Control of IkappaBalpha proteolysis by the ubiquitin-proteasome pathway

Potential applications of components of aged garlic extract in mitigating pro-inflammatory gene expression linked to human diseases (Review)

In the present review, simple approaches for the screening and characterization of natural compound agents that alter pro-inflammatory gene expression are described, with a particular focus on aged garlic extract (AGE), which has been the subject of several investigations that have supported its potential application as an anti-inflammatory agent. Additionally, evidence regarding the possible effects and mechanisms of action of two major AGE components, S-allyl cysteine (SAC) and S-1-propenyl-l-cysteine (S1PC), is reviewed. The proposed molecular targets of SAC and S1PC are IKKβ kinase, the Kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor 2 complex, peroxisome proliferator-activated receptor-γ, histone deacetylase and toll-like receptor 4 (TLR4). Targeting these molecules causes a marked reduction in NF-κB activity accompanied by a notable decrease in the transcription of NF-κB-regulated genes. Another main objective of the present review was to discuss the possibility that AGE and its bioactive components could be employed in the treatment of several human pathologies that are characterized by a hyperinflammatory state resulting from dysregulation of the TLR4 and NF-κB pathways. SAC is of interest in the treatment of lung pathologies, neurological diseases, osteoarthritis, muscular atrophy, cardiovascular diseases, diabetes and cancer. Additionally, the anti-oxidative activities of AGE, SAC and S1PC are compatible with their employment in the treatment of diseases characterized by oxidative stress, such as sickle cell disease and β-thalassemia.

Entamoeba histolytica activation of caspase-1 degrades cullin that attenuates NF-κB dependent signaling from macrophages

While Entamoeba histolytica (Eh)-induced pro-inflammatory responses are critical in disease pathogenesis, the downstream signaling pathways that subsequently dampens inflammation and the immune response remains unclear. Eh in contact with macrophages suppresses NF-κB signaling while favoring NLRP3-dependent pro-inflammatory cytokine production by an unknown mechanism. Cullin-1 and cullin-5 (cullin-1/5) assembled into a multi-subunit RING E3 ubiquitin ligase complex are substrates for neddylation that regulates the ubiquitination pathway important in NF-κB activity and pro-inflammatory cytokine production. In this study, we showed that upon live Eh contact with human macrophages, cullin-1/4A/4B/5 but not cullin-2/3, were degraded within 10 minutes. Similar degradation of cullin-1/5 were observed from colonic epithelial cells and proximal colonic loops tissues of mice inoculated with live Eh. Degradation of cullin-1/5 was dependent on Eh-induced activation of caspase-1 via the NLRP3 inflammasome. Unlike cullin-4B, the degradation of cullin-4A was partially dependent on caspase-1 and was inhibited with a pan caspase inhibitor. Cullin-1/5 degradation was dependent on Eh cysteine proteinases EhCP-A1 and EhCP-A4, but not EhCP-A5, based on pharmacological inhibition of the cysteine proteinases and EhCP-A5 deficient parasites. siRNA silencing of cullin-1/5 decreased the phosphorylation of pIκ-Bα in response to Eh and LPS stimulation and downregulated NF-κB-dependent TNF-α mRNA expression and TNF-α and MCP-1 pro-inflammatory cytokine production. These results unravel a unique outside-in strategy employed by Eh to attenuate NF-κB-dependent pro-inflammatory responses via NLRP3 activation of caspase-1 that degraded cullin-1/5 from macrophages.

The protozoan parasite Entamoeba histolytica (Eh) is the etiologic agent for the disease amebiasis. It is a potent pathogen that deploys an arsenal of virulence factors to trigger and subvert host immune defenses. One of the hallmark features of the disease is amebic colitis and in extreme cases, it can lead to abscesses of the liver and brain. For unknown reasons, the parasite breaches colonic mucosal barriers and invade underlying tissues. The host immune system plays a decisive role in determining the outcome of the disease. At the molecular level, the interaction of Eh with macrophage is a turning point in shaping pro-inflammatory responses. Understanding host-pathogen intricacies at the molecular level is key in determining the complexity of the disease. In the context of amebiasis, the underlying molecular events that occur at the Eh-macrophage intercellular junction are partly unravelled. Here we sought to interrogate the mechanisms by which NF-κB signaling is aborted following Eh-macrophage contact and found two regulatory scaffold proteins, cullin-1 and -5 (cullin-1/5) of the multiple E3 ligase complex, are degraded leading to dampening of NF-κB signaling. During Eh-macrophage contact, cullin-1/4A/4B/5 were rapidly degraded whereas cullin-2/3 were not. The degradation of cullin-1/5 was highly dependent on Eh-induced caspase-1 activation via the NLRP3 inflammasome. In contrast, the degradation of cullin-4A but not cullin-4B, was partially dependent on caspase-1 and was inhibited with a cell-permeable pan caspase inhibitor. Intriguingly, we found that Eh virulence factor EhCP-A1 and EhCP-A4, but not EhCP-A5, played an important role in mediating the degradation of these proteins. Silencing cullin-1/5 decreased the phosphorylation of Iκ-Bα in response to Eh and LPS stimulation that markedly downregulated NF-κB-dependent TNF-α mRNA expression and TNF-α and MCP-1 pro-inflammatory cytokine production. This study unravelled a novel role for Eh-induced NLRP3 inflammasome activation of caspase-1 that intersected with the NF-κB pathway leading to the degradation of the novel substrates cullin-1/5 that regulates NF-κB-dependent pro-inflammatory cytokine production.

The effect of alcoholic extract from Eucalyptus camaldulensis leaves on HTLV-1 Tax activities

HTLV-1 is a human retrovirus responsible for adult T-cell leukemia (ATL) and certain other clinical disorders. The viral Tax oncoprotein plays a central role in HTLV-1 pathogenicity, mainly due to its capacity of inducing the transcriptional activity of various transcriptional factors like NFқB. Eucalyptus camaldulensis (Ec) is considered as a traditional medicinal plant with valuable therapeutic effects. Here we evaluated the activity of its ethanolic leave extract on different Tax activities by testing its influence on Tax-induced activity of NFқB and HTLV-1 LTR in Jurkat cells. Our results showed that Ec inhibited Tax induced activation of NFқB -, SRF- dependent promoters and HTLV-1 LTR. Ec extract has no effect on the binding of Tax to NFқB while it strongly prevented the degradation of IҝBα induced by Tax probably as a result of preventing the link between Tax and IKKγ. In addition, increasing the cellular level of P-TEFb-cyclinT1 significantly reduced the inhibitory effect of Ec on Tax activities, probably by preventing the interaction between Tax and P-TEFb-cyclin T1. The 40%-MeOH fraction of this extract, which is rich with polyphenols, offered the highest inhibitory effect against Tax activities. Further studies are required for the isolation and identification of active component/s in this extract which may be developed in the future as preventive/curing drugs for HTLV-1 related diseases.

MG-132 attenuates cardiac deterioration of viral myocarditis via AMPK pathway

BACKGROUND

Coxsackievirus B3 (CVB3) is the primary cause of infectious myocarditis. Aggressive immunological activation and apoptosis of myocytes contributes to progressive dysfunction of cardiac contraction and poor prognosis. MG-132, a proteasome inhibitor, regulates mitochondrial-mediated intrinsic myocardial apoptosis and downregulates NF-κB-mediated inflammation. Here, we determined whether AMPK pathway participates in MG-132-mediated myocardial protection in viral-induced myocarditis.

METHODS AND RESULTS

Acute viral myocarditis models were established by intraperitoneal inoculation of CVB3 in male BALB/c mice. Myocarditis and age-matched control mice were administered MG-132 and/or BML-275 dihydrochloride (BML) (AMPK antagonist) intraperitoneally daily from the day following CVB3 inoculation. MG-132 improved hemodynamics and inhibited the structural remodeling of the ventricle in mice with myocarditis, while BML largely blunted these effects. TUNEL staining and immunochemistry suggested that MG-132 exerts anti-apoptotic and anti-inflammatory effects against CVB3-induced myocardial injuries. BML attenuated the effects of MG-132 on anti-apoptosis and anti-inflammation.

CONCLUSION

MG-132 modulated apoptosis and inflammation, improved hemodynamics, and inhibited the structural remodeling of ventricles in a myocarditis mouse model via regulation of the AMPK signal pathway.

