All growth factors significantlyactivated ERK in SH-SY5Y neuroblastoma cells, in particular after induction ofcell differentiation with retinoic acid and treatment of cells with the ERKinhibitor SCH772984(Fig. 3A).The growth factors also activated ERK in thecontrol U-251 astrocytoma cells (treated with DMSO only) and SCH772984-treatedcells (Fig. 3A).However, treatment of U-251 cells with retinoic acid resultedin less pronounced effects of EGF, IGF-1, and BDNF. Here, IGF1 is linked to astrocytoma (excluding glioblastoma).