Epigenetic properties of the diarrheic marine toxin okadaic acid: Inhibition of the gap junctional intercellular communication in a human intestine epithelial cell line
Laboratory of Toxicology and Applied Hygiene, University Victor Segalen Bordeaux 2, 146, rue Léo-Saignat, 33076, Bordeaux, France.Archive für Toxikologie (Impact Factor: 5.98). 12/2003; 77(11):657-62. DOI: 10.1007/s00204-003-0460-0
Okadaic acid (OA) is produced by several types of dinoflagellates (marine plankton) and has been implicated as the causative agent of diarrhetic shellfish syndrome. Previous studies have shown that okadaic acid is a tumor promoter and a specific potent inhibitor of protein phosphatases and protein synthesis. These effects in turn affect intracellular processes such as metabolism, contractility, gene transcription, and the maintenance of cytoskeletal structure. Gap junctional intercellular communication (GJIC) is a means of maintaining cellular homeostasis in organs, the disruption of which favors tumor cell growth. The GJIC involves the transfer of small water-soluble molecules through intercellular channels (gap junctions), composed of proteins called connexins. OA disrupts cellular homeostasis in Caco-2 cells through several mechanisms including protein synthesis inhibition, apoptosis, and clastogenic effects. The aim of this study was then to evaluate the expression of the connexin 43 (Cx 43) mRNA in relation with the cytotoxicity induced by OA (3.75-60 ng/ml) in a human colonic epithelial cell line in culture (Caco-2 cells). OA produced a dose-dependent inhibition of GJIC in Caco-2 cells, along with a parallel decrease in the expression of Cx 43 as shown by immunohistochemistry using anti-Cx 43 antibody. Since Cx 43 is implicated in the suppression of tumors and OA is a tumor promoter, the inhibition of GJIC may play an important role in its carcinogenesis. These data are discussed in relation to the toxicity of OA, total RNA synthesis, and possible specificity of Cx 43 inhibition in the GJIC.
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- "The toxicological data obtained in the present study together with data previously reported (López et al., 2011) provide more information about the immunotoxic activity of YTX and OA. Moreover, OA has been reported to possess tumor promoting activity, teratogenic and genotoxic activity (Creppy et al., 2002;Matias et al., 1996;SouidMensi et al., 2008;Traoré et al., 2003). Since OA is involved in tumor production, the most threatening effects are those possibly connected with DNA modification and/or regulation of gene expression, such as the ratio f methylation . "
ABSTRACT: Yessotoxin (YTX) and okadaic acid (OA), algal toxins accumulated in edible shellfish, were previously shown to induce a specific and reversible T Cell Receptor (TCR) down-regulation in T lymphocyte EL-4 cells, in a time and concentration-dependent manner, via protein kinase C (PKC) and serine/threonine protein phosphatase 2A (PP2A) activities. In this study we have evaluated the development of other signs of toxicity induced by low concentrations of YTX or OA for 3 days of treatment. Concentrations of YTX as low as 1 nM decreased a 35% the concentration of viable cells after 48 h exposure to the toxin, while concentrations as little as 5 nM YTX or OA were sufficient to induce membrane blebbing. The concentration of YTX that produced after 24 h of incubation a 50% reduction in maximum cell viability (EC50(24)) was approximately 46 nM, whereas with OA over 75% of the cells were still viable after exposure to 100 nM OA. According to our results, the cytoskeleton of EL-4 cells seems to be a cell component particularly sensitive to YTX and OA with disruption of F-actin cytoskeleton in these cells treated with concentrations of YTX or OA as low as 5 nM at 48 h incubation. Toxicity by YTX or OA involved typical hallmarks of apoptosis and an increase of reactive oxygen species (ROS) production. The cytotoxic effects of YTX and OA reported here, and the previously demonstrated potential of these toxins to regulate the activity of EL-4 cells through the regulation of TCR expression, rise reasonable concern about possible risks for human health associated to the chronic exposure to low amounts of YTX or OA itself or enhanced by the presence of other shellfish toxins specially by a population potentially at risk such as immunocompromised patients.
