DYNAMIC CHANGES IN THE COMPOSITION OF THE AP-1 TRANSCRIPTION FACTOR DNA-BINDING ACTIVITY IN RAT-BRAIN FOLLOWING KAINATE-INDUCED SEIZURES AND CELL-DEATH

Kainate, a potent excitatory and neurotoxic agent, has also proved useful in studies on other glutamate-driven phenomena, such as neuronal plasticity. Long-term effects of kainate are apparently dependent on its influence on the expression of various genes, including those encoding the AP-1 transcription factor, consisting of proteins belonging to the Fos and Jun families. In our studies we analysed c-fos, fos B, c-jun, jun B and jun D mRNA levels as well as a functional feature of AP-1, its DNA-binding activity, in the rat brain following systemic injection of kainate. Two phases of elevated AP-1 DNA-binding activity were observed in the hippocampus and entorhinal cortex, and were correlated with period of seizures (2 and 6 h after kainate injection) and neuron damage (48 - 72 h). At 72 h after kainate treatment DNA fragmentation, believed to be diagnostic of apoptotic processes typical of programmed cell death phenomena, was noted. Two and six hours after the treatment, AP-1 consisted predominantly of Fos B, c-Fos, Fra-2 and Jun B, while at 72 h Jun D constituted the major AP-1 component in place of Jun B, and no c-Fos was detected. Only a slight AP-1 increase was seen 24 h after kainate treatment. In the sensory cortex, only the late phase of AP-1 elevation was detected. Contrary to AP-1, no effect of kainate on levels of two other transcription factors, CREB/ATF (cAMP-responsive element binding proteins) and OCT (octamer element DNA-binding activity) was seen. However, the level of OCT DNA-binding activity was higher in the sensory cortex than in other two structures examined. These data point to a selective effect of kainate on AP-1 in brain structures known to be particularly vulnerable to kainate, and suggest a role of AP-1 transcription factor, and more selectively Jun D protein, in kainate-driven programmed neuronal death.