Human T-cell lymphotropic virus type 1 tax induction of biologically Active NF-kappaB requires IkappaB kinase-1-mediated phosphorylation of RelA/p65

Increased H19/miR-675 Expression in Adult T-Cell Leukemia Is Associated with a Unique Notch Signature Pathway

The Notch pathway is a key cancer driver and is important in tumor progression. Early research suggested that Notch activity was highly dependent on the expression of the intracellular cleaved domain of Notch-1 (NICD). However, recent insights into Notch signaling reveal the presence of Notch pathway signatures, which may vary depending on different cancer types and tumor microenvironments. Herein, we perform a comprehensive investigation of the Notch signaling pathway in adult T-cell leukemia (ATL) primary patient samples. Using gene arrays, we demonstrate that the Notch pathway is constitutively activated in ATL patient samples. Furthermore, the activation of Notch in ATL cells remains elevated irrespective of the presence of activating mutations in Notch itself or its repressor, FBXW7, and that ATL cells are dependent upon Notch-1 expression for proliferation and survival. We demonstrate that ATL cells exhibit the expression of pivotal Notch-related genes, including notch-1, hes1, c-myc, H19, and hes4, thereby defining a critical Notch signature associated with ATL disease. Finally, we demonstrate that lncRNA H19 is highly expressed in ATL patient samples and ATL cells and contributes to Notch signaling activation. Collectively, our results shed further light on the Notch pathway in ATL leukemia and reveal new therapeutic approaches to inhibit Notch activation in ATL cells.

Plitidepsin as an Immunomodulator against Respiratory Viral Infections

Plitidepsin is a host-targeted compound known for inducing a strong anti-SARS-CoV-2 activity, as well as for having the capacity of reducing lung inflammation. Because IL-6 is one of the main cytokines involved in acute respiratory distress syndrome, the effect of plitidepsin in IL-6 secretion in different in vitro and in vivo experimental models was studied. A strong plitidepsin-mediated reduction of IL-6 was found in human monocyte-derived macrophages exposed to nonproductive SARS-CoV-2. In resiquimod (a ligand of TLR7/8)-stimulated THP1 human monocytes, plitidepsin-mediated reductions of IL-6 mRNA and IL-6 levels were also noticed. Additionally, although resiquimod-induced binding to DNA of NF-κB family members was unaffected by plitidepsin, a decrease in the regulated transcription by NF-κB (a key transcription factor involved in the inflammatory cascade) was observed. Furthermore, the phosphorylation of p65 that is required for full transcriptional NF-κB activity was significantly reduced by plitidepsin. Moreover, decreases of IL-6 levels and other proinflammatory cytokines were also seen in either SARS-CoV-2 or H1N1 influenza virus-infected mice, which were treated at low enough plitidepsin doses to not induce antiviral effects. In summary, plitidepsin is a promising therapeutic agent for the treatment of viral infections, not only because of its host-targeted antiviral effect, but also for its immunomodulatory effect, both of which were evidenced in vitro and in vivo by the decrease of proinflammatory cytokines.

JAK-STAT signalling shapes the NF-κB response in CLL towards venetoclax sensitivity or resistance via Bcl-XL

Preventing or overcoming resistance to the Bcl-2 inhibitor venetoclax is an emerging unmet clinical need in patients with chronic lymphocytic leukaemia (CLL). The upregulation of anti-apoptotic Bcl-2 members through signalling pathways within the tumor microenvironment appears as a major factor leading to resistance to venetoclax. Previously, we reported that T cells can drive resistance through CD40 and non-canonical NF-κB activation and subsequent Bcl-XL induction. Moreover, the T cell-derived cytokines IL-21 and IL-4 differentially affect Bcl-XL expression and sensitivity to venetoclax via unknown mechanisms. Here, we mechanistically dissected how Bcl-XL is regulated in the context of JAK-STAT signalling in primary CLL. First, we demonstrated a clear antagonistic role of IL-21/STAT3 signalling in the NF-κB-mediated expression of Bcl-XL, whereas IL-4/STAT6 further promoted the expression of Bcl-XL. In comparison, Bfl-1, another NF-κB target, was not differentially affected by either cytokine. Second, STAT3 and STAT6 affected Bcl-XL transcription by binding to its promoter without disrupting the DNA-binding activity of NF-κB. Third, in situ proximity ligation assays (isPLAs) indicated crosstalk between JAK-STAT signalling and NF-κB, in which STAT3 inhibited canonical NF-κB by accelerating nuclear export, and STAT6 promoted non-canonical NF-κB. Finally, NF-κB inducing kinase (NIK) inhibition interrupted the NF-κB/STAT crosstalk and resensitized CLL cells to venetoclax. In conclusion, we uncovered distinct crosstalk mechanisms that shape the NF-κB response in CLL towards venetoclax sensitivity or resistance via Bcl-XL, thereby revealing new potential therapeutic targets.

IKKα plays a major role in canonical NF-kB signalling in colorectal cells

Inhibitor of kappa B (IκB) kinase β (IKKβ) has long been viewed as the dominant IKK in the canonical nuclear factor-κB (NF-κB) signalling pathway, with IKKα being more important in non-canonical NF-κB activation. Here we have investigated the role of IKKα and IKKβ in canonical NF-κB activation in colorectal cells using CRISPR–Cas9 knock-out cell lines, siRNA and selective IKKβ inhibitors. IKKα and IKKβ were redundant for IκBα phosphorylation and turnover since loss of IKKα or IKKβ alone had little (SW620 cells) or no (HCT116 cells) effect. However, in HCT116 cells IKKα was the dominant IKK required for basal phosphorylation of p65 at S536, stimulated phosphorylation of p65 at S468, nuclear translocation of p65 and the NF-κB-dependent transcriptional response to both TNFα and IL-1α. In these cells, IKKβ was far less efficient at compensating for the loss of IKKα than IKKα was able to compensate for the loss of IKKβ. This was confirmed when siRNA was used to knock-down the non-targeted kinase in single KO cells. Critically, the selective IKKβ inhibitor BIX02514 confirmed these observations in WT cells and similar results were seen in SW620 cells. Notably, whilst IKKα loss strongly inhibited TNFα-dependent p65 nuclear translocation, IKKα and IKKβ contributed equally to c-Rel nuclear translocation indicating that different NF-κB subunits exhibit different dependencies on these IKKs. These results demonstrate a major role for IKKα in canonical NF-κB signalling in colorectal cells and may be relevant to efforts to design IKK inhibitors, which have focused largely on IKKβ to date.

3-(3-Hydroxyphenyl)propionic acid, a microbial metabolite of quercetin, inhibits monocyte binding to endothelial cells via modulating E-selectin expression

Adhesion of monocytes to endothelial cells is an important initiating step in atherogenesis. One of the most abundant flavonoids in the diet, quercetin has been reported to inhibit monocyte adhesion to endothelial cells. However, it is poorly absorbed in the upper gastrointestinal tract during oral intake but rather is metabolized by the intestinal microbiota into various phenolic acids. Since the biological properties of the microbial metabolites of quercetin remain largely unknown, herein, we investigated how the microbial metabolite of quercetin, 3-(3-hydroxyphenyl)propionic acid (3HPPA) impact monocyte adhesion to endothelial cells. Direct treatment with 3HPPA for 24 h was not cytotoxic to human aortic endothelial cells (HAECs). Cotreatment with 3HPPA inhibited tumor necrosis factor α (TNFα)-induced adhesion of THP-1 monocytes to HAECs, and suppressed the upregulation of cell adhesion molecule E-selectin but not intercellular adhesion molecule 1 or vascular cell adhesion molecule 1. Furthermore, 3HPPA was found to inhibit TNFα-induced nuclear translocation and phosphorylation of the p65 subunit of nuclear factor κB (NF-κB). We conclude that 3HPPA mitigates the adhesion of monocytes to endothelial cells by suppressing the expression of the cell adhesion molecule E-selectin in HAECs via inhibition of the NF-κB pathway, providing additional evidence for the health benefits of dietary flavonoids and their microbial metabolites as therapeutic agents in atherosclerosis.

