Phosphoinositide-dependent kinase-1 inhibits TRAF6 ubiquitination by interrupting the formation of TAK1-TAB2 complex in TLR4 signaling

Dioscin ameliorates doxorubicin-induced heart failure via inhibiting autophagy and apoptosis by controlling the PDK1-mediated Akt/mTOR signaling pathway

Heart failure (HF) is a disease with high mortality and morbidity rate. Autophagy is critically implicated in HF progression. The current research was designed to investigate the function of Dioscin on oxidative stress, autophagy, and apoptosis in HF. In this study, doxorubicin (Dox) was employed to induce HF model and HL-1 cell damage model. Echocardiography implied that Dioscin could dramatically relieve heart function in vivo. Western blotting determined that Dioscin treatment reversed the promotive effect of autophagy caused by Dox through modulating levels of key autophagy-associated molecules, including Atg5 and Beclin1. Dioscin also impaired apoptosis by regulating apoptosis-related protein, including Bcl-2 and cleaved caspase-3 following Dox treatment in vivo and in vitro. Furthermore, the impacts of Dioscin were mediated by upregulation of PDK1-mediated Akt/mTOR signaling. The mTOR inhibitor (rapamycin) could counteract the therapeutic impact of Dioscin in vitro. Taken together, Dioscin could relieve cardiac function through blocking apoptosis and autophagy by activating the PDK1-elicited Akt/mTOR pathway.

circWHSC1: A circular RNA piece in the human cancer puzzle

Circular RNAs (circRNAs) are a group of non-coding RNAs with a closed loop shape, which are transcribed via non-canonical splicing. They are mainly formed by reverse splicing of a precursor mRNA. circWHSC1 (Hsa_circ_0001387), is a cancer-related circRNA that originated from the Wolf-Hirschhorn syndrome candidate 1 (WHSC1) gene on chromosome 4. circWHSC1 has been found to be overexpressed in different neoplastic conditions. circWHSC1 acts as a sponge for many different miRNAs, including miR-195-5p, miR-532-3p, miR-646, miR-142-3p, miR-7, miR-296-3p, miR-145, miR-1182, miR-212-5p, etc. It can also moderate several signaling pathways, including FASN/AMPK/mTOR, LTBP2, NPM1, HOXA1, TAB2, AKT3, hTERT, and MUC1. Studies have shown that circWHSC1 may leads to an increase in cell growth, tumor size, cell migration, invasion, and metastasis, but a reduction in apoptosis rates. Moreover, upregulation of CircWHSC1 has been associated with reduced patient's survival in different cancers, representing the function of this circRNA as a novel prognostic marker. Nevertheless, there are no reviews focusing on the relationship between circWHSC1 and cancers. Therefore, in the current review, we will first describe the oncogenic effect of circWHSC1 in various tissues according to the evidence from in vitro, in vivo, and human studies.

hnRNPub inhibits LPS-induced NF-κB pathway by targeting TRAF6 for K48-linked ubiquitination in miiuy croaker (Miichthys miiuy)

As an important adaptor protein in innate immunity, TRAF6 is not only responsible for the transduction of signal pathways, but its E3 ligase activity to transfer ubiquitination has also been widely studied. Under LPS stimulation, TRAF6 transfers the K63-linked ubiquitination chain to TAK1, which in turn activates the transcription factor NF-κB and cell signaling factors downstream of the signaling pathway. However, how TRAF6 expression is regulated remains largely unknown, especially in teleost. In this study, we identified hnRNPub as a suppressor of TRAF6 expression. The mRNA level of hnRNPub significantly increased under LPS stimulation, and hnRNPub inhibited NF-κB signaling pathway by targeting TRAF6. Knockdown of hnRNPub potentiated inflammatory cytokines, such as TNFα,IL-1β,IL-8. Mechanistically, hnRNPub inhibited NF-κB signaling pathway through mediating K48-linked ubiquitination and proteasomal degradation of TRAF6. Thus, our findings reveal that hnRNPub limits LPS-induced innate activation by promoting K48-linked polyubiquitination and proteasomal degradation of TRAF6.

