The adaptor protein FADD and the initiator caspase-8 mediate activation of NF-��B by TRAIL

Besides inducing apoptosis, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates NF-κB. The apoptosis signaling pathway of TRAIL is well characterized involving TRAIL receptors, Fas-associated protein with death domain (FADD) and caspase-8. In contrast, the molecular mechanism of TRAIL signaling to NF-κB remains controversial. Here, we characterized the receptor–proximal mediators of NF-κB activation by TRAIL. Deletion of the DD of TRAIL receptors 1 and 2 revealed that it is essential in NF-κB signaling. Because FADD interacts with the TRAIL receptor DD, FADD was tested. RNAi-mediated knockdown of FADD or FADD deficiency in JURKAT T-cell leukemia cells decreased or disabled NF-κB signaling by TRAIL. In contrast, TRAIL-induced activation of NF-κB was maintained upon loss of receptor interacting protein 1 (RIP1) or knockdown of FLICE-like inhibitory protein (FLIP). Exogenous expression of FADD rescued TRAIL-induced NF-κB signaling. Loss-of-function mutations of FADD within the RHDLL motif of the death effector domain, which is required for TRAIL-induced apoptosis, abrogated FADD''s ability to recruit caspase-8 and mediate NF-κB activation. Accordingly, deficiency of caspase-8 inhibited TRAIL-induced activation of NF-κB, which was rescued by wild-type caspase-8, but not by a catalytically inactive caspase-8 mutant. These data establish the mechanism of TRAIL-induced NF-κB activation involving the TRAIL receptor DD, FADD and caspase-8, but not RIP1 or FLIP. Our results show that signaling of TRAIL-induced apoptosis and NF-κB bifurcates downstream of caspase-8.     

The acetylation of RelA in Lys310 dictates the NF-��B-dependent response in post-ischemic injury

The activation of nuclear factor kappa B (NF-κB) p50/RelA is a key event in ischemic neuronal injury, as well as in brain ischemic tolerance. We tested whether epigenetic mechanisms affecting the acetylation state of RelA might discriminate between neuroprotective and neurotoxic activation of NF-κB during ischemia. NF-κB activation and RelA acetylation were investigated in cortices of mice subjected to preconditioning brain ischemia or lethal middle cerebral artery occlusion (MCAO) and primary cortical neurons exposed to preconditioning or lethal oxygen-glucose deprivation (OGD). In mice subjected to MCAO and in cortical neurons exposed to lethal OGD, activated RelA displayed a high level of Lys310 acetylation in spite of reduced total acetylation. Also, acetylated RelA on Lys310 interacted strongly with the CREB-binding protein (CBP). Conversely, RelA activated during preconditioning ischemia appeared deacetylated on Lys310. Overexpressing RelA increased Bim promoter activity and neuronal cell death both induced by lethal OGD, whereas overexpressing the acetylation-resistant RelA-K310R, carrying a mutation from Lys310 to arginine, prevented both responses. Pharmacological manipulation of Lys310 acetylation by the sirtuin 1 activator resveratrol repressed the activity of the Bim promoter and reduced the neuronal cell loss. We conclude that the acetylation of RelA in Lys310 dictates NF-κB-dependent pro-apoptotic responses and represents a suitable target to dissect pathological from neuroprotective NF-κB activation in brain ischemia.     

TNF-induced necroptosis in L929 cells is tightly regulated by multiple TNFR1 complex I and II members