Uric Acid Neuroprotection Associated to IL-6/STAT3 Signaling Pathway Activation in Rat Ischemic Stroke

Despite the promising neuroprotective effects of uric acid (UA) in acute ischemic stroke, the seemingly pleiotropic underlying mechanisms are not completely understood. Recent evidence points to transcription factors as UA targets. To gain insight into the UA mechanism of action, we investigated its effects on pertinent biomarkers for the most relevant features of ischemic stroke pathophysiology: (1) oxidative stress (antioxidant enzyme mRNAs and MDA), (2) neuroinflammation (cytokine and Socs3 mRNAs, STAT3, NF-κB p65, and reactive microglia), (3) brain swelling (Vegfa, Mmp9, and Timp1 mRNAs), and (4) apoptotic cell death (Bcl-2, Bax, caspase-3, and TUNEL-positive cells). Adult male Wistar rats underwent intraluminal filament transient middle cerebral artery occlusion (tMCAO) and received UA (16 mg/kg) or vehicle (Locke's buffer) i.v. at 20 min reperfusion. The outcome measures were neurofunctional deficit, infarct, and edema. UA treatment reduced cortical infarct and brain edema, as well as neurofunctional impairment. In brain cortex, increased UA: (1) reduced tMCAO-induced increases in Vegfa and Mmp9/Timp1 ratio expressions; (2) induced Sod2 and Cat expressions and reduced MDA levels; (3) induced Il6 expression, upregulated STAT3 and NF-κB p65 phosphorylation, induced Socs3 expression, and inhibited microglia activation; and (4) ameliorated the Bax/Bcl-2 ratio and induced a reduction in caspase-3 cleavage as well as in TUNEL-positive cell counts. In conclusion, the mechanism for morphological and functional neuroprotection by UA in ischemic stroke is multifaceted, since it is associated to activation of the IL-6/STAT3 pathway, attenuation of edematogenic VEGF-A/MMP-9 signaling, and modulation of relevant mediators of oxidative stress, neuroinflammation, and apoptotic cell death.

DING Protein Inhibits Transcription of HIV-1 Gene through Suppression of Phosphorylation of NF-κB p65

Introduction:

Novel plant DING proteins (full-length 38 kDa p38SJ, and 27 kDa p27SJ) exhibit phosphatase activity and modulate HIV-1 gene transcription. Previously, we demonstrated that DING regulates HIV-1 gene transcription by dephosphorylation and inactivation of CTD RNA polymerase II, the major elongating factor of HIV-1 Long Terminal Repeats (LTR). Because the transcription of HIV-1 is controlled by several viral and cellular factors, including p65/p50 subunits of NF-κB, we hypothesized that DING phosphatase can also affect the phosphorylation and activity of p65 NF-κB, in addition to C-terminal Domain (CTD) of RNA Polymerase II (RNAPII), to suppress HIV-1 gene transcription and inhibit HIV-1 infection.

Methods:

Here, we describe the inhibition of HIV-1 infection and the p65/p50 NF-κB phosphorylation by DING protein, analyzed by ELISA and northern-blot assays, western-blot assays, cell fractionation, and promoter-reporter assays in DING-expressing cells, using a pTet-on inducible system.

Results:

Results from HIV-1 infection assays demonstrate a strong inhibition of HIV-1 and HIV-LTR RNA expression by DING protein, determined by p24 ELISA and by northern blot assay. Results from the western blot assays and cell fractionation assays show that there is an increase in the level of hypo-phosphorylated form of p65 NF-κB in DING-expressing cells. Both fractions of p65/p50, nuclear or cytoplasmic, are affected by DING phosphatase, but more cytoplasmic accumulation of p65 NF-κB was found in the presence of DING, suggesting that subsequent activation and nuclear import of active NF-κB is affected by DING. The major portion of nuclear p65 was dephosphorylated in DING-expressing cells. The promoter-reporter assay demonstrated that DING-mediated dephosphorylation and dysregulation of NF-κB p65 lead to the suppression of its binding to HIV-1 LTR, and resulted in the inhibition of p65-mediated activation of LTR transcription. Mapping of the region within LTR that was affected by DING revealed that both, NF-κB and CTD RNA Polymerase II binding sites were important, and cooperativity of these cellular factors was diminished by DING. In addition, mapping of the region within DING-p38SJ that affected LTR transcription, revealed that phosphate-binding domain is essential for this inhibitory activity.

Conclusion:

We have demonstrated the effect of DING phosphatases on HIV-1 infection, phosphorylation of p65 NF-κB, and transcription of HIV-1 LTR. Our studies suggest that one possible mechanism by which DING can regulate the expression of HIV-1 LTR can be through dysregulation of the transcription factor NF-κB p65 by preventing its phosphorylation and translocation to the nucleus and binding to the HIV-1 LTR, an action that could contribute to the utility of DING p38SJ as an antiviral agent. Importantly, DING not only inhibits HIV-1 LTR gene transcription in the presence of increased p65 NF-κB, but also suppresses HIV-1 infection. DING protein improved inhibitory effects of the known anti-retroviral drugs, Tenofovir (TFV) and Emtricitabine (FTS) on HIV-1, since in the combination with these drugs; the suppression of HIV-1 by DNG was significantly higher when it was in combination with these drugs, compared to controls or cases without DING. Thus, our data support the use of neuroprotective DING proteins as novel therapeutic antiviral drugs that suppress HIV-1 LTR transcription by interfering with the function of NF-κB.

Upregulated expression and function of the α4β1 integrin in multiple myeloma cells resistant to bortezomib

The interaction of multiple myeloma (MM) cells with the bone marrow (BM) microenvironment promotes MM cell retention, survival, and resistance to different anti-MM agents, including proteasome inhibitors (PIs) such as bortezomib (BTZ). The α4β1 integrin is a main adhesion receptor mediating MM cell-stroma interactions and MM cell survival, and its expression and function are downregulated by BTZ, leading to inhibition of cell adhesion-mediated drug resistance (CAM-DR) and MM cell apoptosis. Whether decreased α4β1 expression and activity are maintained or recovered upon development of resistance to BTZ represents an important question, as a potential rescue of α4β1 function could boost MM cell survival and disease progression. Using BTZ-resistant MM cells, we found that they not only rescue their α4β1 expression, but its levels were higher than in parental cells. Increased α4β1 expression in resistant cells correlated with enhanced α4β1-mediated cell lodging in the BM, and with disease progression. BTZ-resistant MM cells displayed enhanced NF-κB pathway activation relative to parental counterparts, which contributed to upregulated α4 expression and to α4β1-dependent MM cell adhesion. These data emphasize the upregulation of α4β1 expression and function as a key event during resistance to BTZ in MM, which might indirectly contribute to stabilize this resistance, as stronger MM cell attachment to BM stroma will regain CAM-DR and MM cell growth and survival. Finally, we found a strong correlation between high ITGB1 (integrin β1) expression in MM and poor progression-free survival (PFS) and overall survival (OS) during treatment of MM patients with BTZ and IMIDs, and combination of high ITGB1 levels and presence of the high-risk genetic factor amp1q causes low PFS and OS. These results unravel a novel prognostic value for ITGB1 in myeloma. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Herpes Simplex Virus 1 UL2 Inhibits the TNF-α-Mediated NF-κB Activity by Interacting With p65/p50

Herpes simplex virus 1 (HSV-1) is a large double-stranded DNA virus that encodes at least 80 viral proteins, many of which are involved in the virus-host interaction and are beneficial to the viral survival and reproduction. However, the biological functions of some HSV-1-encoded proteins are not fully understood. Nuclear factor κB (NF-κB) activation is the major antiviral innate response, which can be triggered by various signals induced by cellular receptors from different pathways. Here, we demonstrated that HSV-1 UL2 protein could antagonize the tumor necrosis factor α (TNF-α)-mediated NF-κB activation. Co-immunoprecipitation assays showed that UL2 could interact with the NF-κB subunits p65 and p50, which also revealed the region of amino acids 9 to 17 of UL2 could suppress the NF-κB activation and interact with p65 and p50, and UL2 bound to the immunoglobulin-like plexin transcription factor functional domain of p65. However, UL2 did not affect the formation of p65/p50 dimerization and their nuclear localizations. Yet, UL2 was demonstrated to inhibit the NF-κB activity by attenuating TNF-α-induced p65 phosphorylation at Ser536 and therefore decreasing the expression of downstream inflammatory chemokine interleukin 8. Taken together, the attenuation of NF-κB activation by UL2 may contribute to the escape of host's antiviral innate immunity for HSV-1 during its infection.

