Constitutive expression of cytoplasmic activator protein-1 with DNA binding activity and responsiveness to ionotropic glutamate signals in the murinehippocampus

Gel retardation electrophoresis revealed that cytosolic fractions contained DNA binding activity of the transcription factor activator protein-1 with profiles different from those reported in nuclear extracts in murine brain. In particular, activator protein-1 DNA binding was almost undetectable at 25 degrees C in the presence of both KCl and MgCl2 in cytosol fractions. Mo reover, cytoplasmic activator protein-1 binding occurred at three different mobilities on the gel when determined at 2 degrees C in the absence of MgC l2. Systemic administration of N-methyl-D-aspartate and kainate led to mark ed potentiation of cytoplasmic activator protein-1 binding detected as slow bands in the murine hippocampus, without markedly affecting that as a fast band. Immunoblotting and supershift assays revealed much higher expression of both immunoreactive c-Jun and c-Fos in hippocampal cytosolic fractions in response to the administration of kainate than N-methyl-D-aspartate. These results suggest that activator protein-1 may be constitutively expres sed in the cytoplasm with DNA binding activity and responsiveness to ionotr opic glutamate signals in a manner different from that in the nucleus in th e murine hippocampus. (C) 1999 IBRO. Published by Elsevier Science Ltd.