cis-Acting Element-specific Transcriptional Activity of Differentially Phosphorylated Nuclear Factor-κB

Post-translational modifications of p65: state of the art

P65, a protein subunit of NF-κB, is a widely distributed transcription factor in eukaryotic cells and exerts diverse regulatory functions. Post-translational modifications such as phosphorylation, acetylation, methylation and ubiquitination modulate p65 transcriptional activity and function, impacting various physiological and pathological processes including inflammation, immune response, cell death, proliferation, differentiation and tumorigenesis. The intricate interplay between these modifications can be antagonistic or synergistic. Understanding p65 post-translational modifications not only elucidates NF-κB pathway regulation but also facilitates the identification of therapeutic targets and diagnostic markers for associated clinical conditions.

8-Oxoguanine DNA glycosylase 1 selectively modulates ROS-responsive NF-κB targets through recruitment of MSK1 and phosphorylation of RelA/p65 at Ser276

Nuclear factor kappa B (NF-κB) activity is regulated by various posttranslational modifications, of which Ser276 phosphorylation of RelA/p65 is particularly impacted by reactive oxygen species (ROS). This modification is responsible for selective upregulation of a subset of NF-κB targets; however, the precise mechanism remains elusive. ROS have the ability to modify cellular molecules including DNA. One of the most common oxidation products is 8-oxo-7,8-dihydroguanine (8-oxoGua), which is repaired by the 8-oxoguanine DNA glycosylase1 (OGG1)-initiated base excision repair pathway. Recently, a new function of OGG1 has been uncovered. OGG1 binds to 8-oxoGua, facilitating the occupancy of NF-κB at promoters and enhancing transcription of pro-inflammatory cytokines and chemokines. In the present study, we demonstrated that an interaction between DNA-bound OGG1 and mitogen-and stress-activated kinase 1 is crucial for RelA/p65 Ser276 phosphorylation. ROS scavenging or OGG1 depletion/inhibition hindered the interaction between mitogen-and stress-activated kinase 1 and RelA/p65, thereby decreasing the level of phospho-Ser276 and leading to significantly lowered expression of ROS-responsive cytokine/chemokine genes, but not that of Nfkbis. Blockade of OGG1 binding to DNA also prevented promoter recruitment of RelA/p65, Pol II, and p-RNAP II in a gene-specific manner. Collectively, the data presented offer new insights into how ROS signaling dictates NF-κB phosphorylation codes and how the promoter-situated substrate-bound OGG1 is exploited by aerobic mammalian cells for timely transcriptional activation of ROS-responsive genes.

Pterocarpus santalinus Selectively Inhibits a Subset of Pro-Inflammatory Genes in Interleukin-1 Stimulated Endothelial Cells

Based on the traditional use and scientific reports on the anti-inflammatory potential of red sandalwood, i.e., the heartwood of Pterocarpus santalinus L., we investigated its activity in a model of IL-1 stimulated endothelial cells. Endothelial cells were stimulated with IL-1 with or without prior incubation with a defined sandalwoodextract (PS), and analyzed for the expression of selected pro-inflammatory genes. The activity of NF-κB, a transcription factor of central importance for inflammatory gene expression was assessed by reporter gene analysis, Western blotting of IκBα, and nuclear translocation studies. In addition, microarray studies were performed followed by verification of selected genes by qPCR and supplemented by bioinformatics analysis. Our results show that PS is able to suppress the induction of E-selectin and VCAM-1, molecules that mediate key steps in the adhesion of leukocytes to the endothelium. It also suppressed the activity of an NF-κB reporter, IκBα phosphorylation and degradation, and the nuclear translocation of NF-κB RelA. In contrast, it stimulated JNK phosphorylation indicating the activation of the JNK signaling pathway. Gene expression profiling revealed that PS inhibits only a specific subset of IL-1 induced genes, while others remain unaffected. Most strongly suppressed genes were the signal transducer TRAF1 and the chemokine CX3CL1, whereas IL-8 was an example of a non-affected gene. Notably, PS also stimulated the expression of certain genes, including ones with negative regulatory function, e.g., members of the NR4A family, the mRNA destabilizing protein TTP as well as the transcription factors ATF3 and BHLHB40. These results provide mechanistic insight into the anti-inflammatory activity of PS, and suggest that it acts through the interplay of negative and positive regulators to achieve a differential inhibition of inflammatory gene expression.

Interleukin-1 promotes autoimmune neuroinflammation by suppressing endothelial heme oxygenase-1 at the blood-brain barrier

The proinflammatory cytokine interleukin 1 (IL-1) is crucially involved in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). Herein, we studied the role of IL-1 signaling in blood-brain barrier (BBB) endothelial cells (ECs), astrocytes and microglia for EAE development, using mice with the conditional deletion of its signaling receptor IL-1R1. We found that IL-1 signaling in microglia and astrocytes is redundant for the development of EAE, whereas the IL-1R1 deletion in BBB-ECs markedly ameliorated disease severity. IL-1 signaling in BBB-ECs upregulated the expression of the adhesion molecules Vcam-1, Icam-1 and the chemokine receptor Darc, all of which have been previously shown to promote CNS-specific inflammation. In contrast, IL-1R1 signaling suppressed the expression of the stress-responsive heme catabolizing enzyme heme oxygenase-1 (HO-1) in BBB-ECs, promoting disease progression via a mechanism associated with deregulated expression of the IL-1-responsive genes Vcam1, Icam1 and Ackr1 (Darc). Mechanistically, our data emphasize a functional crosstalk of BBB-EC IL-1 signaling and HO-1, controlling the transcription of downstream proinflammatory genes promoting the pathogenesis of autoimmune neuroinflammation.

A Symphytum officinale Root Extract Exerts Anti-inflammatory Properties by Affecting Two Distinct Steps of NF-κB Signaling

Symphytum officinale, commonly known as comfrey, constitutes a traditional medicinal plant with a long-standing therapeutic history, and preparations thereof have been widely used for the treatment of painful muscle and joint complaints, wound and bone healing, and inflammation. Today, its topical use is based on its analgesic and anti-inflammatory effects, which have been substantiated by modern clinical trials. However, the molecular basis of its action remained elusive. Here, we show that a hydroalcoholic extract of comfrey root impairs the development of a pro-inflammatory scenario in primary human endothelial cells in a dose-dependent manner. The extract, and especially its mucilage-depleted fraction, impair the interleukin-1 (IL-1) induced expression of pro-inflammatory markers including E-selectin, VCAM1, ICAM1, and COX-2. Both preparations inhibit the activation of NF-κB, a transcription factor of central importance for the expression of these and other pro-inflammatory genes. Furthermore, our biochemical studies provide evidence that comfrey inhibits NF-κB signaling at two stages: it dampens not only the activation of IKK1/2 and the subsequent IκBα degradation, but also interferes with NF-κB p65 nucleo-cytoplasmatic shuttling and transactivation. These results provide a first mechanistic insight into the mode of action of a century-old popular herbal medicine.

Characterization of Site-Specific Phosphorylation of NF-κB p65 in Retinal Cells in Response to High Glucose and Cytokine Polarization

Background

Inflammation is an important contributor to the pathogenesis of diabetic retinopathy (DR). NF-κB is a master transcriptional regulator for numerous inflammatory genes. Although NF-κB is comprised of multiple subunits, p65 has received the most attention. However, the p65 subunit can be phosphorylated at numerous sites, for which the effects of DR-related conditions are not well characterized. Since dysregulation of NF-κB has been linked to chronic inflammation, the current study examines site-specific p65 phosphorylation in retinal cells exposed to high glucose and investigates the effects of cytokine polarization.

