Joo Weon Lim

Helicobacter pylori in a Korean isolate activates mitogen-activated protein kinases, AP-1 and NF-κB and induces chemokine expression in gastric epithelial AGS cells

Oxidant-sensitive transcription factors, nuclear factor-κB (NF-κB), and activator protein-1 (AP-1) have been considered as the regulators of inducible genes such as chemokines. Since oxygen radicals are considered as an important regulator in the pathogenesis of Helicobacter pylori (H. pylori)-induced gastric ulceration and carcinogenesis, chemokines such as interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) may be regulated by NF-κB and/or AP-1. Ras, the upstream activator for mitogen-activated protein kinase (MAPK) and MAPK cascade regulate AP-1 activation. The present study aims to investigate whether H. pylori in a Korean isolate (HP99) induces the expression of chemokines (IL-8, MCP-1), which is regulated by Ras, MAPK, AP-1, and NF-κB in gastric epithelial AGS cells, and whether these transcriptional regulations of chemokines are inhibited by transfection with mutant genes for Ras (ras N-17), c-Jun (TAM-67), and IκBα (MAD-3) or treatment with MAPK inhibitors (U0126 for extracellular signal-regulated kinase or SB203580 for p38 kinase). In addition, virulence factors of HP99 were characterized by PCR analysis for the isolated DNA. As a result, HP99 is identified as cagA+, vacA s1b, m2, iceA1 H. pylori strain. HP99 induced a time-dependent expression of mRNA and protein for IL-8 and MCP-1 via mediation of MAPK, AP-1, and NF-κB. Transfection with mutant genes for Ras, c-Jun, and IκBα and treatment with MAPK inhibitors suppressed H. pylori-induced activation of transcription factors (NF-κB, AP-1) and expression of chemokines (IL-8, MCP-1) in AGS cells. In conclusion, Ras and MAPK cascade may act as the upstream signaling for the activation of AP-1 and NF-κB, which induce chemokine expression in H. pylori-infected AGS cells. Specific targeting of the activation of NF-κB and AP-1 may be effective for the prevention or treatment of gastric inflammation associated with H. pylori infection.

Nuclear Factor-κB Regulates Cyclooxygenase-2 Expression and Cell Proliferation in Human Gastric Cancer Cells

Nuclear factor-κB (NF-κB) is a transcriptional regulator of inducible expression of genes including cyclooxygenase-2 (COX-2), regulating cell proliferation. NF-κB is kept silent in the cytoplasm via interaction with the inhibitory protein IκBα and transmigrated into the nucleus upon activation. However, constitutive NF-κB has been found in the nucleus of some cancer cells. We investigated the role of NF-κB in COX-2 expression and cell proliferation in human gastric cancer AGS cells. AGS cells were treated with antisense oligodeoxynucleotide (AS ODN) or sense oligodeoxynucleotide (S ODN) for the NF-κB subunit p50, or they were transfected with a mutated IκBα gene (MAD-3 mutant) or a control vector, pcDNA-3. AGS cells were treated with COX-2 inhibitors such as indomethacine and NS-398 or prostaglandin E2. mRNA expression for COX-2, and protein levels for p50, IκBα, and COX-2 were determined by reverse transcription polymerase chain reaction and Western blot analysis. The NF-κB levels were examined by electrophoretic mobility shift assay. Thromboxane B2 (TXB2) and 6-keto-prostaglandin F1α (6-keto-PGF1α) levels were determined by enzyme-linked immunosorbent assay. Cell proliferation was assessed by viable cell counting, [3H] thymidine incorporation, and colony formation. The nuclear level of p50 decreased in AGS cells treated with AS ODN. The IκBα mutant was observed in cells transfected with the mutated IκBα gene. NF-κB was inhibited in cells treated with AS ODN or transfected with the mutated IκBα gene, compared with the cells treated with S ODN or transfected with control vector. Cell proliferation, mRNA expression and protein level of COX-2, and production of TXB2 and 6-keto-PGF1α were inhibited in cells treated with AS ODN or transfected with the mutated IκBα gene, which had lower NF-κB levels than cells treated with S ODN or transfected with control vector. COX-2 inhibitors suppressed cell proliferation and production of TXB2 and 6-keto-PGF1α, in a dose-dependant manner. Prostaglandin E2 prevented the inhibition of proliferation in cells treated with AS ODN or transfected with the mutated IκBα gene. In conclusion, NF-κB mediates COX-2 expression, which may be related to cell proliferation, in human gastric cancer cells.

