RACK1 modulates NF-κB activation by interfering with the interaction between TRAF2 and the IKK complex

OTUD1 deficiency attenuates myocardial ischemia/reperfusion induced cardiomyocyte apoptosis by regulating RACK1 phosphorylation

Myocardial infarction (MI) is an important risk factor of cardiovascular disease (CVD) and its incidence has been on the rise globally. Myocardial ischemia/reperfusion (I/R) injury is frequently detected in the ischemic myocardium. Recent studies have shown that ubiquitination plays an important role in the cardiac pathophysiological processes. Herein, we investigated the role and molecular mechanism of Ovarian tumor deubiquitinase 1 (OTUD1) in I/R induced myocardial injury. It was observed that the myocardial OTUD1 was upregulated in I/R-induced heart tissues and global deletion of OTUD1 significantly ameliorated I/R induced myocardial injury and dysfunction. Similarly, silencing or overexpression OTUD1 affected the hypoxia/reoxygenation (H/R) induced cell apoptosis in cultured cardiomyocytes. Mechanistically, immunoprecipitation-mass spectrometry revealed that OTUD1 directly bound to receptor for activated C-kinase 1 (RACK1) which has been identified as a scaffold protein for multiple kinases including mitogen-activated protein kinase (MAPKs) and Inhibitor of nuclear factor kappa B kinase (IKK). OTUD1 could cleave K63-linked polyubiquitin chains to enhance RACK1 phosphorylation, thus modulating MAPKs and nuclear factor kappa B (NF-κB) signaling. Finally, silencing of RACK1 reverses OTUD1-promoted H/R induced myocardial apoptosis. In conclusion, our findings suggest that OTUD1 promotes I/R-induced heart injury by deubiquitinating RACK1, suggesting that OTUD1 is a potential therapeutic target for myocardial I/R.

Nematode serine protease inhibitor SPI-I8 negatively regulates host NF-κB signalling by hijacking MKRN1-mediated polyubiquitination of RACK1

Parasitic roundworms are remarkable for their ability to manipulate host immune systems and ameliorate inflammatory diseases. Although much is known about the nature of nematode effectors in immune modulation, little is known about the action mode of these molecules. Here, we report that a serine protease inhibitor SPI-I8 in the extracellular vesicles of blood-feeding nematodes like Ancylostoma ceylanicum, Haemonchus contortus and Nippostrongylus brasiliensis, effectively halts excessive inflammatory responses in vitro and in vivo. We demonstrate that H. contortus SPI-I8 promotes the role of a negative regulator of RACK1 and enhances the effects of RACK1 on tumor necrosis factor (TNF)-α-IκB kinases (IKKs)-nuclear factor kappa beta (NF-κB) axis in mammalian cells, by hijacking E3 ubiquitin protein ligase MKRN1-mediated polyubiquitination of RACK1. Administration of recombinant N. brasiliensis SPI-I8 effectively protects mice from dextran sulfate sodium (DSS)-induced colitis and lipopolysaccharide (LPS)-induced sepsis. Considering the structural and functional conservation of SPI-I8s among Strongylida nematodes and the conservation of interactive mediators (i.e., MKRN1 and RACK1) among mammals, our findings provide insights into the host-parasite interface where parasitic roundworms secret molecules to suppress host inflammatory responses. Harnessing these findings should underpin the exploitation of nematode's immunomodulators to relief excessive inflammation associated diseases in animals and humans.

Magnesium cantharidate inhibits hepatocellular cancer by targeting RACK1

OBJECTIVE

The aim of this study was to investigate whether magnesium cantharidate (MC) exerts anti-hepatocellular carcinoma (anti-HCC) effects by targeting receptor for activated C kinase 1 (RACK1).

METHODS

The Cancer Genome Atlas (TCGA) database was used to analyze the expression of RACK1 in liver tissues. Molecular docking was used to examine the binding interactions between MC and RACK1. Huh-7 and SK-Hep-1 liver cancer cells' viability, proliferation, and apoptosis were assessed by using the Cell Counting Kit-8 (CCK-8) assay, 5-ethynyl-2'-deoxyuridine (EdU), and flow cytometry, respectively. RNA sequencing was used to explore the underlying mechanisms. Quantitative real-time PCR, immunohistochemistry, and western blotting were performed to explore the expression of key genes and proteins.

RESULTS

TCGA analysis revealed significant upregulation of RACK1 in liver cancer tissues that was correlated with tissue type, grade, TP53 mutation, and overall survival. Molecular docking results revealed that the minimum binding energy between MC and RACK1 was -5.8 kcal/mol. Moreover, RACK1 overexpression significantly promoted cell viability and proliferation, and inhibited apoptosis in liver cancer cells. However, MC significantly reversed the viability, proliferation, and apoptosis effects induced by RACK1 overexpression in liver cancer cells. MC significantly inhibited the growth of subcutaneously transplanted tumors in vivo. RNA sequencing revealed that MC inhibited proliferation and apoptosis by targeting RACK1 to regulate calcium ion transport, ion channels, and cell adhesion in liver cancer cells.

CONCLUSION

MC exerts anti-HCC effects by targeting RACK1.

Recent progress of endoplasmic reticulum stress in the mechanism of atherosclerosis

The research progress of endoplasmic reticulum (ER) stress in atherosclerosis (AS) is of great concern. The ER, a critical cellular organelle, plays a role in important biological processes including protein synthesis, folding, and modification. Various pathological factors may cause ER stress, and sustained or excessive ER stress triggers the unfolded protein response, ultimately resulting in apoptosis and disease. Recently, researchers have discovered the importance of ER stress in the onset and advancement of AS. ER stress contributes to the occurrence of AS through different pathways such as apoptosis, inflammatory response, oxidative stress, and autophagy. Therefore, this review focuses on the mechanisms of ER stress in the development of AS and related therapeutic targets, which will contribute to a deeper understanding of the disease's pathogenesis and provide novel strategies for preventing and treating AS.

RACK1 enhances STAT3 stability and promotes T follicular helper cell development and function during blood-stage Plasmodium infection in mice

CD4+ T cells are central mediators of protective immunity to blood-stage malaria, particularly for their capacity in orchestrating germinal center reaction and generating parasite-specific high-affinity antibodies. T follicular helper (Tfh) cells are predominant CD4+ effector T cell subset implicated in these processes, yet the factors and detailed mechanisms that assist Tfh cell development and function during Plasmodium infection are largely undefined. Here we provide evidence that receptor for activated C kinase 1 (RACK1), an adaptor protein of various intracellular signals, is not only important for CD4+ T cell expansion as previously implied but also plays a prominent role in Tfh cell differentiation and function during blood-stage Plasmodium yoelii 17XNL infection. Consequently, RACK1 in CD4+ T cells contributes significantly to germinal center formation, parasite-specific IgG production, and host resistance to the infection. Mechanistic exploration detects specific interaction of RACK1 with STAT3 in P. yoelii 17XNL-responsive CD4+ T cells, ablation of RACK1 leads to defective STAT3 phosphorylation, accompanied by substantially lower amount of STAT3 protein in CD4+ T cells, whereas retroviral overexpression of RACK1 or STAT3 in RACK1-deficient CD4+ T cells greatly restores STAT3 activity and Bcl-6 expression under the Tfh polarization condition. Further analyses suggest RACK1 positively regulates STAT3 stability by inhibiting the ubiquitin-proteasomal degradation process, thus promoting optimal STAT3 activity and Bcl-6 induction during Tfh cell differentiation. These findings uncover a novel mechanism by which RACK1 participates in posttranslational regulation of STAT3, Tfh cell differentiation, and subsequent development of anti-Plasmodium humoral immunity.

