Oxidative stress activates the human histidine decarboxylase promoter in AGS gastric cancer cells

Oxidant stress is thought to play a role in the pathogenesis of many gastric disorders. We have recently reported that histidine decarboxylase (HDC) promoter activity is stimulated by gastrin through a protein kinase C- and extracellular signal-regulating kinase (ERK)-dependent pathway in gastric cancer (AGS-B) cells, and this transcriptional response is mediated by a downstream cis-acting element, the gastrin response element (GAS-RE). To study the mechanism through which oxidant stress affects gastric cells, we examined the effects of hydrogen peroxide (H₂O₂) on HDC promoter activity and intracellular signaling in AGS-B cells. H₂O₂ (10 mM) specifically activated the HDC promoter 10-12-fold, and this activation was blocked by both mannitol and N-acetylcysteine. Hydrogen peroxide treatment of AGS-B cells increased the phosphorylation and kinase activity of ERK-1 and ERK-2, but did not affect Jun kinase tyrosine phosphorylation or kinase activity. In addition, treatment of AGS-B cells with H₂O₂ resulted in increased c- fos/c-jun mRNA expression and AP-1 activity, and also led to increased phosphorylation of epidermal growth factor receptor (EGFR) and Shc. H₂O₂- dependent stimulation of HDC promoter activity was completely inhibited by kinase-deficient ERKs, dominant-negative (N17 and N15) Ras, and dominant- negative Raf, and partially blocked by a dominant-negative EGFR mutant. In contrast, protein kinase C blockade did not inhibit H₂O₂-dependent induction of the HDC promoter. Finally, deletion analysis demonstrated that the H₂O₂ response element could be mapped to the GAS-RE (nucleotides 2 to 24) of the basal HDC promoter. Overall, these studies suggest that oxidant stress activates the HI)C promoter through the GAS-RE, and through an Ras-, Raf-, and ERK-dependent pathway at least partially involving the EGFR.