Fos-B expression is required for polyamine-induced increase in nuclear activator protein-1 DNA binding in discrete structures of murine brain

Abstract

Spermidine (SPD) and spermine (SPN) have been shown to be endogenous agonists for N-methyl-D-aspartate (NMDA) receptors that could lead to expression of the nuclear transcription factor activator protein-1 (AP1) complex in the mammalian central nervous system both in vitro and in vivo. In nuclear extracts of murine whole brain, AP1 DNA binding increased significantly in a concentration-dependent manner with the addition of either SPD or SPN at a concentration range of 50-500 microM. Similarly, the nuclear proteins histone and dephosphorylated casein, but not phosphorylated casein, significantly increased AP1 DNA binding alone but in the presence of either SPD or SPN did not increase further binding. By contrast, another endogenous polyamine, putrescine, significantly prevented AP1 DNA binding increases by histone and dephosphorylated casein, but did not by itself significantly alter binding. Invariably, SPD and SPN effected significantly increased AP1 DNA binding in neocortex, hippocampus, striatum, midbrain, hypothalamus and cerebellum, but not in medulla-pons and spinal cord. Supershift and Western blotting analyses revealed relatively high constitutive expression of Fos-B protein in neocortex and hippocampus, but not in medulla-pons and spinal cord. Immunoprecipitation of Fos-B led to complete abolition of the ability of SPN and SPD to increase AP1 DNA binding in neocortical and hippocampal nuclear extracts. These results suggest that expression of Fos-B protein may be required for modulation of nuclear gene transcription by both SPD and SPN through stimulation DNA-binding activity of AP1 complex in murine central structures.