Caspase-3 and gasdermin E mediate macrophage pyroptosis in periodontitis

BACKGROUND AND OBJECTIVES

Periodontitis is a chronic inflammatory disease linked to pyroptosis, an inflammatory cell death process. Macrophages are essential for maintaining microenvironment homeostasis, which is crucial for periodontal health. This study explores the mechanisms underlying the relationship between macrophage pyroptosis and periodontitis.

METHODS

Expression of the pyroptosis marker gasdermin E (GSDME) and the macrophage surface marker CD68 was examined by immunofluorescence double staining in healthy and periodontitis gingival tissues. In an in vitro pyroptosis model, RAW264.7 cells were irritated using Porphyromonas gingivalis-lipopolysaccharide (P. gingivalis-LPS) after treatment with either a nuclear factor kappa-B (NF-κB) agonist or inhibitor. The mRNA and protein levels of NF-κB, caspase-3, GSDME, and interleukin-1β (IL-1β) were evaluated through qRT-PCR, western blotting, and ELISA techniques.

RESULTS

GSDME and CD68 were heavily elevated in inflamed gingival tissues compared to healthy tissues and co-localized in the same region. Furthermore, exposure to P. gingivalis-LPS resulted in a significant upregulation of NF-κB, caspase-3, GSDME, and IL-1β at both the mRNA and protein levels in RAW264.7 cells. NF-κB agonist or inhibitor pretreatment enhanced or inhibited these effects.

CONCLUSIONS

GSDME-mediated macrophage pyroptosis is implicated in periodontitis. Based on in vitro experiments, P. gingivalis-LPS causes pyroptosis in RAW264.7 cells through the caspase-3/GSDME pathway. Furthermore, NF-κB regulates this pyroptotic pathway.

The matrix protein of respiratory syncytial virus suppresses interferon signaling via RACK1 association

IMPORTANCE

Respiratory syncytial virus (RSV) matrix (M) protein is indispensable for virion assembly and release. It is localized to the nucleus during early infection to perturb host transcription. However, the function of RSV M protein in other cellular activities remains poorly understood. In this study, several interferon response-associated host factors, including RACK1, were identified by proteomic analysis as RSV M interactors. Knockdown of RACK1 attenuates RSV-restricted IFN signaling leading to enhanced host defense against RSV infection, unraveling a role of M protein in antagonizing IFN response via association with RACK1. Our study uncovers a previously unrecognized mechanism of immune evasion by RSV M protein and identifies RACK1 as a novel host factor recruited by RSV, highlighting RACK1 as a potential new target for RSV therapeutics development.

RACK1 mediates NLRP3 inflammasome activation during Pasteurella multocida infection

Pasteurella multocida is a gram-negative bacterium that causes serious diseases in a wide range of animal species. Inflammasomes are intracellular multimolecular protein complexes that play a critical role in host defence against microbial infection. Our previous study showed that bovine P. multocida type A (PmCQ2) infection induces NLRP3 inflammasome activation. However, the exact mechanism underlying PmCQ2-induced NLRP3 inflammasome activation is not clear. Here, we show that NLRP3 inflammasome activation is positively regulated by a scaffold protein called receptor for activated C kinase 1 (RACK1). This study shows that RACK1 expression was downregulated by PmCQ2 infection in primary mouse peritoneal macrophages and mouse tissues, and overexpression of RACK1 prevented PmCQ2-induced cell death and reduced the numbers of adherent and invasive PmCQ2, indicating a modulatory role of RACK1 in the cell death that is induced by P. multocida infection. Next, RACK1 knockdown by siRNA significantly attenuated PmCQ2-induced NLRP3 inflammasome activation, which was accompanied by a reduction in the protein expression of interleukin (IL)-1β, pro-IL-1β, caspase-1 and NLRP3 as well as the formation of ASC specks, while RACK1 overexpression by pcDNA3.1-RACK1 plasmid transfection significantly promoted PmCQ2-induced NLRP3 inflammasome activation; these results showed that RACK1 is essential for NLRP3 inflammasome activation. Furthermore, RACK1 knockdown decreased PmCQ2-induced NF-κB activation, but RACK1 overexpression had the opposite effect. In addition, the immunofluorescence staining and immunoprecipitation results showed that RACK1 colocalized with NLRP3 and that NEK7 and interacted with these proteins. However, inhibition of potassium efflux significantly attenuated the RACK1-NLRP3-NEK7 interaction. Our study demonstrated that RACK1 plays an important role in promoting NLRP3 inflammasome activation by regulating NF-κB and promoting NLRP3 inflammasome assembly.

Prognostic and clinicopathological role of RACK1 for cancer patients: a systematic review and meta-analysis

Background

The receptor for activated C kinase 1 (RACK1) expression is associated with clinicopathological characteristics and the prognosis of various cancers; however, the conclusions are controversial. As a result, this study aimed to explore the clinicopathological and prognostic values of RACK1 expression in patients with cancer.

Methodology

PubMed, Embase, Web of Science, Cochrane Library, and Scopus were comprehensively explored from their inception to April 20, 2023, for selecting studies on the clinicopathological and prognostic role of RACK1 in patients with cancer that met the criteria for inclusion in this review. Pooled hazard ratios (HRs) and 95% confidence intervals (CIs) were used to assess the prognosis-predictive value of RACK1 expression, while pooled odds ratios (ORs) and 95% CIs were used to evaluate the correlation between RACK1 expression and the clinicopathological characteristics of patients with cancer. The quality of the included studies was evaluated using the Newcastle-Ottawa Scale.

Results

Twenty-two studies (13 on prognosis and 20 on clinicopathological characteristics) were included in this systematic review and meta-analysis. The findings indicated that high RACK1 expression was significantly associated with poor overall survival (HR = 1.62; 95% CI, 1.13-2.33; P = 0.009; I2 = 89%) and reversely correlated with disease-free survival/recurrence-free survival (HR = 1.87; 95% CI, 1.22-2.88; P = 0.004; I2 = 0%). Furthermore, increased RACK1 expression was significantly associated with lymphatic invasion/N+ stage (OR = 1.74; 95% CI, 1.04-2.90; P = 0.04; I2 = 79%) of tumors.

Conclusions

RACK1 may be a global predictive marker of poor prognosis in patients with cancer and unfavorable clinicopathological characteristics. However, further clinical studies are required to validate these findings.

