H7, AN INHIBITOR OF PROTEIN-KINASE-C, PREVENTS SERUM-INDUCED PHOSPHORYLATION OF RAF AND MAP KINASE IN NEUROBLASTOMA-CELLS

We have previously shown that 1-(5-isoquinolinylsulfonyl)-2-methylpipe razine (H7), an inhibitor of protein kinase C, inhibits proliferation of neuroblastoma cells in culture. We have now tested whether the effe ct of 117 is mediated by MAP kinase and Raf. It is shown that, in Neur o 2a cells, activation of protein kinase C by addition of 4 beta-phorb ol-12 beta-myristate-13 alpha-acetate (PMA), leads to phosphorylation of Raf and Mitogen-activated protein kinase (MAP kinase). PMA-induced phosphorylation of these proteins is prevented by H7. When quiescent N euro 2a were stimulated to proliferate by addition of serum, Raf and M AP kinase were rapidly phosphorylated. Serum-induced phosphorylation o f Raf and MAP kinase is prevented by H7. These results suggest that, i n Neuro ia cells, the control of proliferation by protein kinase C cou ld be mediated by phosphorylation (and concomitant activation) of Raf and MAP kinase.