Nerve growth factor- and epidermal growth factor-regulated gene transcription in PC12 pheochromocytoma and INS-1 insulinoma cells

PC12 and INS-1 cells both express the nerve growth factor (NGF) receptors t rkA and p75NTR and the epidermal growth factor receptor (EGF). In PC12 cell s, NGF treatment initiates a signaling cascade that ultimately leads to a c hange of the genetic program of the cell. We have investigated the role of NGF in regulating gene transcription in PC12 and INS-1 cells, in order to d efine if there are NGF-regulated genes per se. Furthermore, to distinguish between growth factor stimulation via receptor tyrosine kinases in general and NGF-specific changes in gene transcription, we analyzed the effects of EGF on gene transcription. First, we tested the biological activities of fu sion proteins consisting of the DNA-binding domain of the yeast transcripti on factor GAL4 and the phosphorylation-dependent activation domains of the transcription factors Elk1, CREB, ATF2 and c-jun in NGF- or EGF-treated PC1 2 cells. We found a striking increase in the transcriptional activity of th e GAL4-Elk1 fusion protein that is a major substrate for the extracellular signal-regulated protein kinase (ERK). This effect eras observed in NGF- as well as in EGF-treated PC12 cells, In INS-1 cells, however, the activity o f the GAL4-Elk1 fusion protein was induced by NGF but not by EGF, The effec ts of NGF and EGF on gene transcription were subsequently studied with plas mids containing reporter genes under control of the Egr-1, c-jun, HES-1 or Bcl2 regulatory sequences. NGF stimulated Egr-1 promoter activities in PC12 and INS-1 cells, although the effect was much more pronounced in PC12 cell s than in INS-1 cells. EGF also stimulated Egr-1 promoter activity in both PC12 and INS-1 cells. Stimulation of c-jun promoter activity by NGF was obs erved only. in PC12 cells. Deletion mutagenesis demonstrated the importance of the 12-O-tetradecanoylphorbol-13-acetate response elements within the c -jun promoter for basal and NGF-mediated transcriptional induction. Likewis e, NGF activated HES1 and Bcl2 P1 promoter activities in PC12 cells but not in INS-1 cells and EGF did not show any effects on these promoters, We con clude that in PC12 and INS-I cells, NGF signaling leads to an activation of the ERK subtype of mitogen-activated protein kinases in the nucleus and a subsequent activation of Egr-1 gene transcription, The NGF-induced transcri ption of the c-jun, HES1 and Belt genes is, in contrast, cell type-specific , indicating that NGF can trigger different gene expression programs depend ent on the signaling pathways present in a particular cell type. EGF is cle arly able to activate gene transcription, suggesting that the differences i n the biological activities of EGF and NGF cannot be explained by the inabi lity of EGF to stimulate gene transcription.