14-3-3ζ-TRAF5 axis governs interleukin-17A signaling

14-3-3ζ suppresses RANKL signaling by destabilizing TRAF6

Macrophages are essential regulators of inflammation and bone loss. Receptor activator of nuclear factor-κβ ligand (RANKL), a pro-inflammatory cytokine, is responsible for macrophage differentiation to osteoclasts and bone loss. We recently showed that 14-3-3ζ-knockout (YwhazKO) rats exhibit increased bone loss in the inflammatory arthritis model. 14-3-3ζ is a cytosolic adaptor protein that actively participates in many signaling transductions. However, the role of 14-3-3ζ in RANKL signaling or bone remodeling is unknown. We investigated how 14-3-3ζ affects osteoclast activity by evaluating its role in RANKL signaling. We utilized 14-3-3ζ-deficient primary bone marrow-derived macrophages obtained from wildtype and YwhazKO animals and RAW264.7 cells generated using CRISPR-Cas9. Our results showed that 14-3-3ζ-deficient macrophages, upon RANKL stimulation, have bigger and stronger tartrate-resistant acid phosphatase-positive multinucleated cells and increased bone resorption activity. The presence of 14-3-3ζ suppressed RANKL-induced MAPK and AKT phosphorylation, transcription factors (NFATC1 and p65) nuclear translocation, and subsequently, gene induction (Rank, Acp5, and Ctsk). Mechanistically, 14-3-3ζ interacts with TRAF6, an essential component of the RANKL receptor complex. Upon RANKL stimulation, 14-3-3ζ-TRAF6 interaction was increased, while RANK-TRAF6 interaction was decreased. Importantly, 14-3-3ζ supported TRAF6 ubiquitination and degradation by the proteasomal pathway, thus dampening the downstream RANKL signaling. Together, we show that 14-3-3ζ regulates TRAF6 levels to suppress inflammatory RANKL signaling and osteoclast activity. To the best of our knowledge, this is the first report on 14-3-3ζ regulation of RANKL signaling and osteoclast activation.

Structural Features and Physiological Associations of Human 14-3-3ζ Pseudogenes

There are about 14,000 pseudogenes that are mutated or truncated sequences resembling functional parent genes. About two-thirds of pseudogenes are processed, while others are duplicated. Although initially thought dead, emerging studies indicate they have functional and regulatory roles. We study 14-3-3ζ, an adaptor protein that regulates cytokine signaling and inflammatory diseases, including rheumatoid arthritis, cancer, and neurological disorders. To understand how 14-3-3ζ (gene symbol YWHAZ) performs diverse functions, we examined the human genome and identified nine YWHAZ pseudogenes spread across many chromosomes. Unlike the 32 kb exon-to-exon sequence in YWHAZ, all pseudogenes are much shorter and lack introns. Out of six, four YWHAZ exons are highly conserved, but the untranslated region (UTR) shows significant diversity. The putative amino acid sequence of pseudogenes is 78-97% homologous, resulting in striking structural similarities with the parent protein. The OMIM and Decipher database searches revealed chromosomal loci containing pseudogenes are associated with human diseases that overlap with the parent gene. To the best of our knowledge, this is the first report on pseudogenes of the 14-3-3 family protein and their implications for human health. This bioinformatics-based study introduces a new insight into the complexity of 14-3-3ζ's functions in biology.

Scaffold Proteins in Autoimmune Disorders

Cells transmit information to the external environment and within themselves through signaling molecules that modulate cellular activities. Aberrant cell signaling disturbs cellular homeostasis causing a number of different diseases, including autoimmunity. Scaffold proteins, as the name suggests, serve as the anchor for binding and stabilizing signaling proteins at a particular locale, allowing both intra and intercellular signal amplification and effective signal transmission. Scaffold proteins play a critical role in the functioning of tight junctions present at the intersection of two cells. In addition, they also participate in cleavage formation during cytokinesis, and in the organization of neural synapses, and modulate receptor management outcomes. In autoimmune settings such as lupus, scaffold proteins can lower the cell activation threshold resulting in uncontrolled signaling and hyperactivity. Scaffold proteins, through their binding domains, mediate protein- protein interaction and play numerous roles in cellular communication and homeostasis. This review presents an overview of scaffold proteins, their influence on the different signaling pathways, and their role in the pathogenesis of autoimmune and auto inflammatory diseases. Since these proteins participate in many roles and interact with several other signaling pathways, it is necessary to gain a thorough understanding of these proteins and their nuances to facilitate effective target identification and therapeutic design for the treatment of autoimmune disorders.

