| Primary gallbladder carcinoma (PGC) is the most common and aggressivemalignancy in the biliary system and its incidence ranks fifth among digestive tracttumors in our country. Due to lacking characteristic signs or symptoms, patientsdiagnosed as PGC have mostly been in advanced stage with a low resection ratio andits morbility has been rising year by year (1,2). Various therapeutic measures areavailable for gallbladder carcinoma, including chemical therapy, surgical therapy,radiotherapy and so on. However, the clinical effects are far from satisfaction. Surgeryis still the preferred method, but only10%to20%of those patients were able to getradical surgical resection and5-year survival rate is only4.9%(3). Therefore, it isurgent to explore new treatments to improve the pessimistic situation of PGC.Immunotherapy has become the focus of tumor treatment to prevent tumor frommetastasis and recurrence due to its promising advantages—cleaning away tumorcells in stationary phase, cancer stem cells and a small amount of residual tumor cells.At present, tumor immunotherapeutic methods can be divided into tumor vaccine oractive immunotherapy, monoclonal antibodies, adoptive cell immunotherapy, stemcell therapy and cytokine therapy. With the in-depth understanding of the immune system and its regulation, we found the clinical outcomes of most immunotherapeuticstrategies have been less effective than anticipated. It has been demonstrated that thereasons behind the attenuated clinical outcomes of cancer vaccines were mainlybecause of the tumor immune tolerance induced by many immune tolerance factors,which originate from the tumor and tumor microenvironment. Indoleamine2,3-dioxygenase (IDO), as one of the main factors, plays a crucial role intumor-induced immune tolerance (4-8).IDO can be derived from tumor cells, dendritic cells, surrounding stromal cellsand so on. Most scholars believe that tumor cells are the main source of IDO (9). IDOis a heme-containing monomeric oxidoreductase that catalyzes the first andrate-limiting step in the degradation of the essential amino acid tryptophan toN-formylkynurenine, and it induces tryptophan starvation and accumulation ofdownstream breakdown products (10,11). Because tryptophan is the essential aminoacid in the process of T-cell activation and proliferation, tryptophan starvationresulting from IDO consumption inhibits T-cell activation and proliferation. Therefore,T cells cannot synthesize sufficient protein to proliferate and result in immunetolerance of the local micro-environment.More importantly, our previous studies have reported that IFN-γ can stimulatethe expression of IDO most effectively via activating Janus kinase/signal transducerand activator of transcription1(JAK/STAT1) signaling pathway (12-15). Based onthese backgrounds, we wondered whether inhibition of the JAK/STAT1signalingpathway could down-regulate the expression of IDO in gallbladder carcinoma cellsand restore the tumor antigen-specific T-cell proliferation, and then eventually breaktumor immune tolerance and enhance the effect of tumor immunotherapy.SAHA, a kind of histone deacetylases inhibitors (HDACI), is a promising newanticancer agent due to its low toxicity in cancer treatment and protective actionagainst intracellular events including IFN-γ-mediated signaling transduction. HDACIare a group of compound regulating the expression of different regulatory geneswhich are responsible for cell growth, proliferation, apoptosis and regulation of othermechanisms involved in tumor development and growth (16,17). Therefore, we treated SGC-996cells with histone deacetylases inhibitor SAHAto investigate the role of inhibition of the JAK/STAT1signaling pathway. Byexploring the mechanism of regulating JAK/STAT1signaling pathway on thedown-regulation of IDO expression, we hope to provide a new strategy to break tumorimmune tolerance in the gallbladder carcinoma immunotherapy aspects.ObjectiveTo investigate the role of the JAK/STAT1signaling pathway in suberoylanilidehydroxamic acid (SAHA)-mediated down-regulation of indoleamine2,3-dioxygenase(IDO) in gallbladder carcinoma cells.MethodsGallbladder carcinoma SGC-996cells were treated with IFN-γ and SAHA.Western blotting was used to detect the expression of IDO, signal transducer andactivator of transcription1(STAT1) phosphorylation and interferon regulatory factorgenes-1(IRF-1). Confocal microscopy analysis was used to detect STAT1translocation. Transient transfections and reporter genes assay was used in detectingthe activation of γ-activated sites (GAS) and interferon stimulated response elements(ISRE).Results1. IDO expressed in SGC-996cells in dose-and time-dependent manners whenstimulated with IFN-γ;2. SAHA down-regulated the expression of IDO induced by IFN-γ in adose-dependent manner;3. SAHA blocked the expression of IRF-1induced by IFN-γ;4. SAHA inhibited IFN-γ-induced STAT1phosphorylation and nucleartranslocation; 5. SAHA down-regulated IFN-γ-induced activation of GAS and ISRE.ConclusionSAHA down-regulated the IDO expression via inhibiting the activation ofmembers in JAK/STAT1signaling pathway. Regulation of the JAK/STAT1signalingpathway may provide a new gallbladder carcinoma immunotherapeutic strategy tobreak tumor immune tolerance. |
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