Sodium butyrate inhibits interferon-gamma induced indoleamine 2,3-dioxygenase expression via STAT1 in nasopharyngeal carcinoma cells

Aims: Indoleamine 2,3-dioxygenase (IDO) inhibits T-cell proliferation by catalyzing the conversion of L-tryptophan to L-kynurenine. IDO-induced immune tolerance weakens the clinical outcomes of immunotherapies. Sodium butyrate (NaB), one of the histone deacetylase inhibitors (HDACIs), has potential anti-tumor effects. Our previous studies revealed that NaB could inhibit IFN-gamma induced IDO expression in nasopharyngeal carcinoma cells, CNE2. In the present study, we aim to investigate to the mechanism of NaB interfering with the interferon-gamma (IFN-gamma)-mediated IDO expression signaling transduction. Main methods: IDO expression and STAT1 phosphorylation in CNE2 cells were analyzed by western blotting and STAT1 acetylation was evaluated by immunoprecipitation. STAT1 nuclear translocation and NF-kappa B activity were detected by transient transfection and reporter gene assay. Key findings: We found that NaB inhibited IFN-gamma-induced IDO expression in CNE2 cells via decreasing phosphorylation and nuclear translocation of STAT1, but not via down-regulation of IFN-gamma-receptor (IFNGR). Immunoprecipitation assays revealed that NaB increased STAT1 acetylation. Furthermore, NaB elevated the activity of NF-kappa B in CNE2 cells, and blocking the NF-kappa B activity had no effect on the IFN-gamma-induced IDO expression. Significance: These results suggest that NaB inhibited IFN-gamma-induced IDO expression via STAT1 increased acetylation, decreased phosphorylation, and reduced nuclear translocation. These provided new evidence for the antitumor action of NaB and potential drug targets to reduce the IDO-induced immune tolerance. (c) 2013 Elsevier Inc. All rights reserved.