The human T-cell leukemia virus type-1 tax oncoprotein dissociates NF-κB p65RelA-Stathmin complexes and causes catastrophic mitotic spindle damage and genomic instability

Genomic instability is a hallmark of many cancers; however, the molecular etiology of chromosomal dysregulation is not well understood. The human T-cell leukemia virus type-1 (HTLV-1) oncoprotein Tax activates NF-κB-signaling and induces DNA-damage and aberrant chromosomal segregation through diverse mechanisms which contribute to viral carcinogenesis. Intriguingly, Stathmin/oncoprotein-18 (Op-18) depolymerizes tubulin and interacts with the p65^RelA subunit and functions as a cofactor for NF-κB-dependent transactivation. We thus hypothesized that the dissociation of p65^RelA-Stathmin/Op-18 complexes by Tax could lead to the catastrophic destabilization of microtubule (MT) spindle fibers during mitosis and provide a novel mechanistic link between NF-κB-signaling and genomic instability. Here we report that the inhibition of Stathmin expression by the retroviral latency protein, p30^II, or knockdown with siRNA-stathmin, dampens Tax-mediated NF-κB transactivation and counters Tax-induced genomic instability and cytotoxicity. The Tax-G148V mutant, defective for NF-κB activation, exhibited reduced p65^RelA-Stathmin binding and diminished genomic instability and cytotoxicity. Dominant-negative inhibitors of NF-κB also prevented Tax-induced multinucleation and apoptosis. Moreover, cell clones containing the infectious HTLV-1 ACH. p30^II mutant provirus, impaired for p30^II production, exhibited increased multinucleation and the accumulation of cytoplasmic tubulin aggregates following nocodozole-treatment. These findings allude to a mechanism whereby NF-κB-signaling regulates tubulin dynamics and mitotic instability through the modulation of p65^RelA-Stathmin/Op-18 interactions, and support the notion that p30^II enhances the survival of Tax-expressing HTLV-1-transformed cells.

Inhibition of nuclear factor-κB p65 phosphorylation by 3,4-dihydroxybenzalacetone and caffeic acid phenethyl ester

3,4-Dihydroxybenzalacetone (DBL) and caffeic acid phenethyl ester (CAPE) are both catechol-containing phenylpropanoid derivatives with various bioactivities. In the present study, we compared the effects of these compounds and other phenylpropanoid derivatives on the activation of nuclear factor-κB (NF-κB) signaling, a major pathway in the inflammatory response, using RAW 264.7 cells. Lipopolysaccharide (LPS)- and interferon γ-induced production of nitrite was strongly suppressed by CAPE and, to a lesser extent, by DBL and caffeic acid ethyl ester. Consistent with these results, induction of NF-κB downstream genes, such as Nitric oxide synthase, interleukin 1 beta, and interleukin 6, and translocation of NF-κB p65 to the nucleus were reduced after LPS stimulation, to a greater extent with CAPE than with DBL. Interestingly, the phosphorylation of p65 was reduced by both compounds, especially by CAPE, even when the level of IκB was not altered. Furthermore, the thiol groups of p65 were modified by CAPE, and the inhibitory effects of CAPE and DBL on the p65 phosphorylation and nitrite production were reversed by pretreatment with thiol-containing reagents. These results suggest that CAPE has strong inhibitory effects on the NF-κB activation that are associated with the modification of thiol groups and phosphorylation of p65.

Triptolide suppresses growth and hormone secretion in murine pituitary corticotroph tumor cells via NF-kappaB signaling pathway

Triptolide is a principal diterpene triepoxide from the Chinese medical plant Tripterygium wilfordii Hook. f., whose extracts have been utilized in dealing with diverse diseases in traditional Chinese medicine for centuries. Recently, the antitumor effect of triptolide has been found in several pre-clinical neoplasm models, but its effect on pituitary corticotroph adenomas has not been investigated so far. In this study, we are aiming to figure out the antitumor effect of triptolide and address the underlying molecular mechanism in AtT20 murine corticotroph cell line. Our results demonstrated that triptolide inhibited cell viability and colony number of AtT20 cells in a dose- and time-dependent pattern. Triptolide also suppressed proopiomelanocortin (Pomc) mRNA expression and extracellular adrenocorticotropic hormone (ACTH) secretion in AtT20 cells. Flow cytometry prompted that triptolide leaded to G2/M phase arrest, apoptosis program and mitochondrial membrane depolarization in AtT20 cells. Moreover, dose-dependent activation of caspase-3 and decreased Bcl2/Bax proportion were observed after triptolide treatment. By western blot analysis we found that triptolide impeded phosphorylation of NF-κB p65 subunit and extracellular signal-regulated kinase (ERK), along with reduction of cyclin D1, without any impact on other NF-κB related protein expression like total p65, p50, IκB-α, p-IκB-α. Furthermore, the mouse xenograft model revealed the inhibition of tumor growth and hormone secretion after triptolide administration. Altogether this compound might be a potential pharmaceutical choice in managing Cushing's disease.

Crosstalk between signals initiated from TLR4 and cell surface BAFF results in synergistic induction of proinflammatory mediators in THP-1 cells

Cellular response to stimulation is mediated by meshwork of signaling pathways that may share common signaling adaptors. Here, we present data demonstrating that signaling pathways initiated from the membrane-bound form of B-cell activating factor (BAFF) can crosstalk with lipopolysaccharide (LPS)-induced signaling for synergistic expression of proinflammatory mediators in the human macrophage-like cell line THP-1. Co-treatment of the cells with BAFF-specific monoclonal antibody and LPS resulted in enhanced mitogen-activated protein kinase (MAPK)/mitogen- and stress-activated protein kinase (MSK)-mediated phosphorylation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 subunit (Ser276), which then interacts with CREB binding protein (CBP) for subsequent acetylation. Simultaneously, the phosphorylation of cyclic AMP-response element binding protein (CREB) was enhanced through the combined action of phosphatidylinositol-3-kinase (PI3K)/AKT and MAPK/MSK pathways, and the resulting phospho-CREB interacted with the NF-κB/CBP complex. Transfection of CREB-specific siRNA inhibited the BAFF-mediated enhancing effect indicating that the formation of the CREB/NF-κB/CBP complex is required for the synergistic induction of the proinflammatory genes. These findings indicate that BAFF-mediated reverse signaling can modulate LPS-induced inflammatory activation through regulation of NF-κB and CREB activity and point out the necessity to re-evaluate the role of BAFF in diseases where its expression is high in macrophages.

Protein Kinase R Mediates the Inflammatory Response Induced by Hyperosmotic Stress

High extracellular osmolarity results in a switch from an adaptive to an inflammatory gene expression program. We show that hyperosmotic stress activates the protein kinase R (PKR) independently of its RNA-binding domain. In turn, PKR stimulates nuclear accumulation of nuclear factor κB (NF-κB) p65 species phosphorylated at serine-536, which is paralleled by the induction of a subset of inflammatory NF-κB p65-responsive genes, including inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), and IL-1β. The PKR-mediated hyperinduction of iNOS decreases cell survival in mouse embryonic fibroblasts via mechanisms involving nitric oxide (NO) synthesis and posttranslational modification of proteins. Moreover, we demonstrate that the PKR inhibitor C16 ameliorates both iNOS amplification and disease-induced phenotypic breakdown of the intestinal epithelial barrier caused by an increase in extracellular osmolarity induced by dextran sodium sulfate (DSS) in vivo Collectively, these findings indicate that PKR activation is an essential part of the molecular switch from adaptation to inflammation in response to hyperosmotic stress.

