The endoribonuclease N4BP1 prevents psoriasis by controlling both keratinocytes proliferation and neutrophil infiltration

N4BP1 coordinates ubiquitin-dependent crosstalk within the IκB kinase family to limit Toll-like receptor signaling and inflammation

The ubiquitin-binding endoribonuclease N4BP1 potently suppresses cytokine production by Toll-like receptors (TLRs) that signal through the adaptor MyD88 but is inactivated via caspase-8-mediated cleavage downstream of death receptors, TLR3, or TLR4. Here, we examined the mechanism whereby N4BP1 limits inflammatory responses. In macrophages, deletion of N4BP1 prolonged activation of inflammatory gene transcription at late time points after TRIF-independent TLR activation. Optimal suppression of inflammatory cytokines by N4BP1 depended on its ability to bind polyubiquitin chains, as macrophages and mice-bearing inactivating mutations in a ubiquitin-binding motif in N4BP1 displayed increased TLR-induced cytokine production. Deletion of the noncanonical IκB kinases (ncIKKs), Tbk1 and Ikke, or their adaptor Tank phenocopied N4bp1 deficiency and enhanced macrophage responses to TLR1/2, TLR7, or TLR9 stimulation. Mechanistically, N4BP1 acted in concert with the ncIKKs to limit the duration of canonical IκB kinase (IKKα/β) signaling. Thus, N4BP1 and the ncIKKs serve as an important checkpoint against over-exuberant innate immune responses.

RNA Metabolism Governs Immune Function and Response

Inflammation is a complex process that protects our body from various insults such as infection, injury, and stress. Proper inflammation is beneficial to eliminate the insults and maintain organ homeostasis, however, it can become detrimental if uncontrolled. To tightly regulate inflammation, post-transcriptional mechanisms governing RNA metabolism play a crucial role in monitoring the expression of immune-related genes, such as tumor necrosis factor (TNF) and interleukin-6 (IL-6). These mechanisms involve the coordinated action of various RNA-binding proteins (RBPs), including the Regnase family, Roquin, and RNA methyltransferases, which are responsible for mRNA decay and/or translation regulation. The collaborative efforts of these RBPs are essential in preventing aberrant immune response activation and consequently safeguarding against inflammatory and autoimmune diseases. This review provides an overview of recent advancements in our understanding of post-transcriptional regulation within the immune system and explores the specific roles of individual RBPs in RNA metabolism and regulation.

Alendronate augments lipid A‑induced IL‑1β release by ASC‑deficient RAW264 cells via AP‑1 activation

Alendronate (ALN) is an anti-bone-resorptive drug with inflammatory side effects. ALN upregulates lipid A-induced interleukin (IL)-1α and IL-1β release by J774.1 cells via apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) activation. The present study examined whether ALN augmented lipid A-induced proinflammatory cytokine production using ASC-deficient mouse macrophage-like RAW264 cells. Pretreatment of RAW264 cells with ALN significantly augmented lipid A-induced IL-1β release, although ALN did not upregulate the expression of Toll-like receptor 4, myeloid differentiation factor 88 (MyD88) and caspase-11. Moreover, pretreatment of caspase-11-deficient RAW264.7 cells with ALN significantly augmented lipid A-induced IL-1β release. Notably, ALN upregulated the activation of FosB, c-Jun or JunD, but not c-Fos or NF-κB in RAW264 cells. Furthermore, pretreatment with the activator protein 1 (AP-1) inhibitor SR11302, but not the c-Fos inhibitor T-5224, before addition of ALN inhibited ALN-augmented IL-1β release by lipid A-treated RAW264 cells. SR11302 also reduced ALN-augmented lactate dehydrogenase release by the cells. These findings collectively suggested that ALN augmented lipid A-induced IL-1β release and cell membrane damage in ASC-deficient RAW264 cells via activation of AP-1, but not NF-κB.

N4BP1 mediates RAM domain-dependent notch signaling turnover during neocortical development

Notch signaling pathway activity, particularly fluctuations in the biologically active effector fragment NICD, is required for rapid and efficient dynamic regulation of proper fate decisions in stem cells. In this study, we identified NEDD4-binding protein 1 (N4BP1), which is highly expressed in the developing mouse cerebral cortex, as a negative modulator of Notch signaling dynamics in neural progenitor cells. Intriguingly, N4BP1 regulated NICD stability specifically after Notch1 S3 cleavage through ubiquitin-mediated degradation that depended on its RAM domain, not its PEST domain, as had been extensively and previously described. The CoCUN domain in N4BP1, particularly the "Phe-Pro" motif (862/863 amino acid), was indispensable for mediating NICD degradation. The Ring family E3 ligase Trim21 was, in contrast to other NEDD4 family members, required for N4BP1-regulated NICD degradation. Overexpression of N4BP1 in cortical neural progenitors promoted neural stem cell differentiation, whereas neural progenitor cells lacking N4BP1 were sensitized to Notch signaling, resulting in the maintenance of stem-like properties in neural progenitor cells and lower production of cortical neurons.

