title: Stat3 is tyrosine-phosphorylated through the interleukin-6/glycoprotein 130/Janus kinase pathway in breast cancer.
abstract: BACKGROUND
  Signal transducer and activator of transcription 3 (Stat3) is constitutively tyrosine-phosphorylated in approximately 50% of primary breast carcinomas. A number of different mechanisms responsible for Stat3 activation, including abnormal activation of receptor tyrosine kinases, Src, and Janus kinases (Jaks), have been implicated in breast cancer.
  
  
  METHODS
  We examined six breast cancer-derived cell lines expressing high or low levels of tyrosine-phosphorylated Stat3 (pStat3) as well as primary breast cancer specimens.
  
  
  RESULTS
  Inhibition of Src or EGFR (epidermal growth factor receptor) tyrosine kinases had no effect on pStat3 levels, whereas pan-Jak inhibitor P6 resulted in complete abrogation of Stat3 phosphorylation and inhibition of growth. Jaks are required for cytokine signaling, and the glycoprotein 130 (gp130) receptor-associated Jaks are known mediators of Stat3 phosphorylation. Blockade of the gp130 receptor or sequestration of the interleukin-6 (IL-6) ligand led to a decrease of pStat3 levels. Conditioned media from those cell lines expressing high levels of pStat3 contained IL-6 and were capable of stimulating Stat3 phosphorylation. We examined IL-6 levels in primary breast tumors and found a positive correlation between pStat3 and IL-6 expression.
  
  
  CONCLUSIONS
  In summary, a principal mechanism of Stat3 activation in breast cancer is through the IL-6/gp130/Jak pathway.
authors.affiliation: Department of Medicine, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021 USA.
authors.forename: Marjan
authors.initials: M
authors.lastname: Berishaj
authors.forename: Sizhi Paul
authors.initials: SP
authors.lastname: Gao
authors.forename: Simi
authors.initials: S
authors.lastname: Ahmed
authors.forename: Kenneth
authors.initials: K
authors.lastname: Leslie
authors.forename: Hikmat
authors.initials: H
authors.lastname: Al-Ahmadie
authors.forename: William L
authors.initials: WL
authors.lastname: Gerald
authors.forename: William
authors.initials: W
authors.lastname: Bornmann
authors.forename: Jacqueline F
authors.initials: JF
authors.lastname: Bromberg
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006023:Glycoproteins / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D015850:Interleukin-6 / Q000502:physiology*; D053612:Janus Kinases / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D006023:Glycoproteins; D015850:Interleukin-6; D050796:STAT3 Transcription Factor; C480482:glycoprotein 130, human; D019000:Phosphotyrosine; D053612:Janus Kinases