Oenanthe Javanica Extract Protects Mouse Skin from UVB Radiation via Attenuating Collagen Disruption and Inflammation

In recent years, the use of botanical agents to prevent skin damage from solar ultraviolet (UV) irradiation has received considerable attention. Oenanthe javanica is known to exert anti-inflammatory and antioxidant activities. This study investigated photoprotective properties of an Oenanthe javanica extract (OJE) against UVB-induced skin damage in ICR mice. The extent of skin damage was evaluated in three groups: control mice with no UVB, UVB-exposed mice treated with vehicle (saline), and UVB-exposed mice treated with 1% extract. Photoprotective properties were assessed in the dorsal skin using hematoxylin and eosin staining, Masson trichrome staining, immunohistochemical staining, quantitative real-time polymerase chain reaction, and western blotting to analyze the epidermal thickness, collagen expression, and mRNA and protein levels of type I collagen, type III collagen, and interstitial collagenases, including matrix metalloproteinase (MMP)-1 and MMP-3. In addition, tumor necrosis factor (TNF)-α and cyclooxygenase (COX)-2 protein levels were also assessed. In the UVB-exposed mice treated with extract, UV-induced epidermal damage was significantly ameliorated. In this group, productions of collagen types I and III were increased, and expressions of MMP-1 and MMP-3 were decreased. In addition, TNF-α and COX-2 expressions were reduced. Based on these findings, we conclude that OJE displays photoprotective effects against UVB-induced collagen disruption and inflammation and suggest that Oenanthe javanica can be used as a natural product for the treatment of photodamaged skin.

Different molecular mechanisms of HTLV-1 and HIV LTR activation by TPA

HTLV-1 and HIV-1 are retroviruses involved in different human diseases. However, following infection, these viruses inter into a latent state. Tax and Tat are regarded as trans-activators of HTLV-1 and HIV-1 respectively. As it known, during the latent state the infected cells contain low Tax and Tat protein levels, so the activation of these viruses must be independent of these proteins. Here we focus on exploring the mechanism of activation of these viruses by 12-O-tetradecanoylphorbol-13-acetate (TPA), which is a potent activator of protein kinase C (PKC) and considered as a stress-inducing agent. Our results showed that short exposure to TPA considerably stimulated only the HIV-1 LTR expression, while long exposure stimulated only the HTLV-1 LTR and that their activation is agonized or antagonized by PKC respectively. It was found that TPA induced interaction between the transcriptional factors Sp1 and P53 producing Sp1-p53 complex which strongly interacted with c-Jun only after short exposure to TPA. In addition, TPA treatment highly induced the expression of CREB which attached to the Sp1-p53 complex mainly after a long exposure to TPA. A strong binding of sp1, p53 and CREB proteins with HTLV-1 LTR and strong binding of NF-κB with HIV-1 LTR were observed after long (24 h) and short (6 h) exposures to TPA respectively by Chip assay. These results support the possibility that sp1, p53 and CREB are involved in the TPA induced HTLV-1 LTR expression while TPA activation of HIV-1 LTR seems to be dependent on PKC activity through the NF-κB pathway.

Protective effect of Juglans regia L. against ultraviolet B radiation induced inflammatory responses in human epidermal keratinocytes

BACKGROUND

Juglans regia L. has a history of traditional medicinal use for the treatment of various maladies and have been documented with significant antioxidant and antiinflammatory properties. Although all parts of the plant are medicinally important, but male the flower of the plant has not been yet investigated against the photo-damage.

PURPOSE

The present study, we sought to determine the photoprotective effect of the male flower of J. regia L. against ultraviolet-B radiation-induced inflammatory responses in human skin cells.

METHODS

The profile of pharmacological active compounds present in the male flower of J. regia was analyzed by GC-MS. Then, the antioxidant property of methanolic extract of J. regia (MEJR) was analyzed by in vitro free radical scavenging assays. Further, we analyzed the sun protection factor of this extract by spectrophotometry. Moreover, we investigated the photoprotective effect of MEJR against UVB induced inflammatory signaling in human epidermal cells. Human skin epidermal keratinocytes (HaCaT) were pretreated with the MEJR (80 µg/ml), 30 min prior to UVB-irradiation at a dose of 20 mJ/cm² and were investigated for lipid peroxidation, enzymatic antioxidants activity, apoptosis and inflammatory markers expression level.

RESULTS

The GC-MS results showed the presence of good amount of pharmacologically active compounds in the MEJR. We observed that the MEJR possess significant free radical scavenging activity and it was comparable with standard antioxidants. Further, the MEJR exhibits 8.8 sun-protection-factor (SPF) value. Pretreatment with MEJR, 30 min prior to UVB-irradiation, prevented ROS generation, lipid peroxidation and restored the activity of antioxidant status in HaCaT cells. Moreover, MEJR pretreatment significantly prevented UVB activated inflammatory markers like TNF-α, IL-1, IL-6, NF-κB, COX-2 in HaCaT.

CONCLUSION

The present findings suggest that MEJR exhibit photoprotective effects and hence it may be useful for the treatment of inflammation related responses. The pharmacological mechanism of MEJR partly associated with its UV absorbance, modulation of inflammatory signaling as well as due to its free radical scavenging capability.

Regulation of the ubiquitylation and deubiquitylation of CREB-binding protein modulates histone acetylation and lung inflammation

Cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB)-binding protein (CBP) is a histone acetyltransferase that plays a pivotal role in the control of histone modification and the expression of cytokine-encoding genes in inflammatory diseases, including sepsis and lung injury. We found that the E3 ubiquitin ligase subunit FBXL19 targeted CBP for site-specific ubiquitylation and proteasomal degradation. The ubiquitylation-dependent degradation of CBP reduced the extent of lipopolysaccharide (LPS)-dependent histone acetylation and cytokine release in mouse lung epithelial cells and in a mouse model of sepsis. Furthermore, we demonstrated that the deubiquitylating enzyme USP14 (ubiquitin-specific peptidase 14) stabilized CBP by reducing its ubiquitylation. LPS increased the stability of CBP by reducing the association between CBP and FBXL19 and by activating USP14. Inhibition of USP14 reduced CBP protein abundance and attenuated LPS-stimulated histone acetylation and cytokine release. Together, our findings delineate the molecular mechanisms through which CBP stability is regulated by FBXL19 and USP14, which results in the modulation of chromatin remodeling and the expression of cytokine-encoding genes.

Effect of TPA and HTLV-1 Tax on BRCA1 and ERE controlled genes expression

Interference with the expression and/or functions of the multifunctional tumor suppressor BRCA1 leads to a high risk of breast and ovarian cancers. BRCA1 expression is usually activated by the estrogen (E2) liganded ERα receptor. Activated ERα is considered as a potent transcription factor which activates various genes expression by 2 pathways. A classical pathway, ERα binds directly to E2-responsive elements (EREs) in the promoters of the responsive genes and a non-classical pathway where ERα indirectly binds with the appropriate gene promoter. In our previous study, HTLV-1Tax was found to strongly inhibit ERα induced BRCA1 expression while stimulating ERα induced ERE dependent genes. TPA is a strong PKC activator which found to induce the expression of HTLV-1. Here we examined the effect of TPA on the expression of BRCA1 and genes controlled by ERE region in MCF-7 cells and on Tax activity on these genes. Our results showed strong stimulatory effect of TPA on both BRCA1 and ERE expression without treatment with E2. Tax did not show any significant effect on these TPA activities. It seems that TPA activation of BRCA1 and ERE expression is dependent on PKC activity but not through the NFκB pathway. However, 53BP1 may be involved in this TPA activity because its overexpression significantly reduced the TPA stimulatory effect on BRCA1 and ERE expression. Additionally, our Chip assay results probably exclude possible involvement of ERα pathway in this TPA activity because TPA did not interfere with the binding of ERα to both BRCA1 promoter and ERE region.

