REGULATION OF GLIAL-CELL LINE-DERIVED NEUROTROPHIC FACTOR RELEASE FROM RAT C6 GLIOBLASTOMA CELLS

We have monitored glial cell line-derived neurotrophic factor (GDNF) s ecretion from rat C6 glioblastoma cells by ELISA. Representative cytok ines, neurotrophins, growth factors, neuropeptides, and pharmacologica l agents were tested for their ability to modulate GDNF release. Where as most factors tested had minimal effect, a 24-h treatment with fibro blast growth factor-1, -2, or -9 elevated secreted GDNF protein levels five-to 10-fold. The proinflammatory cytokines interleukin-l beta, in terleukin-6, tumor necrosis factor-alpha, and lipopolysaccharide eleva ted GDNF release 1.5- to twofold. Parallel studies aimed at elucidatin g intracellular events that may regulate GDNF synthesis/release demons trated the involvement of multiple signaling pathways. GDNF levels wer e increased by phorbol 12,13-didecanoate (10 nM) activation of protein kinase C, the Ca2+ ionophore A23187 (1 mu M), okadaic acid (10 nM) in hibition of type-2A protein phosphatases, nitric oxide donors (1 mM), and H2O2 (1 mM)-induced oxidative stress. Elevation of cyclic AMP leve ls by either forskolin (10 mu M) or dibutyryl cyclic AMP (1 mM) repres sed GDNF secretion, as did treatment with the glucocorticoid dexametha sone (1 mu M). Our results demonstrate that diverse biological factors are capable of modulating GDNF protein levels and that multiple signa l transduction systems can regulate GDNF synthesis and/or release.