Docosahexaenoic acid enhances the sensitivity of esophageal carcinoma cell line EC9706 to cisplatin via inhibiting endoplasmic reticulum stress

Abstract

Objective To investigate the effect of docosahexaenoic acid (DHA) on the sensitivity of esophageal carcinoma cell line EC9706 to cisplatin and the mechanism behind this effect. Methods EC9706 cells were randomly divided into 5 groups: control group, DHA group, cisplatin (DDP) group, DHA+ DDP group and endoplasmic reticulum stress (ERS) activation tunicamycin (TM) group (DHA+ DDP+ TM group). MTT method was used to evaluate inhibition ratio of cell proliferation. The apoptotic ratio was examined by flow eytometry.Western blot was used to detect the protein expressions of apoptosis cytokines (caspase-3 and Bcl-2) and ERS cytokines [glucose-regulated protein 78 (GRP78) and inositol-requiring enzyme 1 (IRE-1)]. Results DHA causes concentration-dependent and time-dependent inhibition of the proliferation of EC9706 cells (P=0.00). DHA significantly enhanced the sensitivity of esophageal carcinoma cell line EC9706 to cisplatin. Compared to DDP treatment alone, the inhibition ratio[(60.19±5.05)% vs. (36.72±3.52)%, P=0.02] and apoptotic ratio [(54.88±4.94)% vs. (39.74±4.64)%, P=0.03] of EC9706 cells were enhanced by DHA+ DDP treatment. Western blot showed that the expression of apoptotic factor caspase-3 protein was increased by DHA+ DDP treatment. Meanwhile, the protein expressions of anti-apoptotic factor (Bcl-2) and ERS-related factors (GRP78 and IRE-1) were significantly inhibited by DHA+ DDP treatment (P=0.01). However, the salutary effects of DHA were reversed by ERS activation tunicamycin. Conclusion DHA enhances the sensitivity of esophageal carcinoma cell line EC9706 to cisplatin, the mechanism of which may be the suppression of ERS response. Key words: Esophageal carcinoma cells; Docosahexaenoic acid; Cisplatin; Endoplasmic reticulum stress