Methods

Phosphorylation of NF-κB p65 sites was examined in human primary retinal endothelial cells (HREC) and MIO-M1 Müller cells after exposure to high glucose (HG) and pro- or anti-inflammatory cytokines. Related downstream gene activation was selectively measured by real-time RT-PCR, ELISA, and/or Western blot.

Results

HG exposure resulted in differential phosphorylation of p65 subunit sites between HREC and Müller cells. Proinflammatory cytokines further increased phosphorylation of these sites and additional sites that were not altered in HG. In contrast, IL-4 exhibited a suppressive effect on the phosphorylation of p65 sites in both cell types and promoted IκBα expression. Downstream inflammatory mediators were increased in response to proinflammatory cytokine treatment versus HG exposure. IL-4 inhibited proinflammatory cytokines, while IL-10 was enhanced despite HG exposure.

Conclusion

The current study is the first to characterize HG-induced NF-κB p65 phosphorylation after cytokine polarization. By understanding NF-κB phosphorylation and cytokine influence during hyperglycemic conditions, intervention points can be identified for early-stage treatment of DR.

A Chemically Modified Curcumin (CMC 2.24) Inhibits Nuclear Factor κB Activation and Inflammatory Bone Loss in Murine Models of LPS-Induced Experimental Periodontitis and Diabetes-Associated Natural Periodontitis

The purpose of this study was to assess the effect of a novel chemically modified curcumin (CMC 2.24) on NF-κB and MAPK signaling and inflammatory cytokine production in two experimental models of periodontal disease in rats. Experimental model I: Periodontitis was induced by repeated injections of LPS into the gingiva (3×/week, 3 weeks); control rats received vehicle injections. CMC 2.24, or the vehicle, was administered by daily oral gavage for 4 weeks. Experimental model II: Diabetes was induced in adult male rats by streptozotocin injection; periodontal breakdown then results as a complication of uncontrolled hyperglycemia. Non-diabetic rats served as controls. CMC 2.24, or the vehicle, was administered by oral gavage daily for 3 weeks to the diabetics. Hemimaxillae and gingival tissues were harvested, and bone loss was assessed radiographically. Gingival tissues were pooled according to the experimental conditions and processed for the analysis of matrix metalloproteinases (MMPs) and bone-resorptive cytokines. Activation of p38 MAPK and NF-κB signaling pathways was assessed by western blot. Both LPS and diabetes induced an inflammatory process in the gingival tissues associated with excessive alveolar bone resorption and increased activation of p65 (NF-κB) and p38 MAPK. In both models, the administration of CMC 2.24 produced a marked reduction of inflammatory cytokines and MMPs in the gingival tissues, decreased bone loss, and decreased activation of p65 (NF-κB) and p38 MAPK. Inhibition of these cell signaling pathways by this novel tri-ketonic curcuminoid (natural curcumin is di-ketonic) may play a role in its therapeutic efficacy in locally and systemically associated periodontitis.

Presenting a New Standard Drug Model for Turmeric and Its Prized Extract, Curcumin

Various parts of the turmeric plant have been used as medicinal treatment for various conditions from ulcers and arthritis to cardiovascular disease and neuroinflammation. The rhizome's curcumin extract is the most studied active constituent, which exhibits an expansive polypharmacology with influence on many key inflammatory markers. Despite the expansive reports of curcucmin's therapeutic value, clinical reliability and research repeatability with curcumin treatment are still poor. The pharmacology must be better understood and reliably mapped if curcumin is to be accepted and used in modern medical applications. Although the polypharmacology of this extract has been considered, in mainstream medicine, to be a drawback, a perspective change reveals a comprehensive and even synergistic shaping of the NF-kB pathway, including transactivation. Much of the inconsistent research data and unreliable clinical outcomes may be due to a lack of standardization which also pervades research standard samples. The possibility of other well-known curcumin by-products contributing in the polypharmacology is also discussed. A new flowchart of crosstalk in transduction pathways that lead to shaping of nuclear NF-kB transactivation is generated and a new calibration or standardization protocol for the extract is proposed which could lead to more consistent data extraction and improved reliability in therapy.

Dynamic phosphorylation of RelA on Ser42 and Ser45 in response to TNFα stimulation regulates DNA binding and transcription

The NF-κB signalling module controls transcription through a network of protein kinases such as the IKKs, as well as inhibitory proteins (IκBs) and transcription factors including RelA/p65. Phosphorylation of the NF-κB subunits is critical for dictating system dynamics. Using both non-targeted discovery and quantitative selected reaction monitoring-targeted proteomics, we show that the cytokine TNFα induces dynamic multisite phosphorylation of RelA at a number of previously unidentified residues. Putative roles for many of these phosphorylation sites on RelA were predicted by modelling of various crystal structures. Stoichiometry of phosphorylation determination of Ser45 and Ser42 revealed preferential early phosphorylation of Ser45 in response to TNFα. Quantitative analyses subsequently confirmed differential roles for pSer42 and pSer45 in promoter-specific DNA binding and a role for both of these phosphosites in regulating transcription from the IL-6 promoter. These temporal dynamics suggest that RelA-mediated transcription is likely to be controlled by functionally distinct NF-κB proteoforms carrying different combinations of modifications, rather than a simple ‘one modification, one effect’ system.

Oxidized Low-Density Lipoprotein Loading of Macrophages Downregulates TLR-Induced Proinflammatory Responses in a Gene-Specific and Temporal Manner through Transcriptional Control

Hypercholesterolemia is a key risk factor for atherosclerosis and leads to the uptake of native and oxidized low-density lipoprotein (oxLDL) by macrophages (Mϕs) and foam cell formation. Inflammatory processes accompany Mϕ foam cell formation in the artery wall, yet the relationship between Mϕ lipid loading and their response to inflammatory stimuli remains elusive. We investigated proinflammatory gene expression in thioglycollate-elicited peritoneal Mϕs, bone marrow-derived Mϕs and dendritic cells, and RAW264.7 cells. Loading with oxLDL did not induce peritoneal Mϕ apoptosis or modulate basal-level expression of proinflammatory genes. Upon stimulation of TLR4, the rapid induction of IFN-β was inhibited in cells loaded with oxLDL, whereas the induction of other proinflammatory genes by TLR4 (LPS), TLR3 (polyriboinosinic-polyribocytidylic acid), TLR2 (Pam₃CSK₄), and TLR9 (CpG) remained comparable within the first 2 h. Subsequently, the expression of a subset of proinflammatory genes (e.g., IL-1β, IL-6, CCL5) was reduced in oxLDL-loaded cells at the level of transcription. This phenomenon was partially dependent on NF erythroid 2-related factor 2 (NRF2) but not on nuclear liver X receptors α and β (LXRα,β), peroxisome proliferator-activated receptor-γ (PPARγ), and activating transcription factor 3 (ATF3). LPS-induced NF-κB reporter activity and intracellular signaling by NF-κB and MAPK pathways were comparable in oxLDL-loaded Mϕs, yet the binding of p65/RelA (the prototypic NF-κB family member) was reduced at IL-6 and CCL5 promoters. This study revealed that oxLDL loading of Mϕs negatively regulates transcription at late stages of TLR-induced proinflammatory gene expression and implicates epigenetic mechanisms such as histone deacetylase activity.