Extracellular Hsp70 Enhances Mesoangioblast Migration via an Autocrine Signaling Pathway

Mouse mesoangioblasts are vessel-associated progenitor stem cells endowed with the ability of multipotent mesoderm differentiation. Therefore, they represent a promising tool in the regeneration of injured tissues. Several studies have demonstrated that homing of mesoangioblasts into blood and injured tissues are mainly controlled by cytokines/chemokines and other inflammatory factors. However, little is known about the molecular mechanisms regulating their ability to traverse the extracellular matrix (ECM). Here, we demonstrate that membrane vesicles released by mesoangioblasts contain Hsp70, and that the released Hsp70 is able to interact by an autocrine mechanism with Toll-like receptor 4 (TLR4) and CD91 to stimulate migration. We further demonstrate that Hsp70 has a positive role in regulating matrix metalloproteinase 2 (MMP2) and MMP9 expression and that MMP2 has a more pronounced effect on cell migration, as compared to MMP9. In addition, the analysis of the intracellular pathways implicated in Hsp70 regulated signal transduction showed the involvement of both PI3K/AKT and NF-κB. Taken together, our findings present a paradigm shift in our understanding of the molecular mechanisms that regulate mesoangioblast stem cells ability to traverse the extracellular matrix (ECM). J. Cell. Physiol. 232: 1845-1861, 2017. © 2016 Wiley Periodicals, Inc.

Triptolide Combined with Radiotherapy for the Treatment of Nasopharyngeal Carcinoma via NF-κB-Related Mechanism

Advanced nasopharyngeal carcinoma (NPC) has a poor prognosis because of the lack of an effective treatment. Here we explored the efficiency and the molecular mechanisms of combined treatment with triptolide and ionizing radiation for treating NPC. Human nasopharyngeal carcinoma (CNE) cells were treated with triptolide, ionizing radiation, or triptolide plus ionizing radiation in vitro. Tumor potency was examined in an in vivo CNE cell xenograft mouse model, which was treated as above. Our results demonstrated that triptolide caused a significant reduction in cell growth and colony number, and induced a marked apoptosis that was further enhanced with increasing doses of ionizing radiation. Combination treatment synergistically reduced tumor weight and volume without obvious toxicity. Western blot analysis in vitro and in vivo showed that triptolide induced apoptotic protein Bax expression and inhibited phosph-NF-κB p65, Bcl-2 and VEGF proteins without affecting other NF-κB related protein expression. In conclusion, our findings revealed that triptolide plus ionizing radiation had synergistic anti-tumor and anti-angiogenesis effects in NPC via down-regulating NF-κB p65 phosphorylation. The combination therapy may provide novel mechanism insights into inhibit NPC.

Myeloid-Specific Gene Deletion of Protein Phosphatase 2A Magnifies MyD88- and TRIF-Dependent Inflammation following Endotoxin Challenge

Protein phosphatase 2A (PP2A) is a member of the intracellular serine/threonine phosphatases. Innate immune cell activation triggered by pathogen-associated molecular patterns is mediated by various protein kinases, and PP2A plays a counter-regulatory role by deactivating these kinases. In this study, we generated a conditional knockout of the α isoform of the catalytic subunit of PP2A (PP2ACα). After crossing with myeloid-specific cre-expressing mice, effective gene knockout was achieved in various myeloid cells. The myeloid-specific knockout mice (lyM-PP2A^fl/fl) showed higher mortality in response to endotoxin challenge and bacterial infection. Upon LPS challenge, serum levels of TNF-α, KC, IL-6, and IL-10 were significantly increased in lyM-PP2A^fl/fl mice, and increased phosphorylation was observed in MAPK pathways (p38, ERK, JNK) and the NF-κB pathway (IKKα/β, NF-κB p65) in bone marrow-derived macrophages (BMDMs) from knockout mice. Heightened NF-κB activation was not associated with degradation of IκBα; instead, enhanced phosphorylation of the NF-κB p65 subunit and p38 phosphorylation-mediated TNF-α mRNA stabilization appear to contribute to the increased TNF-α expression. In addition, increased IL-10 expression appears to be due to PP2ACα-knockout-induced IKKα/β hyperactivation. Microarray experiments indicated that the Toll/IL-1R domain-containing adaptor inducing IFN-β/ TNFR-associated factor 3 pathway was highly upregulated in LPS-treated PP2ACα-knockout BMDMs, and knockout BMDMs had elevated IFN-α/β production compared with control BMDMs. Serum IFN-β levels from PP2ACα-knockout mice treated with LPS were also greater than those in controls. Thus, we demonstrate that PP2A plays an important role in regulating inflammation and survival in the setting of septic insult by targeting MyD88- and Toll/IL-1R domain-containing adaptor inducing IFN-β-dependent pathways.

Negative regulation of NF-κB p65 activity by serine 536 phosphorylation

Nuclear factor κB (NF-κB) is a master regulator of inflammation and cell death. Whereas most of the activity of NF-κB is regulated through the inhibitor of κB (IκB) kinase (IKK)-dependent degradation of IκB, IKK also phosphorylates subunits of NF-κB. We investigated the contribution of the phosphorylation of the NF-κB subunit p65 at the IKK phosphorylation site serine 536 (Ser(536)) in humans, which is thought to be required for the activation and nuclear translocation of NF-κB. Through experiments with knock-in mice (S534A mice) expressing a mutant p65 with an alanine-to-serine substitution at position 534 (the murine homolog of human Ser(536)), we observed increased expression of NF-κB-dependent genes after injection of mice with the inflammatory stimulus lipopolysaccharide (LPS) or exposure to gamma irradiation, and the enhanced gene expression was most pronounced at late time points. Compared to wild-type mice, S534A mice displayed increased mortality after injection with LPS. Increased NF-κB signaling in the S534A mice was at least in part explained by the increased stability of the S534A p65 protein compared to that of the Ser(534)-phosphorylated wild-type protein. Together, our results suggest that Ser(534) phosphorylation of p65 in mice (and, by extension, Ser(536) phosphorylation of human p65) is not required for its nuclear translocation, but instead inhibits NF-κB signaling to prevent deleterious inflammation.

Induction of ROS generation and NF-κB activation in MARC-145 cells by a novel porcine reproductive and respiratory syndrome virus in Southwest of China isolate

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is the cause of an economically important swine disease that has devastated the swine industry since the late 1980s. The aim of the present study was to investigate the interaction between reactive oxygen species (ROS) and NF-κB by PRRSV infection.

Results

We isolated the local strain of PRRSV from southwest China, designated YN-2011, then sequenced and analyzed the genome. YN-2011 was then used to evaluate the interaction of ROS and NF-κB. In PRRSV infected MARC-145 cells, there was a time-dependent increase in ROS and Maleic Dialdehyde (MDA). Accordingly, NF-κB activation was also increased as PRRSV infection progressed. Degradation of IκB mRNA was detected late in PRRSV infection, and overexpression of the dominant negative form of IκBα significantly suppressed NF-κB induced by PRRSV.

Conclusions

The results indicate that the generation of ROS is involved in PRRSV replication and this progression is associated with the alteration in NF-κB activity induced by ROS. These results should extend our better understanding the interaction between PRRSV and host MARC-145 cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0480-z) contains supplementary material, which is available to authorized users.

Strategies of oncogenic microbes to deal with WW domain-containing oxidoreductase

WW domain-containing oxidoreductase (WWOX) is a well-documented tumor suppressor protein that controls growth, survival, and metastasis of malignant cells. To counteract WWOX's suppressive effects, cancer cells have developed many strategies either to downregulate WWOX expression or to functionally inactivate WWOX. Relatively unknown is, in the context of those cancers associated with certain viruses or bacteria, how the oncogenic pathogens deal with WWOX. Here we review recent studies showing different strategies utilized by three cancer-associated pathogens. Helicobactor pylori reduces WWOX expression through promoter hypermethylation, an epigenetic mechanism also occurring in many other cancer cells. WWOX has a potential to block canonical NF-κB activation and tumorigenesis induced by Tax, an oncoprotein of human T-cell leukemia virus. Tax successfully overcomes the blockage by inhibiting WWOX expression through activation of the non-canonical NF-κB pathway. On the other hand, latent membrane protein 2A of Epstein-Barr virus physically interacts with WWOX and redirects its function to trigger a signaling pathway that upregulates matrix metalloproteinase 9 and cancer cell invasion. These reports may be just "the tip of the iceberg" regarding multiple interactions between WWOX and oncogenic microbes. Further studies in this direction should expand our understanding of infection-driven oncogenesis.

