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

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.