Activity and expression of JNK1, p38 and ERK kinases, c-Jun N-terminal phosphorylation, and c-jun promoter binding in the adult rat brain following kainate-induced seizures
K. Mielke et al., Activity and expression of JNK1, p38 and ERK kinases, c-Jun N-terminal phosphorylation, and c-jun promoter binding in the adult rat brain following kainate-induced seizures, NEUROSCIENC, 91(2), 1999, pp. 471-483
The activity and/or expression of the mitogen-activated protein kinases c-J
un N-terminal kinase 1, p38 and extracellular signal-regulated kinases 1/2,
as well as their substrates, the transcription factors c-Jun and activatin
g transcription factor-2, were examined following systemic application of k
ainate in the cortex and hippocampus of the adult rat brain. The protein ex
pression levels of all three mitogen-activated protein kinases remained con
stant during the observation period. Unexpectedly, c-Jun N-terminal kinase
1 was the only mitogen-activated protein kinase activated in this model of
excitotoxicity, its activity raised from between 1 and 3 h moderate basal t
o maximal levels between 6 and 12 h, In contradistinction, activity of extr
acellular signal-regulated kinases 1/2 fell from their substantial basal le
vels and did not recover; activity of p38 was characterized by a high basal
level that almost entirely disappeared and did not return to basal levels
even 10 days after kainate application. c-Jun protein was rapidly expressed
, with a maximum after 3 h and a slow decline after 12 h. Supershift assays
revealed that, during the early induction phase of the c-jun gene, the pro
ximal activator protein-1 (jun1) site of the c-jun promoter was mainly occu
pied by the constitutively expressed activating transcription factor-2, whe
reas the late induction correlated with the predominant binding of c-Jun an
d, to a lesser extent, activating transcription factor-2 to the distal acti
vator protein-1 (jun2) site. The time-course of the N-terminal phosphorylat
ion of c-Jun as determined by immunocytochemistry paralleled the activity o
f c-Jun N-terminal kinase 1 and showed a compartment-specific regulation be
tween 3 and 12 h. A second set of supershift experiments demonstrated that
c-Jun, but not activating transcription factor 2, bound to activator protei
n-1 sites in the promoter of substance P and collagenase genes, but not of
the cyclo-oxygenase-2 gene.
Our results demonstrate that activation of c-Jun N-terminal kinase I, phosp
horylation of c-Jun and selective occupation of the c-jun promoter by activ
ating transcription factor-2 or c-Jun are part of the neuronal response fol
lowing excitotoxicity that is considered as the mechanism for neuronal apop
tosis in vivo. Some of these findings differ substantially from in vitro ex
periments and underline the necessity to analyse the neuronal stress pathwa
ys in the adult brain. (C) 1999 IBRO. Published by Elsevier Science Ltd.