Gastroesophageal reflux disease (GERD) affects more than one in ten adults over 40 years of age and one in four adults over 60. Approximately 10% of GERD patients develop Barrett's esophagus (BE), which is associated with nearly a 30-125-fold increased risk for the development of esophageal adenocarcinoma (EA). The mechanism of progression from BE to dysplasia and to EA is unknown. We will therefore examine some of the pathways that may be involved in this progression. Reactive oxygen species (ROS) are elevated in BE and EA, and may play a key role in the progression from BE to EA. We found that a novel isoform of NADPH oxidase NOX5-S is overexpressed in EA cell lines, EA tissues, and BE mucosa with high grade dysplasia. NOX5-S was first identified in human fetal kidney and has not been described in other tissues. In SEG1 EA cells pulsed acid exposure causes upregulation of NOX5-S and increases H2O2 production. NOX5-S-derived ROS contribute to increased cell proliferation and decreased apoptosis in SEG1 cells. However, the mechanisms of acid-induced NOX5-S upregulation and NOX5-S-dependent increase in cell proliferation and decrease in apoptosis are not fully understood. We will therefore test the hypothesis that acid exposure upregulates NADPH oxidases via activation of Rho kinases and MAP kinases in Barrett's metaplastic cells, causing overproduction of free radicals, which in turn may further enhance the expression of NADPH oxidases through activation of the nuclear factor kappaB (NF-kB). In addition, ROS may upregulate cyclin D1 and the silencer of the death domain (SODD). Upregulation of cyclin D1 and SODD will increase cell proliferation and decrease apoptosis in these cells. Thus the persistent acid reflux present in BE patients may cause high levels of ROS, increased cell proliferation and decreased apoptosis, which may lead to DNA damage and increased mutations, contributing to the progression from BE to dysplasia and to EA. To test this hypothesis we will: 1) Examine the signal transduction pathway of acid-induced expression of NADPH oxidases in a BE cell line, in Barrett's mucosal biopsies, and in EA cells (SEG1, FLO, and OE33). We will focus on the role of Rho kinase, MAP kinases and NF-kB. 2) Examine the mechanisms of NADPH oxidase-dependent increase in cell proliferation and decrease in apoptosis, concentrating on the role of cyclin D1 and SODD, and examine whether NADPH oxidase-derived ROS cause DNA damage. 3) Examine the regulatory proteins required for NOX5-S to function, focusing on Rac1 and p22phox. A better understanding of the signal transduction pathway of acid induced upregulation of NADPH oxidases, leading to increased cell proliferation and decreased apoptosis, may provide a rational approach to the prevention of development of EA. In addition, NOX5-S may be a potential biomarker for early detection of esophageal dysplasia. Our model may also be applicable to other inflammation-associated cancers.
This proposal studies the role of a particular enzyme NOX5-S in the progression from Barrett's esophagus, a condition where cells in the esophagus have been altered by acid reflux, to esophageal cancer. This project is designed to find potential therapeutic targets to prevent this progression.
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