Deactivation of the kinase IKK by CUEDC2 through recruitment of the phosphatase PP1

Protein phosphatase 1 regulatory subunit 15 A promotes translation initiation and induces G2M phase arrest during cuproptosis in cancers

Copper ions play a crucial role as cofactors for essential enzymes in cellular processes. However, when the intracellular concentration of copper ions exceeds the homeostatic threshold, they become toxic to cells. In our study, we demonstrated that elesclomol, as a carrier of copper ions, caused an upregulation of protein phosphatase 1 regulatory subunit 15 A (PPP1R15A), which plays a role in regulating substrate selectivity of protein phosphatase 1 during cuproptosis. Mechanistically, we investigated that PPP1R15A activated translation initiation by dephosphorylating eukaryotic translation initiation factor 2 subunit alpha at the S51 residue through protein phosphatase 1 and phosphorylating eukaryotic translation initiation factor 4E binding protein 1 at the T70 residue. In addition, PPP1R15A reduced H3K4 methylation by altering the phosphorylation of histone methyltransferases, which led to the silencing of MYC and G2M phase arrest.

Emerging roles of the Protein Phosphatase 1 (PP1) in the context of viral infections

Protein Phosphatase 1 (PP1) is a major serine/threonine phosphatase in eukaryotes, participating in several cellular processes and metabolic pathways. Due to their low substrate specificity, PP1's catalytic subunits do not exist as free entities but instead bind to Regulatory Interactors of Protein Phosphatase One (RIPPO), which regulate PP1's substrate specificity and subcellular localization. Most RIPPOs bind to PP1 through combinations of short linear motifs (4-12 residues), forming highly specific PP1 holoenzymes. These PP1-binding motifs may, hence, represent attractive targets for the development of specific drugs that interfere with a subset of PP1 holoenzymes. Several viruses exploit the host cell protein (de)phosphorylation machinery to ensure efficient virus particle formation and propagation. While the role of many host cell kinases in viral life cycles has been extensively studied, the targeting of phosphatases by viral proteins has been studied in less detail. Here, we compile and review what is known concerning the role of PP1 in the context of viral infections and discuss how it may constitute a putative host-based target for the development of novel antiviral strategies.

The PPP1R15 Family of eIF2-alpha Phosphatase Targeting Subunits (GADD34 and CReP)

The vertebrate PPP1R15 family consists of the proteins GADD34 (growth arrest and DNA damage-inducible protein 34, the product of the PPP1R15A gene) and CReP (constitutive repressor of eIF2α phosphorylation, the product of the PPP1R15B gene), both of which function as targeting/regulatory subunits for protein phosphatase 1 (PP1) by regulating subcellular localization, modulating substrate specificity and assembling complexes with target proteins. The primary cellular function of these proteins is to facilitate the dephosphorylation of eukaryotic initiation factor 2-alpha (eIF2α) by PP1 during cell stress. In this review, we will provide a comprehensive overview of the cellular function, biochemistry and pharmacology of GADD34 and CReP, starting with a brief introduction of eIF2α phosphorylation via the integrated protein response (ISR). We discuss the roles GADD34 and CReP play as feedback inhibitors of the unfolded protein response (UPR) and highlight the critical function they serve as inhibitors of the PERK-dependent branch, which is particularly important since it can mediate cell survival or cell death, depending on how long the stressful stimuli lasts, and GADD34 and CReP play key roles in fine-tuning this cellular decision. We briefly discuss the roles of GADD34 and CReP homologs in model systems and then focus on what we have learned about their function from knockout mice and human patients, followed by a brief review of several diseases in which GADD34 and CReP have been implicated, including cancer, diabetes and especially neurodegenerative disease. Because of the potential importance of GADD34 and CReP in aspects of human health and disease, we will discuss several pharmacological inhibitors of GADD34 and/or CReP that show promise as treatments and the controversies as to their mechanism of action. This review will finish with a discussion of the biochemical properties of GADD34 and CReP, their regulation and the additional interacting partners that may provide insight into the roles these proteins may play in other cellular pathways. We will conclude with a brief outline of critical areas for future study.

CUEDC2 Drives β-Catenin Nuclear Translocation and Promotes Triple-Negative Breast Cancer Tumorigenesis

Hyperactivation of Wnt signaling is crucial in tumor formation. Fully elucidating the molecular details of how the cancer-specific Wnt signaling pathway is activated or contributes to tumorigenesis will help in determining future treatment strategies. Here, we aimed to explore the contribution of CUEDC2, a novel CUE-domain-containing protein, to the activation of Wnt signaling and the tumorigenesis of triple-negative breast cancer (TNBC) and to determine the underlying mechanisms. TNBC patient samples and disease-free survival (DFS) data were used to determine the association between CUEDC2 and TNBC progression. The effects of CUEDC2 on TNBC were examined in TNBC cells in vitro and in subcutaneous xenograft tumors in vivo. Gene knockdown, immunoprecipitation plus liquid chromatography–tandem mass spectrometry, pull-down, co-immunoprecipitation, localized surface plasmon resonance, and nuclear translocation analysis were used to uncover the mechanisms of CUEDC2 in regulating Wnt signaling and TNBC development. CUEDC2 is sufficient to maintain the hyperactivation of Wnt signaling required for TNBC tumorigenesis. The contribution of CUEDC2 plays a major role in determining the outcome of oncogenic Wnt signaling both in vitro and in vivo. Mechanistically, the CUE domain in CUEDC2 directly bound to the ARM (7–9) domain in β-catenin, promoted β-catenin nuclear translocation and enhanced the expression of β-catenin targeted genes. More importantly, an 11-amino-acid competitive peptide targeting the CUE domain in CUEDC2 blocked the interactions of CUEDC2 and β-catenin and abrogated the malignant phenotype of TNBC cells in vitro and in vivo. We observed that TNBC patients who exhibited higher levels of CUEDC2 showed marked hyperactivation of the Wnt signaling pathway and poor clinical outcomes, highlighting the clinical relevance of our findings. CUEDC2 promotes TNBC tumor growth by enhancing Wnt signaling through directly binding to β-catenin and accelerating its nuclear translocation. Targeting the interactions of CUEDC2 and β-catenin may be a valuable strategy for combating TNBC.

Elimination of negative feedback in TLR signalling allows rapid and hypersensitive detection of microbial contaminants

The exquisite specificity of Toll-like receptors (TLRs) to sense microbial molecular signatures is used as a powerful tool to pinpoint microbial contaminants. Various cellular systems, from native human blood cells to transfected cell lines exploit TLRs as pyrogen detectors in biological preparations. However, slow cellular responses and limited sensitivity have hampered the replacement of animal-based tests such as the rabbit pyrogen test or lipopolysaccharide detection by Limulus amoebocyte lysate. Here, we report a novel human cell-based approach to boost detection of microbial contaminants by TLR-expressing cells. By genetic and pharmacologic elimination of negative control circuits, TLR-initiated cellular responses to bacterial molecular patterns were accelerated and significantly elevated. Combining depletion of protein phosphatase PP2ACA and pharmacological inhibition of PP1 in the optimized reporter cells further enhanced the sensitivity to allow detection of bacterial lipoprotein at 30 picogram/ml. Such next-generation cellular monitoring is poised to replace animal-based testing for microbial contaminants.

Histone deacetylase 5 deacetylates the phosphatase PP2A for positively regulating NF-κB signaling

Histone deacetylase 5 (HDAC5) has been reported to have a strong regulatory function in the proinflammatory response, but the mechanism is still unknown. Here, we identified HDAC5 as a positive regulator of NF-κB signaling in vivo. HDAC5-deficient mice exhibited enhanced survival in response to LPS challenge. Using LPS, TNFα, different kinds of viruses, hydrogen peroxide, or ultraviolet stimulation, we demonstrate that HDAC5-mediated regulation of NF-κB occurs in manners both dependent on and independent of IKK, an upstream kinase in the NF-κB signaling pathway. Deficiency in HDAC5 impaired the phosphorylation of IKKβ, subsequent phosphorylation of the NF-κB inhibitor protein IκBα and NF-κB subunit p65. We also show that the phosphatase PP2A repressed transcriptional activation of NF-κB by decreasing phosphorylation of IKKβ, p65, and IκBα. In vitro deacetylation experiments and site-directed mutagenesis experiments indicated that HDAC5 directly deacetylated PP2Ac at Lys136, which resulted in the deactivation of PP2A. Our data add mechanistic insight into the cross talk between epigenetic and posttranslational modifications regulating NF-κB signaling and protein phosphatase activation that mediate survival in response to inflammatory challenges.