RNA sequencing of blood from sex- and age-matched discordant siblings supports immune and transcriptional dysregulation in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition with onset in early childhood, still diagnosed only through clinical observation due to the lack of laboratory biomarkers. Early detection strategies would be especially useful in screening high-risk newborn siblings of children already diagnosed with ASD. We performed RNA sequencing on peripheral blood, comparing 27 pairs of ASD children vs their sex- and age-matched unaffected siblings. Differential gene expression profiling, performed applying an unpaired model found two immune genes, EGR1 and IGKV3D-15, significantly upregulated in ASD patients (both p adj = 0.037). Weighted gene correlation network analysis identified 18 co-expressed modules. One of these modules was downregulated among autistic individuals (p = 0.035) and a ROC curve using its eigengene values yielded an AUC of 0.62. Genes in this module are primarily involved in transcriptional control and its hub gene, RACK1, encodes for a signaling protein critical for neurodevelopment and innate immunity, whose expression is influenced by various hormones and known "endocrine disruptors". These results indicate that transcriptomic biomarkers can contribute to the sensitivity of an intra-familial multimarker panel for ASD and provide further evidence that neurodevelopment, innate immunity and transcriptional regulation are key to ASD pathogenesis.

Characterization of the RACK1 gene of Aips cerana cerana and its role in adverse environmental stresses

Receptors for Activated C Kinase 1 (RACK1s) are a kind of multifunction scaffold protein that plays an important role in cell signal transductions and animal development. However, the function of RACK1 in the Chinese honeybee Apis cerana cerana is little known. Here, we isolated and identified a RACK1 gene from Apis cerana cerana, named AccRACK1. By bioinformatic analysis, we revealed a high nucleic acid homology between AccRACK1 and RACK1 of Apis cerana. RT-qPCR analyses demonstrated AccRACK1 was mostly expressed in 3rd instar larvae, darked-eyed pupae and adults (one and thirty days post-emergence), suggesting it might participate in the development of A. cerana cerana. Moreover, the expression of AccRACK1 was highest in the thorax, followed by the venom gland. Compared to the blank control group, AccRACK1 was induced by 24 and 44 °C, HgCl2 and pesticides (paraquat, pyridaben and methomyl) but inhibited by 14 °C, H2O2, UV light and cyhalothrin. Additionally, 0.05, 0.1, 1, 5 and 10 mg/ml PPN (juvenile hormone analogue pyriproxyfen) could promote the expression of AccRACK1, with 1 mg/ml showing the highest upregulation, suggesting it was regulated by hormones. Further study found that after knockdown of AccRACK1 by RNAi, the expression of the eukaryotic initiation factor 6 of A. cerana cerana (AcceIF6), an initiation factor regulating the initiation of translation, was inhibited, indicating AccRACK1 might affect cellular responses by translation. These findings, taken together, suggest AccRACK1 is involved in the development and responses to abiotic stresses of A. cerana cerana, and therefore, it may be of critical importance to the survival of A. cerana cerana.

The phytochemical and pharmacological profile of taraxasterol

Taraxasterol is one of the bioactive triterpenoids found in dandelion, a member of the family Asteraceae. In the animal or cellular models of several ailments, including liver damage, gastritis, colitis, arthritis, pneumonia, tumors, and immune system diseases, taraxasterol has been shown to have significant preventive and therapeutic effects. This review aims to evaluate the current state of research and provide an overview of the possible applications of taraxasterol in various diseases. The reported phytochemical properties and pharmacological actions of taraxasterol, including anti-inflammatory, anti-oxidative, and anti-carcinogenic properties, and its potential molecular mechanisms in developing these diseases are highlighted. Finally, we further explored whether taraxasterol has protective effects on neuronal death in neurodegenerative diseases. In addition, more animal and clinical studies are also required on the metabolism, bioavailability, and safety of taraxasterol to support its applications in pharmaceuticals and medicine.

Stabilization of CCDC102B by Loss of RACK1 Through the CMA Pathway Promotes Breast Cancer Metastasis via Activation of the NF-κB Pathway

Background

Breast cancer is one of the leading causes of cancer-related death among women, and the pathological status of axillary lymph nodes is an important predictor of prognosis. However, the mechanism involved in this early stage of metastasis remains largely unknown.

Methods

Microarray analysis was used to carry out differential genomics analyses between matched pairs of metastatic sentinel lymph node tissues and breast primary tumors. The CRISPR/Cas9 gene editing system was used for in vivo screening by transplanting a loss-of-function cell pool into immunocompromised mice. MAGeCK was used to analyze the screening results. Survival analysis was performed via the Kaplan–Meier method. Cell proliferation, wound healing, migration and invasion assays were performed to confirm the phenotype. A tail vein model and subcutaneous xenotransplanted tumor model were used for the in vivo study. The relationship between coiled-coil domain containing 102B (CCDC102B) and receptor for activated C kinase 1 (RACK1) was examined using coimmunoprecipitation, mass spectrometry, nuclear protein extraction and immunofluorescence assays. The primary biological functions and pathways related to CCDC102B were enriched by RNA sequencing.

Results

We identified CCDC102B through screening and found that it was significantly upregulated in metastatic lesions in lymph nodes compared to matched primary tumors. Increased expression of CCDC102B promoted breast cancer metastasis in vitro and in vivo. Additionally, high expression of CCDC102B was correlated with poor clinical outcomes in breast cancer patients. We further identified that CCDC102B was stabilized by the loss of RACK1, a protein negatively correlated with breast cancer metastasis. Mechanistically, we found that RACK1 promoted CCDC102B lysosomal degradation by mediating chaperone-mediated autophagy (CMA). The aggressive behavior of CCDC102B in breast cancer cells could be reversed by the expression of RACK1. Moreover, CCDC102B was correlated with the significant enrichment of NF-κB pathway components. Overexpressing CCDC102B led to less interaction between RACK1 and IKKa. Thus, CCDC102B positively regulates the NF−κB pathway by interacting with RACK1.

Conclusion

Taken together, our findings uncover a novel role of CCDC102B in breast cancer metastasis. CCDC102B serves as a potential metastasis promoter by regulating the activation of the NF-κB pathway and can be degraded by RACK1 via CMA.

Identifying predictive signalling networks for Vedolizumab response in ulcerative colitis

BACKGROUND

In ulcerative colitis (UC), the molecular mechanisms that drive disease development and patient response to therapy are not well understood. A significant proportion of patients with UC fail to respond adequately to biologic therapy. Therefore, there is an unmet need for biomarkers that can predict patients' responsiveness to the available UC therapies as well as ascertain the most effective individualised therapy. Our study focused on identifying predictive signalling pathways that predict anti-integrin therapy response in patients with UC.

METHODS

We retrieved and pre-processed two publicly accessible gene expression datasets (GSE73661 and GSE72819) of UC patients treated with anti-integrin therapies: (1) 12 non-IBD controls and 41 UC patients treated with Vedolizumab therapy, and (2) 70 samples with 58 non-responder and 12 responder UC patient samples treated with Etrolizumab therapy without non-IBD controls. We used a diffusion-based signalling model which is mainly focused on the T-cell receptor signalling network. The diffusion model uses network connectivity between receptors and transcription factors.

