OXIDATIVE STRESS ACTIVATES THE HUMAN HISTIDINE-DECARBOXYLASE PROMOTERIN AGS GASTRIC-CANCER CELLS

Oxidant stress is thought to play a role in the pathogenesis of many g astric disorders. We have recently reported that histidine decarboxyla se (HDC) promoter activity is stimulated by gastrin through a protein kinase C- and extracellular signal-regulating kinase (ERK)-dependent p athway in gastric cancer (AGS-B) cells, and this transcriptional respo nse is mediated by a downstream cis-acting element, the gastrin respon se element (GAS-RE). To study the mechanism through which oxidant stre ss 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-acetylcystein e. Hydrogen peroxide treatment of AGS-B cells increased the phosphoryl ation and kinase activity of ERK-1 and ERK-2, but did not affect Jun k inase tyrosine phosphorylation or kinase activity. In addition, treatm ent of AGS-B cells with H2O2 resulted in increased c-fos/c-jun mRNA ex pression and AP-1 activity, and also led to increased phosphorylation of epidermal growth factor receptor (EGFR) and Shc. H2O2-dependent sti mulation of HDC promoter activity was completely inhibited by kinase-d eficient ERKs, dominant-negative (N17 and N15) Ras, and dominant-negat ive Raf, and partially blocked by a dominant-negative EGFR mutant. In contrast, protein kinase C blockade did not inhibit H2O2-dependent ind uction of the HDC promoter. Finally, deletion analysis demonstrated th at the H2O2 response element could be mapped to the GAS-RE (nucleotide s 2 to 24) of the basal HDC promoter. Overall, these studies suggest t hat oxidant stress activates the HDC promoter through the GAS-RE, and through an Ras-, Raf-, and ERK-dependent pathway at least partially in volving the EGFR.