PROTEIN-KINASE-C ISOFORMS AND GROWTH, DIFFERENTIATION AND PHOSPHATIDYLCHOLINE TURNOVER IN HUMAN NEUROBLASTOMA-CELLS

Neuroblastoma and glioma cells differentially express isoforms of prot ein kinase C (PKC) and myristoylated PKC substrates (e.g. MARCKS). Cor relation with metabolism of membrane phospholipids suggests that PKC-a lpha and MARCKS may be required to mediate phosphatidylcholine turnove r stimulated by phorbol ester (beta-TPA). To evaluate relationships to neural cell differentiation, SK-N-SH human neuroblastoma cells were t reated with 20 nM beta-TPA. In beta-TPA-treated cells, growth arrest a nd differentiation occurred (neurite extension; 40-60% decrease in cel l number, total protein and RNA). By day 4, mRNA for PKC-alpha and MAR CKS increased and, after an initial decrease, PKC-alpha protein also i ncreased. At day 4, phosphatidylcholine synthesis was 3-5 fold greater than in control cells. In contrast, C6 glioma cells treated with beta -TPA showed no growth arrest, decreased PKC-alpha-protein (< 20%) and lower phosphatidylcholine synthesis. Thus, induced differentiation of human neuroblastoma cells involved increased expression of PKC-alpha a nd MARCKS and synthesis of phosphatidylcholine, consistent with involv ement of PKC-alpha and MARCKS in regulation of phosphatidylcloline tur nover during neurite growth.