title: Synergy of IL-12 and IL-18 for IFN-gamma gene expression: IL-12-induced STAT4 contributes to IFN-gamma promoter activation by up-regulating the binding activity of IL-18-induced activator protein 1.
abstract: IL-12 and IL-18 synergistically enhance IFN-gamma mRNA transcription by activating STAT4 and AP-1, respectively. However, it is still unknown how STAT4/AP-1 elicit IFN-gamma promoter activation. Using an IL-12/IL-18-responsive T cell clone, we investigated the mechanisms underlying synergistic enhancement of IFN-gamma mRNA expression induced by these two cytokines. Synergy was observed in a reporter gene assay using an IFN-gamma promoter fragment that binds AP-1, but not STAT4. An increase in c-Jun, a component of AP-1, in the nuclear compartment was elicited by stimulation with either IL-12 or IL-18, but accumulation of serine-phosphorylated c-Jun was induced only by IL-18 capable of activating c-Jun N-terminal kinase. The binding of AP-1 to the relevant promoter sequence depended on the presence of STAT4. STAT4 bound with c-Jun, and a phosphorylated c-Jun-STAT4 complex most efficiently interacted with the AP-1-relevant promoter sequence. Enhanced cobinding of STAT4 and c-Jun to the AP-1 sequence was also observed when activated lymph node T cells were exposed to IL-12 plus IL-18. These results show that STAT4 up-regulates AP-1-mediated IFN-gamma promoter activation without directly binding to the promoter sequence, providing a mechanistic explanation for IL-12/IL-18-induced synergistic enhancement of IFN-gamma gene expression.
authors.affiliation: Department of Oncology, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Masakiyo
authors.initials: M
authors.lastname: Nakahira
authors.forename: Hyun-Jong
authors.initials: HJ
authors.lastname: Ahn
authors.forename: Woong-Ryeon
authors.initials: WR
authors.lastname: Park
authors.forename: Ping
authors.initials: P
authors.lastname: Gao
authors.forename: Michio
authors.initials: M
authors.lastname: Tomura
authors.forename: Cheung-Seog
authors.initials: CS
authors.lastname: Park
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Hamaoka
authors.forename: Tsunetaka
authors.initials: T
authors.lastname: Ohta
authors.forename: Masashi
authors.initials: M
authors.lastname: Kurimoto
authors.forename: Hiromi
authors.initials: H
authors.lastname: Fujiwara
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D002999:Clone Cells; D017077:Culture Media, Conditioned; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000378:metabolism / Q000502:physiology; D004357:Drug Synergism; D007371:Interferon-gamma / Q000096:biosynthesis / Q000235:genetics*; D018664:Interleukin-12 / Q000378:metabolism / Q000502:physiology*; D020382:Interleukin-18 / Q000502:physiology*; D008213:Lymphocyte Activation; D051379:Mice; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000276:immunology*; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis / Q000378:metabolism; D050797:STAT4 Transcription Factor; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis* / Q000378:metabolism / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000096:biosynthesis / Q000378:metabolism*; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology*
chemical_list: D017077:Culture Media, Conditioned; D004268:DNA-Binding Proteins; D020382:Interleukin-18; D016755:Proto-Oncogene Proteins c-jun; D050797:STAT4 Transcription Factor; C494091:Stat4 protein, mouse; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D018664:Interleukin-12; D012694:Serine; D007371:Interferon-gamma