USP8 regulates liver cancer progression via the inhibition of TRAF6-mediated signal for NF-κB activation and autophagy induction by TLR4

Herein, we aimed to elucidate the molecular and cellular mechanism in which ubiquitin-specific protease 8 (USP8) is implicated in liver cancer progression via TRAF6-mediated signal. USP8 induces the deubiquitination of TRAF6, TAB2, TAK1, p62, and BECN1, which are pivotal roles for NF-κB activation and autophagy induction. Notably, the LIHC patient with low USP8 mRNA expression showed markedly shorter survival time, whereas there was no significant difference in the other 18-human cancers. Importantly, the TCGA data analysis on LIHC and transcriptome analysis on the USP8 knockout (USP8KO) SK-HEP-1 cells revealed a significant correlation between USP8 and TRAF6, TAB2, TAK1, p62, and BECN1, and enhanced NF-κB-dependent and autophagy-related cancer progression/metastasis-related genes in response to LPS stimulation. Furthermore, USP8KO SK-HEP-1 cells showed an increase in cancer migration and invasion by TLR4 stimulation, and a marked increase of tumorigenicity and metastasis in xenografted NSG mice. The results demonstrate that USP8 is negatively implicated in the LIHC progression through the regulation of TRAF6-mediated signal for the activation of NF-κB activation and autophagy induction. Our findings provide useful insight into the LIHC pathogenesis of cancer progression.

Circular RNA WHSC1 exerts oncogenic properties by regulating miR-7/TAB2 in lung cancer

Circular RNA is a newly discovered member of non‐coding RNA (ncRNA) and regulates the target gene by acting as a micro‐RNA sponge. It plays vital roles in various diseases. However, the functions of circular RNA in non‐small cell lung cancer (NSCLC) remain still unclear. Our data showed that circ‐WHSC1 was highly expressed in NSCLC cells and tissues. Both in vitro and in vivo experiments showed that circ‐WHSC1 promoted NSCLC proliferation. circ‐WHSC1 also promoted the migration and invasion of lung cancer cells. Through bioinformatic analysis and functional experiments, we showed that circ‐WHSC1 could act as a sponge for micro‐RNA‐7 (miR‐7) and regulate the expression of TAB2 (TGF‐beta activated kinase one binding protein two). Inhibition of the circ‐WHSC1/miR‐7/TAB2 pathway could effectively attenuate lung cancer progression. In summary, this study confirmed the existence and oncogenic function of circ‐WHSC1 in NSCLC. The research suggests that the circ‐WHSC1/miR‐7/TAB2 axis might be a potential target for NSCLC therapy.

E3 ubiquitin ligases: styles, structures and functions

E3 ubiquitin ligases are a large family of enzymes that join in a three-enzyme ubiquitination cascade together with ubiquitin activating enzyme E1 and ubiquitin conjugating enzyme E2. E3 ubiquitin ligases play an essential role in catalyzing the ubiquitination process and transferring ubiquitin protein to attach the lysine site of targeted substrates. Importantly, ubiquitination modification is involved in almost all life activities of eukaryotes. Thus, E3 ligases might be involved in regulating various biological processes and cellular responses to stress signal associated with cancer development. Thanks to their multi-functions, E3 ligases can be a promising target of cancer therapy. A deeper understanding of the regulatory mechanisms of E3 ligases in tumorigenesis will help to find new prognostic markers and accelerate the growth of anticancer therapeutic approaches. In general, we mainly introduce the classifications of E3 ligases and their important roles in cancer progression and therapeutic functions.