Multiple UBXN family members inhibit retrovirus and lentivirus production and canonical NFκΒ signaling by stabilizing IκBα

UBXN proteins likely participate in the global regulation of protein turnover, and we have shown that UBXN1 interferes with RIG-I-like receptor (RLR) signaling by interacting with MAVS and impeding its downstream effector functions. Here we demonstrate that over-expression of multiple UBXN family members decreased lentivirus and retrovirus production by several orders-of-magnitude in single cycle assays, at the level of long terminal repeat-driven transcription, and three family members, UBXN1, N9, and N11 blocked the canonical NFκB pathway by binding to Cullin1 (Cul1), inhibiting IκBα degradation. Multiple regions of UBXN1, including its UBA domain, were critical for its activity. Elimination of UBXN1 resulted in early murine embryonic lethality. shRNA-mediated knockdown of UBXN1 enhanced human immunodeficiency virus type 1 (HIV) production up to 10-fold in single cycle assays. In primary human fibroblasts, knockdown of UBXN1 caused prolonged degradation of IκBα and enhanced NFκB signaling, which was also observed after CRISPR-mediated knockout of UBXN1 in mouse embryo fibroblasts. Knockout of UBXN1 significantly up- and down-regulated hundreds of genes, notably those of several cell adhesion and immune signaling pathways. Reduction in UBXN1 gene expression in Jurkat T cells latently infected with HIV resulted in enhanced HIV gene expression, consistent with the role of UBXN1 in modulating the NFκB pathway. Based upon co-immunoprecipitation studies with host factors known to bind Cul1, models are presented as to how UBXN1 could be inhibiting Cul1 activity. The ability of UBXN1 and other family members to negatively regulate the NFκB pathway may be important for dampening the host immune response in disease processes and also re-activating quiescent HIV from latent viral reservoirs in chronically infected individuals.

The NR4A subfamily of nuclear receptors: potential new therapeutic targets for the treatment of inflammatory diseases

INTRODUCTION

Prolonged inflammatory response contributes to the pathogenesis of chronic disease-related disturbances. Among nuclear receptors (NRs), the orphan NR4A subfamily, which includes Nur77 (NR4A1), Nurr1 (NR4A2) and NOR1 (NR4A3), has recently emerged as a therapeutic target for the treatment of inflammation. Areas covered: This review focuses on the capacity of NR4A receptors to counter-regulate the development of the inflammatory response, with a special focus on the molecular transrepression mechanisms. Expert opinion: Recent studies have highlighted the role of NR4A receptors as significant regulators of the inflammatory response. NR4A receptors are rapidly induced by inflammatory stimuli, thus suggesting that they are required for the initiation of inflammation. Nevertheless, NR4A anti-inflammatory properties indicate that this acute regulation could be a protective reaction aimed at resolving inflammation in the later stages. Therefore, NR4A receptors are involved in a negative feedback mechanism to maintain the inflammatory balance. However, the underlying mechanisms are not entirely clear. Only a small number of NR4A-target genes have been identified, and the transcriptional repression mechanisms are only beginning to emerge. Despite further research is needed to fully understand the role of NR4A receptors in inflammation, these NRs should be considered as targets for new therapeutic approaches to inflammatory diseases.

Regulation of inflammasomes by ubiquitination

Inflammasomes are multi-protein complexes that regulate the innate immune response by facilitating the release of inflammatory cytokines in response to pathogen exposure or cellular damage. Pro-inflammatory inflammasome signaling is vital to host defense and helps initiate the process of tissue repair following an insult to the host, but can be injurious, when excessive or chronic. As such, inflammasome activity is tightly regulated. Here we discuss one critical mechanism of inflammasome regulation, ubiquitination, that functions as a universal modulator of protein stability and trafficking. Recent studies have provided important insights into the regulation of inflammasome activation by protein ubiquitination. We review the molecular regulation of inflammasome function, specifically, as it relates to ubiquitination, and discuss the implications for the development of therapeutics to specifically target aberrant inflammasome signaling.

Neddylation is required for herpes simplex virus type I (HSV-1)-induced early phase interferon-beta production

Type I interferons such as interferon-beta (IFN-β) play essential roles in the host innate immune response to herpes simplex virus type I (HSV-1) infection. The transcription of type I interferon genes is controlled by nuclear factor-κB (NF-κB) and interferon regulatory factor (IRF) family members including IRF3. NF-κB activation depends on the phosphorylation of inhibitor of κB (IκB), which triggers its ubiqitination and degradation. It has been reported that neddylation inhibition by a pharmacological agent MLN4924 potently suppresses lipopolysaccharide (LPS)-induced proinflammatory cytokine production with the accumulation of phosphorylated IκBα. However, the role of neddylation in type I interferon expression remains unknown. Here, we report that neddylation inhibition with MLN4924 or upon UBA3 deficiency led to accumulation of phosphorylated IκBα, impaired IκBα degradation, and impaired NF-κB nuclear translocation in the early phase of HSV-1 infection even though phosphorylation and nuclear translocation of IRF3 were not affected. The blockade of NF-κB nuclear translocation by neddylation inhibition becomes less efficient at the later time points of HSV-1 infection. Consequently, HSV-1-induced early phase IFN-β production significantly decreased upon MLN4924 treatment and UBA3 deficiency. NF-κB inhibitor JSH-23 mimicked the effects of neddylation inhibition in the early phase of HSV-1 infection. Moreover, the effects of neddylation inhibition on HSV-1-induced early phase IFN-β production diminished in the presence of NF-κB inhibitor JSH-23. Thus, neddylation contributes to HSV-1-induced early phase IFN-β production through, at least partially, promoting NF-κB activation.

Identification of a NFKBIA polymorphism associated with lower NFKBIA protein levels and poor survival outcomes in patients with glioblastoma multiforme

The aberrant constitutive activation of nuclear factor-κB (NF-κB) has been observed in glioblastomas, while NF-κB inhibitor alpha (NFKBIA) inhibits the NF-κB signaling pathway under several physiological processes. However, the contribution of NFKBIA to glioblastomas is poorly understood. In the present study, using gene sequencing, we identified rs1957106 as a novel single nucleotide polymorphism (SNP) in NFKBIA in glioblastoma and found that it was more frequently present in glioblastoma patients. In addition, we examined the association between different genotypes of the rs1957106 SNP of NFKBIA and the gene copy number, mRNA level and protein expression of NFKBIA. The SNP rs1957106 CT and TT genotypes were found to be associated with lower NFKBIA protein levels and a poor prognosis of pateints with glioblastoma. Hence, by identifying rs1957106 as a novel SNP in NFKBIA in glioblastoma patients, we provide a new platform for further investigating the function of NFKBIA in the pathobiology of glioblastoma.

EVM005: an ectromelia-encoded protein with dual roles in NF-κB inhibition and virulence

Poxviruses contain large dsDNA genomes encoding numerous open reading frames that manipulate cellular signalling pathways and interfere with the host immune response. The NF-κB signalling cascade is an important mediator of innate immunity and inflammation, and is tightly regulated by ubiquitination at several key points. A critical step in NF-κB activation is the ubiquitination and degradation of the inhibitor of kappaB (IκBα), by the cellular SCF^β-TRCP ubiquitin ligase complex. We show here that upon stimulation with TNFα or IL-1β, Orthopoxvirus-infected cells displayed an accumulation of phosphorylated IκBα, indicating that NF-κB activation was inhibited during poxvirus infection. Ectromelia virus is the causative agent of lethal mousepox, a natural disease that is fatal in mice. Previously, we identified a family of four ectromelia virus genes (EVM002, EVM005, EVM154 and EVM165) that contain N-terminal ankyrin repeats and C-terminal F-box domains that interact with the cellular SCF ubiquitin ligase complex. Since degradation of IκBα is catalyzed by the SCF^β-TRCP ubiquitin ligase, we investigated the role of the ectromelia virus ankyrin/F-box protein, EVM005, in the regulation of NF-κB. Expression of Flag-EVM005 inhibited both TNFα- and IL-1β-stimulated IκBα degradation and p65 nuclear translocation. Inhibition of the NF-κB pathway by EVM005 was dependent on the F-box domain, and interaction with the SCF complex. Additionally, ectromelia virus devoid of EVM005 was shown to inhibit NF-κB activation, despite lacking the EVM005 open reading frame. Finally, ectromelia virus devoid of EVM005 was attenuated in both A/NCR and C57BL/6 mouse models, indicating that EVM005 is required for virulence and immune regulation in vivo.