The adaptor protein 14-3-3zeta modulates intestinal immunity and aging in Drosophila

The proteins that coordinate the complex transcriptional networks of aging have not been completely documented. Protein 14-3-3zeta is an adaptor protein that coordinates signaling and transcription factor networks, but its function in aging is not fully understood. Here, we showed that the protein expression of 14-3-3zeta gradually increased during aging. High levels of 14-3-3zeta led to shortened lifespan and imbalance of intestinal immune homeostasis in Drosophila, but the decrease in 14-3-3zeta protein levels by RNAi was able to significantly promote the longevity and intestinal immune homeostasis of fruit flies. Importantly, we demonstrate that adult-onset administration of TIC10, a compound that reduces the aging-related AKT and extracellular signal-regulated kinase (ERK) signaling pathways, rescues the shortened lifespan of 14-3-3zeta-overexpressing flies. This finding suggests that 14-3-3zeta plays a critical role in regulating the aging process. Our study elucidates the role of 14-3-3zeta in natural aging and provides the rationale for subsequent 14-3-3zeta-based antiaging research.

IL-17 promotes melanoma through TRAF2 as a scaffold protein recruiting PIAS2 and ELAVL1 to induce EPHA5

An abnormal immune response induces melanoma development. IL-17 and the classical downstream signal STAT1 are associated with melanoma development. TRAF2 also mediates the downstream signaling of IL-17; however, its role in IL-17-stimulated melanoma remains unclear. Bioinformatic analysis revealed that TRAF2 can bind to PIAS2 (a SUMO E3 ligase), ELAVL1 (an RNA-binding protein), and EPHA5 (an ephrin receptor of the tyrosine kinase family). To elucidate the IL-17 downstream signal, the IL-17 receptor (R), STAT1, TRAF2, PIAS2, ELAVL1, and EPHA5 were knocked down before melanoma cells were treated with recombinant IL-17A protein. Co-immunoprecipitation and RNA immunoprecipitation were conducted to determine the interaction of TRAF2 with PIAS2, ELAVL1, and EPHA5 proteins, as well as the interaction of ELAVL1 protein with EPHA5 mRNA. STAT1 knockdown suppressed the proliferation and invasion triggered by IL-17A, but the suppressive effects were much weaker than those caused by IL-17R knockdown. This implies that another nonclassical signal mediates IL-17 effects. IL-17A induces TRAF2 recruitment of ELAVL1, PIAS2, and EPHA5 proteins. We speculated that ELAVL1 bound to the AU-rich elements in the 3' untranslated region of the EPHA5 mRNA, thereby enhancing mRNA stability. Furthermore, PIAS2 induced EPHA5 SUMOylation, which suppressed EPHA5 ubiquitination and degradation. Through pre- and post-translational regulation, IL-17A induced EPHA5 expression in melanoma, and EPHA5 knockdown markedly suppressed IL-17A-induced proliferation and invasion. This study revealed a non-classical signaling mechanism responsible for the effects of IL-17 in melanoma.

Sirt1 Overexpression Inhibits Fibrous Scar Formation and Improves Functional Recovery After Cerebral Ischemic Injury Through the Deacetylation of 14-3-3ζ

Cerebral ischemic stroke is one of the leading causes of human death. The fibrous scar is one of major factors influencing repair in central nervous system (CNS) injury. Silencing information regulator 2-related enzyme 1 (Sirt1) can regulate peripheral tissue and organ fibrosis. However, it is unclear how the fibrous scar forms and is regulated and it is unknown whether and how Sirt1 regulates the formation of the fibrous scar after cerebral ischemic stroke. Therefore, in the present study, we examined the effects of Sirt1 on the formation of the fibrotic scar after middle cerebral artery occlusion/reperfusion (MCAO/R) injury in vivo and on the transforming growth factor β1 (TGF-β1)-induced meningeal fibroblast fibrotic response in vitro, and we explored the molecular mechanisms underlying the Sirt1-regulated fibrosis process in vitro. We found that MCAO/R injury induced fibrotic scar formation in the ischemic area, which was accompanied by the downregulation of Sirt1 expression. The overexpression of Sirt1 reduced the infarct volume, improved Nissl body structure and reduced neurons injury, attenuated formation of fibrotic scar, upregulated growth associated protein43 (GAP43) and synaptophysin (SYP) expression, and promoted neurological function recovery. Similarly, Sirt1 expression was also downregulated in the TGF-β1-induced fibrosis model. Sirt1 overexpression inhibited fibroblast migration, proliferation, transdifferentiation into myofibroblasts, and secretion of extracellular matrix(ECM) by regulating the deacetylation of lysine at K49 and K120 sites of 14-3-3ζ in vitro. Therefore, we believe that Sirt1 could regulate fibrous scar formation and improve neurological function after cerebral ischemic stroke through regulating deacetylation of 14-3-3ζ.

