OVEREXPRESSION OF MARCKS, BUT NOT PROTEIN-KINASE C-ALPHA, INCREASES PHORBOL ESTER-STIMULATED SYNTHESIS OF PHOSPHATIDYLCHOLINE IN HUMAN SK-N-MC NEUROBLASTOMA-CELLS

To investigate the regulation of phorbol ester-stimulated synthesis of phosphatidylcholine (PtdCho), myristoylated alanine-rich protein kina se C substrate (MARCKS) and the alpha-isoform of protein kinase C (PKC -alpha) were overexpressed in a human neuroblastoma (SK-N-MC) cell lin e that does not increase PtdCho synthesis in response to 4 beta-12-O-t etradecanoylphorbol 13-acetate (TPA). In five clones with a less than fivefold increase in MARCKS protein level, the synthesis of PtdCho fro m [methyl-H-3] choline was stimulated 1.88-2.34-fold in the presence o f 100-200 nM TPA. In clones overexpressing PKC-alpha (30-40-fold incre ased level of protein) or in mock-transfected vector controls, TPA had much less of a stimulatory effect (1.04-1.43-fold) on PtdCho synthesi s. TPA caused translocation of PKC-alpha and increased phosphorylation of MARCKS, indicating that both overexpressed proteins responded to s timulation. Thus, in SK-N-MC cells, MARCKS is required for TPA-stimula ted synthesis of PtdCho, and PKC-alpha alone is insufficient for suppo rting enhanced synthesis.