Lactacystin-Induced Model of Hypertension in Rats: Effects of Melatonin and Captopril

Lactacystin is a proteasome inhibitor that interferes with several factors involved in heart remodelling. The aim of this study was to investigate whether the chronic administration of lactacystin induces hypertension and heart remodelling and whether these changes can be modified by captopril or melatonin. In addition, the lactacystin-model was compared with NG-nitro-l-arginine-methyl ester (L-NAME)- and continuous light-induced hypertension. Six groups of three-month-old male Wistar rats (11 per group) were treated for six weeks as follows: control (vehicle), L-NAME (40 mg/kg/day), continuous light (24 h/day), lactacystin (5 mg/kg/day) alone, and lactacystin with captopril (100 mg/kg/day), or melatonin (10 mg/kg/day). Lactacystin treatment increased systolic blood pressure (SBP) and induced fibrosis of the left ventricle (LV), as observed in L-NAME-hypertension and continuous light-hypertension. LV weight and the cross-sectional area of the aorta were increased only in L-NAME-induced hypertension. The level of oxidative load was preserved or reduced in all three models of hypertension. Nitric oxide synthase (NOS) activity in the LV and kidney was unchanged in the lactacystin group. Nuclear factor-kappa B (NF-κB) protein expression in the LV was increased in all treated groups in the cytoplasm, however, in neither group in the nucleus. Although melatonin had no effect on SBP, only this indolamine (but not captopril) reduced the concentration of insoluble and total collagen in the LV and stimulated the NO-pathway in the lactacystin group. We conclude that chronic administration of lactacystin represents a novel model of hypertension with collagenous rebuilding of the LV, convenient for testing antihypertensive drugs or agents exerting a cardiovascular benefit beyond blood pressure reduction.

Nuclear translocation of STAT3 and NF-κB are independent of each other but NF-κB supports expression and activation of STAT3

NF-κB and STAT3 are essential transcription factors in immunity and act at the interface of the transition from chronic inflammation to cancer. Different functional crosstalks between NF-κB and STAT3 have been recently described arguing for a direct interaction of both proteins. During a systematic analysis of NF-κB/STAT3 crosstalk we observed that appearance of the subcellular distribution of NF-κB and STAT3 in immunofluorescence heavily depends on the fixation procedure. Therefore, we established an optimized fixation protocol for the reliable simultaneous analysis of the subcellular distributions of both transcription factors. Using this protocol we found that cytokine-induced nuclear accumulation of NF-κB or STAT3 did not alter the subcellular distribution of the other transcription factor. Both knockout and overexpression of STAT3 does not have any major effect on canonical TNFα-NF-κB signalling in MEF or HeLa cells. Similarly, knockout of p65 did not alter nuclear accumulation of STAT3 in response to IL-6. However, p65 expression correlates with elevated total cellular levels of STAT3 and STAT1 and supports activation of these transcription factors. Our findings in MEF cells argue against a direct physical interaction of free cellular NF-κB and STAT3 but point to more intricate functional interactions.

Controls of Nuclear Factor-Kappa B Signaling Activity by 5'-AMP-Activated Protein Kinase Activation With Examples in Human Bladder Cancer Cells

Generally, both lipopolysaccharide (LPS)- and hypoxia-induced nuclear factor kappa B (NF-κB) effects are alleviated through differential posttranslational modification of NF-κB phosphorylation after pretreatment with 5´-AMP-activated protein kinase (AMPK) activators such as 5´-aminoimidazole-4-carboxamide ribonucleotide (AICAR) or the hypoglycemic agent metformin. We found that AICAR or metformin acts as a regulator of LPS/NF-κB-or hypoxia/NF-κB-mediated cyclooxygenase induction by an AMPK-dependent mechanism with interactions between p65-NF-κB phosphorylation and acetylation, including in a human bladder cancer cell line (T24). In summary, we highlighted the regulatory interactions of AMPK activity on NF-κB induction, particularly in posttranslational phosphorylation and acetylation of NF-κB under inflammatory conditions or hypoxia environment.

The Regulation of NF-κB Subunits by Phosphorylation

The NF-κB transcription factor is the master regulator of the inflammatory response and is essential for the homeostasis of the immune system. NF-κB regulates the transcription of genes that control inflammation, immune cell development, cell cycle, proliferation, and cell death. The fundamental role that NF-κB plays in key physiological processes makes it an important factor in determining health and disease. The importance of NF-κB in tissue homeostasis and immunity has frustrated therapeutic approaches aimed at inhibiting NF-κB activation. However, significant research efforts have revealed the crucial contribution of NF-κB phosphorylation to controlling NF-κB directed transactivation. Importantly, NF-κB phosphorylation controls transcription in a gene-specific manner, offering new opportunities to selectively target NF-κB for therapeutic benefit. This review will focus on the phosphorylation of the NF-κB subunits and the impact on NF-κB function.

The ubiquitin ligase HERC3 attenuates NF-κB-dependent transcription independently of its enzymatic activity by delivering the RelA subunit for degradation

Activation of NF-κB-dependent transcription represents an important hallmark of inflammation. While the acute inflammatory response is per se beneficial, it can become deleterious if its spatial and temporal profile is not tightly controlled. Classically, NF-κB activity is limited by cytoplasmic retention of the NF-κB dimer through binding to inhibitory IκB proteins. However, increasing evidence suggests that NF-κB activity can also be efficiently contained by direct ubiquitination of NF-κB subunits. Here, we identify the HECT-domain ubiquitin ligase HERC3 as novel negative regulator of NF-κB activity. We find that HERC3 restricts NF-κB nuclear import and DNA binding without affecting IκBα degradation. Instead HERC3 indirectly binds to the NF-κB RelA subunit after liberation from IκBα inhibitor leading to its ubiquitination and protein destabilization. Remarkably, the regulation of RelA activity by HERC3 is independent of its inherent ubiquitin ligase activity. Rather, we show that HERC3 and RelA are part of a multi-protein complex containing the proteasome as well as the ubiquitin-like protein ubiquilin-1 (UBQLN1). We present evidence that HERC3 and UBQLN1 provide a link between NF-κB RelA and the 26S proteasome, thereby facilitating RelA protein degradation. Our findings establish HERC3 as novel candidate regulating the inflammatory response initiated by NF-κB.

