title: Caveolae are negative regulators of transforming growth factor-beta1 signaling in ureteral smooth muscle cells.
abstract: OBJECTIVE
  The mechanisms underlying ureteral cell regulation are largely unknown. Previous studies have identified lipid rafts/caveolae as regulators of growth stimulatory signals in ureteral smooth muscle cells (USMCs). In this study we determined whether growth inhibitory signaling by transforming growth factor-beta1 (TGF-beta1) is also regulated by caveolae in USMC.
  
  
  METHODS
  Expression of components of the TGF-beta1 signaling axis in USMCs was determined by immunoblot and mRNA analyses. Growth regulatory activity of TGF-beta1 was assessed by H-thymidine incorporation. In select experiments caveolae were disrupted reversibly by cholesterol depletion and replenishment prior to TGF-beta1 treatment. TGF-beta1-responsive gene expression was evaluated using the TGF-beta1 responsive promoter-reporter construct 3TP-Lux.
  
  
  RESULTS
  USMCs expressed TGF-beta1, types I and II TGF-beta1 receptors, and the effector Smad-2. TGF-beta1 potently inhibited DNA synthesis in USMCs (IC50 60 pM). TGF-beta1 mediated DNA synthesis inhibition was potentiated following the disruption of caveolae by cholesterol depletion. This effect was reversible with membrane cholesterol restoration. TGF-beta1 stimulated gene activity was augmented by caveolae disruption, while caveolae reformation returned promoter activity to baseline levels.
  
  
  CONCLUSIONS
  TGF-beta1 is a potent growth inhibitor of USMCs and its activity can be enhanced by caveolae ablation. These findings suggest a role for TGF-beta1 in the growth regulation of normal ureteral cells and implicate caveolar membrane domains in the negative regulation of TGF-beta1 signaling. These studies may be relevant to ureteral pathologies that are characterized by smooth muscle dysplasia.
authors.affiliation: Department of Urology (Urological Diseases Research Center), Children's Hospital Boston, Massachusetts 02115, USA.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Stehr
authors.forename: Carlos R
authors.initials: CR
authors.lastname: Estrada
authors.forename: Joseph
authors.initials: J
authors.lastname: Khoury
authors.forename: Theodora E
authors.initials: TE
authors.lastname: Danciu
authors.forename: Maryrose P
authors.initials: MP
authors.lastname: Sullivan
authors.forename: Craig A
authors.initials: CA
authors.lastname: Peters
authors.forename: Keith R
authors.initials: KR
authors.lastname: Solomon
authors.forename: Michael R
authors.initials: MR
authors.lastname: Freeman
authors.forename: Rosalyn M
authors.initials: RM
authors.lastname: Adam
mesh_terms: D000818:Animals; D021941:Caveolae / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology* / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000502:physiology*; D053773:Transforming Growth Factor beta1; D014513:Ureter / Q000166:cytology* / Q000502:physiology*
chemical_list: C508962:Tgfb1 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1