The role of caspase-8 in inflammatory signalling and pyroptotic cell death

The programmed cell death machinery exhibits surprising flexibility, capable of crosstalk and non-apoptotic roles. Much of this complexity arises from the diverse functions of caspase-8, a cysteine-aspartic acid protease typically associated with activating caspase-3 and - 7 to induce apoptosis. However, recent research has revealed that caspase-8 also plays a role in regulating the lytic gasdermin cell death machinery, contributing to pyroptosis and immune responses in contexts such as infection, autoinflammation, and T-cell signalling. In mice, loss of caspase-8 results in embryonic lethality from unrestrained necroptotic killing, while in humans caspase-8 deficiency can lead to an autoimmune lymphoproliferative syndrome, immunodeficiency, inflammatory bowel disease or, when it can't cleave its substrate RIPK1, early onset periodic fevers. This review focuses on non-canonical caspase-8 signalling that drives immune responses, including its regulation of inflammatory gene transcription, activation within inflammasome complexes, and roles in pyroptotic cell death. Ultimately, a deeper understanding of caspase-8 function will aid in determining whether, and when, targeting caspase-8 pathways could be therapeutically beneficial in human diseases.

N4BP1 regulates keratinocytes development and plays protective role in burn- and adhesive-related skin injury via MMP9

Extensive studies have demonstrated critical roles of Regnase-1 in skin inflammation; however the role of N4BP1, a member of Regnase-1 family, in skin is largely unexplored. Here, we found that N4BP1 was highly expressed in skin and its expression was further increased upon skin injury. Compared to wildtype mice, N4BP1 deficient mice showed severe skin injury upon tape-stripping and burns. Overexpression of N4BP1 in HaCaT cells caused more cuboidal with higher cell-to-cell packing, while reduced expression of N4BP1 made cells become more spindle shaped and loosely packed. Overexpression of N4BP1 promoted cell migration, while silence of N4BP1 reduced migration. N4BP1 deficient HaCaT cells were more sensitive to heats compared to control cells. RNA profiling in N4BP1 genetically modified cells demonstrated that N4BP1 broadly affects cellular behaviors such as epithelium development. RNA profiling, RT-PCR verification, WB analysis and RNA immunoprecipitation demonstrated that MMP9 was one of N4BP1 targets that significantly increased in N4BP1 deficient HaCaT cells and skin tissues. Collectively, our results demonstrate a protective role of N4BP1 in skin injury through broadly affecting cellular behaviors of keratinocytes. Furthermore, we identified MMP9 is a target of N4BP1 in keratinocytes. Our findings provide new insight to understand how N4BP1 protects skin under injury.

Transcutaneous amorphous preparation co-delivering curcumin and modified aptamer as a synergistic approach for the amelioration of psoriasis-like skin inflammation

The aim is to achieve the targeting function of Aptamer 21-2 (Apt) by modifying glycyrrhizic acid (GA) to obtain Apt-GA and by delivering it through mesoporous silica in μm-size (μmS). Moreover, it is planned to induce synergistic effects of the novel amorphous preparation of Apt-GA with curcumin (Cur) in the treatment of psoriasis. UV/vis spectrophotometric analysis and Fourier transform infrared spectroscopy were performed to demonstrate the linkage of Apt and GA. The replacement of GA with Apt-GA in GA-Cur-μmS did not make a difference in the amorphous state, but showed superior fluorescence of Cur in the inflamed dermis similar to psoriatic induced by imiquimod. Consequently, compared to GA-Cur-μmS and Apt, Apt-GA-Cur-μmS exhibited less pronounced psoriatic characteristics in vivo, including Psoriasis Area and Severity Index, histological image, immunohistochemistry and immuno-fluorescence labeling neutrophils. The enzyme-linked immunosorbent assay showed a similar phenomenon that less IL-17A was observed after treatment with Apt-GA-Cur-μmS than with GA-Cur-μmS or Apt. Our finding suggests that this novel Apt delivery system achieved the Apt targeting function in the dermis by taking advantage of GA and μmS, and exhibited synergistic anti-psoriatic effect by co-delivering curcumin.

Eupatilin inhibits keratinocyte proliferation and ameliorates imiquimod-induced psoriasis-like skin lesions in mice via the p38 MAPK/NF-κB signaling pathway

BACKGROUND

Psoriasis is a chronic inflammatory skin disease that is currently incurable and causes long-term distress to patients. Therefore, there is an urgent need to develop safe and effective psoriatic drugs. Eupatilin is a natural flavone, that has a variety of pharmacological effects. However, the anti-psoriatic effect of eupatilin and its underlying mechanism remain unclear.

