Fig. 7.

Tyrosine kinase activity mediates acetaldehyde-induced occludin dephosphorylation. A: protein extracts from Caco-2 cell monolayers treated with acetaldehyde (400 μM) for 30 or 60 min were immunoblotted for methyl-PP2A-C. B: cell monolayers were pretreated with genistein for 1 h prior to incubation with acetaldehyde for 30 min. Occludin from native cell extracts was immunoprecipitated, and the immunocomplexes were immunoblotted for PP2A and occludin. PP2A band densities were quantitated and normalized to corresponding occludin band densities. Values are calculated percent of control value for each experiment. Values are means ± SE (n = 3). *Significantly different from control value; #different from value for acetaldehyde without genistein. C and D: phospho-threonine was immunoprecipitated from denatured protein extracts of Caco-2 cells exposed to 400 μM acetaldehyde with or without genistein (Gen) pretreatment and immunoblotted for occludin or claudin-5. Occludin band densities from different experiments were quantitated and presented as arbitrary units. Values are means ± SE (n = 3). *Significantly different from control value; #different from value for acetaldehyde without genistein.