title: Role of the Stat4 N domain in receptor proximal tyrosine phosphorylation.
abstract: Stat4 is activated by the cytokines interleukin 12 and alpha interferon (IFN-alpha) and plays a significant role in directing development of naïve CD4(+) T cells to the Th1 phenotype. Signal transducers and activators of transcription (STAT) proteins undergo phosphorylation on a conserved tyrosine residue, resulting in homo- and heterodimerization, nuclear translocation, and DNA binding. Stat4 can bind to single IFN-gamma-activated sites (GASs) as a dimer or bind two tandem GASs as a pair of STAT dimers, or tetramer, stabilized through N-terminal domain (N domain) interactions between dimers. We uncovered an unexpected effect of the Stat4 N domain in controlling the proximal activation of Stat4 by tyrosine phosphorylation at activated receptor complexes. Mutation of the N domain at tryptophan residue W37, predicted to interrupt N domain dimer formation, unexpectedly prevented IFN-alpha-induced tyrosine phosphorylation of the Stat4 monomer, blocking dimer formation and nuclear translocation. Furthermore, N domains appear to exert private STAT functions, since interchanging the N domains between Stat1 and Stat4 prevented receptor-mediated tyrosine phosphorylation in one case and interrupted STAT-specific gene activation in another. Finally, replacement of the N domain of Stat1 with that of Stat4 abrogated the normal Stat2 dependence of Stat1 phosphorylation, again suggesting the domains are not equivalent. Thus, in addition to its role in STAT tetramerization, the conserved STAT N domain appears to participate in very proximal steps of receptor-mediated ligand-induced tyrosine phosphorylation.
authors.affiliation: Department of Pathology and Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Murphy
authors.forename: E D
authors.initials: ED
authors.lastname: Geissal
authors.forename: J D
authors.initials: JD
authors.lastname: Farrar
authors.forename: K M
authors.initials: KM
authors.lastname: Murphy
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D019281:Dimerization; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology; D007371:Interferon-gamma / Q000494:pharmacology; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000096:biosynthesis*; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000235:genetics; D017434:Protein Structure, Tertiary; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D053633:Receptor, Interferon alpha-beta; D017471:Receptors, Interferon / Q000187:drug effects / Q000378:metabolism; D015375:Receptors, Interleukin-2 / Q000187:drug effects / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D011994:Recombinant Proteins / Q000494:pharmacology; D050794:STAT1 Transcription Factor; D050797:STAT4 Transcription Factor; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D008024:Ligands; D017471:Receptors, Interferon; D015375:Receptors, Interleukin-2; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050797:STAT4 Transcription Factor; C494090:STAT4 protein, human; C494080:Stat1 protein, mouse; C494091:Stat4 protein, mouse; D015534:Trans-Activators; D053633:Receptor, Interferon alpha-beta; D019000:Phosphotyrosine; D014443:Tyrosine; D007371:Interferon-gamma; D017027:Protein Tyrosine Phosphatases