title: SFRP1 reduction results in an increased sensitivity to TGF-β signaling.
abstract: BACKGROUND
  Transforming growth factor (TGF)-β plays a dual role during mammary gland development and tumorigenesis and has been shown to stimulate epithelial-mesenchymal transition (EMT) as well as cellular migration. The Wnt/β-catenin pathway is also implicated in EMT and inappropriate activation of the Wnt/β-catenin signaling pathway leads to the development of several human cancers, including breast cancer. Secreted frizzled-related protein 1 (SFRP1) antagonizes this pathway and loss of SFRP1 expression is frequently observed in breast tumors and breast cancer cell lines. We previously showed that when SFRP1 is knocked down in immortalized non-malignant mammary epithelial cells, the cells (TERT-siSFRP1) acquire characteristics associated with breast tumor initiating cells. The phenotypic and genotypic changes that occur in response to SFRP1 loss are consistent with EMT, including a substantial increase in the expression of ZEB2. Considering that ZEB2 has been shown to interact with mediators of TGF-β signaling, we sought to determine whether TGF-β signaling is altered in TERT-siSFRP1 cells.
  
  
  METHODS
  Luciferase reporter assays and real-time PCR analysis were employed to measure TGF-β transcriptional targets. Western blot analysis was used to evaluate TGF-β-mediated ERK1/2 phosphorylation. Migration chamber assays were utilized to quantify cellular migration. TERT-siSFRP1 cells were transfected with Stealth RNAi™ siRNA in order to knock-down the expression of ZEB2.
  
  
  RESULTS
  TERT-siSFRP1 cells exhibit a significant increase in both TGF-β-mediated luciferase activity as well as TGF-β transcriptional targets, including Integrin β3 and PAI-1. Phosphorylation of ERK1/2 is increased in TERT-siSFRP1 cells in response to enhanced TGF-β signaling. Furthermore, when the TGF-β pathway is blocked with a TGF-βR antagonist (LY364947), cellular migration is significantly hindered. Finally, we found that when ZEB2 is knocked-down, there is a significant reduction in the expression of exogeneous and endogenous TGF-β transcriptional targets and cellular migration is impeded.
  
  
  CONCLUSIONS
  We demonstrate that down-regulation of SFRP1 renders mammary epithelial cells more sensitive to TGF-β signaling which can be partially ameliorated by blocking the expression of ZEB2.
authors.affiliation: Pioneer Valley Life Sciences Institute, Baystate Medical Center, Springfield, MA 01199, USA. kelly.gauger@bhs.org
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Gauger
authors.forename: Kerry L
authors.initials: KL
authors.lastname: Chenausky
authors.forename: Molly E
authors.initials: ME
authors.lastname: Murray
authors.forename: Sallie S
authors.initials: SS
authors.lastname: Schneider
mesh_terms: D000818:Animals; D015536:Down-Regulation; D058750:Epithelial-Mesenchymal Transition; D055785:Gene Knockdown Techniques; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D011720:Pyrazoles / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D015398:Signal Transduction; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D000074165:Zinc Finger E-box Binding Homeobox 2; D011804:Quinolines; D000094742:Secreted Frizzled-Related Proteins
chemical_list: D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D011720:Pyrazoles; D011758:Pyrroles; D012097:Repressor Proteins; D019098:Telomerase; D016212:Transforming Growth Factor beta; D000074165:Zinc Finger E-box Binding Homeobox 2; C506615:HTS 466284; D011804:Quinolines; C117636:SFRP1 protein, human; D000094742:Secreted Frizzled-Related Proteins; C492363:ZEB2 protein, human