NF-kB as a key player in regulation of cellular radiation responses and identification of radiation countermeasures

Nuclear factor (NF)-κB is a transcription factor that plays significant role in immunity, cellular survival and inhibition of apoptosis, through the induction of genetic networks. Depending on the stimulus and the cell type, the members of NF-κB related family (RelA, c-Rel, RelB, p50, and p52), forms different combinations of homo and hetero-dimers. The activated complexes (Es) translocate into the nucleus and bind to the 10bp κB site of promoter region of target genes in stimulus specific manner. In response to radiation, NF-κB is known to reduce cell death by promoting the expression of anti-apoptotic proteins and activation of cellular antioxidant defense system. Constitutive activation of NF-κB associated genes in tumour cells are known to enhance radiation resistance, whereas deletion in mice results in hypersensitivity to IR-induced GI damage. NF-κB is also known to regulate the production of a wide variety of cytokines and chemokines, which contribute in enhancing cell proliferation and tissue regeneration in various organs, such as the GI crypts stem cells, bone marrow etc., following exposure to IR. Several other cytokines are also known to exert potent pro-inflammatory effects that may contribute to the increase of tissue damage following exposure to ionizing radiation. Till date there are a series of molecules or group of compounds that have been evaluated for their radio-protective potential, and very few have reached clinical trials. The failure or less success of identified agents in humans could be due to their reduced radiation protection efficacy. In this review we have considered activation of NF-κB as a potential marker in screening of radiation countermeasure agents (RCAs) and cellular radiation responses. Moreover, we have also focused on associated mechanisms of activation of NF-κB signaling and their specified family member activation with respect to stimuli. Furthermore, we have categorized their regulated gene expressions and their function in radiation response or modulation. In addition, we have discussed some recently developed radiation countermeasures in relation to NF-κB activation

PKCλ/ι signaling promotes triple-negative breast cancer growth and metastasis

Triple-negative breast cancer (TNBC) is a distinct breast cancer subtype defined by the absence of estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2/neu), and the patients with TNBC are often diagnosed with higher rates of recurrence and metastasis. Because of the absence of ER, PR and HER2/neu expressions, TNBC patients are insensitive to HER2-directed and endocrine therapies available for breast cancer treatment. Here, we report that expression of atypical protein kinase C isoform, PKCλ/ι, significantly increased and activated in all invasive breast cancer (invasive ductal carcinoma or IDC) subtypes including the TNBC subtype. Because of the lack of targeted therapies for TNBC, we choose to study PKCλ/ι signaling as a potential therapeutic target for TNBC. Our observations indicated that PKCλ/ι signaling is highly active during breast cancer invasive progression, and metastatic breast cancers, the advanced stages of breast cancer disease that developed more frequently in TNBC patients, are also characterized with high levels of PKCλ/ι expression and activation. Functional analysis in experimental mouse models revealed that depletion of PKCλ/ι significantly reduces TNBC growth as well as lung metastatic colonization. Furthermore, we have identified a PKCλ/ι-regulated gene signature consisting of 110 genes, which are significantly associated with indolent to invasive progression of human breast cancer and poor prognosis. Mechanistically, cytokines such as TGFβ and IL1β could activate PKCλ/ι signaling in TNBC cells and depletion of PKCλ/ι impairs NF-κB p65 (RelA) nuclear localization. We observed that cytokine-PKCλ/ι-RelA signaling axis, at least in part, involved in modulating gene expression to regulate invasion of TNBC cells. Overall, our results indicate that induction and activation of PKCλ/ι promote TNBC growth, invasion and metastasis. Thus, targeting PKCλ/ι signaling could be a therapeutic option for breast cancer, including the TNBC subtype.

Analysis of the RelA:CBP/p300 interaction reveals its involvement in NF-κB-driven transcription

NF-κB plays a vital role in cellular immune and inflammatory response, survival, and proliferation by regulating the transcription of various genes involved in these processes. To activate transcription, RelA (a prominent NF-κB family member) interacts with transcriptional co-activators like CREB-binding protein (CBP) and its paralog p300 in addition to its cognate κB sites on the promoter/enhancer regions of DNA. The RelA:CBP/p300 complex is comprised of two components--first, DNA binding domain of RelA interacts with the KIX domain of CBP/p300, and second, the transcriptional activation domain (TAD) of RelA binds to the TAZ1 domain of CBP/p300. A phosphorylation event of a well-conserved RelA(Ser276) is prerequisite for the former interaction to occur and is considered a decisive factor for the overall RelA:CBP/p300 interaction. The role of the latter interaction in the transcription of RelA-activated genes remains unclear. Here we provide the solution structure of the latter component of the RelA:CBP complex by NMR spectroscopy. The structure reveals the folding of RelA-TA2 (a section of TAD) upon binding to TAZ1 through its well-conserved hydrophobic sites in a series of grooves on the TAZ1 surface. The structural analysis coupled with the mechanistic studies by mutational and isothermal calorimetric analyses allowed the design of RelA-mutants that selectively abrogated the two distinct components of the RelA:CBP/p300 interaction. Detailed studies of these RelA mutants using cell-based techniques, mathematical modeling, and genome-wide gene expression analysis showed that a major set of the RelA-activated genes, larger than previously believed, is affected by this interaction. We further show how the RelA:CBP/p300 interaction controls the nuclear response of NF-κB through the negative feedback loop of NF-κB pathway. Additionally, chromatin analyses of RelA target gene promoters showed constitutive recruitment of CBP/p300, thus indicating a possible role of CBP/p300 in recruitment of RelA to its target promoter sites.

The complexity of NF-κB signaling in inflammation and cancer

The NF-κB family of transcription factors has an essential role in inflammation and innate immunity. Furthermore, NF-κB is increasingly recognized as a crucial player in many steps of cancer initiation and progression. During these latter processes NF-κB cooperates with multiple other signaling molecules and pathways. Prominent nodes of crosstalk are mediated by other transcription factors such as STAT3 and p53 or the ETS related gene ERG. These transcription factors either directly interact with NF-κB subunits or affect NF-κB target genes. Crosstalk can also occur through different kinases, such as GSK3-β, p38, or PI3K, which modulate NF-κB transcriptional activity or affect upstream signaling pathways. Other classes of molecules that act as nodes of crosstalk are reactive oxygen species and miRNAs. In this review, we provide an overview of the most relevant modes of crosstalk and cooperativity between NF-κB and other signaling molecules during inflammation and cancer.

Role of lysine methylation of NF-κB in differential gene regulation

Lysine methylation of the p65 subunit of nuclear factor κB (NF-κB) on K218 and K221 together or K37 alone strongly enhances gene expression in response to cytokines. We analyzed the effects of K-to-Q mutations in the REL homology domain of p65 on the response to IL-1β in 293 cells with low levels of p65. The K218/221Q mutation greatly reduced the expression of 39 of 82 genes, whereas the K37Q mutation reduced the expression of 23 different genes. Enhanced expression of the lysine demethylase FBXL11, which catalyzes the demethylation of K218 and K221 specifically, inhibited the expression of most of the genes that were inhibited by the DKQ mutation. CHIP-Seq analysis showed that the K218/221Q mutation greatly reduces the affinity of p65 for many promoters and that the K37Q mutation does not. Structural modeling showed that the newly introduced methyl groups of K218 and K221 interact directly with DNA to increase the affinity of p65 for specific κB sites. Thus, the K218/221Q and K37Q mutations have dramatically different effects because methylations of these residues affect different genes by distinct mechanisms.

Targeting nuclear factor-kappa B to overcome resistance to chemotherapy

Intrinsic or acquired resistance to chemotherapeutic agents is a common phenomenon and a major challenge in the treatment of cancer patients. Chemoresistance is defined by a complex network of factors including multi-drug resistance proteins, reduced cellular uptake of the drug, enhanced DNA repair, intracellular drug inactivation, and evasion of apoptosis. Pre-clinical models have demonstrated that many chemotherapy drugs, such as platinum-based agents, antracyclines, and taxanes, promote the activation of the NF-κB pathway. NF-κB is a key transcription factor, playing a role in the development and progression of cancer and chemoresistance through the activation of a multitude of mediators including anti-apoptotic genes. Consequently, NF-κB has emerged as a promising anti-cancer target. Here, we describe the role of NF-κB in cancer and in the development of resistance, particularly cisplatin. Additionally, the potential benefits and disadvantages of targeting NF-κB signaling by pharmacological intervention will be addressed.

