Formation of STAT1-STAT2 heterodimers and their role in the activation of IRF-1 gene transcription by interferon-alpha.
An upstream inverted repeat (IR) element mediates transcriptional activation of the interferon response factor-1 gene (IRF-1) by interferon (IFN)-alpha and IFN-gamma. IFN-alpha and IFN-gamma fail to induce IRF-1 in cells that lack signal transducer and activator of transcription 1 (STAT1), and STAT1 homodimers bind to IR elements in extracts of IFN-alpha-treated cells. We now report that STAT2 also plays an important role in the IFN-alpha-mediated transcriptional activation of the IRF-1 gene. A new factor, most likely a STAT1-STAT2 heterodimer, was detected with an IR probe in extracts of IFN-alpha-treated cells. STAT1 and STAT2 are already known to combine with p48, a DNA-binding protein, to form IFN-stimulated gene factor 3 (ISGF3), which binds to IFN-stimulated response elements (ISREs) distinct from the IR of the IRF-1 gene. In extracts of U2A cells, which lack p48, STAT1-STAT2 heterodimers were still formed, indicating that they do not contain p48. We manipulated the intracellular levels of STAT1-STAT2 heterodimers and STAT1 homodimers to examine their roles in the induction of IRF-1 by IFN-alpha. Although both dimers can induce IRF-1 transcription, the heterodimers are more potent and thus may be the major activators in vivo. Deletion analysis reveals that the C-terminal domain of STAT2 is important for transcriptional activation mediated by both STAT1-STAT2 heterodimers and ISGF3.
Li
X
X
Department of Molecular Biology, Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Leung
S
S
Qureshi
S
S
Darnell
J E
JE
Stark
G R
GR
D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D050856:Interferon Regulatory Factor-1; D007370:Interferon Type I / Q000494:pharmacology*; D050832:Interferon-Stimulated Gene Factor 3; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D007371:Interferon-gamma / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000096:biosynthesis*; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D017384:Sequence Deletion; D015398:Signal Transduction; D015534:Trans-Activators / Q000096:biosynthesis / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*
D017931:DNA Primers; D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; C494227:IRF9 protein, human; D050856:Interferon Regulatory Factor-1; D007370:Interferon Type I; D050832:Interferon-Stimulated Gene Factor 3; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D046911:Macromolecular Substances; D010750:Phosphoproteins; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D007371:Interferon-gamma