Localization of nuclear coactivators p300 and steroid receptor coactivator 1 in the rat hippocampus

Cofactors (coactivators and corepressors) play an important role in mediating ligand-dependent transcription by steroid hormone receptors, but little has been reported about the distribution of coactivators in the brain. The present study represents the first immunohistochemical attempt to elucidate the localization of coactivators p300 and steroid receptor coactivator 1 (SRC-1) in the hippocampus of the rat. p300- and SRC-1-immunoreactivities were observed in CA1-CA4 pyramidal cell layers of the hippocampus and the granular cell layer of the dentate gyrus, and their localization was in the cell nucleus. Double-labeling immunohistochemistry of p300 and SRC-1 indicated that both coactivators were colocalized in the same cell. Antibodies against neuron specific enolase (NSE) and glial fibrillary acidic protein (GFAP) were used to identify whether neuron and glia contained p300 or SRC-1. Most p300- or SRC-1-containing cells showed NSE-immunoreactivity, but a limited number of these cells showed GFAP-immunoreactivity. These findings suggest that in the hippocampus p300 and SRC-1 synergistically play an important role in activating ligand-dependent transcription by steroid hormone receptor.