APE1-mediated DNA damage repair provides survival advantage for esophageal adenocarcinoma cells in response to acidic bile salts
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Jun Hong1, Zheng Chen1, Dunfa Peng1, Alexander Zaika1,2,3, Frank Revetta4, M. Kay Washington4, Abbes Belkhiri1, Wael El-Rifai1,2,3
1Department of Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA
2Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, Tennessee, USA
3Department of Veterans Affairs, Tennessee Valley Healthcare System, Nashville, Tennessee, USA
4Department of Pathology, Vanderbilt University Medical Center, Nashville, Tennessee, USA
Wael El-Rifai, e-mail: firstname.lastname@example.org
Keywords: APE1, acidic bile salts, JNK, p38, base excision repair
Received: January 08, 2016 Accepted: February 11, 2016 Published: February 25, 2016
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.
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