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Glial cell line-derived neurotrophic factor (GDNF) is synthesized as a precursor, proGDNF. However, the molecular mechanisms for the processing and secretion of GDNF are not fully characterized, since the amount of its biosynthesis and secretion in glial cells are below the detection limit of western blotting. We established stably GDNF-overexpressing C6 cells, and this enabled us to monitor its spontaneous secretion, as well as its processed forms in the cells. GDNF secretion was augmented by stimulation with high potassium, while it was inhibited by treatment with either tunicamycin, an inhibitor of protein glycosylation, or brefeldin A, a disturbing factor of ER-Golgi transport. Wild-type GDNF transfected cells secreted three forms of processed GDNF. After deglycosylation, the highest molecular weight of secreted GDNF showed the same mobility on electrophoresis as recombinant human GDNF without a …