title: TGF-β Suppresses COX-2 Expression by Tristetraprolin-Mediated RNA Destabilization in A549 Human Lung Cancer Cells.
abstract: OBJECTIVE
  Overexpression of cyclooxygenase 2 (COX-2) is thought to promote survival of transformed cells. Transforming growth factor β (TGF-β) exerts anti-proliferative effects on a broad range of epithelial cells. In the current study, we investigated whether TGF-β can regulate COX-2 expression in A549 human lung adenocarcinoma cells, which are TGF-β-responsive and overexpress COX-2.
  
  
  METHODS
  Western blotting, Northern blotting, and mRNA stability assays were performed to demonstrate that COX-2 protein and mRNA expression were suppressed by TGF-β. We also evaluated the effects of tristetraprolin (TTP) on COX-2 mRNA using RNA interference.
  
  
  RESULTS
  We demonstrated that COX-2 mRNA and protein expression were both significantly suppressed by TGF-β. An actinomycin D chase experiment demonstrated that COX-2 mRNA was more rapidly degraded in the presence of TGF-β, suggesting that TGF-β-induced inhibition of COX-2 expression is achieved via decreased mRNA stability. We also found that TGF-β rapidly and transiently induced the expression of TTP, a well-known mRNA destabilizing factor, before suppression of COX-2 mRNA expression was observed. Using RNA interference, we confirmed that increased TTP levels play a pivotal role in the destabilization of COX-2 mRNA by TGF-β. Furthermore, we showed that Smad3 is essential to TTP-dependent down-regulation of COX-2 expression in response to TGF-β.
  
  
  CONCLUSIONS
  The results of this study show that TGF-β down-regulated COX-2 expression via mRNA destabilization mediated by Smad3/TTP in A549 cells.
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Soyeong
authors.initials: S
authors.lastname: Kang
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Ahrum
authors.initials: A
authors.lastname: Min
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea ; Department of Translational Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Seock-Ah
authors.initials: SA
authors.lastname: Im
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Song
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Sang Gyun
authors.initials: SG
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Hyun-Ah
authors.initials: HA
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea ; Department of Internal Medicine, Chung-Ang University College of Medicine, Seoul, Korea.
authors.forename: Hee-Jun
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Do-Youn
authors.initials: DY
authors.lastname: Oh
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Hyun-Soon
authors.initials: HS
authors.lastname: Jong
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea ; Department of Translational Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Tae-You
authors.initials: TY
authors.lastname: Kim
authors.affiliation: Cancer Research Institute, Seoul National University, Seoul, Korea ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Yung-Jue
authors.initials: YJ
authors.lastname: Bang
keywords: Cyclooxygenase 2; RNA stability; Smad3; Transforming growth factor beta; Tristetraprolin