METHODS

HaCaT cells were treated with 20 μg/mL LPS for 24 h to establish the proliferation model of HaCaT cells. Cell viability was measured by MTT assay. Western blotting was used to detect the expression of p-p38 MAPK, p38 MAPK, p-NF-κB p65 and NF-κB p65 in HaCaT cells. Imiquimod (IMQ) was used to induce psoriasis-like mouse model. Psoriasis Area Severity Index (PASI) score was used to evaluate the degree of skin injury, H&E staining was used to observe the pathological damage of skin tissues, and the expression levels of TNF-α, IL-6, IL-23 and IL-17 in the serum were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Eupatilin could inhibit the hyperproliferation of LPS-stimulated HaCaT cells through p38 MAPK/NF-κB signaling pathway in vitro. In psoriatic mice, eupatilin could significantly reduce skin erythema, scales and thickening scores, ameliorate skin histopathological lesions, and decrease the levels of TNF-α, IL-6, IL-23 and IL-17 in the serum.

CONCLUSION

Eupatilin had a good anti-proliferative effect in LPS-stimulated HaCaT cells, and significantly alleviated IMQ-induced psoriasis-like lesions in mice. Eupatilin was a promising drug for the treatment of psoriasis.

Porcine Reproductive and Respiratory Syndrome Virus Adapts Antiviral Innate Immunity via Manipulating MALT1

To fulfill virus replication and persistent infection in hosts, viruses have to find ways to compromise innate immunity, including timely impedance on antiviral RNases and inflammatory responses. Porcine reproductive and respiratory syndrome virus (PRRSV) is a major swine pathogen causing immune suppression. MALT1 is a central immune regulator in both innate and adaptive immunity. In this study, MALT1 was confirmed to be induced rapidly upon PRRSV infection and mediate the degradation of two anti-PRRSV RNases, MCPIP1 and N4BP1, relying on its proteolytic activity, consequently facilitating PRRSV replication. Multiple PRRSV nsps, including nsp11, nsp7β, and nsp4, contributed to MALT1 elicitation. Interestingly, the elevated expression of MALT1 began to decrease once intracellular viral expression reached a high enough level. Higher infection dose brought earlier MALT1 inflection. Further, PRRSV nsp6 mediated significant MALT1 degradation via ubiquitination-proteasome pathway. Downregulation of MALT1 suppressed NF-κB signals, leading to the decrease in proinflammatory cytokine expression. In conclusion, MALT1 expression was manipulated by PRRSV in an elaborate manner to antagonize precisely the antiviral effects of host RNases without excessive and continuous activation of inflammatory responses. These findings throw light on the machinery of PRRSV to build homeostasis in infected immune system for viral settlement.

Regnase-1-related endoribonucleases in health and immunological diseases

Dynamic changes in gene expression are key factors in the development and activation of immune cells. RNA metabolism is one of the critical steps for the control of gene expression. Together with transcriptional regulation, mRNA decay by specific ribonucleases (RNases) plays a vital role in shaping gene expression. In addition to the canonical exoribonuclease-mediated mRNA degradation through the recognition of cis-elements in mRNA 3' untranslated regions by RNA-binding proteins (RBPs), endoribonucleases are involved in the control of mRNAs in immune cells. In this review, we gleam insights on how Regnase-1, an endoribonuclease necessary for regulating immune cell activation and maintenance of immune homeostasis, degrades RNAs involved in immune cell activation. Additionally, we provide insights on recent studies which uncover the role of Regnase-1-related RNases, including Regnase-2, Regnase-3, and Regnase-4, as well as N4BP1 and KHNYN, in immune regulation and antiviral immunity. As the dysregulation of immune mRNA decay leads to pathologies such as autoimmune diseases or impaired activation of immune responses, RNases are deemed as essential components of regulatory feedback mechanisms that modulate inflammation. Given the critical role of RNases in autoimmunity, RNases can be perceived as emerging targets in the development of novel therapeutics.

Post-transcriptional regulation of immunological responses by Regnase-1-related RNases

Regulation of messenger RNA (mRNA) decay plays a crucial role in the control of gene expression. Canonical mRNA decay pathways are initiated by deadenylation and decapping, and are followed by exonucleolytic degradation. However, recent studies revealed that endoribonucleolytic cleavage also mediates mRNA decay, and both exoribonucleolytic and endoribonucleolytic decay pathways are important for the regulation of immune responses. Regnase-1 functions as an endoribonuclease to control immunity by damping mRNAs. Particularly, Regnase-1 controls cytokines and other inflammatory mediators by recognizing their mRNAs via stem-loop structures present in the 3' untranslated regions. Regnase-1 was found to be critical for human inflammatory diseases such as ulcerative colitis and idiopathic pulmonary fibrosis. Furthermore, a set of Regnase-1-related RNases contribute to immune regulation as well as antiviral host defense. In this review, we provide an overview of recent findings as to immune-related RNA-binding proteins (RBPs) with an emphasis on stem-loop-mediated mRNA decay via Regnase-1 and related RNases and discuss how the function of these RBPs is regulated and contributes to inflammatory disorders.