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Rat Liver Epithelial Cells (rat + liver_epithelial_cell)
Selected AbstractsEffect of byproducts from the ozonation of pyrene: Biphenyl-2,2,,6,6,-tetracarbaldehyde and biphenyl-2,2,,6,6,-tetracarboxylic acid on gap junction intercellular communication and neutrophil functionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2005Stephanie L. Luster-Teasley Abstract In this study, biphenyl-2,2,,6,6,-tetracarbaldehyde, an initial by product formed from the ozonation of pyrene, and biphenyl-2,2,,6,6,-tetracarboxylic acid, a subsequent pyrene ozonation byproduct, were evaluated using two toxicology assays to compare the toxicity of ozonation byproducts with that of the parent compound. The first assay measured the potential for the compounds to block gap junctional intercellular communication (GJIC) using the scrape loading/dye transfer technique in normal WB-344 rat liver epithelial cells. The second assay evaluated the ability of the compounds to affect neutrophil function by measuring the production of superoxide in a human cell line (HL-60). Pyrene significantly blocked intercellular communication (f= 0.2,0.5) at 40 ,M and complete inhibition of communication (f < 0.2) occurred at 50 ,M. Gap junctional intercellular communication in cells exposed to biphenyl-2,2,,6,6,-tetracarbaldehyde reached f < 0.5 at a concentration of 15 ,M. At concentrations greater than 20 ,M, biphenyl-2,2,,6,6,-tetracarbaldehyde was cytotoxic and the inhibition of GJIC was caused by cell death. Biphenyl-2,2,,6,6,-tetracarboxylic acid was neither cytotoxic nor inhibitory to GJIC at the concentrations tested (10,500 ,M). Exposure to biphenyl-2,2,,6,6,-tetracarbaldehyde resulted in a concentration-dependent decrease in phorbol 12-myristate 13-acetate,stimulated O12 production. Neither exposure to pyrene nor biphenyl-2,2,,6,6,-tetracarboxylic acid caused a significant toxic effect on neutrophil function. [source] HuR regulates gap junctional intercellular communication by controlling ,-catenin levels and adherens junction integrity,HEPATOLOGY, Issue 5 2009Niloofar Ale-Agha Gap junctional intercellular communication (GJIC) plays a critical role in the regulation of tissue homeostasis and carcinogenesis and is modulated by the levels, subcellular localization, and posttranslational modification of gap junction proteins, the connexins (Cx). Here, using oval cell-like rat liver epithelial cells, we demonstrate that the RNA-binding protein HuR promotes GJIC through two mechanisms. First, HuR silencing lowered the levels of Cx43 protein and Cx43 messenger RNA (mRNA), and decreased Cx43 mRNA half-life. This regulation was likely due to the direct stabilization of Cx43 mRNA by HuR, because HuR associated directly with Cx43 mRNA, a transcript that bears signature adenylate-uridylate-rich (AU-rich) and uridylate-rich (U-rich) sequences in its 3,-untranslated region. Second, HuR silencing reduced both half-life and the levels of ,-catenin mRNA, also a target of HuR; accordingly, HuR silencing lowered the levels of whole-cell and membrane-associated ,-catenin. Coimmunoprecipitation experiments showed a direct interaction between ,-catenin and Cx43. Small interfering RNA (siRNA)-mediated depletion of ,-catenin recapitulated the effects of decreasing HuR levels: it attenuated GJIC, decreased Cx43 levels, and redistributed Cx43 to the cytoplasm, suggesting that depletion of ,-catenin in HuR-silenced cells contributed to lowering Cx43 levels at the membrane. Finally, HuR was demonstrated to support GJIC after exposure to a genotoxic agent, doxorubicin, or an inducer of differentiation processes, retinoic acid, thus pointing to a crucial role of HuR in the cellular response to stress and in physiological processes modulated by GJIC. Conclusion: HuR promotes gap junctional intercellular communication in rat liver epithelial cells through two related regulatory processes, by enhancing the expression of Cx43 and by increasing the expression of ,-catenin, which, in turn, interacts with Cx43 and is required for proper positioning of Cx43 at the plasma membrane. (HEPATOLOGY 2009.) [source] Curcumin reduces the toxic effects of iron loading in rat liver epithelial cellsLIVER INTERNATIONAL, Issue 1 2009Donald J. Messner Abstract Background/Aims: Iron overload can cause liver toxicity and increase the risk of liver failure or hepatocellular carcinoma in humans. Curcumin (diferuloylmethane), a component of the food spice turmeric, has antioxidant, iron binding and hepatoprotective properties. The aim of this study was to quantify its effects on iron overload and the resulting downstream toxic effects in cultured T51B rat liver epithelial cells. Methods: T51B cells were loaded with ferric ammonium citrate (FAC) with or without the iron delivery agent 8-hydroxyquinoline. Cytotoxicity was measured by methylthiazolyldiphenyl-tetrazolium