Inhibition of nuclear factor κB and phosphatidylinositol 3‐kinase/Akt is essential for massive hepatocyte apoptosis induced by tumor necrosis factor α in mice

Background/aims: Tumor necrosis factor (TNF)‐α itself does not induce liver injury in normal mice or hepatocytes. Rather, this event, especially in vitro, is explained by the fact that the TNF‐α/TNF receptor system not only triggers downstream signals leading to apoptosis but also induces an antiapoptotic pathway through the activation of nuclear factor (NF)‐κB. The aim of this study was to determine whether inhibition of antiapoptotic pathways influences the susceptibility of mice to TNF‐α. Here, we focused on the roles of NF‐κB and phosphatidylinositol 3‐kinase (PI3K)‐regulated serine/threonine kinase Akt. Methods: TNF‐α was administered to BALB/c mice after treatment with an adenovirus expressing a mutant form IκBα (Ad5IκB), the PI3K inhibitor wortmannin, or both. Liver injury was assessed biochemically and histologically. The expression of Bcl‐2 family members and caspase activity were examined. Results: In the mice livers, treatment with Ad5IκB or the wortmannin suppressed the activation of NF‐κB or Akt, respectively. Suppression of either NF‐κB or Akt showed a slight increase in transaminase levels and focal liver cell death after TNF‐α administration. However, in mice treated with both Ad5IκB and wortmannin, TNF‐α administration resulted in massive hepatocyte apoptosis and hemorrhagic liver destruction in mice. The combination of Ad5IκB, wortmannin, and TNF‐α markedly increased the activation of caspase‐3 and ‐9, and activated caspase‐8 to a lesser degree, suggesting that TNF‐α‐induced hepatocyte apoptosis is dependent on type II cell death signaling pathway, probably through the mitochondria. Inhibition of the NF‐κB and PI3K/Akt pathways had no effect on expression of Bcl‐2 families. Conclusion: The inducible activation of NF‐κB and constitutive activation of Akt regulate hepatocyte survival against TNF‐α, which occurs independent of Bcl‐2 families.     

Melatonin attenuates TNF‐α and IL‐1β expression in synovial fibroblasts and diminishes cartilage degradation: Implications for the treatment of rheumatoid arthritis

The hormone melatonin has many properties, including antioxidant, anti‐inflammatory, and immunomodulatory effects. Melatonin has been demonstrated to be beneficial in several inflammatory autoimmune diseases, but its effects in rheumatoid arthritis (RA) remain controversial. We sought to determine how melatonin regulates inflammation in RA. We found that melatonin dose‐dependently inhibits tumor necrosis factor‐α (TNF‐α) and interleukin (IL)‐1β expression through the PI3K/AKT, ERK, and NF‐κB signaling pathways. We also identified that melatonin inhibits TNF‐α and IL‐1β production by upregulating miR‐3150a‐3p expression. Synovial tissue specimens from RA patients and culture of human rheumatoid fibroblast‐like synoviocytes confirmed that the MT1 receptor is needed for the anti‐inflammatory activities of melatonin. Importantly, melatonin also significantly reduced paw swelling, cartilage degradation, and bone erosion in the collagen‐induced arthritis mouse model. Our results indicate that melatonin ameliorates RA by inhibiting TNF‐α and IL‐1β production through downregulation of the PI3K/AKT, ERK, NF‐κB signaling pathways, as well as miR‐3150a‐3p overexpression. The role of melatonin as an adjuvant treatment in patients with RA deserves further clinical studies.     

Acute liver injury upregulates microRNA‐491–5p in mice,and its overexpression sensitizes Hep G2 cells for tumour necrosis factor‐α‐induced apoptosis