Inhibitory feedback control of NF-κB signalling in health and disease

Cells must adapt to changes in their environment to maintain cell, tissue and organismal integrity in the face of mechanical, chemical or microbiological stress. Nuclear factor-κB (NF-κB) is one of the most important transcription factors that controls inducible gene expression as cells attempt to restore homeostasis. It plays critical roles in the immune system, from acute inflammation to the development of secondary lymphoid organs, and also has roles in cell survival, proliferation and differentiation. Given its role in such critical processes, NF-κB signalling must be subject to strict spatiotemporal control to ensure measured and context-specific cellular responses. Indeed, deregulation of NF-κB signalling can result in debilitating and even lethal inflammation and also underpins some forms of cancer. In this review, we describe the homeostatic feedback mechanisms that limit and ‘re-set’ inducible activation of NF-κB. We first describe the key components of the signalling pathways leading to activation of NF-κB, including the prominent role of protein phosphorylation and protein ubiquitylation, before briefly introducing the key features of feedback control mechanisms. We then describe the array of negative feedback loops targeting different components of the NF-κB signalling cascade including controls at the receptor level, post-receptor signalosome complexes, direct regulation of the critical ‘inhibitor of κB kinases’ (IKKs) and inhibitory feedforward regulation of NF-κB-dependent transcriptional responses. We also review post-transcriptional feedback controls affecting RNA stability and translation. Finally, we describe the deregulation of these feedback controls in human disease and consider how feedback may be a challenge to the efficacy of inhibitors.

MicroRNA-324-5p-CUEDC2 Axis Mediates Gain-of-Function Mutant p53-Driven Cancer Stemness

Regulation of cancer stemness has recently emerged as a new gain-of-function (GOF) property of mutant p53. In this study, we identify miR-324-5p as a critical epigenetic regulator of cancer stemness and demonstrate its role in mediating GOF-mutant p53-driven stemness phenotypes. We report that miR-324-5p is upregulated in human cancer cell lines and non-small cell lung carcinoma (NSCLC) tumors carrying TP53 GOF mutations. Mechanistically, we show that GOF mutant p53 upregulates miR-324-5p expression via c-Myc, an oncogenic transcription factor in cancer cells. Our experimental results suggest that miR-324-5p-induced CSC phenotypes stem from the downregulation of CUEDC2, a downstream target gene of miR-324-5p. Accordingly, CUEDC2 complementation diminishes elevated CSC marker expression in miR-324-5p-overexpressing cancer cells. We further demonstrate that mutant p53 cancer cells maintain a low level of CUEDC2 that is rescued upon miR-324-5p inhibition. Importantly, we identify CUEDC2 downregulation as a novel characteristic feature of TP53-mutated human cancers. We show that activation of NF-κB due to downregulation of CUEDC2 by miR-324-5p imparts stemness in GOF mutant p53 cancer cells. Finally, we provide evidence that TP53 mutations coupled with high miR-324-5p expression predict poor prognosis in patients with lung adenocarcinoma. Thus, our study delineates an altered miR-324-5p-CUEDC2-NF-κB pathway as a novel regulator of GOF mutant p53-driven cancer stemness. IMPLICATIONS: Our findings implicate miRNA-324-5p as a novel epigenetic modifier of human cancer stemness.

Epithelial PBLD attenuates intestinal inflammatory response and improves intestinal barrier function by inhibiting NF-κB signaling

Intestinal barrier function defects and dysregulation of intestinal immune responses are two key contributory factors in the pathogenesis of ulcerative colitis (UC). Phenazine biosynthesis-like domain-containing protein (PBLD) was recently identified as a tumor suppressor in gastric cancer, hepatocellular carcinoma, and breast cancer; however, its role in UC remains unclear. Therefore, we analyzed colonic tissue samples from patients with UC and constructed specific intestinal epithelial PBLD-deficient (PBLD^IEC-/-) mice to investigate the role of this protein in UC pathogenesis. We found that epithelial PBLD was decreased in patients with UC and was correlated with levels of tight junction (TJ) and inflammatory proteins. PBLD^IEC-/- mice were more susceptible to dextran sulfate sodium (DSS)- and 2,4,6-trinitrobenzene sulfonic acid-induced colitis compared with wild-type (WT) mice. In DSS-induced colitis, PBLD^IEC-/- mice had impaired intestinal barrier function and greater immune cell infiltration in colonic tissue than WT mice. Furthermore, TJ proteins were markedly reduced in PBLD^IEC-/- mice compared with WT mice with colitis. Nuclear factor (NF)-κB activation was markedly elevated and resulted in higher expression levels of downstream effectors (C-C motif chemokine ligand 20, interleukin [IL]-1β, IL-6, and tumor necrosis factor [TNF]-α) in colonic epithelial cells isolated from PBLD^IEC-/- mice than WT mice with colitis. PBLD overexpression in intestinal epithelial cells (IECs) consistently inhibited TNF-α/interferon-γ-induced intestinal barrier disruption and TNF-α-induced inflammatory responses via the suppression of NF-κB. In addition, IKK inhibition (IKK-16) rescued excessive inflammatory responses induced by TNF-α in PBLD knockdown FHC cells. Co-immunoprecipitation assays showed that PBLD may interact with IKKα and IKKβ, thus inhibiting NF-κB signaling, decreasing inflammatory mediator production, attenuating colonic inflammation, and improving intestinal barrier function. Modulating PBLD expression may provide a novel approach for treatment in patients with UC.

Protein phosphatases in TLR signaling

Toll-like receptors (TLRs) are critical sensors for the detection of potentially harmful microbes. They are instrumental in initiating innate and adaptive immune responses against pathogenic organisms. However, exaggerated activation of TLR receptor signaling can also be responsible for the onset of autoimmune and inflammatory diseases. While positive regulators of TLR signaling, such as protein serine/threonine kinases, have been studied intensively, only little is known about phosphatases, which counterbalance and limit TLR signaling. In this review, we summarize protein phosphorylation events and their roles in the TLR pathway and highlight the involvement of protein phosphatases as negative regulators at specific steps along the TLR-initiated signaling cascade. Then, we focus on individual phosphatase families, specify the function of individual enzymes in TLR signaling in more detail and give perspectives for future research. A better understanding of phosphatase-mediated regulation of TLR signaling could provide novel access points to mitigate excessive immune activation and to modulate innate immune signaling.

Phosphatases in toll-like receptors signaling: the unfairly-forgotten

Over the past 2 decades, pattern recognition receptors (PRRs) have been shown to be on the front line of many illnesses such as autoimmune, inflammatory, and neurodegenerative diseases as well as allergies and cancer. Among PRRs, toll-like receptors (TLRs) are the most studied family. Dissecting TLRs signaling turned out to be advantageous to elaborate efficient treatments to cure autoimmune and chronic inflammatory disorders. However, a broad understanding of TLR effectors is required to propose a better range of cures. In addition to kinases and E3 ubiquitin ligases, phosphatases emerge as important regulators of TLRs signaling mediated by NF-κB, type I interferons (IFN I) and Mitogen-Activated Protein Kinases signaling pathways. Here, we review recent knowledge on TLRs signaling modulation by different classes and subclasses of phosphatases. Thus, it becomes more and more evident that phosphatases could represent novel therapeutic targets to control pathogenic TLRs signaling. Video Abstract.

CUEDC2 ablation enhances the efficacy of mesenchymal stem cells in ameliorating cerebral ischemia/reperfusion insult

Mesenchymal stem cell (MSC) therapy has been reported to be a promising therapeutic option for cerebral ischemia/reperfusion (I/R) insult. However, the poor survival rate of engrafted MSCs under unfavorable cerebral I/R-induced microenvironment inhibits their efficiency during clinical application. CUE domain-containing 2(CUECD2) exhibits its protective role on cardiomyocytes by mediating the antioxidant capacity. Our study explored the functional role of CUEDC2 in cerebral I/R challenge and determined whether CUECD2-modified MSCs could improve the efficacy of treatment of the insulted neurons. We also evaluated the possible mechanisms involved in cerebral I/R condition. Cerebral I/R stimulation suppressed CUEDC2 levels in brain tissues and neurons. siRNA-CUEDC2 in neurons significantly inhibited cerebral I/R-induced apoptosis and oxidative stress levels in vitro. Moreover, siRNA-CUEDC2 in the MSCs group remarkably enhanced the therapeutic efficacies in cerebral I/R-induced neuron injury and brain tissue impairment when compared to the non-genetic MSCs treatment group. At the molecular level, siRNA-CUEDC2 in MSCs markedly enhanced its antioxidant and anti-inflammatory effect in co-cultured neurons by upregulating glutathione peroxidase 1 (GPX1) expression levels while suppressing NF-kB activation. These findings provide a novel strategy for the utilization of MSCs to promote cerebral ischemic stroke outcomes.