Lymphotoxin β receptor activation promotes bladder cancer in a nuclear factor-κB-dependent manner

Bladder cancer (BCa) is the most common tumor of the urinary system. Chronic inflammation in the papillary urothelial neoplasm of low malignant potential (PUNLMP)may contribute to carcinogenesis, including that of BCa, via poorly understood mechanisms. In this study, we show that the lymphotoxin β receptor (LTβR) is upregulated in BCa via activation of the canonical and non-canonical nuclear factor-κB (NF-κB) pathways. The mRNA expression of LTβR in 81 BCa, 10 chronic cystitis and 23 healthy bladder mucosa tissues was investigated by reverse transcription-fluorescent quantitative polymerase chain reaction (RT-FQ-PCR), and protein expression was studied in 73 BCa, 30 cystitis and 15 healthy paraffin-embedded tissue sections by immunohistochemistry. Both LTβR mRNA and protein were upregulated in BCa and cystitis compared to the healthy group (P<0.05). The mRNA level of the downstream NF-κB canonical pathway p65 gene and of the non-canonical pathway RelB gene were higher in the BCa and cystitis groups compared to the healthy one. The level of phosphorylated p65 (p-p65) protein of the canonical NF-κB pathway and that of p52, a protein of the non-canonical NF-κB pathway, were also higher in the BCa and cystitis group compared to the healthy group. The levels of these proteins significantly correlated to the pathological grade, clinical stage and lymph node metastasis of BCa patients (P<0.05). In addition, there was a positive correlation between LTβR and NF-κB pathway proteins. Thus, LTβR signaling may be involved in promoting BCa through the NF-κB pathway, and which may represent the molecular link between inflammation and BCa.

Regulation of HTLV-1 tax stability, cellular trafficking and NF-κB activation by the ubiquitin-proteasome pathway

Human T-cell leukemia virus type 1 (HTLV-1) is a complex retrovirus that infects CD4+ T cells and causes adult T-cell leukemia/lymphoma (ATLL) in 3%–5% of infected individuals after a long latent period. HTLV-1 Tax is a trans-activating protein that regulates viral gene expression and also modulates cellular signaling pathways to enhance T-cell proliferation and cell survival. The Tax oncoprotein promotes T-cell transformation, in part via constitutive activation of the NF-κB transcription factor; however, the underlying mechanisms remain unknown. Ubiquitination is a type of post-translational modification that occurs in a three-step enzymatic cascade mediated by E1, E2 and E3 enzymes and regulates protein stability as well as signal transduction, protein trafficking and the DNA damage response. Emerging studies indicate that Tax hijacks the ubiquitin machinery to activate ubiquitin-dependent kinases and downstream NF-κB signaling. Tax interacts with the E2 conjugating enzyme Ubc13 and is conjugated on C-terminal lysine residues with lysine 63-linked polyubiquitin chains. Tax K63-linked polyubiquitination may serve as a platform for signaling complexes since this modification is critical for interactions with NEMO and IKK. In addition to NF-κB signaling, mono- and polyubiquitination of Tax also regulate its subcellular trafficking and stability. Here, we review recent advances in the diverse roles of ubiquitin in Tax function and how Tax usurps the ubiquitin-proteasome pathway to promote oncogenesis.

The oncometabolite fumarate promotes pseudohypoxia through noncanonical activation of NF-κB signaling

Inactivating mutations of the gene encoding the tricarboxylic acid cycle enzyme fumarate hydratase (FH) have been linked to an aggressive variant of hereditary kidney cancer (hereditary leiomyomatosis and renal cell cancer). These tumors accumulate markedly elevated levels of fumarate. Fumarate is among a growing list of oncometabolites identified in cancers with mutations of genes involved in intermediary metabolism. FH-deficient tumors are notable for their pronounced accumulation of the transcription factor hypoxia inducible factor-1α (HIF-1α) and aggressive behavior. To date, HIF-1α accumulation in hereditary leiomyomatosis and renal cell cancer tumors is thought to result from fumarate-dependent inhibition of prolyl hydroxylases and subsequent evasion from von Hippel-Lindau-dependent degradation. Here, we demonstrate a novel mechanism by which fumarate promotes HIF-1α mRNA and protein accumulation independent of the von Hippel-Lindau pathway. Here we demonstrate that fumarate promotes p65 phosphorylation and p65 accumulation at the HIF-1α promoter through non-canonical signaling via the upstream Tank binding kinase 1 (TBK1). Consistent with these data, inhibition of the TBK1/p65 axis blocks HIF-1α accumulation in cellular models of FH loss and markedly reduces cell invasion of FH-deficient RCC cancer cells. Collectively, our data demonstrate a novel mechanism by which pseudohypoxia is promoted in FH-deficient tumors and identifies TBK1 as a novel putative therapeutic target for the treatment of aggressive fumarate-driven tumors.

Bromodomain and extraterminal (BET) protein inhibition suppresses human T cell leukemia virus 1 (HTLV-1) Tax protein-mediated tumorigenesis by inhibiting nuclear factor κB (NF-κB) signaling

The etiology of human T cell leukemia virus 1 (HTLV-1)-mediated adult T cell leukemia is associated with the ability of viral oncoprotein Tax to induce sustained NF-κB activation and the expression of many NF-κB target genes. Acetylation of the RelA subunit of NF-κB and the subsequent recruitment of bromodomain-containing factor Brd4 are important for the expression of NF-κB target genes in response to various stimuli. However, their contributions to Tax-mediated NF-κB target gene expression and tumorigenesis remain unclear. Here we report that Tax induced the acetylation of lysine 310 of RelA and the binding of Brd4 to acetylated RelA to facilitate Tax-mediated transcriptional activation of NF-κB. Depletion of Brd4 down-regulated Tax-mediated NF-κB target gene expression and cell proliferation. Inhibiting the interaction of Brd4 and acetylated RelA with the bromodomain extraterminal protein inhibitor JQ1 suppressed the proliferation of Tax-expressing rat fibroblasts and Tax-positive HTLV-1-infected cells and Tax-mediated cell transformation and tumorigenesis. Moreover, JQ1 attenuated the Tax-mediated transcriptional activation of NF-κB, triggering the polyubiquitination and proteasome-mediated degradation of constitutively active nuclear RelA. Our results identify Brd4 as a key regulator for Tax-mediated NF-κB gene expression and suggest that targeting epigenetic regulators such as Brd4 with the bromodomain extraterminal protein inhibitor might be a potential therapeutic strategy for cancers and other diseases associated with HTLV-1 infection.

Astrocyte elevated gene-1 is associated with metastasis in head and neck squamous cell carcinoma through p65 phosphorylation and upregulation of MMP1

Background

The survival rate of head and neck squamous cell carcinoma (HNSCC) at advanced stage is poor, despite contemporary advances in treatment modalities. Recent studies have indicated that astrocyte elevated gene-1 (AEG-1), a single transmembrane protein without any known functional domains, is overexpressed in various malignancies and is implicated in both distant metastasis and poor survival.

Results

High expression of AEG-1 in HNSCC was positively correlated with regional lymph node metastasis and a poor 5-year survival rate. Knockdown of AEG-1 in HNSCC cell lines reduced their capacity for colony formation, migration and invasion. Furthermore, decreased tumor volume and metastatic foci were observed after knockdown of AEG-1 in subcutaneous xenografts and pulmonary metastasis assays in vivo, respectively. We also demonstrated that AEG-1 increased phosphorylation of the p65 subunit of NF-κB, and regulated the expression of MMP1 in HNSCC cells. Moreover, compromised phosphorylation of the p65 (RelA) subunit of NF-κB at serine 536 was observed upon silencing of AEG-1 in both HNSCC cell lines and clinical specimens.

Conclusion

High expression of AEG-1 is associated with lymph node metastasis and its potentially associated mechanism is investigated.

