Activation of EGFR-DNA-PKcs pathway by IGFBP2 protects esophageal adenocarcinoma cells from acidic bile salts-induced DNA damage

Zhangjian Zhou,Heng Lu,Jin Yan,Ahmed Gomaa,Chengxue Dang,Zheng Chen,Shoumin Zhu,Dunfa Peng,Wael El-Rifai,Kay Washington

doi:10.1186/s13046-018-1021-y

Abstract

BackgroundThe incidence of esophageal adenocarcinoma (EAC) is rising rapidly in the US and Western countries. The development of Barrett’s esophagus (BE) and its progression to EAC have been linked to chronic gastroesophageal reflux disease (GERD). Exposure of BE and EAC cells to acidic bile salts (ABS) in GERD conditions induces high levels of oxidative stress and DNA damage. In this study, we investigated the role of insulin-like growth factor binding protein 2 (IGFBP2) in regulating ABS-induced DNA double-strand breaks.MethodsReal-time RT-PCR, western blot, immunohistochemistry, immunofluorescence, co-immunoprecipitation, flow cytometry, and cycloheximide (CHX) chase assays were used in this study. To mimic GERD conditions, a cocktail of acidic bile salts (pH 4) was used in 2D and 3D organotypic culture models. Overexpression and knockdown of IGFBP2 in EAC cells were established to examine the functional and mechanistic roles of IGFBP2 in ABS-induced DNA damage.ResultsOur results demonstrated high levels of IGFBP2 mRNA and protein in EAC cell lines as compared to precancerous Barrett’s cell lines, and IGFBP2 is frequently overexpressed in EACs (31/57). Treatment of EAC cells with ABS, to mimic GERD conditions, induced high levels of IGFBP2 expression. Knocking down endogenous IGFBP2 in FLO1 cells (with constitutive high levels of IGFBP2) led to a significant increase in DNA double-strand breaks and apoptosis, following transient exposure to ABS. On the other hand, overexpression of exogenous IGFBP2 in OE33 cells (with low endogenous levels of IGFBP2) had a protective effect against ABS-induced double-strand breaks and apoptosis. We found that IGFBP2 is required for ABS-induced nuclear accumulation and phosphorylation of EGFR and DNA-PKcs, which are necessary for DNA damage repair activity. Using co-immunoprecipitation assay, we detected co-localization of IGFBP2 with EGFR and DNA-PKcs, following acidic bile salts treatment. We further demonstrated, using cycloheximide chase assay, that IGFBP2 promotes EGFR protein stability in response to ABS exposure.ConclusionsIGFBP2 protects EAC cells against ABS-induced DNA damage and apoptosis through stabilization and activation of EGFR - DNA-PKcs signaling axis.

Highlights

The incidence of esophageal adenocarcinoma (EAC) is rising rapidly in the US and Western countries
We hypothesized that insulin-like growth factor binding protein 2 (IGFBP2) upregulation is due to adaption to acidic bile salts under gastroesophageal reflux disease (GERD) conditions
Of note, following transient exposure of 20 min, we detected a remarkable induction of IGFBP2 in protein and mRNA levels in FLO1 (Fig. 2a and c), OE33 (Fig. 2b and d) and OE19 (Additional file 2: Figure S1) cells

Summary

Introduction

The incidence of esophageal adenocarcinoma (EAC) is rising rapidly in the US and Western countries. Abnormal exposure of esophageal cells to a mixture of acid and bile salts in patients with chronic gastroesophageal reflux disease (GERD) is a major risk factor for the development of pre-malignant Barrett’s esophagus (BE) and its progression to EAC [3, 4]. DNA-dependent protein kinase, catalytic subunit (DNA-PKcs) is an enzyme encoded by PRKDC in humans [9] It contributes to the repair of DNA double-strand breaks (DSBs) by accessing broken ends of DNA in combination with the other two DNA-binding factors, Ku70 and Ku80 [10]. Earlier reports have shown that epidermal growth factor receptor (EGFR) plays an important role in the regulation of DNA-PKcs activity in response to radiation or anti-cancer drugs that induce DNA damage [17, 18]. EGFR nuclear localization is required for modulation of the repair of cisplatin and ionizing radiation-induced DNA damage [17,18,19]

Methods

Results

Discussion

Conclusion