Early inhibition of IL-1β expression by IFN-γ is mediated by impaired binding of NF-κB to the IL-1β promoter but is independent of nitric oxide

The significance of bacterial RNA recognition for initiating innate immune responses against invading pathogens has only recently started to be elucidated. Bacterial RNA is an important trigger of inflammasome activation, resulting in caspase-1-dependent cleavage of pro-IL-1β into the active form. It was reported previously that prolonged treatment with IFN-γ can inhibit IL-1β production at the level of both transcription and Nlrp3 inflammasome activation in an NO-dependent manner. As a result of the delayed kinetics of NO generation after IFN-γ stimulation, these effects were only observed at later time points. We report that IFN-γ suppressed bacterial RNA and LPS induced IL-1β transcription in primary murine macrophages and dendritic cells by an additional, very rapid mechanism that was independent of NO. Costimulation with IFN-γ selectively attenuated binding of NF-κB p65 to the IL-1β promoter, thus representing a novel mechanism of IL-1β inhibition by IFN-γ. Transcriptional silencing was specific for IL-1β because expression of other proinflammatory cytokines, such as TNF, IL-6, and IL-12p40, was not affected. Furthermore, by suppressing IL-1β production, IFN-γ impaired differentiation of Th17 cells and production of neutrophil chemotactic factor CXCL1 in vitro. The findings provide evidence for a rapid immune-modulating effect of IFN-γ independent of NO.

Differential phosphorylation of Smad1 integrates BMP and neurotrophin pathways through Erk/Dusp in axon development

Sensory axon development requires concerted actions of growth factors for the precise control of axonal outgrowth and target innervation. How developing sensory neurons integrate different cues is poorly understood. We demonstrate here that Smad1 activation is required for neurotrophin-mediated sensory axon growth in vitro and in vivo. Through differential phosphorylation, Smad1 exerts transcriptional selectivity to regulate the expression and activity of Erk1 and Erk2-two key neurotrophin effectors. Specifically, bone morphogenetic proteins (BMPs) signal through carboxy-terminal phosphorylation of Smad1 (pSmad1C) to induce Erk1/2 transcription for enhanced neurotrophin responsiveness. Meanwhile, neurotrophin signaling results in linker phosphorylation of Smad1 (pSmad1L), which in turn upregulates an Erk-specific dual-specificity phosphatase, Dusp6, leading to reduced pErk1/2 and constituting a negative-feedback loop for the prevention of axon overgrowth. Together, the BMP and neurotrophin pathways form a tightly regulated signaling network with a balanced ratio of Erk1/2 and pErk1/2 to direct the precise connections between sensory neurons and peripheral targets.

Parthenolide attenuates LPS-induced activation of NF-κB in a time-dependent manner in rat myocardium

Parthenolide (PTN), a selective nuclear factor kappa B (NF-κB) inhibitor, has been used extensively to inhibit NF-κB activation. The duration of the inhibitory effect of PTN on NF-κB in vivo remains unclear. This study was to determine whether a lipopolysaccharide (LPS) challenge 6, 12 and 24 h after the administration of PTN could activate NF-κB. Rats were devided into five groups. The rats in the PTN, PTN+LPS and DMSO groups were injected intraperitoneally with PTN or DMSO. After 6, 12 or 24 h, LPS was administered in LPS and PTN+LPS groups. The expressions of NF-κB p50, IκBα and p-IκBα were inhibited in both PTN and PTN+LPS group at end of 6 and 12 h and no effects at 24 h. In summary, myocardial NF-κB expression occurs 1 h after the administration of LPS. PTN blocks this effect given at 6 h and no inhibitory effect 24 h after administration in vivo.

DNA damage-induced cytotoxicity is mediated by the cooperative interaction of phospho-NF-κB p50 and a single nucleotide in the κB-site

Phosphorylation of the NF-κB subunit, p50, is necessary for cytotoxicity in response to DNA methylation damage. Here, we demonstrate that serine 329 phosphorylation regulates the interaction of p50 with specific NF-κB binding elements based on the identity of a single κB-site nucleotide. Specifically, S329 phosphorylation reduces the affinity of p50 for κB-sites that have a cytosine (C) at the -1 position without affecting binding to sequences with a -1 adenine. The differential interaction between phospho-p50 and the -1 base regulates the downstream transcriptional response and underlies the inhibition of anti-apoptotic gene expression following DNA damage. In genes with multiple κB-sites, the presence of a single -1C κB-site enables inhibition of NF-κB-dependent activity. The data suggest that interaction between phospho-p50 and the -1 κB nucleotide facilitates cytotoxicity in response to DNA damage. Moreover, although conservation of the entire κB-site sequence is not seen across species, the identity of the -1 nt in critical anti-apoptotic genes is conserved such that the overall response to DNA damage is maintained.

Site-specific phosphorylation of the p65 protein subunit mediates selective gene expression by differential NF-κB and RNA polymerase II promoter recruitment

Phosphorylation of NF-κB plays an important role in modulating transcriptional activity of NF-κB independently of inhibitor of κB (IκB) proteins. For the p65 subunit, multiple phosphorylation sites have been mapped in and adjacent to both the N-terminal Rel homology domain and the C-terminal transactivation domain. Their impact on NF-κB-dependent transcription, however, has never been assessed at a broader level. In this study, we evaluate the importance of differential p65 phosphorylation on four serine acceptor sites in the Rel homology domain for the expression of an array of NF-κB-dependent genes in endothelial cells. We find that inhibition of p65 phosphorylation on these serine residues targets NF-κB activity to distinctive gene subsets in a κB enhancer element-specific context. We show that the phosphorylation-dependent alterations in gene and protein expression are reflective of the amount of p65 and phosphorylated RNA polymerase II (p-RNAP II) bound to respective gene promoter regions. Depending on the gene subset, impaired gene expression was either a result of decreased p65 promoter recruitment or of a failure of bound p65 to recruit p-RNAP II. In conclusion, our findings demonstrate that site-specific p65 phosphorylation targets NF-κB activity to particular gene subsets on a global level by influencing p65 and p-RNAP II promoter recruitment.

Regulation of nuclear factor κB (NF-κB) transcriptional activity via p65 acetylation by the chaperonin containing TCP1 (CCT)

The NF-κB family member p65 is central to inflammation and immunity. The purpose of this study was to identify and characterize evolutionary conserved genes modulating p65 transcriptional activity. Using an RNAi screening approach, we identified chaperonin containing TCP1 subunit η (CCTη) as a regulator of Drosophila NF-κB proteins, Dorsal and Dorsal-related immunity factor (Dif). CCTη was also found to regulate NF-κB-driven transcription in mammalian cells, acting in a promoter-specific context, downstream of IκB kinase (IKK). CCTη knockdown repressed IκBα and CXCL2/MIP2 transcription during the early phase of NF-κB activation while impairing the termination of CCL5/RANTES and CXCL10/IP10 transcription. The latter effect was associated with increased DNA binding and reduced p65 acetylation, presumably by altering the activity of histone acetyltransferase CREB-binding protein (CBP). We identified p65 lysines (K) 122 and 123 as target residues mediating the CCTη-driven termination of NF-κB-dependent transcription. We propose that CCTη regulates NF-κB activity in a manner that resolves inflammation.

