Background: Our previous study has demonstrated that knockdown of activated ERK1/2(pERK1/2) sensitizes pancreatic cancer cells to chemotherapeutic drug gemcitabine (Gem) treatment. However, the details of this survival mechanism remain undefined. It has also shown that Bcl-2 confers resistance and Bax sensitizes to gemcitabine-induced apoptosis in pancreatic cancer cells. Furthermore, the extracellular signaling-regulated kinase (ERK) signaling pathway regulates Bcl-2/Bax expression ratio. We therefore tested the hypothesis that pancreatic cancer cells are resistant to gemcitabine and this resistance is due to activation of ERK1/2 and subsequent upregulation of Bcl-2 and downregulation of Bax.
Methods: Pancreatic cancer cell BXPC-3 was used in the study. The effect of pharmacological inhibition of ERK1/2 on resistance of pancreatic cancer cells to apoptosis induced by treatment with gemcitabine was analyzed. The following methods were utilized: TUNEL and ELISA were used to detect apoptosis. Western blot was used to detect the protein expression.
Results: Gemcitabine treatment enhanced the activity of ERK1/2 in the BXPC-3 cells. Inhibition of the ERK1/2 by PD98059 could downregulate Bcl-2 and upregulate Bax and was associated with restoration of sensitivity to gemcitabine in BXPC-3 cells. Depletion of endogenous Bcl-2 expression by specific small interfering RNA transfection significantly increased gemcitabine-induced cell apoptosis. Combined treatment with PD98059 and Bax siRNA transfection could decrease gemcitabine-induced ERK1/2 and Bax activation, which subsequently resulted in decreased apoptosis.
Conclusions: The upregulation of ERK1/2-dependent Bcl-2 and downregulation of ERK1/2-dependent Bax can protect human pancreatic cancer cells from gemcitabine-induced apoptosis. Targeting the ERK1/2-Bax/Bcl-2 pathway may in part lead to sensitization of pancreatic cancer to gemcitabine.