COX-2 Induction by Unconjugated Bile Acids Involves Reactive Oxygen Species-Mediated Signaling Pathways in Barrett's Oesophagus and Oesophageal Adenocarcinoma

Shumei Song ¹, Sushovan Guha ¹, Kaifeng Liu ¹, Navtej Buttar ² and Robert S Bresalier ^1*

¹ The University of Texas MD Anderson Cancer Center, United States
² Mayo Clinic, United States

^* To whom correspondence should be addressed. E-mail: rbresali{at}mdanderson.org.

Accepted 13 June 2007

Abstract

Objectives: Bile reflux contributes to oesophageal injury and neoplasia. COX-2 is involved in both inflammation and carcinogenesis; however the precise mechanisms by which bile acids promote COX-2 expression in the oesophagus are largely unknown. We analyzed the molecular mechanisms that govern bile acid-mediated expression of COX-2 in Barrett's oesophagus (BO) and oesophageal adenocarcinoma (OA).

Design: The effects of bile acids on COX-2 expression were analyzed in immortalized BO and OA cells using immunoblotting and transient transfections. Pharmacologic inhibitors, phospho-specific antibodies, dominant-negative (DN) mutants, and siRNA techniques were utilized to identify relevant signaling pathways. Flow cytometry and reactive oxygen species (ROS) scavengers were used to examine ROS involvement. Immunohistochemistry (IHC) was performed on oesophageal mucosa obtained from an established rat model of bile-reflux.

Results: Unconjugated bile acids potently stimulated COX-2 expression and induced AKT and ERK1/2 phosphorylation in concert with COX-2 induction. These findings were mimicked in the in vivo rat model. DN AKT and LY294002 (PI3K inhibitor) or U0126 (MEK-1/2 inhibitor) blocked CD and DC-mediated COX-2 induction. CD and DC also induced CREB phosphorylation and AP-1 activity. CREB-specific siRNA and DN AP-1 blocked CD and DC-induced COX-2 induction. Finally, CD and DC increased intracellular ROS, while ROS scavengers blocked COX-2 induction and the signaling pathways involved.

Conclusions: Unconjugated bile acids induce CREB and AP-1-dependent COX-2 expression in BO and OA through ROS-mediated activation of PI3K/AKT and ERK1/2. This study enhances our understanding of the molecular mechanisms by which bile acids promote the development of esophageal adenocarcinoma.

Keywords: Barrett's esophagus, bile acids, carcinogenesis, cyclooxygenase-2, reactive oxygen species

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