Suppression of Cerulein-Induced Cytokine Expression by Antioxidants in Pancreatic Acinar Cells

Reactive oxygen species (ROS) has been considered to be an important regulator in the development and pathogenesis of pancreatitis and an activator of the transcription factor, nuclear factor-κB (NF-κB), regulating inflammatory cytokine gene expression. NF-κB activation was demonstrated in cerulein pancreatitis, which rapidly induces an acute, edematous form of pancreatitis. This study aimed to investigate whether cerulein induced ROS generation, lipid peroxide and hydrogen peroxide production, NF-κB activation, and expression of cytokines (IL-1β, IL-6) in pancreatic acinar cells. An additional aim was to establish whether these alterations were inhibited by antioxidants such as glutathione, superoxide dismutase, and catalase and an inhibitor of NF-κB activation, pyrrolidine dithiocarbamate (PDTC). To determine the possible interactions of the antioxidants and PDTC with cerulein-induced signaling, Ca2+ signal and amylase release were monitored in the pancreatic acinar cells treated with cerulein in the presence or absence of either the antioxidants or PDTC. The results showed that cerulein generated ROS and increased lipid peroxide and hydrogen peroxide production in the acinar cells, as determined by dichlorofluorescein diacetate dye. This resulted in NF-κB activation and the induction of cytokine gene expression in the cells. The cerulein-induced NF-κB activation was in parallel to IκBα degradation. Cerulein also induced Ca2+ signals and amylase release in acinar cells. Both antioxidants (glutathione, superoxide dismutase, catalase) and PDTC inhibited the cerulein-induced, oxidant-mediated alterations but did not affect the cerulein-evoked Ca2+ signals and amylase release in acinar cells. In conclusion, ROS, generated by cerulein, activates NF-κB, resulting in the up-regulation of inflammatory cytokine gene expression in acinar cells. NF-κB inhibition by scavenging ROS might alleviate the inflammatory response in pancreatic acinar cells by suppressing cytokine gene expression.

Suppression of NF-κB activation and cytokine production by N-acetylcysteine in pancreatic acinar cells

Reactive oxygen species (ROS), generated by infiltrating neutrophils, are considered as an important regulator in the pathogenesis and development of pancreatitis. A hallmark of the inflammatory response is the induction of cytokine gene expression, which may be regulated by oxidant-sensitive transcription factor, nuclear factor-kappaB (NF-kappaB). Present study aims to investigate whether neutrophils primed by 4beta-phorbol 12beta-myristate 13alpha-acetate (PMA) affect the productions of H(2)O(2) and lipid peroxide (LPO), NF-kappaB activation and cytokine production in pancreatic acinar cells, and whether these alterations were inhibited by N-acetylcysteine (NAC) and superoxide dismutase (SOD). Neutrophils generated ROS by stimulation with PMA, which was inhibited by NAC and SOD. In acinar cells, PMA-primed neutrophils increased the productions of H(2)O(2), LPO, and cytokines both time and dose dependently. PMA-primed neutrophils resulted in the activation of two species of NF-kappaB dimers (a p50/p65 heterodimer and a p50 homodimer) in acinar cells. Both NAC and SOD inhibited neutrophil-induced, oxidant-mediated alterations in acinar cells. In conclusion, ROS, generated by neutrophils, activates NF-kappaB, resulting in upregulation of inflammatory cytokines in acinar cells. Antioxidants such as NAC might be useful antiinflammatory agents by inhibiting oxidant-mediated activation of NF-kappaB and decreasing cytokine production.

NF-κB, inducible nitric oxide synthase and apoptosis by Helicobacter pylori infection