RESULTS

The network diffusion scores were able to separate VDZ responder and non-responder patients before treatment better than the original gene expression. On both anti-integrin treatment datasets, the diffusion model demonstrated high predictive performance for discriminating responders from non-responders in comparison with 'nnet'. We have found 48 receptor-TF pairs identified as the best predictors for VDZ therapy response with AUC ≥ 0.76. Among these receptor-TF predictors pairs, FFAR2-NRF1, FFAR2-RELB, FFAR2-EGR1, and FFAR2-NFKB1 are the top best predictors. For Etrolizumab, we have identified 40 best receptor-TF pairs and CD40-NFKB2 as the best predictor receptor-TF pair (AUC = 0.72). We also identified subnetworks that highlight the network interactions, connecting receptors and transcription factors involved in cytokine and fatty acid signalling. The findings suggest that anti-integrin therapy responses in cytokine and fatty acid signalling can stratify UC patient subgroups.

CONCLUSIONS

We identified signalling pathways that may predict the efficacy of anti-integrin therapy in UC patients and personalised therapy alternatives. Our results may lead to the advancement of a promising clinical decision-making tool for the stratification of UC patients.

N4BP3 Regulates RIG-I-Like Receptor Antiviral Signaling Positively by Targeting Mitochondrial Antiviral Signaling Protein

Mitochondrial antiviral signaling protein (MAVS), an adaptor protein, is activated by RIG-I, which is critical for an effective innate immune response to infection by various RNA viruses. Viral infection causes the RIG-I-like receptor (RLR) to recognize pathogen-derived dsRNA and then becomes activated to promote prion-like aggregation and activation of MAVS. Subsequently, through the recruitment of TRAF proteins, MAVS activates two signaling pathways mediated by TBK1-IRF3 and IKK- NF-κb, respectively, and turns on type I interferon and proinflammatory cytokines. This study discovered that NEDD4 binding protein 3 (N4BP3) is a positive regulator of the RLR signaling pathway by targeting MAVS. Overexpression of N4BP3 promoted virus-induced activation of the interferon-β (IFN-β) promoter and interferon-stimulated response element (ISRE). Further experiments showed that knockdown or knockout N4BP3 impaired RIG-I-like receptor (RLR)-mediated innate immune response, induction of downstream antiviral genes, and cellular antiviral responses. We also detected that N4BP3 could accelerate the interaction between MAVS and TRAF2. Related experiments revealed that N4BP3 could facilitate the ubiquitination modification of MAVS. These findings suggest that N4BP3 is a critical component of the RIG-I-like receptor (RLR)-mediated innate immune response by targeting MAVS, which also provided insight into the mechanisms of innate antiviral responses.

Insulin/IGF-1 signaling promotes immunosuppression via the STAT3 pathway: impact on the aging process and age-related diseases

BACKGROUND

The insulin/IGF-1 signaling pathway has a major role in the regulation of longevity both in Caenorhabditis elegans and mammalian species, i.e., reduced activity of this pathway extends lifespan, whereas increased activity accelerates the aging process. The insulin/IGF-1 pathway controls protein and energy metabolism as well as the proliferation and differentiation of insulin/IGF-1-responsive cells. Insulin/IGF-1 signaling also regulates the functions of the innate and adaptive immune systems. The purpose of this review was to elucidate whether insulin/IGF-1 signaling is linked to immunosuppressive STAT3 signaling which is known to promote the aging process.

METHODS

Original and review articles encompassing the connections between insulin/IGF-1 and STAT3 signaling were examined from major databases including Pubmed, Scopus, and Google Scholar.

RESULTS

The activation of insulin/IGF-1 receptors stimulates STAT3 signaling through the JAK and AKT-driven signaling pathways. STAT3 signaling is a major activator of immunosuppressive cells which are able to counteract the chronic low-grade inflammation associated with the aging process. However, the activation of STAT3 signaling stimulates a negative feedback response through the induction of SOCS factors which not only inhibit the activity of insulin/IGF-1 receptors but also that of many cytokine receptors. The inhibition of insulin/IGF-1 signaling evokes insulin resistance, a condition known to be increased with aging. STAT3 signaling also triggers the senescence of both non-immune and immune cells, especially through the activation of p53 signaling.

CONCLUSIONS

Given that cellular senescence, inflammaging, and counteracting immune suppression increase with aging, this might explain why excessive insulin/IGF-1 signaling promotes the aging process.

RACK1 modulates polyglutamine-induced neurodegeneration by promoting ERK degradation in Drosophila

Polyglutamine diseases are neurodegenerative diseases caused by the expansion of polyglutamine (polyQ) tracts within different proteins. Although multiple pathways have been found to modulate aggregation of the expanded polyQ proteins, the mechanisms by which polyQ tracts induced neuronal cell death remain unknown. We conducted a genome-wide genetic screen to identify genes that suppress polyQ-induced neurodegeneration when mutated. Loss of the scaffold protein RACK1 alleviated cell death associated with the expression of polyQ tracts alone, as well as in models of Machado-Joseph disease (MJD) and Huntington's disease (HD), without affecting proteostasis of polyQ proteins. A genome-wide RNAi screen for modifiers of this rack1 suppression phenotype revealed that knockdown of the E3 ubiquitin ligase, POE (Purity of essence), further suppressed polyQ-induced cell death, resulting in nearly wild-type looking eyes. Biochemical analyses demonstrated that RACK1 interacts with POE and ERK to promote ERK degradation. These results suggest that RACK1 plays a key role in polyQ pathogenesis by promoting POE-dependent degradation of ERK, and implicate RACK1/POE/ERK as potent drug targets for treatment of polyQ diseases.

RACK1 plays a critical role in mast cell secretion and Ca2+ mobilization by modulating F-actin dynamics

Although RACK1 is known to act as a signaling hub in immune cells, its presence and role in mast cells (MCs) is undetermined. MC activation via antigen stimulation results in mediator release and is preceded by cytoskeleton reorganization and Ca2+ mobilization. In this study, we found that RACK1 was distributed throughout the MC cytoplasm both in vivo and in vitro. After RACK1 knockdown (KD), MCs were rounded, and the cortical F-actin was fragmented. Following antigen stimulation, in RACK1 KD MCs, there was a reduction in cortical F-actin, an increase in monomeric G-actin and a failure to organize F-actin. RACK1 KD also increased and accelerated degranulation. CD63+ secretory granules were localized in F-actin-free cortical regions in non-stimulated RACK1 KD MCs. Additionally, RACK1 KD increased antigen-stimulated Ca2+ mobilization, but attenuated antigen-stimulated depletion of ER Ca2+ stores and thapsigargin-induced Ca2+ entry. Following MC activation there was also an increase in interaction of RACK1 with Orai1 Ca2+-channels, β-actin and the actin-binding proteins vinculin and MyoVa. These results show that RACK1 is a critical regulator of actin dynamics, affecting mediator secretion and Ca2+ signaling in MCs. This article has an associated First Person interview with the first author of the paper.

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.