Poxviruses are large dsDNA viruses that are renowned for regulating cellular pathways and manipulating the host immune response, including the NF-κB pathway. NF-κB inhibition by poxviruses is a growing area of interest and this family of viruses has developed multiple mechanisms to manipulate the pathway. Here, we focus on regulation of the NF-κB pathway by ectromelia virus, the causative agent of mousepox. We demonstrate that ectromelia virus is a potent inhibitor of the NF-κB pathway. Previously, we identified a family of four ectromelia virus genes that contain N-terminal ankyrin repeats and a C-terminal F-box domain that interacts with the cellular SCF ubiquitin ligase. Significantly, expression of the ankyrin/F-box protein, EVM005, inhibited NF-κB, and the F-box domain was critical for NF-κB inhibition and interaction with the SCF complex. Ectromelia virus devoid of EVM005 still inhibited NF-κB, indicating that multiple gene products contribute to NF-κB inhibition. Importantly, mice infected with ectromelia virus lacking EVM005 had a robust immune response, leading to viral clearance during infection. The data present two mechanisms, one in which EVM005 inhibits NF-κB activation through manipulation of the host SCF ubiquitin ligase complex, and an additional, NF-κB-independent mechanism that drives virulence.

Protein degradation machinery is present broadly during early development in the sea urchin

Ubiquitin-dependent proteosome-mediated proteolysis is an important pathway of degradation that controls the timed destruction of cellular proteins in all tissues. All intracellular proteins and many extracellular proteins are continually being hydrolyzed to their constituent amino acids as a result of their recognition by E3 ligases for specific targeting of ubiquitination. Gustavus is a member of an ECS-type E3 ligase which interacts with Vasa, a DEAD-box RNA helicase, to regulate its localization during sea urchin embryonic development, and Gustavus mRNA accumulation is highly localized and dynamic during development. We tested if the core complex for Gustavus function was present in the embryo and if other SOCS box proteins also had restricted expression profiles that would inform future research. Expression patterns of the key members of the proteasomal function, such as the E3 core complex which interacts with Gustavus, and other E3-SOCS box proteins, are widely spread and dynamic in early development of the embryo suggesting broad core complex availability in the proteasome degradation pathway and temporal/spatial enrichments of various E3 ligase dependent targeting mechanisms.

Investigations into the role of 26S proteasome non-ATPase regulatory subunit 13 in neuroinflammation

OBJECTIVE

To investigate 26S proteasome non-ATPase regulatory subunit 13 (PSMD13) gene silencing as a potential treatment for neuroinflammatory disorders via regulation of microglial activation and production of inflammatory mediators.

METHODS

RNA interference was used to knockdown PSMD13 gene expression, followed by inhibitors of κB (IκBα) protein degradation and nuclear factor κB (NF-κB) activity measurement in lipopolysaccharide (LPS)-stimulated BV2 microglia. Nitrite (Griess) assay, reporter gene assay, enzyme-linked immunosorbent assay and Western blot were used to investigate the role of PSMD13 in microglial activation and inflammation.

RESULTS

PSMD13 gene knockdown significantly reduced IκBα degradation and NF-κB activation in LPS-stimulated murine BV2 microglia. It also decreased the production of LPS-induced proinflammatory mediators, such as inducible nitric oxide synthase, nitric oxide, cyclooxygenase-2 and prostaglandin E2.

CONCLUSIONS

PSMD13 gene silencing suppressed the production of proinflammatory mediators by modulating ubiquitin-proteasome system-mediated neuroinflammation via the downregulation of IκBα degradation and NF-κB activation in LPS-stimulated BV2 microglia. PSMD13 gene knockdown may have therapeutic implications for the treatment of neuroinflammatory disorders.

Bidirectional regulation of NF-κB by reactive oxygen species: a role of unfolded protein response

Nuclear factor-κB (NF-κB) is a transcription factor that plays a crucial role in coordinating innate and adaptive immunity, inflammation, and apoptotic cell death. NF-κB is activated by various inflammatory stimuli including peptide factors and infectious microbes. It is also known as a redox-sensitive transcription factor activated by reactive oxygen species (ROS). Over the past decades, various investigators focused on the role of ROS in the activation of NF-κB by cytokines and lipopolysaccharides. However, recent studies also suggested that ROS have the potential to repress NF-κB activity. Currently, it is not well addressed how ROS regulate activity of NF-κB in a bidirectional fashion. In this paper, we summarize evidence for positive and negative regulation of NF-κB by ROS, possible redox-sensitive targets for NF-κB signaling, and mechanisms underlying biphasic and bidirectional influences of ROS on NF-κB, especially focusing on a role of ROS-mediated induction of endoplasmic reticulum stress.

Propolis and its constituent caffeic acid suppress LPS-stimulated pro-inflammatory response by blocking NF-κB and MAPK activation in macrophages

ETHNOPHARMACOLOGICAL RELEVANCE

Propolis is a bee product with numerous biological and pharmacological properties, such as immunomodulatory and anti-inflammatory activities. It has been used in folk medicine as a healthy drink and in food to improve health and prevent inflammatory diseases. However, little is known about its mechanism of action. Thus, the goal of this study was to verify the antioxidant activity and to explore the anti-inflammatory properties of propolis by addressing its intracellular mechanism of action. Caffeic acid was investigated as a possible compound responsible for propolis action.

MATERIALS AND METHODS

The antioxidant properties of propolis and caffeic acid were evaluated by using the 2,2-Diphenyl-1-picrylhydrazyl free radical (DPPH) scavenging method. To analyze the anti-inflammatory activity, Raw 264.7 macrophages were treated with different concentrations of propolis or caffeic acid, and nitric oxide (NO) production, a strong pro-inflammatory mediator, was evaluated by the Griess reaction. The concentrations of propolis and caffeic acid that inhibited NO production were evaluated on intracellular signaling pathways triggered during inflammation, namely p38 mitogen-activated protein kinase (MAPK), c-jun NH2-terminal kinase (JNK1/2), the transcription nuclear factor (NF)-κB and extracellular signal-regulated kinase (ERK1/2), through Western blot using specific antibodies. A possible effect of propolis on the cytotoxicity of hepatocytes was also evaluated, since this product can be used in human diets.

RESULTS

Caffeic acid showed a higher antioxidant activity than propolis extract. Propolis and caffeic acid inhibited NO production in macrophages, at concentrations without cytotoxicity. Furthermore, both propolis and caffeic acid suppressed LPS-induced signaling pathways, namely p38 MAPK, JNK1/2 and NF-κB. ERK1/2 was not affected by propolis extract and caffeic acid. In addition, propolis and caffeic acid did not induce hepatotoxicity at concentrations with strong anti-inflammatory potential.

CONCLUSIONS

Propolis exerted an antioxidant and anti-inflammatory action and caffeic acid may be involved in its inhibitory effects on NO production and intracellular signaling cascades, suggesting its use as a natural source of safe anti-inflammatory drugs.

A new mechanism of RhoA ubiquitination and degradation: roles of SCF(FBXL19) E3 ligase and Erk2

RhoA is a small GTPase multifunctional protein that regulates cell proliferation and cytoskeletal reorganization. Regulation of its protein stability plays an important role in its biological functions. We have shown that a Skp1-Cul1-F-box (SCF) FBXL19 E3 ubiquitin ligase targets Rac1, a related member of the Rho family for ubiquitination and degradation. Here, SCF(FBXL19) mediates RhoA ubiquitination and proteasomal degradation in lung epithelial cells. Ectopically expressed FBXL19 decreased RhoA wild type, active, and inactive forms. Cellular depletion of FBXL19 increased RhoA protein levels and extended its half-life. FBXL19 bound the small GTPase in the cytoplasm leading to RhoA ubiquitination at Lys(135). A RhoA(K135R) mutant protein was resistant to SCF(FBXL19)-mediated ubiquitination and degradation and exhibited a longer lifespan. Protein kinase Erk2-mediated phosphorylation of RhoA was both sufficient and required for SCF(FBXL19)-mediated RhoA ubiquitination and degradation. Thus, SCF(FBXL19) targets RhoA for its disposal, a process regulated by Erk2. Ectopically expressed FBXL19 reduced phosphorylation of p27 and cell proliferation, a process mediated by RhoA. Further, FBXL19 cellular expression diminished lysophosphatidic acid (LPA)-induced phosphorylation of myosin light chain (MLC) and stress fiber formation. Hence, SCF(FBXL19) functions as a RhoA antagonist during cell proliferation and cytoskeleton rearrangement. These results provide the first evidence of an F-box protein targeting RhoA thereby modulating its cellular lifespan that impacts cell proliferation and cytoskeleton rearrangement.