Inhibition of NFAM1 suppresses phospho-SAPK/JNK signaling during osteoclast differentiation and bone resorption

We have recently demonstrated NFAT activating protein with ITAM motif 1 (NFAM1) signaling increases osteoclast (OCL) formation/bone resorption associated with the Paget's disease of bone, however, the underlying molecular mechanisms of the NFAM1 regulation of OCL differentiation and bone resorption remains unclear. Here, we showed that RANK ligand stimulation enhances NFAM1 expression in preosteoclast cells. Conditioned media collected from RANKL stimulated RAW264.7 NFAM1 knockdown (KD) stable cells showed inhibition of interleukin-6 (2.5-fold), tumour necrosis factor-α (2.2-fold) and CXCL-5 (3-fold) levels compared to wild-type (WT) cells. Further, RANKL stimulation significantly increased p-STAT6 expression (5.5-fold) in WT cells, but no significant effect was observed in NFAM1-KD cells. However, no changes were detected in signal transducer and activator of transcription 3 levels in either of cell groups. Interestingly, NFAM1-KD suppressed the RANKL stimulated c-fos, p-c-Jun and c-Jun N-terminal kinase (JNK) activity in preosteoclasts. We further showed that the suppression of JNK activity is through inhibition of p-SAPK/JNK in these cells. In addition, NFATc1 expression, a critical transcription factor associated with osteoclastogenesis is significantly inhibited in NFAM1-KD preosteoclast cells. Interestingly, NFAM1 inhibition suppressed the OCL differentiation and bone resorption capacity in mouse bone marrow cell cultures. We also demonstrated inhibition of tartrate-resistant acid phosphatase expression in RANKL stimulated NFAM1-KD preosteoclast cells. Thus, our results suggest that NFAM1 control SAPK/JNK signaling to modulate osteoclast differentiation and bone resorption.

Long noncoding Mirt2 reduces apoptosis to alleviate myocardial infarction through regulation of the miR-764/PDK1 axis

Acute myocardial infarction (AMI) is a common clinical cardiovascular disease, which is the leading cause of death and disability worldwide. Abnormal expression of long noncoding RNAs (lncRNA) is reported to be related to myocardial dysfunctions such as myocardial infarction (MI). In this study, we aimed to investigate the role of lncRNA myocardial infarction-related transcription factors 2 (Mirt2) in AMI and the underlying molecular mechanisms in vivo and in vitro. In vivo AMI model was established by occlusion of the left anterior descending coronary artery. Rats were randomly divided into two groups (five rats per group): the sham group and the AMI group. H9c2 cells were cultured under hypoxia for 4 h and then cultured under normoxia to establish the in vitro hypoxia reoxygenation (H/R) model. Our study shows that the myocardial infarct size and the apoptosis in AMI rats were both significantly increased, indicating that the AMI rat model was successfully established. Additionally, the levels of Mirt2 in AMI rats were increased significantly. Knockdown of Mirt2 by shRNA (shMirt2) had no significant effect on apoptosis and MI in sham rats, but significantly promoted apoptosis and MI in AMI rats. In vitro experiments showed that shMirt2 significantly decreased the level of Mirt2 in H9c2 cells and H9c2 cells treated with H/R. It is worth noting that shMirt2 had no significant effect on H9c2 cells, but significantly increased the levels of oxidative stress markers (malondialdehyde and lactate dehydrogenase), and also increased the number of apoptosis of H/R-treated H9c2 cells. Further mechanistic analysis showed that Mirt2 could protect MI and apoptosis in AMI rats by competitively adsorbing miR-764 and reducing the inhibitory effect of miR-764 on 3-phosphoinositide-dependent kinase 1 (PDK1). More importantly, after overexpression of Mirt2, MI and apoptosis were significantly improved in AMI rats, indicating that Mirt2 showed a protective effect in AMI rats. In summary, these findings suggest that that Mirt2 participated in the regulation of MI through the miR-764/PDK1 axis. Therefore, the current findings provide a theoretical basis for the diagnosis and treatment of clinical MI with changes in Mirt2 levels.

