Nonsteroidal anti-inflammatory drug-activated gene (NAG-1) is a putative tumor suppressor whose expression can be increased by drug treatment. Glioblastoma is the most common central nervous system tumor, is associated with high morbidity and mortality, and responds poorly to surgical, chemical, and radiation therapy. The histone deacetylase inhibitors are under current consideration as therapeutic agents in treating glioblastoma. We investigated whether trichostatin A (TSA) would alter the expression of NAG-1 in glioblastoma cells. The DNA demethylating agent 5-aza-dC did not increase NAG-1 expression, but TSA up-regulated NAG-1 expression and acted synergistically with 5-aza-dC to induce NAG-1 expression. TSA indirectly increases NAG-1 promoter activity and increases NAG-1 mRNA and protein expression in the T98G human glioblastoma cell line. TSA also increases the expression of transcription factors Sp-1 and Egr-1. Small interfering RNA experiments link NAG-1 expression to apoptosis induced by TSA. Reporter gene assays, specific inhibition by small interfering RNA transfections, and chromatin immunoprecipitation assays indicate that Egr-1 and Sp-1 mediate TSA-induced NAG-1 expression. TSA also increases the stability of NAG-1 mRNA. TSA-induced NAG-1 expression involves multiple mechanisms at the transcriptional and post-transcriptional levels.Glioblastoma multiform is the most malignant human primary brain tumor in adults and represents the most malignant stage of astrocytoma progression, has a median survival time of 12 months and a 5-year survival rate of Ͻ3%. The survival rate has not significantly changed despite advances in anti-tumor therapy (1, 2). Malignant gliomas aggressively infiltrate into normal adjacent brain tissue, are incurable by surgery alone, and are relatively resistant to radiotherapy and most forms of chemotherapy.Nonsteroidal anti-inflammatory drug-activated gene (NAG-
1)2 is a divergent member of the transforming growth factor- superfamily that was identified in this laboratory by a PCRbased subtractive hybridization from an indomethacin-induced library obtained from human colorectal cells. The cDNA has been cloned by six different groups (as known as MIC-1, PDF, GDF-15, PLAB, and PTGFB). The previous investigations on the regulation of NAG-1 expression revealed complex mechanisms that can be modulated by a number of drugs and chemicals: cyclooxygenase inhibitors (3), dietary agents (4 -6), PPAR agonist (7-9), and anti-cancer drugs (10). Moreover, NAG-1 is induced by several nonsteroidal anti-inflammatory drugs and other drugs known to have anti-tumorigenic and pro-apoptotic activities (11, 12). In the brain, NAG-1 is expressed in epithelial cells of the choroid plexus and secreted into the cerebral spinal fluid and is reported to function as both a neurotrophic and a neuroprotective factor for midbrain dopaminergic neurons in vivo and in vitro (13,14). Recently, we generated NAG-1 transgenic mice (Cre/NAG-1 Tg/Lox ), which express human NAG-1 in all tissues (15). The anti-tumorigenic...