Abstract
NR4A family orphan nuclear receptors are an important class of transcription factors for development and homeostasis of dopaminergic neurons that also inhibit expression of inflammatory genes in glial cells. The identification of NR4A2 (Nurr1) as a suppressor of nuclear factor κB (NF-κB)-related neuroinflammatory genes in microglia and astrocytes suggests that this receptor could be a target for pharmacologic intervention in neurologic disease, but compounds that promote this activity are lacking. Selected diindolylmethane compounds (C-DIMs) have been shown to activate or inactivate nuclear receptors, including Nurr1, in cancer cells and also suppress astrocyte inflammatory signaling in vitro. Based upon these data, we postulated that C-DIM12 [1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane] would suppress inflammatory signaling in microglia by a Nurr1-dependent mechanism. C-DIM12 inhibited lipopolysaccharide (LPS)-induced expression of NF-κB-regulated genes in BV-2 microglia including nitric oxide synthase (NOS2), interleukin-6 (IL-6), and chemokine (C-C motif) ligand 2 (CCL2), and the effects were attenuated by Nurr1-RNA interference. Additionally, C-DIM12 decreased NF-κB activation in NF-κB-GFP (green fluorescent protein) reporter cells and enhanced nuclear translocation of Nurr1 primary microglia. Chromatin immunoprecipitation assays indicated that C-DIM12 decreased lipopolysaccharide-induced p65 binding to the NOS2 promoter and concurrently enhanced binding of Nurr1 to the p65-binding site. Consistent with these findings, C-DIM12 also stabilized binding of the Corepressor for Repressor Element 1 Silencing Transcription Factor (CoREST) and the Nuclear Receptor Corepressor 2 (NCOR2). Collectively, these data identify C-DIM12 as a modulator of Nurr1 activity that results in inhibition of NF-κB-dependent gene expression in glial cells by stabilizing nuclear corepressor proteins, which reduces binding of p65 to inflammatory gene promoters.