Toll-like receptor-mediated innate immunity against herpesviridae infection: a current perspective on viral infection signaling pathways

Background

In the past decades, researchers have demonstrated the critical role of Toll-like receptors (TLRs) in the innate immune system. They recognize viral components and trigger immune signal cascades to subsequently promote the activation of the immune system.

Main body

Herpesviridae family members trigger TLRs to elicit cytokines in the process of infection to activate antiviral innate immune responses in host cells. This review aims to clarify the role of TLRs in the innate immunity defense against herpesviridae, and systematically describes the processes of TLR actions and herpesviridae recognition as well as the signal transduction pathways involved.

Conclusions

Future studies of the interactions between TLRs and herpesviridae infections, especially the subsequent signaling pathways, will not only contribute to the planning of effective antiviral therapies but also provide new molecular targets for the development of antiviral drugs.

AMPKα1 Regulates Lung and Breast Cancer Progression by Regulating TLR4-Mediated TRAF6-BECN1 Signaling Axis

Simple Summary

TRAF6-BECN1 signaling axis in TLR4 signal plays an essential role for the autophagy induction, thereby it regulates cancer migration and invasion. Here we show that AMPKα1, one of the isoforms of AMPK, is functionally involved in autophagy induction by regulating the TRAF6-BECN1 signaling axis. In this context, AMPKα1-knockout lung or breast cancer cells exhibited the attenuation of cancer cell migration and invasion induced by TLR4 simulation. Additionally, we could find that the expression of AMPKα1 is positively associated with gene expressions related to autophagy, migration, and metastasis of cancer cells in primary non-small cell lung cancers (NSCLCs). These findings demonstrate that AMPKα1 plays a pivotal role in cancer progression by regulating the TRAF6-BECN1 signaling axis for autophagy induction.

Abstract

TRAF6-BECN1 signaling axis is critical for autophagy induction and functionally implicated in cancer progression. Here, we report that AMP-activated protein kinase alpha 1 (AMPKα1, PRKAA1) is positively involved in autophagy induction and cancer progression by regulating TRAF6-BECN1 signaling axis. Mechanistically, AMPKα1 interacted with TRAF6 and BECN1. It also enhanced ubiquitination of BECN1 and autophagy induction. AMPKα1-knockout (AMPKα1KO) HEK293T or AMPKα1-knockdown (AMPKα1KD) THP-1 cells showed impaired autophagy induced by serum starvation or TLR4 (Toll-like receptor 4) stimulation. Additionally, AMPKα1KD THP-1 cells showed decreases of autophagy-related and autophagosome-related genes induced by TLR4. AMPKα1KO A549 cells exhibited attenuation of cancer migration and invasion induced by TLR4. Moreover, primary non-small cell lung cancers (NSCLCs, n = 6) with low AMPKαl levels showed markedly decreased expression of genes related to autophagy, cell migration and adhesion/metastasis, inflammation, and TLRs whereas these genes were significantly upregulated in NSCLCs (n = 5) with high AMPKαl levels. Consistently, attenuation of cancer migration and invasion could be observed in AMPKα1KO MDA-MB-231 and AMPKα1KO MCF-7 human breast cancer cells. These results suggest that AMPKα1 plays a pivotal role in cancer progression by regulating the TRAF6-BECN1 signaling axis for autophagy induction.

