DIFFERENTIAL NUCLEAR-LOCALIZATION OF PROTEIN-KINASE-C ISOFORMS IN NEUROBLASTOMA X GLIOMA HYBRID-CELLS

The protein kinase C (PKC) alpha, beta and epsilon isoforms have distinct nuclear localizations in neuroblastoma X glioma hybrid cells NG 108-15. We found by immunoblotting that PKC alpha, beta(II) delta and epsilon are the predominant isoforms in these cells. In contrast to other neuronal cell lines, none of these isoforms is down-regulated during differentiation. Confocal immunofluorescence microscopy revealed that in undifferentiated cells PKC alpha is located in the cytoplasm and in the nucleus excluding nucleoli. In differentiated cells PKC alpha was almost exclusively located in the cytoplasm. Stimulation of the cells- with phorbol ester resulted in translocation to the plasma membrane, PKC beta(II) was not detectable in the nuclei: PKC delta was found in the nucleoli and in the cytoplasm, in differentiated cells particularly in the neurites. Phorbol ester failed to induce a translocation to other compartments. PKC epsilon was localized with the nuclear-pore complexes at the nuclear envelope. In differentiated cells after stimulation with phorbol ester, partial translocation to the plasma membrane was observed.