PHOSPHORYLATION AND REDISTRIBUTION OF THE PHOSPHATIDYLINOSITOL-TRANSFER PROTEIN IN PHORBOL 12-MYRISTATE 13-ACETATE-STIMULATED AND BOMBESIN-STIMULATED SWISS MOUSE 3T3 FIBROBLASTS

By immunofluorescence microscopy it was shown that the phosphatidylino sitol-transfer protein (PI-TP) becomes associated with the Golgi membr anes when confluent (quiescent) Swiss mouse 3T3 fibroblast cells are s timulated with phorbol 12-myristate 13-acetate (PMA) and bombesin. Dib utyryl cyclic AMP or dexamethasone had no effect on the intracellular redistribution of PI-TP. In exponentially growing cells and in serum-s tarved (semi-quiescent) cells, PI-TP is already associated with Golgi structures. Stimulation of semi-quiescent cells by PMA resulted in a r apid redistribution of PI-TP. A similar yet slower response was observ ed after stimulation with bombesin. Stimulation of semi-quiescent 3T3 cells by PMA significantly increased the phosphorylation of PI-TP, as shown by immunoprecipitation of PI-TP from pre-labelled cells. No sign ificant increase in phosphorylation of PI-TP was observed after stimul ation of these cells by bombesin. Purified PI-TP was shown to be a sub strate for protein kinase C in vitro. The possibility that the phospho rylation of PI-TP after activation of protein kinase C is involved in the observed redistribution of PI-TP is discussed.