Inhibition of porcine reproductive and respiratory syndrome virus by PKC inhibitor dequalinium chloride in vitro

As a severe disease characterized by reproductive failure and respiratory distress, porcine reproductive and respiratory syndrome (PRRS) is one of the most leading threats to the swine industry worldwide. Highly evolving porcine reproductive and respiratory syndrome virus (PRRSV) strains with distinct genetic diversity make the current vaccination strategy much less cost-effective and thus urge alternative protective host directed therapeutic approaches. RACK1-PKC-NF-κB signalling axis was suggested as a potential therapeutic target for PRRS control, therefore we tested the inhibitory effect of PKC inhibitor dequalinium chloride (DECA) on the PRRSV infection in vitro. RT-qPCR, western blot, Co-IP and cytopathic effect (CPE) observations revealed that DECA suppressed PRRSV infection and protected Marc-145 cells and porcine alveolar macrophages (PAMs) from severe cytopathic effects, by repressing the PKCα expression, the interaction between RACK1 and PKCα, and subsequently the NF-κB activation. In conclusion, the data presented in this study shed more light on deeper understanding of the molecular pathogenesis upon PRRSV infection and more importantly suggested DECA as a potential promising drug candidate for PRRS control.

Porcine RACK1 negatively regulates the infection of classical swine fever virus and the NF-κB activation in PK-15 cells

Classical swine fever (CSF) is one of the main viral diseases of swine worldwide. The causative pathogen is CSF virus (CSFV), a small enveloped RNA virus of the genus Pestivirus. Activation of NF-κB is a hallmark of most viral infections and the viral pathogens frequently kidnap NF-κB pathway for their own advantages, however, it is unclear or even controversial about whether CSFV infection can activate NF-κB signal pathway. RACK1 was shown as an interacting host protein with CSFV NS5A protein, but no studies so far have clearly defined the role of RACK1 during CSFV infection and NF-κB activation. In this study, to properly address these open questions, using RT-qPCR, western blot, indirect fluorescence staining, siRNA knockdown and protein overexpression techniques, we demonstrated that CSFV infection reduced the RACK1 expression at both mRNA and protein levels in PK-15 cells. Downregulation of cellular RACK1 enhanced CSFV infection and subsequent NF-κB activation, while RACK1 overexpression inhibited CSFV infection and the NF-κB activation. In conclusion, RACK1 is a negative cellular regulator for CSFV infection and NF-κB activation in PK-15 cells. Our work addressed a novel aspect concerning the regulation of innate antiviral immune response during CSFV infection. This study may provide some insights into the molecular mechanisms of CSFV infection in swine. However, the elaborate mechanism by which CSFV regulates NF-κB activation and how RACK1 plays its roles in CSFV infection and NF-κB induction require further in-depth studies.

RACK1 promotes cancer progression by increasing the M2/M1 macrophage ratio via the NF-κB pathway in oral squamous cell carcinoma

Receptor for activated C kinase 1 (RACK1) has been shown to promote oral squamous cell carcinoma (OSCC) progression, and RACK1 expression levels have been negatively correlated with prognosis in patients with OSCC. Here, we investigated the impact of RACK1 OSCC expression on the recruitment and differentiation of tumor-associated macrophages. High RACK1 expression in OSCC cells correlated with increased M2 macrophage infiltration in tumor samples from a clinical cohort study. Moreover, the combination of RACK1 expression and the M2/M1 ratio could successfully predict prognosis in OSCC. OSCC cells with high RACK1 expression inhibited the migration of THP-1 cells, promoted M2-like macrophage polarization in vitro, and increased the proportion of M2-like macrophages in a xenograft mouse model. Moreover, both M1- and M2-like macrophage polarization-associated proteins were induced in macrophages cocultured with RACK1-silenced cell supernatant. A mechanistic study revealed that the expression and secretion of C-C motif chemokine 2 (CCL2), C-C motif chemokine 5 (CCL5), interleukin-6 (IL-6), and interleukin-1 (IL-1) are closely related to RACK1 expression. In addition, blocking nuclear factor-kappa B (NF-κB) could promote M2-like macrophage polarization. These results indicate that RACK1 and the M2/M1 ratio are predictors of a poor prognosis in OSCC. RACK1 promotes M2-like polarization by regulating NF-κB and could be used as a potential therapeutic target for antitumor immunity.

TRIM25 Promotes TNF-α-Induced NF-κB Activation through Potentiating the K63-Linked Ubiquitination of TRAF2

As an important effector in response to various intracellular or extracellular stimuli, the NF-κB family extensively participates in a wide spectrum of biological events, and its dysregulation may result in many pathological conditions, such as microbial infection, tumor progression, and neurodegenerative disorders. Previous investigations showed that multiple types of ubiquitination play critical roles in the modulation of the NF-κB signaling pathway, yet the molecular mechanisms are still poorly understood. In the current study, we identified TRIM25, an E3 ubiquitin ligase, as a novel positive regulator in mediating NF-κB activation in human embryonic kidney 293T (HEK293T), HeLa cells, THP-1 cells, and PBMCs. The expression of TRIM25 promoted TNF-α-induced NF-κB signaling, whereas the knockdown had the opposite effect. Furthermore, TRIM25 interacted with TRAF2 and enhanced the K63-linked polyubiquitin chains attached to TRAF2. Moreover, TRIM25 bridged the interaction of TRAF2 and TAK1 or IKKβ. To our knowledge, our study has identified a previously unrecognized role for TRIM25 in the regulation of NF-κB activation by enhancing the K63-linked ubiquitination of TRAF2.

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.

Transcriptomic Analysis of Stem Cells Treated with Moringin or Cannabidiol: Analogies and Differences in Inflammation Pathways

Inflammation is a common feature of many neurodegenerative diseases. The treatment of stem cells as a therapeutic approach to repair damage in the central nervous system represents a valid alternative. In this study, using Next-Generation Sequencing (NGS) technology, we analyzed the transcriptomic profile of human Gingival Mesenchymal Stem Cells (hGMSCs) treated with Moringin [4-(α-l-ramanosyloxy)-benzyl isothiocyanate] (hGMSCs-MOR) or with Cannabidiol (hGMSCs-CBD) at dose of 0.5 or 5 µM, respectively. Moreover, we compared their transcriptomic profiles in order to evaluate analogies and differences in pro- and anti-inflammatory pathways. The hGMSCs-MOR selectively downregulate TNF-α signaling from the beginning, reducing the expression of TNF-α receptor while hGMSCs-CBD limit its activity after the process started. The treatment with CBD downregulates the pro-inflammatory pathway mediated by the IL-1 family, including its receptor while MOR is less efficient. Furthermore, both the treatments are efficient in the IL-6 signaling. In particular, CBD reduces the effect of the pro-inflammatory JAK/STAT pathway while MOR enhances the pro-survival PI3K/AKT/mTOR. In addition, both hGMSCs-MOR and hGMSCs-CBD improve the anti-inflammatory activity enhancing the TGF-β pathway.

