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

Abstract

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°C in the presence of both KCl and MgCl 2 in cytosol fractions. Moreover, cytoplasmic activator protein-1 binding occurred at three different mobilities on the gel when determined at 2°C in the absence of MgCl 2. Systemic administration of N-methyl- d-aspartate and kainate led to marked 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 expressed in the cytoplasm with DNA binding activity and responsiveness to ionotropic glutamate signals in a manner different from that in the nucleus in the murine hippocampus.