The two interfaces of the STAT1 N-terminus exhibit opposite functions in IFNγ-regulated gene expression.
Defective cooperative DNA binding of STAT1 (signal transducer and activator of transcription 1) transcription factor has impact on interferon-γ(IFNγ)-regulated transcriptional responses. In this study, we generated N-terminal gain-of-function mutants of this protein which exhibited hyperactive cooperativity and assessed their functional consequences on gene expression. Our data show that four negatively charged, surface-exposed amino acid residues in the N-terminal domain dimer are engaged in the disassembly of tyrosine-phosphorylated tetrameric complexes on DNA and prevent the occurrence of higher-order STAT1 oligomers on low-affinity DNA binding sites. Owing to their improved tetramer stability, the N-terminal mutants showed relaxed sequence requirements for the binding to DNA as compared to the wild-type protein. Similarly to a STAT1 mutant with impaired tetramerization, the N-terminal gain-of-function mutants showed elevated tyrosine-phosphorylation levels and prolonged nuclear accumulation upon stimulation of cells with IFNγ. However, in contrast to the global impairment of IFNγ signalling in tetramerization-deficient mutants, the transcriptional consequences of the N-terminal gain-of-function mutants are rather distinct and affect gene expression locally in a promoter-specific manner. Thus, we conclude that the STAT1 N-domain acts as a double-edged sword: while one interface is crucial for the formation of tetrameric complexes on IFNγ-regulated promoters, the opposite interface harbours an inhibitory mechanism that limits the accumulation of higher-order oligomers simply by disrupting cooperative DNA binding.
Department of Psychosomatic Medicine and Psychotherapy, University of Göttingen, Germany.
Julia
J
Staab
Department of Psychosomatic Medicine and Psychotherapy, University of Göttingen, Germany.
Theresa
T
Riebeling
Department of Cardiology, University of Marburg, Marburg, Germany.
Verena
V
Koch
Department of Psychosomatic Medicine and Psychotherapy, University of Göttingen, Germany.
Christoph
C
Herrmann-Lingen
Department of Psychosomatic Medicine and Psychotherapy, University of Göttingen, Germany. Electronic address: thomas.meyer@med.uni-goettingen.de.
Thomas
T
Meyer
D001224:Aspartic Acid / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D005786:Gene Expression Regulation; D018698:Glutamic Acid / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007371:Interferon-gamma / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D050794:STAT1 Transcription Factor / Q000737:chemistry* / Q000378:metabolism*; D014158:Transcription, Genetic
D050505:Mutant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D019000:Phosphotyrosine; D001224:Aspartic Acid; D018698:Glutamic Acid; D007371:Interferon-gamma; D004247:DNA
Cooperative DNA binding; Interferon signalling; STAT proteins; Tetramerization