CUEDC1 inhibits epithelial-mesenchymal transition via the TβRI/Smad signaling pathway and suppresses tumor progression in non-small cell lung cancer

Lung cancer remains the most lethal cancer worldwide because of its high metastasis potential. Epithelial-mesenchymal transition (EMT) is known as the first step of the metastasis cascade, but the potential regulatory mechanisms of EMT have not been clearly established. In this study, we first found that low CUEDC1 expression correlated with lymph node metastasis in non-small cell lung cancer (NSCLC) patients using immunohistochemistry (IHC). CUEDC1 knockdown promoted the metastasis of NSCLC cells and EMT process and activated TβRI/Smad signaling pathway. Overexpression of CUEDC1 decreased the metastatic potential of lung cancer cells and inhibited the EMT process and inactivated TβRI/Smad signaling pathway. Immunoprecipitation (IP) assays showed that Smurf2 is a novel CUEDC1-interacting protein. Furthermore, CUEDC1 could regulate Smurf2 expression through the degradation of Smurf2. Overexpression of Smurf2 abolished CUEDC1 knockdown induced-EMT and the activation of TβRI/Smad signaling pathway, while siRNA Smurf2 reversed CUEDC1 overexpression-mediated regulation of EMT and TβRI/Smad signaling pathway. Additionally, CUEDC1 inhibited proliferation and promoted apoptosis of NSCLC cells. In vivo, CUEDC1-knockdown cells promoted metastasis and tumor growth compared with control cells. In conclusion, our findings indicate that the crucial role of CUEDC1 in NSCLC progression and provide support for its clinical investigation for therapeutic approaches.

LncRNA BCYRN1 inhibits glioma tumorigenesis by competitively binding with miR-619-5p to regulate CUEDC2 expression and the PTEN/AKT/p21 pathway

Glioma is the most common malignant tumor in the central nervous system. Altered long noncoding RNAs (lncRNAs) are playing regulatory roles in physiological and pathogenic processes in cancer. Here, we uncovered a differentially expressed lncRNA called brain cytoplasmic RNA 1 (BCYRN1), and elucidated its function and molecular mechanism in the progression and development of glioma. Three fresh tumor tissues from glioma patients and three normal brain tissues from craniocerebral trauma patients were prepared for high-throughput RNA sequencing. Differential RNA transcripts and BCYRN1 were identified by RT-qPCR in glioma samples and controls. CCK-8, colony formation assays, flow cytometry, TUNEL assays, cell migration assays, wound-healing assays, and xenograft model were established to investigate the biological function of BCYRN1 both in vitro and in vivo. Various bioinformatics analysis, dual-luciferase reporter assays, biotinylated RNA pulldown assays, and rescue experiments were conducted to reveal the underlying mechanisms of competitive endogenous RNAs (ceRNAs). 183 lncRNAs were identified with significant dysregulation in glioma and randomly selected differential RNAs were further confirmed by RT-qPCR. Among them, BCYRN1 was the most downregulated lncRNA, and its low expression positively correlated with glioma progression. Functionally, BCYRN1 overexpression inhibited cell proliferation, migration in glioma cell lines, whereas BCYRN1 depletion resulted in the opposite way. MiR-619-5p was further confirmed as the direct target of BCYRN1. Mechanistically, miR-619-5p specifically targeted the CUE domain containing protein 2 (CUEDC2), and BCYRN1/miR-619-5p suppressed glioma tumorigenesis by inactivating PTEN/AKT/p21 pathway in a CUEDC2-dependent manner. Overall, our data presented that the reduced expression of BCYRN1 was associated with poor patient outcome in glioma. BCYRN1 functioned as a ceRNA to inhibit glioma progression by sponging miR-619-5p to regulate CUEDC2 expression and PTEN/AKT/p21 pathway. Our results indicated that BCYRN1 exerted tumor suppressor potential and might be a candidate in the diagnosis and treatment of glioma.

Comparison of ADAM19 and CUEDC2 expression in EHCC and their clinicopathological significance

Background: To evaluate the expression and clinicopathological significance of a disintegrin and metalloproteinases 19 (ADAM19) CUE domain containing protein 2 (CUEDC2) in extrahepatic cholangiocarcinoma (EHCC). Materials & methods: Immunostaining of ADAM19 and CUEDC2 was performed by EnVision immunohistochemistry in benign and malignant biliary tract tissues. Result: The expression of ADAM19 and CUEDC2 were significantly higher in EHCC (p < 0.05). ADAM19 expression was positive correlated with CUEDC2 expression in EHCC (p < 0.05). The overall survival time of those with positive expression of ADAM19 and CUEDC2 was lower (p < 0.001). Both positive expression of ADAM19 and CUEDC2 were independent prognostic factors in EHCC. Conclusion: ADAM19 and CUEDC2 have a positive correlation to the pathogenesis and dismal prognosis in EHCC.

Protein phosphatase 1 in tumorigenesis: is it worth a closer look?

Cancer cells take advantage of signaling cascades to meet their requirements for sustained growth and survival. Cell signaling is tightly controlled by reversible protein phosphorylation mechanisms, which require the counterbalanced action of protein kinases and protein phosphatases. Imbalances on this system are associated with cancer development and progression. Protein phosphatase 1 (PP1) is one of the most relevant protein phosphatases in eukaryotic cells. Despite the widely recognized involvement of PP1 in key biological processes, both in health and disease, its relevance in cancer has been largely neglected. Here, we provide compelling evidence that support major roles for PP1 in tumorigenesis.

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

Cells have evolved highly specialized sentinels that detect viral infection and elicit an antiviral response. Among these, the stress-sensing protein kinase R, which is activated by double-stranded RNA, mediates suppression of the host translation machinery as a strategy to limit viral replication. Non-translating mRNAs rapidly condensate by phase separation into cytosolic stress granules, together with numerous RNA-binding proteins and components of signal transduction pathways. Growing evidence suggests that the integrated stress response, and stress granules in particular, contribute to antiviral defense. This review summarizes the current understanding of how stress and innate immune signaling act in concert to mount an effective response against virus infection, with a particular focus on the potential role of stress granules in the coordination of antiviral signaling cascades.

CUEDC2 controls osteoblast differentiation and bone formation via SOCS3-STAT3 pathway

The CUE domain-containing 2 (CUEDC2) protein plays critical roles in many biological processes, such as the cell cycle, inflammation, and tumorigenesis. However, whether CUEDC2 is involved in osteoblast differentiation and plays a role in bone regeneration remains unknown. This study investigated the role of CUEDC2 in osteogenesis and its underlying molecular mechanisms. We found that CUEDC2 is expressed in bone tissues. The expression of CUEDC2 decreased during bone development and BMP2-induced osteoblast differentiation. The overexpression of CUEDC2 suppressed the osteogenic differentiation of precursor cells, while the knockdown of CUEDC2 showed the opposite effect. In vivo studies showed that the overexpression of CUEDC2 decreased bone parameters (bone volume, bone area, and bone mineral density) during ectopic bone formation, whereas its knockdown increased bone volume and the reconstruction percentage of critical-size calvarial defects. We found that CUEDC2 affects STAT3 activation by regulating SOCS3 protein stability. Treatment with a chemical inhibitor of STAT3 abolished the promoting effect of CUEDC2 silencing on osteoblast differentiation. Together, we suggest that CUEDC2 functions as a key regulator of osteoblast differentiation and bone formation by targeting the SOCS3–STAT3 pathway. CUEDC2 manipulation could serve as a therapeutic strategy for controlling bone disease and regeneration.

