Unexpected characteristics of the IFN-gamma reporters in nontransformed T cells.
Analysis of the IFN-gamma promoter has primarily been conducted by transient expression of reporter constructs in transformed cells. However, the activity of cis elements may differ when expressed transiently compared with their activity within native chromatin. Furthermore, the transcription factors and signaling mechanisms in transformed cells may differ from those in normal T cells. To analyze IFN-gamma promoter regulation in normal T cells, we developed a novel retroviral bottom-strand reporter system to allow the chromatin integration of promoter regions in primary developing T cells. As controls, both the IL-2 and IL-4 promoters were inducible in this system, with the IL-4 reporter having Th2-specific activity. Strikingly, the IFN-gamma promoter exhibited constitutive activity in both Th1 and Th2 subsets, in contrast to the behavior of the endogenous IFN-gamma gene, which is inducible only in Th1 cells. In mapping this activity, we found that the AP-1/GM-CSF site in the distal promoter element is the most critical element for the constitutive activity. Transgenic reporter lines for the IFN-gamma promoter confirmed the constitutive behavior of the isolated IFN-gamma promoter. This constitutive activity was resistant to inhibition by cyclosporin A and was independent of Stat4 and p38 mitogen-activated protein kinase. These results suggest that IFN-gamma promoter regulation may require cis elements residing either downstream or >3.4 kb upstream of the transcriptional start site, involving repression of constitutive activity.
Zhu
H
H
Department of Pathology and Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110, USA.
Yang
J
J
Murphy
T L
TL
Ouyang
W
W
Wagner
F
F
Saparov
A
A
Weaver
C T
CT
Murphy
K M
KM
D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D016572:Cyclosporine / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000502:physiology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D017930:Genes, Reporter / Q000276:immunology*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000235:genetics / Q000378:metabolism; D007371:Interferon-gamma / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D008213:Lymphocyte Activation / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D016254:Mutagenesis, Insertional; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000276:immunology; D050797:STAT4 Transcription Factor; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D015534:Trans-Activators / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D050797:STAT4 Transcription Factor; C494091:Stat4 protein, mouse; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D007371:Interferon-gamma; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D016572:Cyclosporine; D020928:Mitogen-Activated Protein Kinases