Background: MicroRNAs (miRNAs) have emerged as novel genetic regulators of cell functions such as proliferation, apoptosis and cancer. Aims: The aim of this study was to evaluate the role of a specific miRNA in modulating hepatic cell functions. Methods: C57Bl/6 mice were administered anti‐fas receptor antibodies to induce liver cell apoptosis. miRNAs were purified from the liver tissue and evaluated using an miRNA microarray. The role of miRNA‐491_5p, which was overexpressed in the model, in modulating hepatic cell functions was evaluated. miRNA‐491_5p was overexpressed in Hep G2 cells, followed by the addition of tumour necrosis factor (TNF)‐α, and induction of apoptosis as well as genes involved in apoptosis pathways were evaluated. The effect of miRNA‐491_5p target genes on apoptosis was also analysed by inhibiting their expression by siRNA‐induced gene silencing. Results: Upregulation of miRNA‐491_5p was found in a high‐dose anti‐fas receptor antibody group. Overexpression of microRNA‐491_5p sensitized Hep G2 cells for TNF‐α‐induced apoptosis, and also caused an inhibition of α‐fetoprotein, (AFP), heat shock protein‐90 (hsp‐90) and nuclear factor‐κB (NF‐κB). Overexpression of miRNA‐491_5p or inhibition of AFP and hsp‐90 resulted in an increased apoptosis in TNF‐α‐treated Hep G2 cells. Conclusions: One of the miRNAs that is associated with the acute liver injury mouse model, miRNA‐491_5p, sensitizes Hep G2 cells for TNF‐α‐induced apoptosis, at least in part, by inhibiting AFP, hsp‐90 and NF‐κB.     

Anti-inflammatory effects of moxifloxacin on rat airway smooth muscle cells exposed to allergen: Inhibition of extracellular-signal-regulated kinase and nuclear factor-κB activation and of interleukin-8 and eotaxin synthesis

Background and objective: Moxifloxacin (MXF) has been shown to possess immunomodulatory properties in addition to its antimicrobial effects. We investigated the effects of MXF on cytokine secretion and signal transduction mechanisms in naive control and allergen‐exposed airway smooth muscle cell (ASMC) stimulated with tumour necrosis factor (TNF)‐α. Methods: An animal model was established. ASMC was derived from rat airway tissue and cultured in vitro, then incubated with 10 ng/mL of TNF‐α. Interleukin (IL)‐8 and eotaxin secretion were measured by enzyme‐linked immunosorbent assay, and activation of extracellular‐signal‐regulated kinase (ERK)1/2 and nuclear factor (NF)‐κB p65 was measured by western blotting, with or without the addition of MXF (20 µg/mL) and/or dexamethasone (DXM) (10^?6 M). Results: Baseline IL‐8 and eotaxin secretion did not differ between control and allergen‐exposed cells. Stimulation with TNF‐α increased IL‐8 and eotaxin secretion, with increased IL‐8 secretion by allergen‐exposed compared with naive control ASMC, post‐TNF‐α stimulation (P = 0.001). Baseline phosphorylation of ERK1/2 (p‐ERK1/2) and NF‐κB p65 was higher in allergen‐exposed than in control ASMC. TNF‐α increased p‐ERK1/2 and NF‐κB p65 levels, with higher levels in allergen‐exposed ASMC, post‐TNF‐α stimulation (P < 0.001). MXF and the combination of MXF with DXM suppressed the secretion of IL‐8 and eotaxin, but DXM alone did not affect IL‐8, post‐TNF‐α stimulation (P > 0.05). MXF, DXM and the combination of MXF with DXM inhibited TNF‐α‐stimulated p‐ERK1/2 and NF‐κB p65 levels by 34, 40 and 62%, and 33, 38 and 64%, respectively. Conclusions: MXF suppressed the secretion of pro‐inflammatory cytokines by allergen‐exposed rat ASMC, partly by inhibiting NF‐κB and ERK activation. DXM may have additional or synergistic effects with MXF.     

Transforming growth factor‐α attenuates hepatic fibrosis: possible involvement of matrix metalloproteinase‐1

Background: The effect of transforming growth factor (TGF)‐α on fibrosis varies between cell types and the role of TGF‐α in hepatic fibrosis has not been fully elucidated. Methods: We examined the effect of TGF‐α on hepatic fibrosis using TGF‐α‐expressing transgenic mice fed a methionine‐ and choline‐deficient (MCD) diet and human hepatic stellate cells (HSCs) line LX‐2, rat and human primary HSCs. Results: Although the expression levels of the tissue inhibitor of metalloproteinases‐1 and α1(I) collagen mRNA were unchanged, feeding the TGF‐α transgenic mice the MCD diet resulted in greater expression of the murine functional analogue of matrix metalloproteinase‐1 (MMP‐1), MMP‐13 mRNA and protein and attenuated hepatic fibrosis compared with wild‐type mice. TGF‐α overexpression did not affect the extent of the steatosis, oxidative stress and hepatic inflammation in the MCD diet‐fed mice. The effect of TGF‐α on the fibrogenic and anti‐fibrogenic gene expressions varied between cell types in vitro. TGF‐α increased MMP‐1 mRNA expressions that were completely blocked by gefitinib in LX‐2 cells. The extracellular signal‐regulated kinase (ERK) 1/2, c‐Jun N‐terminal kinase and p38 pathways were involved in MMP‐1 mRNA expression in LX‐2 cells. Although TGF‐α increased the phosphorylation of p38, the p38 inhibitor activated the RAS‐ERK pathway and increased TGF‐α‐induced MMP‐1 mRNA expression, which suggested that there may be a crosstalk between the RAS‐ERK and the p38 pathways in LX‐2 cells. Conclusions: The TGF‐α may attenuate hepatic fibrosis in part because of upregulation of the expression of MMP‐1. The balance between fibrogenic and anti‐fibrogenic gene expression and between the activity of the RAS‐ERK and the p38 pathways may be crucial for the fibrotic process.     