Overexpression of RACK1 enhanced the replication of porcine reproductive and respiratory syndrome virus in Marc-145 cells and promoted the NF-κB activation via upregulating the expression and phosphorylation of TRAF2

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative pathogen for porcine reproductive and respiratory syndrome (PRRS), which lead to huge loss to porcine industry. RACK1 (receptor of activated protein C kinase 1) was first identified as a receptor for protein kinase C. Mounting evidence demonstrated that RACK1 played diverse roles in NF-κB activation and virus infections. We previously reported that siRNA knockdown of RACK1 inhibited PRRSV replication in Marc-145 cells, abrogated NF-κB activation induced by PRRSV infection and reduced the viral titer. Here we established a Marc-145 cell line which could stably overexpress RACK1 to consolidate our findings. Based on the data from RT-qPCR, western blot, immunofluorescence staining, cytopathic effects and viral titer analysis, we concluded that overexpression of RACK1 could enhance the replication of PRRSV in Marc-145 cells and promote the NF-κB activation via upregulating TRAF2 expression and its phosphorylation. Marc-145 cells overexpressing RACK1exhibited severe cytopathic effects post infection with PRRSV and elevated the viral titer. Taken together, RACK1 plays an essential role for PRRSV replication in Marc-145 cells and NF-κB activation. The results presented here shed more light on the understanding of the molecular mechanisms underlying PRRSV infection and its subsequent NF-κB activation. Therefore, we anticipate RACK1 as a promising target for PRRS control.

Downregulation of tumor suppressor RACK1 by Helicobacter pylori infection promotes gastric carcinogenesis through the integrin β-1/NF-κB signaling pathway

Receptor of activated protein kinase C 1 (RACK1) is downregulated in gastric cancer and is involved in modulating NF-κB signaling pathway activity. However, the underlying molecular mechanisms regulating RACK1 expression are unclear. In this study, we demonstrated that downregulated expression of RACK1 was observed in gastric cancer tissue compared to adjacent normal tissue and was correlated with poor prognosis in patients. Helicobacter pylori (H. pylori) infection downregulated RACK1 expression in concert with canonical NF-κB signaling pathway activation in vivo and in vitro. RACK1 overexpression suppressed NF-κB signaling pathway activation as well as the release of downstream proinflammatory cytokines. In addition, RACK1 downregulation increased integrin β-1 expression, while integrin β-1 silencing decreased NF-κB signaling activation. Moreover, H. pylori infection downregulated RACK1 but upregulated integrin β-1 expression at the precancerous lesion stages in human subjects. Our data indicate that H. pylori infection promotes the upregulation of integrin β-1 expression via downregulation of RACK1 expression, which subsequently leads to the elevated activation of the NF-κB signaling pathway, an essential step in H. pylori-induced carcinogenesis.

Ghrelin protects against contact dermatitis and psoriasiform skin inflammation by antagonizing TNF-α/NF-κB signaling pathways

Contact dermatitis and psoriasis are skin disorders caused by immune dysregulation, yet much remains unknown about their underlying mechanisms. Ghrelin, a recently discovered novel peptide and potential endogenous anti-inflammatory factor expressed in the epidermis, is involved in skin repair and disease. In this study, we investigated the expression pattern and therapeutic effect of ghrelin in both contact dermatitis and psoriasis mouse models induced by oxazolone (OXA) and imiquimod (IMQ), respectively, and in TNF-α-stimulated RAW264.7 macrophages, NHEKs and skin fibroblasts. Ghrelin expression was reduced in both the OXA-induced contact dermatitis and IMQ-induced psoriasis mouse models. Furthermore, treatment with ghrelin attenuated skin inflammation in both the contact dermatitis and psoriasis mouse models. Mice administered PBS after OXA- or IMQ-induced model generation exhibited typical skin inflammation, whereas ghrelin treatment in these mouse models substantially decreased the dermatitis phenotype. In addition, exogenous ghrelin attenuated the inflammatory reaction induced by TNF-α in RAW264.7 cells. Moreover, ghrelin administration limited activation of NF-κB signaling. In summary, ghrelin may represent a potential molecular target for the prevention and treatment of inflammatory skin diseases, including contact dermatitis and psoriasis.

RACK1 attenuates RLR antiviral signaling by targeting VISA-TRAF complexes

Virus-induced signaling adaptor (VISA), which mediates the production of type I interferon, is crucial for the retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling pathway. Upon viral infection, RIG-I recognizes double-stranded viral RNA and interacts with VISA to mediate antiviral innate immunity. However, the mechanisms underlying RIG/VISA-mediated antiviral regulation remain unclear. In this study, we confirmed that receptor for activated C kinase 1 (RACK1) interacts with VISA and attenuates the RIG/VISA-mediated antiviral innate immune signaling pathway. Overexpression of RACK1 inhibited the interferon-β (IFN-β) promoter; interferon-stimulated response element (ISRE); nuclear factor kappa B (NF-κB) activation; and dimerization of interferon regulatory factor 3 (IRF3) mediated by RIG-I, VISA, and TANK-binding kinase 1 (TBK1). A reduction in RACK1 expression level upon small interfering RNA knockdown increased RIG/VISA-mediated antiviral transduction. Additionally, RACK1 disrupted formation of the VISA-tumor necrosis factor receptor-associated factor 2 (TRAF2), VISA-TRAF3, and VISA-TRAF6 complexes during RIG-I/VISA-mediated signal transduction. Additionally, RACK1 enhanced K48-linked ubiquitination of VISA, attenuated its K63-linked ubiquitination, and decreased VISA-mediated antiviral signal transduction. Together, these results indicate that RACK1 interacts with VISA to repress downstream signaling and downregulates virus-induced IFN-β production in the RIG-I/VISA signaling pathway.

Astragalus polysaccharide from Astragalus Melittin ameliorates inflammation via suppressing the activation of TLR-4/NF-κB p65 signal pathway and protects mice from CVB3-induced virus myocarditis

Inflammation plays a crucial role in regulating cardiomyopathy and injuries of coxsackievirus B3 (CVB3)-induced viral myocarditis (VM). It has been reported that Astragalus polysaccharide (AP) from Astragalus Melittin could inhabit inflammatory gene expression under a variety of pathological conditions. However, the functional roles of AP in CVB3-induced VM still remain unknown. Here, we found that AP significantly enhanced survival for CVB3-induced mice. AP protected the mice against CVB3-induced myocardial injuries characterized by the increased body weight and depressed serum level of creatine kinase-MB (CK-MB), aspartate transaminases (AST) and lactate dehydrogenase (LDH), enhanced left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS). At the pathological level, AP ameliorated the mice against CVB3-induced myocardial damage, dilated cardiomyopathy and chronic myocardial fibrosis. We subsequently found that AP significantly suppressed CVB3-induced expression of inflammation marker (IL-1β, IL-6, TNF-α, INF-γ and MCP-1) in heart. Furthermore, we confirmed that AP suppressed the CVB3-induced expression of TLR-4 and phosphorylated NF-κB p65 in heart. Taken together, the data suggest that AP protects against CVB3-induced myocardial damage and inflammation, which may partly attribute to the regulation of TLR-4/NF-κB p65 signal pathway, moreover, suppressive effect of AP on CVB3-induced activation of TLR-4/NF-κB p65 signal was TNF-α-independent.

