title: Structure-function analysis indicates that sumoylation modulates DNA-binding activity of STAT1.
abstract: BACKGROUND
  STAT1 is an essential transcription factor for interferon-γ-mediated gene responses. A distinct sumoylation consensus site (ψKxE) 702IKTE705 is localized in the C-terminal region of STAT1, where Lys703 is a target for PIAS-induced SUMO modification. Several studies indicate that sumoylation has an inhibitory role on STAT1-mediated gene expression but the molecular mechanisms are not fully understood.
  
  
  RESULTS
  Here, we have performed a structural and functional analysis of sumoylation in STAT1. We show that deconjugation of SUMO by SENP1 enhances the transcriptional activity of STAT1, confirming a negative regulatory effect of sumoylation on STAT1 activity. Inspection of molecular model indicated that consensus site is well exposed to SUMO-conjugation in STAT1 homodimer and that the conjugated SUMO moiety is directed towards DNA, thus able to form a sterical hindrance affecting promoter binding of dimeric STAT1. In addition, oligoprecipitation experiments indicated that sumoylation deficient STAT1 E705Q mutant has higher DNA-binding activity on STAT1 responsive gene promoters than wild-type STAT1. Furthermore, sumoylation deficient STAT1 E705Q mutant displayed enhanced histone H4 acetylation on interferon-γ-responsive promoter compared to wild-type STAT1.
  
  
  CONCLUSIONS
  Our results suggest that sumoylation participates in regulation of STAT1 responses by modulating DNA-binding properties of STAT1.
authors.affiliation: Institute of Biomedical Technology, University of Tampere, Biokatu 8, Tampere, FIN-33014, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Grönholm
authors.forename: Sari
authors.initials: S
authors.lastname: Vanhatupa
authors.forename: Daniela
authors.initials: D
authors.lastname: Ungureanu
authors.forename: Jouni
authors.initials: J
authors.lastname: Väliaho
authors.forename: Tuomo
authors.initials: T
authors.lastname: Laitinen
authors.forename: Jarkko
authors.initials: J
authors.lastname: Valjakka
authors.forename: Olli
authors.initials: O
authors.lastname: Silvennoinen
mesh_terms: D000107:Acetylation; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D047369:Chromatin Immunoprecipitation; D003546:Cysteine Endopeptidases; D004247:DNA / Q000378:metabolism*; D019281:Dimerization; D010450:Endopeptidases / Q000737:chemistry / Q000378:metabolism; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D050794:STAT1 Transcription Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D058207:Sumoylation
chemical_list: D006657:Histones; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D004247:DNA; D010450:Endopeptidases; C404512:SENP1 protein, human; D003546:Cysteine Endopeptidases