bromide assay. Iron uptake and iron bioavailability were documented by chemical assay, quench of calcein fluorescence and ferritin induction. Reactive oxygen species (ROS) were measured by a fluorescence assay using 2,,7,-dichlorodihydrofluorescein diacetate. Oxidative stress signalling to jnk, c-jun and p38 was measured by a Western blot with phospho-specific antibodies. Results: Curcumin bound iron, but did not block iron uptake or bioavailability in T51B cells given FAC. However, it reduced cytotoxicity, blocked the generation of ROS and eliminated signalling to cellular stress pathways caused by iron. Inhibition was observed over a wide range of FAC concentrations (50,500 ,M), with an apparent IC50 in all cases between 5 and 10 ,M curcumin. In contrast, desferoxamine blocked both iron uptake and toxic effects of iron at concentrations that depended on the FAC concentration. The effects of curcumin also differed from those of ,-tocopherol, which did not bind iron and was less effective at blocking iron-stimulated ROS generation. Conclusions: Curcumin reduced iron-dependent oxidative stress and iron toxicity in T51B cells without blocking iron uptake. [source] Acquisition of apoptotic resistance in cadmium-induced malignant transformation: Specific perturbation of JNK signal transduction pathway and associated metallothionein overexpression,MOLECULAR CARCINOGENESIS, Issue 8 2006Wei Qu Abstract Prior work has shown that chronic cadmium exposed rat liver epithelial cells (CCE-LE) become malignantly transformed after protracted low level cadmium exposure. Acquisition of apoptotic resistance is common in oncogenesis and the present work explores this possibility in CCE-LE cells. CCE-LE cells were resistant to apoptosis induced by etoposide or an acute high concentration of cadmium as assessed by flow cytometry with annexin/FITC. Three key mitogen-activated protein kinases (MAPKs), namely ERK1/2, JNK1/2, and p38, were phosphorylated in CCE-LE cells after acute cadmium exposure. However, the levels of phosphorylated JNK1/2 were markedly decreased in CCE-LE cells compared to control. JNK kinase activity was also suppressed in CCE-LE cells exposed to cadmium. Epidermal growth factor (EGF), used as a positive control for stimulating JNK phosphorylation, was much less effective in CCE-LE cells than control cells. Ro318220 (Ro), a strong activator of JNK, increased phosphorylated JNK1/2 to levels similar to the cadmium-treated control cells and also enhanced apoptosis in response to cadmium in CCE-LE cells. Metallothionein (MT), which is thought to potentially inhibit apoptosis, was strongly overexpressed in CCE-LE cells. Further, in MT knockout (MT,/,) fibroblasts, JNK1/2 phosphorylation was markedly increased after cadmium exposure compared with similarly treated wild-type (MT+/+) cells. These results indicate cadmium-transformed cells acquired apoptotic resistance, which may be linked to the specific suppression of the JNK pathway and is associated with MT overexpression, which, in turn, may impact this signal transduction pathway. The acquisition of apoptotic resistance may play an important role in cadmium carcinogenesis by contributing to both tumor initiation and malignant progression. Published 2006 Wiley-Liss, Inc. [source] Extraction and chromatographic separation of anticarcinogenic fractions from cacao bean huskBIOFACTORS, Issue 3 2005Ki Won Lee Abstract The utilization of cacao bean husk (CBH), a by-product of chocolate manufacture, would be both environmentally and economically beneficial. For this purpose, a process for effectively separating and fractionating CBH fractions having cancer preventive potential was developed in this study. For screening the fractions with potent cancer preventive activity, we examined the effect of extracts and fractions of CBH on the inhibition of gap-junction intercellular communication (GJIC) and the DNA synthesis of cancer cells, both of which are characteristics of the promotion and progression stages in carcinogenesis. The extracts of CBH (especially, the 60% ethanol fraction after extraction with 50% acetone) containing 43 wt.% polyphenol exerted an excellent protective effect on H2O2 -induced inhibition of GJIC in WB-F344 rat liver epithelial cells as determined by the scrape-loading/dye transfer assay. The enhancement of GJIC by the extracts of CBH was approximately 10-fold higher than that of a well-known dietary chemopreventive component, vitamin C. The extracts of CBH (especially, the 60% ethanol fraction) also suppressed DNA synthesis in all liver, stomach, and colon cancer cells as demonstrated by the 3H-thymidine incorporation assay, by approximately four-fold higher than that of vitamin C. These results imply that the polyphenol extracts and fractions of CBH are effective functional materials to be used in either preventing or inhibiting cancer. [source] | |||||||||||||