NF-kappaB mediated transcriptional repression of acid modifying hormone gastrin

Helicobacter pylori is a major pathogen associated with the development of gastroduodenal diseases. It has been reported that H. pylori induced pro-inflammatory cytokine IL1B is one of the various modulators of acid secretion in the gut. Earlier we reported that IL1B-activated NFkB down-regulates gastrin, the major hormonal regulator of acid secretion. In this study, the probable pathway by which IL1B induces NFkB and affects gastrin expression has been elucidated. IL1B-treated AGS cells showed nine-fold activation of MyD88 followed by phosphorylation of TAK1 within 15 min of IL1B treatment. Furthermore, it was observed that activated TAK1 significantly up-regulates the NFkB subunits p50 and p65. Ectopic expression of NFkB p65 in AGS cells resulted in about nine-fold transcriptional repression of gastrin both in the presence and absence of IL1B. The S536A mutant of NFkB p65 is significantly less effective in repressing gastrin. These observations show that a functional NFkB p65 is important for IL1B-mediated repression of gastrin. ChIP assays revealed the presence of HDAC1 and NFkB p65 along with NCoR on the gastrin promoter. Thus, the study provides mechanistic insight into the IL1B-mediated gastrin repression via NFkB.

Acetylation at lysine 346 controls the transforming activity of the HTLV-1 Tax oncoprotein in the Rat-1 fibroblast model

BACKGROUND

Transformation by the Tax oncoprotein of the human T cell leukemia virus type 1 (HTLV-1) is governed by actions on cellular regulatory signals, including modulation of specific cellular gene expression via activation of signaling pathways, acceleration of cell cycle progression via stimulation of cyclin-dependent kinase activity leading to retinoblastoma protein (pRb) hyperphosphorylation and perturbation of survival signals. These actions control early steps in T cell transformation and development of Adult T cell leukemia (ATL), an aggressive malignancy of HTLV-1 infected T lymphocytes. Post-translational modifications of Tax by phosphorylation, ubiquitination, sumoylation and acetylation have been implicated in Tax-mediated activation of the NF-κB pathway, a key function associated with Tax transforming potential.

RESULTS

In this study, we demonstrate that acetylation at lysine K(346) in the carboxy-terminal domain of Tax is modulated in the Tax nuclear bodies by the acetyltransferase p300 and the deacetylases HDAC5/7 and controls phosphorylation of the tumor suppressor pRb by Tax-cyclin D3-CDK4-p21(CIP) complexes. This property correlates with the inability of the acetylation deficient K(346)R mutant, but not the acetylation mimetic K(346)Q mutant, to promote anchorage-independent growth of Rat-1 fibroblasts. By contrast, acetylation at lysine K(346) had no effects on the ability of Tax carboxy-terminal PDZ-binding domain to interact with the tumor suppressor hDLG.

CONCLUSIONS

The identification of the acetyltransferase p300 and the deacetylase HDAC7 as enzymes modulating Tax acetylation points to new therapeutic targets for the treatment of HTLV-1 infected patients at risk of developing ATL.

Bcl10 links saturated fat overnutrition with hepatocellular NF-kB activation and insulin resistance

Excess serum free fatty acids (FFAs) are fundamental to the pathogenesis of insulin resistance. With high-fat feeding, FFAs activate NF-kB in target tissues, initiating negative crosstalk with insulin signaling. However, the mechanisms underlying FFA-dependent NF-kB activation remain unclear. Here, we demonstrate that the saturated FA, palmitate, requires Bcl10 for NF-kB activation in hepatocytes. Uptake of palmitate, metabolism to diacylglycerol, and subsequent activation of protein kinase C (PKC) appear to mechanistically link palmitate with Bcl10, known as a central component of a signaling complex that, along with CARMA3 and MALT1, activates NF-kB downstream of selected cell surface receptors. Consequently, Bcl10-deficient mice are protected from hepatic NF-kB activation and insulin resistance following brief high-fat diet, suggesting that Bcl10 plays a major role in the metabolic consequences of acute overnutrition. Surprisingly, while CARMA3 also participates in the palmitate response, MALT1 is completely dispensable, thereby revealing an apparent nonclassical role for Bcl10 in NF-kB signaling.

Bcl-3 suppresses Tax-induced NF-κB activation through p65 nuclear translocation blockage in HTLV-1-infected cells

Human T cell leukemia virus type 1 (HTLV-1) Tax-induced persistent activation of the NF-κB pathway is perceived as the primary cause of adult T cell leukemia (ATL), an aggressive leukemia caused by HTLV-1. Although elevated oncoprotein Bcl-3 levels are found in many HTLV-1-infected T cell lines and ATL cells, the role of Bcl-3 in the malignant progression caused by HTLV-1 retrovirus remains poorly understood. We confirmed, in the present study, that the Tax-induced NF-κB activation involves the regulation of Bcl-3. Both knockdown and overexpression of Bcl-3 inhibit the Tax-induced NF-κB activation. Similarly, excessive Bcl-3 inhibits the NF-κB/DNA binding activity and significantly decreases Tax-induced p65 nuclear translocation. The present results demonstrate the pleiotropic roles of Bcl-3 in Tax-induced NF-κB activation and indicate that a balance in the aberrant Bcl-3 expression may be established to play an important role in the maintenance of proliferation and inhibition of apoptosis in HTLV-1-infected and ATL cells.

Modulation of eIF5A expression using SNS01 nanoparticles inhibits NF-κB activity and tumor growth in murine models of multiple myeloma

Despite recent advances in the first-line treatment of multiple myeloma, almost all patients eventually experience relapse with drug-resistant disease. New therapeutic modalities are needed, and to this end, SNS01, a therapeutic nanoparticle, is being investigated for treatment of multiple myeloma. The antitumoral activity of SNS01 is based upon modulation of eukaryotic translation initiation factor 5A (eIF5A), a highly conserved protein that is involved in many cellular processes including proliferation, apoptosis, differentiation and inflammation. eIF5A is regulated by post-translational hypusine modification, and overexpression of hypusination-resistant mutants of eIF5A induces apoptosis in many types of cancer cells. SNS01 is a polyethylenimine (PEI)-based nanoparticle that contains both a B-cell-specific expression plasmid expressing a non-hypusinable mutant of eIF5A and a small interfering RNA (siRNA) which depletes endogenous hypusinated eIF5A. Reducing hypusine-modified eIF5A levels was found to inhibit phosphorylation and activity of ERK MAPK and nuclear factor-κB (NF-κB), and thus sensitize myeloma cells to apoptosis resulting from transfection of a plasmid expressing eIF5A(K50R). SNS01 exhibited significant antitumoral activity in both KAS-6/1 (95% inhibition; P < 0.05) and RPMI 8226 (59% inhibition; P < 0.05) multiple myeloma xenograft models following systemic administration. These results highlight the potential of using this approach as a new therapeutic strategy for multiple myeloma.

HTLV-1 tax-induced rapid senescence is driven by the transcriptional activity of NF-κB and depends on chronically activated IKKα and p65/RelA

The HTLV-1 oncoprotein Tax is a potent activator of classical and alternative NF-κB pathways and is thought to promote cell proliferation and transformation via NF-κB activation. We showed recently that hyperactivation of NF-κB by Tax triggers a cellular senescence response (H. Zhi et al., PLoS Pathog. 7:e1002025, 2011). Inhibition of NF-κB activation by expression of I-κBα superrepressor or by small hairpin RNA (shRNA)-mediated knockdown of p65/RelA rescues cells from Tax-induced rapid senescence (Tax-IRS). Here we demonstrate that Tax-IRS is driven by the transcriptional activity of NF-κB. Knockdown of IKKγ, the primary Tax target, by shRNAs abrogated Tax-mediated activation of both classical and alternative NF-κB pathways and rendered knockdown cells resistant to Tax-IRS. Consistent with a critical role of IKKα in the transcriptional activity of NF-κB, IKKα deficiency drastically decreased NF-κB trans-activation by Tax, although it only modestly reduced Tax-mediated I-κBα degradation and NF-κB nuclear localization. In contrast, although IKKβ knockdown attenuated Tax-induced NF-κB transcriptional activation, the residual NF-κB activation in IKKβ-deficient cells was sufficient to trigger Tax-IRS. Importantly, the phenotypes of NIK and TAK1 knockdown were similar to those of IKKα and IKKβ knockdown, respectively. Finally, double knockdown of RelB and p100 had a minor effect on senescence induction by Tax. These data suggest that Tax, through its interaction with IKKγ, helps recruit NIK and TAK1 for IKKα and IKKβ activation, respectively. In the presence of Tax, the delineation between the classical and alternative NF-κB pathways becomes obscured. The senescence checkpoint triggered by Tax is driven by the transcriptional activity of NF-κB, which depends on activated IKKα and p65/RelA.

