NERVE AND EPIDERMAL GROWTH-FACTOR INDUCE PROTEIN-SYNTHESIS AND EIF2B ACTIVATION IN PC12 CELLS

The regulation of protein synthesis and of eukaryotic initiation facto r eIF2B was studied in PC12 cells. An increase in protein synthesis wa s observed after nerve growth factor (NGF) and epidermal growth a fact or (EGF) treatment of PC12 cells, and this increase coincided with act ivation of eIF2B. Growth factor addition in the presence of the phosph atidylinositol-3'-OH kinase inhibitor wortmannin showed that both NGF- and EGF-induced protein synthesis and eIF2B activation were phosphati dylinasitol-3'-OH kinase dependent. The EGF-induced stimulation of pro tein synthesis and activation of eIF2B was dependent upon FK506-bindin g protein-rapamycin-associated protein, as shown with the immunosuppre ssant rapamycin, whereas NGF induction was partially dependent upon FK 506-bindinag protein-rapamycin-associated protein. The activities of t wo kinases that act on eIF2B, glycogen synthase kinase-3 and casein ki nase II, were measured to assess their potential roles in the activati on of eIF2B in PC12 cells. inactivation of glycogen synthase kinase-3 was seen in response to both NGF and EGF and this coincided with activ ation of eIF2B. However, inactivation of glycogen synthase kinase-3 wa s not rapamycin sensitive, in contrast to the activation of eIF2B. Thi s indicates the involvement of another protein kinase or regulatory me chanism in the eIF2B activation. Both growth factors activated casein kinase II. However, the time course of its activation and its insensit ivity to wortmannin and rapamycin suggest that casein kinase II does n ot play a major regulatory role in eIF2B activation under these condit ions.