title: Serine-727 phosphorylation activates hypothalamic STAT-3 independently from tyrosine-705 phosphorylation.
abstract: Transcriptional activity of signal transducer and activator of transcription-3 (STAT-3) is a key element in the central regulation of appetite and energy homeostasis. Activation of hypothalamic STAT-3 has been attributed to cytokine-promoted phosphorylation at tyrosine-705 (Tyr-705). In nonhypothalamic cells, STAT-3 is also phosphorylated at serine-727 (Ser-727), but the functional significance of Ser-727 in the regulation of hypothalamic STAT-3 is not known. We used 2 hypothalamic cell lines and analyzed the effects of various hormones on STAT-3-dependent reporter gene activity and observed that IFN-γ, epidermal growth factor (EGF), and bradykinin (BK) induce similar STAT-3 reporter activation. EGF and BK solely increased Ser-727 and IFN-γ increased Tyr-705 phosphorylation of STAT-3. Specific inhibition of ERK-1/2 activity blocked EGF- and BK-induced STAT-3 activation and Ser-727 phosphorylation. BK-induced ERK-1/2 activation occurred via EGF receptor transactivation. Consequently, the BK-mediated effects on STAT-3 were blocked by a specific EGF receptor antagonist. Next, we analyzed the effects of IFN-γ and EGF on the expression of the STAT-3-dependent genes thyroliberin-releasing hormone and suppressors of cytokine signaling-3. EGF but not IFN-γ enhanced thyroliberin-releasing hormone expression via STAT-3. With regard to suppressors of cytokine signaling-3, we observed prolonged expression induced by IFN-γ and a transient effect of EGF that required coactivation of the activator protein-1. Thus, EGF-promoted Ser-727 phosphorylation by ERK-1/2 is not only sufficient to fully activate hypothalamic STAT-3, but, in terms of targeted genes and required cofactors, entails distinct modes of STAT-3 actions compared with IFN-γ-induced Tyr-705 phosphorylation.
authors.affiliation: Walther-Straub-Institut für Pharmakologie und Toxikologie (A.B., V.B., H.J.S., S.M., E.G., T.G.), Ludwig-Maximilians-Universität München, München, Germany 80336; and The Institute of Molecular, Cell and Systems Biology (S.J.Y.), College of Medical, Veterinary and Life Science, University of Glasgow, Glasgow GC12 8QQ, United Kingdom.
authors.forename: Andreas
authors.initials: A
authors.lastname: Breit
authors.forename: Valeria
authors.initials: V
authors.lastname: Besik
authors.forename: Hans Jürgen
authors.initials: HJ
authors.lastname: Solinski
authors.forename: Susanne
authors.initials: S
authors.lastname: Muehlich
authors.forename: Evi
authors.initials: E
authors.lastname: Glas
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Yarwood
authors.forename: Thomas
authors.initials: T
authors.lastname: Gudermann
mesh_terms: D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology; D008024:Ligands; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009478:Neuropeptide Y / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D018121:Receptors, Cytokine / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D008024:Ligands; D009478:Neuropeptide Y; D018121:Receptors, Cytokine; D050796:STAT3 Transcription Factor; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D010768:Phosphoserine; D019000:Phosphotyrosine; D013973:Thyrotropin-Releasing Hormone; D004815:Epidermal Growth Factor; D007371:Interferon-gamma; D009074:Melanocyte-Stimulating Hormones; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D001920:Bradykinin