Dimethyl fumarate inhibits dendritic cell maturation via nuclear factor κB (NF-κB) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) and mitogen stress-activated kinase 1 (MSK1) signaling

Dimethyl fumarate (DMF) is an effective novel treatment for multiple sclerosis in clinical trials. A reduction of IFN-γ-producing CD4(+) T cells is observed in DMF-treated patients and may contribute to its clinical efficacy. However, the cellular and molecular mechanisms behind this clinical observation are unclear. In this study, we investigated the effects of DMF on dendritic cell (DC) maturation and subsequent DC-mediated T cell responses. We show that DMF inhibits DC maturation by reducing inflammatory cytokine production (IL-12 and IL-6) and the expression of MHC class II, CD80, and CD86. Importantly, this immature DC phenotype generated fewer activated T cells that were characterized by decreased IFN-γ and IL-17 production. Further molecular studies demonstrated that DMF impaired nuclear factor κB (NF-κB) signaling via reduced p65 nuclear translocalization and phosphorylation. NF-κB signaling was further decreased by DMF-mediated suppression of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and its downstream kinase mitogen stress-activated kinase 1 (MSK1). MSK1 suppression resulted in decreased p65 phosphorylation at serine 276 and reduced histone phosphorylation at serine 10. As a consequence, DMF appears to reduce p65 transcriptional activity both directly and indirectly by promoting a silent chromatin environment. Finally, treatment of DCs with the MSK1 inhibitor H89 partially mimicked the effects of DMF on the DC signaling pathway and impaired DC maturation. Taken together, these studies indicate that by suppression of both NF-κB and ERK1/2-MSK1 signaling, DMF inhibits maturation of DCs and subsequently Th1 and Th17 cell differentiation.

NF-κB, the first quarter-century: remarkable progress and outstanding questions

The ability to sense and adjust to the environment is crucial to life. For multicellular organisms, the ability to respond to external changes is essential not only for survival but also for normal development and physiology. Although signaling events can directly modify cellular function, typically signaling acts to alter transcriptional responses to generate both transient and sustained changes. Rapid, but transient, changes in gene expression are mediated by inducible transcription factors such as NF-κB. For the past 25 years, NF-κB has served as a paradigm for inducible transcription factors and has provided numerous insights into how signaling events influence gene expression and physiology. Since its discovery as a regulator of expression of the κ light chain gene in B cells, research on NF-κB continues to yield new insights into fundamental cellular processes. Advances in understanding the mechanisms that regulate NF-κB have been accompanied by progress in elucidating the biological significance of this transcription factor in various physiological processes. NF-κB likely plays the most prominent role in the development and function of the immune system and, not surprisingly, when dysregulated, contributes to the pathophysiology of inflammatory disease. As our appreciation of the fundamental role of inflammation in disease pathogenesis has increased, so too has the importance of NF-κB as a key regulatory molecule gained progressively greater significance. However, despite the tremendous progress that has been made in understanding the regulation of NF-κB, there is much that remains to be understood. In this review, we highlight both the progress that has been made and the fundamental questions that remain unanswered after 25 years of study.

Human T-cell lymphotropic virus: a model of NF-κB-associated tumorigenesis

Human T-cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma (ATL), whereas the highly related HTLV-2 is not associated with ATL or other cancers. In addition to ATL leukemogenesis, studies of the HTLV viruses also provide an exceptional model for understanding basic pathogenic mechanisms of virus-host interactions and human oncogenesis. Accumulating evidence suggests that the viral regulatory protein Tax and host inflammatory transcription factor NF-κB are largely responsible for the different pathogenic potentials of HTLV-1 and HTLV-2. Here, we discuss the molecular mechanisms of HTLV-1 oncogenic pathogenesis with a focus on the interplay between the Tax oncoprotein and NF-κB pro-oncogenic signaling. We also outline some of the most intriguing and outstanding questions in the fields of HTLV and NF-κB. Answers to those questions will greatly advance our understanding of ATL leukemogenesis and other NF-κB-associated tumorigenesis and will help us design personalized cancer therapies.

Human immunodeficiency virus-1 Tat activates NF-κB via physical interaction with IκB-α and p65

Nuclear factor (NF)-κB is a master regulator of pro-inflammatory genes and is upregulated in human immunodeficiency virus 1 (HIV-1) infection. Mechanisms underlying the NF-κB deregulation by HIV-1 are relevant for immune dysfunction in AIDS. We report that in single round HIV-1 infection, or single-pulse PMA stimulation, the HIV-1 Tat transactivator activated NF-κB by hijacking the inhibitor IκB-α and by preventing the repressor binding to the NF-κB complex. Moreover, Tat associated with the p65 subunit of NF-κB and increased the p65 DNA-binding affinity and transcriptional activity. The arginine- and cysteine-rich domains of Tat were required for IκB-α and p65 association, respectively, and for sustaining the NF-κB activity. Among an array of NF-κB-responsive genes, Tat mostly activated the MIP-1α expression in a p65-dependent manner, and bound to the MIP-1α NF-κB enhancer thus promoting the recruitment of p65 with displacement of IκB-α; similar findings were obtained for the NF-κB-responsive genes CSF3, LTA, NFKBIA and TLR2. Our results support a novel mechanism of NF-κB activation via physical interaction of Tat with IκB-α and p65, and may contribute to further insights into the deregulation of the inflammatory response by HIV-1.

Targeting HTLV-1 activation of NFκB in mouse models and ATLL patients

Of the millions of HTLV-1 infected carriers worldwide, 3-5% will develop an aggressive T-cell neoplasm that is highly refractory to conventional therapy. The virus carries the Tax oncogene which constitutively activates the NFκB pathway. This co-option of signaling through NFκB provides for the HTLV-1 infected cell an escape from cell cycle arrest and apoptosis, a steady source of growth factors, and a mechanism by which the virus can activate its own target cell. Therapies that target the NFκB pathway sensitize adult T-cell leukemia/lymphoma (ATLL) cells to apoptosis. A focus on translational interrogation of NFκB inhibitors in animal models and ATLL patients is needed to advance NFκB-targeted ATLL therapies to the bedside.

The tumor suppressor gene WWOX links the canonical and noncanonical NF-κB pathways in HTLV-I Tax-mediated tumorigenesis

Both the canonical and noncanonical nuclear factor κB (NF-κB) pathways have been linked to tumorigenesis. However, it remains unknown whether and how the 2 signaling pathways cooperate during tumorigenesis. We report that inhibition of the noncanonical NF-κB pathway significantly delays tumorigenesis mediated by the viral oncoprotein Tax. One function of noncanonical NF-κB activation was to repress expression of the WWOX tumor suppressor gene. Notably, WWOX specifically inhibited Tax-induced activation of the canonical, but not the noncanonical NF-κB pathway. Mechanistic studies indicated that WWOX blocked Tax-induced inhibitors of κB kinaseα (IKKα) recruitment to RelA and subsequent RelA phosphorylation at S536. In contrast, WWOX Y33R, a mutant unable to block the IKKα recruitment and RelA phosphorylation, lost the ability to inhibit Tax-mediated tumorigenesis. These data provide one important mechanism by which Tax coordinates the 2 NF-κB pathways for tumorigenesis. These data also suggest a novel role of WWOX in NF-κB regulation and viral tumorigenesis.

The transcription factor Erg inhibits vascular inflammation by repressing NF-kappaB activation and proinflammatory gene expression in endothelial cells

OBJECTIVE

To test whether ETS-related gene (Erg) inhibits tumor necrosis factor (TNF)-α-dependent endothelial activation and inflammation.

