Submitted on June 26, 2007
Accepted on October 12, 2007
STAT5 Mediates Platelet-Activating Factor (PAF)-Induced NADPH Oxidase NOX5-S Expression In Barrett's Esophageal Adenocarcinoma Cells
Jin Si1, Jose Behar1, Jack Wands1, David G. Beer2, David Lambeth3, Y. Eugene Chin1, and Weibiao Cao1*
1 Brown Medical School & Rhode Island Hospital, Providence, Rhode Island, United States
2 University of Michigan Medical School, United States
3 Emory University School of Medicine, United States
* To whom correspondence should be addressed. E-mail: weibiao_cao{at}brown.edu.
We have shown that NADPH oxidase NOX5-S is overexpressed in Barrett's esophageal adenocarcinoma (EA) cells and may contribute to the progression from Barrett's esophagus (BE) to EA presumably by increasing cell proliferation and decreasing apoptosis (J Biol Chem 281(29): 20368-20382, 2006). The mechanism(s) of NOX5-S overexpression in EA, however, is not fully understood. In SEG1 EA cells we found that acid treatment significantly increased platelet activating factor (PAF) production, which in turn markedly increased NOX5-S expression and hydrogen peroxide (H2O2) production. Knockdown of NOX5-S by NOX5-S siRNA blocked PAF-dependent H2O2 production. PAF-dependent induction of NOX5-S expression and H2O2 production were significantly decreased by the mitogen-activated protein kinase (MAPK) kinase 1 inhibitor PD98059, by the cytosolic phospholipase A2 (cPLA2) inhibitor AACOCF3, and by STAT5 down regulation with STAT5 siRNA. PAF significantly increased the phosphorylation of ERK1/2 MAPK, cPLA2 and STAT5. Using inhibitors, we demonstrated that PAF-induced STAT5 phosphorylation depends on activation of ERK1/2 MAPK and cPLA2, while PAF-induced cPLA2 phosphorylation was associated with activation of ERK1/2 MAPK. Given that STAT5 bound to the SIE element (TTCTGGTAA) of the NOX5-S promoter, overexpression of STAT5 significantly increased NOX5-S promoter activity. We conclude that acid-induced NOX5-S expression and H2O2 production is mediated in part by production of PAF in SEG1 EA cells, and that PAF-induced increase in NOX5-S expression depends on sequential activation of ERK MAP kinases, cPLA2, and STAT5 in these cells.