Negative Effects of SIGIRR on TRAF6 Ubiquitination in Acute Lung Injury In Vitro

In this study, the effects of single immunoglobin IL-1 receptor-related protein (SIGIRR) on tumor necrosis factor- (TNF-) receptor-associated factor 6 (TRAF6) ubiquitination in acute lung injury (ALI) were evaluated in both alveolar epithelial cells and alveolar macrophage cells in vitro. Our results found that SIGIRR negatively regulated TRAF6 ubiquitination and such SIGIRR inhibition could enhance the TRAF6 expression in both alveolar epithelial cells (AECs) and alveolar macrophage cells (AMCs). SIGIRR knockdown may increase NF-κB activity via TRAF6 regulation by the classical but not the nonclassical NF-κB signaling pathway. Such modulation between TRAF6 and SIGIRR could affect cytokine secretion and exacerbate the immune response; the IL-8, NFKB1, and NFKBIA mRNA levels were reduced after SIGIRR overexpression. The current study reveals the molecular mechanisms of the negative regulatory roles of SIGIRR on the innate immune response related to the LPS/TLR-4 signaling pathway and provides evidence for strategies to clinically treat inflammatory diseases.

Associations between TAB2 gene polymorphisms and dilated cardiomyopathy in a Chinese population

Aim: The present study aimed to investigate the role of TAB2 gene polymorphisms in dilated cardiomyopathy (DCM) susceptibility and prognosis in a Chinese population. Materials & methods: A total of 343 DCM patients and 451 controls were enrolled and had their blood genotyped. Survival analysis was evaluated with Kaplan-Meier curves and Cox regression analysis. Results: G carriers (AG/GG) and AG genotype of rs237028 had a higher DCM susceptibility as well as a worse DCM prognosis. Additionally, C carriers (CT/CC) of rs652921 and G carriers (TG/GG) of rs521845 had a higher DCM risk and CC homozygote of rs652921 had a worse DCM prognosis. These associations were still significant after adjustment for the Bonferroni correction. Conclusion: TAB2 gene polymorphisms were associated with DCM susceptibility and prognosis in the Chinese population.

FasL-PDPK1 Pathway Promotes the Cytotoxicity of CD8+ T Cells During Ischemic Stroke

CD8⁺ T cells are recognized as key players in exacerbation of ischemic stroke; however, the underlying mechanism in modulating the function of CD8⁺ T cells has not been completely elucidated. Here, we uncovered that FasL enhanced the cytotoxicity of CD8⁺ T cells to neurons after ischemic stroke. Inactivation of FasL specific on CD8⁺ T cells protected against brain damage and neuron loss. Proteomic analysis identified that PDPK1 functioned downstream of FasL signaling and inhibition of PDPK1 effectively reduced cytotoxicity of CD8⁺ T cells and improved ischemic neurological deficits. Taken together, these results highlight an intrinsic FasL-PDPK1 pathway regulating the cytotoxicity of CD8⁺ T cells in ischemic stroke.

p62 Negatively Regulates TLR4 Signaling via Functional Regulation of the TRAF6-ECSIT Complex

Sequestosome 1 (SQSTM1, p62), a ubiquitin binding protein, plays a role in cell signaling, oxidative stress, and autophagy. However, its functional role in inflammatory signaling is controversial. Recent studies have shown that p62 is negatively implicated in inflammatory responses. But, the precise molecular mechanisms by which p62 regulates inflammatory responses remain unclear. In this study, we report on a new regulatory role for p62 in TLR4-mediated signaling. p62 overexpression led to the suppression of NF-κB activation and the production of pro-inflammatory cytokines, TNF-α, IL-6, and IL-1β in response to TLR4 stimulation. In contrast, p62^−/− mouse embryonic fibroblast (MEF) cells exhibited marked enhancement of NF-κB activation and production of pro-inflammatory cytokines by TLR4 stimulation, compared to p62^+/+ MEF cells. Additionally, the TLR4-induced activation of signal transduction was significantly augmented in p62^−/− MEF cells, indicating that p62 was negatively implicated in TLR4-mediated signaling. Biochemical studies revealed that p62 interacted with the internal domain of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT), which is critical for associating with the TNF receptor associated factor 6 (TRAF6)-ECSIT complex to activate NF-κB in TLR4 signaling. Interestingly, p62-ECSIT interaction inhibited the interaction between TRAF6 and ECSIT and attenuated the ubiquitination of ECSIT. Furthermore, upon LPS challenge, the mortality of p62^−/− (p62-knockout) mice was markedly enhanced compared to p62^+/+ (p62 wild-type) mice. Taken together, our data demonstrate that p62 negatively regulated TLR4 signaling via functional regulation of the TRAF6-ECSIT complex.

