ABSTRACT
BACKGROUND AND AIMS: In the liver, stellate cells play several important (patho)physiological roles. They express a broad but variable spectrum of intermediate filament (IF) proteins. The aim of this study was to investigate the expression and functions of the intermediate filament protein synemin in hepatic stellate cells (HSCs). METHODS: In isolated and cultured rat HSCs, synemin expression was examined by quantitative reverse transcriptase polymerase chain reaction, western blotting, and immunocytochemistry. Protein-protein interaction between synemin and possible binding partners was investigated by co-immunoprecipitation and confocal microscopy. RESULTS: Expression of synemin was significantly downregulated with increased culture time. In 1-day cultured HSCs, synemin associated with other IF proteins (GFAP, desmin, and vimentin), and with the focal adhesion proteins vinculin and talin, but not with alpha-actinin or paxillin. Synemin IF and focal adhesion proteins co-localised in long slender processes, but not in the lamellipodia. In human and rat liver tissue, the presence of synemin was investigated by immunohistochemistry. In normal rat and human livers, synemin immunoreactivity was found in HSCs, smooth muscle cells of hepatic arterioles, and nerve bundles in portal tracts, but not in portal fibroblasts. In CCl4-intoxicated rat livers and in human cirrhotic livers, immunoreactivity for synemin in the parenchymal tissue was decreased. Thus synemin was expressed in quiescent HSCs but not in portal fibroblasts; and synemin expression decreased with HSC activation in vivo during chronic liver damage and with HSC activation in culture. CONCLUSIONS: Synemin forms heteropolymeric filaments with type-III IF proteins and acts as a bridging protein between IFs and a specific type of focal adhesions.
Subject(s)
Hepatocytes/metabolism , Intermediate Filament Proteins/biosynthesis , Intermediate Filaments/metabolism , Animals , Blotting, Western/methods , Carbon Tetrachloride , Cells, Cultured , Chemical and Drug Induced Liver Injury , Cytoplasm/metabolism , Down-Regulation , Humans , Intermediate Filament Proteins/genetics , Intermediate Filament Proteins/metabolism , Liver/metabolism , Liver Diseases/metabolism , Microscopy, Confocal , Protein Binding , RNA, Messenger/genetics , Rats , Reverse Transcriptase Polymerase Chain Reaction/methodsABSTRACT
Redox-regulated processes are important elements in various cellular functions. Reducing agents, such as N-acetyl-l-cysteine (NAC), are known to regulate signal transduction and cell growth through their radical scavenging action. However, recent studies have shown that reactive oxygen species are not always involved in ligand-stimulated intracellular signaling. Here, we report a novel mechanism by which NAC blocks platelet-derived growth factor (PDGF)-induced signaling pathways in hepatic stellate cells, a fibrogenic player in the liver. Unlike in vascular smooth muscle cells, we found that reducing agents, including NAC, triggered extracellular proteolysis of PDGF receptor-beta, leading to desensitization of hepatic stellate cells toward PDGF-BB. This effect was mediated by secreted mature cathepsin B. In addition, type II transforming growth factor-beta receptor was also down-regulated. Furthermore, these events seemed to cause a dramatic improvement of rat liver fibrosis. These results indicated that redox processes impact the cell's response to growth factors by regulating the turnover of growth factor receptors and that "redox therapy" is promising for fibrosis-related disease.
Subject(s)
Oxidation-Reduction , Receptor, Platelet-Derived Growth Factor beta/metabolism , Animals , Bile Ducts/metabolism , Blotting, Northern , Blotting, Western , Cathepsin B/metabolism , Cathepsins/pharmacology , Cell Division , Cells, Cultured , Dose-Response Relationship, Drug , Down-Regulation , Fibrosis , Hydrogen Peroxide/pharmacology , Immunohistochemistry , Liver/cytology , Liver/metabolism , Liver/pathology , Muscle, Smooth, Vascular/cytology , Precipitin Tests , Protease Inhibitors/pharmacology , Protein Binding , Rats , Rats, Wistar , Signal Transduction , Time FactorsABSTRACT
We report here a 65-year old man with primary duodenal malignant lymphoma combined with gastric lymphoma and early gastric cancer. Malignant lymphoma in the bulbus of the duodenum was suspected of by endoscopic biopsy during follow up of duodenal ulcer. Preoperative examination revealed an extension of malignant lymphoma from the bulbus to the stomach in combination with early gastric cancer. We performed a pancreaticoduodenectomy because the tumor invaded to the second portion of the duodenum. The postoperative course was uneventful and he received adjuvant chemotherapy following surgery. To our knowledge, this case is the first report of primary duodenal malignant lymphoma combined with gastric lymphoma and early gastric cancer.