title: Expression of the type III TGF-beta receptor is negatively regulated by TGF-beta.
abstract: The type III transforming growth factor-beta receptor (TbetaRIII or betaglycan) is a ubiquitously expressed transforming growth factor-beta (TGF-beta) superfamily coreceptor with essential roles in embryonic development. Recent studies have defined a role for TbetaRIII in the pathogenesis of human cancers, with frequent loss of TbetaRIII expression at the message and protein level. Mechanisms for the loss of TbetaRIII expression remain to be fully defined. Advanced human cancers often have elevated circulating levels of TGF-beta1. Here, we define a specific role for TGF-beta1 in negatively regulating TbetaRIII at the message level in breast and ovarian cancer models. TGF-beta1 decreased TbetaRIII message and protein levels in ovarian (Ovca420) and breast cancer (MDA-MB-231) cell lines in both a dose- and time-dependent manner. TGF-beta1-mediated TbetaRIII repression is mediated by the type I TGF-beta receptor/Smad2/3 pathway as the activin receptor-like kinase 5 (ALK5) inhibitor, SB431542, abrogated this effect, while the expression of constitutively active ALK5 was sufficient to repress TbetaRIII expression. Mechanistically, TGF-beta1 does not affect TbetaRIII messenger RNA (mRNA) stability, but instead directly regulates the TbetaRIII promoter. We define alternative promoters for the TGFBR3 gene, a distal and proximal promoter. Although both promoters are active, only the proximal promoter was responsive and negatively regulated by TGF-beta1 and constitutively active ALK5. Taken together, these studies define TGF-beta1-mediated downregulation of TbetaRIII mRNA expression through effects on the ALK5/Smad2/3 pathway on the TGFBR3 gene proximal promoter as a potential mechanism for decreased TbetaRIII expression in human cancers.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Nadine
authors.initials: N
authors.lastname: Hempel
authors.forename: Tam
authors.initials: T
authors.lastname: How
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Cooper
authors.forename: Tyler R
authors.initials: TR
authors.lastname: Green
authors.forename: Mei
authors.initials: M
authors.lastname: Dong
authors.forename: John A
authors.initials: JA
authors.lastname: Copland
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Wood
authors.forename: Gerard C
authors.initials: GC
authors.lastname: Blobe
mesh_terms: D001549:Benzamides / Q000494:pharmacology; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004149:Dioxoles / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D010051:Ovarian Neoplasms; D011401:Promoter Regions, Genetic; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011509:Proteoglycans / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053773:Transforming Growth Factor beta1 / Q000502:physiology*
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D017931:DNA Primers; D018076:DNA, Complementary; D004149:Dioxoles; D047428:Protein Kinase Inhibitors; D011509:Proteoglycans; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D018125:Receptors, Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C071736:betaglycan