The Role of the Mammalian Target of Rapamycin (mTOR) in Pulmonary Fibrosis

The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR)-dependent pathway is one of the most integral pathways linked to cell metabolism, proliferation, differentiation, and survival. This pathway is dysregulated in a variety of diseases, including neoplasia, immune-mediated diseases, and fibroproliferative diseases such as pulmonary fibrosis. The mTOR kinase is frequently referred to as the master regulator of this pathway. Alterations in mTOR signaling are closely associated with dysregulation of autophagy, inflammation, and cell growth and survival, leading to the development of lung fibrosis. Inhibitors of mTOR have been widely studied in cancer therapy, as they may sensitize cancer cells to radiation therapy. Studies also suggest that mTOR inhibitors are promising modulators of fibroproliferative diseases such as idiopathic pulmonary fibrosis (IPF) and radiation-induced pulmonary fibrosis (RIPF). Therefore, mTOR represents an attractive and unique therapeutic target in pulmonary fibrosis. In this review, we discuss the pathological role of mTOR kinase in pulmonary fibrosis and examine how mTOR inhibitors may mitigate fibrotic progression.

Ubiquitin-Specific Protease 14 Negatively Regulates Toll-Like Receptor 4-Mediated Signaling and Autophagy Induction by Inhibiting Ubiquitination of TAK1-Binding Protein 2 and Beclin 1

Ubiquitin-specific protease 14 (USP14), one of three proteasome-associated deubiquitinating enzymes, has multifunctional roles in cellular context. Here, we report a novel molecular mechanism and function of USP14 in regulating autophagy induction and nuclear factor-kappa B (NF-κB) activation induced by toll-like receptor (TLR) 4 (TLR4). USP14 interacted with tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) and interrupted the association of Beclin 1 with TRAF6, leading to inhibition of TRAF6-mediated ubiquitination of Beclin 1. Reduced expression of USP14 in USP14-knockdown (USP14^KD) THP-1 cells enhanced autophagy induction upon TLR4 stimulation as shown by the increased conversion of cytosolic LC3-I to membrane-bound LC3-II. Moreover, USP14^KD human breast carcinoma MDA-MB-231 cells and USP14^KD human hepatic adenocarcinoma SK-HEP-1 cells showed increased cell migration and invasion, indicating that USP14 is negatively implicated in the cancer progression by the inhibition of autophagy induction. Furthermore, we found that USP14 interacted with TAK1-binding protein (TAB) 2 protein and induced deubiquitination of TAB 2, a key factor in the activation of NF-κB. Functionally, overexpression of USP14 suppressed TLR4-induced activation of NF-κB. In contrast, USP14^KD THP-1 cells showed enhanced activation of NF-κB, NF-κB-dependent gene expression, and production of pro-inflammatory cytokines such as IL-6, IL-1β, and tumor necrosis factor-α. Taken together, our data demonstrate that USP14 can negatively regulate autophagy induction by inhibiting Beclin 1 ubiquitination, interrupting association between TRAF6 and Beclin 1, and affecting TLR4-induced activation of NF-κB through deubiquitination of TAB 2 protein.

TLR2 Plays a Key Role in Platelet Hyperreactivity and Accelerated Thrombosis Associated With Hyperlipidemia

RATIONALE

Platelet hyperreactivity, which is common in many pathological conditions, is associated with increased atherothrombotic risk. The mechanisms leading to platelet hyperreactivity are complex and not yet fully understood.