A ubiquitination-mediated degradation system to target 14-3-3-binding phosphoproteins

The phosphorylation of 14-3-3 binding motif is involved in many cellular processes. A strategy that enables targeted degradation of 14-3-3-binding phosphoproteins (14-3-3-BPPs) for studying their functions is highly desirable for basic research. Here, we report a phosphorylation-induced, ubiquitin-proteasome-system-mediated targeted protein degradation (TPD) strategy that allows specific degradation of 14-3-3-BPPs. Specifically, by ligating a modified von Hippel-Lindau E3-ligase with an engineered 14-3-3 bait, we generated a protein chimera referred to as Targeted Degradation of 14-3-3-binding PhosphoProtein (TDPP). TDPP can serve as a universal degrader for 14-3-3-BPPs based on the specific recognition of the phosphorylation in 14-3-3 binding motifs. TDPP shows high efficiency and specificity to a difopein-EGFP reporter, general and specific 14-3-3-BPPs. TDPP can also be applied for the validation of 14-3-3-BPPs. These results strongly support TDPP as a powerful tool for 14-3-3 related research.

IRF3 inhibits nuclear translocation of NF-κB to prevent viral inflammation

Interferon (IFN) regulatory factor 3 (IRF3) is a transcription factor activated by phosphorylation in the cytoplasm of a virus-infected cell; by translocating to the nucleus, it induces transcription of IFN-β and other antiviral genes. We have previously reported IRF3 can also be activated, as a proapoptotic factor, by its linear polyubiquitination mediated by the RIG-I pathway. Both transcriptional and apoptotic functions of IRF3 contribute to its antiviral effect. Here, we report a nontranscriptional function of IRF3, namely, the repression of IRF3-mediated NF-κB activity (RIKA), which attenuated viral activation of NF-κB and the resultant inflammatory gene induction. In Irf3^-/- mice, consequently, Sendai virus infection caused enhanced inflammation in the lungs. Mechanistically, RIKA was mediated by the direct binding of IRF3 to the p65 subunit of NF-κB in the cytoplasm, which prevented its nuclear import. A mutant IRF3 defective in both the transcriptional and the apoptotic activities was active in RIKA and inhibited virus replication. Our results demonstrated IRF3 deployed a three-pronged attack on virus replication and the accompanying inflammation.

Efficacy and mechanism of essential oil from Abies holophylla leaf on airway inflammation in asthma: Network pharmacology and in vivo study

BACKGROUND

Asthma is one of the most common chronic inflammatory diseases of the airways. Essential oil from Abies holophylla leaf (EOA) has been reported to have anti-inflammatory property. This study aimed to predict the inhibitory effect of EOA against asthma by network analysis and to confirm the underlying mechanism of EOA on airway inflammation.

PURPOSE AND STUDY DESIGN

The effects and underlying mechanisms of EOA on asthma were investigated by in silico network pharmacology and an experimental in vivo study.

METHODS

To define the effectiveness of EOA on asthma, the network pharmacology was constructed using major components of EOA. EOA (0.0003 and, 0.03 v/v%) was aerosolized by nebulizer 3 times a week for 5 min for 7 weeks. After 3 weeks of treating the mice with EOA, asthma was induced by sensitizing them with ovalbumin (OVA) and PM10. The effects of EOA on the IL-17 related signaling pathway was confirmed using an asthmatic model.

RESULTS

The network analysis showed that EOA is highly associated with the IL-17-related signaling pathway. EOA inhibited respiratory epithelium hyperplasia, collagen deposition and goblet cell activation in the lung and trachea tissues. In addition, EOA reduced the number of eosinophils, lymphocytes and macrophages in BALF. Furthermore, in the asthmatic model of mice, we showed that EOA inhibited IL-17-related cytokines, increased Treg-related cytokines and decreased the TRAF6 and MAPK and, suppressed the nuclear transcriptional activities of NF-kB.

CONCLUSIONS

The network pharmacology and in vivo study indicated that EOA may have an inhibitory effect on airway inflammation in asthma exposure through the IL-17-related signaling pathway.

