title: Synergistic transcriptional activation of indoleamine dioxygenase by IFN-gamma and tumor necrosis factor-alpha.
abstract: Interferon-gamma (IFN-gamma)-induced indoleamine 2,3-dioxygenase (IDO) activity inhibits the growth of susceptible intracellular pathogens by catalyzing the oxidative cleavage of the indole ring of L-tryptophan and depleting pools of the essential amino acid. Tumor necrosis factor-alpha (TNF-alpha) synergistically enhances the IDO activity induced by IFN-gamma at the level of transcription in human epithelial cells. The purpose of this study was to characterize the molecular mechanisms responsible for synergistic gene expression in response to IFN-gamma and TNF-alpha. It was found that IFN-gamma-induced mechanisms, such as the binding of Stat1 to gamma activation sequences (GAS) and IFN regulatory factor-1 (IRF-1) to IFN-stimulated response elements (ISREs), are more highly activated following treatment with IFN and TNF-alpha. This enhanced signal transduction may be due to the increase in IFN-gamma receptor (IFNGR) expression following combined cytokine stimulation and is a likely contributor to the synergy. Additionally, the contribution of a third previously uncharacterized GAS element that forms a complex with Stat1 was investigated using a plasmid reporter system that controls for copy number. When the GAS-3 sequence was included in the regulatory region, gene expression was significantly increased relative to a region containing the mutated GAS-3. This suggests that GAS-3 is transcriptionally active and contributes to IFN-gamma-induced regulation of the IDO gene.
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004357:Drug Synergism; D004790:Enzyme Induction; D006367:HeLa Cells; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D050856:Interferon Regulatory Factor-1; D007371:Interferon-gamma / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D017471:Receptors, Interferon / Q000378:metabolism; D020218:Response Elements; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014366:Tryptophan Oxygenase / Q000096:biosynthesis / Q000235:genetics*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000096743:Interferon gamma Receptor
chemical_list: D004268:DNA-Binding Proteins; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D050856:Interferon Regulatory Factor-1; D007371:Interferon-gamma; D010750:Phosphoproteins; D017471:Receptors, Interferon; D014157:Transcription Factors; D014366:Tryptophan Oxygenase; D014409:Tumor Necrosis Factor-alpha; D000096743:Interferon gamma Receptor; C494257:IRF1 protein, human