Abstract
The protocatechuic acid ethyl ester ethyl-3,4-dihydroxybenzoate is an antioxidant found in the testa of peanut seeds. Previous studies have shown that ethyl-3,4-dihydroxybenzoate can effectively reduce breast cancer cell metastasis by inhibiting prolyl-hydroxylase. In this study, we investigated the cytotoxic effect of ethyl-3,4-dihydroxybenzoate on esophageal squamous cell carcinoma cells in vitro and identified key regulators of ethyl-3,4-dihydroxybenzoate-induced esophageal cancer cell death through transcription expression profiling. Using flow cytometry analysis, we found that ethyl-3,4-dihydroxybenzoate induced S phase accumulation, a loss in mitochondrial membrane permeabilization, and caspase-dependent apoptosis. Moreover, an expression profile analysis identified 46 up- and 9 down-regulated genes in esophageal cancer KYSE 170 cells treated with ethyl-3,4-dihydroxybenzoate. These differentially expressed genes are involved in several signaling pathways associated with cell cycle regulation and cellular metabolism. Consistent with the expression profile results, the transcriptional and protein expression levels of candidate genes NDRG1, BNIP3, AKR1C1, CCNG2 and VEGFA were found to be significantly increased in treated KYSE 170 cells by reverse-transcription PCR and western blot analysis. We also found that protein levels of hypoxia-inducible factor-1α, BNIP3, Beclin and NDRG1 were increased and that enriched expression of BNIP3 and Beclin caused autophagy mediated by microtubule-associated protein 1 light chain 3 in the treated cells. Autophagy and apoptosis were activated together in esophageal cancer cells after exposed to ethyl-3,4-dihydroxybenzoate. Furthermore, knock-down of NDRG1 expression by siRNA significantly attenuated apoptosis in the cancer cells, implying that NDRG1 may be required for ethyl-3,4-dihydroxybenzoate-induced apoptosis. Together, these results suggest that the cytotoxic effects of ethyl-3,4-dihydroxybenzoate were mediated by the up-regulation of NDRG1, BNIP3, Beclin and hypoxia-inducible factor-1α, initiating BNIP3 and Beclin mediated autophagy at an early stage and ultimately resulting in esophageal cancer cell apoptosis.
Highlights
Esophageal cancer is the sixth leading cause of cancer-related death worldwide and ranks as the fourth most common cause of cancer-related death in China based on the GLOBOCAN 2008 estimates [1,2]
We focused on identifying the molecular regulators involved in EDHB-induced KYSE 170 cell cytotoxicity
We found that EDHB caused concentration- and time-dependent cell death
Summary
Esophageal cancer is the sixth leading cause of cancer-related death worldwide and ranks as the fourth most common cause of cancer-related death in China based on the GLOBOCAN 2008 estimates (http://globocan.iarc.fr/) [1,2]. Chemoprevention studies based on a phase II clinical trial in esophageal cancer showed that strawberries could significantly reduce the histological grade of precancerous lesions of the esophagus [8]. The mechanism underlying these effects may be associated with the inhibition of cell proliferation, inflammation, and tumor angiogenesis [9,10]. Another trial showed that nutritional intervention significantly prevented ESCC development after dietary supplementation with selenium, vitamin E, and beta-carotene [11]. Whether EDHB can inhibit esophageal cancer cell growth and the possible underlying molecular mechanisms remain unknown
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