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.
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.
Nakahira
Masakiyo
M
Department of Oncology, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan.
Ahn
Hyun-Jong
HJ
Park
Woong-Ryeon
WR
Gao
Ping
P
Tomura
Michio
M
Park
Cheung-Seog
CS
Hamaoka
Toshiyuki
T
Ohta
Tsunetaka
T
Kurimoto
Masashi
M
Fujiwara
Hiromi
H
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*
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