Abstract Oxygen radicals are considered as an important regulator in the pathogenesis of Helicobacter pylori (H. pylori)-induced gastric ulceration and carcinogenesis. Inflammatory genes including inducible nitric oxide synthase (iNOS) may be regulated by oxidant-sensitive transcription factor, nuclear factor-κB (NF-κB). iNOS induction has been related to gastric apoptosis. We studied the role of NF-κB on iNOS expression and apoptosis in H. pylori-stimulated gastric epithelial AGS cells. AGS cells were treated with antisense oligonucleotide (AS ODN) for NF-κB subunit p50, an antioxidant enzyme catalase, an inhibitor of NF-κB activation pyrrolidine dithiocarbamate (PDTC), iNOS inhibitors NG-nitro-L-arginine-methyl ester (L-NAME) and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a peroxynitrite donor SIN-1, and a nitric oxide donor NOC-18 in the presence or absence of H. pylori. H. pylori induced cytotocixity time- and dose-dependently, which occurred with induction in iNOS expression and nitrite production. SIN-1 and NOC-18 induced dose-dependent cytotoxicity in AGS cells. Catalase, PDTC, L-NAME, and AMT prevented H. pylori-induced cytotoxicity and apoptosis. It was related to their inhibition on iNOS expression and nitrite production. The cells treated with AS ODN had low levels of p50 and NF-κB and inhibited H. pylori-induced cytotoxicity, apoptosis, iNOS expression, and nitrite production. In conclusion, NF-κB plays a novel role in iNOS expression and apoptosis in H. pylori-infected gastric epithelial cells.

Helicobacter pylori-induced Expression of Interleukin-8 and Cyclooxygenase-2 in AGS Gastric Epithelial Cells: Mediation by Nuclear Factor-κB

BACKGROUND Helicobacter pylori infection might activate nuclear factor-kappaB (NF-kappaB), a transcriptional regulator of inducible expression of inflammatory genes, interleukin-8 (IL-8) and cyclooxygenase-2 (COX-2). We studied the role of NF-kappaB on expression of IL-8 and COX-2 in H. pylori-stimulated AGS gastric epithelial cells by using antisense oligonucleotide (AS ODN) for NF-kappaB subunit p50 and an antioxidant, glutathione (GSH) as well as a NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC). METHODS AGS cells were treated with p50 AS ODN, GSH or PDTC in the presence of H. pylori. mRNA expression and protein levels for IL-8 and COX-2 were determined by Northern blot analysis and Western blot analysis. Levels of IL-8, 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) and thromboxane B2 (TXB2) were measured in the medium by enzyme-linked immunosorbent assay. NF-kappaB activation was examined by electrophoretic mobility shift assay. RESULTS H. pylori induced a time-dependent expression of mRNA and protein for IL-8 and COX-2 via activation of NF-kappaB and increased the levels of IL-8, 6-keto-PGF1alpha and TXB2, which were inhibited by GSH and PDTC. H. pylori-induced expression of IL-8 and COX-2 was blocked in AGS cells transfected with p50 AS ODN. CONCLUSION NF-kappaB may play a novel role in expression of IL-8 and COX-2 in H. pylori-induced gastric inflammation.

Cell adhesion-related gene expression by Helicobacter pylori in gastric epithelial AGS cells.

Helicobacter pylori (H. pylori) infection leads to gastroduodenal inflammation, peptic ulceration and gastric carcinoma. H. pylori may induce disease-specific gene expression in gastric epithelial cells. cDNA microarray for 352 cancer-related genes was used to identify the genes altered by H. pylori (cagA positive) in gastric epithelial AGS cells. Expressions of the genes identified on the microarray and other genes closely associated with these genes were determined by reverse transcriptase-polymerase chain reaction (RT-PCR). Western blot analysis and cell adhesion assay were performed to confirm the protein levels of the genes and the role of the genes on cell adhesion in H. pylori-infected AGS cells. As a result, the expression of four genes (galectin 1, aldolase A, integrin alpha5, LIM domain only 7 (LMO7)) were up-regulated by H. pylori in AGS cells, determined by cDNA microarray. RT-PCR analysis showed that the genes up-regulated by H. pylori were the genes regulating cell-cell adhesion and cell-extracellular matrix interaction, such as galectin-1 and galectin-3, integrin alpha5, and LIM domain only 7 (LMO7), and cancer-related glycolytic enzyme aldolase A and C. Cell adhesion to extracellular matrix proteins such as poly-L-lysine and fibronectin was mediated by H. pylori-induced expression of integrin alpha5. RT-PCR and Western blot analysis showed that E-cadherin, regulating cell adhesion and contact cell inhibition, was decreased by H. pylori in AGS cells. In conclusion, the increased expression of cell adhesion molecules and decrease in E-cadherin expression by H. pylori might contribute to cell adhesion, invasion and possibly cell proliferation in gastric epithelial cells.