14-3-3ζ and 14-3-3ε are involved in innate immune responses in Pacific abalone (Haliotis discus hannai)

The 14-3-3 proteins play important roles in various cellular processes by binding to different ligands, but little is known about these proteins in mollusks. In this study, two 14-3-3 cDNAs were identified from the Pacific abalone Haliotis discus hannai (designated 14-3-3ζ and 14-3-3ε), possessing 59.40% identity with each other. Both genes were predominantly expressed in the gills of unchallenged abalones, and their mRNA signals could also be detected in several other tissues, including the mantle, hepatopancreas and ovary. However, after Vibrio harveyi challenge, hemocytes were induced significantly (p < 0.01). Meanwhile, phagocytosis was inhibited, but apoptosis, reactive oxygen species formation, and caspase 3 expression were significantly induced (p < 0.01), and they were all suppressed with 14-3-3ζ knockdown (p < 0.01). The differences were that silencing 14-3-3ε reverted the decline in the phagocytic rate derived from bacterial infection, while ROS formation was not influenced significantly. In addition, the expression levels of several antimicrobial peptide and proinflammatory cytokine genes were also decreased with the silencing of 14-3-3 genes. However, with the knockdown of 14-3-3ζ, the expression of 14-3-3ε was further significantly increased (p < 0.01), and vice versa. Overall, our results suggested that 14-3-3ζ and 14-3-3ε should play important roles in innate immunity against V. harveyi infection.

Immune regulations by 14-3-3: A misty terrain

The 14-3-3 proteins are known for their functions related to the cell cycle and play a prominent role in cancer-related diseases. Recent studies show that 14-3-3 proteins are also regulators of immune responses and are involved in the pathogenesis of autoimmune and infectious diseases. This focused review highlights the significant and recent studies on how 14-3-3 proteins influence innate and adaptive immune responses; specifically, their roles as immunogens and cytokine signaling regulators are discussed. These revelations have added numerous questions to the pre-existing list of challenges, including understanding the 14-3-3 proteins' mechanism of immunogenicity to dissecting the isoform-specific immune regulations.

14-3-3ζ: A suppressor of inflammatory arthritis

Inflammatory arthritis (IA) is a common disease that affects millions of individuals worldwide. Proinflammatory events during IA pathogenesis are well studied; however, loss of protective immunity remains underexplored. Earlier, we reported that 14-3-3zeta (ζ) has a role in T-cell polarization and interleukin (IL)-17A signal transduction. Here, we demonstrate that 14-3-3ζ knockout (KO) rats develop early-onset severe arthritis in two independent models of IA, pristane-induced arthritis and collagen-induced arthritis. Arthritic 14-3-3ζ KO animals showed an increase in bone loss and immune cell infiltration in synovial joints. Induction of arthritis coincided with the loss of anti-14-3-3ζ antibodies; however, rescue experiments to supplement the 14-3-3ζ antibody by passive immunization did not suppress arthritis. Instead, 14-3-3ζ immunization during the presymptomatic phase resulted in significant suppression of arthritis in both wild-type and 14-3-3ζ KO animals. Mechanistically, 14-3-3ζ KO rats exhibited elevated inflammatory gene signatures at the messenger RNA and protein levels, particularly for IL-1β. Furthermore, the immunization with recombinant 14-3-3ζ protein suppressed IL-1β levels, significantly increased anti-14-3-3ζ antibody levels and collagen production, and preserved bone quality. The 14-3-3ζ protein increased collagen expression in primary rat mesenchymal cells. Together, our findings indicate that 14-3-3ζ causes immune suppression and extracellular remodeling, which lead to a previously unrecognized IA-suppressive function.

Association of methylation level and transcript level in TRAF5 gene with ankylosing spondylitis: a case-control study

To explore the association between methylation level and transcript level of TNF receptor-associated factor 5 (TRAF5) gene with ankylosing spondylitis (AS) in Chinese Han population. Methylation and mRNA expression level of the TRAF5 gene were tested in 98 patients and 98 healthy controls. Among the 21 CpG sites, methylation levels at eight sites were significantly different between AS patients and healthy controls. However, only three sites remained significantly different after the correction by the Benjamini-Hochberg method. Compared with controls, the CpG island of TRAF5 gene promoter was highly methylated in AS patients, and the relative mRNA expression level of TRAF5 was significantly reduced in AS patients. And the mRNA level was negatively correlated with the methylation level of TRAF5 gene in AS patients (r_s = -0.453, P < 0.001). Subgroup analyses indicated that there was no significant difference in the level of methylation between groups of different status of HLA-B27 and medications in AS patients. Multiple linear regression showed that disease-modifying antirheumatic drugs could reduce methylation levels of AS patients after adjusting for the effects of other drugs. In conclusion, the hypermethylation of the TRAF5 might contribute to the pathogenesis of AS, but many open questions remain.

