The first experiment was designed to reveal the novel action of an antiulcer drug, geranylgeranylacetone (GGA), which rapidly induces resistance of gastric mucosal cells to irritants in vivo and in vitro. GGA induced resistance of cultured guinea pig gastric mucosal cells against ethanol-induced exfoliation and damage within 30 min, proportionally to the induction of the HSPs. This protection was blocked by cycloheximide but not by indomethacin. GGA rapidly activated HSF1 and caused expression of HSP70 mRNA,suggesting that GGA may induce transcriptional activation of HSP genes. Intragastric administration of GGA to rats induced HSPs in gastric mucosa, and additionally augmented the expression of HSP70 mRNA and induction of HSPs in the mucosa of rats confronted with restraint and water-immersion stress. This novel action may increase gastric mucosal defense and reduce damage at times of stress conditions.
Nuclear factor-kappa B (NF-kB) /Rel transcription factors play an important role in
the transcriptional activation of a variety of genes involved in inflammatory and immune responses. The aims of second experiment were to identify the oxidant-sensitive components of NF-kB in gastric epithelial cells and to reveal the roles of this factor under oxidative stress. Gel mobility shift assay with a kB oligonucleotide showed that exposure of primary cultures of guinea pig gastric epithelial cells to hydrogen peroxide and diamide rapidly produced a DNA-protein complex within 5 min. The kB-binding proteins consisted of a p50/p65 heterodimer, which was identified by supershift experiments, UV-crosslinking analysis, immunoprecipitation, and immunocytochemical analyzes with antibodies against p50, p65, and c-Rel. Both hydrogen peroxide and diamide caused the up-requlation of p105 (a p50 precursor) synthesis and the expression of inducible nitric oxide mRNA,which have been suggested to be putative target genes for NF-kB.Thus, our results suggest that the oxidant-sensitive p50/p65 heterodimer may play an important role in the initiation of the responses of gastric epithelial cells to oxidative stress. Less