Caspase activation during hepatocyte apoptosis induced by tumor necrosis factor‐α in galactosamine‐sensitized mice

Abstract: Background/Aims: To clarify the mechanism of hepatocyte apoptosis induced by tumor necrosis factor‐α (TNF‐α), caspase cascade and ceramide formation were investigated in the liver of D‐galactosamine (GalN)‐sensitized mice treated with TNF‐α. Methods: Seven‐week‐old male BALB/c mice were intraperitoneally injected with 20 mg GalN 30 min prior to the intravenous injection of recombinant mouse TNF‐α (0.5 μg/mouse). Cytochrome c release and processing of procaspases in the liver were analyzed by Western blotting. Activities of caspases were measured using chromogenic peptides as substrates. Ceramide content was determined using Escherichia coli diacylglycerol kinase. Results: Apoptosis of hepatocytes was observed in mice treated with both GalN and TNF‐α (GalN/TNF‐α), but not GalN or TNF‐α alone. Activation of caspases‐9 and ‐3, and cytochrome c release were observed only in liver from mice treated with GalN/TNF‐α. In a cell‐free system, processing of procaspases‐9 and ‐3, and cytochrome c release were observed in the postnuclear fraction of liver obtained from GalN/TNF‐α‐treated mice, but not in that from control mice. Processing of procaspase‐3 was inhibited by a caspase‐9 inhibitor, but not by inhibitor for caspase‐8 or ‐2. In a reconstitution assay system, procaspase‐9 processing occurred, when both cytosol and membrane fractions were obtained from the liver of mice treated with GalN/TNF‐α. Ceramide accumulation was observed only in apoptotic liver and preceded cytochrome c release and caspase activation. Conclusion: Cytochrome c release and caspase‐9 activation are required for the activation of executor caspase‐3 in TNF‐α‐induced hepatocyte apoptosis, but caspases‐8 and ‐2 play, if any, a minimal role. Ceramide may be implicated in this apoptotic process.     

Clinicopathological significance of nuclear factor‐κB activation in hepatocellular carcinoma

Aim: Nuclear factor‐κB (NF‐κB) is a critical signaling mediator in inflammation, apoptosis resistance and oncogenesis. It has been reported that NF‐κB is activated in several cancers, including hepatocellular carcinoma (HCC). Studies of genetic disruptions in mice also suggest that NF‐κB plays critical roles in hepatocarcinogenesis. The aim of the present study is to characterize NF‐κB activation and correlate it with the degree of malignancy in HCC. Methods: To examine the correlation between the positivity of the nuclear p50 subunit and HCC recurrence, we analyzed immunostaining of the NF‐κB p50 subunit in two groups of HCC samples with known prognosis and Akt phosphorylation status: 49 patients showing early recurrence within 6 months (group A) and 50 patients who were recurrence‐free for at least for 3 years (group B). Results: In group A, positive nuclear staining of p50 was shown in 18 cases (36.7%), whereas only one case (2.0%) in group B had positive nuclear staining of p50 (P = 2.48839 × 10^–5). This suggests a positive relationship between nuclear p50 and early recurrence and advanced HCC in humans. The presence of phosphorylated Akt correlated with nuclear staining of p50 in HCCs in group A (R² = 0.213, P < 0.001). Conclusion: Our results indicate that nuclear staining of p50 was clearly associated with early recurrent HCC, and the Akt pathway might play a role in NF‐κB activation in a subset of early recurrent HCC.     