Insulin signaling pathway and related molecules: Role in neurodegeneration and Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Its major pathological hallmarks, neurofibrillary tangles (NFT), and amyloid-β plaques can result from dysfunctional insulin signaling. Insulin is an important growth factor that regulates cell growth, energy utilization, mitochondrial function, autophagy, oxidative stress, synaptic plasticity, and cognitive function. Insulin and its downstream signaling molecules are located majorly in the regions of cortex and hippocampus. The major molecules involved in impaired insulin signaling include IRS, PI3K, Akt, and GSK-3β. Activation or inactivation of these major molecules through increased or decreased phosphorylation plays a role in insulin signaling abnormalities or insulin resistance. Insulin resistance, therefore, is considered as a major culprit in generating the hallmarks of AD arising from neuroinflammation and oxidative stress, etc. Moreover, caspases, Nrf2, and NF-κB influence this pathway in an indirect way. Various studies also suggest a strong link between Diabetes Mellitus and AD due to the impairment of insulin signaling pathway. Moreover, studies also depict a strong correlation of other neurodegenerative diseases such as Parkinson's disease and Huntington's disease with insulin resistance. Hence this review will provide an insight into the role of insulin signaling pathway and related molecules as therapeutic targets in AD and other neurodegenerative diseases.

Chronic ghrelin administration suppresses IKK/NF-κB/BACE1 mediated Aβ production in primary neurons and improves cognitive function via upregulation of PP1 in STZ-diabetic rats

Diabetic rats display cognition impairments accompanied by activation of NF-κB signalling and increased Aβ expression. Ghrelin has been suggested to improve cognition in diabetic rats. In this study, we investigated the role of ghrelin on cognition and NF-κB mediated Aβ production in diabetic rats. A diabetic rat model was established with streptozotocin (STZ) injection, and diabetic rats were intracerebroventricularly administered with ghrelin or (D-lys3)-GHRP-6 (DG). Our results showed that diabetic rats had cognition impairment in the Morris water maze test, accompanied by the higher expression of Aβ in the hippocampus. Western blot analysis showed that diabetic rats exhibited significantly decreased levels of GHSR-1a and protein phosphatase 1 (PP1) in the hippocampus and increased activation of the IKK/NF-κB/BACE1 pathway. Chronic ghrelin administration upregulated hippocampal PP1 expression, suppressed IKK/NF-κB/BACE1 mediated Aβ production, and improved cognition in STZ-induced diabetic rats. These effects were reversed by DG. Then, primary rat hippocampal neurons were isolated and treated with high glucose, followed by Ghrelin and DG, PP1 or IKK. Similar to the in vivo results, high glucose suppressed the expression levels of GHSR-1a and PP1, activated the IKK/NF-κB/BACE1 pathway, increased Aβ production. Ghrelin suppressed IKK/NF-κB/BACE1 induced Aβ production. This improvement was reversed by DG and a PP1 antagonist and was enhanced by the IKK antagonist. Our findings indicated that chronic ghrelin administration can suppress IKK/NF-κB/BACE1 mediated Aβ production in primary neurons with high glucose treatment and improve the cognition via PP1 upregulation in diabetic rats.

TGFβ1-induced beta-site APP-cleaving enzyme 2 upregulation promotes tumorigenesis through the NF-κB signalling pathway in human gliomas

Gliomas are the most common primary malignant tumours of the central nervous system, and new molecular biomarkers are urgently needed for diagnosis and targeted therapy. Here, we report that increased beta-site APP-cleaving enzyme 2 (BACE2) expression is associated with increases in the grade of human glioma, the incidence of the mesenchymal molecular glioblastoma multiforme subtype and the likelihood of poor prognoses for patients. BACE2 knockdown suppressed cell invasion, cell migration and tumour growth both in vitro and in vivo, while BACE2 overexpression promoted the mesenchymal transition and cell proliferation. Furthermore, TGFβ1 stimulated BACE2 expression through Smad-dependent signalling, which modulated TNF-α-induced NF-κB activity through the PP1A/IKK pathway to promote tumorigenesis in both U87MG and U251 cells. Our study indicated that BACE2 plays a significant role in glioma development. Therefore, BACE2 is a potential therapeutic target for human gliomas due to its function and ability to be regulated.

IKIP Negatively Regulates NF-κB Activation and Inflammation through Inhibition of IKKα/β Phosphorylation

Stringent regulation of the transcription factor NF-κB signaling is essential for the activation of host immune responses and maintaining homeostasis, yet the molecular mechanisms involved in its tight regulation are not completely understood. In this study, we report that IKK-interacting protein (IKIP) negatively regulates NF-κB activation. IKIP interacted with IKKα/β to block its association with NEMO, thereby inhibiting the phosphorylation of IKKα/β and the activation of NF-κB. Upon LPS, TNF-α, and IL-1β stimulation, IKIP-deficient macrophages exhibited more and prolonged IKKα/β phosphorylation, IκB, and p65 phosphorylation and production of NF-κB-responsive genes. Moreover, IKIP-deficient mice were more susceptible to LPS-induced septic shock and dextran sodium sulfate-induced colitis. Our study identifies a previously unrecognized role for IKIP in the negative regulation of NF-κB activation by inhibition of IKKα/β phosphorylation through the disruption of IKK complex formation.

Distinct Subcellular Compartments of Dendritic Cells Used for Cross-Presentation

Dendritic cells (DCs) present exogenous protein-derived peptides on major histocompatibility complex class I molecules to prime naïve CD8⁺ T cells. This DC specific ability, called cross-presentation (CP), is important for the activation of cell-mediated immunity and the induction of self-tolerance. Recent research revealed that endoplasmic reticulum-associated degradation (ERAD), which was first identified as a part of the unfolded protein response—a quality control system in the ER—plays a pivotal role in the processing of exogenous proteins in CP. Moreover, DCs express a variety of immuno-modulatory molecules and cytokines to regulate T cell activation in response to the environment. Although both CP and immuno-modulation are indispensable, contrasting ER conditions are required for their correct activity. Since ERAD substrates are unfolded proteins, their accumulation may result in ER stress, impaired cell homeostasis, and eventually apoptosis. In contrast, activation of the unfolded protein response should be inhibited for DCs to express immuno-modulatory molecules and cytokines. Here, we review recent advances on antigen CP, focusing on intracellular transport routes for exogenous antigens and distinctive subcellular compartments involved in ERAD.

CUEDC2 Contributes to Cisplatin-Based Chemotherapy Resistance in Ovarian Serious Carcinoma by Regulating p38 MAPK Signaling

Chemoresistance remains an obstacle to the successful treatment of ovarian carcinoma. CUE domain-containing 2 (CUEDC2) plays critical roles in tumor genesis and overexpresses in many solid cancers, including ovarian serous carcinoma. In previous study, we found that overexpression of CUEDC2 might be a promising biomarker to evaluate the progression and to predict likely relapse of serous ovarian carcinoma. In present study, we found that higher expression of CUEDC2 was associated with higher resistance to cisplatin. The overall survival (OS) and disease-free survival time (DFS) of patients with cisplatin resistant was shorter than that of those with cisplatin sensitive, respectively, and the cisplatin sensitivity was independent predictor of a shorter OS time and DFS time. Knockdown of CUEDC2 by small interfering RNA enhanced the cisplatin sensitivity of serous ovarian carcinoma cells in SKOV3 cell lines. Furthermore, the phosphorylation of p38 MAPK were obviously increased after CUEDC2 knockdown, while p38 MAPK signaling contributes to cell growth and cell apoptosis. Our data suggest that CUEDC2 takes part in cisplatin-based chemotherapy resistance by regulating p38 MAPK signaling. And CUEDC2 is a promising biomarker and therapeutic target of cisplatin resistance in ovarian serous carcinoma.