OBJECTIVE

Platelet hyperreactivity and accelerated thrombosis, specifically in dyslipidemia, have been mechanistically linked to the accumulation in the circulation of a specific group of oxidized phospholipids (oxPC_CD36) that are ligands for the platelet pattern recognition receptor CD36. In the current article, we tested whether the platelet innate immune system contributes to responses to oxPC_CD36 and accelerated thrombosis observed in hyperlipidemia.

METHODS AND RESULTS

Using in vitro approaches, as well as platelets from mice with genetic deletion of MyD88 (myeloid differentiation factor 88) or TLRs (Toll-like receptors), we demonstrate that TLR2 and TLR6 are required for the activation of human and murine platelets by oxPC_CD36. oxPC_CD36 induce formation of CD36/TLR2/TLR6 complex in platelets and activate downstream signaling via TIRAP (Toll-interleukin 1 receptor domain containing adaptor protein)-MyD88-IRAK (interleukin-1 receptor-associated kinase)1/4-TRAF6 (TNF receptor-associated factor 6), leading to integrin activation via the SFK (Src family kinase)-Syk (spleen tyrosine kinase)-PLCγ2 (phospholipase Cγ2) pathway. Intravital thrombosis studies using ApoE^-/- mice with genetic deficiency of TLR2 or TLR6 have demonstrated that oxPC_CD36 contribute to accelerated thrombosis specifically in the setting of hyperlipidemia.

CONCLUSIONS

Our studies reveal that TLR2 plays a key role in platelet hyperreactivity and the prothrombotic state in the setting of hyperlipidemia by sensing a wide range of endogenous lipid peroxidation ligands and activating innate immune signaling cascade in platelets.

Peroxiredoxin-6 Negatively Regulates Bactericidal Activity and NF-κB Activity by Interrupting TRAF6-ECSIT Complex

A TRAF6-ECSIT complex is crucial for the generation of mitochondrial reactive oxygen species (mROS) and nuclear factor-kappa B (NF-κB) activation induced by Toll-like receptor 4 (TLR4). Peroxiredoxin-6 (Prdx6) as a member of the peroxiredoxin family of antioxidant enzymes is involved in antioxidant protection and cell signaling. Here, we report on a regulatory role of Prdx6 in mROS production and NF-κB activation by TLR4. Prdx6 was translocated into the mitochondria by TLR4 stimulation and Prdx6-knockdown (Prdx6^KD) THP-1 cells had increased level of mitochondrial reactive oxygen species levels and were resistant to Salmonella typhimurium infection. Biochemical studies revealed Prdx6 interaction with the C-terminal TRAF-C domain of TRAF6, which drove translocation into the mitochondria. Interestingly, Prdx6 competitively interacted with ECSIT to TRAF6 through its C-terminal TRAF-C domain, leading to the interruption of TRAF6-ECSIT interaction. The inhibitory effect was critically implicated in the activation of NF-κB induced by TLR4. Overexpression of Prdx6 led to the inhibition of NF-κB induced by TLR4, whereas Prdx6^KD THP-1 cells displayed enhanced production of pro-inflammatory cytokines including interleukin-6 and -1β, and the up-regulation of NF-κB-dependent genes induced by TLR4 stimulation. Taken together, the data demonstrate that Prdx6 interrupts the formation of TRAF6-ECSIT complex induced by TLR4 stimulation, leading to suppression of bactericidal activity because of inhibited mROS production in mitochondria and the inhibition of NF-κB activation in the cytoplasm.