Nuclear factor‐kappa B as a promising target for selenium chemoprevention in rat hepatocarcinogenesis

Background and Aims: Selenium's molecular mechanism for cancer chemoprevention remains unknown. We aimed to study the gene expression of nuclear factor‐κB (NF‐κB), tumor growth factor‐α (TGF‐α) and cyclin D1 and the effects of sodium selenite using preventive and therapeutic approaches in chemically‐induced hepatocarcinogenesis in rats. Methods: Rats were divided randomly into six groups: negative control, positive control (diethyl nitrosamine [DEN] + 2‐acetylaminofluorene [2‐AAF]), preventive group, preventive control (respective control for preventive group), therapeutic group and therapeutic control (respective control for therapeutic group). The relative gene expression of NF‐κB, TGF‐α and cyclin D1 in liver tissues were measured using real‐time polymerase chain reaction. Results: The findings showed that the gene expression of NF‐κB in the preventive group and its respective control was significantly lower (P < 0.05) when compared with both the negative and positive controls. However, the expression of NF‐κB in the positive controls and therapeutic group was significantly higher (P < 0.05) when compared with the negative controls. The expression of TGF‐α and cyclin D1 was insignificant in all groups. Conclusion: The inhibition of the NF‐κB pathway in the initiation phase of hepatocarcinogenesis could be a promising target for selenium chemoprevention. However, further studies are required.     

Steatosis correlates with hepatic expression of death receptors and activation of nuclear factor‐κB in chronic hepatitis C

Background: Steatosis is recognized as a predictor of the severity as well as the progression of fibrosis in chronic hepatitis C. The mechanisms that cause increased hepatocellular injury associated with steatosis remain largely unknown. Methods: We studied the correlation of hepatic expression of death receptors: Fas and tumour necrosis factor‐α receptor 1 (TNF‐R1), and downstream caspase (caspase‐3) with hepatic steatosis by immunohistochemical study in chronic hepatitis C and determined the role of nuclear factor‐κB (NF‐κB). Results: Ninety patients (49 males and 41 females, mean age of 50.5 ± 10.4 years, genotype 1 or 2) with chronic hepatitis C virus infection were recruited. The factors associated with steatosis grade were body mass index (P=0.004) and fibrosis stage (P=0.034). Moderate/severe steatosis was an independent variable associated with advanced fibrosis stage by stepwise logistic regression analysis. The expression of immunoreactivity for Fas, TNF‐R1 and active caspases‐3 in liver tissues was significantly correlated with the steatosis grade (P<0.001, P<0.001 and P<0.001 respectively). The extent of active caspases‐3 correlated significantly with the expression of Fas (r=0.659, P<0.001) and TNF‐R1 (r=0.617, P<0.001). NF‐κB p65 expression correlated significantly with the extent of Fas (r=0.405, P<0.001), TNF‐R1 (r=0.448, P=0.002) and active caspase‐3 (r=0.313, P=0.003), and correlated with steatosis grade (P<0.001) but not with inflammatory and fibrosis scores. Conclusion: Our observations suggest a mechanism whereby steatosis contributes to the progression of liver injury in chronic hepatitis C through upregulation of death receptors and activation of NF‐κB.     

Tumour necrosis factor‐α promoter region polymorphisms affect the course of spontaneous HBsAg clearance

Background: This study aimed to investigate the roles of tumour necrosis factor‐α (TNF‐α) gene polymorphisms in the spontaneous clearance of HBsAg after a hepatitis B virus (HBV) infection. Methods: Polymorphisms in the TNF‐α (?1031 T to C, ?863 C to A, ?857 C to T, ?308 G to A and ?238 G to A transition) gene were evaluated in 274 chronic HBV‐infected patients and 194 patients with resolved HBV infection. The peripheral blood mononuclear cells (PBMC) isolated from 77 (28%) of the 274 chronic HBV‐infected patients with negative HBeAg and positive antibody to HBeAg were stimulated with HBcAg. Data on TNF‐α genotypes and phenotypes in subjects with/without the A allele at the TNF‐α?863 promoter single nucleotide polymorphism (rs1800630) were compared. Results: The A allele in the ?863 promoter region of the TNF‐α gene was present in 154 (56.2%) chronic HBV‐infected patients and 87 (44.8%) patients who recovered from HBV infection (odds ratio 1.58; P<0.01). The TNF‐α?863 A allele genotype predicted lower TNF‐α production by PBMC after in vitro HBcAg stimulation (P<0.02). Conclusions: The A allele at the ?863 locus of the promoter region of the TNF‐α gene predicts lower HBcAg‐inducible TNF‐α secretion. It is also associated with chronicity of HBV infection.     

