APE1 and GFRα1 increases ERK phosphorylation in response to GDNF. ( A ) MIA PaCa-2 cells were pretreated with MEK-1 inhibitor PD98059 (10 μM) and the PI3K inhibitor Wortmannin (200 μM) and then treated with or without 50 ng/mL GDNF for 24 h. After treatment, cell proliferation was analyzed by WST-1 assay. Data are expressed as mean ± standard deviation from three independent experiments. ** and # denote p