A New Mechanism of Gastric Epithelial Injury Induced by Acid Exposure: The Role of Egr-1 and ERK Signaling Pathways

The molecular mechanisms by which gastric acid causes epithelial injury in the stomach and initiates an inflammatory reaction are poorly understood. We aimed in the present study to investigate the role of the early growth response gene Egr-1 and ERK in gastric epithelial cells following acid exposure, and the signaling pathways involved. Western blotting was used to assess Egr-1 protein levels in AGS cells. A quantitative measurement of acid-induced Egr-1 and ERK translocation was performed using a high content analysis approach. Egr-1 functionality was assessed by transient transfection with Egr-1 antisense oligonucleotide. Exposure of AGS cells to acidic conditions induced Egr-1 protein expression in a pH- and time-dependent manner. Egr-1 expression was markedly increased as the pH was reduced from pH 7.4 to 6.4. High content analysis of Egr-1 activation showed acid-induced Egr-1 nuclear translocation; a maximum observed at 1-2 It followed by a decline to basal levels beyond 4 h. Acidic pH also activated ERK 1/2 phosphorylation, whereas ERK 1/2 inhibitors PD98059 and U0216 blocked both acid-induced Egr-1 and ERK translocation and expression. Moreover, acid exposure up-regulated VEGF expression, which was inhibited by the Egr-1 antisense oligonucleotide. Our results also demonstrate that exposure to acid induces Egr-1 via MEK-ERK 1/2 pathway. These data suggest that Egr-1 activation might play a crucial role in gastric mucosal inflammation and associated epithelial injury. J. Cell. Biochem. 108: 249-260, 2009. (C) 2009 Wiley-Liss, Inc.