Structural feature of TRAFs, their related human diseases and therapeutic intervention

Several studies have been conducted over the years to unravel the structural information on the receptors that bind to tumor necrosis factor receptor-associated factor (TRAF) and the driving forces for the TRAF/receptor complex. In addition, studies have also been performed to highlight the influence of TRAF malfunctioning and mutations on the development of human disease. However, a holistic study that systematically summarizes the available information and the existing clinical trends towards development of the TRAF-targeting drugs has not been conducted to date. Herein, I reviewed existing research that focused on the structural information of various receptors recognized by the different members of the TRAF family. I also reviewed studies on the different human diseases that occur due to TRAF malfunctioning or mutations as well as the clinical trials undertaken to treat TRAF-associated diseases.

Capsaicin protects cardiomyocytes against lipopolysaccharide-induced damage via 14-3-3γ-mediated autophagy augmentation

Background: The myocardium is susceptible to lipopolysaccharide (LPS)-induced damage in sepsis, and cardiac dysfunction is a leading cause of mortality in patients with sepsis. The changes in cardiomyocyte autophagy in sepsis and the effects and mechanism of action of capsaicin (Cap) remain unclear.

Methods and Results: The potential pathway of 14-3-3γ-dependent autophagy and the effects and mechanisms of Cap were studied in LPS-induced injury to primary cultured neonatal rat cardiomyocytes. The results showed that cardiomyocyte viability decreased, lactate dehydrogenase and creatine kinase activities increased, 14-3-3γ expression was downregulated, and autophagy was inhibited after LPS challenge. Cap pretreatment augmented autophagy by upregulating 14-3-3γ expression and activating AMP-activated protein kinase (AMPK) and unc-51 like autophagy-activating kinase 1 (ULK1), suppressing mammalian target of rapamycin (mTOR), alleviating cardiac dysfunction and improving the inflammation response, whereas pAD/14-3-3γ-shRNA nullified the above effects. Cap pretreatment also decreased the levels of IL-1β, TNF-α, IL-6, and IL-10; suppressed intracellular oxidative stress; reduced the intracellular/mitochondrial reactive oxygen species (ROS); balanced GSH/GSSG; increased GSH-Px, catalase, and SOD activities; and decreased MDA contents. It also increased ATP content, activated complex Ⅰ and complex Ⅲ, stabilized the mitochondrial membrane potential, and decreased the mitochondrial permeability transition pore opening, thereby improving mitochondrial function.

Conclusion: Pretreatment with Cap can regulate autophagy by upregulating 14-3-3γ expression, inhibiting oxidative stress and inflammation, maintaining mitochondrial function, and protecting cardiomyocytes against LPS-induced injury.

Cysteinyl-specialized proresolving mediators link resolution of infectious inflammation and tissue regeneration via TRAF3 activation

The recently elucidated proresolving conjugates in tissue regeneration (CTR) maresin-CTR (MCTR), protectin-CTR (PCTR), and resolvin-CTR (RCTR), termed cysteinyl-specialized proresolving mediators (cys-SPMs) each promotes regeneration, controls infection, and accelerates resolution of inflammation. Here, we sought evidence for cys-SPM activation of primordial pathways in planaria (Dugesia japonica) regeneration that might link resolution of inflammation and regeneration. On surgical resection, planaria regeneration was enhanced with MCTR3, PCTR3, or RCTR3 (10 nM), each used for RNA sequencing. The three cys-SPMs shared up-regulation of 175 known transcripts with fold-change > 1.25 and combined false discovery rate (FDR) < 0.002, and 199 canonical pathways (FDR < 0.25), including NF-κB pathways and an ortholog of human TRAF3 (TNFR-associated factor 3). Three separate pathway analyses converged on TRAF3 up-regulation by cys-SPMs. With human macrophages, three cys-SPMs each dose-dependently increased TRAF3 expression in a cAMP-PKA-dependent manner. TRAF3 overexpression in macrophages enhanced Interleukin-10 (IL-10) and phagocytosis of Escherichia coli IL-10 also increased phagocytosis in a dose-dependent manner. Silencing of mouse TRAF3 in vivo significantly reduced IL-10 and macrophage phagocytosis. TRAF3 silencing in vivo also relieved cys-SPMs' actions in limiting polymorphonuclear neutrophil in E. coli exudates. These results identify cys-SPM-regulated pathways in planaria regeneration, uncovering a role for TRAF3/IL-10 in regulating mammalian phagocyte functions in resolution. Cys-SPM activation of TRAF3 signaling is a molecular component of both regeneration and resolution of infectious inflammation.