METHODS AND RESULTS

Endothelial activation underlies many vascular diseases, including atherosclerosis. Endothelial activation by proinflammatory cytokines decreases expression of the ETS transcription factor Erg. By using human umbilical vein endothelial cells (HUVECs), we showed that Erg overexpression by adenovirus (AdErg) repressed basal and TNF-α-induced expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule (VCAM), and interleukin 8 (IL-8). Erg inhibited TNF-α-dependent activation of the ICAM-1 promoter, nuclear factor (NF)-κB activity, and NF-κB p65 phosphorylation. Basal NF-κB activity was also inhibited by Erg overexpression. Chromatin immunoprecipitation showed that Erg binds to the ICAM-1 proximal promoter region, which contains 7 putative ETS binding sites. To test the anti-inflammatory role of Erg in vivo, we used a murine model of TNF-α-dependent acute inflammation. The injection of AdErg into the paw decreased TNF-α-induced inflammation compared with control. Finally, staining of human coronary plaques showed loss of Erg expression from the endothelium overlaying active plaque shoulders.

CONCLUSIONS

We have identified a novel physiological anti-inflammatory pathway under the control of the transcription factor Erg; this pathway inhibits NF-κB-dependent transcription and TNF-α-induced inflammation in vivo. These results suggest a novel approach to anti-inflammatory therapies.

Specification of DNA binding activity of NF-kappaB proteins

Nuclear factor-kappaB (NF-kappaB) is a pleiotropic mediator of inducible and specific gene regulation involving diverse biological activities including immune response, inflammation, cell proliferation, and death. The fine-tuning of the NF-kappaB DNA binding activity is essential for its fundamental function as a transcription factor. An increasing body of literature illustrates that this process can be elegantly and specifically controlled at multiple levels by different protein subsets. In particular, the recent identification of a non-Rel subunit of NF-kappaB itself provides a new way to understand the selective high-affinity DNA binding specificity of NF-kappaB conferred by a synergistic interaction within the whole complex. Here, we review the mechanism of the specification of DNA binding activity of NF-kappaB complexes, one of the most important aspects of NF-kappaB transcriptional control.

Gene-specific repression of proinflammatory cytokines in stimulated human macrophages by nuclear IκBα

We have previously shown that increased nuclear accumulation of IkappaBalpha inhibits NF-kappaB activity and induces apoptosis in human leukocytes. In this study, we wanted to explore the possibility that the nucleocytoplasmic distribution of IkappaBalpha can be used as a therapeutic target for the regulation of NF-kappaB-dependent cytokine synthesis. Treatment of LPS-stimulated human U937 macrophages with an inhibitor of chromosome region maintenance 1-dependent nuclear export, leptomycin B, resulted in the increased nuclear accumulation of IkappaBalpha and inhibition of NF-kappaB DNA binding activity, caused by the nuclear IkappaBalpha-p65 NF-kappaB interaction. Surprisingly, however, whereas mRNA expression and cellular release of TNF-alpha, the beta form of pro-IL-1 (IL-1beta), and IL-6 were inhibited by the leptomycin B-induced nuclear IkappaBalpha, IL-8 mRNA expression and cellular release were not significantly affected. Analysis of in vivo recruitment of p65 NF-kappaB to NF-kappaB-regulated promoters by chromatin immunoprecipitation in U937 cells and human PBMCs indicated that although the p65 recruitment to TNF-alpha, IL-1beta, and IL-6 promoters was inhibited by the nuclear IkappaBalpha, p65 recruitment to IL-8 promoter was not repressed. Chromatin immunoprecipitation analyses using IkappaBalpha and S536 phosphospecific p65 NF-kappaB Abs demonstrated that although the newly synthesized IkappaBalpha induced by postinduction repression is recruited to TNF-alpha, IL-1beta, and IL-6 promoters but not to the IL-8 promoter, S536-phosphorylated p65 is recruited to IL-8 promoter, but not to TNF-alpha, IL-1beta, or IL-6 promoters. Together, these data indicate that the inhibition of NF-kappaB-dependent transcription by nuclear IkappaBalpha in LPS-stimulated macrophages is gene specific and depends on the S536 phosphorylation status of the recruited p65 NF-kappaB.

Regulation of IkappaBalpha function and NF-kappaB signaling: AEBP1 is a novel proinflammatory mediator in macrophages

NF-κB comprises a family of transcription factors that are critically involved in various inflammatory processes. In this paper, the role of NF-κB in inflammation and atherosclerosis and the regulation of the NF-κB signaling pathway are summarized. The structure, function, and regulation of the NF-κB inhibitors, IκBα and IκBβ, are reviewed. The regulation of NF-κB activity by glucocorticoid receptor (GR) signaling and IκBα sumoylation is also discussed. This paper focuses on the recently reported regulatory function that adipocyte enhancer-binding protein 1 (AEBP1) exerts on NF-κB transcriptional activity in macrophages, in which AEBP1 manifests itself as a potent modulator of NF-κB via physical interaction with IκBα and a critical mediator of inflammation. Finally, we summarize the regulatory roles that recently identified IκBα-interacting proteins play in NF-κB signaling. Based on its proinflammatory roles in macrophages, AEBP1 is anticipated to serve as a therapeutic target towards the treatment of various inflammatory conditions and disorders.

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.

Bcl-10 protein highly correlates with the expression of phosphorylated p65 NF-kappaB in peripheral T-cell lymphomas and is associated with clinical outcome

AIMS

In T cells, protein kinase C (PKC) theta plays a major role in T-cell receptor (TCR)-mediated activation of a novel nuclear factor (NF)-kappaB pathway that involves phosphorylation of p65 at serine 536 (Pp65(Ser536)). Bcl-10 acts along the same pathway downstream of PKC theta to activate NF-kappaB. The aim was to investigate the relationship between the expression of PKC theta, Bcl-10 and P-p65(Ser536) proteins and their prognostic significance in peripheral T-cell lymphomas (PTCLs).

METHODS AND RESULTS

Paraffin-embedded tissues from 30 patients with PTCLs treated with curative intention were evaluated retrospectively. Expression of PKC theta, Bcl-10 and P-p65(Ser536) proteins was assessed using immunohistochemistry. Expression of PKC theta was detected in 22 of 30 cases (73%), Bcl-10 in 20 of 30 (67%) and P-p65(Ser536) in 21 of 30 (70%). Bcl-10+ tumours were associated with PKC theta (18 of 22) (P < 0.0001) and Pp65Ser536 (19 of 21) expression (P < 0.0001). Patients with Bcl-10+ or P-p65(Ser536+) tumours fared better, with a 5-year overall survival of 48 and 45%, respectively, versus 0% for negative tumours (P = 0.029 and P = 0.04, respectively).

CONCLUSIONS

Bcl-10 is expressed in PTCLs, correlates with PKC theta and Pp65(Ser536) expression and seems to be associated with better survival.

Nuclear factor kappa B signaling either stimulates or inhibits neurite growth depending on the phosphorylation status of p65/RelA

Nuclear factor kappaB (NF-kappaB) signaling is known to promote neurite growth from developing sensory neurons and to enhance the size and complexity of pyramidal neuron dendritic arbors in the developing cerebral cortex. In marked contrast, here we show that NF-kappaB signaling can also exert a potent inhibitory influence on neurite growth in certain neurons, and can either promote or inhibit neurite growth in the same neurons depending on the mechanism of NF-kappaB activation. In neonatal superior cervical ganglion sympathetic neurons, enhancing NF-kappaB transcriptional activity by overexpressing either the p65 NF-kappaB subunit or the IkappaB kinase-beta (IKKbeta) subunit of the IkappaB kinase complex, or by tumor necrosis factor alpha (TNFalpha) treatment, strongly inhibits neurite growth. Paradoxically in neonatal nodose ganglion sensory neurons, enhancing NF-kappaB transcriptional activity by p65/p50 overexpression increases neurite growth, whereas enhancing NF-kappaB transcriptional activity by IKKbeta overexpression inhibits neurite growth. In addition to activating NF-kappaB, IKKbeta overexpression leads to phosphorylation of p65 on serine 536. Blockade of serine 536 phosphorylation by a S536A-p65 mutant protein prevents the growth-inhibitory effects of IKKbeta overexpression in both sensory and sympathetic neurons and the growth-inhibitory effects of TNFalpha on sympathetic neurons. Furthermore, expression of a p65 S536D phosphomimetic mutant inhibits neurite growth from sensory neurons. These results demonstrate that NF-kappaB can either stimulate or inhibit neurite growth in developing neurons depending on the phosphorylation status of p65.