Involvement of phosphatidylinositol 3-kinase/Akt on basic fibroblast growth factor-induced glial cell line-derived neurotrophic factor release from rat glioma cells.

Basic fibroblast growth factor (FGF-2) has a neuroprotective effect. Astrocytes support neurons by releasing neurotrophic factors including glial cell line-derived neurotrophic factor (GDNF). FGF-2 stimulates GDNF synthesis in astrocytes and the release. It has been reported that FGF-2 induces the activation of p44/p42 mitogen-activated protein (MAP) kinase, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and p38 MAP kinase in C6 glioma cells, and that FGF-2 stimulates GDNF release through p44/p42 MAP kinase or SAPK/JNK, but not p38 MAP kinase. In the present study, we investigated the exact mechanism of FGF-2-induced GDNF release from C6 cells. FGF-2 induced the phosphorylation of Akt and its substrate, glycogen synthase kinase 3β (GSK3β) in addition to three MAP kinases in these cells. FGF-2-stimulated release of GDNF was suppressed by wortmannin (a phosphatidylinositol 3 (PI3)-kinase inhibitor) or LY294002 (another PI3-kinase inhibitor). The FGF-2-induced GDNF release from PI3-kinase-downregulated C6 cells was decreased compared with that in control siRNA-transfected cells. PD98059 (an inhibitor of MEK 1/2) or SP600125 (an inhibitor of SAPK/JNK), which suppressed FGF-2-induced phosphorylation of p44/p42 MAP kinase or SAPK/JNK respectively, did not affect FGF-2-induced Akt phosphorylation. Wortmannin or LY294002, which attenuated FGF-2-induced phosphorylation of Akt and GSK3β, had no effect on FGF-2-induced phosphorylation of p44/p42 MAP kinase or SAPK/JNK. These results strongly suggest that the PI3-kinase/Akt pathway plays a positive role in FGF-2-stimulated GDNF release independently of p44/p42 MAP kinase or SAPK/JNK in C6 glioma cells.