Ets-1 expression and gemcitabine chemoresistance in pancreatic cancer cells

Gemcitabine, a novel pyrimidine nucleoside analog, has become the standard chemotherapeutic agent for pancreatic cancer patients. The clinical impact of gemcitabine remains modest owing to the high degree of inherent and acquired resistance. There are various lines of evidence that confirm the role of Ets-1, a proto-oncoprotein, in tumor invasion, progression, and chemoresistance. This study examines a hypothesis that implicates Ets-1 in the development of gemcitabine-resistance in pancreatic cancer cells. Ets-1 protein expression was assessed in parental pancreatic cancer cells and their gemcitabine-resistant clones. Western blot analysis revealed elevated levels of Ets-1 protein expression in gemcitabine-resistant PANC1(GemRes) (4.8-fold increase; P < 0.05), MIA PaCa2(GemRes) (3.2-fold increase; P < 0.05), and Capan2(GemRes) (2.1-fold increase; P < 0.05) cells as compared to their parental counterparts. A time course analysis was conducted to determine the change in Ets-1 expression in the parental cells after incubation with gemcitabine. Reverse transcriptase quantitative real-time PCR (RT-qPCR) and Western blot analysis revealed a significant increase in Ets-1 expression. All the three parental cells incubated with gemcitabine showed elevated Ets-1 protein expression at 6 h. By 24 h, the expression level had decreased. Using small interfering RNA (siRNA) against Ets-1 in gemcitabine-resistant cells, we demonstrated a reversal in gemcitabine chemosensitivity and also detected a marked reduction in the expression of the Ets-1 target genes MMP1 and uPA. Our novel finding demonstrates the significance of Ets-1 in the development of gemcitabine chemoresistance in pancreatic cancer cells. Based on these results, a new siRNA-based therapeutic strategy targeting the Ets-1 genes can be designed to overcome chemoresistance.