Inhibition of TPL2 by interferon-α suppresses bladder cancer through activation of PDE4D

BACKGROUND

Drugs that inhibit the MEK/ERK pathway have therapeutic benefit in bladder cancer treatment but responses vary with patients, for reasons that are still not very clear. Interferon-α (IFN-α) is also used as a therapeutic agent for bladder cancer treatment but the response rate is low. It was found that IFN-α could enhance the cytotoxic effect of MEK inhibition. However, the potential mechanisms of that are still unclear. Understanding of the cross-talk between the IFN-α and MEK/ERK pathway will help enhance the efficacy of IFN-α or MEK inhibitors on bladder cancer.

METHODS

Immunoprecipitation and pull-down assay were used to reveal the formation of signaling complex. The protein expressions were detected by western blot and immunohistochemistry. The cAMP level, Phosphodiesterase 4D (PDE4D) activity and Prostaglandin E2 (PGE2) concentration in cells, serum and tissues were detected by enzyme-linked immunosorbent assay. The role of PDE4D in bladder tumorigenesis in vivo was examined by the xenograft model. Tissue microarray chips were used to investigate the prognostic roles of PDE4D and tumor progression locus 2 (TPL2) in bladder cancer patients.

RESULTS

IFN-α down-regulated the cyclooxygenase-2 (COX-2) expression in bladder cancer cells through the inhibition of TPL2/NF-κB pathway; IFN-α also inhibited COX-2 expression by suppressing cAMP signaling through TPL2-ERK mediated PDE4D activity. Reduction of the intracellular cAMP level by PDE4D potentiated the antitumor effect of IFN-α against bladder cancer in vitro and in vivo. Further analysis of clinical samples indicated that low PDE4D expression and high level of TPL2 phosphorylation were correlated to the development and poor prognosis in bladder cancer patients.

CONCLUSIONS

Our data reveal that IFN-α can exert its antitumor effect through a non-canonical JAK-STAT pathway in the bladder cancer cells with low activity of IFN pathway, and the TPL2 inhibition is another function of IFN-α in the context of bladder cancer therapy. The antitumor effects of IFN-α and MEK inhibition also depend on the PDE4D-mediated cAMP level in bladder cancer cells. Suppression of the TPL2 phosphorylation and intracellular cAMP level may be possible therapeutic strategies for enhancing the effectiveness of IFN-α and MEK inhibitors in bladder cancer treatment.

Role of RACK1 on cell proliferation, adhesion, and bortezomib-induced apoptosis in multiple myeloma

Receptor for activated C kinase 1 (RACK1), a scaffold protein, plays a crucial role in the progression of various cancers. However, the biological function and underlying mechanism of RACK1 in multiple myeloma (MM) cells remain unclear. The present study aimed to explore the function of RACK1 on the cell proliferation, adhesion, and bortezomib-induced apoptosis in MM. We found that RACK1 was significantly overexpressed in myeloma cell lines and primary myeloma cells compared with normal bone marrow plasma cells. Moreover, immunofluorescence revealed that RACK1 was primarily expressed in the cytoplasm of MM cells. Knockdown of RACK1 impaired growth of MM cells, blocked entry into the S-phase of the cell cycle, and resulted in reduced cell adhesion rates. More importantly, knockdown of RACK1 decreased the proliferation of MM cells by activating P-P38 and P-ERK in the MAPK/ERK signaling pathway. We also found that altered expression of RACK1 is associated with bortezomib-mediated MM cell apoptosis. In summary, these results may provide a possible target for therapy in MM.

S100A4 suppresses cancer stem cell proliferation via interaction with the IKK/NF-κB signaling pathway

Background

Bladder cancer often recurs due to incomplete elimination of the cancer stem cells (CSCs). Therefore, new strategies targeting bladder CSCs are needed and the aim of this study was to investigate the effect of S100A4 on the proliferation capacity of MB49 bladder cancer stem cells (MCSCs).

Methods

MCSCs were established and validated. The expression level of S100A4 in MCSCs and MB49 cells was evaluated using Western blotting and quantitative polymerase chain reaction (QPCR). S100A4 was overexpressed or knocked-down by transfection of pCMV6-XL5-S100A4 plasmid or RNA interference (RNAi) respectively. Proliferation capacity of MCSC was evaluated by cell proliferation assay and in vivo tumorigenicity study. Transcriptional activity of nuclear factor kappa B (NF-κB) was analyzed using luciferase reporter assay, and the level of interleukin (IL)-2 as well as tumor necrosis factor (TNF) was quantified by QPCR. Protein-protein interaction of S100A4 and inhibitor of nuclear factor kappa B NF-κB kinase (IKK) was analyzed by immunoprecipitation.

Results

S100A4 was significantly up-regulated in MCSCs, which positively associated with the proliferation capacity, as well as the level of NF-κB, IKK, IL-2 and TNF in MCSCs. Knock-down of S100A4 could reverse such effects. Using immunoprecipitation assay, an interaction between S100A4 and IKK could be observed.

Conclusions

S100A4 is upregulated in MCSCs and possibly enhance the proliferation ability of MCSCs by way of activating the IKK/NF-κB signaling pathway, and S100A4 maybe a hopeful therapeutic target for MCSCs.

RACK1 deficiency synergizes with all-trans retinoic acid to induce apoptosis in human acute promyelocytic leukemia cells

As a classic differentiation agent, all-trans retinoic acid (ATRA) has been widely used in the treatment of acute promyelocytic leukemia (APL). However, the clinical application of ATRA has strict limitations, for its severe side effects due to the accumulation of peripheral blood leukocytes. The scaffold protein RACK1 (Receptor for activated C kinase 1), which regulates multiple signaling pathways, has been proposed to contribute to the survival of leukemic progenitors. But it remains unclear whether it is also involved in the oncogenic growth of APL. In the present study, we demonstrate that silencing of endogenous RACK1 expression synergized with ATRA to promote the death of NB4 and HL-60 APL cells without effect on cell differentiation induced by ATRA. Interestingly, RACK1 knockdown combined with ATRA treatment mainly induces apoptosis. It is distinct to the necrotic cell death induced by idarubicin in combination with ATRA, a regimen extensively used in the clinic to prevent neutrophil accumulation. Further exploration revealed that the lysosome-autophagy pathway is likely to be responsible for the anti-apoptotic role of RACK1. Taken together, our findings indicate that RACK1 is essential in maintaining the malignant features of APL, and targeting RACK1 may have promising therapeutic implications in the treatment of APL.

