IFN-gamma regulation of the type IV class II transactivator promoter in astrocytes.
The transcriptional activation of class II MHC genes requires the class II transactivator (CIITA) protein, a regulator that is essential for both constitutive and IFN-gamma-inducible class II MHC expression. The CIITA gene is controlled by multiple independent promoters; two promoters direct constitutive expression, while another, the type IV CIITA promoter, mediates IFN-gamma-induced expression. We investigated the molecular regulation of IFN-gamma-induced type IV CIITA promoter activity in astrocytes. IFN-gamma inducibility of the type IV CIITA promoter is dependent on three cis-acting elements contained within a 154-bp fragment of the promoter; the proximal IFN-gamma activation sequence (GAS) element, the E box, and the proximal IFN regulatory factor (IRF) element. Two IFN-gamma-activated transcription factors, STAT-1alpha and IRF-1, bind the proximal GAS and IRF elements, respectively. The E box binds upstream stimulating factor-1 (USF-1), a constitutively expressed transcription factor. Furthermore, STAT-1alpha binding to the proximal GAS element is dependent on the binding of USF-1 to the adjacent E box. Functionally, the proximal IRF element is essential for IFN-gamma induction of type IV CIITA promoter activity, while the proximal GAS and E box elements contribute to the IFN-gamma inducibility of this promoter. In astrocytes, TNF-alpha enhances IFN-gamma-induced class II MHC transcription. Our results demonstrate that TNF-alpha does not enhance IFN-gamma-induced transcriptional activation of the type IV CIITA promoter, indicating that the enhancing effect of TNF-alpha is mediated downstream of CIITA transcription. These results define the molecular basis of IFN-gamma activation of the type IV CIITA promoter in astrocytes.
Dong
Y
Y
Department of Cell Biology, University of Alabama, Birmingham 35294, USA.
Rohn
W M
WM
Benveniste
E N
EN
D000818:Animals; D001253:Astrocytes / Q000276:immunology* / Q000378:metabolism*; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology; D005802:Genes, MHC Class II / Q000276:immunology*; D050856:Interferon Regulatory Factor-1; D050832:Interferon-Stimulated Gene Factor 3; D007371:Interferon-gamma / Q000502:physiology*; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000276:immunology*; D051381:Rats; D020218:Response Elements / Q000276:immunology; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology
D004268:DNA-Binding Proteins; D050856:Interferon Regulatory Factor-1; D050832:Interferon-Stimulated Gene Factor 3; C494259:Irf1 protein, rat; C083728:MHC class II transactivator protein; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D010750:Phosphoproteins; D015534:Trans-Activators; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; C079868:gamma interferon activation factor; D007371:Interferon-gamma; D004247:DNA