Protein kinase C isoforms and growth, differentiation and phosphatidylcholine turnover in human neuroblastoma cells

Neuroblastoma and glioma cells differentially express isoforms of protein kinase C (PKC) and myristoylated PKC substrates (e.g. MARCKS). Correlation with metabolism of membrane phospholipids suggests that PKC-α and MRCKS may be required to mediate phosphatidylcholine turnover stimulated by phorbol ester (β-TPA). To evaluate relationships to neural cell differentiation, SK-N-SH human neuroblastoma cells were treated with 20 nM β-TPA. In β-TPA-treated cells, growth arrest and differentiation occurred (neurite extension; 40–60% decrease in cell number, total protein and RNA). By day 4, mRNA for PKC-α and MARCKS increased and, after an initial decrease, PKC-α protein also increased. At day 4, phosphatidylcholine synthesis was 3–5 fold greater than in control cells. In contrast, C6 glioma cells treated with β-TPA showed no growth arrest, decreased PKC-α protein (<20%) and lower phosphatidylcholine synthesis. Thus, induced differentiation of human neuroblastoma cells involved increased expression of PKC-α and MARCKS and synthesis of phosphatidylcholine, consistent with involvement of PKC-α and MARCKS in regulation of phosphatidylcholine turnover during neurite growth.