Role of NF-κB and AP-1 on Helicobater pylori-induced IL-8 expression in AGS cells

Oxygen radicals are important regulators in Helicobacter pylori-induced gastric ulceration and carcinogenesis. IL-8 may be regulated by oxidant-sensitive transcription factors, NF-κB, and AP-1. The present study aims to investigate whether H. pylori-induced IL-8 expression is regulated by NF-κB and AP-1 in gastric epithelial AGS cells and whether this transcriptional regulation of IL-8 is inhibited by N-acetylcysteine (NAC). As a result, H. pylori induced the expression of mRNA and protein for IL-8 via activation of NF-κB and AP-1. NF-κB activation accompanied by a decrease in I-κBα and activated AP-1 complex was a c-jun/c-fos heterodimer in H. pylori-infected AGS cells. NAC inhibited H. pylori-induced activation of transcription factors and IL-8 expression in AGS cells. In conclusion, oxygen radicals induce the activation of NF-κB and AP-1 and IL-8 expression. Antioxidants such as NAC might be useful anti-inflammatory agents by inhibiting activation of transcription factors and decreasing IL-8 production in H. pylori-induced gastric inflammation.

Oxidative-stress-related proteome changes in Helicobacter pylori-infected human gastric mucosa.

Helicobacter pylori infection leads to gastroduodenal inflammation, peptic ulceration and gastric carcinoma. Proteomic analysis of the human gastric mucosa from the patients with erosive gastritis, peptic ulcer or gastric cancer, which were either infected or not with H. pylori, was used to determine the differentially expressed proteins by H. pylori in the human gastric mucosa in order to investigate the pathogenic mechanism of H. pylori -induced gastric diseases. Prior to the experiment, the expression of the main 18 proteins were identified in the gastric mucosa and used for a proteome map of the human gastric mucosa. Using two-dimensional electrophoresis of the protein isolated from the H. pylori -infected tissues, Coomassie Brilliant Blue staining and computerized analysis of the stained gel, the expression of eight proteins were altered in the H. pylori -infected tissues compared with the non-infected tissues. MS analysis (matrix-assisted laser desorption/ionization-time of flight MS) of the tryptic fragment and a data search allowed the the identification of the four increased proteins (78 kDa glucose-regulated protein precursor, endoplasmin precursor, aldehyde dehydrogenase 2 and L-lactate dehydrogenase B chain) and the four decreased proteins (intracellular chloride channel protein 1, glutathione S-transferase, heat-shock protein 60 and cytokeratin 8) caused by H. pylori infection in the gastric mucosa. These proteins are related to cell proliferation, carcinogenesis, cytoskeletal function and cellular defence mechanism. The common feature is that these proteins are related to oxidative-stress-mediated cell damage. In conclusion, the established gastric mucosal proteome map might be useful for detecting the disease-related protein changes. The H. pylori -induced alterations in protein expression demonstrate the involvement of oxidative stress in the pathogenesis of H. pylori -induced gastric diseases, including inflammation, ulceration and carcinogenesis.

Inhibitory mechanism of omega-3 fatty acids in pancreatic inflammation and apoptosis.

Oxidative stress is regarded as a major pathogenic factor in acute pancreatitis. Inflammation and apoptosis linked to oxidative stress has been implicated in cerulein‐induced pancreatitis as an experimental model of acute pancreatitis. Recently, we found that reactive oxygen species mediate inflammatory cytokine expression and apoptosis of pancreatic acinar cells stimulated with cerulein. Omega‐3 fatty acids show antioxidant action in various cells and tissues. In the present study, we investigated whether omega‐3 fatty acids inhibit cytokine expression in cerulein‐stimulated pancreatic acinar cells and whether omega‐3 fatty acids suppress apoptotic cell death in pancreatic acinar cells exposed to hydrogen peroxide. We found that omega‐3 fatty acids, such as docosahexaenoic acid (DHA) and α‐linolenic acid (ALA), suppressed the expression of inflammatory cytokines (IL‐1β, IL‐6) and inhibited the activation of transcription factor activator protein‐1 in cerulein‐stimulated pancreatic acinar cells. DHA and ALA inhibited DNA fragmentation, inhibited the decrease in cell viability, and inhibited the expression of apoptotic genes (p53, Bax, apoptosis‐inducing factor) induced by hydrogen peroxide in pancreatic acinar cells. In conclusion, omega‐3 fatty acids may be beneficial for preventing oxidative stress‐induced pancreatic inflammation and apoptosis by inhibiting inflammatory cytokine and apoptotic gene expression of pancreatic acinar cells.