The enzymatic activity of the VEGFR2 receptor for the biosynthesis of dinucleoside polyphosphates

The group of dinucleoside polyphosphates encompasses a large number of molecules consisting of two nucleosides which are connected by a phosphate chain of variable length. While the receptors activated by dinucleoside polyphosphates as well as their degradation have been studied in detail, its biosynthesis has not been elucidated so far. Since endothelial cells released the dinucleoside polyphosphate uridine adenosine tetraphosphate (Up4A), we tested cytosolic proteins of human endothelial cells obtained from dermal vessels elicited for enzymatic activity. When incubated with ADP and UDP, these cells showed increasing concentrations of Up4A. The underlying enzyme was isolated by chromatography and the mass spectrometric analysis revealed that the enzymatic activity was caused by the vascular endothelial growth factor receptor 2 (VEGFR2). Since VEGFR2 but neither VEGFR1 nor VEGFR3 were capable to synthesise dinucleoside polyphosphates, Tyr-1175 of VEGFR2 is most likely essential for the enzymatic activity of interest. Further, VEGFR2-containing cells like HepG2, THP-1 and RAW264.7 were capable of synthesising dinucleoside polyphosphates. VEGFR2-transfected HEK 293T/17 but not native HEK 293T/17 cells synthesised dinucleoside polyphosphates in vivo too. The simultaneous biosynthesis of dinucleoside polyphosphates could amplify the response to VEGF, since dinucleoside polyphosphates induce cellular growth via P2Y purinergic receptors. Thus the biosynthesis of dinucleoside polyphosphates by VEGFR2 may enhance the proliferative response to VEGF. Given that VEGFR2 is primarily expressed in endothelial cells, the biosynthesis of dinucleoside polyphosphates is mainly located in the vascular system. Since the vasculature is also the main site of action of dinucleoside polyphosphates, activating vascular purinoceptors, blood vessels appear as an autocrine system with respect to dinucleoside polyphosphates. We conclude that VEGFR2 receptor is capable of synthesising dinucleoside polyphosphates. These mediators may modulate the effects of VEGFR2 due to their proliferative effects.

SCF E3 ligase F-box protein complex SCF(FBXL19) regulates cell migration by mediating Rac1 ubiquitination and degradation

Rac1, a member of the Rho family of GTPases, regulates diverse cellular functions, including cytoskeleton reorganization and cell migration. F-box proteins are major subunits within the Skp1-Cul1-F-box (SCF) E3 ubiquitin ligases that recognize specific substrates for ubiquitination. The role of F-box proteins in regulating Rac1 stability has not been studied. Mouse lung epithelial (MLE12) cells were used to investigate Rac1 stability and cell migration. Screening of an F-box protein library and in vitro ubiquitination assays identified FBXL19, a relatively new member of the F-box protein family that targets Rac1 for its polyubiquitination and proteasomal degradation. Overexpression of FBXL19 decreased both Rac1 active and inactive forms and significantly reduced cellular migration. Protein kinase AKT-mediated phosphorylation of Rac1 at serine(71) was essential for FBXL19-mediated Rac1 ubiquitination and depletion. Lysine(166) within Rac1 was identified as a polyubiquitination acceptor site. Rac1(S71A) and Rac1(K166R) mutant proteins were resistant to FBXL19-mediated ubiquitination and degradation. Further, ectopically expressed FBXL19 reduced cell migration in Rac1-overexpressing cells (P<0.01, Rac1 cells vs. FBXL19+Rac1 cells), but not in Rac1 lysine(166) mutant-overexpressing cells. FBXL19 diminished formation of the migratory leading edge. Thus, SCF(FBXL19) targets Rac1 for its disposal, a process regulated by AKT. These findings provide the first evidence of an F-box protein targeting a small G protein for ubiquitination and degradation to modulate cell migration.

Inhibitory effect of tumor suppressor p53 on proinflammatory chemokine expression in ovarian cancer cells by reducing proteasomal degradation of IκB

Ovarian cancer, one of inflammation-associated cancers, is the fifth leading cause of cancer deaths among women. Inflammation in the tumor microenvironment is associated with peritoneal tumor dissemination and massive ascites, which contribute to high mortality in ovarian cancer. Tumor suppressor p53 is frequently deleted or mutated in aggressive and high-grade ovarian cancer, probably aggravating cancer progression and increasing mortality. We therefore investigated the influence of p53 on proinflammatory chemokines in ovarian cancer cells. A PCR array of the chemokine network revealed that ovarian cancer cells with low or mutated p53 expression expressed high levels of proinflammatory chemokines such as CXCL1, 2, 3 and 8. Transient transfection of p53 into p53-null ovarian cancer cells downregulated proinflammatory chemokines induced by tumor necrosis factor-α (TNF), a proinflammatory cytokine abundantly expressed in ovarian cancer. Furthermore, p53 restoration or stabilization blocked TNF-induced NF-κB promoter activity and reduced TNF-activated IκB. Restoration of p53 increased ubiquitination of IκB, resulting from concurrently reduced proteasome activity followed by stability of IκB. A ubiquitination PCR array on restoration of p53 did not reveal any significant change in expression except for Mdm2, indicating that the balance between p53 and Mdm2 is more important in regulating NF-κB signaling rather than the direct effect of p53 on ubiquitin-related genes or IκB kinases. In addition, nutlin-3, a specific inducer of p53 stabilization, inhibited proinflammatory chemokines by reducing TNF-activated IκB through p53 stabilization. Taken together, these results suggest that p53 inhibits proinflammatory chemokines in ovarian cancer cells by reducing proteasomal degradation of IκB. Thus, frequent loss or mutation of p53 may promote tumor progression by enhancing inflammation in the tumor microenvironment.

LAMP2A overexpression in breast tumors promotes cancer cell survival via chaperone-mediated autophagy

Lysosome-associated membrane protein type 2A (LAMP2A) is a key protein in the chaperone-mediated autophagy (CMA) pathway. LAMP2A helps in lysosomal uptake of modified and oxidatively damaged proteins directly into the lumen of lysosomes for degradation and protein turnover. Elevated expression of LAMP2A was observed in breast tumor tissues of all patients under investigation, suggesting a survival mechanism via CMA and LAMP2A. Reduced expression of the CMA substrates, GAPDH and PKM, was observed in most of the breast tumor tissues when compared with the normal adjacent tissues. Reactive oxygen species (ROS) mediated oxidative stress damages regulatory cellular components such as DNA, proteins and/or lipids. Protein carbonyl content (PCC) is widely used as a measure of total protein oxidation in cells. Ectopic expression of LAMP2A reduces PCC and thereby promotes cell survival during oxidative stress. Furthermore, inhibition of LAMP2A stimulates accumulation of GAPDH, AKT1 phosphorylation, generation of ROS, and induction of cellular apoptosis in breast cancer cells. Doxorubicin, which is a chemotherapeutic drug, often becomes ineffective against tumor cells with time due to chemotherapeutic resistance. Breast cancer cells deficient of LAMP2A demonstrate increased sensitivity to the drug. Thus, inhibiting CMA activity in breast tumor cells can be exploited as a potential therapeutic application in the treatment of breast cancer.

GogB is an anti-inflammatory effector that limits tissue damage during Salmonella infection through interaction with human FBXO22 and Skp1

Bacterial pathogens often manipulate host immune pathways to establish acute and chronic infection. Many Gram-negative bacteria do this by secreting effector proteins through a type III secretion system that alter the host response to the pathogen. In this study, we determined that the phage-encoded GogB effector protein in Salmonella targets the host SCF E3 type ubiquitin ligase through an interaction with Skp1 and the human F-box only 22 (FBXO22) protein. Domain mapping and functional knockdown studies indicated that GogB-containing bacteria inhibited IκB degradation and NFκB activation in macrophages, which required Skp1 and a eukaryotic-like F-box motif in the C-terminal domain of GogB. GogB-deficient Salmonella were unable to limit NFκB activation, which lead to increased proinflammatory responses in infected mice accompanied by extensive tissue damage and enhanced colonization in the gut during long-term chronic infections. We conclude that GogB is an anti-inflammatory effector that helps regulate inflammation-enhanced colonization by limiting tissue damage during infection.