TNF receptor 1 signaling induces NF-κB activation and necroptosis in L929 cells. We previously reported that cellular inhibitor of apoptosis protein-mediated receptor-interacting protein 1 (RIP1) ubiquitination acts as a cytoprotective mechanism, whereas knockdown of cylindromatosis, a RIP1-deubiquitinating enzyme, protects against tumor necrosis factor (TNF)-induced necroptosis. We report here that RIP1 is a crucial mediator of canonical NF-κB activation in L929 cells, therefore questioning the relative cytoprotective contribution of RIP1 ubiquitination versus canonical NF-κB activation. We found that attenuated NF-κB activation has no impact on TNF-induced necroptosis. However, we identified A20 and linear ubiquitin chain assembly complex as negative regulators of necroptosis. Unexpectedly, and in contrast to RIP3, we also found that knockdown of RIP1 did not block TNF cytotoxicity. Cell death typing revealed that RIP1-depleted cells switch from necroptotic to apoptotic death, indicating that RIP1 can also suppress apoptosis in L929 cells. Inversely, we observed that Fas-associated protein via a death domain, cellular FLICE inhibitory protein and caspase-8, which are all involved in the initiation of apoptosis, counteract necroptosis induction. Finally, we also report RIP1-independent but RIP3-mediated necroptosis in the context of TNF signaling in particular conditions.     

TRAIL promotes caspase-dependent pro-inflammatory responses via PKC�� activation by vascular smooth muscle cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is best known for its selective cytotoxicity against transformed tumor cells. Most non-transformed primary cells and several cancer cell lines are not only resistant to death receptor-induced apoptosis, but also subject to inflammatory responses in a nuclear factor-κB (NF-κB)-dependent manner. Although the involvement of TRAIL in a variety of vascular disorders has been proposed, the exact molecular mechanisms are unclear. Here, we aimed to delineate the role of TRAIL in inflammatory vascular response. We also sought possible molecular mechanisms to identify potential targets for the prevention and treatment of post-angioplastic restenosis and atherosclerosis. Treatment with TRAIL increased the expression of intercellular adhesion molecule-1 by primary human vascular smooth muscle cells via protein kinase C (PKC)δ and NF-κB activation. Following detailed analysis using various PKCδ mutants, we determined that PKCδ activation was mediated by caspase-dependent proteolysis. The protective role of PKCδ was further confirmed in post-traumatic vascular remodeling in vivo. We propose that the TRAIL/TRAIL receptor system has a critical role in the pathogenesis of inflammatory vascular disorders by transducing pro-inflammatory signals via caspase-mediated PKCδ cleavage and subsequent NF-κB activation.     

Adenosine 5′-monophosphate ameliorates D-galactosamine/lipopolysaccharide-induced liver injury through an adenosine receptor-independent mechanism in mice

D-galactosamine (GalN)/lipopolysaccharide (LPS)-induced lethality and acute liver failure is dependent on endogenously produced inflammatory cytokines. Adenosine has been proven to be a central role in the regulation of inflammatory response. It is not entirely clear that which adenosine action is actually crucial to limiting inflammatory tissue destruction. Here we showed that GalN/LPS challenge elevated hepatic adenosine and induced lethality in adenosine receptor-deficient mice with equal efficiency as wild-type mice. In GalN/LPS-treated mice, pretreatment with adenosine 5′-monophosphate (5′-AMP) significantly elevated hepatic adenosine level and reduced mortality through decreasing cytokine and chemokine production. In RAW264.7 cells, 5′-AMP treatment inhibited the production of inflammatory cytokines, which is not mediated through adenosine receptors. 5′-AMP failed to attenuate LPS-induced nuclear factor-κB (NF-κB) p65 nuclear translocation, but reduced LPS-induced recruitment of NF-κB p65 to inflammatory gene promoters and decreased LPS-induced enrichment of H3K4 dimethylation at the tumor necrosis factor-α (TNF-α) promoter, which was involved in 5′-AMP-induced elevation of cellular adenosine and a decline of methylation potential. In vitro biochemical analysis revealed that adenosine directly attenuated recruitment of NF-κB to the TNF-α and interleukin-6 promoters. Our findings demonstrate that 5′-AMP-inhibiting inflammatory response is not mediated by adenosine receptors and it may represent a potential protective agent for amelioration of LPS-induced liver injury.     