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- "The predominant OA effects on metabolic processes may be explained by its activity as a PP inhibitor since various enzymes involved in those pathways, such as glycogen synthase or glycogen phosphorylase , are modulated by phosphorylation or dephosphorylation on serine and/or threonine residues (Denton 1986). Specifically, PP1 and PP2A are closely involved in glucose and glycogen metabolism (Hubbard and Cohen 1989; Traoré et al. 2003; Ugi et al. 2004). Further, the existence of OA binding to proteins other than phosphatases, previously demonstrated in several marine organisms (Schröder et al. 2006; Sugiyama et al. 2007), cannot be ruled out in humans. "
ABSTRACT: Okadaic acid (OA) is a widely distributed marine toxin produced by several phytoplanktonic species and responsible for diarrheic shellfish poisoning in humans. At the molecular level OA is a specific inhibitor of several types of serine/threonine protein phosphatases. Due to this enzymic inhibition, OA was reported to induce numerous alterations in relevant cellular physiological processes, including several metabolic pathways such as glucose uptake, lipolysis and glycolysis, heme metabolism, and glycogen and protein synthesis. In order to further understand the underlying mechanisms involved in OA-induced effects on cellular metabolism, the expression levels of six genes related to different catabolic and anabolic metabolism-related processes were analyzed by real-time polymerase chain reaction. Specifically, the expression patterns of GAPDH, TOMM5, SLC25A4, COII, QARS, and RGS5 genes were determined in SHSY5Y human neuroblastoma cells exposed to OA for 3, 24, or 48 h. All these genes showed alterations in their expression levels after at least one of the OA treatments tested. These alterations provide a basis to understand the mechanisms underlying the previously described OA-induced effects on different metabolic processes, mainly regarding glucose and mitochondrial metabolism. However, other OA-induced affected genes can not be ruled out, and further studies are required to more comprehensively characterize in the mechanisms of OA-induced interaction on cell metabolism.
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- "On the basis on these and other previous studies, OA represents other potential threats to human health besides DSP, even at concentrations within the nanomolar range. It is well-known that OA can inhibit specifically the serine/threonine protein phosphatases 1 (PP1) and 2A (PP2A) ; the number of physiological processes in which those phosphatases are involved is immense, including regulation of glycogen metabolism and coordination of the cell cycle and gene expression . So this role of phosphatase inhibition by OA could explain most of the cell effects induced by this toxin . "
ABSTRACT: Okadaic acid (OA), a toxin produced by several dinoflagellate species is responsible for frequent food poisonings associated to shellfish consumption. Although several studies have documented the OA effects on different processes such as cell transformation, apoptosis, DNA repair or embryogenesis, the molecular mechanistic basis for these and other effects is not completely understood and the number of controversial data on OA is increasing in the literature. In this study, we used suppression subtractive hybridization in SHSY5Y cells to identify genes that are differentially expressed after OA exposure for different times (3, 24 and 48 h). A total of 247 subtracted clones which shared high homology with known genes were isolated. Among these, 5 specific genes associated with cytoskeleton and neurotransmission processes (NEFM, TUBB, SEPT7, SYT4 and NPY) were selected to confirm their expression levels by real-time PCR. Significant down-regulation of these genes was obtained at the short term (3 and 24 h OA exposure), excepting for NEFM, but their expression was similar to the controls at 48 h. From all the obtained genes, 114 genes were up-regulated and 133 were down-regulated. Based on the NCBI GenBank and Gene Ontology databases, most of these genes are involved in relevant cell functions such as metabolism, transport, translation, signal transduction and cell cycle. After quantitative PCR analysis, the observed underexpression of the selected genes could underlie the previously reported OA-induced cytoskeleton disruption, neurotransmission alterations and in vivo neurotoxic effects. The basal expression levels obtained at 48 h suggested that surviving cells were able to recover from OA-caused gene expression alterations.
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