The Journal of Neuroscience, March 15, 2000, 20(6):2142-2149
Changes in Activating Protein 1 (AP-1) Composition Correspond
with the Biphasic Profile of Nerve Growth Factor mRNA Expression in Rat
Hippocampus after Hilus Lesion-Induced Seizures
Robert C.
Elliott and
Christine M.
Gall
Department of Anatomy and Neurobiology, University of California,
Irvine, Irvine, California 92697
In adult brain, nerve growth factor (NGF) gene expression is
generally upregulated by neuronal activity. However, a single episode
of hilus lesion (HL)-induced limbic seizures stimulates a biphasic
increase in NGF mRNA expression with peaks at 4-6 and 24 hr after
lesion and an intervening return to control levels at 10-12 hr after
lesion. In vitro studies suggest that NGF transcription is regulated via an activating protein 1 (AP-1) binding site in the
first intron of the NGF gene. To examine the relationship between
seizure-induced AP-1 binding and NGF gene expression in this paradigm,
NGF mRNA levels and AP-1 binding were examined after HL seizures.
Furthermore, to gain insight into the functional composition of the
AP-1 complex, supershift analysis was performed to characterize which
Fos and Jun family members are included in the AP-1-binding complex at
the different time points analyzed. Solution hybridization analysis
verified the biphasic increase in NGF mRNA content of the dentate gyrus
after HL seizures. After an initial increase, AP-1 binding slowly
declined in a stepwise manner that encompassed, but did not correspond
with, the two phases of NGF mRNA expression. However, supershift
analyses demonstrated that the relative contributions of JunD and JunB
to the AP-1 complex exhibited positive and negative correlations,
respectively, with the phases of increased NGF expression after HL.
These results suggest that AP-1 complexes containing JunD promote NGF
transactivation and that transient changes in the relative
contributions of JunD and JunB to AP-1 binding underlie the biphasic
increase in NGF gene expression induced by HL seizures.
Key words:
neurotrophin; nerve growth factor; dentate gyrus; transcription factors; gene expression; JunB; JunD; AP-1
Copyright © 2000 Society for Neuroscience 0270-6474/00/2062142-08$05.00/0