Enhanced susceptibility to lipopolysaccharide-induced arthritis and endotoxin shock in interleukin-32 alpha transgenic mice through induction of tumor necrosis factor alpha

Introduction

The present study assessed the potential functions of interleukin (IL)-32α on inflammatory arthritis and endotoxin shock models using IL-32α transgenic (Tg) mice. The potential signaling pathway for the IL-32-tumor necrosis factor (TNF)α axis was analyzed in vitro.

Methods

IL-32α Tg mice were generated under control of a ubiquitous promoter. Two disease models were used to examine in vivo effects of overexpressed IL-32α: Toll-like receptor (TLR) ligand-induced arthritis developed using a single injection of lipopolysaccharide (LPS) or zymosan into the knee joints; and endotoxin shock induced with intraperitoneal injection of LPS and D-galactosamine. TNFα antagonist etanercept was administered simultaneously with LPS in some mice. Using RAW264.7 cells, in vitro effects of exogenous IL-32α on TNFα, IL-6 or macrophage inflammatory protein 2 (MIP-2) production were assessed with or without inhibitors for nuclear factor kappa B (NFκB) or mitogen-activated protein kinase (MAPK).

Results

Single injection of LPS, but not zymosan, resulted in development of severe synovitis with substantial articular cartilage degradation in knees of the Tg mice. The expression of TNFα mRNA in inflamed synovia was highly upregulated in the LPS-injected Tg mice. Moreover, the Tg mice were more susceptive to endotoxin-induced lethality than the wild-type control mice 48 hours after LPS challenge; but blockade of TNFα by etanercept protected from endotoxin lethality. In cultured bone marrow cells derived from the Tg mice, overexpressed IL-32α accelerated production of TNFα upon stimulation with LPS. Of note, exogenously added IL-32α alone stimulated RAW264.7 cells to express TNFα, IL-6, and MIP-2 mRNAs. Particularly, IL-32α -induced TNFα, but not IL-6 or MIP-2, was inhibited by dehydroxymethylepoxyquinomicin (DHMEQ) and U0126, which are specific inhibitors of nuclear factor kappa B (NFκB) and extracellular signal regulated kinase1/2 (ERK1/2), respectively.

Conclusions

These results show that IL-32α contributed to the development of inflammatory arthritis and endotoxin lethality. Stimulation of TLR signaling with LPS appeared indispensable for activating the IL-32α-TNFα axis in vivo. However, IL-32α alone induced TNFα production in RAW264.7 cells through phosphorylation of inhibitor kappa B (IκB) and ERK1/2 MAPK. Further studies on the potential involvement of IL-32α-TNFα axis will be beneficial in better understanding the pathology of autoimmune-related arthritis and infectious immunity.     

SKLB023 Blocks Joint Inflammation and Cartilage Destruction in Arthritis Models via Suppression of Nuclear Factor-Kappa B Activation in Macrophage

Rheumatoid arthritis (RA) is the most common arthritis and is mainly characterized by symmetric polyarticular joint disorders. Our previous study demonstrated a novel small molecule compound (Z)-N-(3-Chlorophenyl)-2-(4-((2,4-dioxothiazolidin-5-ylidene) methyl) phenoxy) acet-amide (SKLB023) showed potently anti-arthritic effects in a rat arthritis model, however, the underlying mechanisms for this are largely unknown. Both NF-κB and macrophages were reported to play important roles in the pathologic processes of RA. The purposes of this study were to indicate whether NF-κB and macrophages contributed to anti-arthritic effects of SKLB023 in two experimental arthritis models. Our results showed that SKLB023 could significantly improve joint inflammation and cartilage destruction both in adjuvant induced arthritis (AIA) and collagen-induced arthritis (CIA) models. We further found that the binding activation of NF-κB to DNA in joint tissues and RAW264.7 macrophages were suppressed by SKLB023. SKLB023 also inhibited the NF-κB activity in peritoneal macrophages by luciferase assay. Furthermore, the number of macrophages in synovial tissues was decreased after the treatment of different doses of SKLB023. The levels of TNF-α, IL-1β, and IL-6 in plasma, and the levels of TNF-α, NO, and IL-1β in peritoneal macrophages were down-regulated by SKLB023. Finally, SKLB023 attenuated the expression of iNOS and COX-2 in vivo and suppressed the phosphorylations of components of the mitogen-activated protein kinases (MAPKs). These observations identify a novel function for SKLB023 as an inhibitor of NF-κB in macrophages of RA, highlighting that SKLB023 was a potential therapeutic strategy for RA.     