Bacterial pathogens have evolved sophisticated ways to subvert the innate defenses of their host. One way in which pathogens do so is by blocking or dampening the inflammatory response that is triggered once a microorganism is detected by the innate immune system. In this way, the microorganism can limit the activation of innate defenses in the host to promote its own colonization and dissemination. In this work we found that the enteric human pathogen Salmonella enterica serovar Typhimurium limits the activation of innate immune defenses in the host by using a bacterial protein called GogB to interfere with NFκB activation. NFκB is a key human transcription factor involved in the expression of pro-inflammatory cytokines during infection. In this infection situation, Salmonella delivers GogB to the infected cell where it interferes with ubiquitination of the NFκB inhibitor protein called IκBα to prevent translocation of NFκB to the nucleus where it would normally activate pro-inflammatory gene expression. The anti-inflammatory property of GogB is important for the bacteria to reach optimal infection densities in host tissues and to actively limit the tissue damage associated with prolonged inflammatory responses.

The Nrf1 CNC-bZIP protein is regulated by the proteasome and activated by hypoxia

Background

Nrf1 (nuclear factor-erythroid 2 p45 subunit-related factor 1) is a transcription factor mediating cellular responses to xenobiotic and pro-oxidant stress. Nrf1 regulates the transcription of many stress-related genes through the electrophile response elements (EpREs) located in their promoter regions. Despite its potential importance in human health, the mechanisms controlling Nrf1 have not been addressed fully.

Principal Findings

We found that proteasomal inhibitors MG-132 and clasto-lactacystin-β-lactone stabilized the protein expression of full-length Nrf1 in both COS7 and WFF2002 cells. Concomitantly, proteasomal inhibition decreased the expression of a smaller, N-terminal Nrf1 fragment, with an approximate molecular weight of 23 kDa. The EpRE-luciferase reporter assays revealed that proteasomal inhibition markedly inhibited the Nrf1 transactivational activity. These results support earlier hypotheses that the 26 S proteasome processes Nrf1 into its active form by removing its inhibitory N-terminal domain anchoring Nrf1 to the endoplasmic reticulum. Immunoprecipitation demonstrated that Nrf1 is ubiquitinated and that proteasomal inhibition increased the degree of Nrf1 ubiquitination. Furthermore, Nrf1 protein had a half-life of approximately 5 hours in COS7 cells. In contrast, hypoxia (1% O₂) significantly increased the luciferase reporter activity of exogenous Nrf1 protein, while decreasing the protein expression of p65, a shorter form of Nrf1, known to act as a repressor of EpRE-controlled gene expression. Finally, the protein phosphatase inhibitor okadaic acid activated Nrf1 reporter activity, while the latter was repressed by the PKC inhibitor staurosporine.

Conclusions

Collectively, our data suggests that Nrf1 is controlled by several post-translational mechanisms, including ubiquitination, proteolytic processing and proteasomal-mediated degradation as well as by its phosphorylation status.

The NEDD8 Conjugation Pathway and Its Relevance in Cancer Biology and Therapy

Cancer cells depend on signals that promote cell cycle progression and prevent programmed cell death that would otherwise result from cumulative, aberrant stress. These activities require the temporally controlled destruction of specific intracellular proteins by the ubiquitin-proteasome system (UPS). To a large extent, the control points in this process include a family of E3 ubiquitin ligases called cullin-RING ligases (CRLs). The ligase activity of these multicomponent complexes requires modification of the cullin protein situated at their core with a ubiquitin-like protein called NEDD8. Neddylation results in conformational rearrangements within the CRL, which are necessary for ubiquitin transfer to a substrate. The NEDD8 pathway thus has a critical role in mediating the ubiquitination of numerous CRL substrate proteins involved in cell cycle progression and survival including the DNA replication licensing factor Cdt-1, the NF-κB transcription factor inhibitor pIκBα, and the cell cycle regulators cyclin E and p27. The initial step required for attachment of NEDD8 to a cullin is catalyzed by the E1, NEDD8-activating enzyme (NAE). The first-in-class inhibitor of NAE, MLN4924, has been shown to block the activity of NAE and prevent the subsequent neddylation of cullins. Preclinical studies have demonstrated antitumor activity in various solid tumors and hematological malignancies, and preliminary clinical data have shown the anticipated pharmacodynamic effects in humans. Here, we review the NEDD8 pathway, its importance in cancer, and the therapeutic potential of NAE inhibition.

Proteasomal inhibition promotes ATP-binding cassette transporter A1 (ABCA1) and ABCG1 expression and cholesterol efflux from macrophages in vitro and in vivo

OBJECTIVE

ATP-binding cassette transporter A1 (ABCA1) and ABCG1 are key molecules in an initial step of reverse cholesterol transport (RCT), a major antiatherogenic property of high-density lipoprotein (HDL). The ubiquitin-proteasome system (UPS) mediates nonlysosomal pathways for protein degradation and is known to be involved in atherosclerosis. However, little is known about the effects of the UPS on these molecules and overall RCT. We therefore investigated whether UPS inhibition affects ABCA1/G1 expression in macrophages and RCT in vitro and in vivo.

METHODS AND RESULTS

Various proteasome inhibitors increased ABCA1/G1 expression in macrophages, translating into enhanced apolipoprotein A-I- and HDL-mediated cholesterol efflux from macrophages. ABCA1 and ABCG1 were found to undergo polyubiquitination in the macrophages and HEK293 cells overexpressing these proteins, and pulse-chase analysis revealed that proteasome inhibitors inhibited ABCA1/G1 protein degradation. In in vivo experiments, the proteasome inhibitor bortezomib increased ABCA1/G1 protein levels in mouse peritoneal macrophages, and RCT assays showed that it significantly increased the fecal (54% increase compared with saline) and plasma (23%) appearances of the tracer derived from intraperitoneally injected (3)H-cholesterol-labeled macrophages.

CONCLUSIONS

The present study provided evidence that the UPS is involved in ABCA1/G1 degradation, thereby affecting RCT in vivo. Therefore, specific inhibition of the UPS pathway might lead to a novel HDL therapy that enhances RCT.

Effect of propolis and caffeic acid phenethyl ester (CAPE) on NFκB activation by HTLV-1 Tax

HTLV-1 is the etiological agent of aggressive malignancy of the CD4(+) T-cells, adult T-cell leukemia (ATL), and other severe clinical disorders. The viral Tax protein is a key factor in HTLV-1 pathogenicity. A major part of Tax oncogenic potential is accounted for by its capacity of inducing the transcriptional activity of the NFκB factors, which regulate the expression of numerous cellular genes. Propolis (PE), a natural product produced by honeybees, has been used for a long time in folk medicine. One of PE active components, caffeic acid phenylethyl ester (CAPE), was well characterized and found to be a potent inhibitor of NFκB activation. Therefore, the aim of this study was to pursue the possibility of blocking Tax oncogenic effects by treatment with these natural products. Human T-cell lines were used in this study since these cells are the main targets of HTLV-1 infections. We tried to determine which step of Tax-induced NFκB activation is blocked by these products. Our results showed that both tested products substantially inhibited the activation of NFκB-dependent promoter by Tax. However, only PE could efficiently inhibit also the Tax-induced activation of SRF- and CREB-dependent promoters. Our results showed also that PE and CAPE strongly prevented both Tax binding to IκBα and its induced degradation by Tax. However, both products did not interfere in the nuclear transport of Tax or NFκB proteins.

Role of ubiquitin-proteasome-mediated proteolysis in nervous system disease

Proteolysis by the ubiquitin-proteasome pathway (UPP) is now widely recognized as a molecular mechanism controlling myriad normal functions in the nervous system. Also, this pathway is intimately linked to many diseases and disorders of the brain. Among the diseases connected to the UPP are neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases. Perturbation in the UPP is also believed to play a causative role in mental disorders such as Angelman syndrome. The pathology of neurodegenerative diseases is characterized by abnormal deposition of insoluble protein aggregates or inclusion bodies within neurons. The ubiquitinated protein aggregates are believed to result from dysfunction of the UPP or from structural changes in the protein substrates which prevent their recognition and degradation by the UPP. An early effect of abnormal UPP in diseases of the nervous system is likely to be impairment of synaptic function. Here we discuss the UPP and its physiological roles in the nervous system and how alterations in the UPP relate to development of nervous system diseases. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!

Vitamin B6 suppresses serine protease inhibitor 3 expression in the colon of rats and in TNF-α-stimulated HT-29 cells

SCOPE

Previous reports in the areas of animal studies and, recently epidemiology, have linked anti-tumorigenic and anti-inflammatory effects to dietary vitamin B6. This study investigated the molecular mechanism of these effects of vitamin B6.