Lemur tyrosine kinase 2 acts as a positive regulator of NF-κB activation and colon cancer cell proliferation

Lemur tyrosine kinase 2 (LMTK2) belongs to both protein kinase and tyrosine kinase families. LMTK2 is less studied and little is known about its function. Here we demonstrate that LMTK2 modulates NF-κB activity and functions to promote colonic tumorigenesis. We found that LMTK2 protein was abundant in colon cancer cells and LMTK2 knockdown (LMTK2-KD) inhibited proliferation of colon cancer cells through inactivating NF-κB. In unstimulated condition, LMTK2 modulated NF-κB through inhibiting phosphorylation of p65 at Ser468. Mechanistically, LMTK2 phosphorylated protein phosphatase 1A (PP1A) to prevent PP1A from dephosphorylating p-GSK3β(Ser9). The p-GSK3β(Ser9) could not phosphorylate p65 at Ser468, which maintained the basal NF-κB activity. LMTK2 also modulated TNFα-activated NF-κB. LMTK2-KD repressed TNFα-induced IKKβ phosphorylation, IκBα degradation and NF-κB activation, implying that LMTK2 modulates TNFα-activated NF-κB via IKK. These results suggest that LMTK2 modulates basal and TNFα-induced NF-κB activities in different mechanisms. Animal studies show that LMTK2-KD suppressed colon cancer cell xenograft growth, decreased PP1A phosphorylation and increased p-p65(Ser468). Our results reveal the role and underlying mechanism of LMTK2 in colonic tumorigenesis and suggest that LMTK2 may serve as a potential target for chemotherapy of colon cancer.

Elevated pre-activation basal level of nuclear NF-κB in native macrophages accelerates LPS-induced translocation of cytosolic NF-κB into the cell nucleus

Signaling via Toll-like receptor 4 (TLR4) in macrophages constitutes an essential part of the innate immune response to bacterial infections. Detailed and quantified descriptions of TLR4 signal transduction would help to understand and exploit the first-line response of innate immune defense. To date, most mathematical modelling studies were performed on transformed cell lines. However, properties of primary macrophages differ significantly. We therefore studied TLR4-dependent activation of NF-κB transcription factor in bone marrow-derived and peritoneal primary macrophages. We demonstrate that the kinetics of NF-κB phosphorylation and nuclear translocation induced by a wide range of bacterial lipopolysaccharide (LPS) concentrations in primary macrophages is much faster than previously reported for macrophage cell lines. We used a comprehensive combination of experiments and mathematical modeling to understand the mechanisms of this rapid response. We found that elevated basal NF-κB in the nuclei of primary macrophages is a mechanism increasing native macrophage sensitivity and response speed to the infection. Such pre-activated state of macrophages accelerates the NF-κB translocation kinetics in response to low agonist concentrations. These findings enabled us to refine and construct a new model combining both NF-κB phosphorylation and translocation processes and predict the existence of a negative feedback loop inactivating phosphorylated NF-κB.

Absence of GdX/UBL4A Protects against Inflammatory Diseases by Regulating NF-кB Signaling in Macrophages and Dendritic Cells

Nuclear factor-kappa B (NF-κB) activation is critical for innate immune responses. However, cellular-intrinsic regulation of NF-κB activity during inflammatory diseases remains incompletely understood. Ubiquitin-like protein 4A (UBL4A, GdX) is a small adaptor protein involved in protein folding, biogenesis and transcription. Yet, whether GdX has a role during innate immune response is largely unknown. Methods: To investigate the involvement of GdX in innate immunity, we challenged GdX-deficient mice with lipopolysaccharides (LPS). To investigate the underlying mechanism, we performed RNA sequencing, real-time PCR, ELISA, luciferase reporter assay, immunoprecipitation and immunoblot analyses, flow cytometry, and structure analyses. To investigate whether GdX functions in inflammatory bowel disease, we generated dendritic cell (DC), macrophage (Mφ), epithelial-cell specific GdX-deficient mice and induced colitis with dextran sulfate sodium. Results: GdX enhances DC and Mφ-mediated innate immune defenses by positively regulating NF-κB signaling. GdX-deficient mice were resistant to LPS-induced endotoxin shock and DSS-induced colitis. DC- or Mφ- specific GdX-deficient mice displayed alleviated mucosal inflammation. The production of pro-inflammatory cytokines by GdX-deficient DCs and Mφ was reduced. Mechanistically, we found that tyrosine-protein phosphatase non-receptor type 2 (PTPN2, TC45) and protein phosphatase 2A (PP2A) form a complex with RelA (p65) to mediate its dephosphorylation whereas GdX interrupts the TC45/PP2A/p65 complex formation and restrict p65 dephosphorylation by trapping TC45. Conclusion: Our study provides a mechanism by which NF-κB signaling is positively regulated by an adaptor protein GdX in DC or Mφ to maintain the innate immune response. Targeting GdX could be a strategy to reduce over-activated immune response in inflammatory diseases.

Protein Phosphatase 1α and Cofilin Regulate Nuclear Translocation of NF-κB and Promote Expression of the Anti-Inflammatory Cytokine Interleukin-10 by T Cells

While several protein serine/threonine kinases control cytokine production by T cells, the roles of serine/threonine phosphatases are largely unexplored. Here, we analyzed the involvement of protein phosphatase 1α (PP1α) in cytokine synthesis following costimulation of primary human T cells. Small interfering RNA (siRNA)-mediated knockdown of PP1α (PP1^KD) or expression of a dominant negative PP1α (D95N-PP1) drastically diminished interleukin-10 (IL-10) production. Focusing on a key transcriptional activator of human IL-10, we demonstrate that nuclear translocation of NF-κB was significantly inhibited in PP1^KD or D95N-PP1 cells. Interestingly, knockdown of cofilin, a known substrate of PP1 containing a nuclear localization signal, also prevented nuclear accumulation of NF-κB. Expression of a constitutively active nonphosphorylatable S3A-cofilin in D95N-PP1 cells restored nuclear translocation of NF-κB and IL-10 expression. Subpopulation analysis revealed that defective nuclear translocation of NF-κB was most prominent in CD4⁺ CD45RA^- CXCR3^- T cells that included IL-10-producing T_H2 cells. Together these findings reveal novel functions for PP1α and its substrate cofilin in T cells namely the regulation of the nuclear translocation of NF-κB and promotion of IL-10 production. These data suggest that stimulation of PP1α could limit the overwhelming immune responses seen in chronic inflammatory diseases.

Suppression of NF-κB Activity: A Viral Immune Evasion Mechanism

Nuclear factor-κB (NF-κB) is an important transcription factor that induces the expression of antiviral genes and viral genes. NF-κB activation needs the activation of NF-κB upstream molecules, which include receptors, adaptor proteins, NF-κB (IκB) kinases (IKKs), IκBα, and NF-κB dimer p50/p65. To survive, viruses have evolved the capacity to utilize various strategies that inhibit NF-κB activity, including targeting receptors, adaptor proteins, IKKs, IκBα, and p50/p65. To inhibit NF-κB activation, viruses encode several specific NF-κB inhibitors, including NS3/4, 3C and 3C-like proteases, viral deubiquitinating enzymes (DUBs), phosphodegron-like (PDL) motifs, viral protein phosphatase (PPase)-binding proteins, and small hydrophobic (SH) proteins. Finally, we briefly describe the immune evasion mechanism of human immunodeficiency virus 1 (HIV-1) by inhibiting NF-κB activity in productive and latent infections. This paper reviews a viral mechanism of immune evasion that involves the suppression of NF-κB activation to provide new insights into and references for the control and prevention of viral diseases.

CUEDC2, a novel interacting partner of the SOCS1 protein, plays important roles in the leukaemogenesis of acute myeloid leukaemia

Downregulation of suppressor of cytokine signalling-1 (SOCS1) is one of the vital reasons for JAK1-STAT3 pathway activation in acute myeloid leukaemia (AML). CUE domain-containing 2 (CUEDC2) was a novel interacting partner of SOCS1 and a positive correlation between the expression of CUEDC2 and SOCS1 was confirmed in primary AML cells and AML cell lines without SOCS1 promoter methylation. We aimed to explore roles of CUEDC2 in regulating ubiquitin-mediated degradation of SOCS1 in the leukaemogenesis of AML.According to in vitro experiments, CUEDC2 overexpression increased the level of SOCS1 protein, suppressed JAK1-STAT3 pathway activation. The suppression of this pathway inhibited AML cells' proliferation by causing G1 arrest and enhanced AML cells' sensitivity to cytarabine and idarubicin. Similarity, downregulation of CUEDC2 produced opposite results. Knockout or low expression of CUEDC2 in mouse or AML patients displayed lower overall survival and event-free survival rates, compared with these mouse and AML patients had high-CUEDC2 expression. Mechanistic studies revealed that CUEDC2 overexpression attenuated SOCS1 ubiquitination, facilitated its stabilisation by enhancing SOCS1, Elongin C and Cullin-2 (CUL2) interactions, thus inhibited JAK1-STAT3 pathway and leukaemogenesis of AML. Therefore, our novel findings indicated that CUEDC2 interacted with SOCS1 to suppress SOCS1's ubiquitin-mediated degradation, JAK1-STAT3 pathway activation and leukaemogenesis of AML.