Minocycline selectively inhibits M1 polarization of microglia

Minocycline is commonly used to inhibit microglial activation. It is widely accepted that activated microglia exert dual functions, that is, pro-inflammatory (M1) and anti-inflammatory (M2) functions. The in vivo status of activated microglia is probably on a continuum between these two extreme states. However, the mechanisms regulating microglial polarity remain elusive. Here, we addressed this question focusing on minocycline. We used SOD1^G93A mice as a model, which exhibit the motor neuron-specific neurodegenerative disease, amyotrophic lateral sclerosis. Administration of minocycline attenuated the induction of the expression of M1 microglia markers during the progressive phase, whereas it did not affect the transient enhancement of expression of M2 microglia markers during the early pathogenesis phase. This selective inhibitory effect was confirmed using primary cultured microglia stimulated by lipopolysaccharide (LPS) or interleukin (IL)-4, which induced M1 or M2 polarization, respectively. Furthermore, minocycline inhibited the upregulation of NF-κB in the LPS-stimulated primary cultured microglia and in the spinal cord of SOD1^G93A mice. On the other hand, IL-4 did not induce upregulation of NF-κB. This study indicates that minocycline selectively inhibits the microglia polarization to a proinflammatory state, and provides a basis for understanding pathogeneses of many diseases accompanied by microglial activation.     

Gemcitabine/cannabinoid combination triggers autophagy in pancreatic cancer cells through a ROS-mediated mechanism

Gemcitabine (GEM, 2′,2′-difluorodeoxycytidine) is currently used in advanced pancreatic adenocarcinoma, with a response rate of < 20%. The purpose of our work was to improve GEM activity by addition of cannabinoids. Here, we show that GEM induces both cannabinoid receptor-1 (CB1) and cannabinoid receptor-2 (CB2) receptors by an NF-κB-dependent mechanism and that its association with cannabinoids synergistically inhibits pancreatic adenocarcinoma cell growth and increases reactive oxygen species (ROS) induced by single treatments. The antiproliferative synergism is prevented by the radical scavenger N-acetyl--cysteine and by the specific NF-κB inhibitor BAY 11-7085, demonstrating that the induction of ROS by GEM/cannabinoids and of NF-κB by GEM is required for this effect. In addition, we report that neither apoptotic nor cytostatic mechanisms are responsible for the synergistic cell growth inhibition, which is strictly associated with the enhancement of endoplasmic reticulum stress and autophagic cell death. Noteworthy, the antiproliferative synergism is stronger in GEM-resistant pancreatic cancer cell lines compared with GEM-sensitive pancreatic cancer cell lines. The combined treatment strongly inhibits growth of human pancreatic tumor cells xenografted in nude mice without apparent toxic effects. These findings support a key role of the ROS-dependent activation of an autophagic program in the synergistic growth inhibition induced by GEM/cannabinoid combination in human pancreatic cancer cells.     