METHODS AND RESULTS

DNA microarray analysis was used to obtain information on changes in colon gene expression from vitamin B6 (pyridoxine) repletion in vitamin B6-deficient rats. Pyridoxine supplementation down-regulated the inflammatory molecule, serine protease inhibitor clade A member 3 (SPI-3) mRNA expression in the colon. This study also showed that tumor necrosis factor α (TNF-α) induced SPI-3 mRNA expression in HT-29 human colon cancer cells, and vitamin B6 (pyridoxal hydrochloride) pretreatment of HT-29 cells inhibited TNF -induced mRNA expression of SPI-3. Vitamin B6 inhibited TNF-α-induced NF-κB activation via suppression of IκBα degradation in HT-29 cells. HT-29 cells stably expressing epitope-tagged ubiquitin were generated and vitamin B6 pretreatment was shown to inhibit ubiquitination of the IkB protein in response to TNF-α-i.

CONCLUSION

Vitamin B6 suppressed SPI-3 expression in the colon of rats and in TNF-α-stimulated HT-29 cells. Further, this study showed a possible role of vitamin B6 in the regulation of protein ubiquitination.

The ubiquitin-proteasome pathway and synaptic plasticity

Proteolysis by the ubiquitin-proteasome pathway (UPP) has emerged as a new molecular mechanism that controls wide-ranging functions in the nervous system, including fine-tuning of synaptic connections during development and synaptic plasticity in the adult organism. In the UPP, attachment of a small protein, ubiquitin, tags the substrates for degradation by a multisubunit complex called the proteasome. Linkage of ubiquitin to protein substrates is highly specific and occurs through a series of well-orchestrated enzymatic steps. The UPP regulates neurotransmitter receptors, protein kinases, synaptic proteins, transcription factors, and other molecules critical for synaptic plasticity. Accumulating evidence indicates that the operation of the UPP in neurons is not homogeneous and is subject to tightly managed local regulation in different neuronal subcompartments. Investigations on both invertebrate and vertebrate model systems have revealed local roles for enzymes that attach ubiquitin to substrate proteins, as well as for enzymes that remove ubiquitin from substrates. The proteasome also has been shown to possess disparate functions in different parts of the neuron. Here I give a broad overview of the role of the UPP in synaptic plasticity and highlight the local roles and regulation of the proteolytic pathway in neurons.

The nrf1 and nrf2 balance in oxidative stress regulation and androgen signaling in prostate cancer cells

Reactive oxygen species (ROS) signaling has recently sparked a surge of interest as being the molecular underpinning for cancer cell survival, but the precise mechanisms involved have not been completely elucidated. This review covers the possible roles of two ROS-induced transcription factors, Nrf1 and Nrf2, and the antioxidant proteins peroxiredoxin-1 (Prx-1) and Thioredoxin-1 (Txn-1) in modulating AR expression and signaling in aggressive prostate cancer (PCa) cells. In androgen independent (AI) C4-2B cells, in comparison to the parental androgen dependent (AD) LNCaP cells, we present evidence of high Nrf1 and Prx-1 expression and low Nrf2 expression in these aggressive PCa cells. Furthermore, in DHT treated C4-2B cells, increased expression of the p65 (active) isoform of Nrf1 correlated with enhanced AR transactivation. Our findings implicate a crucial balance of Nrf1 and Nrf2 signaling in regulating AR activity in AI-PCa cells. Here we will discuss how understanding the mechanisms by which oxidative stress may affect AR signaling may aid in developing novel therapies for AI-PCa.

Caffeic acid phenethyl ester-mediated Nrf2 activation and IkappaB kinase inhibition are involved in NFkappaB inhibitory effect: structural analysis for NFkappaB inhibition

Caffeic acid phenethyl ester (CAPE) is an active component of propolis from honeybee. We investigated potential molecular mechanisms underlying CAPE-mediated nuclear factor kappa beta (NFkappaB) inhibition and analyzed structure of CAPE for its biological effect. CAPE attenuated expression of NFkappaB dependent luciferase stimulated with TNF-alpha or LPS and suppressed LPS-mediated induction of iNOS, a target gene product of NFkappaB. In HCT116 cells, CAPE interfered with TNF-alpha dependent IkappaBalpha degradation and subsequent nuclear accumulation of p65, which occurred by direct inhibition of inhibitory protein kappaB kinase (IKK). CAPE increased the expression of Nrf2-dependent luciferase and heme oxygenase-1, a target gene of Nrf2, and elevated the nuclear level of Nrf2 protein, indicating that CAPE activated the Nrf2 pathway. In HCT116 cells with stable expression of Nrf2 shRNA, CAPE elicited a reduced inhibitory effect on TNF-alpha-activated NFsmall ka, CyrillicB compared to scramble RNA expressing control cells. On the other hand, the NFkappaB inhibitory effect of CAPE was diminished by removal or modification of the Michael reaction acceptor, catechol or phenethyl moiety in CAPE. These data suggest that CAPE inhibits TNF-alpha-dependent NFkappaB activation via direct inhibition of IKK as well as activation of Nrf2 pathway, in which the functional groups in CAPE may be involved.

Proteinases involved in matrix turnover during cartilage and bone breakdown

The joint is a discrete unit that consists of cartilage, bone, tendon and ligaments. These tissues are all composed of an extracellular matrix made of collagens, proteoglycans and specialised glycoproteins that are actively synthesised, precisely assembled and subsequently degraded by the resident connective tissue cells. A balance is maintained between matrix synthesis and degradation in healthy adult tissues. Different classes of proteinases play a part in connective tissue turnover in which active proteinases can cleave matrix protein during resorption, although the proteinase that predominates varies between different tissues and diseases. The metalloproteinases are potent enzymes that, once activated, degrade connective tissue and are inhibited by tissue inhibitors of metalloproteinases (TIMPs); the balance between active matrix metalloproteinases and TIMPs determines, in many tissues, the extent of extracellular matrix degradation. The serine proteinases are involved in the initiation of activation cascades and some, such as elastase, can directly degrade the matrix. Cysteine proteinases are responsible for the breakdown of collagen in bone following the removal of the osteoid layer and the attachment of osteoclasts to the exposed bone surface. Various growth factors increase the synthesis of matrix and proteinase inhibitors, whereas cytokines (alone or in combination) can inhibit matrix synthesis and stimulate proteinase production and matrix destruction.

Cell cycle-dependent effects of 3,3'-diindolylmethane on proliferation and apoptosis of prostate cancer cells

Epidemiological studies have shown that a diet rich in fruits and cruciferous vegetables is associated with a lower risk of prostate cancer. Indole-3-carbinol (I3C) and its dimeric product 3,3'-diindolylmethane (DIM) have been shown to exhibit anti-tumor activity both in vitro and in vivo. Recently, we have reported that a formulated DIM (B-DIM) induced apoptosis and inhibited growth, angiogenesis, and invasion of prostate cancer cells by regulating Akt, NF-kappaB, VEGF and the androgen receptor (AR) signaling pathway. However, the precise molecular mechanism(s) by which B-DIM inhibits prostate cancer cell growth and induces apoptosis have not been fully elucidated. Most importantly, it is not known how B-DIM affects cell cycle regulators and proteasome activity, which are critically involved in cell growth and apoptosis. In this study, we investigated the effects of B-DIM on proteasome activity and AR transactivation with respect to B-DIM-mediated cell cycle regulation and induction of apoptosis in both androgen-sensitive LNCaP and androgen-insensitive C4-2B prostate cancer cells. We believe that our results show for the first time the cell cycle-dependent effects of B-DIM on proliferation and apoptosis of synchronized prostate cancer cells progressing from G(1) to S phase. B-DIM inhibited this progression by induction of p27(Kip1) and down-regulation of AR. We also show for the first time that B-DIM inhibits proteasome activity in S phase, leading to the inactivation of NF-kappaB signaling and induction of apoptosis in LNCaP and C4-2B cells. These results suggest that B-DIM could be a potent agent for the prevention and/or treatment of both hormone sensitive as well as hormone-refractory prostate cancer.