NF-κB and matrix-dependent regulation of osteopontin promoter activity in allylamine-activated vascular smooth muscle cells

Repeated cycles of oxidative injury by allylamine in vivo induce a proliferative rat vascular (aortic) smooth muscle cell (vSMC) phenotype characterized by matrix-dependent enhancement of mitogenic sensitivity, changes in cell surface integrin expression, and osteopontin (opn) overexpression. Here, we show that constitutive and mitogen-stimulated NF-κB DNA binding activity is enhanced in allylamine vSMCs. Matrix-specific changes in cellular Rel protein expression were observed in allylamine vSMCs. The NF-κB DNA binding element located at -1943 in the 5'-UTR strongly inhibited opn promoter activity in allylamine vSMCs, and this response was regulated by the extracellular matrix. Constitutive increases in opn promoter activity were only seen when allylamine cells were seeded on a fibronectin substrate, and this response was independent of the NF-κB DNA binding sequence within the regulatory region. Thus, NF-κB functions as a critical regulator of the allylamine-induced proliferative phenotype in vSMCs.

Monoubiquitination of nuclear RelA negatively regulates NF-κB activity independent of proteasomal degradation

Termination and resolution of inflammation are tightly linked to the inactivation of one of its strongest inducers, NF-κB. While canonical post-stimulus inactivation is achieved by upregulation of inhibitory molecules that relocate NF-κB complexes to the cytoplasm, termination of the NF-κB response can also be accomplished directly in the nucleus by posttranslational modifications, e.g., ubiquitination of the RelA subunit. Here we reveal a functional role for RelA monoubiquitination in regulating NF-κB activity. By employing serine-to-alanine mutants, we found that hypo-phosphorylated nuclear RelA is monoubiquitinated on multiple lysine residues. Ubiquitination was reversed by IκBα expression and was reduced when nuclear translocation was inhibited. RelA monoubiquitination decreased NF-κB transcriptional activity despite prolonged nuclear presence and independently of RelA degradation, possibly through decreased CREB-binding protein (CBP) co-activator binding. Polyubiquitin-triggered proteasomal degradation has been proposed as a model for RelA inactivation. However, here we show that proteasomal inhibition, similar to RelA hypo-phosphorylation, resulted in nuclear translocation and monoubiquitination of RelA. These findings indicate a degradation-independent mechanism for regulating the activity of nuclear RelA by ubiquitination.

The diverse and complex roles of NF-κB subunits in cancer

It is only recently that the full importance of nuclear factor-κB (NF-κB) signalling to cancer development has been understood. Although much attention has focused on the upstream pathways leading to NF-κB activation, it is now becoming clear that the inhibitor of NF-κB kinases (IKKs), which regulate NF-κB activation, have many independent functions in tissue homeostasis and normal immune function that could compromise the clinical utility of IKK inhibitors. Therefore, if the NF-κB pathway is to be properly exploited as a target for both anticancer and anti-inflammatory drugs, it is appropriate to reconsider the complex roles of the individual NF-κB subunits.

RelA Ser276 phosphorylation-coupled Lys310 acetylation controls transcriptional elongation of inflammatory cytokines in respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a negative-sense single-stranded RNA virus responsible for lower respiratory tract infections (LRTIs) in humans. In experimental models of RSV LRTI, the actions of the nuclear factor κB (NF-κB) transcription factor mediate inflammation and pathology. We have shown that RSV replication induces a mitogen-and-stress-related kinase 1 (MSK-1) pathway that activates NF-κB RelA transcriptional activity by a process involving serine phosphorylation at serine (Ser) residue 276. In this study, we examined the mechanism by which phospho-Ser276 RelA mediates expression of the NF-κB-dependent gene network. RelA-deficient mouse embryonic fibroblasts (MEFs) complemented with the RelA Ser276Ala mutant are deficient in CXCL2/Groβ, KC, and interleukin-6 (IL-6) expression, but NFKBIA/IκBα is preserved. We show that RSV-induced RelA Ser276 phosphorylation is required for acetylation at Lys310, an event required for transcriptional activity and stable association of RelA with the activated positive transcriptional elongation factor (PTEF-b) complex proteins, bromodomain 4 (Brd4), and cyclin-dependent kinase 9 (CDK9). In contrast to gene loading pattern of PTEF-b proteins produced by tumor necrosis factor (TNF) stimulation, RSV induces their initial clearance followed by partial reaccumulation coincident with RelA recruitment. The RSV-induced binding patterns of the CDK9 substrate, phospho-Ser2 RNA polymerase (Pol) II, follows a similar pattern of clearance and downstream gene reaccumulation. The functional role of CDK9 was examined using CDK9 small interfering RNA (siRNA) and CDK inhibitors, where RSV-induced NF-κB-dependent gene expression was significantly inhibited. Finally, although RSV induces a transition from short transcripts to fully spliced mRNA in wild-type RelA (RelA WT)-expressing cells, this transition is not seen in cells expressing RelA Ser276Ala. We conclude that RelA Ser276 phosphorylation mediates RelA acetylation, Brd4/CDK9 association, and activation of downstream inflammatory genes by transcriptional elongation in RSV infection.

Inhibitory effect of 10-hydroxy-trans-2-decenoic acid on LPS-induced IL-6 production via reducing IκB-ζ expression

The effect of 10-hydroxy-trans-2-decenoic acid (10H2DA), a major fatty acid component of royal jelly, was investigated on LPS-induced cytokine production in murine macrophage cell line, RAW264 cells. 10H2DA inhibited LPS-induced IL-6 production dose-dependently, but did not inhibit TNF-α production. 10H2DA inhibited LPS-induced NF-κB activation in a dose-dependent fashion. In addition, NF-κB activation induced by over-expression of either MyD88 or Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF) was also inhibited by 10H2DA. Degradation of IκB-α and phosphorylation of IκB kinase-α were not inhibited by 10H2DA. On the other hand, reduction of LPS-induced IκB-ζ expression was discovered. Production of lipocalin-2 and granulocyte colony-stimulating factor (G-CSF), which is dependent on IκB-ζ, was also inhibited by 10H2DA, whereas that of IκB-ζ-independent cytokines/chemokines, such as IFN-β, murine monocyte chemotactic protein-1 (JE), macrophage inflammatory protein (MIP)-1α and MIP-2, was not. Together, 10H2DA specifically inhibited LPS-induced IκB-ζ expression, followed by inhibition of IκB-ζ-dependent gene production. These results suggest that 10H2DA is one of the components of royal jelly to show anti-inflammatory effects and could be a therapeutic drug candidate for inflammatory and autoimmune diseases associated with IκB-ζ and IL-6 production.

