The rat pheochromocytoma PC12 cell line, which differentiates into sympathetic neurons under nerve growth factor (NGF) treatment, contains at least three phosphoinositidase C (PIC) isozymes, PIC β, PIC γ, PIC δ. These isozymes have been previously shown to display a different subcellular localization. To determine whether or not NGF induces changes in the presence and/or distribution of PIC isozymes during PC12 neural differentiation, studies were carried out by means of in situ immunocytochemistry. After NGF administration the proliferative activity was progressively reduced to very low levels, as measured by bromodeoxy Uridine incorporation, and a neuron-like morphology was displayed by almost all cells. In unstimulated PC12 cells, PIC β was detected in the nucleus whereas PIC δ was only cytoplasmic; PIC γ was found in both cell compartments. In cells treated with NGF for 3 days, neural processes extended to twice the diameter of the cell body; the γ isoform was concentrated near the nucleus, while the immunoreactivity of the β form remained constant and the δ form was increased. After 10 days of treatment with NGF, PIC β was hardly detectable and PIC γ immunostaining was considerably decreased. On the contrary, PIC δ progressively increased and, after 14 days of NGF exposure, fully differentiated cells displayed an intense labelling of cell body and neurites. In the same cells, PIC β and PIC γ were almost negative. These results suggest that NGF dependent neural differentiation is related to the selective down regulation of PIC β and γ and the increase of PIC δ isozyme associated with the decrease of cell proliferation.
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