The regulation of the
preproneuropeptide Y gene (NPY gene) by
nerve growth factor (
NGF) and second messenger systems in PC12 rat
pheochromocytoma cells was studied by means of steady state NPY
mRNA and nuclear run-on transcription analyses. Treatment of cells with 2.5S
NGF increased the NPY
mRNA abundance up to 100-fold over 1-6 days.
Glucocorticoids (e.g.
dexamethasone) potentiated by up to 3-fold the stimulation by
NGF at early times (less than or equal to 7 h), but strongly suppressed it at later times (greater than or equal to 25 h). The response to
NGF was blocked by
cycloheximide, indicating a requirement for ongoing
protein synthesis. Treatment of cells for 24-48 h with combinations of
NGF,
forskolin to elevate cAMP levels, and phorbol-12-myristate-13-acetate (PMA) to activate
protein kinase C synergistically elevated NPY
mRNA levels. The rate of NPY gene transcription in PC12 nuclei was increased by
NGF,
forskolin plus PMA, or
NGF plus
forskolin plus PMA, indicating that these regulators act at least in part at a transcriptional level.
beta-Actin gene transcription also was elevated synergistically by
forskolin and PMA. In summary, NPY gene transcription and NPY
mRNA levels are controlled by multiple, potentially interacting regulatory systems. The striking antagonism between
NGF and
glucocorticoids may reflect the hormonal control of phenotypic choice during neural crest differentiation.