Autoubiquitination of BCA2 RING E3 ligase regulates its own stability and affects cell migration

Accumulating evidence suggests that ubiquitination plays a role in cancer by changing the function of key cellular proteins. Previously, we isolated BCA2 gene from a library enriched for breast tumor mRNAs. The BCA2 protein is a RING-type E3 ubiquitin ligase and is overexpressed in human breast tumors. In order to deduce the biochemical and biological function of BCA2, we searched for BCA2-binding partners using human breast and fetal brain cDNA libraries and BacterioMatch two-hybrid system. We identified 62 interacting partners, the majority of which were found to encode ubiquitin precursor proteins including ubiquitin C and ubiquitin A-52. Using several deletion and point mutants, we found that the BCA2 zinc finger (BZF) domain at the NH(2) terminus specifically binds ubiquitin and ubiquitinated proteins. The autoubiquitination activity of BCA2, RING-H2 mutant, BZF mutant, and various lysine mutants of BCA2 were investigated. Our results indicate that the BCA2 protein is strongly ubiquitinated and no ubiquitination is detected with the BCA2 RING-H2 mutant, indicating that the RING domain is essential for autoubiquitination. Mutation of the K26 and K32 lysines in the BZF domain also abrogated autoubiquitination activity. Interestingly, mutation of the K232 and K260 lysines in and near the RING domain resulted in an increase in autoubiquitination activity. Additionally, in cellular migration assays, BCA2 mutants showed altered cell motility compared with wild-type BCA2. On the basis of these findings, we propose that BCA2 might be an important factor regulating breast cancer cell migration/metastasis. We put forward a novel model for BCA2 E3 ligase-mediated cell regulation.

A therapeutic dose of doxorubicin activates ubiquitin-proteasome system-mediated proteolysis by acting on both the ubiquitination apparatus and proteasome

The ubiquitin proteasome system (UPS) degrades abnormal proteins and most unneeded normal proteins, thereby playing a critical role in protein homeostasis in the cell. Proteasome inhibition is effective in treating certain forms of cancer, while UPS dysfunction is increasingly implicated in the pathogenesis of many severe and yet common diseases. It has been previously shown that doxorubicin (Dox) enhances the degradation of a UPS surrogate substrate in mouse hearts. To address the underlying mechanism, in the present study, we report that 1) Dox not only enhances the degradation of an exogenous UPS reporter (GFPu) but also antagonizes the proteasome inhibitor-induced accumulation of endogenous substrates (e.g., beta-catenin and c-Jun) of the UPS in cultured NIH 3T3 cells and cardiomyocytes; 2) Dox facilitates the in vitro degradation of GFPu and c-Jun by the reconstituted UPS via the enhancement of proteasomal function; 3) Dox at a therapeutically relevant dose directly stimulates the peptidase activities of purified 20S proteasomes; and 4) Dox increases, whereas proteasome inhibition decreases, E3 ligase COOH-terminus of heat shock protein cognate 70 in 3T3 cells via a posttranscriptional mechanism. These new findings suggest that Dox activates the UPS by acting directly on both the ubiquitination apparatus and proteasome.

The proteasome: a target of oxidative damage in cultured human retina pigment epithelial cells

PURPOSE

Dysfunction of the ubiquitin-proteasome pathway (UPP) is associated with several age-related degenerative diseases. The objective of this study was to investigate the effect of oxidative stress on the UPP in cultured human retina pigment epithelial cells.

METHODS

To mimic physiological oxidative stress, ARPE-19 cells were exposed to continuously generated H2O(2) or A2E-mediated photooxidation. Proteasome activity was monitored using fluorogenic peptides as substrates. The ubiquitin conjugation activity and activities of E1 and E2 were determined by the thiolester assays. Levels of ubiquitin and ubiquitin conjugates were determined by Western blotting.

RESULTS

Exposure of ARPE-19 cells to 40 to 50 microM H2O(2) for 4 hours resulted in a 30% to 50% reduction in all three peptidase activities of the proteasome. Similarly, exposure of A2E-loaded ARPE-19 cells to blue light resulted in a 40% to 60% reduction in proteasome activity. Loading of A2E or exposure to blue light alone had little effect on proteasome activity. In contrast, exposure of ARPE-19 to low levels of H2O(2) (10 microM) stimulated ubiquitin conjugation activity. Loading of A2E, with or without exposure to blue light, upregulated the levels of ubiquitin-activating enzyme and increased conjugation activity. Exposure to H2O(2) or A2E-mediated photooxidation also resulted in a twofold to threefold increase in levels of endogenous ubiquitin conjugates.

CONCLUSIONS

These data show that the proteasome in ARPE-19 is susceptible to oxidative inactivation, whereas activities of the ubiquitin-conjugating enzymes are more resistant to oxidative stress. Oxidative inactivation of the proteasome appears to be one of the mechanisms underlying stress-induced accumulation of ubiquitin conjugates in the cells.

Proteasome inhibition attenuates coxsackievirus-induced myocardial damage in mice

Coxsackievirus B3 (CVB3) is one of the most prevalent pathogens of viral myocarditis, which may persist chronically and progress to dilated cardiomyopathy. We previously demonstrated a critical role of the ubiquitin-proteasome system (UPS) in the regulation of coxsackievirus replication in mouse cardiomyocytes. In the present study, we extend our interest to an in vivo animal model to examine the regulation and role of the UPS in CVB3-induced murine myocarditis. Male myocarditis-susceptible A/J mice at age 4-5 wk were randomized to four groups: sham infection + vehicle (n = 10), sham infection + proteasome inhibitor (n = 10), virus + vehicle (n = 20), and virus + proteasome inhibitor (n = 20). Proteasome inhibitor was administered subcutaneously once a day for 3 days. Mice were killed on day 9 after infection, and infected hearts were harvested for Western blot analysis, plaque assay, immunostaining, and histological examination. We showed that CVB3 infection led to an accumulation of ubiquitin conjugates at 9 days after infection. Protein levels of ubiquitin-activating enzyme E1A/E1B, ubiquitin-conjugating enzyme UBCH7, as well as deubiquitinating enzyme UCHL1 were markedly increased in CVB3-infected mice compared with sham infection. However, there was no significant alteration in proteasome activities at 9 days after infection. Immunohistochemical staining revealed that increased expression of E1A/E1B was mainly localized to virus-damaged cells. Finally, we showed that application of a proteasome inhibitor significantly reduced CVB3-induced myocardial damage. This observation reveals a novel mechanism of coxsackieviral pathogenesis, and suggests that the UPS may be an attractive therapeutic target against coxsackievirus-induced myocarditis.

Proteasome inhibitors induce osteoclast survival by activating the Akt pathway

Osteoclasts rapidly undergo spontaneous apoptosis when deprived of survival factors. Regulation of osteoclast survival is important to treat bone-related diseases, such as osteoporosis. In this study, we found that the proteasome inhibitors, MG132 and ALLN, significantly inhibited osteoclast apoptosis induced by etoposide, as well as under conditions of survival factor deprivation. MG132 and ALLN inhibited the release of cytochrome c from mitochondria into the cytosol in the absence of survival factors and suppressed the cleavage of pro-caspase-9 and -3 to its active forms induced by etoposide. In addition, MG132 and ALLN enhanced the phosphorylation of Akt and ERK in osteoclasts. However, MG132 and ALLN did not inhibit the cleavage of caspase-9 and -3 in the presence of the phosphatidylinositol 3-kinase (PI-3K) inhibitor, LY294002, while the inhibitory effect of MG132 and ALLN were intact in presence of the MEK1/2 inhibitor, U0126. LY294002 inhibited the survival of osteoclasts induced by MG132 and ALLN. Taken together, our results have demonstrated that proteasome inhibitors suppressed osteoclast apoptosis under conditions of survival factors deprivation through activation of the PI-3K/Akt pathway.

Long-term memory consolidation depends on proteasome activity in the crab Chasmagnathus

Long-term memory formation depends on protein and mRNA synthesis that subserves synaptic reorganization. The removal of pre-existing inhibitory proteins by the ubiquitin-proteasome system (UPS) is proposed as a crucial step to support these modifications. The activation of the constitutive transcription factor nuclear factor kappaB (NF-kappaB) depends on the degradation of the inhibitor of NF-kappaB (IkappaB) by the UPS. Here we study the effect of a UPS inhibitor, MG132, on long-term memory consolidation and NF-kappaB activation in the learning paradigm of the crab Chasmagnathus, a model in which this transcription factor plays a key role. Here we found that administration of MG132 interferes with long-term memory but not with short-term memory, and no facilitatory effects were found. Then we studied the effect of the UPS inhibitor on NF-kappaB pathway, finding that MG132 blocks the activation of NF-kappaB induced by training. These results suggest that the UPS is necessary for long-term memory consolidation, allowing for the activation of NF-kappaB as one of the target molecular pathways.