Immunocytochemical analysis of phosphatidylinositol-specific phospholipase C in PC12 cells: predominance of the delta isoform during neural differentiation.

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 beta, PIC gamma, PIC delta. 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 beta was detected in the nucleus whereas PIC delta was only cytoplasmic; PIC gamma 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 gamma isoform was concentrated near the nucleus, while the immunoreactivity of the beta form remained constant and the delta form was increased. After 10 days of treatment with NGF, PIC beta was hardly detectable and PIC gamma immunostaining was considerably decreased. On the contrary, PIC delta 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 beta and PIC gamma were almost negative. These results suggest that NGF dependent neural differentiation is related to the selective down regulation of PIC beta and gamma and the increase of PIC delta isozyme associated with the decrease of cell proliferation.