-like receptor 2 engagement by H. pylori and/or its components, contributing to H. pylori-associated pathogenesis by directing the incoming signal toward an NF-kB-mediated proinflammatory response.

PELI1 expression is correlated with MYC and BCL6 expression and associated with poor prognosis in diffuse large B-cell lymphoma

PELI is a family of E3 ubiquitin ligases that regulate protein activity through a post-translational modification, ubiquitination. While PELI1 has been found to play a pivotal role in inflammatory processes through the activation of Toll-like receptor signaling and the NF-kB pathway, the role of PELI1 in oncogenesis has not been the subject of much investigation. We aimed to explore PELI1 expression in various malignant lymphomas and identify clinicopathologic significance. Immunohistochemistry for PELI1 was performed on a total of 502 cases, including 406 B-cell, 76 T or NK-cell, and 20 Hodgkin lymphomas. High expression of PELI1 was found in high-grade B-cell lymphoma cases such as diffuse large B-cell lymphoma, Burkitt lymphoma, and plasmablastic lymphoma, whereas low-grade B-cell lymphoma, T/NK-cell lymphoma, and Hodgkin lymphoma cases showed very low levels of expression. In vitro cell line studies, the results of western blot, and RT-PCR were concordant with those of the immunohistochemical results; RL7, Pfeiffer, SUDHL-2, DOHH2, and Ramos cell lines showed high levels of PELI1 protein and mRNA expression. In 182 diffuse large B-cell lymphoma, PELI1 expression was positively correlated with the expression of MYC, BCL6, BCL2, and MUM1 (Spearman's ρ=0.427, 0.507, 0.246, and 0.137, respectively; P<0.001, <0.001, 0.001, and 0.066, respectively). In diffuse large B-cell lymphoma, high expression of PELI1 was associated with frequent bone marrow involvement (P=0.013) and shorter relapse-free survival (P=0.002). Our results suggest that PELI1 might participate in B-cell maturation or oncogenic activation of aggressive B-cell lymphomas, both during and after germinal center stages.

Endotoxin Tolerance Inhibits Degradation of Tumor Necrosis Factor Receptor-Associated Factor 3 by Suppressing Pellino 1 Expression and the K48 Ubiquitin Ligase Activity of Cellular Inhibitor of Apoptosis Protein 2

Pellino 1 positively regulates Toll-like receptor 4 signaling by regulating tumor necrosis factor receptor-associated factor 3 (TRAF3) degradation and is suppressed with the induction of endotoxin tolerance. However, the role of TRAF3 in endotoxin tolerance is largely unknown. In this study, we found that lipopolysaccharide (LPS) stimulation decreased TARF3 protein expression in mouse Kupffer cells (KCs) and liver tissues, whereas endotoxin tolerization abrogated this effect. Degradative TRAF3 K48-linked ubiquitination and the cytoplasmic translocation of the MYD88-associated multiprotein complex were significantly inhibited in tolerized KCs, which led to markedly impaired activation of MYD88-dependent JNK and p38 and downregulation of inflammatory cytokines. TRAF3 ablation failed to induce a fully endotoxin-tolerant state in RAW264.7 cells. Pellino 1 knockdown in Raw264.7 cells did not impair induction of cIAP2 in response to LPS but inhibited the K63-linked ubiquitination of cellular inhibitor of apoptosis protein 2 (cIAP2) and K48-linked ubiquitination of TRAF3 protein. We also found upregulation of Pellino 1 and downregulation of TRAF3 in liver tissues of patients with cholangitis. Our findings reveal a novel mechanism that endotoxin tolerance reprograms mitogen-activated protein kinase signaling by suppressing Pellino 1-mediated K63-linked ubiquitination of cIAP2, K48-linked ubiquitination, and degradation of TRAF3.

Role of E3 ubiquitin ligases in insulin resistance

E3 ubiquitin ligases are a large family of proteins that catalyse the ubiquitination of many proteins for degradation by the 26S proteasome. E3 ubiquitin ligases play pivotal roles in the process of insulin resistance and diabetes. In this review, we summarize the currently available studies to analyse the potential role of E3 ubiquitin ligases in the development of insulin resistance. We propose two mechanisms by which E3 ubiquitin ligases can affect the process of insulin resistance. First, E3 ubiquitin ligases directly degrade the insulin receptor, insulin receptor substrate and other key insulin signalling molecules via the UPS. Second, E3 ubiquitin ligases indirectly regulate insulin signalling by regulating pro-inflammatory mediators that are involved in the regulation of insulin signalling molecules, such as tumour necrosis factor-α, interleukin (IL)-6, IL-4, IL-13, IL-1β, monocyte chemoattractant protein-1 and hypoxia-inducible factor 1α. Determining the mechanism by which E3 ubiquitin ligases affect the development of insulin resistance can identify a novel strategy to protect against insulin resistance and diabetes.

Molecular mechanisms of regulation of Toll-like receptor signaling

TLRs play a critical role in the detection of microbes and endogenous "alarmins" to initiate host defense, yet they can also contribute to the development and progression of inflammatory and autoimmune diseases. To avoid pathogenic inflammation, TLR signaling is subject to multilayer regulatory control mechanisms, including cooperation with coreceptors, post-translational modifications, cleavage, cellular trafficking, and interactions with negative regulators. Nucleic acid-sensing TLRs are particularly interesting in this regard, as they can both recognize host-derived structures and require internalization of their ligand as a result of intracellular sequestration of the nucleic acid-sensing TLRs. This review summarizes the regulatory mechanisms of TLRs, including regulation of their access to ligands, receptor folding, intracellular trafficking, and post-translational modifications, as well as how altered control mechanism could contribute to inflammatory and autoimmune disorders.

Post-translational control of NF-κB signaling by ubiquitination

The transcription factor nuclear factor-kappa B (NF-κB) controls a number of essential cellular functions, including the immune response, cell proliferation, and apoptosis. NF-κB signaling must be engaged temporally and spatially and well orchestrated to prevent aberrant activation because loss of normal regulation of NF-κB is a major contributor to a variety of pathological diseases, including inflammatory diseases, autoimmune diseases, and cancers. Thus, understanding the molecular mechanisms controlling NF-κB activation is an important part of treatment of these relevant diseases. Although NF-κB transcriptional activity is largely regulated by nuclear translocation, post-translational modification of NF-κB signaling components, including phosphorylation, ubiquitination, acetylation, and methylation, has emerged as an important mechanism affecting activity. Many proteins have been shown to ubiquitinate and regulate NF-κB activation at the receptor signaling complex in response to a variety of ligands, such as tumor necrosis factor, interleukin-1, and Toll-like receptor ligands. In this review, we discuss our current knowledge of ubiquitination patterns and their functional role in NF-κB regulation.