SIRT6 Acts as a Negative Regulator in Dengue Virus-Induced Inflammatory Response by Targeting the DNA Binding Domain of NF-κB p65

Dengue virus (DENV) is a mosquito-borne single-stranded RNA virus causing human disease with variable severity. The production of massive inflammatory cytokines in dengue patients has been associated with dengue disease severity. However, the regulation of these inflammatory responses remains unclear. In this study, we report that SIRT6 is a negative regulator of innate immune responses during DENV infection. Silencing of Sirt6 enhances DENV-induced proinflammatory cytokine and chemokine production. Overexpression of SIRT6 inhibits RIG-I-like receptor (RLR) and Toll-like receptor 3 (TLR3) mediated NF-κB activation. The sirtuin core domain of SIRT6 is required for the inhibition of NF-κB p65 function. SIRT6 interacts with the DNA binding domain of p65 and competes with p65 to occupy the Il6 promoter during DENV infection. Collectively, our study demonstrates that SIRT6 negatively regulates DENV-induced inflammatory response via RLR and TLR3 signaling pathways.

Novel phosphorylated TAK1 species with functional impact on NF-κB and β-catenin signaling in human Cutaneous T-cell lymphoma

Cutaneous T-cell lymphomas (CTCLs) represent different subtypes of lymphoproliferative disorders with no curative therapies for the advanced forms of the disease (namely mycosis fungoides and the leukemic variant, Sézary syndrome). Molecular events leading to CTCL progression are heterogeneous, however recent DNA and RNA sequencing studies highlighted the importance of NF-κB and β-catenin pathways. We here show that the kinase TAK1, known as essential in B-cell lymphoma, is constitutively activated in CTCL cells, but tempered by the MYPT1/PP1 phosphatase complex. Blocking PP1 activity, both pharmacologically and genetically, resulted in TAK1 hyperphosphorylation at residues T344, S389, T444, and T511, which have functional impact on canonical NF-κB signaling. Inhibition of TAK1 precluded NF-κB and β-catenin signaling and induced apoptosis of CTCL cell lines and primary Sézary syndrome cells both in vitro and in vivo. Detection of phosphorylated TAK1 at T444 and T344 is associated with the presence of lymphoma in a set of 60 primary human samples correlating with NF-κB and β-catenin activation. These results identified TAK1 as a potential biomarker and therapeutic target for CTCL therapy.

At the crossway of ER-stress and proinflammatory responses

Immune cells detect specific microbes or damage to tissue integrity in order to initiate efficient immune responses. Abnormal accumulation of proteins in the endoplasmic reticulum (ER) can be seen as a sign of cellular malfunction and stress that triggers a collection of conserved emergency rescue programs. These different signaling cascades, which favor ER proteostasis and promote cell survival, are collectively known as the unfolded protein response (UPR). In recent years, a synergy between the UPR and inflammatory cytokine production has been unraveled, with different branches of the UPR entering in a cross-talk with specialized microbe sensing pathways, which turns on or amplify inflammatory cytokines production. Complementary to this synergetic activity, UPR induction alone, can itself be seen as a danger signal, and triggers directly or indirectly inflammation in different cellular and pathological models, this independently of the presence of pathogens. Here, we discuss recent advances on the nature of these cross-talks and how innate immunity, metabolism dysregulation, and ER-signaling pathways intersect in specialized immune cells, such as dendritic cells (DCs), and contribute to the pathogenesis of inflammatory diseases.

Guanabenz inhibits TLR9 signaling through a pathway that is independent of eIF2α dephosphorylation by the GADD34/PP1c complex

Endoplasmic reticulum (ER) stress triggers or amplifies inflammatory signals and cytokine production in immune cells. Upon the resolution of ER stress, the inducible phosphatase 1 cofactor GADD34 promotes the dephosphorylation of the initiation factor eIF2α, thereby enabling protein translation to resume. Several aminoguanidine compounds, such as guanabenz, perturb the eIF2α phosphorylation-dephosphorylation cycle and protect different cell or tissue types from protein misfolding and degeneration. We investigated how pharmacological interference with the eIF2α pathway could be beneficial to treat autoinflammatory diseases dependent on proinflammatory cytokines and type I interferons (IFNs), the production of which is regulated by GADD34 in dendritic cells (DCs). In mouse and human DCs and B cells, guanabenz prevented the activation of Toll-like receptor 9 (TLR9) by CpG oligodeoxynucleotides or DNA-immunoglobulin complexes in endosomes. In vivo, guanabenz protected mice from CpG oligonucleotide-dependent cytokine shock and decreased autoimmune symptom severity in a chemically induced model of systemic lupus erythematosus. However, we found that guanabenz exerted its inhibitory effect independently of GADD34 activity on eIF2α and instead decreased the abundance of CH25H, a cholesterol hydroxylase linked to antiviral immunity. Our results therefore suggest that guanabenz and similar compounds could be used to treat type I IFN-dependent pathologies and that CH25H could be a therapeutic target to control these diseases.

Proteomic analysis of chicken embryo fibroblast cells infected with recombinant H5N1 avian influenza viruses with and without NS1 eIF4GI binding domain

Non-structural 1 (NS1) protein is a key virulence factor that regulates replication of influenza virus. A recombinant H5N1 virus lacking the eIF4GI-binding domain of NS1 (rNS1-SD30) exhibits significantly lower pathogenicity than H5N1 virus with an intact eIF4GI-binding domain (rNS1-wt). To further investigate this phenomenon, we performed comparative proteomics analyses to profile host proteins in chicken embryo fibroblasts (CEFs) infected with rNS1-wt and rNS1-SD30 viruses. In total, 81 differentially expressed (DE) proteins were identified at 12, 24, and 36 h post-infection. These proteins are mainly involved in the cytoskeletal, apoptotic and stress responses, transcription regulation, transport and metabolic processes, mRNA processing and splicing, and cellular signal transduction. Overexpression of DE proteins revealed that ANXA7 suppresses propagation of rNS1-SD30, but not rNS1-wt viruses. Moreover, ALDH7A1, ANXA7, and DCTN2 strongly enhanced IFN-β promoter activity induced by chicken MDA5 (chMDA5), and in the case of ANXA7, also by the rNS1-SD30 viral strain. NS1-wt co-transfection suppressed the ANXA7-mediated increase in IFN-β promoter activity induced by chMDA5. These findings highlight the role of NS1 eIF4GI binding domain in H5N1 pathogenicity, and may contribute to the design of antiviral strategies to reduce the high morbidity and mortality associated with this pathogen.

Noncoding RNAs: Master Regulators of Inflammatory Signaling

Inflammatory signaling underlies many diseases, from arthritis to cancer. Our understanding of inflammation has thus far been limited to the world of proteins, because we are only just beginning to understand the role that noncoding RNAs (ncRNA) might play. It is now clear that ncRNA do not constitute transcriptional 'noise' but instead harbor physiological functions in controlling signaling pathways. In this review, we cover the newly discovered mechanisms and functions of ncRNAs in the regulation of inflammatory signaling. We also describe advances in experimental techniques allowing this field of research to take root. These findings have opened new avenues for putative therapeutic intervention in inflammatory diseases, which may be seen translated into clinical outcomes in the future.

Distinct B subunits of PP2A regulate the NF-κB signalling pathway through dephosphorylation of IKKβ, IκBα and RelA

PP2A is composed of a scaffolding subunit (A), a catalytic subunit (C) and a regulatory subunit (B) that is classified into four families including B, B′, B′′ and B′′′/striatin. Here, we found that a distinct PP2A complex regulates NF‐κB signalling by dephosphorylation of IKKβ, IκBα and RelA/p65. The PP2A core enzyme AC dimer and the holoenzyme AB′′′C trimer dephosphorylate IKKβ, IκBα and RelA, whereas the ABC trimer dephosphorylates IκBα but not IKKβ and RelA in cells. In contrast, AB′C and AB′′C trimers have little effect on dephosphorylation of these signalling proteins. These results suggest that different forms of PP2A regulate NF‐κB pathway signalling through multiple steps each in a different manner, thereby finely tuning NF‐κB‐ and IKKβ‐mediated cellular responses.