Peroxiredoxin-3 Is Involved in Bactericidal Activity through the Regulation of Mitochondrial Reactive Oxygen Species

Peroxiredoxin-3 (Prdx3) is a mitochondrial protein of the thioredoxin family of antioxidant peroxidases and is the principal peroxidase responsible for metabolizing mitochondrial hydrogen peroxide. Recent reports have shown that mitochondrial reactive oxygen species (mROS) contribute to macrophage-mediated bactericidal activity in response to Toll-like receptors. Herein, we investigated the functional effect of Prdx3 in bactericidal activity. The mitochondrial localization of Prdx3 in HEK293T cells was confirmed by cell fractionation and confocal microscopy analyses. To investigate the functional role of Prdx3 in bactericidal activity, Prdx3-knockdown (Prdx3^KD) THP-1 cells were generated. The mROS levels in Prdx3^KD THP-1 cells were significantly higher than those in control THP-1 cells. Moreover, the mROS levels were markedly increased in response to lipopolysaccharide. Notably, the Salmonella enterica serovar Typhimurium infection assay revealed that the Prdx3^KD THP-1 cells were significantly resistant to S. Typhimurium infection, as compared with control THP-1 cells. Taken together, these results indicate that Prdx3 is functionally important in bactericidal activity through the regulation of mROS.

MicroRNA-7 Deficiency Ameliorates the Pathologies of Acute Lung Injury through Elevating KLF4

Recent evidence showed that microRNA-7 (miR-7) played an important role in the pathologies of lung-related diseases. However, the potential role of miR-7 in acute lung injury (ALI) still remains poorly understood. Here, we assessed the effect of miR-7 deficiency on the pathology of ALI. We, first, found that the expression of miR-7 was upregulated in lung tissue in murine LPS-induced ALI model. Notably, we generated miR-7 knock down mice by using miRNA-Sponge technique and found that miR-7 deficiency could ameliorate the pathologies of lung as evidenced by accelerated body weight recovery, reduced level of bronchoalveolar lavage (BAL) proinflammatory cytokines and decreased number of BAL cells in ALI mice. Moreover, the proportion and number of various immune cells in BAL, including innate immune cell F4/80⁺ macrophages, γδT cells, NK1.1⁺ T cells, and CD11c⁺DCs, as well as adaptive immune cell CD4⁺ T cells and CD8⁺ T cells, also significantly changed, respectively. Mechanistic evidence showed that KLF4, a target molecule of miR-7, was upregulated in lung tissues in ALI model, accompanied by altered transduction of NF-κB, AKT, and ERK pathway. These data provided a previously unknown role of miR-7 in pathology of ALI, which could ultimately aid the understanding of development of ALI and the development of new therapeutic strategies against clinical inflammatory lung diseases.

Cereblon negatively regulates TLR4 signaling through the attenuation of ubiquitination of TRAF6

Cereblon (CRBN) is a substrate receptor protein for the CRL4A E3 ubiquitin ligase complex. In this study, we report on a new regulatory role of CRBN in TLR4 signaling. CRBN overexpression leads to suppression of NF-κB activation and production of pro-inflammatory cytokines including IL-6 and IL-1β in response to TLR4 stimulation. Biochemical studies revealed interactions between CRBN and TAK1, and TRAF6 proteins. The interaction between CRBN and TAK1 did not affect the association of the TAB1 and TAB2 proteins, which have pivotal roles in the activation of TAK1, whereas the CRBN-TRAF6 interaction critically affected ubiquitination of TRAF6 and TAB2. Binding mapping results revealed that CRBN interacts with the Zinc finger domain of TRAF6, which contains the ubiquitination site of TRAF6, leading to attenuation of ubiquitination of TRAF6 and TAB2. Functional studies revealed that CRBN-knockdown THP-1 cells show enhanced NF-κB activation and p65- or p50-DNA binding activities, leading to up-regulation of NF-κB-dependent gene expression and increased pro-inflammatory cytokine levels in response to TLR4 stimulation. Furthermore, Crbn^−/− mice exhibit decreased survival in response to LPS challenge, accompanied with marked enhancement of pro-inflammatory cytokines, such as TNF-α and IL-6. Taken together, our data demonstrate that CRBN negatively regulates TLR4 signaling via attenuation of TRAF6 and TAB2 ubiquitination.