Increased apoptosis in HepG2.2.15 cells with hepatitis B virus expression by synergistic induction of interferon‐γ and tumour necrosis factor‐α

Background: Interferon‐γ (IFN‐γ) and tumour necrosis factor‐α (TNF‐α) were thought to be important immune mediators in host defence against hepatitis B virus (HBV) infection. Aims: To examine the synergistic effect of IFN‐γ and TNF‐α on HBV‐expressing HepG2.2.15 cells and its potential mechanisms. Methods: Cell viability was quantitatively measured by 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyl tetrazolium bromide assay. Cell morphology was captured using light microscopy. The typical DNA ladder test was performed using agarose gel electrophoresis. HBsAg and HBeAg titre changes were quantified by the enzyme‐linked immunosorbent assay method. Gene expression was analysed using cDNA macroarrays. Results: Interferon‐γ (1000 U/ml) alone or combined with TNF‐α (5 ng/ml) treatment resulted in apoptosis in HepG2.2.15 cells, but no significant apoptosis in the parent non‐virus expressing HepG2 cells. IFN‐γ‐ and TNF‐α‐mediated apoptosis was reduced by lamivudine treatment in HepG2.2.15 cells. IFN‐γ combined with TNF‐α reduced the titre of hepatitis B surface antigen and hepatitis B e antigen in the HepG2.2.15 cell line. For apoptosis‐related gene changes, IFN regulatory factor 1 (IRF‐1) (12.2‐fold), c‐myc (V00568 4.7‐fold, L00058 2.4‐fold) and caspase 7 (2.3‐fold) genes were upregulated in the combination treatment group. Conclusion: Interferon‐γ and TNF‐α play a role in the cell death of HBV‐expressing HepG2.2.15 cells. Expression of HBV leads to IFN‐γ‐ and TNF‐α‐mediated apoptosis in the cells. Increased IRF‐1, c‐myc and caspase 7 gene expression may be responsible for the synergistic induction of apoptosis by IFN‐γ and TNF‐α.     

Effects of gut barrier dysfunction and NF‐κB activation on aggravating mechanism of severe acute pancreatitis

OBJECTIVE: To study the effects of gut‐derived endotoxin translocation and NF‐κB activation on the aggravating mechanism of severe acute pancreatitis (SAP) and of treatment with pyrrolidine dithiocarbamate (PDTC) on rats with SAP. METHODS: SD rats were randomly divided into sham operation group (SO), SAP group, SAP + lipopolysaccharide(LPS) group, pyrrolidine dithiocarbamate (PDTC) treatment group and LPS group. Biochemical parameters and cytokines were examined in the serum. Multiple organs pathological slices were examined. Expression of NF‐κB mRNA in the liver tissue was detected by RT‐PCR. Activation of NF‐κB by the method of streptomycin avidin‐peroxidase (SP) and expression of NF‐κB p65 protein and its binding activity were analyzed by Western blot and electrophoretic mobidity shift assay (EMSA). RESULTS: Compared with sham operation group, the concentration of TNF‐α, alanine aminotransferase (ALT), and diamine oxidase (DAO) in serum significantly increased in SAP + LPS group (P < 0.05). Pathological changes were markedly observed in tissues and the expression of NF‐κB mRNA in the liver significantly increased (P < 0.05) also, the activation of NF‐κB and binding activity of NF‐κB p65 protein in the liver markedly increased (P < 0.01) in SAP + LPS group. Treatment with PDTC markedly reduced concentration of ALT, DAO and TNF‐α, and the expression of NF‐κB, and the pathologic scores, as well as significantly decreased the expression of NF‐κB p65 protein. CONCLUSION: The activation and overexpression of NF‐κB may participate in the aggravating mechanism of SAP. Treatment with PDTC has a protective effect on multiple organs damage in SAP.     

Giardia lamblia binding immunoglobulin protein triggers maturation of dendritic cells via activation of TLR4‐MyD88‐p38 and ERK1/2 MAPKs

