title: Protein tyrosine phosphatase Meg2 dephosphorylates signal transducer and activator of transcription 3 and suppresses tumor growth in breast cancer.
abstract: BACKGROUND
  Signal transducer and activator of transcription 3 (STAT3) is over-activated or phosphorylated in breast cancers. The hyper-phosphorylation of STAT3 was attributed to either up-regulated phosphorylation by several tyrosine-kinases or down-regulated activity of phosphatases. Although several factors have been identified to phosphorylate STAT3, it remains unclear how STAT3 is dephosphorylated by PTPMeg2. The aim of this study was to determine the role of PTPMeg2 as a phosphatase in regulation of the activity of STAT3 in breast cancers.
  
  
  METHODS
  Immunoprecipitation assays were used to study the interaction of STAT3 with PTPMeg2. A series of biochemistry experiments were performed to evaluate the role of PTPMeg2 in the dephosphorylation of STAT3. Two breast cancer cell lines MCF7 (PTPMeg2 was depleted as it was endogenously high) and MDA-MB-231 (PTPMeg2 was overexpressed as it was endogenously low) were used to compare the level of phosphorylated STAT3 and the tumor growth ability in vitro and in vivo. Samples from breast carcinoma (n = 73) were subjected to a pair-wise Pearson correlation analysis for the correlation of levels of PTPMeg2 and phosphorylated STAT3.
  
  
  RESULTS
  PTPMeg2 directly interacts with STAT3 and mediates its dephosphorylation in the cytoplasm. Over-expression of PTPMeg2 decreased tyrosine phosphorylation of STAT3 while depletion of PTPMeg2 increased its phosphorylation. The decreased tyrosine phosphorylation of STAT3 is coupled with suppression of STAT3 transcriptional activity and reduced tumor growth in vitro and in vivo. Levels of PTPMeg2 and phosphorylated STAT3 were inversely correlated in breast cancer tissues (P = 0.004).
  
  
  CONCLUSIONS
  PTPMeg2 is an important phosphatase for the dephosphorylation of STAT3 and plays a critical role in breast cancer development.
authors.affiliation: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Medicine, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Fuqin
authors.initials: F
authors.lastname: Su
authors.forename: Fangli
authors.initials: F
authors.lastname: Ren
authors.forename: Yu
authors.initials: Y
authors.lastname: Rong
authors.forename: Yangmeng
authors.initials: Y
authors.lastname: Wang
authors.forename: Yongtao
authors.initials: Y
authors.lastname: Geng
authors.forename: Yinyin
authors.initials: Y
authors.lastname: Wang
authors.forename: Mengyao
authors.initials: M
authors.lastname: Feng
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Ju
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.forename: Zhizhuang J
authors.initials: ZJ
authors.lastname: Zhao
authors.forename: Kun
authors.initials: K
authors.lastname: Meng
authors.forename: Zhijie
authors.initials: Z
authors.lastname: Chang
mesh_terms: D000818:Animals; D001483:Base Sequence; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D055786:Gene Knockout Techniques; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008969:Molecular Sequence Data; D010766:Phosphorylation; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000235:genetics / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494087:Stat3 protein, mouse; D014443:Tyrosine; C447615:PTPN9 protein, human; D054558:Protein Tyrosine Phosphatases, Non-Receptor