title: Identification of STAT2 serine 287 as a novel regulatory phosphorylation site in type I interferon-induced cellular responses.
abstract: STAT2 is a positive modulator of the transcriptional response to type I interferons (IFNs). STAT2 acquires transcriptional function by becoming tyrosine phosphorylated and imported to the nucleus following type I IFN receptor activation. Although most STAT proteins become dually phosphorylated on specific tyrosine and serine residues to acquire full transcriptional activity, no serine phosphorylation site in STAT2 has been reported. To find novel phosphorylation sites, mass spectrometry of immunoprecipitated STAT2 was used to identify several phosphorylated residues. Of these, substitution of serine 287 with alanine (S287A) generated a gain-of-function mutant that enhanced the biological effects of IFN-α. S287A-STAT2 increased cell growth inhibition, prolonged protection against vesicular stomatitis virus infection and enhanced transcriptional responses following exposure of cells to IFN-α. In contrast, a phosphomimetic STAT2 mutant (S287D) produced a loss-of-function protein that weakly activated IFN-induced ISGs. Our mechanistic studies suggest that S287A-STAT2 likely mediates its gain-of-function effects by prolonging STAT2/STAT1 dimer activation and retaining it in transcriptionally active complexes with chromatin. Altogether, we have uncovered that in response to type I IFN, STAT2 is serine phosphorylated in the coiled-coil domain that when phosphorylated can negatively regulate the biological activities of type I IFNs.
authors.affiliation: Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Håkan C
authors.initials: HC
authors.lastname: Steen
authors.forename: Shoko
authors.initials: S
authors.lastname: Nogusa
authors.forename: Roshan J
authors.initials: RJ
authors.lastname: Thapa
authors.forename: Suresh H
authors.initials: SH
authors.lastname: Basagoudanavar
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Gill
authors.forename: Salim
authors.initials: S
authors.lastname: Merali
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Barrero
authors.forename: Siddharth
authors.initials: S
authors.lastname: Balachandran
authors.forename: Ana M
authors.initials: AM
authors.lastname: Gamero
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D001665:Binding Sites; D045744:Cell Line, Tumor; D002843:Chromatin / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D057809:HEK293 Cells; D006801:Humans; D007370:Interferon Type I / Q000737:chemistry*; D016898:Interferon-alpha / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D050795:STAT2 Transcription Factor / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000737:chemistry*
chemical_list: D002843:Chromatin; D018076:DNA, Complementary; D007370:Interferon Type I; D016898:Interferon-alpha; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D012694:Serine; D000409:Alanine