Dynamic Imaging of Pancreatic Nuclear Factor κB (NF-κB) Activation in Live Mice Using Adeno-associated Virus (AAV) Infusion and Bioluminescence

Nuclear factor κB (NF-κB) is an important signaling molecule that plays a critical role in the development of acute pancreatitis. Current methods for examining NF-κB activation involve infection of an adenoviral NF-κB-luciferase reporter into cell lines or electrophoretic mobility shift assay of lysate. The use of adeno-associated viruses (AAVs) has proven to be an effective method of transfecting whole organs in live animals. We examined whether intrapancreatic duct infusion of AAV containing an NF-κB-luciferase reporter (AAV-NF-κB-luciferase) can reliably measure pancreatic NF-κB activation. We confirmed the infectivity of the AAV-NF-κB-luciferase reporter in HEK293 cells using a traditional luciferase readout. Mice were infused with AAV-NF-κB-luciferase 5 weeks before induction of pancreatitis (caerulein, 50 μg/kg). Unlike transgenic mice that globally express NF-κB-luciferase, AAV-infused mice showed a 15-fold increase in pancreas-specific NF-κB bioluminescence following 12 h of caerulein compared with baseline luminescence (p < 0.05). The specificity of the NF-κB-luciferase signal to the pancreas was confirmed by isolating the pancreas and adjacent organs and observing a predominant bioluminescent signal in the pancreas compared with liver, spleen, and stomach. A complementary mouse model of post-ERCP-pancreatitis also induced pancreatic NF-κB signals. Taken together these data provide the first demonstration that NF-κB activation can be examined in a live, dynamic fashion during pancreatic inflammation. We believe this technique offers a valuable tool to study real-time activation of NF-κB in vivo.     

The Preventive Effects of Lactobacillus casei on Acute Lung Injury Induced by Lipopolysaccharide

Lactobacillus has been reported to inhibit acute lung injury (ALI). However, the molecular mechanism of Lactobacillus casei (L. casei) in preventing ALI has not been identified, so we investigated whether L. casei pretreatment could inhibit the activation of TLR4/MyD88/NF-κB signaling pathway following ALI. ALI model was established by intraperitoneal injection of 2 mg/kg lipopolysaccharide (LPS) to female BALB/c mice. In L. casei LC2W group, mice were intragastrically administrated L. casei LC2W for a week, before the ALI modeling. The serum of normal BALB/c mice after intragastric administration of L. casei LC2W was used for in vitro cell assays. The serum was pre-incubated with mouse macrophage cell line (RAW264.7) and human lung cell line (HLF-A), then LPS was added to co-incubate. Compared with ALI model group, L. casei LC2W pretreatment significantly reduced lung pathological damage, the number of neutrophils and total cells in bronchoalveolar lavage fluid. Besides, L. casei LC2W pretreatment could significantly reverse the abnormal expression of ICAM-1, IL-6, TNF-α and IL-10 in lung tissue and serum, plus, L. casei LC2W significantly reduced the phosphorylation levels of IRAK-1 and NF-κB p65. In vitro, the serum decreased the up-regulation of IL-6 and TNF-α in cell lines induced by LPS. In conclusion, L. casei LC2W intragastric administration pretreatment could significantly improve LPS-induced ALI in mice, probably through circulation to reach the lungs so as to inhibit the inflammatory response induced by activation of TLR4/MyD88/NF-κB signaling pathway.     

Nuclear factor-κB modulates osteogenesis of periodontal ligament stem cells through competition with β-catenin signaling in inflammatory microenvironments

Inflammation can influence multipotency and self-renewal of mesenchymal stem cells (MSCs), resulting in their awakened bone-regeneration ability. Human periodontal ligament tissue-derived MSCs (PDLSCs) have been isolated, and their differentiation potential was found to be defective due to β-catenin signaling indirectly regulated by inflammatory microenvironments. Nuclear factor-κB (NF-κB) is well studied in inflammation by many different groups. The role of NF-κB needs to be studied in PDLSCs, although genetic evidences have recently shown that NF-κB inhibits osteoblastic bone formation in mice. However, the mechanism as to how inflammation leads to the modulation of β-catenin and NF-κB signaling remains unclear. In this study, we investigated β-catenin and NF-κB signaling through regulation of glycogen synthase kinase 3β activity (GSK-3β, which modulates β-catenin and NF-κB signaling) using a specific inhibitor LiCl and a phosphatidylinositol 3-kinase (PI3K) inhibitor LY 294002. We identified that NF-κB signaling might be more important for the regulation of osteogenesis in PDLSCs from periodontitis compared with β-catenin. BAY 11-7082 (an inhibitor of NF-κB) could inhibit phosphorylation of p65 and partly rescue the differentiation potential of PDLSCs in inflammation. Our data indicate that NF-κB has a central role in regulating osteogenic differentiation of PDLSCs in inflammatory microenvironments. Given the molecular mechanisms of NF-κB in osteogenic differentiation governed by inflammation, it can be said that NF-κB helps in improving stem cell-mediated inflammatory bone disease therapy.     