Protective cross talk between activated protein C and TNF signaling in vascular endothelial cells: implication of EPCR, noncanonical NF-κB, and ERK1/2 MAP kinases

Activated protein C (APC) is a natural anticoagulant protease that displays cytoprotective and antiinflammatory activities and has been demonstrated to reduce mortality of patients with severe sepsis. However, APC signaling is not fully understood. This study further investigated the antiinflammatory effects of APC in vascular endothelial cells (EC) and examined the cross talk between APC and TNF signaling. Analysis of the regulatory mechanisms mediated by APC on vascular human EC shows that APC impairs TNF signaling by triggering a preemptive activation of intracellular pathways. We found that APC signaling causes a moderate but significant induction of cell adhesion molecules (CAMs) including VCAM-1 at mRNA and protein levels. Activation of the noncanonical NF-κB and ERK1/2 are both pivotal to APC signaling leading to VCAM-1 expression. APC upregulates TNF receptor-associated factor 2 (TRAF2) and phosphorylates NF-κB p65 at Ser276 and Ser536 independently of IκB degradation. The ultimate protective antiinflammatory effect of APC in response to TNF is associated with a sustained activation of ERK1/2 and Akt while phosphorylation of NF-κB p65 is precluded. Inhibitors of ERK (PD98059 and U0126) abolish the antiinflammatory signal mediated by APC. Blocking antibodies and silencing assays also suggest that, in EC, protease-activated receptor 1 and endothelial protein C receptor (EPCR) both conduct ERK activation and VCAM-1 induction in response to APC. To conclude, APC protects EC by attenuating CAM expression during inflammation. APC engages a regulatory cross talk involving EPCR, ERK, and NF-κB that impairs TNF signaling.

Nuclear factor kappa B and tumor necrosis factor-alpha modulation of transcription of the mouse testis- and pre-implantation development-specific Rnf33/Trim60 gene

We have previously reported a mouse Rnf33/Trim60 gene that is temporally expressed in the pre-implantation embryo. The Rnf33 structural gene is composed of a short noncoding exon 1 and an intronless coding exon 2. In the present work, Rnf33 was shown to be expressed in the mouse testis and in the testicular cell lines TM3 and TM4. To elucidate Rnf33 transcriptional modulation, a 2.5-kb Rnf33 sequence, inclusive of the upstream regulatory region, exon 1 and the associated intronic sequence, was dissected in transient transfection and luciferase assays. An initiator and an atypical TATA-box were shown to act as the core promoter elements of the gene. Deletion and mutagenesis of the 2.5-kb sequence in luciferase constructs further demonstrated that an intronic and palindromic kappa B (κB) sequence was an important cis element targeted by the nuclear factor-κB (NF-κB) subunits p65/RELA and p50/NFκB1, and also through modulation by tumor necrosis factor α. Transcriptional up-regulation of Rnf33 by NF-κB and tumor necrosis factor-α was directly demonstrated in TM3 and TM4 cells by real-time PCR quantification of the Rnf33 mRNA levels. Small interfering RNA knockdown of p65 and p50 confirmed Rnf33 down-regulation by p65/p50. Spermatogenesis is regulated by a wide range of stimuli, including NF-κB, which, in turn, is regulated by other signals. Hence, demonstration of NF-κB-regulated Rnf33 expression in testicular cells, particularly in Sertoli cells, implicates functional involvement of the putative RNF33 protein in spermatogenesis through association of the RNF33 protein with the microtubule via interaction with kinesin motor proteins, as previously demonstrated [Huang et al., submitted].

Specification of the NF-kappaB transcriptional response by p65 phosphorylation and TNF-induced nuclear translocation of IKK epsilon

Here we investigated the regulation of NF-κB activity by post-translational modifications upon reconstitution of NF-κB p65-deficient cells with the wild-type protein or phosphorylation-defect mutants. Analysis of NF-κB target gene expression showed that p65 phosphorylations alone or in combination function to direct transcription in a highly target gene-specific fashion, a finding discussed here as the NF-κB barcode hypothesis. High-resolution microscopy and surface rendering revealed serine 536 phosphorylated p65 predominantly in the cytosol, while serine 468 phosphorylated p65 mainly localized in nuclear speckles. TNF stimulation resulted in the translocation of the cytosolic p65 kinase IKKε to the nucleus and also to promyelocytic leukemia (PML) nuclear bodies. This inducible IKKε translocation was dependent on p65 phosphorylation and was prevented by the oncogenic PML-RARα fusion protein. Chromatin immunoprecipitation experiments revealed the inducible association of IKKε to the control regions of several NF-κB target genes. In the nucleus, the kinase contributes to the expression of a subset of NF-κB-regulated genes, thus revealing a novel role of IKKε for the control of nuclear NF-κB activity.

Posttranslational modifications of NF-kappaB: another layer of regulation for NF-kappaB signaling pathway

The eukaryotic transcription factor NF-kappaB regulates a wide range of host genes that control the inflammatory and immune responses, programmed cell death, cell proliferation and differentiation. The activation of NF-kappaB is tightly controlled both in the cytoplasm and in the nucleus. While the upstream cytoplasmic regulatory events for the activation of NF-kappaB are well studied, much less is known about the nuclear regulation of NF-kappaB. Emerging evidence suggests that NF-kappaB undergoes a variety of posttranslational modifications, and that these modifications play a key role in determining the duration and strength of NF-kappaB nuclear activity as well as its transcriptional output. Here we summarize the recent advances in our understanding of the posttranslational modifications of NF-kappaB, the interplay between the various modifications, and the physiological relevance of these modifications.

Mechanisms of cell protection by heme oxygenase-1

Heme oxygenases (HO) catabolize free heme, that is, iron (Fe) protoporphyrin (IX), into equimolar amounts of Fe(2+), carbon monoxide (CO), and biliverdin. The stress-responsive HO-1 isoenzyme affords protection against programmed cell death. The mechanism underlying this cytoprotective effect relies on the ability of HO-1 to catabolize free heme and prevent it from sensitizing cells to undergo programmed cell death. This cytoprotective effect inhibits the pathogenesis of a variety of immune-mediated inflammatory diseases.

Thr435 phosphorylation regulates RelA (p65) NF-kappaB subunit transactivation

Phosphorylation of the RelA (p65) NF-κB (nuclear factor κB) subunit has been previously shown to modulate its ability to induce or repress transcription. In the present study we have investigated the consequences of Thr⁴³⁵ phosphorylation within the C-terminal transactivation domain of RelA. We confirm that Thr⁴³⁵ is phosphorylated in cells and is induced by TNFα (tumour necrosis factor α) treatment. Mutational analysis of this site revealed gene-specific effects on transcription, with a T435D phosphomimetic mutant significantly enhancing Cxcl2 (CXC chemokine ligand 2) mRNA levels in reconstituted Rela^−/− mouse embryonic fibroblasts. Chromatin immunoprecipitation analysis revealed that this mutation results in enhanced levels of histone acetylation associated with decreased recruitment of HDAC1 (histone deacetylase 1). Moreover, mutation of this site disrupted RelA interaction with HDAC1 in vitro. Thr⁴³⁵ phosphorylation of promoter-bound RelA was also detected at NF-κB target genes following TNFα treatment in wild-type mouse embryonic fibroblasts. Phosphorylation at this site therefore provides an additional mechanism through which the specificity of NF-κB transcriptional activity can be modulated in cells.

