Transcription factor activator protein-1 expressed by kainate treatment can bind to the non-coding region of mitochondrial genome in murine hippocampus

Abstract

We have demonstrated previously that the transcription factor activator protein-1 (AP-1) complex is translocated into mitochondria into the nucleus in murine hippocampus after systemic kainate injection (Ogita et al. [2002] J. Neurosci. 22:2561-2570). The present study investigates whether the mitochondrial AP-1 complex translocated in response to kainate treatment binds to AP-1-like sites located at the non-coding region of the mitochondrial genome in mouse hippocampus. There are 10 sites with sequences similar to the nuclear AP-1 site in the non-coding region. Of 10 pieces (MT-1-MT-10) of synthesized double-stranded oligonucleotides, each containing a mitochondrial AP-1-like site, MT-3, MT-4, and MT-9 were effective in inhibiting mitochondrial AP-1 DNA binding enhanced by kainate. Electrophoresis mobility shift analysis using radiolabeled MT-3 and MT-9 probes demonstrated marked enhancement with binding of these 2 probes in hippocampal mitochondrial extracts prepared 2-6 hr after kainate treatment. Unlabeled AP-1 probe was more potent than unlabeled MT-9 probe in inhibiting the mitochondrial MT-9 binding. Supershift analysis revealed participation of particular Fos/Jun family proteins, such as c-Fos, Fos-B, c-Jun, Jun-B, and Jun-D, in MT-9 binding in hippocampal mitochondrial extracts prepared 4 hr after kainate treatment. Immunoprecipitation analysis using anti-c-Fos antibody demonstrated that c-Fos associated with the mitochondrial genome in hippocampal mitochondria prepared from kainate-treated animals. These results suggest that the AP-1 complex expressed by in vivo kainate treatment would bind to AP-1-like sites in the non-coding region of the mitochondrial genome after translocation into mitochondria from murine hippocampus.