Serine-727 phosphorylation activates hypothalamic STAT-3 independently from tyrosine-705 phosphorylation

Mol Endocrinol. 2015 Mar;29(3):445-59. doi: 10.1210/me.2014-1300. Epub 2015 Jan 13.

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.

MeSH terms

  • Animals
  • Bradykinin / pharmacology
  • Cell Line
  • Epidermal Growth Factor / pharmacology
  • ErbB Receptors / metabolism
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Genes, Reporter
  • Humans
  • Hypothalamus / metabolism*
  • Interferon-gamma / pharmacology
  • Ligands
  • Melanocyte-Stimulating Hormones / pharmacology
  • Mice
  • Neurons / drug effects
  • Neurons / metabolism
  • Neuropeptide Y / metabolism
  • Phosphorylation / drug effects
  • Phosphoserine / metabolism*
  • Phosphotyrosine / metabolism*
  • Promoter Regions, Genetic / genetics
  • Receptors, Cytokine / metabolism
  • STAT3 Transcription Factor / metabolism*
  • Suppressor of Cytokine Signaling 3 Protein
  • Suppressor of Cytokine Signaling Proteins / metabolism
  • Thyrotropin-Releasing Hormone / genetics
  • Thyrotropin-Releasing Hormone / metabolism
  • Transcriptional Activation / drug effects

Substances

  • Ligands
  • Neuropeptide Y
  • Receptors, Cytokine
  • STAT3 Transcription Factor
  • Socs3 protein, mouse
  • Suppressor of Cytokine Signaling 3 Protein
  • Suppressor of Cytokine Signaling Proteins
  • Phosphoserine
  • Phosphotyrosine
  • Thyrotropin-Releasing Hormone
  • Epidermal Growth Factor
  • Interferon-gamma
  • Melanocyte-Stimulating Hormones
  • ErbB Receptors
  • Extracellular Signal-Regulated MAP Kinases
  • Bradykinin