MSK1 regulates the transcription of IL-1ra in response to TLR activation in macrophages

The activity of the pro-inflammatory cytokine IL (interleukin)-1 is closely regulated in vivo via a variety of mechanisms, including both the control of IL-1 production and secretion as well as naturally occurring inhibitors of IL-1 function, such as IL-1ra (IL-1 receptor antagonist). IL-1ra is homologous with IL-1, and is able to bind but not activate the IL-1 receptor. IL-1ra can be produced by a variety of cell types, and its production is stimulated by inflammatory signals. In the present study, we show that in macrophages the TLR (Toll-like receptor)-mediated induction of IL-1ra from both its proximal and distal promoters involves the p38 and ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPK (mitogen-activated protein kinase) cascades. In addition, we show that MSK1 and 2 (mitogen- and stress-activated kinase 1 and 2), kinases activated by either ERK1/2 or p38 in vivo, are required for the induction of both IL-1ra mRNA and protein. MSKs regulate IL-1ra transcription via both IL-10-dependent and -independent mechanisms in cells. Consistent with this, knockout of MSK in mice was found to result in a decrease in IL-1ra production following LPS (lipopolysaccharide) injection. MSKs therefore act as important negative regulators of inflammation following TLR activation.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Identification of a small molecule inhibitor of serine 276 phosphorylation of the p65 subunit of NF-kappaB using in silico molecular docking

NF-kappaB is activated in many types of cancer. Phosphorylation of p65 at serine 276 is required for the expression of a subset of NF-kappaB regulated genes, including vascular cell adhesion molecule-1 (VCAM-1) and interleukin-8 (IL-8). Thus, inhibition of serine 276 phosphorylation may prevent metastasis and angiogenesis in certain tumor types. Using in silico molecular docking, small molecules that are predicted to bind to a structural pocket near serine 276 were identified. One compound, NSC-127102, hinders serine 276 phosphorylation and the expression of IL-8 and VCAM-1. Small molecules such as NSC-127102 may be optimized for the future treatment of cancer.

Role of hydrogen peroxide in NF-kappaB activation: from inducer to modulator

Hydrogen peroxide (H2O2) has been implicated in the regulation of the transcription factor NF-kappaB, a key regulator of the inflammatory process and adaptive immunity. However, no consensus exists regarding the regulatory role played by H2O2. We discuss how the experimental methodologies used to expose cells to H2O2 produce inconsistent results that are difficult to compare, and how the steady-state titration with H2O2 emerges as an adequate tool to overcome these problems. The redox targets of H2O2 in the NF-kappaB pathway--from the membrane to the post-translational modifications in both NF-kappaB and histones in the nucleus--are described. We also review how H2O2 acts as a specific regulator at the level of the single gene, and briefly discuss the implications of this regulation for human health in the context of kappaB polymorphisms. In conclusion, after near 30 years of research, H2O2 emerges not as an inducer of NF-kappaB, but as an agent able to modulate the activation of the NF-kappaB pathway by other agents. This modulation is generic at the level of the whole pathway but specific at the level of the single gene. Therefore, H2O2 is a fine-tuning regulator of NF-kappaB-dependent processes, as exemplified by its dual regulation of inflammation.

Modulation of NF-kappaB-dependent gene expression by H2O2: a major role for a simple chemical process in a complex biological response

We recently observed that H2O2 regulates inflammation via upexpression of a few NF-kappaB-dependent genes, while leaving expression of most NF-kappaB-dependent genes unaltered. Here we test the hypothesis that this differential gene expression depends on the apparent affinity of kappaB sites in the gene-promoter regions toward NF-kappaB. Accordingly, cells were transfected with three reporter plasmids containing kappaB sequences with different affinities for NF-kappaB. It was observed that the lower the affinity, the higher the range of TNF-alpha concentrations where H2O2 upregulated gene expression. Mathematical models reproduced the key experimental observations indicating that H2O2 upregulation ceased when NF-kappaB fully occupied the kappaB sites. In vivo, it is predicted that genes with high-affinity sites remain insensitive to H2O2, whereas genes with lower-affinity sites are upregulated by H2O2. In conclusion, a simple chemical mechanism is at the root of a complex biologic process such as differential gene expression caused by H2O2.

Oxidized hemoglobin is an endogenous proinflammatory agonist that targets vascular endothelial cells

Several pathologic conditions are associated with hemolysis, i.e. release of ferrous (Fe(II)) hemoglobin from red blood cells. Oxidation of cell-free hemoglobin produces (Fe(III)) methemoglobin. More extensive oxidation produces (Fe(III)/Fe(IV) O) ferryl hemoglobin. Both cell-free methemoglobin and ferryl hemoglobin are thought to contribute to the pathogenesis of hemolytic disorders. We show hereby that ferryl hemoglobin, but not hemoglobin or methemoglobin, acts as a potent proinflammatory agonist that induces vascular endothelial cells in vitro to rearrange the actin cytoskeleton, forming intercellular gaps and disrupting the integrity of the endothelial cell monolayer. Furthermore, ferryl hemoglobin induces the expression of proinflammatory genes in endothelial cells in vitro, e.g. E-selectin, Icam-1, and Vcam-1, through the activation of the nuclear factor kappaB family of transcription factors. This proinflammatory effect, which requires actin polymerization, involves the activation of the c-Jun N-terminal kinase and the p38 mitogen-activated protein kinase signal transduction pathways. When administered to naïve mice, ferryl hemoglobin induces the recruitment of polymorphonuclear cells, demonstrating that it acts as a proinflammatory agonist in vivo. In conclusion, oxidized hemoglobin, i.e. ferryl hemoglobin, acts as a proinflammatory agonist that targets vascular endothelial cells.

Respiratory syncytial virus infection induces a reactive oxygen species-MSK1-phospho-Ser-276 RelA pathway required for cytokine expression

Respiratory syncytial virus (RSV) is a human pathogen that induces airway inflammation, at least in part, by modulating gene expression programs in airway epithelial cells. The presence of RSV replication is detected by the intracellular retinoic acid-inducible gene I (RIG-I) RNA helicase that forms a productive signaling complex with the mitochondrion-anchored MAVS protein, resulting in nuclear translocation of the NF-kappaB transcription factor. Although nuclear translocation is a prerequisite for activation of the innate inflammatory response, recent studies show that separate pathways governing RelA activation are also required for target gene expression. In this study, we examine the mechanism of RelA phosphorylation and its requirement for RSV-induced gene expression. RSV infection produced a time-dependent RelA phosphorylation on serine (Ser) residues Ser-276 and Ser-536 in parallel with enhanced reactive oxygen species (ROS) stress. Inhibition of RSV-induced ROS inhibited formation of phospho-Ser-276 RelA without affecting phospho-Ser-536 RelA formation. RSV potently induced activation of cytoplasmic mitogen- and stress-related kinase 1 (MSK1) in an ROS-dependent manner. Inhibition of MSK1 using H89 and small interfering RNA knockdown both reduced RSV-induced phospho-Ser-276 RelA formation and expression of a subset of NF-kappaB-dependent genes. Direct examination of the role of phospho-Ser-276 in target gene expression by expression of a RelA Ser-276-to-Ala site mutation in RelA(-/-) mouse embryonic fibroblasts showed that the mutation was unable to mediate RSV-induced NF-kappaB-dependent gene expression. We conclude that RSV induces RelA activation in the innate inflammatory response via a pathway separate from that controlling RelA cytoplasmic release, mediated by ROS signaling to cytoplasmic MSK1 activation and RelA Ser-276 phosphorylation.