Abstract 3793: Bile acids and autophagy resistance in Barrett's esophagus

Abstract

Abstract Background: Barrett's esophagus (BE) is a premalignant lesion of the distal esophagus that is associated with increased risk of esophageal cancer (EAC). Bile acids are implicated in BE development. Autophagy is a tightly-regulated process involving degradation and recycling of cellular proteins and organelles. The genetic links between autophagy defects and cancer suggest that autophagy is involved in tumor suppression. We have previously shown that acute exposure to bile acids induces autophagy. In this study we tested the hypothesis that chronic exposure to bile acids leads to loss of capability to undergo autophagy and that BE is resistant to autophagy. Methods: Tissue biopsies from sixty patients with different grades of BE dysplasia, EAC and control tissues were evaluated for the expression of Beclin, p-mTOR, p-AKT by immunohistochemistry. Transmission electron microscopy (TEM) was used to evaluate autophagy in tissues starved for 4 hours in Hank's balanced salt solution (HBSS, autophagy inducer). To study chronic effects of DCA in vitro we developed CP-A cells resistant to DCA. These new CP-AR cells are able to survive and proliferate in medium containing 0.2mM DCA. Both control CP-A cells and CP-AR cells were treated with DCA and then evaluated for autophagic markers, Beclin 1 and p62. Autophagy was also assessed by quantification of cells with the punctuate pattern of GFP-LC3. Results: Our data indicate that tissue biopsies from patients with BE dysplasia and esophageal adenocarcinoma: (1) are resistant to autophagy induced by HBSS, (2) express increased levels of proteins associated with autophagy resistance [phosphorylated Akt (p-Akt) and p-mTOR] and (3) express decreased levels of the key pro-autophagic protein Beclin-1. In addition, the levels of Beclin-1 in non-dysplastic tissue or control tissues (duodenum, squamous epithelium) were high, while p-mTOR and p-Akt were low. CP-AR cells treated with DCA expressed same levels of p62 and Beclin 1 as untreated cells. In contrast, the levels of these proteins were increased in parental CP-A cells exposed to DCA indicating an increase in autophagy. Furthermore, there was no significant difference in number of GFP-LC3 positive cells with punctuate pattern between untreated and DCA treated resistant CP-AR cells. However, 103% increase in GFP-LC3 positive cells with punctuate pattern was observed after DCA treatment in sensitive CP-A cells compared to untreated CP-A cells. Conclusion: Dysplastic BE and EAC have decreased capability to undergo autophagy. In vitro studies show that chronic exposure to bile acids may be crucial factor in the development of autophagy resistance in BE esophagus. These alterations may cause a consequent increase in DNA damage leading to cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3793. doi:10.1158/1538-7445.AM2011-3793