Abstract 2097: A novel J-series prostamide induces ER stress-mediated apoptosis and upregulates ER oxidoreductase 1 alpha (ERO1α) in human colon cancer cells

Colon cancer is the third most common cancer and the third leading cause of cancer-related death in the United States. The endoplasmic reticulum (ER) is a cellular organelle responsible for protein synthesis and oxidative folding. ER stress occurs when the protein folding load exceeds the protein folding capacity. Low levels of ER stress promote survival while excessive ER stress causes cell death. An important regulator of the cytotoxic ER stress pathway is the transcription factor, C/EBP homologous protein 10 (CHOP10). It has been shown that CHOP10 regulates the transcription of ER oxidoreductase 1α (ERO1α). ERO1α promotes ER luminal oxidation and under conditions of excessive ER stress releases H2O2 into the cytoplasm, resulting in oxidative stress-mediated apoptosis. Previous studies from our laboratory showed that 15deoxy, Δ12,14 prostamide J2 (15d PMJ2) induced ER stress-mediated apoptosis, leading to a reduction in cell viability in tumorigenic keratinocytes and melanocytes. In addition, 15d PMJ2-induced ER stress-apoptosis was decreased in the presence of ER stress inhibitors, 4-phenylbuterate (PBA) and salubrinal. However, the specific pathway involved in 15d PMJ2-induced ER stress-apoptosis have not been identified. In this study, we hypothesize that 15d PMJ2 causes ER stress-mediated apoptosis in colon tumor cells by activating CHOP10 and its downstream transcriptional target, ERO1α. To examine the anti-proliferative effect of 15d PMJ2, tumorigenic colon cells (HCT116) and non-tumorigenic colon cells (FHC) were treated with different concentrations of 15d PMJ2 or 10µM thapsigargin (TG) for 24 hours and cytotoxicity was measured by lactate dehydrogenase (LDH) assay. A significant increase in cell death was observed in HCT116 cells treated with 5µM 15d PMJ2 and this cytotoxic effect was 3-fold greater in HCT116 compared to FHC cells. Apoptotic measurements showed a significant increase in caspase 3/7 activity and annexin-V positivity following 15d PMJ2 treatment. The expression of CHOP10 was significantly enhanced in the 15d PMJ2-treated group. In addition, 15d PMJ2-induced apoptosis was decreased in the presence of ER stress inhibitors, PBA and salubrinal, suggesting that ER stress is essential for 15d PMJ2-induced apoptosis. Western blot analysis revealed an increase in ERO1α protein expression following 15d PMJ2 treatment. Apoptosis measurements showed a significant inhibition in 15d PMJ2-mediated apoptosis in the presence of ERO1α inhibitor, EN460, suggesting that ERO1α is important for 15d PMJ2-induced apoptosis. These findings suggest that 15d PMJ2-induced apoptosis is mediated via the ER stress pathway. CHOP10 and its transcriptional target, ERO1α, play a potential role in 15d PMJ2-induced ER stress-apoptosis, suggesting that 15d PMJ2 could be a potential anti-neoplastic agent with a unique mechanism for colon cancer. Citation Format: Hussam M. Albassam, Daniel A. Ladin, Rukiyah Van Dross. A novel J-series prostamide induces ER stress-mediated apoptosis and upregulates ER oxidoreductase 1 alpha (ERO1α) in human colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2097. doi:10.1158/1538-7445.AM2017-2097