RACK1 is indispensable for porcine reproductive and respiratory syndrome virus replication and NF-κB activation in Marc-145 cells

Porcine reproductive and respiratory syndrome virus (PRRSV) causes porcine reproductive and respiratory syndrome (PRRS), which is currently insufficiently controlled. RACK1 (receptor of activated protein C kinase 1) was first identified as a receptor for protein kinase C, with increasing evidence showing that the functionally conserved RACK1 plays important roles in cancer development, NF-κB activation and various virus infections. However, the roles of RACK1 during PRRSV infection in Marc-145 cells have not been described yet. Here we demonstrated that infection of Marc-145 cells with the highly pathogenic PRRSV strain YN-1 from our lab led to activation of NF-κB and upregulation of RACK1 expression. The siRNA knockdown of RACK1 inhibited PRRSV replication in Marc-145 cells, abrogated NF-κB activation induced by PRRSV infection and reduced the viral titer. Furthermore, knockdown of RACK1 could inhibit an ongoing PRRSV infection. We found that RACK1 is highly conserved across different species based on the phylogenetic analysis of mRNA and deduced amino acid sequences. Taken together, RACK1 plays an indispensable role for PRRSV replication in Marc-145 cells and NF-κB activation. The results would advance our further understanding of the molecular mechanisms underlying PRRSV infection in swine and indicate RACK1 as a promising potential therapeutic target.

Knockdown of miR-155 protects microglia against LPS-induced inflammatory injury via targeting RACK1: a novel research for intracranial infection

Background

Intracranial infection, one of the complications of traumatic brain injury, is usually associated with inflammation. Several microRNAs (miRNAs), including miR-155, have been reported to be critical modulators in peripheral and central nervous system inflammation. In this study, we investigated the role of miR-155 in lipopolysaccharide (LPS)-induced inflammatory injury in mouse microglia BV2 cells.

Results

The expression level of miR-155 was significantly up-regulated after LPS stimulation in BV2 cells. LPS administration decreased BV2 cell viability, promoted apoptosis and increased the release of pro-inflammatory cytokines; while miR-155 knockdown rescued BV2 cell from LPS-induced injury. RACK1 was a directly target of miR-155. Interestingly, miR-155 knockdown did not attenuate LPS-induced inflammatory injury when RACK1 was knocked down. The mechanistic study indicated that miR-155 knockdown deactivated MAPK/NF-κB and mTOR signaling pathways under LPS-treated conditions.

Conclusions

Knockdown of miR-155 protected mouse microglia BV2 cells from LPS-induced inflammatory injury via targeting RACK1 and deactivating MAPK/NF-κB and mTOR signaling pathways.

RACK1 promotes radiation resistance in esophageal cancer via regulating AKT pathway and Bcl-2 expression

RACK1 is a seven Trp-Asp 40 repeat protein, which interacts with a wide range of kinases and proteins. RACK1 plays an important role in the proliferation and progression of various cancers. The aim of this study is to detect the role of RACK1 in the radioresistance in esophageal cancer. The results indicated that downregulation of RACK1 reduced the colony formation ability, proliferation ability and resistance of cells to radiation effection through regulating the radiation-related proteins including pAKT, Bcl-2 and Bim; whereas upregulation of RACK1 promoted the ability and radioresistance of ESCC cells. Our findings suggest that RACK1 promotes proliferation and radioresistance in ESCC cells by activating the AKT pathway, upregulating Bcl-2 expression and downregulating protein levels of Bim. Our study fills in gaps in the field of RACK1 and radiation resistance and may provide new possibilities for improving strategies of radiotherapy in esophageal cancer.

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.

Tyrosine phosphorylation of RACK1 triggers cardiomyocyte hypertrophy by regulating the interaction between p300 and GATA4

The zinc finger protein GATA4 is a transcription factor involved in cardiomyocyte hypertrophy. It forms a functional complex with the intrinsic histone acetyltransferase (HAT) p300. The HAT activity of p300 is required for the acetylation and transcriptional activity of GATA4, as well as for cardiomyocyte hypertrophy and the development of heart failure. In the present study, we have identified Receptor for Activated Protein Kinase C1 (RACK1) as a novel GATA4-binding protein using tandem affinity purification and mass spectrometry analyses. We found that exogenous RACK1 repressed phenylephrine (PE)-induced hypertrophic responses, such as myofibrillar organization, increased cell size, and hypertrophy-associated gene transcription, in cultured cardiomyocytes. RACK1 physically interacted with GATA4 and the overexpression of RACK1 reduced PE-induced formation of the p300/GATA4 complex and the acetylation and DNA binding activity of GATA4. In response to hypertrophic stimulation in cultured cardiomyocytes and in the hearts of hypertensive heart disease model rats, the tyrosine phosphorylation of RACK1 was increased, and the binding between GATA4 and RACK1 was reduced. In addition, the tyrosine phosphorylation of RACK1 was required for the disruption of the RACK1/GATA4 complex and for the formation of the p300/GATA4 complex. These findings demonstrate that RACK1 is involved in p300/GATA4-dependent hypertrophic responses in cardiomyocytes and is a promising therapeutic target for heart failure.

RACK1 antagonizes TNF-α-induced cell death by promoting p38 activation

p38 mitogen-activated protein kinase (MAPK) activity has been reported to either promote or suppress cell death, which depends on cell type and stimulus. Our previous report indicates that p38 exerts a protective role in tumor necrosis factor (TNF)-α-induced cell death in L929 fibroblastoma cells. However, key molecules regulating p38 activation remain unclear. Here, we show that ectopic expression of scaffold protein receptor for activated C kinase 1 (RACK1) suppressed TNF-α-induced cell death in L929 cells, which was associated with enhanced p38 activation. Knockdown of endogenous RACK1 expression exhibited opposite effects. The protective role of RACK1 in TNF-α-induced cell death diminished upon blockade of p38 activation. Therefore, RACK1 antagonizes TNF-α-induced cell death through, at least partially, augmenting p38 activation. Further exploration revealed that RACK1 directly bound to MKK3/6 and enhanced the kinase activity of MKK3/6 without affecting MKK3/6 phosphorylation. Similar effects of RACK1 were also observed in primary murine hepatocytes, another cell type sensitive to TNF-α-induced cell death. Taken together, our data suggest that RACK1 is a key factor involved in p38 activation as well as TNF-α-induced cell death.

hCINAP negatively regulates NF-κB signaling by recruiting the phosphatase PP1 to deactivate IKK complex

Tight regulation of nuclear factor-κB (NF-κB) signaling is essential to maintain homeostasis in immune system in response to various stimuli, which has been studied extensively and deeply. However, the molecular mechanisms responsible for its negative regulation are not completely understood. Here we demonstrate that human coilin-interacting nuclear ATPase protein (hCINAP) is a novel negative regulator in NF-κB signaling by deactivating IκB kinase (IKK) complex. In response to TNF stimulation, hCINAP dynamically associates with IKKα and IKKβ and inhibits IKK phosphorylation. Notably, hCINAP directly interacts with the catalytic subunits of protein phosphatase 1 (PP1) and mediates the formation of IKK-hCINAP-PP1 complex, serving as an adaptor protein that recruits PP1 to dephosphorylate IKK. Furthermore, decreased levels of hCINAP are observed in several inflammatory diseases with NF-κB hyperactivity. Our study suggests a novel mechanism underlying deactivation of IKK and provides new insight into the negative regulation of NF-κB signaling.