Chronic oxidative stress promotes GADD34-mediated phosphorylation of the TAR DNA-binding protein TDP-43, a modification linked to neurodegeneration

Oxidative and endoplasmic reticulum (ER) stresses are hallmarks of the pathophysiology of ALS and other neurodegenerative diseases. In these stresses, different kinases phosphorylate eukaryotic initiation factor eIF2α, enabling the translation of stress response genes; among these is GADD34, the protein product of which recruits the α-isoform of protein phosphatase 1 catalytic subunit (PP1α) and eIF2α to assemble a phosphatase complex catalyzing eIF2α dephosphorylation and resumption of protein synthesis. Aberrations in this pathway underlie the aforementioned disorders. Previous observations indicating that GADD34 is induced by arsenite, a thiol-directed oxidative stressor, in the absence of eIF2α phosphorylation suggest other roles for GADD34. Here, we report that arsenite-induced oxidative stress differs from thapsigargin- or tunicamycin-induced ER stress in promoting GADD34 transcription and the preferential translation of its mRNA in the absence of eIF2α phosphorylation. Arsenite also stabilized GADD34 protein, slowing its degradation. In response to oxidative stress, but not ER stress, GADD34 recruited TDP-43, and enhanced cytoplasmic distribution and cysteine modifications of TDP-43 promoted its binding to GADD34. Arsenite also recruited a TDP-43 kinase, casein kinase-1ϵ (CK1ϵ), to GADD34. Concomitant with TDP-43 aggregation and proteolysis after prolonged arsenite exposure, GADD34-bound CK1ϵ catalyzed TDP-43 phosphorylations at serines 409/410, which were diminished or absent in GADD34^-/- cells. Our findings highlight that the phosphatase regulator, GADD34, also functions as a kinase scaffold in response to chronic oxidative stress and recruits CK1ϵ and oxidized TDP-43 to facilitate its phosphorylation, as seen in TDP-43 proteinopathies.

Progress in Pharmacological Sciences in China

Pharmacology is the science that investigates the interactions between organisms and drugs and their mechanisms. Pharmacology plays a translational role in modern medicine, bridging basic research and the clinic. With its economy booming, China has invested an enormous amount of financial and human resources in pharmacological research in the recent decade. As a result, major breakthroughs have been achieved in both basic and clinical research, with the discovery of many potential drug targets and biomarkers that has made a sizable contribution to the overall advancement of pharmacological sciences. In this article, we review recent research efforts and representative scientific achievements and discuss future challenges and directions for the pharmacological sciences in China.

CUEDC2 suppresses glioma tumorigenicity by inhibiting the activation of STAT3 and NF-κB signaling pathway

CUEDC2, a CUE domain containing 2 protein, plays critical roles in many biological processes, such as cell cycle, inflammation and tumorigenesis. However, whether CUEDC2 was involved in tumorigenesis of glioma and the possible mechanism remains to be elucidated. In the present study, our results implied that the expression of CUEDC2 was lower in the glioma tissue and glioma cell lines than that of normal tissue and asctrocyte cells. Downregulation of endogenous CUEDC2 in glioma U251 cell lines by RNAi promoted the tumor cells proliferation, migration, invasion and glioma neurosphere formation, while, overexpression of CUEDC2 showed the opposite effect. Further studies showed that overexpression of CUEDC2 suppressed the activation and nuclear translocation of phosphorylated-STAT3 (p-STAT3) but the level of p-STAT3 increased after interfering with the expression of CUEDC2. Moreover, CUEDC2 expression has an inhibitory effect on the activation of NF-κB. Thus, our studies suggested that the decreased expression of CUEDC2 in glioma led to the activation of transcription factor STAT3 and NF-κB signaling pathway which may be related to the tumorigenicity in glioma.

RNF8 negatively regulates NF-kappaB signaling by targeting IkappaB kinase: implications for the regulation of inflammation signaling

Persistent or excess activation of NF-κB leads to cancer, autoimmune and inflammatory diseases. Therefore, activated NF-κB needs to be terminated after induction, which highlights the physiological significance of NF-κB-negative regulators. However, the molecular mechanisms that negatively regulate NF-κB are not well understood. Here, we report that Ring Finger Protein 8 (RNF8), an E3 ubiquitin ligase, inhibits TNFα-mediated NF-κB activation by targeting IκB kinase (IKK). Upon TNFα stimulation, RNF8 binds to the catalytic subunits of IKK complex, resulting in inhibition of IKKα/β phosphorylation and subsequent NF-κB activation. RNF8 targets the IKK complex in a manner independent of its RING domain. We further provide evidence that the silencing of RNF8 results in enhanced TNFα-induced IKK activation, and an increase expression of NF-κB-induced inflammatory cytokine IL-8. Our study identifies a previously unrecognized role for RNF8 in the negative regulation of NF-κB activation by targeting and deactivating the IKK complex.

FTY720 (fingolimod) regulates key target genes essential for inflammation in microglial cells as defined by high-resolution mRNA sequencing

Although microglial cells have an essential role in the host defense of the brain, the abnormal activation of microglia can lead to devastating outcomes, such as neuroinflammation and neurodegeneration. Emerging evidence indicates that FTY720 (fingolimod), an FDA-approved drug, has beneficial effects on brain cells in the central nervous system (CNS) and, more recently, immunosuppressive activities in microglia via modulation of the sphingosine 1 phosphate (S1P) 1 receptor. However, the exact molecular aspects of FTY720 contribution in microglia remain largely unaddressed. To understand the molecular mechanisms underlying the roles of FTY720 in microglia, we performed gene expression profiling in resting, FTY720, LPS and LPS + FTY720 challenged primary microglial (PM) cells isolated from 3-day-old ICR mice, and we identified FTY720 target genes and co-regulated modules that were critical in inflammation. By examining RNA sequencing and binding motif datasets from FTY720 suppressed LPS-induced inflammatory mediators, we also identified unexpected relationships between the inducible transcription factors (TFs), motif strength, and the transcription of key inflammatory mediators. Furthermore, we showed that FTY720 controls important inflammatory genes targets by modulating STAT1 and IRF8 levels at their promoter site. Our unprecedented findings demonstrate that FTY720 could be a useful therapeutic application for neuroinflammatory diseases associated with microglia activation, as well as provide a rich resource and framework for future analyses of FTY720 effects on microglia interaction.

CUE domain-containing protein 2 promotes the Warburg effect and tumorigenesis

Cancer progression depends on cellular metabolic reprogramming as both direct and indirect consequence of oncogenic lesions; however, the underlying mechanisms are still poorly understood. Here, we report that CUEDC2 (CUE domain-containing protein 2) plays a vital role in facilitating aerobic glycolysis, or Warburg effect, in cancer cells. Mechanistically, we show that CUEDC2 upregulates the two key glycolytic proteins GLUT3 and LDHA via interacting with the glucocorticoid receptor (GR) or 14-3-3ζ, respectively. We further demonstrate that enhanced aerobic glycolysis is essential for the role of CUEDC2 to drive cancer progression. Moreover, using tissue microarray analysis, we show a correlation between the aberrant expression of CUEDC2, and GLUT3 and LDHA in clinical HCC samples, further demonstrating a link between CUEDC2 and the Warburg effect during cancer development. Taken together, our findings reveal a previously unappreciated function of CUEDC2 in cancer cell metabolism and tumorigenesis, illustrating how close oncogenic lesions are intertwined with metabolic alterations promoting cancer progression.

Nitric Oxide Overproduction in Tomato shr Mutant Shifts Metabolic Profiles and Suppresses Fruit Growth and Ripening

Nitric oxide (NO) plays a pivotal role in growth and disease resistance in plants. It also acts as a secondary messenger in signaling pathways for several plant hormones. Despite its clear role in regulating plant development, its role in fruit development is not known. In an earlier study, we described a short root (shr) mutant of tomato, whose phenotype results from hyperaccumulation of NO. The molecular mapping localized shr locus in 2.5 Mb region of chromosome 9. The shr mutant showed sluggish growth, with smaller leaves, flowers and was less fertile than wild type. The shr mutant also showed reduced fruit size and slower ripening of the fruits post-mature green stage to the red ripe stage. Comparison of the metabolite profiles of shr fruits with wild-type fruits during ripening revealed a significant shift in the patterns. In shr fruits intermediates of the tricarboxylic acid (TCA) cycle were differentially regulated than WT indicating NO affected the regulation of TCA cycle. The accumulation of several amino acids, particularly tyrosine, was higher, whereas most fatty acids were downregulated in shr fruits. Among the plant hormones at one or more stages of ripening, ethylene, Indole-3-acetic acid and Indole-3-butyric acid increased in shr, whereas abscisic acid declined. Our analyses indicate that the retardation of fruit growth and ripening in shr mutant likely results from the influence of NO on central carbon metabolism and endogenous phytohormones levels.

