Protein kinase C isoenzymes in human neuroblasts involvement of PKCε in cell differentiation

Although neuronal cells are a major target of phorbol ester action, the activity of the various protein kinase C (PKC) isoenzymes have not been studied in detail in human neuroblasts. Differentiation of the LAN-5 human neuroblastoma cell line by interferon-γ (IFN-γ) is accompanied by a twofold increase in PKC activity. Since PKC is a multigene family, we investigated which isoforms were expressed in control and differentiated cells, and which of these isoenzymes is involved in neuronal differentiation. We found that: (1) PKC activity is higher in differentiated than in undifferentiated cells; (2) RT-PCR analysis showed the expression of mRNA for PKCα, -γ, -δ -ε and-ζ and the absence of mRNA for β in untreated LAN-5 cells; (3) Western blot evaluation with PKC isoform-specific antibodies showed the same pattern of PKC expression in non-differentiated cells; (4) Expression of PKCε mRNA was significantly enhanced by IFN-γ-induced differentiation, while the other isoforms were not affected; (5) Differentiation of LAN-5 cells with IFN-γ or retinoic acid induced overexpression of the PKCε protein, while inhibition of cell proliferation by fetal calf serum starvation was without effect. These findings suggest that expression of PKCε isoform is tightly coupled with neuronal differentiation and may play a role in the maintenance of the differentiated state.