Abstract
Chronic Gastroesophageal Reflux Disease (GERD) is the main risk factor for the development of Barrett's esophagus (BE) and its progression to esophageal adenocarcinoma (EAC). Accordingly, EAC cells are subjected to high levels of oxidative stress and subsequent DNA damage. In this study, we investigated the expression and role of Apurinic/apyrimidinic endonuclease 1 (APE1) protein in promoting cancer cell survival by counteracting the lethal effects of acidic bile salts (ABS)-induced DNA damage. Immunohistochemistry analysis of human tissue samples demonstrated overexpression of APE1 in more than half of EACs (70 of 130), as compared to normal esophagus and non-dysplastic BE samples (P < 0.01). To mimic in vivo conditions, we treated in vitro cell models with a cocktail of ABS. The knockdown of endogenous APE1 in EAC FLO-1 cells significantly increased oxidative DNA damage (P < 0.01) and DNA single- and double-strand breaks (P < 0.01), whereas overexpression of APE1 in EAC OE33 cells reversed these effects. Annexin V/PI staining indicated that the APE1 expression in OE33 cells protects against ABS-induced apoptosis. In contrast, knockdown of endogenous APE1 in FLO-1 cells increased apoptosis under the same conditions. Mechanistic investigations indicated that the pro-survival function of APE1 was associated with the regulation of stress response c-Jun N-terminal protein kinase (JNK) and p38 kinases. Pharmacological inhibition of APE1 base excision repair (BER) function decreased cell survival and enhanced activation of JNK and p38 kinases by ABS. Our findings suggest that constitutive overexpression of APE1 in EAC may be an adaptive pro-survival mechanism that protects against the genotoxic lethal effects of bile reflux episodes.
Highlights
The incidence of esophageal adenocarcinoma (EAC) has risen rapidly over the past few decades in the United States and the Western world [1, 2]
Because of the high expression levels of apyrimidinic endonuclease 1 (APE1) in neoplastic Barrett’s (HGD and EAC) and its role in DNA repair, we evaluated the DNA damage levels by Western blot analysis of p-H2AX (S139) in response to acidic bile salts in OE33 and FLO-1 EAC cell lines with different levels of APE1 expression
We found that p-H2AX was substantially induced in response to acidic bile salts in OE33 cells, which exhibit low APE1 expression (Figure 1F)
Summary
The incidence of esophageal adenocarcinoma (EAC) has risen rapidly over the past few decades in the United States and the Western world [1, 2]. BE is a premalignant metaplastic columnar epithelial lesion that can progress to EAC through intermediate stages of lowand high-grade dysplasia (reviewed by [6]) This abnormal exposure of esophageal cells to a mixture of acid and bile salts is not limited to BE, but exists in the continuum www.impactjournals.com/oncotarget of neoplastic progression to EAC. Previous reports have shown that several genes that function as ROS-buffering system in normal cells are silenced in EAC [17,18,19], raising important questions about regulation of oxidative DNA damage levels in cancer cells This chronic exposure to high levels of ROS in neoplastic Barrett’s generates high levels of oxidative DNA damage, if unrepaired will lead to accumulation of lethal levels of DNA damage
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