5?-Nucleotidase in PC12 cells as revealed by immunocytochemistry

5′-Nucleotidase hydrolyzes 5′-mononucleotides to their nucleosides but is also thought to have a function in neuronal differentiation and synapse formation. The distribution of the enzyme, a glycosyl-phosphatidylinositol-anchored sialoglycoprotein, was investigated in PC12 cells using immunofluorescence microscopy. 5′-Nucleotidase was located both in intracellular compartments and at the cell surface. There was no principal difference in the cellular distribution between undifferentiated cells and after neuritogenic differentiation by nerve growth factor. Intracellularly, 5′-nucleotidase often revealed a sickle-shaped perinuclear distribution and a dotted pattern throughout the cytoplasm, including that of neurites and growth cones. The intracellular distribution was clearly different from that of the synaptic vesicle protein synaptophysin. However, the dotted fluorescence resembled that obtained after uptake of the endosomal marker acridine orange. 5′-Nucleotidase was present on the entire cell surface including all neurites formed after differentiation. There was no increase in 5′-nucleotidase fluorescence at synapse-like contacts between the tips of neurites and other PC12 cells. Surfacelocated 5′-nucleotidase could no longer be detected after the application of glycosyl-phosphatidylinositol-specific phospholipase C to cultured cells. This treatment did not affect PC12 cell differentiation. Our results thus reveal 5′-nucleotidase both at the surface and within organelles and suggest that PC12 cells may be used as a model system for the study of the physiological function of 5′-nucleotidase in neural cells.