title: Loss of TGF-beta or Wnt5a results in an increase in Wnt/beta-catenin activity and redirects mammary tumour phenotype.
abstract: BACKGROUND
  The tumour-suppressive effects of transforming growth factor-beta (TGF-beta) are well documented; however, the mechanistic basis of these effects is not fully understood. Previously, we showed that a non-canonical member of the Wingless-related protein family, Wnt5a, is required for TGF-beta-mediated effects on mammary development. Several lines of evidence support the hypothesis that Wnt5a acts as a tumour suppressor. In addition, it has been shown that Wnt5a can antagonise canonical Wnt/beta-catenin signalling in various cell types. Here we test the hypothesis that TGF-beta and Wnt5a can antagonise Wnt/beta-catenin signalling and redirect mammary tumour phenotype. The results provide a new mechanism for the tumour-suppressive effects of TGF-beta.
  
  
  METHODS
  Wnt/beta-catenin signalling was measured in tumours with altered TGF-beta (dominant-negative TGF-beta type II receptor, DNIIR) or Wnt5a (Wnt5a-/-) signalling as the accumulation of nuclear beta-catenin using both confocal microscopy and cell fractionation. RT-PCR was used to measure the expression of Wnt/beta-catenin target genes. Sca1 expression was determined by western blot and keratin (K) 6- and K14-positive populations were determined by immunohistochemistry.
  
  
  RESULTS
  Loss of TGF-beta or Wnt5a signalling resulted in stabilisation of nuclear beta-catenin and expression of Wnt/beta-catenin target genes suggesting that TGF-beta and Wnt5a act to inhibit Wnt/beta-catenin signalling in mammary epithelium. Increased expression of Sca-1 was observed in developing DNIIR and Wnt5a-/- mammary glands. DNIIR and Wnt5a-/- tumours demonstrated an expanded population of K6- and K14-expressing cells typically seen in Wnt/beta-catenin-induced tumours.
  
  
  CONCLUSIONS
  The key findings here are that: TGF-beta and Wnt5a regulate Wnt/beta-catenin activity; and loss of TGF-beta and Wnt5a redirect the phenotype of tumours so that they resemble tumours induced by activation of Wnt/beta-catenin. The findings suggest a new mechanism for the tumour-suppressive effects of TGF-beta.
authors.affiliation: Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294-0005, USA. roarty@bcm.tmc.edu
authors.forename: Kevin
authors.initials: K
authors.lastname: Roarty
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Baxley
authors.forename: Michael R
authors.initials: MR
authors.lastname: Crowley
authors.forename: Andra R
authors.initials: AR
authors.lastname: Frost
authors.forename: Rosa
authors.initials: R
authors.lastname: Serra