Transient expression of the mitogen-activated protein kinase phosphatase MKP-1 (3CH134/ERP1) in the rat brain after limbic epilepsy.

The immediate early gene-encoded enzyme, MAP kinase phosphatase 1 (MKP-1), is thought to be a key element in controlling cellular signalling pathways activated by MAP kinases. Since MAP kinase have been demonstrated to participate in neuronal stimulus-transcription coupling following seizure activity, the present study investigated the induction of MKP-1 in the rat brain after limbic epilepsy. MKP-1 expression was studied with a polyclonal antiserum by Western blots, immunocytochemistry and immuno-electron microscopy at different time periods between 1 and 24 h after kainic acid-induced limbic seizures. MKP-1 induction was identified in dentate granule cells of the hippocampus but not in pyramidal neurons, furthermore in neurons of the outer layers of the neocortex, as well as in neurons of the lateral nucleus of the bed of the stria terminalis. Immuno-electron microscopy demonstrated that MKP-1 was localized in the neuronal nucleus, where the substrate of MKP-1, activated MAP kinases, are also found. In view of the restricted areas of MKP-1 expression and the widespread areas of altered MAP kinases activity it can be concluded that in the majority of CNS populations other mechanisms than MKP-1 induction are responsible for the shut-off of MAP kinases following seizure activity. MKP-1 may contribute in the specific subpopulations where it is induced to the post-translational control of inducible transcription factors of the fos, jun and myc family.