Much remains unknown about the mammalian immune response to Giardia lamblia, a protozoan pathogen that causes diarrhoeal outbreaks. We fractionated protein extracts of G. lamblia trophozoites by Viva‐spin centrifugation, DEAE ion exchange and gel filtration chromatography. Resultant fractions were screened for antigenic molecules by western blots analysis using anti‐G. lamblia antibodies (Abs), resulting in identification of G. lamblia binding immunoglobulin protein (GlBiP). Maturation of mouse dendritic cells (DCs) in response to recombinant GlBiP (rGlBiP) was detected by increased expression of surface molecules such as CD80, CD86 and MHC class II; these mature DCs, produced pro‐inflammatory cytokines (TNF‐α, IL‐12 and IL‐6). Especially, the truncated rGlBiP containing the heat‐shock protein 70 domain‐induced cytokine production from mouse DCs. rGlBiP‐induced DC activation was initiated by TLR4 in a MyD88‐dependent way and occurred through activation of p38 and ERK1/2 MAPKs as well as increased activity of NF‐κB and AP‐1. Moreover, CD4⁺ T cells stimulated with rGlBiP‐treated DCs produced high levels of IL‐2 and IFN‐γ. Together, our results suggest that GlBiP contributes to maturation of DCs via activation of TLR4‐MyD88‐p38, ERK1/2 MAPK, NF‐κB and AP‐1.     

Monocytic differentiation of leukemic HL‐60 cells induced by co‐treatment with TNF‐α and MK886 requires activation of pro‐apoptotic machinery

The block of hematopoietic differentiation program in acute myeloid leukemia cells can be overcome by differentiating agent like retinoic acid, but it has several side effects. A study of other differentiation signaling pathways is therefore useful to predict potential targets of anti‐leukemic therapy. We demonstrated previously that the co‐treatment of HL‐60 cells with Tumor necrosis factor‐α (TNF‐α) (1 ng/mL) and inhibitor of 5‐lipoxygenase MK886 (5 μm ) potentiated both monocytic differentiation and apoptosis. In this study, we detected enhanced activation of three main types of mitogen‐activated protein kinases (MAPKs) (p38, c‐Jun amino‐terminal kinase [JNK], extracellular signal‐regulated kinase [ERK]), so we assessed their role in differentiation using appropriate pharmacologic inhibitors. The inhibition of pro‐apoptotic MAPKs (p38 and JNK) suppressed the effect of MK886 + TNF‐α co‐treatment. On the other hand, down‐regulation of pro‐survival ERK pathway led to increased differentiation. Those effects were accompanied by increased activation of caspases in cells treated by MK886 + TNF‐α. Pan‐caspase inhibitor ZVAD‐fmk significantly decreased both number of apoptotic and differentiated cells. The same effect was observed after inhibition of caspase 9, but not caspase 3 and 8. To conclude, we evidenced that the activation of apoptotic processes and pathways supporting apoptosis (p38 and JNK MAPKs) is required for the monocytic differentiation of HL‐60 cells.     

RhoA‐mediated,tumor necrosis factor α–induced activation of NF‐κB in rheumatoid synoviocytes: Inhibitory effect of simvastatin

Objective

Increasing evidence indicates that RhoA may play a central role in the inflammatory response. This study was conducted to examine the role of RhoA in mediating the activation of NF‐κB in tumor necrosis factor α (TNFα)–stimulated rheumatoid synoviocytes, and to evaluate the modulatory effects of statins on the TNFα‐induced activation of RhoA and NF‐κB and the secretion of proinflammatory cytokines by rheumatoid synoviocytes.

Methods

Rheumatoid synoviocytes obtained from patients with active rheumatoid arthritis were stimulated with TNFα and incubated with simvastatin (SMV) (1 μM). RhoA activity was assessed by a pull‐down assay. NF‐κB DNA binding activity and nuclear translocation of NF‐κB were measured by a sensitive multiwell colorimetric assay and confocal fluorescence microscopy, respectively.

Results

TNFα stimulation elicited a robust increase in RhoA activity in a dose‐dependent manner, and SMV mitigated this increase. TNFα also hastened NF‐κB nuclear translocation of subunit p65 and increased DNA binding activity, luciferase reporter gene expression, degradation of IκB, and secretion of interleukin‐1β (IL‐1β) and IL‐6. SMV prevented the increase in NF‐κB activation and rise in IL‐1β and IL‐6 levels induced by TNFα, whereas mevalonate and geranylgeranyl pyrophosphate reversed the inhibitory effects of SMV on activation of NF‐κB and RhoA. Furthermore, cotransfection with a dominant‐negative mutant of RhoA demonstrated that the TNFα‐induced signaling pathway involved sequential activation of RhoA, leading to NF‐κB activation and, ultimately, to secretion of cytokines.

Conclusion

This study identifies RhoA as the key regulator of TNFα‐induced NF‐κB activation, which ultimately results in the secretion of proinflammatory cytokines in rheumatoid synoviocytes. The findings provide a new rationale for the antiinflammatory effects of statins in inflammatory arthritis.