Journal of Neuroscience, Vol 10, 1398-1406, Copyright © 1990 by Society for Neuroscience
Factors influencing GAP-43 gene expression in PC12 pheochromocytoma cells
B Costello, A Meymandi and JA Freeman
Department of Cell Biology, Vanderbilt Medical School, Nashville, Tennessee 37232.
We have studied factors controlling message levels for the neuronal growth-
and plasticity-associated protein, GAP-43. Following exposure of PC12 cells
to various effectors, cytoplasmic RNA was isolated and analyzed by Northern
transfer and autoradiography using a GAP-43 cDNA probe. Induction by NGF is
apparent after 3 hr exposure and reaches maximal levels at 24 hr. Beyond 24
hr, levels remain constant in the continued presence of NGF. Induction is
insensitive to variations in culture conditions, such as plating density or
substrate, which influence NGF-induced neurite outgrowth. Other inducers,
in order of decreasing efficacy, are FGF, dBcAMP, TPA, K+, and EGF. Insulin
and retinoic acid are ineffective. Dexamethasone partially inhibited basal
expression as well as induction by NGF, FGF, dBcAMP, and TPA. The
methyltransferase inhibitor 5'-S-(2-methyl-propyl)adenosine completely
inhibited induction by NGF, FGF, and dBcAMP. Inhibition of protein
synthesis by cycloheximide partially decreased induction by NGF, FGF, and
TPA but slightly enhanced dBcAMP induction. Complete down- regulation of
protein kinase C by chronic TPA treatment completely eliminated the TPA
response but slightly enhanced induction by NGF. These findings and the
results of additivity experiments in which cells were stimulated with
various combinations of NGF, dBcAMP and TPA suggest that NGF induction of
GAP-43 RNA (1) does not involve activation of protein kinase C but (2) may
be mediated partially via activation of protein kinase A.