HSCARG downregulates NF-κB signaling by interacting with USP7 and inhibiting NEMO ubiquitination

Nuclear factor κB (NF-κB) signaling is a central pathway that participates in a variety of key processes, including immunity, inflammation, cell growth and differentiation. The activity of NF-κB is strictly regulated by a cluster of proteins, and modifications of these proteins either promote or suppress signal transduction at various steps. Here we demonstrated that HSCARG suppresses TNFα-stimulated NF-κB signaling under physiological conditions. We elucidated the detailed mechanism through which HSCARG inhibits NF-κB activation. HSCARG interacts with NEMO and suppresses polyubiquitination of NEMO by interacting with the deubiquitinase USP7. HSACRG attenuates its inhibitory effect on NEMO ubiquitination in USP7 knockdown cells, and inhibition of NEMO polyubiquitination by USP7 is impaired in HSCARG^−/− cells as well. Moreover, we demonstrated that USP7 is a negative regulator of TNFα-stimulated NF-κB activity. Altogether, our data indicate that HSCARG and USP7 function in concert in inhibiting polyubiquination of NEMO, thus inhibiting NF-κB activity.     

TLR4/NF-κB Signaling Contributes to Chronic Unpredictable Mild Stress-Induced Atherosclerosis in ApoE-/- Mice

Objective

Chronic stress is an important risk factor for atherosclerotic diseases. Our previous studies have shown that chronic unpredictable mild stress (CUMS) accelerates atherosclerosis and up-regulates TLR4/NF-κB expression in apoE^-/- mice. However, TLR4/NF-κB signaling whether directly contributes to the development of atherosclerosis in CUMS mice is unclear. We hypothesized that the interference of TLR4/NF-κB can ameliorate CUMS-induced inflammation and atherosclerosis in apoE^-/- mice.

Methods

ApoE^-/- mice were exposed to 12 weeks CUMS. Ad-siRNA TLR4 was given by tail vein injection (10 μl/mouse, every 5 days), and PDTC (an inhibitor of NF-κB) was given by intraperitoneal injection (60 mg/kg, once a day). Plasma corticosterone concentrations were determined by solid-phase ¹²⁵I radioimmunoassay. Atherosclerosis lesions in aortic sinuses were evaluated and quantified by IMAGEPRO PLUS. Western blotting was used to detect the expression of TLR4, NF-κB, and IL-1β in aortas of the mice. Plasma lipid profiles, IL-1β, TNF-α, and MCP-1 were measured by ELISA.

Results

Our results indicated that CUMS apoE^-/- mice treatment with siRNA TLR4 significantly decreased atherosclerosis and down-regulated TLR4, NF-κB, and inflammatory cytokines. PDTC also remarkably reduced atherosclerosis and the levels of IL-1β, TNF-α and MCP-1 in plasma. However, Treatment with siRNA TLR4 or PDTC had no effect on plasma corticosterone levels, and lipid profiles.

Conclusions

TLR4/NF-κB pathway may participate in CUMS-induced atherosclerosis through activation of proinflammatory cytokines in apoE^-/- mice. Our data may provide a new potential therapeutic target for prevention of CUMS -induced atherosclerosis.