The effect of inhibition of PP1 and TNFα signaling on pathogenesis of SARS coronavirus

BACKGROUND

The complex interplay between viral replication and host immune response during infection remains poorly understood. While many viruses are known to employ anti-immune strategies to facilitate their replication, highly pathogenic virus infections can also cause an excessive immune response that exacerbates, rather than reduces pathogenicity. To investigate this dichotomy in severe acute respiratory syndrome coronavirus (SARS-CoV), we developed a transcriptional network model of SARS-CoV infection in mice and used the model to prioritize candidate regulatory targets for further investigation.

RESULTS

We validated our predictions in 18 different knockout (KO) mouse strains, showing that network topology provides significant predictive power to identify genes that are important for viral infection. We identified a novel player in the immune response to virus infection, Kepi, an inhibitory subunit of the protein phosphatase 1 (PP1) complex, which protects against SARS-CoV pathogenesis. We also found that receptors for the proinflammatory cytokine tumor necrosis factor alpha (TNFα) promote pathogenesis, presumably through excessive inflammation.

CONCLUSIONS

The current study provides validation of network modeling approaches for identifying important players in virus infection pathogenesis, and a step forward in understanding the host response to an important infectious disease. The results presented here suggest the role of Kepi in the host response to SARS-CoV, as well as inflammatory activity driving pathogenesis through TNFα signaling in SARS-CoV infections. Though we have reported the utility of this approach in bacterial and cell culture studies previously, this is the first comprehensive study to confirm that network topology can be used to predict phenotypes in mice with experimental validation.

LRRC14 attenuates Toll-like receptor-mediated NF-κB signaling through disruption of IKK complex

Activation of NF-κB signaling plays pivotal roles in innate immune responses against pathogens. It requires strict control to avert inflammatory diseases. However, the mechanisms underlying this tight regulation are not completely understood. Here, we identified LRRC14, a novel member of LRR (leucine-rich repeat) protein family, as a negative regulator in TLR signaling. Expression of LRRC14 resulted in decreased activation of NF-κB, whereas knockdown of LRRC14 enhanced NF-κB activation as well as the production of inflammatory cytokines. Mechanistically, LRRC14 bound to HLH domain of IKKβ to block its interaction with NEMO and thereby inhibiting the phosphorylation of IKKβ and NF-κB activation. In addition, our data showed that TLR signaling led to lower expression of LRRC14. Together, LRRC14 may function as a checkpoint to prevent overzealous inflammation.

CUEDC2 down-regulation is associated with tumor growth and poor prognosis in lung adenocarcinoma

CUE domain-containing 2 (CUEDC2) is a multi-functional protein, which regulates cell cycle, growth factor signaling and inflammation. We found that CUEDC2 was low in lung adenocarcinoma cell lines and lung adenocarcinoma tissues at both mRNA and protein levels. Low levels of CUEDC2 were correlated with a shorter survival time in patients with lung adenocarcinoma (p = 0.004). CUEDC2 expression was correlated with tumor T classification (P = 0.001) at clinical stage (P = 0.001) and tumor size (P = 0.033). Multivariate analysis suggested that CUEDC2 expression is an independent prognostic indicator for patients with lung adenocarcinoma. Ectopic expression of CUEDC2 decreased cell proliferation in vitro and inhibited tumor growth in nude mice in vivo. Knockdown of endogenous CUEDC2 by short hairpin RNAs (shRNAs) increased tumor growth. Inhibition of proliferation by CUEDC2 was associated with inactivation of the PI3K/Akt pathway, induction of p21 and down-regulation of cyclin D1. Our results suggest that decreased expression of CUEDC2 contributes to tumor growth in lung adenocarcinoma, leading to a poor clinical outcome.

Kelch-like Protein 21 (KLHL21) Targets IκB Kinase-β to Regulate Nuclear Factor κ-Light Chain Enhancer of Activated B Cells (NF-κB) Signaling Negatively

Activation of IKKβ is the key step in canonical activation of NF-κB signaling. Extensive work has provided insight into the mechanisms underlying IKKβ activation through the identification of context-specific regulators. However, the molecular processes responsible for its negative regulation are not completely understood. Here, we identified KLHL21, a member of the Kelch-like gene family, as a novel negative regulator of IKKβ. The expression of KLHL21 was rapidly down-regulated in macrophages upon treatment with proinflammatory stimuli. Overexpression of KLHL21 inhibited the activation of IKKβ and degradation of IκBα, whereas KLHL21 depletion via siRNA showed the opposite results. Coimmunoprecipitation assays revealed that KLHL21 specifically bound to the kinase domain of IKKβ via its Kelch domains and that this interaction was gradually attenuated upon TNFα treatment. Furthermore, KLHL21 did not disrupt the interaction between IKKβ and TAK1, TRAF2, or IκBα. Also, KLHL21 did not require its E3 ubiquitin ligase activity for IKKβ inhibition. Our findings suggest that KLHL21 may exert its inhibitory function by binding to the kinase domain and sequestering the region from potential IKKβ inducers. Taken together, our data clearly demonstrate that KLHL21 negatively regulates TNFα-activated NF-κB signaling via targeting IKKβ, providing new insight into the mechanisms underlying NF-κB regulation in cells.

CUEDC2 modulates cardiomyocyte oxidative capacity by regulating GPX1 stability

The irreversible loss of cardiomyocytes due to oxidative stress is the main cause of heart dysfunction following ischemia/reperfusion (I/R) injury and ageing-induced cardiomyopathy. Here, we report that CUEDC2, a CUE domain-containing protein, plays a critical role in oxidative stress-induced cardiac injury. Cuedc2(-/-) cardiomyocytes exhibited a greater resistance to oxidative stress-induced cell death. Loss of CUEDC2 enhanced the antioxidant capacity of cardiomyocytes, promoted reactive oxygen species (ROS) scavenging, and subsequently inhibited the redox-dependent activation of signaling pathways. Notably, CUEDC2 promoted E3 ubiquitin ligases tripartite motif-containing 33 (TRIM33)-mediated the antioxidant enzyme, glutathione peroxidase 1 (GPX1) ubiquitination, and proteasome-dependent degradation. Ablation of CUEDC2 upregulated the protein level of GPX1 in the heart significantly. Strikingly, in vivo, the infarct size of Cuedc2(-/-) heart was significantly decreased after I/R injury, and aged Cuedc2(-/-) mice preserved better heart function as the overall ROS levels in their hearts were significantly lower. Our results demonstrated a novel role of CUEDC2 in cardiomyocyte death regulation. Manipulating CUEDC2 level might be an attractive therapeutic strategy for promoting cardiomyocyte survival following oxidative stress-induced cardiac injury.

eIF2α-Independent Inhibition of TNF-α-Triggered NF-κB Activation by Salubrinal

Salubrinal is a selective inhibitor of cellular complexes that dephosphorylate eukaryotic translation initiation factor 2α (eIF2α). In previous reports, salubrinal was shown to have the potential to inhibit the activation of nuclear factor-κB (NF-κB) by several stimuli. However, the effects of salubrinal on NF-κB signaling are largely unknown. In this study, we investigated whether and how salubrinal affects NF-κB activation induced by tumor necrosis factor (TNF)-α and interleukin (IL)-1β. We found that salubrinal selectively blocked TNF-α- but not IL-1β-induced activation of NF-κB. This inhibitory effect occurred upstream of transforming growth factor (TGF)-β-activated kinase 1 (TAK1). Further experiments revealed that salubrinal blocked TNF-α-triggered NF-κB activation independent of its action on eIF2α because knockdown of eIF2α by small interfering RNA (siRNA) did not reverse the inhibitory effect of salubrinal on NF-κB. Moreover, guanabenz, a selective inhibitor of the regulatory subunit of protein phosphatase (PP) 1, also preferentially inhibited TNF-α-triggered activation of NF-κB. These findings raise the possibility that salubrinal may selectively block TNF-α-triggered activation of the NF-κB pathway through inhibition of the PP1 complex.