Role of protein tyrosine phosphorylation in acetaldehyde-induced disruption of epithelial tight junctions.
ABSTRACT Acetaldehyde-induced cytotoxicity is an important factor in pathogenesis of alcohol-related diseases; however, the mechanism of this toxicity is unknown. We recently showed that acetaldehyde increases epithelial paracellular permeability. We asked whether protein tyrosine phosphorylation via modulation of tyrosine kinases and/or PTPases is a mechanism involved in acetaldehyde-induced disruption of the tight junctions in the Caco-2 cell monolayer. Immunofluorescence localization of occludin and ZO-1 showed disruption of the tight junctions in acetaldehyde-treated cell monolayer. Administration of genistein prevented acetaldehyde-induced permeability. Acetaldehyde increased tyrosine phosphorylation of three clusters of proteins with molecular masses of 30-50, 60-90, and 110-150 kDa; three of these proteins were ZO-1, E-cadherin, and beta-catenin. Acetaldehyde reduced PTPase activity in plasma membrane and soluble fractions, whereas tyrosine kinase activity remained unaffected. Treatment with acetaldehyde resulted in a 97% loss of protein tyrosine phosphatase (PTP)1B activity and a partial reduction of PTP1C and PTP1D activities. These results strongly suggest that acetaldehyde inhibits PTPases to increase protein tyrosine phosphorylation, which may result in disruption of the tight junctions.
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ABSTRACT: This report is a summary of the symposium on Alcohol, Intestinal Bacterial Growth, Intestinal Permeability to Endotoxin, and Medical Consequences, organized by National Institute on Alcohol Abuse and Alcoholism, Office of Dietary Supplements, and National Institute of Diabetes and Digestive and Kidney Diseases of National Institutes of Health in Rockville, Maryland, October 11, 2006. Alcohol exposure can promote the growth of Gram-negative bacteria in the intestine, which may result in accumulation of endotoxin. In addition, alcohol metabolism by Gram-negative bacteria and intestinal epithelial cells can result in accumulation of acetaldehyde, which in turn can increase intestinal permeability to endotoxin by increasing tyrosine phosphorylation of tight junction and adherens junction proteins. Alcohol-induced generation of nitric oxide may also contribute to increased permeability to endotoxin by reacting with tubulin, which may cause damage to microtubule cytoskeleton and subsequent disruption of intestinal barrier function. Increased intestinal permeability can lead to increased transfer of endotoxin from the intestine to the liver and general circulation where endotoxin may trigger inflammatory changes in the liver and other organs. Alcohol may also increase intestinal permeability to peptidoglycan, which can initiate inflammatory response in liver and other organs. In addition, acute alcohol exposure may potentiate the effect of burn injury on intestinal bacterial growth and permeability. Decreasing the number of Gram-negative bacteria in the intestine can result in decreased production of endotoxin as well as acetaldehyde which is expected to decrease intestinal permeability to endotoxin. In addition, intestinal permeability may be preserved by administering epidermal growth factor, l-glutamine, oats supplementation, or zinc, thereby preventing the transfer of endotoxin to the general circulation. Thus reducing the number of intestinal Gram-negative bacteria and preserving intestinal permeability to endotoxin may attenuate alcoholic liver and other organ injuries.Alcohol 09/2008; 42(5):349-61. DOI:10.1016/j.alcohol.2008.03.131 · 2.04 Impact Factor
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ABSTRACT: Human intestinal Caco-2 cells differentiated for 15-17 days on transparent filter inserts were treated for up to 3 h with 50 and 100 microM CuCl(2) or FeSO(4) in the AP compartment at pH 6.0. Trans-epithelial electrical resistance (TEER) showed a progressive decrease during the course of the experiment that was slower in cells treated with 50 microM CuCl(2) than in those treated with 100 microM CuCl(2). Both 50 and 100 microM FeSO(4) produced a similar decrease in TEER over time, tailing off after 120 min. F-actin localization by fluorescent phalloidin binding in control cells and in cells treated for 3 h with 50 microM CuCl(2) or FeSO(4) highlighted striking differences in the two treatments. Cu(II) led to an overall reduction in F-actin staining with extensive depolymerization in areas of the monolayer, in the absence of cellular loss. Conversely, Fe(II) treatment produced disorganization of F-actin and decreased staining of the perijunctional actin filaments. No changes in the localization and intensity of staining of the junctional proteins ZO1, occludin and E-cadherin were observed after treatment with 100 microM FeSO(4) in analogy with previous observations in Cu(II)-treated cells. The data presented suggest that different mechanisms are responsible for the changes to tight junction permeability produced by the two metals.Toxicology in Vitro 09/2002; 16(4):399-404. DOI:10.1016/S0887-2333(02)00020-6 · 3.21 Impact Factor
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ABSTRACT: The regulation of protein phosphatase 2A (PP2A) and protein threonine phosphorylation by H(2)O(2) was determined in Caco-2 cell monolayer. Incubation with H(2)O(2) (20 microM) resulted in threonine phosphorylation of a cluster of proteins at the molecular mass range of 170-250 kDa. PKC activity and plasma membrane localization of several isoforms of PKC were not affected by H(2)O(2). However, H(2)O(2) reduced 80-85% of okadaic acid-sensitive protein phosphatase activity. Immunocomplex protein phosphatase assay demonstrated that H(2)O(2) reduced the activity of PP2A, but not that of PP2C or PP1. Oxidized glutathione inhibited PP2A activity in plasma membranes prepared from Caco-2 cells and the phosphatase activity of an isolated PP2A. PP2A activity was also inhibited by N-ethylmaleimide, iodoacetamide, and p-chloromercuribenzoate. Inhibition of PP2A by oxidized glutathione was reversed by reduced glutathione. Glutathione also restored the PP2A activity in plasma membranes isolated from H(2)O(2)-treated Caco-2 cell monolayer. These results indicate that PP2A activity can be regulated by glutathionylation, and that H(2)O(2) inhibits PP2A in Caco-2 cells, which may involve glutathionylation of PP2A.Biochemical and Biophysical Research Communications 05/2002; 293(1):610-6. DOI:10.1016/S0006-291X(02)00268-1 · 2.28 Impact Factor